Help with Center Channel Amplification

If you've got a "3.1" system, you need a system that can feed it the signals it needs. A 5.1 system can be configured to feed a 3.1 speaker system. It will route the 5.1 channels to the best place for the reduced number of speakers, and can Pro Logic decode stereo for 3.1. Those are the only ways to get the correct signals to your center speaker.

With all the 5.1 programmig around today, you should consider the possibilities of adding surround speakers. If all you expect to hear is stereo, adding a center channel and "feeding it in mono" is the worst thing to do. It just messes up the stereo presentation.

You can use your your stereo preamp and a simple resistor network to mix the channels; don't just use a Y cable. Something like this should work if you have separate preamp outputs with level control (the drawing below is the only way I could get the spacing to work):


+------- 27k ----------< L pre out
|
+------- 27k ----------< R pre out
|
+----------------------> C amp in

Preamp ground ---------- C amp ground


Use the RCA shield for the ground connection; resistors go in-line with the center conductors.

27 kOhm 1/2-Watt resistors were suggested in Paul Klipsch's "Dope From Hope" Vol 14, No. 4, July 1974.

If you need to adjust the center channel level relative to L & R, or if you share a single set of preamp outputs with L&R and Center, use the more elaborate network he shows in the article. [I can't seem to find the .pdf for that online anymore, but it may still be out there.]

How would this work, exactly? The center channel info is discreet. The center channel info CAN be left in the 2 front channels when they are used in stereo. If you added a center channel to a front channel's pre-out (still not sure how you plan to get both channel's info to the center), you'll just have duplicate center channel info in all 3 of your front channels and all the stereo info in the center channel as mono. That sorta defeats the whole purpose of having 3 separate speakers in the first place.



You don't need to spend $2500. All you need is an AV receiver.

How will this give him a discreet center channel? This will only make the center channel speaker play the content of both the L/R channels as mono, right? So, then the center channel info will be duplicated in all 3 front speakers and the individual stereo info that IS in the left and right front channels will come from the center as a mono signal. Hardly desirable.

What you're describing is how the old Dolby Pro-Logic processing system extracted the center channel information from a simple 2 channel stereo signal. In a similar fashion, the surround channel info was extracted from a simple 2-channel stereo signal by the Dolby Pro-Logic processor. But multichannel proccessing today is done by DolbyDigital 5.1 or DTS 5.1 processors. The digital 5.1 channel audio soundtrack of DD/DTS 5.1 material really is, unlike the simple 2-channel stereo soundtrack of old, specifically engineered to have 6 completely different, unique, and discreet channels of information; front L/R, center, surround L/R, and subwoofer. This is what the whole party is about!

Recording, transmitting, and decoding 6 channels of discreet and unique information is only possible in the digital realm. Simple 2-channel stereo obviously cannot contain 6 full channels of discreet and unique information. This is why a digital connection between a DVD player and an AV receiver is necessary. A digital processor, capable of DD/DTS 5.1 processing, processes the 5.1 channel digital soundtrack into the number of channels for which you have speakers. If you have 5 speakers and a subwoofer, the processor is capable of "teasing" out all 6 channels of discreet and unique information from the digital soundtrack, providing for a truly immersive surround sound experience. But a DD/DTS processor is actually capable of doing the opposite of what you described. Instead of extracting info from only 2 stereo channels, if you do NOT have a full compliment of 5 speakers and a subwoofer, it can actually reroute the info from those channels for which you have no speaker to other channels where you DO have a speaker. For example, if you only have 2 front channel speakers, the AV receiver's processor will split the discreet center channel information evenly across the front 2 channels. The 2 surround channels' info will also be distributed appropriately to the front 2 speakers in this situation. The subwoofer channel (0.1) information is also distributed to the 2 front speakers in a 2-channel setup if you do not have a subwoofer. If you have a 3 channel setup, with a center channel speaker, then the center channel information IS maintained as discreet center channel info, but the surround info is still rerouted appropriately to the front 2 channels, and the subwoofer channel info is rerouted to the front 2 speakers if you do not have a subwoofer.

In much the same way that a 2-channel stereo soundtrack from a CD (or LP) contains information unique to the left and right channels only, so too does a 5.1 soundtrack contain information that is unique to all of the 6 channels.

Join the party!

OP has a dilemma whether or not to pick up a matching center speaker 1) while he still can 2) for a good price. He was asking if he could drive a center channel amp from the L & R outputs of a stereo preamp. The answer is yes.

Adding a third, center, channel to a 2-ch stereo, if properly done, can help in some situations. Among other benefits, it "nails down" the L+R information for listeners not seated equidistant from the left and right speakers; this helps those watching movies from the side.

Hey, I'm a 2-channel (as in 2.0) kinda guy - and plan to stay that way for the forseeable future. I listen to mostly music, but also use the stereo for movies occasionally. My understanding is that movies with 5.1 (or whatever.1) soundtracks also provide 2-channel sound systems by mixing the front center channel equally to the front left and right. Using a 2-channel stereo with a "phantom" center (what I do), this sound appears to be coming from midway between the speakers for people sitting close to the center; for those well to the sides the effect is lost. Guess what? The simple resistor network adding left and right extracts this information and sends it to a physical center channel if you have one. Extracting "ambiance" or surround information from 2-channel has never worked well - and can't, really.

At the risk of seeming indiscreet, I think the word you want is discrete.

Zing.............

You are correct, sir.

The answer is probably "Yes, but..."


It actually "nails down" everything to the center speaker, reducing separation in proportion to how loud the center channel speaker is. If you turn up that speaker until all you hear is that speaker, you've got mono.


The stereo track on a DVD is usually the surround-encoded stereo-compatible version of the 5.1 track that is also placed on the analog "optical" soundtrack on the film. It could just be a simple downmix of the center channel into the left and right, but it often includes some dynamic range compression because the optical sound system doesn't have the headroom of the digital system. FYI, 5.1 digital TV broadcasts do not include a separate stereo. DTV receivers downmix the signal automatically for stereo viewers.

The simple resisitor you suggest just provides a way to feed the signal into the left and center speakers (or right and center speakers) reducing separation in the process. Extracting ambience and intentional surround information information can be done, and very convincingly.