Dirac vs REW vs DSPeaker

This is quite a long blog about Dirac at WBF and it was all worth reading.

DSPeaker like REW appears to be minimum phase and IIR based.  Dirac is mixed phase and so can correct some additional time delay problems.

I just can't use full range correction with electrostatic speakers because they are very complex in the high frequencies.  Tiny changes in position make huge differences in response.

Sonos Hum caused by STP cables

I'd started to think it was inevitable that there would be hum in the 2nd bedroom Sonos unless I ground lifted the amplifier.  The previous version of the Parasound Zamp V.3 did have a ground lift switch, but mine does not.  It seemed possible that it had been shipped with a 2 wire power cord, but I have been unable to get that confirmed.  I tossed the original power cord into my spare box without checking until later, and when checking later the cord that most likely came with Zamp has only two connectors on the plug (but three slots in the IEC female portion that connects to chassis).

Ground lifting the amplifier might not meet electrical code UNLESS the amplifier was supplied with the ground lifted cord.  And even then, a paranoid electrician might say you are better off having the actual ground connected, which the 3 connector IEC on the chassis permits.  Some equipment is deliberately designed with 2 wire IEC connectors which can't be grounded no matter what kind of cord you attach.  But not in this case, grounding is clearly an option, and an option which would be better used if possible, any good electrician would say.  It protects both against breakdown of the insulation in the amplifier transformer, and current which might be carried inadvertently by the network cables (say, if they had an insulation failure in the attic).

An extra line of defense in my case is that the circuit to which the amplifier is attached has an upstream GFCI outlet which provides GFCI to this outlet.  I tested it with a GFCI tester to be sure.

However, despite all my precautions, my friend who is interested in staying in the Queen's room is never convinced I'm a safety freak (compared with most audiophiles, anyway, who often ground lift and neutral reverse with enthusiasm).  She's constantly convinced I'm creating some kind of electrical safety hazard, even though the truth is I'm constantly thinking about safety issues that hardly anyone else thinks about.  "Everybody does it" would not be an acceptable alibi if she discovers something arguably substandard about the wiring.  This would prove, finally, that I'm a reckless fool to be watched constantly.  So I do really want to do things "the right way" especially in this room.

I have not had a hum problem with any other of my Sonos connections.  I suspect Sonos uses ethernet transformers for the network connections.  But it occurred to me that a ground loop could be caused by the shielding in my Cat6a STP network wiring.

So I tried isolating the ground by using an ethernet coupler to attach a second piece of unshielded network cable.  Sure enough, that fixed the hum!

(Other "fixes" like using short and stout RCA line cords didn't help.)

Now I had been persuaded that shielded network needs to be shielded everywhere.  And I think that's generally desirable.  But this is only one line that goes straight back to the main fast switch in the kitchen.  I believe it won't cause any harm to the rest of the network to have the very end of this line unshielded and ungrounded.  The ethernet line is way shorter than the maximum run of 330 meters, more like 40 meters.

In fact, I've seen this specifically advised for home networks.  Only shield ethernet cables at one end, some people say.  Others, a whole slew of professionals, recommend avoiding shielded cables altogether, and especially in the home, saying that it's incredibly complicated and difficult to terminate the shielding correctly.  But my thinking now is that the solution is easy.  When ground loops occur, lift the cable shields at one end.

The problem here must be that the Sonos modules wouldn't be correctly designed for use with shielded cables because they have no ground connection themselves.  It's funny, however, that this has never caused a problem before, especially for the last year (that's how long it's been) since I installed an all new home network with all Cat6a STP cables.  When an ethernet shield enters the Sonos chassis it becomes, for all purposes, the effective ground.

I've decided to make the permanent solution a new 10 ft length of unshielded Cat6a cable, from the wall panel to the Sonos box in the queen's room.  Using a coupler is ugly (and the current coupler is especially ugly because it's a Cat6a Shielded coupler, and I think all exposed metal is connected to the shield, making it no good for wet noses.

I don't think the 10 foot length of unshielded cable on one dedicated line will adversely affect my overall network at all.  And the Queen's room is a relatively low RFI/EMI area anyway.  The main purpose of the shielding was to protect the long runs of cable in the attic.

I did also order a 1 foot length of unshielded cable and could use that with a nice unshielded coupler.  That way I could limit the amount of unshielded cable to 1 foot.

EQ thoughts

I'm now leaning toward getting the OpenDRC-DI hardware for room correction, and using Room EQ Wizard to design the filters.  I like the fact that OpenDRC-DI has AES/EBU digital connectors, which can plug right into my existing system, and make the best digital connections over short range.  I like the fact that R.E.W. is an open software product, and I can see what it is doing, and possibly what I would like to change.  The downside of this solution is that I believe it does not allow for multipoint correction.  In contrast, DSPeaker dual core does have a multipoint correction feature, though it is not clear how well it works (and the manual doesn't talk about it much).  And it has only Toslink digital connections, which don't work well with much of my stuff (such as the DCX2496, which has no Toslink input, and my Tact 2.0 RCS, for which the Toslink output seems to be no longer working).

OpenDRC is actually more powerful than some other MiniDSP products.  It has enough power to run both IIR and FIR filters.  REW apparently creates IIR filters, much like old fashioned analog filters.  FIR filters allow for the correction of phase and amplitude separately, which makes it possible to do lots of interesting things, such as remove the time delay variation produced by a speaker crossover, or design a speaker crossover with no group delay.

Sophisticated commercial correction products (Acourate and probably Dirac) use FIR to correct system phase response, but that goes along with doing a full range correction.  I strongly dislike full range correction and want bass EQ only.

http://www.minidsp.com/forum/minidsp-for-newbies/7204-can-i-use-rew-with-opendrc-di-for-roomcorrection-answered

Belden 1695a is Teflon FEP (not the holy grail, Teflon PTFE)

Teflon is an audiophile holy grail.  It has superior dielectric properties to all other plastic dielectrics.

So based on that, I was about to buy a Belden 1695a cable for the final stretch of my SPDIF line from kitchen servers to living room stereo.  Instead of 1694a, which is basically the same, but uses PE foam instead of "teflon."  Even though it's a digital line, the dielectric properties could be important.

But reading the fine print, I see that the Teflon used in 1695a is Teflon FEP.  This is not the Teflon that audiophiles seek out (if they know what they are doing, anyway).  Teflon FEP has dielectric nonlinearities 6 times greater than Teflon PTFE.  Comparing the linearity of FEP with Foamed Polyethylene, I'm not sure which is actually better, but I suspect it might well be the Foamed Polyethylene.  I know that's what my friend Tim thinks.

So I'm getting the cheaper 1694a.

I feel similarly about the FEP used in Valhalla cables.  I don't think much of it.

I wonder about the Teflon used in Cardas cables.

Meanwhile, I've decided to get 1695a to connect the Oppo to the SPDIF panel in the kitchen, because the 1695a is said to be slightly more flexible.  I used 1505F for the line from Mac to SPDIF panel because I thought that needed some more flexibility also.  Now I think I might have used 1695a for that one as well, regarding the solid core 1695a to be the better cable compared with 1505F.

Linkwitz on Room Acoustics

Linkwitz has an in depth discussion of room acoustics.

His take is that generally room acoustic treatments aren't worth bothering with.  Instead, choose ordinary furniture and decorations wisely.  So this is not Ethan Winer's advice…

Generally Linkwitz believes lively rooms sound better.  This is very much like my friend George Louis, who eschews both bass traps and EQ.  OTOH, it is not like my friend Tim, who feels that all reflected sound is distortion.  I believe it is correct that lively rooms, though not too lively, sound better.  Rooms where I have replaced carpet with vinyl plank flooring with acoustical underlayment sound much better for that reason.  Old carpet has an old carpet sound, and it is wonderful to be rid of it.  Vinyl plank flooring with acoustical underlayment is the best I have heard.

For technical reasons, room mode calculation is worthless, and it may not help much to build rooms to acoustic dimensions either.  There are simply too many variables.

The closed box bass radiator design inherently excites room modes several times more than dipolar bass radiator.  Dipole bass should be used when possible.

WRT bass modes, attempts to treat room with absorbers can make only marginal differences.  It is best to attenuate peaks with EQ, but holes cannot be filled in.

Like Winer, Linkwitz also believes that response away from the optimal listening position matters:

The response should not be optimized merely at the listening position. Few commercial products deal with this adequately.

On another page, he praises the Lyngdorf TDA2200 amplifier and correction module, which has correction algorithm by Jan Abildgaard Pedersen--which samples from random points in the room!

What Ethan Winer writes about EQ

Ethan Winer sells bass traps, so not surprisingly he is critical of claims made by sellers of automated EQ systems--who sometimes suggest EQ will handle everything.  I think his criticism is somewhat refreshing in an industry that generally refrains from being critical of any excuse for you to spend money.

But he is also somewhat contradictory.  At the top level he makes exaggerated recommendations like "Just say no to Room EQ."  But when you get down into the fine print, he does suggest that the use of EQ is warranted to tame the 1 or 2 most serious modal peaks.  He uses the EQ feature of his SVS sub to do that.

He also recommends Room EQ Wizard to do measurements and filter calculations, and the use of a $150 Behringer Equalizer to do the corrections.  That's excellent cheapskate advice, straight from Home Theater Shack!

Since EQ can only correct response at one location at the expense of others (a claim that Ethan reiterates a lot…but hardly anyone else in hifi does…especially those who accept the idea that there can only really be only one really good listening position), Ethan suggests only using half as much reduction as measurements indicate.  That's the kind of fudging I've been doing since I started with EQ in 2005.

I continue to do a bit more than just tame the two worst modal peaks (as his recommendations do also), though I've only done manual EQ adjustments, doing measurements with Tact and SPL meters.

The downside of acoustic treatments is different.  You can't make much difference without giving up a lot of wall space and a significant chunk of floor space.  You can spend a huge amount of money to only get a couple dB of difference at modal peaks.  With many rooms, you could line the walls and fill the corners with acoustical treatments, spending $30k or more, and still have bad room modes.  In fact, in most rooms, it's simply impossible to add sufficient bass trapping, let alone too much.  That's why many acoustical absorbers are designed to trap little or no highs…because if you fill the room with high frequency traps the room will sound horribly dull.

In my multipurpose living room I find it hard to imagine where I would put traps to make any significant difference at all.  There is so little room for traps, and the modes so large, I'm strongly tempted to use an active absorber, like the one from Bag End.

I'm currently thinking about a living room redesign to make it better for parties and watching TV.  The result will be even less space available for room treatments.

Review of Acourate

Here's a great review of the Acourate room and speaker correction system.

The review also shows many other things, such as the calibrated mic kit from iSEMCON, calibrated microphones from Cross-Spectrum, and more.

My collection of calibrated microphones is in bad shape.  I have a calibrated mike for LAUD V3, which works only with that program running on a Win 98 PC with Fiji card.  But I'm unsure that the calibration file is properly loaded.  I haven't run the program in years.

I have two Tact RCS 2.0 preamps which both came with calibrated microphones.  I can't remember which microphone went with which preamp, and the Win7 laptop I run the old 2software on makes it unclear whether mic calibration file is loaded or not (the window is blacked out), or which one is loaded (if I could even remember which was which).  Many Tact users decided that the factory calibration wasn't any good anyway, you'd be better off simply using an "average" calibration file for these microphones (similar to ECM8000) to avoid false correction, especially in the highs.

Somewhere I have a Mighty Mike which was never removed from the box the ebay seller shipped it in.

I have an IVIE IE-30 which I haven't used in a long time and needs battery replacement.  It came with an ACO mike in preamp holder.

I have several Bruel and Kjaer microphone capsules with paper curves made in the 1960's.  They must be use with appropriate microphone holder such as the one on the now non-functional IE-30.  B&K also use very unintuitive way of describing the frequency response/polar characteristics of these microphones.

I have several General Radio microphones which came with my GR1933 SPL meter.  These have even more specialized mounting requirements than the B&K's.  I also have some barely working B&K SPL meters.

I have a pile of Behringer ECM8000 microphones which I got in various ways, and I can't remember which is which.

I have Galaxy meter which was tested by Home Theatre Shack and said to be within parameters of their standard Galaxy correction file.

I can never decide whether the time has come to buy M30 or similar serious measurement microphone, though it could be argued I should have done that a decade ago and avoided some of the other things (especially the Ivie, B&K and GR meters).

At this time, I'm not much adjusting anything but bass anyway, so why do I need microphone with 30kHz response?  Though I would like to measure super tweeters anyway.