From: lesnyd@monsanto.com (Larry E. Snyder)
Subject: Cheap surround sound
Organization: DSC
Date: Fri, 21 Aug 1992 18:40:59 GMT

I picked up a nifty tip from rec.audio (or something like that) for adding
rear speakers that pretty much serve as surround rear speakers. The circuit
described puts ONLY the difference between the two channels in the rear
speakers. So something that is identical in both channels will not appear
in the rear speakers. This works GREAT for Star Trek: The Next Generation,
which is uplinked in stereo. The first thing I did when I got my stereo
processor was watch the full black feed of "The Next Phase" in surround
sound. It's a different experience...

Anyway, here's the post:

This system works quite well.  There is no mono sound hole in the center
and all the Surround comes out the rear speakers fine.  Sit in about the
center of the speaker placement.  This single speaker nonsense is getting
annoying.  You need TWO rear speakers to get proper Surround sonic imaging.

   +---------------+                            +---------------+
   |  front left   |                            |  front right  |
   |   speaker     |                            |   speaker     |
   |               |                            |               |
   |               |         no more than       |               |
   |               |         15 feet apart      |               |
   |               |                            |               |
   |               |                            |               |
   |  pos     neg--|------------       ---------|--pos     neg  |
   |   |           |           |       |        |           |   |
   +---------------+           |       |        +---------------+
       |                       |       |                    |
       ------------------      |       |       --------------
                        |      |       |       |
                     +----------------------------+
                     |  |      |       |       |  |
                     |  | LEFT |       | RIGHT |  |
      ---------------|-pos    neg     pos     neg |
      |              +-----------------|----------+
      |                     STEREO AMP |
      |                                |
      |   left rear                    |          right rear
      |    speaker                     |           speaker
      |  +----------+                  |         +----------+
      |  |          |   placed up      |         |          |
      |  |          |   high and can   |         |          |
      |  |          |   be up to 20    |         |          |
      ---|-pos  neg |   feet apart     ----------|-pos  neg |
         |       |  |                            |       |  |
         +-------|--+                            +-------|--+
                 |               **                      |
                 -----------------------------------------

** An optional volume control (lowering it in referance to the front speakers
volume) can be added here, use an 8 ohm wire wound potentiometer rated at about
10 watts.

Little or no bass comes out of the rear, so small speakers work fine as rear
speakers.  If you want some bass in the rear speakers, mix a little front
channel sound into the rear by connecting two 8 ohm (10 watt) resistors from
the ** on the chart, one to the right and one to left negative amplifier
outputs (the ** will be a node or connection point in this case).  The use of
separate resistors is recommended because some amplifiers get upset if their
negative speaker output terminals are cross connected.

This system works great, try it (if you don't already have an official Surround
system) you'll like it. Improves standard CD, LP, etc audio as well, anything
with a stereo signal.                                   Rdemarti@pica.army.mil

Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU