Thanks for emailing the image.
There's a problem with the center channel mixing circuit as you've drawn it. The amount of center channel attenuation is overly dependent on the source impedance of L and R. And, with the resistors chosen to give 3dB attenuation of the center channel working against the source impedances of L and R, the loading on L and R will be excessive.
The circuit below will mix in the center channel with the center down by about 3dB
relative to left or right, while maintaining source and load impedances that should work reasonably well with typical "consumer" equipment.
Problem is, it reduces your
overall signal level by one half. But that's the name of the game with passive mixing! Most CD players have fairly hot outputs, though.
the amount of crosstalk between L and R will depend on the source impedances of L, C and R. If it's excessive, then the 3.3K and 2.2K resistors can be increased in value--as long as you maintain the same
ratio between them. The price will be increased insertion loss, and also a higher source impedance driving the cable to your amplifier. In any case, the mixing network should be located close to your amplifier, connected with a reasonably short cable if possible.
October 26, 2005, 02:46:40 AM