From: chrisc@gold.gvg.tek.com (Chris Christensen)
Newsgroups: rec.audio
Subject: Re: need recommendations for center channel speaker
Date: 6 Oct 92 21:45:18 GMT
Organization: Grass Valley Group, Grass Valley, CA

In article <1992Oct05.183115.10141@bmerh85.bnr.ca> stud1b53@bnr.ca 
Anshu Prasad writes:
>In article <5376@gold.gvg.tek.com>, chrisc@gold.gvg.tek.com (Chris Christensen) writes:

>|> The surround speakers should be located
>|> behind the viewing position and the surround speakers should be like a "wall
>|> of sound"  behind you.  you do not want localization of the surround
>|> source.

>When you say "behind the viewing position", you run the risk of misleading
>people into believing that this means that the surround speakers must be
>mounted on the rear wall of the room (ie: on the wall directly opposite of
>the television/screen).  This need not be the case. 

I stand by my statement as being correct as written.   The "normal" theater
configuration is a row of speakers at the back of the theater, facing
forward.  But on to the qualification of your point.

>For example, dipolar
>surround speakers are expressly designed to be mounted on the side walls,
>though I concede that they should still be slightly behind the viewing
>position.  A large room may also benefit by side-mounting conventional
>surround speakers, as long as "localization of the surround source" does
>not occur (thus, this arrangement won't work if the room is narrow). 

As noted above I was not talking about "dipolar" speakers.  The best
surround effect will still be had with a row of speakers behind the
viewing position. 

The design objective of the "dipolar" speaker is to provide a source
of surround information that is non directional to the listener.  This
effect is achieved by using two speakers facing opposite directions
and wired out of phase.  The speaker is mounted so that the viewing
position is at the null of the speaker thus the surround information
heard by the listener seems to come from behind.

The problem with this design is that the surround effect works by the
amplitude cancellation between the front and the surround (rear)
speakers and the viewer must be imersed in this field.

If you are unable to do the wall of surround from behind then I
suggest that you mount unipolar speakers on the wall beside and behind
the viewing position and point the speakers at the center of the rear
wall behind the viewing position.

This method will achieve the same basic result as side mounted
"dipolar" speakers as well as not "wasting" the front speaker......(the
front speaker in this implementation of a "dipolar" speaker only
serves to provide the nulling function.

The position where the "dipolar" speaker may be of use,  is mounted
BEHIND the viewing position with the speakers pointed to the sidewalls
and the null pointed to the listening position.

>Sorry about picking nits here, but I've had too many salespeople try to
>tell me the wrong way to build a home theatre was the only way. :-)

Please feel to pick nits and qualify them with a smily face.  I am not
an audio store sales person!  :-)
-- 
Chris Christensen                  The opinions I express are my own,
chrisc@gold.gvg.tek.com            and sometimes they are wrong!
916-478-3419 FAX 916-478-3887      After all, I *AM* only human.
Newsgroups: rec.audio