Burn in, turn on, tune out ...
Upon receiving two identical (same manufacturer, same model) amplifiers for review I suddenly realized that here was my opportunity to do something -- via the blind testing route -- that had never been done before. To wit: test the tweak claim that an amplifier which has been burned in has superior sound to an identical amplifier right out of the box.
From time immemorial some tweaks have been claiming that, just like a fine wine, an amplifier needs a period of time to reach its ultimate peak in aural satisfaction. I believe this old tweak tale got its start from the heyday of the tube amplifier when aging tubes had to constantly be rebiased for their always changing electrical parameters. Add to this some noted tweak reviewers' penchant for comparing sound to a fine aged wine (perhaps this group should call themselves "oenaudiophiles"), and an often-stated but definitely dubious idea becomes an accepted "fact" in the tweak audio world.
The tweak claims for amplifier aging have ranged from slight improvement of the sound to such improvements in sound that the tweak reviewer can't believe it is the same amplifier he listened to when played right out of the box! But unfortunately, no blind test has ever been done to refute or confirm this belief. There are several reasons for this lack of scientific testing.
Most objectively oriented individuals write off the idea that amplifier aging affects sound quality as dubious at best. Moreover, performing an objective test of the aging hypothesis is a proverbial pain in the backside. You need two identical amplifiers. Then you have to burn in one for a period of time while the second amplifier sits unused in the shipping box. After this aging period you then have to set up a blind comparison of the two amplifiers. And all of this is dependent on borrowing two amplifiers from a manufacturer who is understanding enough to loan out two pieces of saleable inventory for the sake of science.
Fortuitously enough, I was recently sent two identical amplifiers for review, presenting me with an opportunity of possibly becoming a short footnote in the annals of the great men who developed and perfected blind testing as a means to discover audio truth. I immediately went into action. One amplifier was incorporated into my system, playing music and test signals 24 hours a day for two weeks without letup. The amplifier was never turned off and never just idling. When not at home (at work) I played all sorts of music and test signals at horrific sound pressure levels. To keep the house from being shaken to the ground (and to keep the neighbors from shaking me to death) I configured my system for mono operation, connected the speakers 180 degrees out of phase, and placed them face-to-face, resulting in minimal sound from maximum wattage. Upon arriving home I would reconfigure the speakers to a normal stereo setup. At no time during this two-week period was the amplifier ever turned off.
At the end of two weeks I conducted three single-blind tests between the "aged" amplifier and the amplifier taken directly from the shipping box. The tests were performed over a period of slightly more than three hours and the results indicated no audible differences between the two amplifiers.
But this was not the end of my experiment. After this session was complete I immediately shut off the "unaged" amplifier. For another two weeks I endured twice-daily self-imposed flagellation of moving speakers and reconfiguring my system. The aged amplifier was always playing music or test signals and the unaged amplifier was never turned on. Two weeks later another round of three blind tests (three blind tests, three blind tests, they all ran after ...), checking for audible differences between the two amplifiers. No audible differences.
Another two weeks (see above for test procedure and setup) and a third (and final) session of blind testing with a result of no audible differences between the two amplifiers. One amplifier on continuously for over six weeks and the other amplifier on for slightly more than six hours! As of this writing I never want to do another blind test. So much for "sacrifice is good for the soul." And to hell with the footnote; I feel good doing something that the tweaks wouldn't know how to do (wouldn't dare do!) and the double-blind contingent is too lazy to do.
By the way, I've saved the best for last. One of the objections to blind testing by the tweak contingent is the (supposedly) degradation of the audio signal as it passes through the switch contacts in the AB switchbox. I don't think it affects the signal (As Peter Aczel notes, if this is true then the function selector switch in a $10,000 preamp also degrades the sound, huh) but unlike the blind testing fraternity I have taken the bull by the horns. All of my blind testing mentioned in this article was done without the use of a switching box. How? Simple!
Identical setups (amplifier and preamp) were used with a common CD player and speakers being switched by moving cables from one system to the other. Absolutely no switch contacts causing possible degradation of the signal. No need for a switchbox when doing blind testing; something that the blind testing fraternity has not explained in any detail, nor have they performed any blind testing sans the switchbox (to the best of my knowledge). Anyway, if you object to switch contacts you'll now have to come up with another objection. And another. And another. And another.
The editor has requested that I identify the various components used in this experiment. This requested information has been passed on to Karl but I am requesting that the information not be part of this article. Coming to blind-testing somewhat later than most I realize that to argue "science" with zealots who believe in audio voodoo is rather fruitless. But -- I am more than willing to have a sane and rational dialogue with those who wish to learn (I don't exempt myself!), think they have credible evidence to prove me wrong, or, more importantly, prove that blind testing is flawed. All of the individuals who contact me (firstname.lastname@example.org) will be given the courtesy of a reply and the list of equipment used and the test results.
One caveat: Please don't use an argument based on what a dealer has told you or what you heard in a dealer's showroom. If you can't understand why then there's no need to go any further. This is not a knock against dealers, they're the lifeblood of the audio world, but you don't need a Ph.D. in psychology to realize that there's a vested interest in the dealer having you believe in differences.
On a humorous note and for extra credit, what popular three letter identifier for a switchbox have I not included in this review? (Hint: It begins with an A and ends with an X, and the middle letter is between A and C in the alphabet.
Speaking of switchboxes and blind testing, I thought it might also be interesting to relate some of my experiences with a commercially available switchbox called the WireWorld Comparator. WireWorld is a company in Ft. Lauderdale, FL that manufactures and sells speaker cables and interconnects via a dealer network. I normally wouldn't get too involved with a cable company, but the following blurb included in WireWorld's ads for the Comparator caught my attention: "Is there any difference at all between interconnect cables?" Obviously. "Can the value of cables be proven under double-blind test conditions?" Certainly. The WireWorld interconnect Comparator is an audiophile-grade switching device which facilitates comparisons between two pairs of interconnects or between one pair of cables and a reference bypass.
Being curious, I purchased a Comparator and evaluated the claims made for it. My original review was five pages long (and still growing) when I realized it was becoming a scientific paper, not a source of information for the audiophile consumer. What follows is a short and concise evaluation of the Comparator.
The unit sells for $450, and that's what I paid, folks. Twelve gold-plated RCA jacks are mounted to a ruggedly built metal box. Looking inside the box, I found that three Switchcraft four-pole/double-throw (4P2T) slide switches are part of the circuitry. These particular switches, which I found priced in the Newark parts catalog at $3.00 each, are inexpensive run-of-the-mill switches with brass contacts. Why gold-plated high-quality RCA jacks, excellent build quality for the box itself, but cheap slide switches? A smattering of small-gauge wire and soldered connections completes the internal circuitry.
The claim for double-blind testing is an overstatement. A single-blind test could be performed using the Comparator, but before you take this as an endorsement, please read on. Does having an expensive A/B switchbox qualify an audio dealer or tweak audiophile to perform scientifically defensible double-blind tests? Even if these guys have the knowledge of how to set up such a test properly (which I doubt), there's the obvious problem with someone performing a blind test who will profit financially (the dealer) or emotionally (the audiophile) from one possible outcome of the test (expensive interconnects "sound" better) and suffer from the other outcome (expensive interconnect "sound" is not audibly distinguishable from Radio Shack interconnects). My requests to WireWorld asking for details of their double-blind testing procedures have gone unanswered.
The Comparator has a minimal component circuit referred to as the "reference bypass." Comparing the reference bypass minimal circuitry (neutral) to an interconnect will make obvious the interconnect's influence on the audio signal. So say the ads.
Just for the heck of it, I performed several rigorous single-blind tests between the reference bypass and a homemade cable, six feet long, made of assorted wire sizes, and terminated with cheap RCA plugs (cost: less than a dollar). No audible difference between the reference bypass and my homemade cable. Continuing the testing I compared a rather expensive $500 (borrowed!) interconnect against the reference bypass. No audible differences.
You can also compare one set of interconnects against a second (different) set of interconnects. This I did. No audible difference between the Radio Shack interconnect and the expensive interconnect did I detect.
The objectivists will complain that the test was not double-blind, the tweaks can always fall back on the "cheap switches coloring the sound" argument, so it looks as though neither camp is well-served by the Comparator. Hey -- you just can't please all the people all the time!
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|Title Annotation:||testing amplifiers|
|Date:||May 1, 1998|
|Next Article:||Speaker Sound/Room Sound.|