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Discussion Starter · #1 ·
Below is an article by one of our members, Izzy Marrone (windowman99), that he wrote at a member of the NJ Audio Society. I thought it was very interesting and worthy of posting here for discussion and/or comments, with his permission of course.

Logic, Semantics, Conclusions and Philosophy
(For the sake of this discussion, I am assuming acoustical instrument recordings in a hall)

The last meeting got me to thinking about a few things in this hobby of ours. I’d like to share them with you. If you’re old enough, you may remember an early ad campaign for that favorite audiophile whipping-boy product, the Bose 901 speaker (version 1!). I remember a particular ad which tried to explain why this was such a “breakthrough” speaker. You see, Bose researcher’s found out that at a live concert, only 11% of the music that reaches your ears gets there in a direct path from the source. The overwhelming majority comes from various reflections in the hall. So, the ad stated, our speaker is better because it “mimics” the live hall in that only 11% of its’ sound is direct. Hence the phrase “direct/reflecting” speaker. (Remember the Bose has only 1 out of 9 drivers (exactly 11.1%) facing directly forward). You’ll see why this is relevant soon.

Fast forward to present day. A new audio company’s researchers discover that the best instrumental sources of live music have a quality called “harmonized resonance”. And further, this resonance is “perfectly balanced”. So, a “new approach to the treatment of resonance” is realized by treating it as “an essential element that adds warmth and fullness to the sound”.

What do BOTH companies (incorrectly) conclude? That the reproducing system (the home stereo) must have the same characteristics as the original event (the live concert). This seems to make sense at first glance. Shouldn’t we pursue as a reference in our home listening the original source? But the flaw lies in bad logic. The two events have VASTLY different physical characteristics. Production of sound is VERY different that reproduction. In fact, in many ways they are diametrically opposed.

In the first example, a home speaker’s dispersion should have nothing at all to do with the original event. Why not? Well, the very act of capturing sound changes the original event, and demands completely different rules upon playback. For example, the microphone(s) pickup patterns, the number of playback channels, and other variables can affect what the “optimum” dispersion should be. Speaker designers to this day do not agree on the ideal model (line or point source, for example). And the recording itself imprints a certain amount of reflection cues (the “89%” factor). Deliberately superimposing new, unpredictable ones via the speaker is not necessarily an advantage. Complicating this is the fact that a typical home system’s room is nowhere near as large as the original. The acoustical properties of small rooms are VERY DIFFERENT than large ones. (I am speaking primarily of reverberation decay times and reflections). You don’t really want it to (nor can it) have the same qualities (ie, 89% reflective) of the original. And even “bad” recordings with little or no “hall” sound will not be helped by this idea; if the original ambience is not recorded, your home room will never get it back. You’d be better off in these situations trying to electronically generate ambience. (Surround sound/DTS/Dolby, anyone?)

In the second example, since resonance is a given in all acoustic instruments, shouldn’t it be a desirable quality in reproduction? By all means NO!! (Here is where semantics may come into play). Engineers have a very specific definition of this word, and it DOES NOT have a pleasant, positive connotation. To explain: All physical things have a frequency of vibration at which they naturally want to move. This is called the “resonant frequency” (“RF” for short). A good example to think of is a guitar string. The RF changes depending on its’ tension as it is tuned. This is literally “tuning” the RF. When all the strings are tuned to each other, the guitar sounds “right” and pleasing. I believe some people think this tuning can be done to a stereo system by assorted “tweaking”.

But in a PLAYBACK situation, any part of the system that gets its’ RF excited will superimpose that RF over the desired signal. This is bad news. By definition it is a distortion of the signal. It cannot be correct to “tune” the RF here. Philosophically, you should want to KILL it! (Or at the very least damp the hell out of it). What competent designers try to do is make sure that a devices’ RF will never be excited by the signal passing through it, or that if it does, it will be well damped. Think of damping as putting a brick over the guitar string as you strum it. The string will try to vibrate, but be prevented by the weight of the brick. This is called mass-damping.

It gets more involved when complex things are assembled. Ideally, you’d want to design a complex thing (like a speaker) so that each parts’ resonant frequency, when assembled together, would “cancel” out, or at least not add up in the same place. To a designer at the reproduction end, resonance is BAD, something to be AVOIDED at all costs. On an absolute basis, the less resonance there is, the less distorted the signal will be. This is why I cringe at the idea of “tuning” the RF instead of trying to reduce or eliminate it. So why would this idea (of “desirable” resonances) be pursued? I think maybe this is an area where non-technical people may be guilty of misusing the language. Maybe they are describing a pleasing “warmth” or “fullness” to reproduced sound that they call “resonance tuning” when a system is pleasantly tweaked. But I’d call this “voicing” a system, which I’ll define as assembling a group of components together that complement one another in sound quality. It shouldn’t be called “resonance tuning”, unless you want to hear certain distortions, even if they’re pleasant. Then it would truly be a case of assembling a bunch of “desirable” resonances. As pleasant as this might be, it is nothing more than a collection of colorations, which ultimately limits the purity of the music. The difference is philosophical. I don’t want to tune multiple resonances in a system like a tuned guitar, but to minimize them. This maximizes resolution, which should go hand with hand with greater purity and more ultimate enjoyment of the music.

The difference in philosophies is crucial, because it acts as a guide to what types of things one would consider doing in a system to improve it. Someone trying to “tune” a RF might be more prone, let’s say, to put a preamp on a wooden base or foot, to hear the “desirable” resonance of it. I, on the other hand, would hardly consider it. First give me something heavy and (acoustically) dead to put on top, for mass-damping (like the brick mentioned above). Second, something underneath that would have some self-damping properties and very little resonance of its own, with the added ability to dissipate any resonances reaching it from above. (Hint: it’s not hard, is ridiculously cheap, and not an audio-related product). More sophisticated and costly products specifically made for audio are also available. An excellent article about such matters is on Stereophile’s website, titled “Bad Vibes!” by Shannon Dickson, November 1995.
 

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Discussion Starter · #6 ·
“Best instrumental sources” – what on earth does that mean? That some musical instruments are better than others? :huh: Sure, all instruments have “resonances,” but the only job of a sound system is to accurately reproduce what the instrument sounds like, plain and simple. For a sound system to try to mimic the resonances of musical instruments is plain silly.
In the context of the article, I took this to mean the venue. :ponder:
 
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