How does one connect Matrix surround and center sum-mono derived sound?

Question

How does one derive a center/mono (L+R) and a ambient surround (L_R) from two channel stereo?

The summed-mono is one speaker and the ambient surround is two.

Without actually connecting the L and R speakers?

I have read about matrix and Hafler and Klipsch; about in and out of phase, but I just want to make sure and do it without the L and R


http://kantack.com/surround/surround2.html

http://peavey.com/support/technotes/poweramps/bridgemode.cfm

http://www.termpro.com/asp/pubs.asp?ID=115

Answer 1

Creating a surround effect channel via L-R is easy. Back in the quadraphonic days, many companies added either resistors or an inductor to the otherwise missing ground connection that tied it back to common ground - this allowed either a less than total out of phase matrix surround, or blended the bass back to traditional stereo to prevent bass cancellation.



On lower priced / less audiophile grade electronics, I typically find high wattage resistors that simply add resistance to that missing ground - diluting the pure L-R effect by having front channel leakage in the rear, but leaving it acceptable. On higher quality, true receivers with the matrix quad, I've often found an inductor used to tie the missing ground back to common. This allows the midrange and up to be full L-R but the bass is still stereo and does not "fight" the front speakers.



To sum L+R requires some form of a buffer. In the early days of stereophonic sound, a center channel output was not unusual - however it was at a line level (after the volume / loudness control) and an additional amplifier was needed. Obviously you can't just connect the left and right together to a speaker as the amplifiers will see a dead short (the output of the other channel) and combining L+R without any isolation at the preamp point will blend everything to mono. Thus a buffer amp stage is needed.

Answer 2

There were several wiring experiments in the early quad era. One was to connect the wire terminals of a extra speaker so that the positive of one channel and the negative output wire of other channel, were connected to the extra speakers terminals so that only sound that occurred in both the left and right stereo channels would be reproduced in the added speaker, These signals being largely the indirect, reflected sounds entering microphone pickups for both the left and right channels at the same time. How well this worked, of course, depended on how the performance was recorded and mixed, better usually, with some symphonic recordings, worse with studio recordings, However, with modern amplifiers, this could be a dangerous experiment and was based on stereo, not surround sound amplifiers, IT does work, after a fashion. Somewhat similar schemes were suggested to provide a center fill Chanel for wide set speakers like Corner kilpshorns, that required being set up in room corners by design, and were often too far apart to avoid a hole in the center effect. You can google such setups online, but again, these were all used with older model amplifiers which were largely more tolerant of messing around with.

Answer 3

The difference signal can be -- but should not be -- derived without connecting the left and right speakers.



Many amplifiers can be damaged if a suitable load is not connected to each output in the normal fashion, but a speaker is connected across the two "hots".





Summed mono should be derived, if at all possible, by mixing preamp output signals,

not speaker outputs.

An active mixer is best if good channel separation is to be maintained for the left and right speakers.





Messing about with this sort of thing unaided should be done only after you understand enough about audio systems.