[sdiy] ot: rotating speaker simulation or stupid approach

[Glen]

At 04:05 AM 7/4/03 , jhaible at debitel.net wrote:

>I'm not familiar with the details of surround systems. But that's just 5
>speakers, isn't it? Probably not enough to cause that effect. Probably
>the phase canellation will be more prominent than the delay effects.

There is another thing to consider. With surround sound systems, the
listener is in the center, and the speakers might even be placed an equal
distance from the listener. There is very little difference in
speaker-to-listener distance, when switching from one speaker to another.
Even if there is a change in distance, it probably isn't going to be an
orderly progression from long to short, and back to long again. In a
situation like this, the dominant effect isn't as much of a  change in
delay time, as it is a change in phase. 

The Doppler effect would need a change in the distance from the sound
source to the listener. A rotating speaker will give you this, because the
listener isn't located in the center of the rotating apparatus. Surround
systems with the listener in the middle won't give a change in distance, or
time delay. A purpose-built array of several speakers, with all the
speakers located in front of the listener, just might give an effect
similar to a Doppler shift--I just don't know for sure. At least the
different speakers would be different distances from the listener. It would
be interesting to try it out.

A circular topology has been referenced here, but would a linear array of
speakers possibly be more practical? Imagine a linear array of speakers
that "pointed" in the direction of the listener, to maximize the variation
in signal delay. The signal would cyclically be swept along the array from
front to rear, and then from rear to front. If it worked, it might be
something of a cardiod-patterned Leslie effect. (A directional Leslie!)

If this speaker-array Doppler-shift idea worked, and was fairly practical,
it would be a silent alternative to all the annoying mechanical noises
present in a Leslie speaker. In fact, I've yet to see a Leslie that was
truly free from annoying mechanical background noises.


later,
Glen Berry