Combining speaker level signals (L+R, L-R)

[zobsky]

How would one achieve this in practice i.e. combine the speaker level outputs from the amplifier to provide a signal that represents the sum (or difference) of the left and right channels?

I need to improve the sound from my TV in the living room and was thinking of a implementing a crude pseudo surround speaker system with the random drivers I have lying around.

Thanks

[PeteMcK]

Probably best to do it at line level, L+R is easy, a simple resistive summing network will do, to get L-R, you'll need an inverting op-amp: http://sound.westhost.com/dwopa.htm

If your amp can handle the load, you could try this:
http://www.gregselectronics.com/stersurr.html

[BlueWizard]

To sum the channels or to create a differential signal, there must be some resistance isolating the amp channels from each other.

Here are two ways to create a differential =

Rt.Amp(+)-----(+)spkr1(-)------(-)spkr2(+)----(+)Lft.Amp

The second method is to do the same but only use one speaker.

Rt.Amp(+)-----(+)spkr1(-)----(+)Lft.Amp

This was a methods used many years ago to creates something approximating four channel or front and rear speakers.

When the output form the channels is equal, you hear nothing, the left and right channels are equally opposing each other. When on channel dominates, you will hear it primarily through the near channel and to a lesser extent through the far channel.

One of the many drawbacks is that when the channel are near equal or moving into exactly equal, you will hear a crackling from both rear speakers.

The next one is going to be difficult to draw using text graphics.

Rt.Amp(+)----[Resistor]------
.........................................====(+)Spkr1(-)----(-)Amp
Lt.Amp(+)----[Resistor]------

The idea is that the signals pass through the two resistor and merge at the speaker, then the signal returns via common ground.

Note of course, with a resistor in series with the speaker, the speaker will not get full signal and will therefor be quieter. It will also sink or source signal into the other amp channel, though presumably the path through the speakers is the path of least resistance.

But I personally think you would do a much better job of obtaining better sound simply by getting a better stereo to play the TV sound.

I've got a pair of Diamond 9.6 with 2x 8" woofers each, for action movies I add a second set of DIY 12" 3-way speaker. My brother stopped by to take a shower (pluming problems at his house) while I was watching an action movie, he said he could feel the whole house shaking. Plus with these particular speakers, midrange or voice range is crystal clear.

Still, I've experimented with both ideas though more so with the difference signal using two speakers. They may enhance a sense of ambiance, but they don't really add much in the area of clarity. So, most people tire of them eventually.

Just a few thoughts.

Steve/bluewizard

[PeteMcK]

another variation on 'phantom' surround
http://kantack.com/surround/surround2.html

[kipman725]

Had this txt file on my HD for a while, never tried it but I presume it works quite well as I have fixed a high quality rotel amplifier that had a simlar circuit in it.

[zobsky]

Thanks All, ...will look at the suggestions.