Surround sound from an integrated stereo receiver ?

[fireman]

Merry Christmas to you all !

If I remember correctly, a few years ago when HT were just arriving on the market, I had read somewhere that one could get surround sound from a stereo receiver by connecting a second pair of speakers in some other way to the stereo receiver.

If my memory serves me right, it looked something like Left + with Right - for one speaker and Left - with Right + for the second one.

Was it some kind or urban legend or does this really work. I might have tried it myself but I'm afraid I might blow something up and spend Christmas without my receiver

If it is indeed true that one can get surround from a stereo receiver, is there also a way to get the signal for a center channel ? If I had to choose between surround or center channel, I would probably go with the center channel as I find the imaging of my speaker is not all that good rignt now.

Eventually, when my budget improves, I will "enhance" my setup but for now, it'll have to do.

[sreten]

Its the so called Hafler circuit (of which there were two variations).


The "surround" varaition involved wiring two speakers (out of
phase) in series and in series will a variable resistor across
R+ and L+ of a common ground stereo amplifier.

It doesn't work well mainly due to a lack of delay in the derived
channel, other than that its very similar to the rear channels of
basic Pro-Logic decoding.
(Basic pro-logic is crude because of the bucket brigade delay lines
they used for this delay.)

Extracting the centre channel from Pro-Logic requires some phase
shifting and de-emphasis cannot be easily done.

The "image enhancer" variation of the Hafler circuit is identically
wired but with carefully placed speakers near the front speakers,
I've never tried it, imagine the sweet spot is small.

For more info see here :

http://www.dai.ed.ac.uk/homes/cam/gadgets/hifi.html

Though it doesn't cover the "image enhancer" variation.

sreten.

[purplepeople]

The passive matrix effect is quite good, even without the delay to the rear channel. If you're going to do it, make sure the amp has enough power to handle the mixed impedances and extra speakers.

If you are looking to create delay, do it with physical space. Since mach = 1000 ft/s (approx), you get 1ms delay for every extra foot the sound has to travel. Dolby recommended a net delay of about 10-15 ms for the psychoacoustic effect so you will need at least 10 feet of extra distance from your head to the rears as from your head to the mains. In 20 foot room, your head would be placed about 5 feet from the front speakers.

After trying this, I discovered that even 5 ms delay is more than enough to give the effect for properly matrixed material like Empire Strikes Back or even Star Wars-EP4.

Enjoy...

:)ensen.

[Vidgamer]

I've used the surround (L-R) design (similar to the surround portion of that circuit) in my car audio wiring. It works pretty well, if you have a separate sub to give you some bass.

However, I have a question about the listed circuits. How often do you have a "common ground"? In car audio, at least, you get situations where there are different internal designs (perhaps to increase power?). Unfortunately, I do not understand amp design to tell when I can assume there is a common ground, and when I can't. Is there way I can use a multimeter to tell?

When I experimented with an L+R center channel in the car (in a circuit by itself), I wasn't too excited about it, but I wonder if it would be different if I wired the entire circuit, with L, R, and C all on one amp? In other words,when you adjust the volume of the center, how does it affect the L & R? Would it image better?

[eStatic]

Originally posted by purplepeople
If you are looking to create delay, do it with physical space.

Purple, Why not with digital delay?