michaelk@tekmdp.UUCP (Michael Kersenbrock) (09/26/83)
It seems to me that if you add an additional tweeter to a speaker system, and move it around, what probably is being changed is not the "phase response" per se, but the high frequency directionality patterns. When there are two sources (like in an RF antenna phased array, say, like a simple two element Uda-yagi) substantial interference patterns result. Moving one source a substantial portion of a wavelength (not far for 20Khz audio) should really move things around direction-wise and probably would mask any phase (group delay) effect. Unfortunately even with a single source, moving the source has great effect on interference patterns in respect to wall reflections, etc. (This would be one good reason to move one's speakers around the room for best imaging). Additionally, it would be a technically useful thing to correct for groupdelay effects, but unless the speaker has 1/3 octive drivers to be moved about it might not be too practical on a post design basis. Tweeters are generally known for high directionality, and so, it would probably be quite useful to have a pointable tweeter should the rest of the speaker cabinetry have to be fixed in some way (say for aesthetics). Mike Kersenbrock Tektronix Microcomputer Development Products Aloha, Oregon
shacklet@ittral.UUCP (Cliff Shackelton) (09/27/83)
All this talk about directionality and phase response, speaker wire size and this speaker is better than that one. I say PHOOEY! When I want to listen to a recording ACCURATELY, I use my Koss ESP-9 electrostatic headphones. I distinguish the difference between listening TO something and listing AT something. Since I haven't found speakers that sound good for the different types of music I listen to at the level that won't wake up the kids and the neiborhood, I use my speakers to listen AT not TO. Cliff(What's that you said?)Shackelton ITT Telecom
kimr@tektronix.UUCP (Kim Rochat) (09/30/83)
My speaker system consists of a pair of Yamaha NS-10m speakers with KEF-T27
tweeters added on. The Yamaha's have not been modified in any way, and the
crossover to the KEFs is first order at 20kHz. The position of the tweeters
was derived by comparative listening. I have no idea what the actual
resulting phase response is, but it must be pretty good, since I prefer these
to other speakers known to have good phase response. The important point is
that the position of the tweeters was easily arrived at. The movement of the
tweeters changed the "focus" of the 3-dimensional sonic image, just like
focusing a camera. The actual impression was that of the harmonics of the
instrument being in a difference plane (depthwise) than the instrument
itself. By moving the tweeters forward or backward, I could make the location
of the harmonics correspond with the location of the instrument. Anyway, a
movement of 1/4" resulted in a clearly audible difference, which corresponds
to about 180 degrees of phase shift at 20kHz, relative to the Yamaha speaker.
So, in my experience, high frequency phase shift does impair imaging.
Ps: Equipment I used to have made it more difficult to arrive at a tweeter
position since the image was not as precisely defined in space,
so good associated equipment is needed.