david@uwm.UUCP (David Robinson) (01/08/91)
The following article is from POSITIVE FEEDBACK, the newsletter of the Oregon Triode Society, and is Copyright 1990, all rights reserved. This article may be reposted or reprinted, as long as it is not resold, and as long as proper attribution of the source is made in full. Please keep this header in all copies made of this article. David W. Robinson Editor, POSITIVE FEEDBACK david@agora.rain.com ---------------------------------------------------------------------------- THE ABSOLUTE TRUTH Bob Carver What I am about to say may challenge some long-held beliefs about how things work in general, and audio works in particular, and what makes things sound the way they do. This first column will be about interconnects between the amplifier and the loudspeaker. While science is at the heart of electronics, long-perpetuated myths enshroud many of its basic principles. This column is intended to de-mystify several critical issues. Throughout history, science has been most threatening to those who make their living endorsing myths and magic, because myth and magic can be much more fun and exciting than science and reality. You shouldn't be surprised when many audiophiles will more often, or as often, or regularly, embrace myth and magic rather than science. Far more people will go to a magic show than will attend a science lecture. And far more people buy the National Enquirer than Scientific American by a factor of a zillion to one. AN EVENING WITH TWO AUDIOPHILES Audiophile A and Audiophile B compare two amplifiers. They both agree that the Dynowhizmatic has a deeper sound stage and far better ambience retrieval. They are not hearing things; there really is a difference. Audiophile A attributes this to: 1) Hummongo Brand Wonder Capacitors, 2) the over one hundred pound weight of the amplifier, and 3) a magic brick that has been placed on top of the amplifier. Audiophile B knows that the frequency response of the Dynowhizmatic varies plus or minus 1db when measured at the loudspeaker input terminals because the amplifier output impedance has interacted with the input impedance of the loudspeaker. This has caused a frequency response variation of plus or minus 1db, specifically in the range between 100Hz and 400Hz where most of the ambient information lies. "Pish posh," snickers Audiophile A. "That's a microscopic difference! What possible effect can a plus or minus 1db variation in frequency response over a couple of octaves have on something as audible as ambience retrieval and sound stage depth?" Audiophile B goes to the blackboard, kept in another room to prevent live- end reflections, and writes the following: +/- 1db = 2db total variation 2 db = 1.25 ...or a 25% variation in voltage at the loudspeaker terminals. Now power (energy) varies as a function of voltage squared, so... 1.25^2 = 1.58 or 58% more energy delivered into the listening room in the 100Hz to 400Hz range, which is precisely the range where the ambience lives, both in live concert halls and recordings. "Uhmm. Fifty-eight percent more energy from a plus-or-minus 1db variation? Huh?" Audiophile A is suddenly interested. "That could be audible as better sound staging and ambience retrieval. One db. Never would have thought it." "Nah, bull shit. Even though it's got 58 percent more energy output because of the interaction of cables, amplifier and loudspeaker, and just because the 58 percent extra energy is in the range of 100Hz and 400Hz where the ambience is in both a live concert hall and in recordings, I don't believe that's the reason. I think the reason that the Dynowhizmatic amplifier has better ambience retrieval is because of the magic brick and the Humongo Brand Wonder capacitor. I'm unconvinced. The Dynowhizmatic amplifier absolutely blows away the other amplifier!" Audiophile A also remains unconvinced about magic bricks. He understands that minute changes in frequency response AS MEASURED AT THE SPEAKER TERMINALS have a direct effect on audible sound characteristics. A lot begins to fall into place. "That favorite amp of yours has a soft, silky high end when hooked up with Balls-o-Matic cables? A roll-off as little as 0.75db at 15kHz will result in a 20 percent reduction in high energy treble. Awesomely solid bass from that Gravitronic 5000 amplifier? Since many 4 ohm speakers exhibit an impedance jump to 45 ohms right at their resonance point and the combined impedance of the amplifier and the cables can be, say, 1 ohm at 40Hz, the resulting variations in frequency response and energy balance will increase ultra-low end power 55 percent in the 20Hz to 40Hz range. Very, very audible." FREQUENCY RESPONSE??? Uh?? This may be a hard concept for many of you to become comfortable with. At first it sounds like an oversimplified panacea, but what I've said is really true. ANOTHER INTERESTING PHENOMENON: Heated debates about speaker/amplifier interconnects have raged for decades. I'm not here to tell you or anyone that it's all in your head and that there are no differences. Instead, the wrong characteristics have been and are being scrutinized. No one denies that different kinds of speaker wire have different impedances. When you realize the importance of spectral energy content (frequency response) and that frequency response is the combination of the amplifier's output impedance and the speaker wire's impedance as measured at the speaker terminals, it's easy to understand how different interconnects can have an effect. In the middle ages, alchemists and magicians would use one magnetized disk to move another. They, and the people they amazed with this phenomenon, described the "levitation" as black magic. Centuries later, the effect was correctly explained as repulsion of magnetic poles. Science had replaced myth. This analogy directly applies to speaker interconnects. Yes, there are differences. No, they're not attributable to interweaving geometry, or diameter of strands, or dielectric makeup or the cost of the cables. The differences are only attributable to the pedestrian impedance of the cable and the way the cable interacts with the impedance of the amplifier. This impedance all occurs inside the normal audio band, not at mega-Hz or at gamma wave frequencies. And remember this: The overall makeup of the cable can and will change overall energy balance in various parts of the frequency spectrum by as much as 100 percent. That's science, not myth. HOW TO EXPERIENCE MANY DIFFERENT AMPLIFIER BRANDS WITHOUT HAVING TO ACTUALLY BUY THEM Step One - Go to Radio Shack and purchase several 20w resistors. Purchase them in the following increments: Approximately .25 ohms, .5 ohms, .75 ohms, 1 ohm, and maybe even 2 ohms. Buy a pair of each, one for each channel. Step Two - Connect, in turn, any of the resistors to the positive terminal of your loudspeaker and then the wire from the amplifier to the other end of the resistor so that the resistor is in series with your loudspeaker. What you will do in this experiment is to change the impedance of the cable and the effective output impedance of the cable and the effective output impedance of the amplifier. The interaction that the loudspeaker and the new impedance conforms to will modify the sound of the amplifier. That single resistor will be responsible and will modify all of the terms and descriptions that we all hold near and dear to our hearts: The warmth of the loudspeaker sound--its bass quality, its upper register definition, its sound stage dimensions. It will change the transparency of the sound stage- -its authoritativeness, its effortlessness, and its accuracy. Your job, after careful listening to each one of these resistors, will be to choose the one that gives you...well, that's a matter of taste. Do you want a warm, rich rolling bass, or do you want a dry-type bass? Do you like a forward sound with a mid-range that literally glows and floats, or do you like a mid-range that's recessed and makes the sound stage deeper and wider? Do you like the high end to be soft and silky or up front with lots of tinkly definition? Whatever your preference, you can change all of that simply by changing one of those resistors. So...give it a try. One more thing: If you believe in magic, you won't hear much change. If you believe in science, you will hear the changes that I've just described. Sometime in the future, let's hold a fun contest at one of the [Oregon Triode Society] meetings. I'll do a demonstration to illustrate what happens with interconnects when these changes are made. We'll use a pair of Silver Seven power amplifiers and my new Silver One all vacuum tube (not hybrid) preamplifier which sells for approximately $7,000.00. It's brand new and hasn't been released. It's really a beautiful preamp. [No objections here, Bob. And I have a feeling that the OTS Board and membership wouldn't mind a bit... Ian, Larry, Richard, Alan: What say you? We'll keep you all posted on this one, and get it on the calendar just as soon as possible. --DWR] That's all for now. If I'm invited down again to give another presentation, we'll have some fun. I have a dynamite experiment and sound stage demonstration to do. 'Till next time, may you have many GMIAs*. Regards, Bob Carver * "Great Moments In Audio."