Sidebar: Some Thoughts I’ve Been Having About Speakers

Some years back I got involved in the invention and development of sound lenses that changed the dispersion of high frequency sound from conventional drivers. As I worked with this technology, I noticed that stereophonic sound exhibited some interesting and somewhat unexpected behaviors when high frequency content was extremely broadly dispersed or omnidirectional. This led me to an in-depth investigation of what goes on in small reverberant rooms, and specifically, to the thinking of Art Benade, a major acoustician who specialized in instrumental and musical room acoustics.

Acoustic Signal Transmission In A Reverberant Space

What Benade pointed out was that the original sound made by a musical instrument was straightforward, well-defined and unequivocal, even when it was quite complex. He then noted that our perception of such a sound was similarly straightforward, well-defined and unequivocal. A violin plays, we hear a violin. No problem. Doesn’t matter, within reason, where in the room it is or we are. Here’s the tricky part: even though the source and the perception are well-defined and unequivocal, the transmission path(s) through air are virtually chaos! Physically speaking, we don’t hear one violin, we hear a hundred of ‘em, all coming from different points in space, at slightly different times. From an auditory standpoint, we’re in the mirror room in the Fun House.

It stands to reason, then, that music should work best in an anechoic chamber, where all those pesky reflections that induce chaos are suppressed by the absorbent walls. Then we’d really be able to hear, right? Not! Benade pointed out that musicians hate to perform outdoors, which is the ultimate anechoic chamber. Why? Because there aren’t any reflections! They can’t “hear” themselves or each other. Nothing sounds right.

Benade theorized (and I’m convinced he’s right) that we use the chaotic reflected signal paths as a central element in our hearing process, and that early room reflections of sound are good data as opposed to bad data, particularly in terms of our abilities to detect and enjoy timbre and to localize sound. I believe such early reflections should contain frequencies from the entire audible spectrum for best musical results.

Dispersion

Traditional musical instruments radiate sound wildly in all directions, with chaotic distribution of energy at different frequencies. If you wish to hear instruments fully, Benade’s thinking went, you must hear the complete volley of early reflections, which contain all of the various spectral versions of that instrument’s sound.

We don’t think this way about loudspeakers. Loudspeakers are directional at high frequencies, so that any early reflections from loudspeakers will be deficient in high frequency content. As a result, we’ve come to think of such reflections as bad, when in fact that is a serious deficiency in thinking about loudspeaker design.

So, we’ve tried to suppress reflections of such “deficient” loudspeaker sounds. Actually, ironically, all we do is suppress their high frequency components (that’s what Sonex does, f’rinstance), because it is too difficult and expensive to suppress the mid and low frequencies reflections, and we really don’t like the resulting sound when we try that. In any case, we assume that if we hear just the direct sound from the loudspeaker, that sound will be the best possible recorded reality. Such an assumption is not consistent with physical or psychological reality.

In fact, when we use loudspeakers that have broad high-frequency dispersion in a reverberant room, the reproduction of recorded sound may be significantly better – I’m beginning to get a stack of anecdotal evidence to support this. Improvements include both the quality of the recorded direct sound of the instruments and, get this, the recorded sounds of ambience and reverberance. Other goodnesses accrue as well, in terms of apparent depth, loudness and presence of sounds.

This, then, leads to another dimension to consider in a reference loudspeaker: the equal dispersion of frequency response in various directions, particularly to the sides.

I bring this up because a former student of mine, Manny LaCarrubba, whose day gig is Chief Engineer at The Plant Studios, in Sausalito, CA, has developed some prototypes that are not only flat to 20 kHz. on-axis, but maintain that flatness all the way to 90° off-axis on each side. An interesting thing happened when he began to audition these speakers to other engineers working on production projects at the Plant: they all began to hear out and identify various problems with their individual projects. They found the speakers extraordinarily easy to make musical decisions with, and there was general consensus that they would be extremely easy to mix on.

Why should this be so? Such speakers do not fit the Range Rule very well, and they aren’t typical monitors at all. I personally believe it has to do with the broad dispersion of high frequencies in a reverberant space, and the fact that our ears actually make use of such information, giving us a clearer, not muddier sense of sound as a result, illogical as that might seem.

I’m busy studying this. Right now, I’m trying to develop, test and prove (or disprove) this theory. If it’s true, an expanded definition of stereo may be in order and we may have stumbled on some considerably improved reference monitor types for our music production work.

I’ll keep you posted.

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