December:

Acoustical Design Element 4: Front LCR speakers should be placed at a similar height (+/- 2 feet between tweeter/midrange center point).

Humans hear sound differently depending on the height of the sonic source. Speakers placed at different heights will present different apparent tonal qualities and thus provide a discontinuity across the soundstage. In worst cases, the imaging is all but destroyed. One of the requirements of a well matched speaker system is tonal matching of speakers. Failure to keep the presentation height of the front channels similar defeats this important goal.

This may seem like an innocuous enough design element but it is surprising how audible the result of a flawed approach can be. The human ear has an innate ability to determine the apparent height of sound sources. This ability is a result of the variable acoustical filtering of sounds depending upon the angle they enter the ear. I found this link that shows this phenomenon in technical terms http://www2.sfu.ca/sonic-studio/handbook/Pinna.html. The human brain deciphers the frequency response of the signal and attaches a spatial position to the source. This is a complex subject and this is not the forum but suffice it to say placing the center speaker at a significantly different height from it's right and left channel brothers can threaten the focus and cohesiveness of the front soundstage.

The flaw is not presented as obviously as say a buzzing tweeter or one channel turned off but it is easily detected. We strive to present individual sounds precisely positioned in a enveloping soundstage, this flaw like others injects an ambiguity that robs us of that sense of surprisingly realism.

I am occasionally confronted in well meaning discussions about the relevance of one acoustical flaw or another. Does it really matter that much? At the end of the day, what is missing due to such tiny misalignments? Perhaps the answer is only fathomable from the perspective of the music lover teleported in time and space by the majesty of an amazing performance. If never on a quiet evening in your home, a recording has astonished you with its realism and moved you emotionally, which among many subtle acoustical distortions has robbed you of the experience? If you have not been surprised recently by your sound system perhaps Element 4 could be a contributing factor, of course, don't forget about the other 34 elements in the mix. Next month Element 19.

Gerry Lemay