Easy/cheap way to try out trinaural/derived center speaker setup?

I've been curious about the derived center/trinaural/trifield/etc. speaker setup. I've seen some old threads on here and other forums about it. I'm curious what the easiest/cheapest way to try this out. Assume that I've already got the third speaker. Would a used home theater receiver be the way to go?

(I should clarify that this is purely for music listening, so actual "home theater" use isn't a consideration.)

 

Music is 99.8% recorded in stereo and the rest is quad or 5.1. Also a properly positioned pair of stereo speakers will achieve a centre image without a centre speaker.
There's really no point in having a centre channel if it's just for music.

 

I would try our host and Kevin Gray's efforts with Nat "King" Cole.
Acoustic Sounds
It's 5.1 without the subwoofer and rear channel. There is a stereo mix along with the 3-channel mix. I only own the vinyl edition which is crazy good in only stereo. If there is anything else out there. I really don't know.

 

I'm looking for recommendations about the hardware necessary to try it out, not music that was made for multichannel. (Though I do appreciate the recommendation.)

 

OK- easy and cheap to try is diagrammed here, from Hafler of Dynaco. It is a speaker wiring scheme that does not need a third amp. Be sure to read the whole document and observe impedance and connection changes to the amp. This could be dangerous and could blow certain amps. Best results with three identical speaker systems, and an amp that won't blow when connected this way.
https://www.updatemydynaco.com/HistoricDocuments/DynacoCenterChannel.pdf

Edit: this is especially dangerous if you do not have all the +'s and -'s and/or red and black connections correct!

 

Seems to be relying on the presence of a "C" output lug which no amp I have ever used has.

 

A lot of amps (but not all) have that ("-" or black connections) essentially tied together internally anyway. In that diagram the "C" means Common, or ground.

I tried this setup when I was a kid, and it did work. Unfortunately then my center speaker was definitely lower quality than my newer stereo speakers, and the effect was not perfect that way. But this connection removes some of the mono information from the left and right speakers, correctly, and sends it through the center speaker correctly. When everything is perfect--same speakers for all three, and the amp doesn't blow--it works and the stereo image is the same as before, but more solid in the center.

 

If I understand correctly, that Dynaco wiring scheme doesn't allow one to change the volume of the center independent of the left/right, correct? Adding that requirement to the equation, where does that leave me?

 

Correct, pretty much.

You could add a potentiometer or L-pad to reduce (only) the volume of that center speaker, but that won't be useful. If all three speakers are identical it should be a nice effect as I described. It could be truly useful if the main stereo speakers must be widely spaced and there is room for an identical speaker in the center.
Beyond that, you would need a 5.1 or 7.1 amp or more, or any amp with a true center channel output.

You asked for "Easy/cheap way to try out trinaural/derived center speaker" and there is nothing cheaper or easier than free plus a speaker and some wire.

 

Anyone else have thoughts about this?

 

What has been described in this thread so far is simply adding a mono speaker in between the two stereo speakers. This only serves to narrow the sound stage.

There is no easy way to process audio so that center or mono content only goes to a center speaker, while left is only reproduced by the left and right by the right speaker.

One can mix the channels subtractively so the stereo speakers become more like "stereo effect" speakers.

Left = Left - Right signal
Center = Left + Right
Right = Right - Left.

This removes the mono signal component from the speakers on the side - mono is only reproduced by the center. However, it makes the output of the stereo speakers "ultra wide", and gives an in-air cancellation effect to stereo signals, requiring good placement, speaker balance, and seating position.

For example, where an instrument is placed so the left signal is twice as loud as the right, putting the image reproduction position 33% of the way towards the left speaker (just based on volume):

Left Signal: 2 ; Right Signal: 1. Sum=3

Matrix Speakers:
L-R: 1; L+R: 3; R-L: -1. Sum = 3

One can imagine the right speaker and its out of phase component cancelling 1/3 of the center speaker's output, which gives left speaker 1 and center speaker 2 as the final output volume, putting the image still 33% towards the left speaker.

However, it is the audio that each ear receives, and their differences, that forms the stereo image, which is much harder to depict. Properly recorded music also has phase and timing information, which can be more important than the volume in placing instruments in the sound stage.

 

I'm getting interested in this technology.

If you read chapter 7 in Floyd Toole's Sound Reproduction Third Edition you will note that he describes the flaws in the phantom image generated by the two stereo speakers, namely a dip around 2kHz of something like 6dB. This is often partly filled in by side wall reflections. He calls it 'interaural crosstalk' and says it's cause is an 'acoustical interference comb filter' resulting from the slight delay of the arrival at your left ear of the sound from your right speaker compared to the sound from the left speaker, and of course the same at your right ear. That delay is caused by the slight increase in the distance of travel to get round your head.

I can hear one of the symptoms of this that Toole describes, namely if I lean my head to the left, say, the sound is a bit brighter.

In order to solve this problem there seems to be:

Ambiophonics

Part 1: Problems with Stereo Reproduction and How to Fix Them

Basically you block the signal to the left ear from the right speaker etc., either physically with an acoustic panel (placed right up to your nose!) or some sort of electronic processing.

The Trinaural Processor

Trinaural Processor

This takes the stereo signal and processes it for three channels, including a third centre speaker. I presume that processing plus the set up of all three speakers tries to solve the phantom image problem.

I'm going to conduct some experiments with my room treatment to see what that can do on the ambiophonics front. One of the things I'll look at is if I can place an absorbent panel on the inside of both left and right speakers to stop the crosstalk but still get a full signal at the relevant ears.

I also use an equaliser so perhaps tinkering a bit with that may do something.

I would also be interested to know if anyone has or is using the Trinaural Processor. Did you get an identical centre channel speaker? How did you buy a single speaker?

 

I don't know what you hope to achieve. You have a stereo source you could run a mono center channel. I don't see what you would gain from doing this?

Sometimes a mono center channel is used to fill in the center in situations where the speakers might be place far apart, like with corner speakers.

Other than that, what exactly is the point? What are you looking to gain by doing this?

 

Solving the issue of the flawed phantom image as described by Toole in my post.

 

PWK was a big proponent of "phantom channeling" and in fact the Belle Klipsch was originally intended for exactly this purpose. Any sizable stereo power amp can be used as long as one side of the output terminals are at ground potential. Either an L-pad or a tapped transformer or autoformer can be used to control the level relative to the main speakers.


This was also very common in car audio installs in the 70s and 80s. I had an early sixties Buick that had been set up that way with an aftermarket radio with the left and right speakers in the door panels and the phantom channel speaker in the original position under the rear window. Worked fairly well.

The merits or demerits of this are purely subjective, i.e., either you like it or you do not. It seems to work well on some records and poorly on others.
Most users fit a DPST switch to simply disconnect the speaker when not desired.