Scott,
> your head moves through few % points of this axis just sipping a cup of coffee. <
No kidding. Not sure if you ever saw my "Believe" article, but the graphs below show the low frequency and broadband response at two locations only four inches apart in the RealTraps lab room.
Conventional wisdom holds that the bass response in a room cannot change much over small distances because the wavelengths are very long. (A 40 Hz sound wave is more than 28 feet long.) Yet you can see in the top graph that the peak at 42 Hz varies by 3 dB for these two nearby locations, and there's still a 1 dB difference even as low as 27 Hz. The reason the frequency response changes so much even at low frequencies is because many reflections, each having different time and phase delays, combine in different amounts at each point in the room. In small rooms the reflections are strong because the reflecting boundaries are all nearby, so that further increases the contribution from each reflection. Also, nulls tend to occupy a relatively narrow physical space, which is why the nulls on either side of the 92 Hz marker have very different depths. Indeed, the null at 71 Hz in one location becomes a peak at the other.
The two responses in the lower graph are so totally different you'd never guess this is even the same room and loudspeakers!
At the risk of starting a flame war among the audiophiles in attendance
here's the full article:
www.ethanwiner.com/believe.html
--Ethan
