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Answering some unanswered questions
Arnold B. Kruege...
post Oct 18 2012, 14:28
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I've been reading up on ABX tests all week and i just give up. I don't get it. There seem to be a few stand-outs such as cables, and devices with D/A converters that don't make any difference, but i'm about ready to throw up my hands in frustration. I just don't get it.

I read a lot of misapprehensions.

Speakers can be so physically different. I've got the Anthony Gallo Acoustic Reference 3.1's. They are about 3' tall, have rounded "cabinets" around the cones, a cylindrical tweeter and a 10" side firing driver. How can they sound the same as a speaker built around a single fostex driver, or an 8' tall 3' wide Sound Labs panel speaker or a Wilson Audio Maxx ( http://www.wilsonaudio.com/product_images/...groom_large.jpg ).

Asked and answered. Speakers almost always sound different, and I'm surprised you don't already get this. What hasn't been said is that the same speakers sound different in ABX tests if they differ only by small changes in location or orientation. The hard-headed businessmen over at Harman built a lab with hydraulic speaker positioners so that this variable can be controlled.

It is the consensus of the forum that tube amps, class t/d and class A/AB of the same relative power sound the same for the most part?

Yes and no. Many modern tubed amps measure out to have very different and non-flat frequency response depending on which speaker they are connected to. Its simple - they have high output impedances and their frequency response is strongly dependent on the impedance curve of the speaker. Not only do those amps sound different from other amps that lack this fault, they sound different from themselves if you test them with different speakers. There are some SS amps that have this same basic kind of fault, especially those that are based on switchmode operation. They all must have output filter networks to contain the massive HF within, and it is hard to maintain low source impedances through these networks.

What about different tubes in tube amps? Is tube rolling pointless from a sonic perspective?

Depends on which tubes. Some tube types vary considerably from other examples of the same tubes. All tubes degrade, some very rapidly, depending on the circuits they are used in, some due to basic poor quality construction. Basic bench tests for frequency response with loudspeaker-like loads can predict the outcomes of ABX tests.

I mean again, tube amps. and the other types are working in a very different physical manner so how can they not be detectable from one another?

Just because there is a measurable difference doesn't mean that there is an audible difference. The thresholds of audibility for many kinds of measurable defects are known well enough to predict the outcome of good listening tests.

I suspect that a lot of tube rolling is masterbation from a technical and audible performance standpoint. On balance while I spent over 20 years as an audiophle and equipment designer in tube hell, its been over 30 years since I looked at them seriously. I don't know how bad the Chinese and Indian tubes really are, or how the minor technical progress that the Russians made helped. An important point - there were sonically transparent tubed amps and preamps back in the day and they are still around. Again its all about quantification - its not the implementation that matters so much as the actual performance.

I saw some snickering at room treatments.


If you are talking about Totem beaks, then yes lets have a good laugh. If you are talking about room treatments that actually make audible differences, which take a little effort but not that much, then no joke.

Is the forum suggesting that room treatments and digital room correction make little to no difference in sound quality? I mean hard/absorbent surfaces do effect what frequencies reach your ears at what times (or at all), so my mind says that logically has to make a difference.

It is all about quantification.

Digitally flattening out a response curve has to effect the sound, right? Now, i'm not talking about the *value* of such treatments. Most of the time i see an expensive bass trap or a pricey colorful audiophile pillow that i'm supposed to put on my wall i think "I bet my mate who's a quilter could make me something that would do that same thing or i could just hang a blanket on the wall"

It turns out that stuff like quilts and rugs aren't very good room treatments. But they can make audible differences if large enough and positioned in the right places. The problem is that the differences they make may not be all that euphonic. For example I would say that you might be better off with a polished wood floor and ceiling treatments that have the right absorbance versus frequency characteristics that can't be put into a practical rug or quilt.

Regardless of whether or not you use the $2k room treatment, change your curtains or move the couch for the same effect, the effect wouldn't likely be a placebo would it? Why would recording studios and concert halls work so hard at it?

Again It is all about quantification. Most recording studios that have professionally-designed room treatments are based on more significant and better thought out kinds of treatments.

This post has been edited by Arnold B. Krueger: Oct 18 2012, 14:31
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