Placing your speakers atop a stand - acoustic considerations
As if there weren't enough things to worry about .... here is a new one! Now first to say, this is just for your general curiosity; I can show you later why well established acoustic theory shows that the normal human ear is unlikely to actually hear this effect, so don't waste too much time convincing yourself one way or another! But certainly, when making precision measurements with a dumb microphone, it certainly can detect and display the reflection. But it can't evaluate how it would sound.
Now I have a permanent acoustic measurement set-up here in this beautiful, restored 16 century barn, I'm able to explore micro-issues which I couldn't before. And one came to light yesterday - why there is a spike of wide-band (up to about 10kHz) energy that follows the initial impulse about 1mS (one thousandth of a second) later. Could it be the grille? No, removing the Harbeth SuperGrille proves that has nothing to do with that. So what could it be? Well, the answer is that the humble wooden plinth the speaker sits on is the culprit. With the bottom edge of the speaker flush with the speaker's lower lip - which common sense says is the correct position, and looks attractive too - there is a distinct reflection - see picture - but with the speaker pulled forward by about 25mm, reflection eliminated. Incidentally, draping the edge of the platform with VetBed (the white furry material - an excellent general purpose absorber in the higher frequencies) made no worthwhile difference at all.
So - maybe we should bring our speakers just a fraction forward of the stand edge, or is this a degree of precision far beyond what we can hear? Better to consider only cosmetics and stability perhaps.
Alan A. Shaw
Harbeth Audio UK