Recap tweeter info

I'm still enamored of the Dynaudio D21 AF above all, even the various Esotars.

These are very hard to find, and even used and 40 years old command prices like 330 Euros.  There has not been one on US Ebay in awhile.

Anyway, needing something at least for the back if not the front (either having D21AF or ribbon in the front) I investigated other tweeters, and wrote these comments to a friend:

I thought I would like "wood" but having the LS 3/5A on one side of the Acoustats is, I have decided, too "woody."  Also it blocks too much of the airspace, now that I understand that diffraction is unimportant.  The smaller the blockage the better.  Though I also just bought a $249 32 inch stand with 4 heavy sand fillable pedestals (that's cheap for something like that).  Now that I'm no longer thinking necessarily to have the elacs or the LS 3/5A's on it, a slender steel rod attached to a very heavy base would do, if something like that could be attained.
These Vifas are the best thing I've seen at Madisound as an inexpensive super tweeter.  Not perfect, just the most extended HF response in a cloth dome.  The usual D21AF replacement suggestion is the Eton 19SD-1
https://www.madisoundspeakerstore.com/eton-soft-dome-tweeters/eton-19sd-1-%C2%BE-soft-dome-tweeter/
That costs twice as much, is already rolling off at 20kHz, is only curved to 30kHz (though it looks as if it could extend to 40kHz with less than 10dB loss, which may be all the Vifa does, but I suspect it collapses right above 30kHz instead).
Nobody seems to want to build a supertweeter cloth dome, but it looks eminently doable, just as good as the Dynaudio D21AF.  What you need is a flat plate, no inward curvature, and a small dome with good damping.  The Eton above has the usual trick inward curvature, which captures some air mass and hence lowers the resonant frequency of the tweeter, making it more useful in 2 and 3 way box systems.
Almost everyone does that always.  When they don't have as much inward curvature, they apply lots more damping, including ferrofluid, like this scanspeak:
https://www.madisoundspeakerstore.com/scanspeak-soft-dome-tweeters/scanspeak-classic-d2010/8513-20-mm-dome-tweeter/
Both of these however do have smoother looking curves, they just start falling off too much for a super tweeter.
The Vifa does a trick I don't really like that much, but it works.  It does really have a kind of ring, a large surround bulge.  So what happens is the inner part vibrates at "lower" frequencies, up to (one can guess, looking at the response) about 25kHz.  That gives the tweeter excellent performance from 10-20kHz, excellent dispersion (even if you don't want it, most do).  Then what happens is the surround takes over at 25kHz and extends the response to 40kHz, because it has less mass, the resonant frequency is higher.  The dispersion collapses at that point like a rocket because there's a wider radiator...but it's still only 3/4 inch.  The 40khz response may be a kind of accident, they didn't care, they just wanted the excellent performance (in dispersion up to 30 degrees) up to 25kHz, which comes from that bi-radial kind of design.
Anyway, it seems to me now any of these highly capable manufacturers could build a real D21AF nearly flat 3-40kHz equivalent they just don't want to, nobody cares, the high end super tweeter market it dominated by ribbons and AMT's as cheap as $20...but have their own, usually hidden, issues of metallic resonance (hidden best when brand new).  Reading DIYAudio I hear one trick ribbon makers often use is to hide scales so you may not really know how flat they are.  And then they extremely rarely show waterfall plots (Raal does, and looks amazingly clean, but you can still see dots at the metallic resonant points).
I've discovered one essential problem is that ribbons can exceed their own centering force, and become increasingly bent, which I don't think is good.  When you get bends you start to get internal reflections, resonances, and so on.  The restoring force is lost beyond a certain point, which seems often to be exceeded.
Now it may be that some of the better ribbons, like the Raal, actually use a non-metal suspension on both ends.  It's not totally clear from reading their info that is exactly what they do but I think so.  Then you have the problem of low mass wiring, for that they famously use circuit board trace.
I'm still thinking about that possibility.  I may try to sell my Raven 2's before I damage them myself.  They'd be better in a certain kind of multiway system, since they do have pretty good response down to 2kHz or so which is amazing for ribbons.  There's one on ebay now for $680 (I bought mine for $250 IIRC).  But that's not what I want.

Actually, I was wrong about the Vifa's.  Vifa shows a very high resolution graph in which even 1dB response variation looks large.  They are not quite as flat 10-40k as the D21AF, but not all that unflat either, not much different (though indeed slighly less "flat" but far more extended than) the Eton and ScanSpeak.  The Vifa response is quite respectably flat compared to most finished speaker systems.

(In both the Vifa and D21AF I detect a double upper resonance in the frequency response, rather than the usual highly damped resonance.  In both cases you can see 1dB peaks spaced fairly close together, in the case of the Vifa it's 21 and 23 Hz, for the Dynaudio slighly lower.  I suspect this is the surround resonance in both cases playing the role of response extender.  The upper resonance probably also pulls the resonance below it upwards.  I would generally prefer no resonance, but the sad truth is that all tweeter materials have resonances, and typical metal resonances (I understand beryllium and diamond are fine...but extremely costly) are the worst sounding, and oiled cloth resonances the least offensive.

Which was an extension to an earlier message

After more pondering, I decided to get 2 Vifa 3/4 inch domes.  If I really like them, I might get to more for dipoles.  Otherwise, they might be fine firing backwards from something better, like ribbons.

https://www.madisoundspeakerstore.com/vifa-soft-dome-tweeters/vifa-ne19vts-04-3/4-silk-dome-tweeter-4-ohms/

Incredibly nice for the $33 price, response to 40k and decent dispersion at 20k.  About the closest I've seen to D21AF, and the only D21AF I can locate now is in Italy and the seller wants 330 Euros for a 40 yo used unit.

I've decided I don't like ring radiators at all.  The Mundorf dipoles have limited dispersion and I've always been suspicious of AMT (and they use metal also).

Linkwitz has studied diffraction and determined it's less important than many people think.

http://www.linkwitzlab.com/diffraction.htm

Since I'm crossing over at 20khz, where even this driver has very limited response at 60 degrees, 90 degrees is moot.  I don't even have to bother with a 3" square baffle, no baffle at all will do fine.  I think resonance (such as from a wood baffle) is a more important issue than diffraction, and if I use no wood, there will be no wood resonance.  (I might use heavy wood and bolts to attach the speakers to the stands though, then taped with hockey tape).

If I use a ribbon, I could tape the exterior box with hockey tape also, no need to build a fancy wood enclosure (which I'm basically incapable of doing anyway).

And that was a follow on to an earlier message, which was also somewhat repeated here before:

I've been studying super tweeters.  The unused Raven R2's I have are well respected, were used in some very pricey speakers too.

But they use a relatively thick foil, which means they could have metallic resonances.  9 microns.

Magnepan uses a 2 micron foil, maybe better sounding but also easy to break.

A newer generation of Ravens includes a "point source" tweeter with 5.6 micron foil, which is about the best compromise.  But it's still corrugated foil.  Price is $400 each.  Other than the foil, the build quality of Raven tweeters is monumental, all the exterior parts are 1/4 thick or thicker metal.  It would look beautiful on the outside of a pricey speaker (but probably should be inside).  Response to 50khz.

A newer company Raal uses embossed flat rather than corrugated foil, also 5.6 microns, that sounds best of all, and they have a point source model also, and an upgraded one with amorphous core transformers for $400 each.  Looks are very plain compared to the Raven, but if I were buying one now, that is what I would get (and I might).  Response to 100kHz, just like the old Sequerra T1.

It does worry me now about all aluminum ribbons that they may have metallic resonances.  When brand new and tight, perhaps not, but as they get older and looser the metal can flop around, as has happened to my used and mistakenly abused Elacs.  Audible resonances can be stimulated by ultrasonic higher frequencies, it seemed to me that was happening with my left Elac tweeter.

A plasma tweeter was being sold as recently as 2000 for $2500, was used in the Acapella $120,000 speaker.  It generates plasma electronically using some kind of RF circuit.  No helium, etc.  Still seems a bit risky to me, even if I had money to burn.

Few soft dome tweeters have the extended high frequency response of the Dynaudio D21AF's I bought around 1979, almost flat to 40khz.  I'm still considering using them instead of ribbons.  But in that case, I would get a second pair for the backside, or something else for the backside.  They have been almost unobtanium for decades, hifishark shows one for sale in east europe.  Dynaudio's most prestigious Esotar tweeters do not have extended ultrasonic response (and they're also unobtanium mostly, except there are now clones).

I do think it is essential to have extra super tweeter on the back side, or omnidirection, or dipolar.  I can hear the difference in current setup.

Other decent dynamic drivers are berylium domes and diamond domes, but extremely expensive!!!

Metal domes and we're back to dealing with resonances again.  Beryllium is special because of extremely high resonance, like 60khz.  Diamond tweeters go to 100kHz, but now we're talking prices like $10k.

Among the soft domes, the most expensive drivers, such as ScanSpeak Illuminator, have only so-so ultrasonic response, if any at all.  Most designers don't seem to care about the ultrasonic response.  The cheaper ScanSpeak Discovery have better ultrasonic response in the smallest sizes.

To get decent response, very small domes 3/4 inch and smaller, and/or ring radiator style, can get to 30-40khz with some rolloff.

So one idea might be to combine D21AF on the front and cheap ring radiator or ScanSpeak Discovery on the back.

Or Raal supertweeter on front, with D21AF on the back side.

Or Mundorf AMT (air motion transformer) which is dipolar, light, and could be attached to the Acoustats.

I might also enquire if Elac can fix my supertweeters.  That would probably be more expensive than getting brand new Raals, if it could be done at all.

The Krell was shipped back to factory this week.

Don't rely on me !!!

I see many times over I've been wrong about many things.  The record is so endless I couldn't possibly be expected to correct every past mistake.

I especially feel guilty about declaring people "late" (dead) when they are not.  I may have done that wrt the wonderful Keith Johnson.

One of my bigger mistakes, back in about 1985 or so, was to decide to bypass the internal crossovers in my LS 3/5 A speaker, which which I had a love/hate relationship (especially after having blown two modified T21 tweeters...a tweeter whose high end always sounded wrong to me, and I blamed the  perforated metal foil around it.  But equally as much, the T21 wouldn't take much before burning out, I discovered.

I discovered the Dynaudio D21AF tweeter sometime before then, perhaps around 1979.  I used them with the Advent speakers in a previous bi-amplified setup (something I have long believed in, and practiced).

I bought a Pioneer D23 3 way 6/12/18dB octave crossover, and used that with the D21AF and the B110 woofer inside the LS 3/5 A.  I wired both drivers straight to the outside, and removed the crossover board.

A friend of mine gave me a severe dressing down for daring to mess with the engineering of the LS 3/5A in such a gross way.

It turned there was some truth to what he was saying, as I discovered around 2003.  I discovered that my re-engineered LS 3/5A, which still sounded excellent to me (except the D23 which had been "on" all the time was beginning to hum a tiny amount) had a very serious peak, about 10dB or so, at 1kHz.

The reason was the doped bextrene driver itself...which had nice properties at other frequencies being light and rigid...had a resonance right there.  Much of the complexity of the LS 3/5 A crossover was the mitigation of this 1kHz peak.

In all the reams of consumer writings on the LS 3/5A I had never seen any mention of this.  Perhaps they were hiding the crude nature of the drivers...limited by early 1970's driver technlology.  Instead, it was said, the crossovers performed the magical trick of providing sufficient bass, by boosting the response at 120 Hz because of the lack of bass at 60 Hz.  Actually, I don't recall anything specifically like that when I examined the crossover.  But if you disengaged the 1000 Hz peak cancellation, the bass at 120 Hz and everywhere else will get relatively lower than the reference frequency 1kHz, so, yes, the 1000 Hz cancellation does sort of enhance the bass...and everything else that isn't 1000 Hz.  (I think this shows the danger of relying on "public" information, which is often highly affected by spin.)

Anyway, before just diving in, I should have done measurements, I believe now.  It's pretty obvious actually.  But I didn't bother, I just connected up the crossover, and boom, I could have anything I wanted, including the magical 12dB/octave linkwitz riley, which makes more out of less power at the crossover (both sides are 6dB down at the crossover frequency) by projecting more efficiently toward the listner.  (Now, btw, I strongly prefer the double order Linkwitz Riley crossovers such as 24 and 48 dB/octave, because both sides can have the correct polarity.)

So, anyway, for 18 years or so, I had a huge midrange peak.  The bass was relatively attenuated to 1kHz, making for a slightly thin sound (I was also using a pair of McIntosh ML2's as subwoofers... another interesting story...).  But I did have full spectrum response which sounded very very clear and transparent and I loved it.  I always loved the top end, which I believe extends to 40 kHz, of the D21AF tweeters.  It appears nothing like it has been made since, the later far more expensive Dynaudios have been larger and with more low end capability and clarity.  It seems manufactures of cloth domes don't care too much about 20-40kHz, the range for a decent super tweeter.  They are endlessly trying to give tweeters better low end for woofer integration.

I have however found one 3/4 inch Vifa speaker, only $33 at Madisound, with rated response to 40kHz (where, it is 3 dB down).  That's what I may use in combination with the D21AF pair I have, as supertwetters.  The superb D21AF's would go in front, and the Vifa's facing backwards.

Anyway, regardless of how "wrong" I was, I loved my ultimately tri-amped system.  It felt great to have something sound so transparent and with deep base and clear effortless transparent highs.

When I got my Revel M20's, it was absolutely clear these were the more transparent and full sounding speaker.  And I have relied on two pairs of M20's since around 2005, one in kitchen and one in bedroom, and the bedroom was the Main System until I got Acoustats in 2008.

I wouldn't say however, that I have actually loved the M20's any more than what I had before, before I discovered how un-neutral it was.

I had fun making my own mistakes, relying on my own judgments, even if they were wrong in some ways.  And...they were actually right in other ways...the extended highs of the D21AF are fabulously effortless and transparent, and no peaks either.

But if you want to get things right the first time, every time, etc., then don't rely on this blog.  I'm not promising that.  Only adventure and discovery, ocasionally correcting earlier mistakes, but always having fun, and thinking on as grand a scale as possible, perhaps about not much of anything.

The PMD 100 is innocent

I still wonder why I get 13dB higher noise levels from my Denon DVD-9000 players than my Denon DVD-5000 players, the RMAA measurement goes from 88.9dB for the 9000 to 112dB for the 5000.

But it would appear that the PMD 100 is innocent, from all information I have.  PMI spec'd the alias suppression at 120dB, for example, better than many other chips.  Another highly esteemed player using the PMD 100 is the Linn Sondek LP12, which had excellent measurements, with John Atkinson saying (at the time) it was as good as he had ever seen.  The LP12 uses dual differential 1702's, which are usually regarded as inferior to the dual differential 1704's of the DVD-9000.

On the DVD-5000 and DVD-9000, the analog circuitry after the dual differential 1704's is almost the same.  The 9000 does seem to use fewer OP275's and more 5534's, and the output goes through a muting transistor rather than muting by shorting the inputs to a OP275.  To my inexperienced eye, the analog circuitry of the 5000 does look slightly better, still not exactly what I would want.  I would want at least LM4562's, if not OPA211's.  But with noise and distortion levels as low as they are in either case (and certainly by the specs for the 9000, which are far better than I measure) the circuitry is "good enough" to likely fail every attempt to distinguish it in blind testing.

The DVD-9000 uses 5534 to initially amplify the 1mV "current" output of the 1704.  The DVD-5000 uses a slightly more advanced chip.  The DVD-9000 uses a single transistor in the muting circuit.  The DVD-5000 uses a OP275 instead.  Other amplification stages see OP275's in the 5000 replaced with inferior 5534's in the 9000.  These are the "slight" differences I see, enough to account for maybe 3dB of difference, not 13dB.  The Denon noise spec is 3dB better for the 9000 actually (118 vs 115dB).  Perhaps my two units have deteriorated with age?  That seems most likely, but another possibility is that Denon used a different weighting in measuring the noise than RMAA uses.

Back when I was "flying" with the Eagle 2 amplifier, some of the most intense audio ecstasy I've ever experienced, I happened to have been very temporarily using the DVD-9000 as my DAC, and the 9000 did initially distinguish itself by having the smoothest yet most detailed sound of any of my players (I've never used the DVD-5000 as a player).  I do wonder if the 9000 might actually "sound better" than the 5000 despite the increased noise level.  Along with higher noise, it has lower distortion, so maybe the distortion is better hidden in the noise.  I'm beginning to think that distortion should always be hidden like that (which generally is the case in very high feedback designs like the Eagle 2, for example).

In order to use the DVD-9000 as my system DAC, however, I would need 3 of them in addition to the one I now use as an HDCD/DVD-Audio player.  That's because they have far more latency than any other DAC I have, up to 330 msec, and it varies a lot depending on sample rate.

I now have 2x DVD-5000 and just missed an opportunity to get a third.  I'm thinking I might like a 3-stack of DVD-5000 for my system, though it would add a lot of physical complications because I'm running out of room for more equipment.  I can fit 2x DVD-5000's and 1x Emotiva Stealth DC-1 I now use on the subs without any issues.  If I got a third DVD-5000 I would also need a single-ended-to-balanced buffer with some attenuation, and additional space for the two units.  I'd also need a 3rd AES to SPDIF converter (about $135).

Super Tweeters

I've long been a believer in super tweeter magic.  I've been enthralled by all the systems featuring super tweeters, from the MQD with Decca Tweeters which I heard long ago, to the Hill Plasmatronics which I heard many times, to the Iverson corona massless speaker I've only heard about.

Once you step down this path, as I did around 2011 by getting a pair of Elac 4PI's in slightly used condition, you end up spending more and more time keeping it going at the same or higher levels.  And if you've got a critical sense, you also do begin to wonder, sometimes, if it's all a waste of time, effort, and money.

Hardly anyone in blogs I've looked at is even aware of the Elac 4PI super tweeters.  No doubt this is mainly because of rarity and high price.  But I do wonder if they are as good as the best of the others anymore.  Now that I've determined that one unit is not working good anymore (most likely due to an accident in 2011 which resulted in very high power being blasted into them by a 500W amplifier I was using just because it was the best spare amp I had on hand), I'm not sure if I'd spend $2000 for a new pair, or whatever it would cost to fix them (which might be impossible, but in any case not cheap).  I bought the used pair I have as an impulse, just seeing them on eBay for $995.

At the time, I knew of little other than the Sequerra T1, which also sells for thousands of dollars, even used and needing ribbon replacments (T1 foils are apparently relatively easily replaced).  But now I see a world of other options in the ribbon category (including Raven and Raal), and many other categories (AMT, plasma, high frequency domes and ring radiators of various kinds, even very HF electrostatics).

But it appears a 14kHz resonance is a very common problem among ribbon tweeters when (1) the aluminum looses tension and "flaps around", (2) the aluminum falls out of the magnetic gap and isn't being controlled by a continuous magnetic fields, (3) the aluminum was too thick or improperly corrugated.

That is one advantage of the "fake" ribbon tweeters that have aluminum bonded to a plastic membrane.  The plastic membrane (and adhesive) does provide some damping to the aluminum so you are unlikely to get the metallic aluminum resonant signature (which is very nasty sounding) even when everything isn't 100% perfect (as things with more than a few days heavy usage may not be anymore--and you might not be aware of it at first).  On the other hand, then you get a plastic resonant signature.  The general "consensus" if there is one is that pure aluminum is better.  It gets way more respect anyway.  But many of the popular ribbons like Founteks are the bonded type.  Generally the real aluminum ribbons are more expensive, like the Sequerra T1, and the Raven R1, R2, R3, Line Source and Point Source, and the various ribbons made by RAAL.  (I just discovered the RAAL's as I am updating this entry, and they look like they might be the best of all, they have 100kHz bandwidth like the Sequerra, and uniquely they used embossed rather than folded foils, thinner than many others also.  One poster at DIYAudio says that foils thicker than 5 microns sizzle to his ears, and below 5 microns there is enough material damping to resist that.  The RAAL's are 5 microns, as is the new Raven Point Source, but the earlier Ravens may have been 9 microns.  Household aluminum foil varies from 12.5 to 25 microns.)

I happen to have purchased but never used a pair of Raven R2's, and from what I read now (it was a spur of the moment ebay buy for me) there are indeed highly respected, certainly the build quality is top notch (reminding me of the far more expensive Sequerra).  The spectrum plots I've seen show no trace of a 14kHz resonance, and the response goes to 50 kHz.  The Sequerra apparently uses an even stronger magnet, by legend it was from a defunct particle accelerator, and goes to 100 kHz.

I'm thinking of using the Ravens real soon now, but I also like my Dynaudio D21AF tweeters.  They have response to an astounding 40khz according to published specs and graphs.  I've always thought this tweeter sounded effortlessly transparent, which is why I used it in my modified LS3/5A which has been unused since 2005.  I still think so, and I wonder if it isn't a competitor to the ribbons.

Sadly soon after I bought my pair, Dynaudio quit making the D21AF and stopped selling raw drivers as well, only making extremely pricey box speakers.  I am not sure if they ever sold their most legendary tweeter to speaker builders, the Esotar 330D, priced about tenfold higher than the D21AF.  But even the Esotar doesn't seem to have the fully flat and extended to 40kHz high frequency response of the D21AF.  I took a long look at tweeters today and it seemed only a few had response extended beyone 30kHz.  Typically the most expensive tweeters have the least extended response, showing how unimportant that is to most builders.  Many of the lesser expensive tweeters have the most extended response.  The cheaper Discovery tweeters by ScanSpeak have more extended range than the pricey Illuminators which have the ugly projection.  I found a number of other good looking high frequency extensions below $30.  Ring radiators look to have good high frequency extension generally, but there are other choices with similarly good high frequency extension.  Generally one looks for the smallest domes or ring radiators.  Metal, ceramic, and diamond drivers also have good extension, but at much higher prices, and wrt the metal drivers at least I worry about resonances.

The soft domes that have extended response, like my D21AF, must be flapping around under their own mass (NOT the air resistance primarily, I believe) at higher frequencies.  But it seems like it hardly matters that much, distortion continues to be low, etc, and there seems to be little HF resonance.  A "floppy" soft dome tweeter "works" well enough.  Trying to make a hard tweeter immediately creates difficulties.  The earliest domes were harder plastic materials, and those were all unsuccessful because of internal resonances.  This would amuse Lao Tsu.

Meanwhile I worry about when and where an aluminum ribbon actually bends or how "surround" materials give to allow the ribbon to move.  The ribbon story is not so clear cut when you think about the suspension and how that works.  Or diffraction.

In principle, the lower mass and higher velocity ribbons should be the best super tweeters.  But in practice, all the details count, and possibly the domes are still more refined in many ways.

I knew of the Hill Plasmatronics in 1978, and heard many stories about the Iverson Corona speakers, but I hadn't realized that plasma speakers have been made more recently.  The Acapella Plasma is one of the most well known, and was once available for $2500.  The plasma is generated electronically.

I imagine a significant problem with aluminum ribbons: when there is no current flowing, there is no restoring force on the speaker.  Conventional dynamic drivers have an elastic restoring force which always returns the speaker to the center position.   While Dick Sequerra said that ribbons are at least as reliable as dynamics...I wonder about that.  I've seen lots of ribbons bent out of shape, especially Sequerra ribbons.

It seems to me now that if there is *any* visible deformation on a ribbon speaker, that is a significant flaw which could impact performance.  At least for the deformed part, it is not properly within the magnetic field, and the material junction between the deformed and undeformed part could cause internal reflections and resonances.  The bottom line is, just like with any other speaker driver, any visible damage is serious damage, and there could be other damage that isn't visible.  And with super tweeters, since it must process sound which can't be directly heard, it's problematic to determine if there is damage by listening also.

So maybe ribbons are not the ultimate great idea after all.  There are some other possibilities I hadn't mentioned so far:

The Sopranino electrostatic super tweeter (8kHz - 40kHz) looks interesting, however very expensive, and despite the inherent dipole nature of electrostats, it doesn't seem to be intended as a dipole, since it has all the transformer and stuff behind the driver.

The "Walsh Tweeter" is arguably not a real Walsh and it has no termination and faces up rather than down.  It was first used by Infinity, and only later by Ohm.  They haven't been made for a long time, though there are a few people who have made similar units and/or claim to repair them.  Since it involves using a very thin rigid foil in order to work something along Walsh principles, but isn't terminated, it seems like an open invitation for resonances, just as with ribbons, if not more so.

Piezo's and polymer tweeters?  Piezo's have always sounded nasty to me and I wouldn't want one as a super tweeter either.  Chemical action isn't necessarily as fast as electronic, and the electro-polymer based "super tweeters" on the Pioneer HPM 150 and 1500 were not noted for the best sounding transients.

Mundorf now makes a whole line of AMT type supertweeters, small enough to be nailed onto the frames of my Acoustats.  AMT's have a huge advantage in not requiring transformers and naturally permitting dipolar operation.

Fans of ceramic and "diamond" drivers are very suspicious about ribbon resonances and distortions.  They also point out that the "speed" doesn't entirely depend on mass, it's F/M.  Dynamic driver motors can produce enough force for basically anything.  The problem getting HF response out of dynamic drivers first comes from breakup resonances--which can be fixed with high strength such as ceramic or diamond domes--and secondly from voice coil inductances, which can be reduced by using less coil and higher strength magnets.

While I believe in and of itself an omnidirectional radiating pattern would be best...or best yet omni but notched out where it would otherwise "fire into" the side of the main speakers...and I'd even say this with dipolar main speakers...dipolar dispersion might well be good enough, and eliminates a lot of technical issues as well as giving many more choices.  (I only know one maker of omni ribbons--Elac--and no other omni supertweeters are worth considering...the Infinity Walsh isn't a true walsh since it is not terminated.)

I remain impressed by the textile domed D21AF I have.  I remember when I bought them in 1979, IIRC I had planned to buy more than two because I thought the price was only $29, but actually that was for the D21, the D21AF were $49.  I was outraged that I had misunderstood the ad (the "response to 40kHz and $29 price were not the same unit) and they were that expensive.  $49!  I had driven all the way from San Diego to LA to buy them.  I pondered whether I could be happy with the D21's and decided I couldn't be happy without the 40kHz response.  So I got a pair of D21AF's, more angry about the higher price than anything.  It did dawn on me about a year later (or was it the next weekend, I can't be sure now)...I should have bought as many D21AF's as I could.  I drove back to LA, went back to the same store, but D21AF's were long gone.

Now I see that the D21/2 was about the same, supposedly an improved version, still having the essential 40kHz response (though, the specs only say 30kHz).

And, surprise surprise, there *is* a close to equivalent speaker still made and sold by Dynaudio today.  It is the Esotar 110.  Performance looks very similar to D21/2, and there's ferrofield cooling.  It's probably a more rugged speaker, not that I need that sort of thing (my D21AF's are, as far as I can tell, perfect, despite having been directly driven by power amps for 20 years in crude biamp setups) now for 19-40kHz duties.  I'd prefer not to have the ferrofluid, actually, but I'd get some of these except for the new price I see: $1399.99.  The Esotar 110, though it has extended hf performance is actually the larger 28 mm size like the old D28, with more setback, and I'd prefer a D21AF actually.

R2R Magic!

I've been struggling with trying to make Hot House (Arturo Sandoval) sound listenable.

I've been adjusting EQ.  I balanced the two supertweeter channels, connecting the DAC directly to the Parasound Power amp, not using the Harrison Labs -6dB attenuator (which isn't perfect and increases load to 2k) and instead using the Parasound attenuators.

None of that seemed to cure the problem.  But one more change seems to have magically changed everything, not expected at all, and it's all probably bias and measurement error.  But sure enough swapping my second Denon DVD-5000 for the Emotiva Stealth DC-1, and readjusting the digital gain a bit since the DVD-5000 doesn't have gain control like the Emotiva (which I had set to -6dB after removing the attenuators).

I had to do a lot of rethinking the digital delays, since now for the first time both panels and supertweeters are on the same kind of DAC, and that wasn't true when I did the Tact setup.

Now, strangely, I have pretty flat response to 20kHz.  The added steelyness is gone.

And yet, there isn't really any audible output from the super tweeters any more, or very much.  I can measure the 18-20k they are putting out, pretty much as before.  But now I hear nothing.

Some strange force leakse out of sigma delta dacs, ,a force below the actual audio signal they carry, a kind of low frequency force which makes other sound waves vary their phase, making things sound bad, even though it's not a measureable sound as such, just a magic force field that affects other sounds.  The feedback of the sigma delta is "correcting" everything else in the room in an undesireable way.

Or maybe the story is just that I should always be using the same kind of dac for super tweeters and panels.  That might not seem like a bad idea for a lot of reasons.  And possibly the bass too.

In fact I made this change not expecting it to make any difference, but after testing the new DVD-5000 to be the same as the other (excellent, the best of the Dual Differential 1704 Dacs I have measured)  I thought it would make things more convenient because now I don't really need to bother readjusting the midrange delay for 44.1k vst 96k or whatever, since they are now the both kind of dac.  I don't know the sub delay even as close as the 0.44msec difference, so it hardly matters to the bass.  But maybe having another DVD-5000 for the bass would be the final magic touch (and it just seems so much like my kind of all antiques system).

Maybe in that case whatever the drift it, it stays the same, rather than constantly going out of phase with each other or something, even while the average delay has been compensated for.  There is still the matter of the supertweeter delay because of physical distance, and I've tried to re-figure that, but maybe needs redetermination using something better than the Tact program (which is very weird, btw, I think it uses an essentially analog stimulus and shows you the uncorrected response of that stimulus rather than a corrected impulse, which many programs show).  But even though changing that seems to make a slight difference, it's not like the vast improvement that has occurred.

But I'm not sure it entirely matters either, as the long length of the acoustats mean there are different possible delays for every position, and if most sound you hear is reflected, the average matters almost as much as the direct path distance.

Update: Maybe true, maybe not.  Further testing confirmed what was suggested by earlier Tact impulse responses.  There is a 14kHz resonance in the left Elac tweeter, from an earlier accident.  The other channel does not seem affected.  To fix it for now, I have replaced the left supertweeter with a Dynaudio D21, mounted in a modified LS 3/5A cabinet, with the tweeter wired in directly.

The result looks a little crooked, since for now I've left the right Elac on the right side.  I'll have to come up with a more elegant replacement for the left side also, but for now the combination seems to work fine and has been level adjusted.  There's a 0.5 uF cap on the D21 to attenuate the fairly noisy power supply of the old HCA-1000A.  The Elacs have long had such attenuation with their own crossover, which I think works at about 12k, which I have largely ignored since I cross over much steeply.

Oh, yes I'm now crossing over 48dB quasi Linkwitz-Riley with 4 series "HC" filters each 12dB/octave, and at 20kHz.  Need to get all that super tweeter stuff out of the lower audioband.

High frequency response up to 20kHz is flattest ever, for some reason the system just got a lot flatter recently, I still don't understand why, about the same time as I replaced the DAC on the supertweeters with the Denon DVD-5000, but with or without the supertweeters running.  And no notch filter at 12-14kHz is needed, the strange ringing there is mostly if not entirely gone, playing music I see all the bands from "flowing" naturally with the program, the very top 20kHz being slightly depressed, but I don't want to crank up the gain any more (already at +4 for the super tweeter, less the dialed in attenuation in the back of the Parasound amp, which I've readjusted for the same effective 20kHz output at the listening position.

Tough Tracks

My system can be loafing along, playing classical guitar, and sounding beautiful and pure.

And then, I can be playing "Hot House," by Arturo Sandoval, and it can sound pretty rough.  Abrasive, screechy, harsh.  I don't think it was always this bad, say when using the Krell amplifier.  When using the Aragon I become more aware of these things, possibly because the Aragon is not quite as good, and possibly because I let myself hear problems more.

I played Hot House on Thursday and then Friday night.  Finally I decided to do something about it.

My first idea was to substitute the Emotiva DC-1 dac for the Denon DVD-5000.  After all, the Emotiva is the cleanest DAC I own, by measured THD and distortion spectrum (which looks almost perfect, and I will not say that I disagree with the measurments either...it sounds like it's not there, only a bit too much so generally I felt in a few minutes of critical midrange listening).

But the distortion I've seen generated by the Denon is around 0.003%.  I think it would be hard if not impossible to hear that, even if it were all 7th harmonic, and actually the Denon has mostly 3rd harmonic with a fair amount of 2nd, plus higher harmonics but only at even smaller levels.

The amplifier might be a bigger factor, but the Krell has not been sent in for repair yet.  (I accepted a freight shipping quote on Friday so it goes out next week.)  I have measured the Aragon at 0.02% distortion at moderate level.  It had been over 0.1% until I fixed the bias problem 2 years ago.  Still, this doesn't seem like the big factor I'm looking for.

So, instead, I decided to go after some of the lumps in the high frequency response of the Acoustats using my DEQ.  I have avoided using EQ on the Acoustats except for the crossover itself and my Gundry/Linkwitz/Peterson dip.  And also a tad of resonance control around 115 Hz.  It may very well need more than I've done (though solving resonances by fixing things is better than correcting them with EQ, but I have zero idea how to fix the response bumps now).

Deeply rolling off the treble seems to do no good.  I still hear the harshness in there, no matter how well rolled back.  And then it just gets boring also.

I am thinking that small peaks which result from tiny resonances in the speaker catch on the natural odd harmonics of the brass instrument as the instrument itself is sweeping through the spectrum.  However you imagine it, it does seem like rough looking response could create rough sound.

I experimented first with attenuating a slightly rough spot around 12kHz, just before the speaker begins to roll off somewhat in my off-axis position.  I can see this same spot regardless of angle with the speaker.  I'm using the 1/6 octave display of an app, so I know that "12 kHz" isn't exactly the spot, but pretty close.  Really when tuning a parametric EQ, you should use something even finer that 1/6 octave, in my opinion a hand tuned oscillator is best--then you can totally zero in on the resonant frequency.

Then it seemed also that there was an elevated sticky frequency on the RTA just below 12 kHz, so I made the bandwidth 1/3 octave and moved the center frequency down to 11.8.  That's where it is now.  Before doing much wider than 1/3 octave a good oscillator test is called for.  After measurements and listening I settled on attenuation of -4dB.  I only weaken such peaks, never total cancellation, because overcorrecting is worse than undercorrecting IMO.  But this did seem to eliminate any tendency to either peak or shelf at 12khz (before plunging down above that), only now there's still a bit of bulge at 10kHz left that wasn't by itself visible before, an indication of the tuning of the parametric correction is still a bit off.

I similarly attacked a small peak around 638 Hz.  When I turned the parametric correction from off to "PARAMETRIC" a previous correction of 638 Hz was turned on (though, when such things are partly saved by the DEQ, the attenuation goes back to 0).  Now it's pretty much gone though there's a similar peak also around 500 Hz.

Despite my Gundry/Linkwitz/Peterson dip (centered at 3.8kHz) there is elevation at 6kHz, the worst frequency for there to be elevation at.  So I added a new 1/3 octave correction just at 6kHz, to keep that down, blending better into the rest of the dip also.

I had also noticed a large difference between the output in left and right super tweeters.  The much more wrinkled looking (from a previous high power mistake) left ribbon showed a nearfield peak (which it needs, in order to have any impact at all compared with the giant Acoustats) which was much larger than the right.  I had always assumed that the ugly looking eft ribbon had less output.  But in fact it has (or at least had) much higher output.  AND in this case, I decided to toss the Harrison Labs 6dB attenuators, dialing in 6dB of attenuation to the Stealth DC-1, and then also using the gain controls on the Parasound HCA-1000A amplifier driving the super tweeters, hand adjusting to about a 6dB (possibly inadequate) nearfield peak.  This may have actually been higher than before on the right side, and now I am worried if there isn't some issue in the right channel, but it could also be the crossover in the left is burned out.  Anyway now both supertweeters are adjusted to the same reasonable level.

One damned thing about the DEQ's is they don't have per channel level--just a convoluted "Image" control.  I'm now appreciating the level controls on the Parasound amp.  The DEQ's should also have  level to 0.1db, per channel polarity controls, and delay up to 10 sec (not 300 msec).

This set of changes did seem to improve the sound of Hot House.  I was able to listen to nearly the whole album again (after chains couldn't have done that) at a Tact level of 89 (approximately -3dB) which is quite loud.  Still, I'd say considerably more improvement is needed, and I'm thinking of doing more testing and possibly switching to graphic eq as well.  But I'm thinking a good oscillator test of the 11-12kHz and 6 kHz resonances might be revealing...

Acoustic Fields

Acoustic Fields has a unique tuned low bass absorber, tuned to 35-50 Hz, a range which is very difficult to effectively trap with conventional passive bass traps (which is why I went to an active cancellation device, the Bag End, which I tune to 35-50Hz) but which is most useful in most small to medium sized rooms.

Are Synchronous DAC receivers reappearing?

Truth be told, of course, synchronous DAC receivers had never gone away.  While some of the earlier ones are discontinued, the DIR 9001 continues, and is often the receiver chosen by DIY'ers, I have noticed.  I'm talking SPDIF/AES only, as you may already know I despise everything else for practical/personal reasons, AND that's a pretty cut and dried case about which I need not comment anyway.

But from barely respectable on up in manufactured gear, asynchronous receivers have/had become the norm.  Few except for cranks were raising the old "puts your jitter into the data" arguments.  Some equipment was giving you a choice--that's fine.  But generally since the asynchronous receivers were showing better measured performance, anyone who cared was using them.  Except for the universe of contrarians.

I'm using one right now with my DVD-5000 dac, which has CS8414 and dual differential 1704's.  CS8414 might not have the best self-jitter, DIR 9001 may be better in that regards.

But anywayz it seems to me that synchronous receivers are required for things like HDCD, aren't they?  You can get away with any sort of interpolation with that, I would think, there's meanings to certain exact sets of bits.

Then, I also think about MQA.  Once again, it seems if you are encoding any extra information into the audio, that isn't the kind of thing which may be interpolated or whatever.

So I noticed in review of the latest and greatest Meridian DAC, which is wonderful for sure, mention is made of a FIFO buffer which gets jitter to below 0.5 Hz.

OK, that sounds like a synchronous receiver with a 1 second buffer, though I could be wrong about the buffer size.

Most of the receiver chips get away with what seem like tiny buffers, then often spec jitter suppression only above 20kHz.  That is surely wrong, it should be at least spec'd down to 1Hz.  With a long enough buffer, the DAC clock can vary slowly yet stay in line with whatever the source does, and therefore only subsonic jitter remains.  I understand that people are quite sensitive in the usually subsonic 3-10 Hz range to FM, aka jitter or wow, so you have got to get below that.

Now I really do wonder what is going on inside the Denon DVD-9000 with it's 330 msec latency compared to other DACs.  Is it an anti-jitter mechanism?  How well does that work?

I know there's no question I have to get beyond my very limited so far jitter measurements and do a better investigation of all this, with J test and so on.

BTW, the J-test harmonics appear in most cases to be way way below -110dB, often in the -130dB range.  That's a worst case jitter situation, which maybe occurs for a few seconds in a lifetime of playing.  Mostly, the jitter sidebands must be way below that.  And that's so negligible it's a wonder we even think about it.  (Well, that's a long story of course.  And it also relates to the lack of controlled blind testing.  And people don't want to write off uncontrolled impressions they have had.  And with digital transmission there can only be two things, data and time.  And the data can be checked and shown to be perfect.  So the only thing left is time.  SO time MUST explain all!!!)

This seems way below the importance of more easily measured things, like harmonic (and therefore IM) distortion, which often reaches high in audiophile designs.  Often distortion sidebands reach -60dB or higher, possibly 3,000 times or more larger than the sidebands being caused by jitter even through toslink, etc.

DAC low level pictures

Marvey at SuperBestAudioFriends has posted pictures of low level resolution of 3 DAC's, the Schiit Yggdrasil, the MSB analog DAC (which has long been on my want list), and the Nad M51.

At -90.31 dBFS (basically near the limits of 16 bit audio) the Schiit is showing a trifle of notchiness around the zero crossing point, otherwise a fairly smooth recongnizable sine wave.

The MSB is showing notching all over the wave.  (And Marvey comments that John Atkinson didn't give this DAC any crap for only achieving 18 bits resolution, etc.) and looks a lot worse.

The NAD M51 (which uses a very high frequency PWM conversion--the very kind I find the least intellectually acceptable) is showing an almost perfect looking sine wave, just a slight bit of lumpiness at the extremes.  This may be the best looking sine I've ever seen at -90dBFS.

Sigma Delta "Impulsivity"

One thing I've noticed recently in both 1-bit and multibit sigma delta DACs is something I call "impulsivity."  Peaks of loudness seem to get peakier, like tiny highlight spots of glare.

Now, firstly this could be just my imagination, I'm not going to even try to prove otherwise.

Secondly, sigma delta DACs, at least the better ones for quite some time have had better S/N and dynamic range specs than even the best, yes even my sacred 1704's.  So you could really say, black is blacker and therefore things rise up from the black with more contrast.  More contrast means more "peakier."

I'm suggesting something different.  I'm suggesting that when the sigma delta DAC has to output it peak it has to "work harder."  The way sigma delta dacs work is by a feedback loop, which drives the narrow converter to push the output into the correct signal.  When there is an actual peak in the signal, the overload is higher and the feedback has to work "harder," or at least more consistently, to one direction.  This is precisely the kind of thing our neural networks are designed to detect: correlation and causality and therefore intensity of effort.  We feel when things are struggling, or just loafing along.

The PCM dac, on the other hand, never "struggles."  It has the large jumps pre-fabricated and ready to go when needed.  It simply assembles the pieces for any given sample, and that is that.  It is therefore imperturbable (just loafing along).

Now I'm not suggesting some sort of ESP being involved, so how could we sense such things?  The answer is: it's below the noise floor, and the ultimate timing of things.

Time Alignment using Tact

It's pretty easy to set the supertweeter time alignment using the Tact as measurement tool, using the mid way Behringer DEQ to set the delay because the supertweeters are about 6 inches back.  The Tact stimulus is a high frequency rich "snap", and it's easy to see where the high frequency wiggles of the supertweeter line up with the initial impulse in the panels.  The initial impulse in the panels appears to go down in the Tact display apparently because of some weirdness in the Tact stimulus and display.  I use SpeakerPop to set polarity.

I've determined the correct setting to require 0.2 ms delay in the panels.  However, since Tact uses a 48kHz signal, which is delaying the panel approximately an additional 0.35 ms due to the DVD-5000, the total delay is about 0.55 ms, or about what it physically looks to be.  I actually set the relative delay at 0.55 because I am "optimizing" for 96kHz.  If I am seriously listening to 44.1 I can subtract 0.35 ms delay in the mid way DEQ to compensate for the added latency in the DVD-5000 at 44.1.

Setting the time alignment for the subs is as clear as mud.  The Tact stimulus doesn't produce very much bass energy, and if you play the system normally the "bass" is just endless LF ringing.

What I have historically done, only it isn't working as good anymore (and never worked great) is separate the channels.  To set right time alignment, I disconnect the left panel and sub, reverse the panel channels.  Then both Tact channels play the right side, with the left panel channel actually playing the right channel.  This gives a display with sub in one channel, and panel in the other channel, and you can sort of see how they line up.

But it's pretty hard to tell, because the sub is only making very small and slow waves in the Tact display, and it's not always exactly clear where the "beginning" is.

The Tact doesn't make this any easier.  It does not save the previous measurement(s) so you can see how things changed.  Because the snap stimulus has very little low frequency information, the subs are barely even audible.  This lack of information means that each plot is going to differ from the previous one, randomly, even if you didn't make any changes (unless you do endless averaging, I suppose, I do only 10 trial averaging which already requires long waits).

Anyway, after hours of futzing with this anyway, I finally came to the idea that about 5.4 ms was the correct panel delay time align the subs.  (Because the subs are further back, the panels need to be delayed to compensate, by 5.4 ms?)  This makes no sense because the panels are not that far back.  I made that judgement on the left side, for which the subs may be as much as 3 feet back (they're only as much as 28 inches on the other side).

Anyway, on the other side, things were even less clear.  The number could have been as low as 2 ms (about what it looks) or as high as 5 ms.

Finally I came up with a clever trick in programming the DEQ's.  I indeed do delay the subs (even though they are the farthest back) by 4ms.  Then I delay the panels by 7.5ms and the super tweeters by 6.95 ms and I can leave those two alone.  Then, I can adjust the sub delay simply by turning one knob.

And this control is very nice.  Now it is very clear how the sub delay affects the sound, and exactly the opposite as I had thought.  At the "minimum" measured sub delay of 3.5 ms the sound is a trifle boomy.  If I dial the sub delay more, it tightens up.  I had figured you always want the panels to "lead" and therefore provide the initial more perfect sound.  But it appears what is really important is to not have the subs lag too far behind.

Anyway, now I have a control and I can just keep tuning by ear.  By turning the sub delay up to 7.5 I could in effect make the relative delay 0, or by turning the sub delay down to 0 I can make the relative delay 7.5.  So I have all the range I need in one control.

(Sadly there appears to be no way to add relative delay to the subs.)

With this control, so far I have gravitated to 3.6 ms, which would mean the panels are delayed 7.5-3.6  or 3.9 ms relative to the subs (maybe some different numbers would make this easier).  I had previously been using a 3.3 ms delay as handed down from endless re-thinkings mainly.

I went ahead and put the panels at 10 ms delay.  That puts the super tweeters at 9.46 ms (only 0.02 adjustments available) and the subs at 6.10 ms for the same relative delays as above, and gives me full adjustability down to panel delay of up to 10 ms or down to relative negatives just by turning the sub delay knob which turns out to have a very interesting subjective effect.

Then I discovered that running the Tact test at precisely 6.25ms (relative to 10.00 ms in the panels) show the right channel going down (the sub leading) over 100's of MS, and the left channel going up (the sub lagging).  This has to be the perfect in-between compromise.  At 6.00 ms and 6.5 ms both channels go either up (one more  than the other) or down.  So I've settled on 6.25 as my best guestimate (equal to 3.75 ms difference from the panels which are delayed by 10 ms for convenience now).

Tact Impulse Response at 6.25 ms dub delay

At 6.50 ms both channels "rising"

At 6.0 ms both channels "falling"

When I play 96kHz, I merely dial up the mid way delay from 10.00 (calibrated at Tact's 48 khz) to 10.38.  To play 44.1kHz I should dial down the mid way delay to 9.94 (if I care).  To change the bass alignment I can just adjust the bass.

Actually I'm finding that 6.50 msec delay, relative to 10.38 (for 96kHz sampling).or whatever I've set the panels to, works better than 6.25.  6.50 subjectively lets the bass be bass, to hang a bit.  6.25, what I called the "compromise" position, is too dry, the reverse angle taken by the two sides cancel or something and it sounds dry.

Each time I do these alignments via Tact some trick like this arises and gives me an "angle" to make an objective/subjective judgement.  Who knows I could be off by more than 1 ms.

The Dacs I use now are Nearly time aligned (within 0.44 msec)

I finally tested delay, using my ancient test file LoudPolarityTest.wav, which outputs a large scale signal (not -20dB, but I can't remember how high, perhaps -5dB) postive only narrow pulses at about 20 Hz.  I couldn't get a clear oscilloscope picture of both dacs at the same time using SpeakerPop, which has much lower frequency of "pops".

At 96kHz, the Emotive and Denon DVD-5000 DACs are nearly perfectly aligned.  I found the two traces line up more perfectly adding 0.06msec to the Emotiva Stealth DC-1--which apparently has 0.06msec less latency at 96kHz than the Denon (I'm lucky it's not a much larger difference).

But at 44.1kHz, the alignment slips apart a bit, and the Emotiva there leads by about 0.50 msec.  So there is a 0.44 msec difference between the two excess latencies, which is really the important factor in the system design (since I can always align the different ways to accomodate the constant latency differences, at least up to about 300 msec...and in fact I must adjust latency anyway because of speaker offsets, though if doing so by guesswork as I mostly do I would need to keep this in mind).  But here the constant latency is actually quite trivial at 0.06 msec (less than one inch sound travel) but the variable latency at 0.44 msec (at more than 6 inches) may be worth thinking about, if not always compensating for.

Initial offset at 44.1kHz, about 50 msec

Aligned to compensate in DEQ

This isn't perfect, but it's fairly trivial.  I can't say my time alignments are necessarily even accurate to  0.44 msec, they may not be "accurate" to 1 msec, though I try for 0.02 msec accuracy when I do such things (not frequently) by measurement, and I have believed rightly or not that I can hear balance differences down to 0.02 msec.  I can adjust down to 0.01 msec.  I haven't done a measured alignment in years and it could be as much as 2msec off, but I'd guess it is still within about 1msec.  Nowadays I set the alignment by guesswork mostly.

However, the lenght of the Acoustat being what it is, time alignment at some point is going to differ as much as 8 msec from time alignment at another part on the same speaker, fwiw.

I could just let this slide, adjusting for best response at 96kHz and leaving that to be that.  Or, I could split the difference, leaving a barely audible if at all difference of 0.2 msec on each side (equivalent to  about 2 inches of air distance) which is even less noticeable, or I could resample everything to 96 kHz, or I could adjust if I am being super critical.  Is it more important that the tweeters align with the panels (you'd think so based on the frequency relationships, but not on the large length of the acoustats, which is going to make any precise alighnment moot, and it's barely audible anyway) or the subs?  Right now with DC-1's on subs and tweeters, those are always in the same (mis-) alignment, and they are both point sources, which maybe matters.

I had a lot of concern when just looking at 44.1 whether they were actually within 0.5 msec, or it was 50 msec times some number plus 0.5 msec.  But since they line up nearly perfectly at 96kHz, it seems likely there's only a small extra at 44.1 as I observe, and the possibilities of lining up perfectly at 96kHz by chance even though there's a huge difference...seems very unlikely.  (I spent much time thinking about this though.)

Testing the RD-V1, which I used for a year before getting the Audio GD Dac 19, it has 0.32 msec less latency than the DC-1, amazing for such an ancient device (there's the Apogee clock, which must be an asynchronous receiver system).  AND the latency stays constant at both 44.1 kHz and 96 kHz with the DC-1, which suggests they must both have constant latency (and it was the DVD-5000 et al that have variable latency).

Since I live in the old fashioned world where sources rule because of SPDIF and AES, and Dac's aren't the master with slave control over the source, I put the RD-V1 as my digital transport for CD's, figuring the more accurate clock more important to me there.  But, look what it could do as a DAC, perfect time alignment at every rate.

Sadly my recently purchased RDC-7 has blown outputs, that might have been even better than RDV-1 because balanced output and dual differential 1704's.  But perhaps I was wrong, actually, in believing the RDV-1 does not have dual differential, as I just read somewhere that it does.

The RDV-1 does not beat the DVD-5000 however in RMAA testing.  In fact it's considerably behind in S/N and dynamic range, and about exactly the same in THD.  So it would not necessarily be a better mid way dac.

So we have this ultimate jewel configuration of dual differential 1704's in 19 year old DAC's, lots of them, it seems, not as esoteric as Wadia or even Levinson.  They vary with state of repair or something.  And the analog circuitry, which can generally be assumed to be equivalent to 5534's, which are actually pretty good, I think 5534 distortion is typically below 0.0005%, but not as good as LM 4562.  Compared to OPA2134...a very common choice...I'm not sure the 5534's are clearly worse, they're about the same level.  The OPA 211 are best of all.

Or maybe my poor measurements of my first DVD-9000 are not a matter of state of repair.  The second Denon DVD-9000 measures almost exactly the same 95.8dB S/N ratio, dynamic range, frequency response, the same except distortion in the first DVD-9000 at 0.0014% was actually lower, the second DVD-9000 pretty much matches most of my older dual differential 1704 stuff at 0.003%.

The second DVD-9000 also shows the same hashy looking highest octave noise (but below -110dB) that the first DVD-9000 does.  I'm beginning to wonder if that's an artifact of the PMI 100 digital filter being used.  I love the sound of the DVD-9000 on HDCD's, that was my original reason for having it, but then I decided it was great on other discs too, except my first wouldn't play DVD-Audio because of a problem Denon Service couldn't fix.  Well maybe the smoothing digital filters are actually producing a kind of noise.  Perhaps it even sounds good while measuring poorly.  But this is all speculation now, though the DVD-9000's are the only players to show that noise, and the only ones with real PMI 100's, it may be coincidence.

Here's a picture showing the 9000's and the 5000, and more:

Clearly the DVD-5000 is the winner as an R2R dac in my collection now.  The DVD-9000's both show identical weird top octave noise during the slapped together RMAA test.  However there's no reason not to use the newest DVD-9000 as an HDCD player despite higher nominal measured THD which may be measurement artifact from loading differences.  The two 9000's differ by the second one having a tad more third harmonic, which contributes to only a tiny rise in IM (because, strangely enough, not an even harmonic).  Meanwhile the 5000 is far cleaner at the top, you can see the noise threshold all the way to 20k at least with only a few peaks, but it has more 2nd harmonic, still quite low at -106dB, a flaw I would not consider too serious.  The 9000's apparently cancel that better, but have more distotion elsewhere.  The 5000 does have a bit more power supply ripple though still -120dB.

The RDV-1 does show much lower jitter as a transport, right at my limits of measurement around 170ps.  I think that's what you get from simply tracking a SPDIF stream, the limits of SPDIF itself so to speak, though SPDIF receivers can then reduce it to almost zero using PLL or asynchronous interpolators.  The clock inside the RDV-1 is what ultimately matters, and that could be considerably better than 170ps but no worse.  Meanwhile, the second DVD-900 measures 500 ps playing the same 880 Hz disc (my current test for this, such as it is), clearly worse, not as good as SPDIF itself.

Emotiva!

I've been too disparaging of Emotiva at times.  The truth is, I own and rely on many Emotiva products.  Because they work and are not stratospherically priced like many others.

I'm relying on my tiny Emotive XPS-1 moving coil phono.  It blew away my dB systems dB HG1 even with the extra large power supply.  (They both use the same excellent chip, btw, the LT 1115, basically the lowest noise audio IC in general use, and has voltage (but not current) noise slightly lower than my generally preferred OPA 211.)  The Emotiva has a sweeter sound, is quieter, and has slightly more gain.  I think it has a more sophisticated circuit as well as better parts and an on-board voltage regulator.  I true miracle of miniaturized audio design, sold at tiny price.  Plus the load selections work very well for me, I choose the 470 ohm loading for my Dynavector 17D3.

The S/N spec is 78dB for moving coil (re: 0.5mV).  This is 3dB better than a $2199 Manley Chinook (though I've often and still lust after those).

I've come to believe it might even be about as quiet as the legendary Vendetta SCP-2a.  There's nothing in the design of the Vendetta that should necessarily give it better noise performance than a LT 1115 based design.  Plus, the Vendetta actually trades away noise performance in various ways, such as putting the high frequency RIAA pole in front of everything, where it can't help noise performance.  It does that allegedly to improve IM performance, but it's not clear that is useful either, and the IM spec isn't super outstanding in comparison with the uniqueness of the design.  Though I have seen the 90dB spec for the Vendetta, I strongly believe serious specmanship was involved in creating that number...by the more usual 0.5mV A weighted (which itself is a lie, but whatever) 20-20k spec, 78dB is actually incredibly quiet.  Cranking up the Tact level to 95.8 I still hear no noise from the XPS-1 (I lost my bid on the Vendetta...good thing as it turned out considering all the needed expenses I've had since).

Anyway, I'm also relying on 2 (!) Steath DC-1's.  Since finally dumping the Behringer DCX in favor of Behringer DEQ's for each way, I immediately adopted the Stealth for my subs because it had all the essentials, and good specs, and looked well built.  I needed AES input and XLR outputs so subs could theoretically run on a separate circuit (as, in fact, they now do) without ground look issues.  And the volume control is a big plus too.  Often in other brands you have to pay $2000 to get AES and XLR outputs.

Then, when I (following longstanding prejudices perhaps) decided to use the Denon DVD-5000 as my mid-way DAC (in preference to both the Audio GD Dac 19 and the Stealth DC-1) the DC-1 took its place as the tweeter DAC, in which role it has been outstanding, and in fact it may be quieter, but adds to the realism with its super dynamic sound (possibly my imagination too just because it is so quiet and distortion free), perfect for subs and super tweeters.

And then the Emotive Preamp, XSP-1 (gen 2 I believe) which has made all my Bedroom analog stuff including turntable work for the last few years, and is now proving invaluable as a instrumentation amplifier measuring other stuff...because it's noise and distortion is so low it can usefully measure other equipment.

Now I've devolved my Aragon 28k into a glorified selector switch in my main front end (and removing the tape output series resistors and potentiometer loadings was a big improvement)...I used to use that for instrumentation amplification but it doesn't have balanced outputs and therefore I could never exceed 110dB S/N in instrumentation use and not reliably either.  Now with balanced outputs of the Emotiva I can.  Plus, of course, I can measure true balanced all the way.

I've heard good things about the amps but I've been more interested in more esoteric options for awhile.  If I needed more generic amps (which I now have covered by almost 20 yo Parasound units) I'd consider the Emotivas.

So I love Emotiva and I use them and I'm sad to see the Stealth DC-1 be discontinued just as I'm discovering what a fine product it is.  I'd certainly have lower distortion using all 3 DC-1's instead of the other things I have and continue doing, now with 2 DC-1's.

Distortion is never good

Rod Elliott has some very interesting thoughts about intermodulation distortion.  Basically it requires asymmetry, either in the nonlinearity or the signal.  He then kind of dismisses his own idea with the quip that music is asymmetrical anyway.

But as I was just thinking, the asymmetry is only partial.  There is also partial symmetry, so in fact his observation does relate to music reproduction...in a major part.

The other strange thing is that supposedly good sounding even harmonics are precisely the asymmetrical ones.  Or more precisely, asymetrical non-linearity is what gives rise to even harmonics, and symmetrical non-linearities give rise to odd ones.  So the supposedly good sounding even harmonics are the ones in greater part contributing to the overall IM distortion, in music.

So basically this comes down to, you can't hand wave or excuse distortion away, as a wide swath of serious audiophiles do, with SET, NOS, zero feedback, whatever the rationale, if it leads to significant distortion, that is not good.  (This is not to say, that you might always claim some benefit of greater need, but it has to overcome a significant loss...not a nothing...if harmonic distortion AND IM are added.)

And my own personal threshold of good performance I've noted as 0.01%, however, that should also be weighted by the audibility of harmonics, irritability of the harmonics, and then also rated for contribution to IM.

I was going to say that the requirement for a even-harmonic cancelling balanced device like the Master 7 Dac should be made more stringent because of relative audibility and irritation of odd harmonics left over after the cancellation.  However, when IM is considered...and pure balanced operation cancels asymmetrical linearity generally, and hence the IM associated with it as well, perhaps one should not be so critical as an odd-mostly distortion spectrum such as the one so produced, as long as it is low enough.  And the same applies to all true balanced operating devices and perhaps nearly as much for quasi balanced arrangements like push pull.  These arrangements tend to be beneficial, despite the odd mostly distortion spectrum ultimately produced at low levels.  Of course the best thing is...linearity all the way.

Not that I'm claiming odds are good per se, but I did see one poster claim that the 5th harmonic adds "sweetness" like musical fifths.

I seem to recall some higher ones, and especially combinations of ones, can be quite nasty.

But there's nothing good about asymmetrical nonlinearity either.

Elliott points out that traditional IM measures barely capture the possibilities of IM.

Happy Endings, but wait this never ends

A pleasant surprise discovery on Saturday was the modern-DAC-compatible low latency of the Denon DVD-5000.  And it has pretty good measurments too, though the distortion is just a tad higher than the DVD-9000 at 0.0017% (my measurement is identical to Denon's spec), but the noise is more than 10dB down at -111dB, and all the hashy looking upper octave noise is gone, so it looks to be the better sounding unit in present condition.  The DVD-9000 should have better noise as well as distortion, mine has some problem it looks like, though I now have a 2nd unit not yet tested, to be fair, subjectively I felt DVD-9000 to be my best sounding player (among the 4 "players" I have: Denon DVD-9000, Sony DVP-9000ES, Integra Research RDV-1, Pioneer PD-75)...and I never even bothered to listen to the DVD-5000 as a player I just immediately put it to work as a tweeter DAC, and there it was, possibly better sounding still than my Dac 19 even with the Krell, but I just never bothered to try it.

The low latency makes the DVD-5000 compatible with my other DACs in my multiway system.  RMAA was showing the same latency numbers for DVD-5000 as Dac 19 and Master 7, though in all cases the latency jumps around a lot probably because of the windows computer itself, and the dacs may have very little.  By ear so far it also seems to be perfectly compatible, though I do think I should do a very precise differential latency measurment with oscilloscope to be sure.

So, the DVD-5000 has been elevated to be the DAC for the Acoustats, for the moment, and I think it has less excess highs (including distortion and noise) than the DAC 19 and as nearly as much definition as the Master 7, a kind of budget Master 7, lacking balanced outputs but with the same dual differential 1704's.  (DVD-5000 actually measures better by RMAA than the Master 7, which I'm hoping will get reversed by repair of the Master 7, after all, the specs of the Master 7 are better.)  Reducing excess highs is also especially helpful now that the Aragon is being used for amplification, though I still think I'll chose DVD-5000 over Dac 19 even with most other amplifiers.

Distortion
Spectrum of DVD-5000 (green) vs Dac 19

And now after a month of testing DACs, amplifiers,  and speakers, often only playing one channel at a time or shutting down for the night after 45 minutes...I finally have a fully working system back online that can play all day and night in stereo at any reasonable level.  I even put the super tweeters back online, but it took many hours of readjusting them to achieve, once again, the magic sound, that's just there, which I can finally relax and enjoy.

Anyway, I'm sure it wasn't this way before (and it may be measurement error from my now almost 2 year old phone, or it could be the Aragon vs Krell difference on the Acoustats) but the RTA app is now showing the Acoustats considerably rolled off above 16 kHz.

I could conveniently fill in all the missing highs with my supertweeters.  Or so I am often tempted, and I tried again this time for several hours with many different tunings.  But it doesn't work.  A metallic sound emerges, I think my supertweeters are damaged.  They play OK so long as not stimulated much below 18 Khz.

That's what I've long done, actually crossing over at 19.3khz.  But I've often been tempted to use only one LC filter (12dB/octave).  That also doesn't work, the metallic sound can come back at high enough levels.

What does work is 3 HC filters, for a total of 36dB/octave, starting at 18,811 Hz, or at least that's the magic combination I'm using now.  This doesn't fill in the 16+Khz gap, but the 20kHz band is almost up to the peak level around 1kHz, and there's not too much depression before that.  I'm really only adding to the two highest bands shown (as I can see from other measurements), and there's just a tiny bit of audible mist coming from the super tweeters, but that's enough to make them worthwhile.  They don't actually seem to add to the highs, they soften the highs by the tiniest amount, but add definition to the bass and eliminate beaming.  In short, they push it into hologram territory.

(Depending upon source, there is also info above 20kHz.)

I tried using the Dac 19 on the amp driving the supertweeters, but decided it could actually make some pops (though before it seemed perfectly behaved on sampling rate changes and muting).  So I switch to using the Emotiva Stealth DC-1, I now have 2 of them, one for the subwoofers (which take full advantage of the balanced connection, and the subs are now on a different AC circuit so that helps) and one for the supertweeters, with the DVD-5000 handling the midrange.  This also provides guaranteed identical latency (with time delay adjusted elsewhere to account for the physical position of the speakers).  The

This and some more adjustments to the bass (I added a 2.5dB rise at 20Hz gradually decreasing to 0dB at 63 Hz using the graphic EQ feature of the DEQ), and I'm playing Dylan and the Doors LP's at 99.9 and loving it.

It's spooky good again, and it's a good audiophile talent to be able to turn the combination of units at hand into something that way (which I heard, for example, John Iverson was extremely good at, in has days as a speaker designer, he showed workers how to get the crossovers working to make imperfect drivers sound great).

There are also the times, and audiophiles who just give up, sometimes for months or years, not playing anything anymore because the sounds of memory can't be achieved again.

Update: On axis, the Acoustats are much flatter and don't roll off as much.  The graphs above show listening position approximately, I tried to better guestimate ear positions and powered the right speaker (one with all film caps...though the other hasn't measured different) only, and essentially produced the same results.

Right on axis, the response looks flatter, but it sounds peaky to me, I much prefer the gentle rolloff of the off axis, which I understand is the typical subjective respose and may have some psychoacoustic merit...our relationship to sound producers is generally not on the the axis of best HF response.  Plus, off axis, there much less change with slight change in position, and most off axis positions have excess rather than too little highs, extending audibility throughout my little house.  And then there's the supertweeters, which add to the axis independence also.

Though to be fair, I might prefer a bit less rolloff, or in the present setup, less dip just below 20kHz before the super tweeters kick in.  But making that better integration, removing the 18kHz dip, would require much work...possibly going to a 4 way system???

As is, Friday night playing Side Two of Dave Grusin's Night-Lines at 95.8, it sounds absolutely fabulous (more fabulous than this disk may deserve but anyway).  I'm sure I might prefer a different amplifier or set of speaker adjustments, but maybe not so much a dac.