July/August Recap (up to August 12, with Audio Party on August 13)

1. Did final and definitive test showing that both Acoustat speakers were actually OK, and spare interface was not OK even if treble transformer was disconnected.  So ordered and have now received replacement HF and LF transformers to fix the spare interface when I have time.  Years ago those replacement transformers were unobtanium--so best get now while the getting is good.  Michael Savuto at Analog Associates is now the source for replacement Acoustat transformers now manufactured by Galaxy Transformers who makes them to the original design.  I contected Galaxy first, and they told me to contact Michael, who was helpful and gracious.

2.  Changed Acoustat fuse values to 3A slow blow,  first with fuses from the last Radio Shack store which was soon to close, and now with HiFi Tuning Gold Fuses from Parts Connexion.  3A is latest recommendation from Roy Esposito, and he says it was actually the first recommendation from James Strickland who reluctantly increased to to 5A to reduce nuisance blowing at dealers, but post 1985 high power and high current amplifiers are now capable of blowing the transformers faster than a 5A fuse will blow and do so all too frequently.  I was disappointed, however, that Roy flatly refused to work on my modified Acoustat interfaces.  He told me he un-modifies any such modifications (external polypropylene crossover cap replacing the original electroylitic capacitor inside) without warning, AND he seems to think I'm dangerous or something for even thinking about fuse-less operation.  I don't think he understood me that I have never myself operated Acoustats w/o fuses, but it seems many famous Acoustat users have, and I was merely trying to suggest in my email that those people should at least temporarily use fuses when testing new equipment, which I do often, and which specifically led to my latest failure, I thought at the time.  I did not know at the time that my original interfaces were actually OK.  As dangerous as I might be, now it appears I have not damaged my Acoustat interfaces in 7 years, and it's quite possible the one I broke in 2010 had actually been broken by a previous user.  Also I renewed my understanding of the interface and thought a lot about other interface modifications, reading about half of the Acoustat AnswerMan thread at DIYAudio, where lots of people have done a film capacitor substitution similar to mine, and Andy Savuto, former Acoustat engineer, thought it was an excellent idea.  Reading that forum there are many many people who have done far more risky modifications than I have.

3. Hooked up and tested the Eagle 2 amplifier, quickly deciding that it is indeed very special, as I remembered from 1988.  But under-current and/or my unit needs work.  Purchased two more Eagles for High Current (one of two options) mono conversion.  Tested one of these and it stated snapping inside--it needs work!  Learned a lot about Eagle options, etc.  Now I see why there is a 7, but mono'd 2's should work for me as the output level is ok with 2's, they just need high current mono conversion to deal with impedance below 2 ohms.

4.  Purchased cheap Integra Research RDC-7.  But turns out to be dysfunctional.  I'm now thinking Denon's quality level is at least as high as Integra Research in Denon statement models like DVD-5000.

5.  Mass tested DACs using RMAA, reaching some new conclusions.  Also tested time delays---they must be controlled I see now.  Determined conclusively my Master 7 needs repair.  Decided that Denon DVD-5000 looked to be the best of my remaining dacs, so I bought another one.  Now have two Denon DVD-5000's online as mid range and super tweeter DAC's.  Also got second Emotiva Stealth DC-1, the first one measured best of all distortion and noise.  But that is now a backup.  Considered getting third DVD-5000 (I could have them on all 3 ways, but would give up XLR digital and XLR audio connections unless I got an additional amplifiying device, so lots of extra space and complications).  Forgot to increase bid and lost out on incredibly good deal on one with 14 day guarantee.

6.  Set up Laboratory (2nd bedroom) for first time in 6 years.  Finally cleared big toolbox from bench by buying and putting up a rolling support rack for the toolbox instead (just as mechanics do, and it was my ultimate plan from a decade ago, but there had been many delays until I finally recycled some boat anchor equipment in December).  Set up RMAA computer on top of bench and continued doing RMAA testing there, using Emotive XPS-1 as buffer amplifier.

7.  Tested old DVD-9000, which I had previously determined to be my best sounding player, as my living room mid way DAC.  Sounded great but it is too much trouble to keep adjusting delays for each sampling rate, and needs huge 330 msec latency adjustment at 44.1kHz which requires putting 3rd or more DEQ online because each one can only compensate for 300 msec.  Bought second DVD-9000 which is fully functional, including DVD-Audio.  Put the new DVD-9000 online as my new HDCD/DVD-Audio player to replace my original DVD-9000 which was unable to play DVD's at all and is now offline.  Set menu settings on the DVD-9000 for best 2-channel use.  Also strangely the DVD-5000 measures 15dB better S/N, though DVD-9000 has slightly lower distortion according to RMAA.  That held true for both 5000's and both 9000's.

8.  Determined my Integra Research RDV-1 as a CD transport has my best jitter performance and I am now using that for CD digital, which sounds great!  Not long ago, I would rarely even do this, always ether resampling or playing off my harddrive.  The RDV-1 does not have as good S/N from analog output as DVD-5000, but it has 2.5 times less jitter than the DVD-9000 as transport.  Actually the jitter from the RDV-1 measures 180 psec, which appears to be the limit of SPDIF itself, or my Sencore jitter meter, since I have never seen it go lower than that, you could call that my "residual" (though I'm not actually sure it is, the Sencore is marked down to 20ps but nothing I've measured has been lower than 180ps, what I measure for the RDV-1).   The DVD-9000 measured 500 psec at the SPDIF output, somewhat disappointing, but at the analog output it is probably internally synchronous so there is little jitter in that.  After testing, I restored the hockey tape insulators that help silence the noisy RDV-1 drive system, which is not especially quiet and noiser than most CD players when playing CD's and there's no fancy "seal" system like many pricey players.  But with my hockey tape, it's no worse than the typical CD player.  The RDV-1 boasts a clock by Apogee, likely that is far better than most players, and when using SPDIF and AES as the system interconnection method, everything past the transport must follow the clock of the transport in some way, so it's arguably most important (a DAC need not even have a clock, in principle, just a pll locked to the incoming data stream).  BTW my Denon DVD-5000 dacs use the Crystal Semiconductor CS 8414 input receiver, which is fully synchronous.  I like the idea of synchronous.  However the newer DIR9001 synchronous receiver has an order of magnitude lower internal jitter (from 200 ps to 20 ps) and may have better jitter rejection as well, though the 8412 and 8414 were highly regarded in the late 1990's when the DVD-5000 was made.  (The 8416 was considered somewhat inferior, and some consider the 8412 the best of all.)  When I tested jitter at the very end of many digital interconnections in my very complex system, it was still only 220 pS or so, regardless of source, if I ultimately used coax...I've never tried that using a Denon as transport however.  Presumably a DAC could reduce that to essentially zero above 1kHz with only 1mS of latency with well tuned PLLs.  It might already have been reduced by the Tact or Behringer, which have their own PLL's.

9.  Determined more-damaged-looking left Elac ribbon super tweeter had 14kHz resonance (evinced by long decay on RTA) and perhaps others, contributing to metallic sound.  Researched new ribbon, dome, and other super tweeter options.  The smallest RAAL looks most interesting, uses flat foil damped with etching and has response to 100kHz, and looks very (if not perfectly) clean in decay waterfall.  But for now I bought two Vifa NE19VTS tweeters, and cobbled together a bipolar super tweeter box with my old (and best of all) Dynaudio D21AF's in front, and the new Vifa's in back.  The back supertweeters seemed essential for best result.  Cobbled together crossover and adjustments for it also.  Much experimentation demonstrated how the supertweeter adds missing "power" to the sound, strangely adding a sound very much like when I had the Eagle 2's playing the Acoustats with no super tweeters.

When I turn the super tweeters off, the system sounds wimpy.  And yet, I can barely hear anything coming from the new super tweeters if nothing else is turned on, especially after I've made the cutoff much steeper in past couple months.  New Hakko soldering iron worked very well to set up the new blocking capacitors for the two tweeters, and I've done more soldering already this year than most of the past 30 years.  So what is going on here?  Is it a physical effect, perhaps some sort of summing going on in the air itself.  Or is it some process going on inside the brain alone?  (Or am I just imagining that I even hear an effect...I'm not sure I want to know.  I certainly don't want to bother to try to prove it yet.)

10.  Verified that Krell FBP 300 right channel was not working correctly.  Checked freight rates at a different company first, then chose Ocean Air again.  Packed and shipped it out.  After trying Eagle 2,  and having it shut down twice, I set up Aragon 8008 BB as current backup amplifier.

11. Found that off tuning certain stations, including KRTU and KSYM, by +25kHz, gives best result.  This, along with sampling through Lavry AD10, has dramtically improved FM radio sound, even on "oldies" FM stations and the like, sounding better than ever, and somehow similar to the sound of the Marantz 20B on those oldie stations.  I think the off tuning enhances rejection of on-channel alternate station.  Rejection by off tuning with Wide bandwidth does something good that Narrow never does, and I think it's related to capture effect, blocking on-channel or adjacent channel signals.  I had always thought the 25kHz L-1000T tuning to be inadequate, but in fact it works great.  I never had such a clear win with the 10kHz tuning of the Yamaha T-85 years ago.  Kenwood engineers seem to have picked the perfect off-tuning amount for their detector.

12.  Researched cartridge loading.  IAR suggests going as low as you can, 5 or maybe 2 ohms if possible, with lowest impedances reducing IM, if you can deal with the level reduction.  I was using 470 ohms, so I tested the 100 and 47 ohm settings of my XPS-1.  I determined that 100 sounds best, and that 47 ohms both reduces the level too much and makes it sound slightly strained.  I also changed tracking force from 2.2g to 2g and re-leveled turntable.  Also oriented XPS-1 (now held in place with with hockey tape) and moved the 220V transformer for L-1000T further away, reducing hum as much as 20dB so that hum and noise are now below -80dB rms in both channels at 97.7.

13.  Used Tact measurement mode to adjust 3 way time alignments, first time in at least a year.  Was difficult to see exactly what to do, and I need a better program.  Also did many, many adjustments to PEQ's, levels, and time delays, which yielded far flatter response, more solid bass, and sweeter highs.  Did adjustments based on 1/6 octave RTA app and Stereophile pink noise mainly, and when things didn't sound good I made more changes until it sounded good.

14.  Tested new Marantz PMD661MkII digital recorder, recording the output of the Lavry AD10 digitizing the output of the Kenwood L-1000T playing KPAC which was playing a local pipe organ concert.  This may be a far easier way to make digital recordings from FM radio and vinyl than the Masterlink, primarily because I can upload so easily to my computer afterwards.

15.  Digital from the kitchen Oppo reaches the living room system fine when using the DVD-5000 Dac's.  No issues on any disc tested so far, except that SACD, which is supposed to output 88kHz when PCM mode is selected...as it is...is not going through.  But playing the HRx discs from Reference Recordings at 88kHz works fine.  I discovered back in May or June that I could actually do that now, for some reason, unlike the first time I tried in 2014, and it has been a boon.  That means I can play any disc with high res files on it.  But I still need my 9000ES player to play SACD's.

16.  I've been discussiog preamp designs with my friend Tim, and I bought a very expensive book by Vogel on solid state phono design.  We've both become very interested in balanced phono stage for MC, which should reduce IM.  I read about the Vacuum State Electronics balanced preamp design and was fascinated by the ideas used.  Tim felt that the tubes were not usefully deployed in that circuit, and would be better replaced with OPA 211 circuitry following the initial amplification device, for both greater linearity and lower noise.  We've been discussing impedances, use of transformer, etc, etc.

17.  Reading about jitter, obtained but barely started reading the Dunn paper for AP.  Bought two books on acoustics, one by Toole.

18.  Added, yet again, infrared remote capability to control my L-1000T and Tact 2.0 RCS from the kitchen.  The L-1000T is pretty reliable, the Tact less so.  This is simply a placement of the Radioshack IR extender transmitter in the living room bookcase.  An idea I somehow hadn't thought about before.  I tuned up a bunch of stations into the L-1000T memory.

Interesting Links

Here's Joe D'Appolito on loudspeaker measurements.

Here's Julian Dunn on Digital Audio measurements.

Here's Audiophile Nirvana's Resource Library.

Pictures and bios of people associated with the Boston Audio Society, including Hadaway (I've bought lots of stuff from him at dB Audio Systems, great guy), Meyer, Moran, and others.

Distortion Analyzer recommendations (from 2007, but I think John Curl still uses his modified Sound Technology).

Pictures and info about Sound Technology 1701A analyzer (just checked and mine is actually a 1700B, said to be the same as 1701A except for a few opamps were upgraded to 5534 and the oscillator changed).

Vintage audio publications, including 1700AB manual.

Repairing a 1700B, one person's experience.  He says the common view that LDR's and VCR's are what goes bad help up in his repair--once those were replaced everything else was fine.

Ethan Winer's book The Audio Expert (which I have just now purchased).

My current page at the Restaurant at the End of the Universe, more commonly known as the Blowtorch Forum Part II.

Soundoctor on Surround Sound.

Amazing history of Dynaudio (interleaved with many other speaker driver manufacturers).

Archive "A" of Dynaudio spec sheets.

Archive "B" of Dynaudio spec sheets.

My preferred supertweeter, the D21AF, has the most extended flat high frequency response (+/- 1dB to 40kHz) of anything shown, including the Esotar^2 110 (which sells for $1400).  After the D21AF and D21/2, Dynaudio has avoided building 21mm tweeters, basically specializing on 28mm tweeters which had started with the D28.

The D21AF does have an (proprietary) damping fluid (probably aka ferrofluid).  For supertweeter usage, the preferred approach would probably be no damping fluid.  Later models use ferrofluid also.

My sense now is that the Vifa NE19VTS is a decent substitute for D21AF in supertweeter applications, though the D21AF *is* better and looks to be far more rugged (my D21AF have survived over 18 years of triamplification...powered directly by amplifiers such as MC 225 with no protective capacitor, etc., because I was relying on electronic crossover.  But I am sure I pulled the audio cords by mistake at least once, sending large low frequency hum and/or transients into the D21AF and it always shrugged them off without damage.


Downloadable audible jitter tests.  The author produced elevated jitter levels high enough that they can supposedly be reliably heard.

Jitter comments by Steve Nugent of Empirical audio.  The thresholds he described were derived by computer models and not actual human testing.  Human testing has not shown jitter to be reliably audible until being many orders of magnitude higher.  Empirical was selling products with low jitter as an important feature.  So I don't trust what he says very much.

Another interesting discussion of jitter, with both viewpoints.  A graph from J. Dunn does show jitter less than 100 ps being audible!  However, that is only jitter above 3kHz.  There is an incredibly steep curve, with 20 Hz jitter being audible only above 1uS, to 20kHz jitter being audible down to about 30  ps (!!!).  This might be based on the same "simulation" Nugent talked about, but he didn't note the low audibility of lower frequency jitter.

The Richard C. Heyser memorial lecture published by Stereophile in 2011.  I notice that Heyser was unmentioned by The Audio Critic when it listed White and Black hats.  John Atkinson, who gave this lecture, was not so lucky (however, he Atkinson reacted very kindly IMO and said he was actually a Grey Hat).  Perhaps Heyser, an actual physicist, would be the quintessential Grey Hat.  BTW, John Atkinson, John Curl, and Bob Carver all have physics degrees.  Anyway, one more interesting fact about Heyser is that (at least according to a poster on the Blowtorch blog) never participated in blind testing.  He simply refused every time.

Refurbing a Parasound HCA-1000A amplifier.  I may be doing this before too long, because the 1000A powering my super tweeters does have significant power supply hum, which gets stopped now by a blocking capacitor, but really shouldn't be there in the first place.  The power supply caps, which were marginal because of space and cost at the time, apparently are the main thing to replace with something slightly better.

A poster in the blowtorch forum mentions a few other DBT protocols other than ABX: ABC/HR, PEAQ, ABC/HR, PEAQ, MUHSRA, duo-trio, triangle.  And he says there are more.

Funny way way back in the mid 1970's before I even worked at an audio store, I believed that determination of audible limits required forced-choice tests, rather than preferences.  I reasoned then that preferences could be more than one-dimensional, and could change over time, including during the test itself.

ABX appeared in the early 1980's, and it clearly was the kind of test I thought should be used.

However now (August 22, 2017) I am thinking that ABX is too cumbersome, difficult, and loaded with baggage that typical audiophiles won't like.  I'm thinking a simple blind A/B preference test, repeated to reach "decision" level probability.  The test could be relatively open ended...I think it's possibly the statistics can be made slightly more stringent (such as 0.02 instead of 0.05) to allow for early quitting or extended testing as desired.  The "proctor" tells the "testee" whether or not their decision has been made (meaning, enough trials and consistency at p<0.02 level) and they can keep going or not.  If consistency is not reached, a fair proctor will not reveal which devices was the "better" one.  Of course the level should also be controlled--and that is one of the biggest factors in the traditional lousy audiophile A/B test.  ALSO, the "testee" must reveal if he believes his "preferred unit" has changed.  Precisely at that point, the Proctor should reverse the previous entries.  However, the testee may also chose never to reveal which actual unit he prefers.

Discussion of the best sounding shortwave receivers.  Some say the famous Collins R-390A isn't good for station hopping as it's really intended for long term monitoring, though it is an engineering feat and blast to play with (others say the R390A is fine for band cruising if in good repair).  For listening to shortwave broadcasts (??? does anyone do that anymore ???) the Collins 75A4 is among the best.  People also like the Drake 4B but not the cheapened 4C unless it comes with all the options.  The Hallicrafters SX-115, SB-303, and Hammarlund HQ-215 are prone to overload now.

Here is a comparison of Drake R4B and R4C.

Now, however, I have learned that the R4B and R4C were only Ham receivers, receiving bands assigned to amateur operators, and NOT general coverage receivers.  You could convert them to general coverage using an external LFO (however, I wonder if that is really as good as having the general coverage built in.)

OTOH, the Drake R7, TR7, and R8 units all have general coverage receivers, with very good reputations.  The R7 and TR7 do not have identical receivers however.  The R7 receiver is triple conversion and it has more bandwidth selections on certain ranges, and may have a better blanker (there were apparently several used during the production runs of the R7).

Watkins-Johnson made some very nice looking VHF/UHF receivers including scope.  Audio quality out the back panel jacks said not always good because of digital grundge, but audio out to headphones said to be OK, and could be amplified.

Finding shortwave stations.

A discussion of loudspeaker measuring systems.  Speakers and the Room are the most important things, and I need to be getting back to loudspeaker measuring for my 3 way system.  DIYLoudspeakers.com looks to be a useful resource.

Pano, a DIYAudio moderator, has had a level test inquiry.  He provides test signals to see how much voltage your speakers actually need.

A discussion of speaker driver materials.  It confirms (and corrects) what I have long said about the Kef B110 woofer used in LS3/5A.  The crossover uses a 6dB notch to correct the 1.5kHz resonance.  I discovered that the hard way, because for 18 years I used a standard electronic crossover with amplifiers driving the woofer and tweeter.  I begin to think there was some reason I could never get it to sound exactly correct, then I discovered the 6dB peak.  (Actually, I had recalled the peak being 12dB.)  The woofer has other resonance problems also and is very inefficient.  He says what I've long believed, that it is very strange that people still revere this design based on now very outdated drivers.

New Super Tweeters! and some more adjustments

I didn't know how long it was going to take to get new super tweeters online.  I am kind of slow about putting together new stuff.  Even old stuff which just needs to be set up, can wait months, just to get set up.

But the new super tweeters went up quickly last weekend, then survived a second unexpected (but required) important modification.

Actually I put up the first Dynaudio D21AF the previous weekend, replacing the one measurably resonant Elac 4PI in the left channel.  That was a huge dosage of relief.  Much cleaner highs, with each cymbal sounding unique.

There was clearly a lot of asymmetry, having the wood boxed one directional tweeter on one side, and the shiny metal encased omnidirectional ribbon tweeter on the other side.  Though it still seemed having both supertweeters turned on was far better than having them off, and much more so than ever before in a long time.  I figured I could live with the assymetry, maybe, for a few more weeks.

I didn't set up the new super tweeter on the right side firstly because that side is near the entrance to the living room, where I and many other people are constantly brushing against (or hanging on to) the  Elac supertweeter, held in place with a clamp.  Until I get the new stands put together, I won't have any way of holding up the LS3/5A cabinets which now "host" the D21AF tweeters (part of my experiments 1986-2004 with highly modified "LS3/5A" speakers...including the new tweeter).

I first figured that in order to have the D21AF inside a LS3/5A cabinet on the right side, without getting constantly knocked over and possibly damaging any or all of the new super expensive and super unobtanium components (the speaker box, the B110 woofer, the D21AF tweeter).  The new stand has a "split" post which means I could wrap a series of nylon tie straps under the stand platform and over the speaker, securing the speaker to the stand.  The new stands would also be lower, which I figured would mean less chance of getting knocked over.

But I took another look at this problem Friday night.  It appeared to me that having the speaker lower than 40 inches would not make it less likely to get knocked over.  If anything, a speaker placed at 32 inches on top of the shorter stands (which will require a weekend of assembly now) would be *more* likely to get knocked over.  The higher speaker is actually not in the way of swinging hands.

Only then I sought an answer to the essential question online.  How does one hold a speaker to a stand so it doesn't get knocked over?  I hadn't faced the problem before because I had only used stands in the bedroom near the corners, where there was no chance of the speaker getting knocked over.

And the answer is, as I should have known: Use Blu Tac !

Just a matter of months ago I had renewed my supply of Blu Tac (for which supermarket tac made by Dap and others is useless, useless, useless and only blu tac works correctly).  So I had several unopened packs of Blu Tac ready to go.

This turned out to be pretty easy.  Except that I first blu tac'd the wrong end of the speaker onto the right 40 inch stand, and had to peel it off (almost completely), wipe clean, and I decided also to use some of the moisturizing Pledge, sprayed on a cloth in the kitchen (and the overspray temporarily made the kitchen floor slippery, maybe this should be done outside).  Finally I had the speaker blu tac'd into place and hooked up with a 0.5uF capacitor as on the left side (the actual 6dB "cutoff" into an 8 ohm load would be 40,000 Hz...but since the level is set reasonably well at 20kHz, this means that there is an extra boost of 6dB at 40,000, which might even be somewhat helpful).  This seems to work well.

But now it was clear that the lack of super tweeting toward the back wall was flattening the image.  Where the image should be behind the plane of the speakers sounded strangely sucked out, the image want to be only in the plane of the speakers or more forward.  I really really wanted to go ahead with adding the Vifa NE19VTS tweeters I had purchased recently to the back of my supertweeters.  After  a quick survey of tweeters below $1000, and in cloth domes which dampen the high frequency resonances, the NE19VTS is a stand out winner with nearly flat--actually slightly elevated--response to 40kHz, which actually looks remarkably similar to the D21AF on the charts.  The more expensive cloth domes, especially including the 19mm Eton suggested as replacement for D21AF, just don't reach 40kHz.

I had imagined this as an elaborate wood working project, making a small box for the D21AF in front, and the NE19VTS in back.  Such a box would need to be very non-resonant.  It should be big enough to house and protect the two tweeters, and have enough space for crossover components, but otherwise be as small as possible.

Well it turns out I already have the D21AF mounted in about as non-resonant a box as I could ever make...the LS3/5A cabinet.  It is somewhat too big for the new intended purpose, and has a useless B110 driver mounted up top which surely isn't an advantage now.  But otherwise, it works, and it might take me hundreds of hours to come up with something better (I'm no wood worker, though I have access to a maker space).  Hundreds of hours I'm not likely to have until I retire in 5 years.  And, lets face it, there are more important things in stereo, let alone life, than perfectly sized supertweeters.

But I would be extremely loath to modify the LS3/5A cabinet more than I have done already (to mount the D21AF, I very slightly enlarged the inner circumference of the hole for the original D27, which could still be re-mounted at some point, and I have two NOS T27's ready to go for that day).

I wouldn't even like to make a small hole in the back, near the top center, for a single small screw to hold in the Vifa tweeter, and the tiny size of the mounting ring on the Vifa suggests that wouldn't work very well either.  For a number of years in the late 1970's and early 1980's I used tweeters mounted with one screw to flat piece of particleboard which sat atop my Advent speakers.  As with the LS3/5A, I hated the Original Advent tweeters.

I agonized for quite awhile over the possibility of making a small screw hole.  But I feared in might cause air leakage, and for sure it would reduce the resale value of my LS3/5A's, should I ever have time to put everything back in place enough to resell them.

But now that I could see how strong Blu Tac is, I figured I could just Blu Tac the tiny Vifa tweeters to the top of the LS3/5A cabinet.  And sure enough, it works and seems quite strong and perfectly stable.

At first, I just connected them to the same 0.5uF capacitor which cuts out the non-ultrasonic from the D21AF.  But I immediately measured and noticed a large drop in output on both sides.  It took a few minutes for the idea to hit me--of course I am changing the load from 8 ohms to 3 ohms (4 and 8 ohm tweeters in parallel) with the same capacitor, so the cutoff is now 3 times higher, or that much more loss (8dB or so) because of the way the high pass is attenuating below the "cutoff" frequency.

While I think I normally have pretty good electronic intuitions, this one had just blasted past me, though I was thinking a lot about the effect of the "3 ohm" load on my Parasound HCA-1000A amplifier.  But it should be able to handle any load with low enough output and this is very very low output, and it isn't tnat unreasonable of a load for such an amplifier either, and actually the tweeters themselves are getting higher and higher impedance...the ultimate limiting factor, the voltage attenuation of the capacitors merely being *additional load*.  So the only place where the capacitor drops to a low value like 2 ohms is going to be close to 100 kHz, and at that point the tweeters themselves will have way above normal impedance because of voice coil inductance, so their parallel impedance will be much higher, perhaps around 8 ohms.  So, there is no real "load" problem here, despite having two tweeters in parallel, at least as far as being a problem for the amplifier, the capacitor attenuation network takes care of that, and there basically wouldn't be anyway.

But I needed to add capacitance.  It seemed a better way was to simply use a second capacitor for the new Vifa's, which I probably should have thought of right off.

Since the Vifa has lower impedance, it would help, I figured, to have a higher capacitor value, such as 1 ohm, but I didn't have a nice matching pair of 1uF poly caps in my junk box, just a second pair of the 0.5uF's, so I decided to go with those.

Very carefully I've done all the new soldering, after the attachment of the right super tweeter to the stand with Blu Tac, actually in the living room, while the cat was not around, and without spilling the least bit of solder (except at one point a wire dripped the tiniest amount behind the speaker, which I cleaned up).

In fact, I even did all the second capacitor soldering with the music playing, and got treated to some tiny sparks.  In retrospect, I wonder if that's the best way.  The currents must have been tiny though.  Nothing seemed to have been harmed and the solder joints seemed as good as I have ever done, using my relatively new (NOS) classic soldering iron I bought from recommendations at DIYAudio.

And when it was done, it was wonderful.  Though the back level is indeed a few dB lower because of the load, it nevertheless works wonderfully, and there almost seems to be an omnidirectional effect when I measure with my iPhone RTA app.  Having two tweeters, front and back, somehow produces sound all around at 20kHz.  Possibly mostly reflected sound, but it decreases with distance from the speaker.

The ultimate effect is far better than the semi-broken Elacs 4PI's  (To compete now, the Elacs will need to be fixed.)  The 3D time machine is back.

I proceeded to re-adjust the DSP to make the RTA spectrum smoother and flatter.  I moved around the control frequency above 2k and around 6k, for an utterly smooth rolloff above 3kHz.  I added two new filter frequencies 630 and 500, and first went after the bigger 630, but later found that if I fixed 500, I could then tweak 630 just a little.  I was afraid to do this just on the advice of a 1/6 octave RTA, but that is better than what many have used and still do.  I prefer to set these things using oscillator to find actual center frequency, but I didn't have time for that, though I was intending to do so.

Noticing that my GEQ of deep bass to a 3dB rise at 20kHz (in the face of many  many PEQ"s which cancel in this very area) wasn't helping at higher bass frequencies--which were depressed, I raised the entire subwoofer level 4dB instead, which greatly flattened the bass response, but then lowered to only 2.5 dB higher.

These and other changes led to the smoothest RTA I may have ever seen.

And it has sounded wonderful, playing CD's, FM and LP's.

More transparent than ever before.

Turning the panels off when playing pink noise, the ultrasonics seem to make a huge effect on the bass from the subs.  With the super tweeters, the bass sounds thunderous and authoritative.  Without the super tweeters, the bass sounds artificial.

Ionovac and Ionofone tweeters

http://www.roger-russell.com/ionovac/ionovac.htm#otherionovac

Ionic speakers go way back, even before other types.  The first ionic speakers were demonstrated in the late 1800's.

The 'modern' ionic speaker is the Ionovac tweeter (and it's Ionofone cousin) which were invented in 1946 by Siegfried Klein.  They were used in a variety of speakers, one being the ElectroVoice Patrician system.

The Ionovac has smooth and extended response into the ultrasonic free of resonances.  However, the basic design is plagued by relatively high IM distortion at high output levels.  Early units required frequent replacement of the quartz emission tube and this only got somewhat better over time.  There are also regular amplifiying tubes that need periodic replacement.

The Hill Plasmatronic is mentioned but based on a different concept.

I would think the Iverson Corona speaker is a full range version of something more like the original Ionovac--which is often called a corona speaker.

Another issue: ozone is definitely created.  That kills the idea for me.

This builder says it is safe because it is actually very little ozone.


This all seems silly to me now when it's clear you can have 40kHz response with relatively low distortion from a fabric covered dome, in the Dynaudio D21AF or Vifa NE19VTS.  The domes have very damped high frequency resonances.  Also, an endless variety of ribbon tweeters.


Update: I see the problem with dome super tweeters now.  The problem is dispersion.  Where the wavelength gets smaller than the dome (10-20kHz) it begins to beam more and more.  The dispersion quickly falls to nothing, typically around 30khz.

Electrostatic panels beam also, but since they are fairly wide to begin with, the beaming isn't quite as narrow.

Ionic drivers can be omnidirectional.  The "corona" naturally radiates in all directions.  Or they can have whatever dispersion you engineer your horn or waveguide for.

About the only other trick for that is what I already have (and need to get fixed): the Elac 4PI's.  The 4PI an omnidirectional speaker, in which the ribbon is almost a complete circle, suspended in a toroidal field.  This is, indeed, a kind of engineering miracle.

Replacing the left Elac with a D21AF has resulted in a huge increase in the audibility of beaming type artifacts as I move around the room, far beyond what I had noticed beforehand.

Adding a back dome (like the Vifa NE19's I now have) might help somewhat, but I doubt it would do the job as well as an omnidirectional tweeter.

Well there are other trick, in general you can use horns, acoustic lenses, and other tricks to make a normal beamy driver into a wide dispersion or omnidirectional one.  The newer Walsh-type drivers by German Physiks I think have pretty good response into the ultrasonic.  The original Walsh units made by Ohm did not have super extended HF response.