3 channel question

[Al Klappenberger]

Guys,

PWK wrote a paper on this subject. "Sstereophonic Sound With Two Tracks, Three Channels By Means if a Phantom Circuit (2PH3)"

It was published April 1958 in the Journal of the Audio Engineering Society". It's 6 pages. I have it here and could scan it, but I'm lazy! Does anybody else have it already scaned? Gil McDermott maybe!

Al K.

[NOSValves]

Al your wasting your time.

[sfogg]

Al,

I have the paper but not in a handy electronic format.

Have you read some of PWKs setups in there though?

A couple are pretty odd to say the least.

One setup used mismatched L/Rs with yet another differing speaker in

the center. PWK specifically notes the difference in bass response

between the three speakers in that setup. In fact that three speaker

arrangement of a K'Horn and Heresy and a Shorthorn appear to be what he

used quite a bit in his tests. Lack of bass response in two of the

three speakers is interesting and might explain why he didn't note bass

boosting in this setup. How many here would use mismatched L/Rs for 2

channel stereo listening?

One of the methods of deriving the center speaker in that paper is by

using the difference signal between L/R channels. In other words the

material that is out of phase between left and right. That is a very

odd recomendation and in fact PWK said this gave more performance then

the 'mini-box' approach.

Anyone can take any Stereophile test CD they may have (or many others)

and listen to the phase test on it. Note the section in phase and how

it should give a nice focused center image... then listen to what

happens on the out of phase material. It won't give a central image and

should sound very diffuse. Very odd to recommend putting that

diffuse/phasey sounding material right up front dead center which is

what PWK recommended using that diffrence signal to drive a center

speaker. This is about the dead opposite of how any ambiance extraction

processing works today... they all follow what the sound sounds like on

two channel listening. The out of phase material will go to surrounds

which is more or less where it sounds like it should go based on two

channel listening. Material in phase and equal amplitude will go to the

center... where it would image from in a two channel setup anyway. I

believe later on PWK changed his mind on this configuration as well as

the mismatched speaker recomendation. (Which is a good thing... showed

he was learning more as he went on)

Of course this was all written in the very early days of the

availability of stereo music on LP. A lot still had to be learned about

recording and mixing for stereo back then.

PWK was ahead of his time for recognizing the earlier work at Bell Labs

and stressing the importance of a center speaker pretty much his entire

life. But the sum total of how a center can be used and what can be

done to derive a center channel didn't start and end with PWK.

Shawn

[Erik Mandaville]

Al:

I actually wasn't aware of the fact that you are using a center channel. I've been to your website a couple of times, but mainly to have a look at the network schematics (very generous of you to share those, by the way...).

Thinking about this some more yesterday evening, I think part of the response problem we were having had to do with the fact that all three front speakers were on the short wall. This put the center La Scala within about three feet of the Klipschorns. Beyond a certain point, the combined bass response became immediately 'peaky' and out of proportion -- to me, in this particular suspended-wooden-floor-listening area. However, within a certain small 'window,' I was able to blend the La Scala with the Klipschorns quite well. For an experiment, I turned the center channel 'off' when my wife left the room for a moment, and she noticed instantly that something had changed in the overall character of the sound. Even at this close proximity between the speakers, I very much prefer a carefully applied center channel to two-channel stereo listening. It's far and away the most significant transformation our system has undergone, and only took a trip to my parts bin and about 20 minutes of work.

Had I had the speakers along the 21 foot wall, where the distance between the three would be much greater, this bass boom may not have been evident. As I said, the room itself is not ideal, and it's taken some work to get things to sound right.

I think it's interesting you're also using a center channel. When I first built and tried the minibox, the response here was generally that I had just ruined my system. I think it's been fairly well-confirmed at this point that the idea is nothing new, and that there are many who appreciate three front channels to two. The minibox is a great first way to go about it. Since then I have found something that works much better (for me), but Paul Klipsch's minibox was/is a pretty innovative and effective device.

Craig: Would you like to contribute something here?

Erik

[Al Klappenberger]

Greg,

I know I'm wasting my time, but I got nothing better to do!

Shawn,

If you think about the phasing between left and right at it's extremes, if left and right were 180 degrees out of phase, the combination should be nothing. They would canell out in the room. This is exactly what happens in the resistor sumation scheme too. In the same way, in-phase left and right will add. This is also what happens in the resistor scheme. It works fine.

Erik,

My speakers are along the long wall of the room. They are about 18 feet apart and my listening chair is about 8 feet back from the center speaker. Just for a little "plug" here, since I installed the extreme-slope networks I find that I really don't even need the center speaker! Anyhow, running the system with the subwoofer off and the middle Belle running alone full-range, frequency response testing shows a peak at one frequency that is probably caused by wall bounce. I set up the Rane EQ to flaten out that peak. When the other two speakers are turned back on (with or withOUT the sub working) the bass response is fine. If I turn the EQ off I can hear a boomy effect on speach. This could well be what is causing the illusion of bass exaguration. Remember that Khorns sit flush into the corners so there is no wall bounce. If you add a center speaker, it is setting against the wall in the middle between the Khorns. It WILL be subject to the wall bounce effect and there's the mid-bass peak that could be percieved as bass exaguration with a center.

Al K.

[sfogg]

Al,

"If you think about the phasing between left and right at it's extremes, if left and right were 180 degrees out of phase, the combination should be nothing. "

Nope. A sound at hard left is only in the left channel... it doesn't have any information at all in the right channel. Ditto hard right. There is no cancelation of that material when it is mixed down to mono for the center speaker... it goes to the center as well as left or right. Even though it is supposed to only be heard from left or right.

Besides, listen to a phase test which puts the same material in L/R and inverts one channel 180 degrees and tell me you don't hear anything at the listening position. If you don't have a test CD with a phase test play mono pink noise on L/R and reverse the wiring to one of the speakers and listen to what occurs.

The bass gets some cancelation occuring but the higher frequencies don't get the same amount. The system will get light in the bass.

Again illustrates the point of the 1/4 wavelength spacing.

This is exactly the same thing (except out of phase... IE reversed) as what occurs when you add additional speakers running duplicated material between them. The bass gets reinforced more then the higher frequencies.

"This is also what happens in the resistor scheme."

I was talking about that with regards to PWKs scheme of running a center channel off the two 4 ohm connections on an amp, like what you posted above. The center in that configuration is run off the out of phase material between both channels. That same material in the L/Rs stays in the L/Rs and gives that diffuse sound... yet OTOH the connection between the two 4 ohm connections is routing that same material which is imaging as 'diffuse' in the L/Rs to the center speaker. You get conflicting information/imaging.

"When the other two speakers are turned back on (with or withOUT the sub working) the bass response is fine."

Turn up the level on the center Belle to equal your L/Rs and remeasure your bass response. Again... this is one of the reasons why you have to turn down the centers level on a passive mixed mono center. If you don't do this the system sounds lousy because of bass bloat and the lack of time alignment and discrete material between the center and the L/R speakers. The center (which is receiving hard left and hard right) is typically closer to the listener then L/R so the listener hears that information from the center first. The Haas effect then kicks in and that becomes where the sound is localized too. The apparent soundstage width shrinks considerably because of the mixed mono + Haas effect.

If you had discrete three channel source material your center would be run at the same level as L/R. Ditto with more advanced ways of deriving a center speaker. In those situations something hard left or hard right will only be reproduced by L or R so there is no Haas effect pulling the width narrower from L or R material coming from the center... it doesn't come from the center. Some other ways of doing this will also allow time alignment between the center and the L/Rs such that they all have the same arrival time to the listener.

"If you add a center speaker, it is setting against the wall in the middle between the Khorns. It WILL be subject to the wall bounce effect and there's the mid-bass peak that could be percieved as bass exaguration with a center."

If the center causes a bass peak that *is* bass bloat that occured when a center was added to the system. I mentioned the room bounce issue with a centrally located speaker in my first post in this thread.

Shawn

PS. For all these tests above run the Belles full range without the sub.

[PrestonTom]

I amazed by the tolerance that Al is showing. It must be very frustrating.

There are three points that have been made that I must comment on since this topic is near and dear to my heart (and at that the risk of me becoming frustrated).

First is the simple fact that if I add two identical signals (same phase, amplitude, frequency - or from an identical noise generator) they will now add up to +6 dB more (SPL or voltage). If they are not identical in frequency or uncorrelated in phase or from another noise generator, they will add up +3 dB. There is no debate about this and please do not bring up some arcane example.

Second is that the center channel should not be at an equal level to the L & R speakers. This is best understood by considering the phasors (I realize not all are familar with this, sorry). This is standard view used by folks like Ben Bauer and others when "stereophony" was first conceived and understood. If the level of the Center and Left speaker were identical in level then the resultant would be mid-position (half way between Center and left, or "halfway to the left"). . Importantly, this resultant is indistinguisable from the signal you would get by a single speaker placed halfway to the left (if measuring & using a 2-channel scope etc). Please notice that, this is essentially the same thing as a "phantom". A comparable statement can be made about the Center and Right speaker. Let me make the leap. If the center were at a comparable level as the L & R, then the sterophonic spread would be reduced. It would no loner extend from L to R, but rather from " half way left to halfway right". You have decreased the percieved angle in half. Yes, it would be the same as moving the 2 speakers inward.

At a great distance, then the angle would become smaller (with a constant distance between the speakers) then the phantom center would be fine and no derived center would be necessary. At closer distances (larger angles) a derived center is helpful (it is difficult to explain why this is so).

Regarding the possibility of excessive bass. Please see the first comment and also remember that these are very large wavelengths. There are standing waves and you will be exciting room modes. This also is a simple fact and not subject to debate or arcane examples that will get us off track. Personally, I would not use a high pass filter on the center channel. If there are problems in room acoustics that you are trying to clean up, filters are not the first weapon of choice and it would not be limited to only using them on just the Center channel.

I am sorry if I am being pendantic. Over the last couple of years I have seen so many topics that have plenty of engineering, physics and psychoacoustics behind. Unfortunately, they are being discussed so poorly. I would love to to jump in and correct some of the confusions. Perhaps even doing so without a great deal of math. But I look at these antagonistic discussions where simple issues like phase delay, group delay, Haas effect, Fletcher-Munson curves, impedance etc can not be discussed without folks attacking one another in some weird pissing contest.

I am done ranting now.

Good Luck,

-Tom

[sfogg]

Tom,

"Second is that the center channel should not be at an equal level to the L & R speakers....."

Again, depends upon the manor in which the center channel is derived. If you have a three channel discrete source (or a more advanced method of deriving the center) the center channel is supposed to be the exact same level as L and R.

Try listening to a three channel recording with the center channel turned down 7dB.. it sounds lousy. Esp. if the mix took full advantage of the center speaker.... and not all do.

" A comparable statement can be made about the Center and Right speaker. Let me make the leap. If the center were at a comparable level as the L & R, then the sterophonic spread would be reduced."

Only when the center is nothing more then a duplication of L+R. If the center receives material unique from L and R (and the L and R receives material unique to them) this doesn't occur.

" It would no loner extend from L to R, but rather from " half way left to halfway right". You have decreased the percieved angle in half. Yes, it would be the same as moving the 2 speakers inward."

Not when the center channel receives its own individual information. With three channels of information equal amplitude in left and center would image between left and center just like you said... and that is exactly where it is *supposed* to image between. That is why the information was mixed equally between center and left in the first place. Something supposed to come from dead center will be in the center channel alone.... something hard left will be in hard left....etc...etc...

"If the level of the Center and Left speaker were identical in level then the resultant would be mid-position (half way between Center and left, or "halfway to the left"). . Importantly, this resultant is indistinguisable from the signal you would get by a single speaker placed halfway to the left (if measuring & using a 2-channel scope etc). "

No, it wouldn't be indisinguisable. Simple example... move laterly in the room. The 'phatom' image will change position as the relative levels and timing of L+C changes along with the listener. If there was an actual speaker between L and C the image position won't move. L+C will comb filter between each other, an actual speaker position between L+C won't comb.

" can not be discussed without folks attacking one another in some weird pissing contest. "

Where is anyone attacking anyone in *this* thread? We are having a discussion. There are no insults or anything like that occuring here. Granted the above happens very often in this forum but so far this thread hasn't degraded into that.

Shawn

[dbflash]

Tom,

How is the Cornwall working out for you as the center channel?

I have a pair of Khorns that I am using now and I have a pair of Cornwalls that are sitting in the corner doing nothing.

I have read that a Cornwall can be used and then I have read that a Cornwall should not be used.

I am going to try 3 channel once I get my room redone. If I can use the Cornwall and not have to buy a Belle that would really be great.

Thanks,

Danny

[rigma]

What about this.(See sketch) I have always run the 2 centers in mono about 4-6 db down. What do you guys think of the idea of running the center LaScalas in stereo maybe even reversed stereo. By that I mean the left center running the hard right signal and right center the hard left. Just looking for opinions.

Rigma

[Al Klappenberger]

Shawn,

Nope. A sound at hard left is only in the left channel... it doesn't have any information at all in the right channel. Ditto hard right. There is no cancelation of that material when it is mixed down to mono for the center speaker... it goes to the center as well as left or right. Even though it is supposed to only be heard from left or right.

A signal hard left or hard right will be 6 db lower in the center than if it were in both channels in phase. It will move the image toward the center only very slightly. Acoustic signals from the left ad right will act virtually the same.

........

I was talking about that with regards to PWKs scheme of running a center channel off the two 4 ohm connections on an amp, like what you posted above. The center in that configuration is run off the out of phase material between both channels. That same material in the L/Rs stays in the L/Rs and gives that diffuse sound... yet OTOH the connection between the two 4 ohm connections is routing that same material which is imaging as 'diffuse' in the L/Rs to the center speaker. You get conflicting information/imaging.

It does not matter how sum up to signals. If you do it at high level at the output of the amps or at low level with resistors or even with two sereis resistor into the virtual ground of an op amp. The two channels will add to a nice center equally well. BELIEVE me, I have been doing this for years and it works fine.

You can make whatever agruments you like. This is a time proven technique and it works well.

Al K.

[sfogg]

"It does not matter how sum up to signals. If you do it at high level at the output of the amps or at low level with resistors or even with two sereis resistor into the virtual ground of an op amp. The two channels will add to a nice center equally well."

Those different methods combine *different* information into the resulting channel. Don't you see that? The mini-box does L+R, the method using the 4ohm taps on the amplifier results in a L-R signal. What information ends up in that resulting channel isn't the same... one is a sum the other is a difference signal.

That they combine to another channel isn't the point. I am not questioning that they do. The question is where that difference information should be reproduced from.

The point is passing material that is imaging as diffuse in the L/Rs (the difference signal... L-R ) then taking that exact same information and putting it into the center channel makes no sense. You are putting conflicting imaging ques together when you do that.

Like I have posted several time... listen to a phase test in 2 channel. A phase test is literally changing from a signal that is just a sum signal to a signal that is just a difference signal. The sum signal will image as a strong phantom center speaker. However the difference signal will sound like it is coming from anywhere *but* the center, it will not be easily localized and it will sound diffuse.

Why then would you take that difference signal and use that to feed the center speaker? It doesn't make sense.

Spend five minutes with a phase test CD listening in 2 channel and you will hear this. Any of the Stereophile test CDs have phase tests tracks on them.

"This is a time proven technique and it works well."

Actually, using a difference signal at the center channel is not a time proven technique at all. PWK himself later on changed his mind about it. Read his later papers on this if you don't agree.

The method of deriving that channel of information using the difference signal is a *far* more used technique for extracting a surround channel of information. This is the so called 'Hafler Matrix.' And it makes far more sense to use it in that manor if you compare what a difference signal sounds like in two channel. It will sound diffuse with non-specific imaging.... IOW... sort of like a surround effect. It will not image as a hard center at all..... as anyone here can try for themselves using the phase test track on any of the Stereophile Test CDs. (Or many others)

The downside with this passive method is little channel seperation (around 3dB) and the Haas effect can screw up the imaging up front if the surrounds are closer then the mains as there is no built in delay available for the surrounds.

That difference signal is the basis for surround information in pretty much every surround sound extraction algorythm out there. None of them direct a difference signal to the center speaker as that isn't where those sounds will image from in two channel.

" I have been doing this for years and it works fine."

I have stated the L+R Sum method can work but it has limitations, I have done it myself. I have also said it is not the last word in how a center channel can be extracted.

Do you have any experience with alternate extraction methods? You might be suprised how effective some can be. Not to mention actual three channel source material such as the RCA 'Living Stereo' SACD re-releases that were originally recorded in three channel and are finally being delivered that way.

Shawn

[PrestonTom]

Danny:

The Cornwall works pretty well as a center between 2 K-Horns. I got a sweetheart deal on the Cornwalls - I could not resist.....

The voicing is somewhat comparable and I did not have the money or space for full horn system (LS or Belle). The objection is that the radiating woofer (rather than loaded horn) is less efficient. It is this loss of efficiency that translates to increased distortion. PWK was concerned that mixing a Cornwall with K-Horns would corrupt the sound. The difference in efficiency (inversely proportional to distortion) is about 4.5 to 1. So the Cornwall, in terms of distortion, would be the weak link of the system. Although remember that the center is also turned down in level, so it is not as bad as first appears.

Shawn:

Perhaps we are talking about different things. I am referring to a center channel that is a summation of the L & R channels. There are schemes of using a difference signal (which I consider to be more of a gimmick to give a "lively" sound) or the steering methods that require a more elaborate circuit. I beleive this is what most of the other folks were talking about also. Given that, my comments hold true. My comments about the "tone" of these disscussions does not merely pertain to the current discussion. It is rampant across many of these threads. It is unfortunate since there is some real talent here and we could all learn a great deal about cabinet refinishing, crossovers, measurement, physics, history, trouble-shooting and recording etc. My comment is actually a tribute to folks like Al and others who continue to share their knowledge. Given the direction and exchange in some of these threads, I am surprised that they bother.

Incidentally, the phasor analysis holds true (for a summed center) even when the listener is at the side. Such a phasor analysis was nicely derived and presented at an Acoustical Society of America conference several years ago (I don't think it was ever published however).

Good Luck,

-Tom

[oscarsear]

Whilst y'all bounce about the center channel theories I have a related question. Regardless of which method of deriving the mono center channel is used could it be made better by specific speaker design? Instead of using a La Scala or a Heresy could the imaging be enhanced with a speaker/crossover devised soley for this purpose? For example a 2 channel (squawker and tweeter) that excludes bass but employs an adjuctive sub-woofer in it's place. A mid-range that matches exactly the side speakers or one that shoulders over the mid frequency high and low range? Are we force fitting speakers for this role?

[Hardhead]

oscarsear--

It makes the most sense to me that the absolute best imaging and timbre matching would result from using the exact same model for the 3 speakers across the front. Using the exact same drivers, horns, and crossovers for all 3 would be necessary as well--again, for the absolute best imaging and timbre matching.

If that weren't possible or practical, then matching the same drivers, horns, and crossovers as much as possible would give the next best result.

Considering that the lead singer or featured instrument(s) are almost always in the center of the stereo spread and that HT puts the dialogue in the center channel, it makes the most sense to me to have a full range speaker in the center that is of the same quality as the left and right speakers.

That reasoning also holds true for all the speakers in a multi-channel setup, especially as the rear and side speakers are beginning to have signals of more acoustic importance sent to them.

[artto]

I agree with Tom & Al.

Just for the record, I have been experimenting with 3 channel for more than (YIKES) 30 years now, ever since I first read about it in the Klipsch Audio Papers that Mrs. Belle Klipsch had so kindly sent me after purchasing my first Klipsch, Cornwalls in 72'.

[DrWho]

I agree with Tom & Al.

Just for the

record, I have been experimenting with 3 channel for more than (YIKES)

30 years now, ever since I first read about it in the Klipsch Audio

Papers that Mrs. Belle Klipsch had so kindly sent me after purchasing

my first Klipsch, Cornwalls in 72'.

I don't remember how wide your room is, but your 1/4 wavelength

distance is probably greater than the lowest frequency being reproduced

by your center belle. I seem to recall a 19' depth, so let's just use

this as the distance between your belle and khorn. This means the bass

coupling will start occuring at a wavlength of 76 feet, or 15Hz. This

is definetly below the LF capability of the Belle so you don't notice

it in your room....

That doesn't mean the theory is debunk though.

An easy way to demonstrate the effects for yourself would be to take a

pair of speakers outside and measure their frequency response (pink

noise with an RTA should be sufficient to demonstrate it). Spead the

speakers out really far apart and then gradually move them closer

together. You will notice summing occuring at the lower frequencies and

this summing will gradually move up in frequency as the speakers get

closer together. This is the same reason why you get a 6dB gain when

you have subwoofers stacked, but only 3dB when spread out through the

room.

Another thing you will notice, though this is kind of unrelated, is

that the dispersion pattern of the two speakers gets narrower the

further apart they get, and gets wider the closer together they are!

Talk about counterintuitive []

[Erik Mandaville]

Al:

"Erik,

My speakers are along the long wall of the room. They are about 18 feet apart and my listening chair is about 8 feet back from the center speaker. Just for a little "plug" here, since I installed the extreme-slope networks I find that I really don't even need the center speaker!"

The plug is totally fine, Al. I really think that the personal taste and preference element factors in with this, just as it does with virtually everything discussed here. I have heard only good things about all your networks, particularly the ES, and I'm sure they sound excellent. It would be interesting to be able to audition a pair sometime, but that probably won't happen unless I build them. Right now, I'm using a 'cobbled' version of the very simple type 'A'. It's a good sounding network, which I'm sure would 'bettered' by any of your designs. It's what I have right now, and I'm making do (for the time being).

For me, the minibox was very honestly nothing short of a revalation. That's really the truth! It's not the first time I have experimented with this, however. Brian Eno (Ambient Music, etc.) once included in one of his album notes a diagram showing his experiments with a third channel that is identical to the very simple one several posts back. It's just the addition of a third speaker, which Eno used BEHIND and above the listening position rather than in front. Rather than using the variable L-pad you suggested, he just used a fixed resistor to reduce the output of the third speaker to a favorable level. It's exactly the same thing, though, and is something I experimented with when I was in high school.

In any event, I have no doubt I would still be using the minibox if Shawn hadn't sent along his first Lexicon processor for me to try. I was amazed, and completely unshaken by the initial response this got when I mentioned it. It was simply too good (to me) to not investigate further. The steering and individual adjustments the Lexicon provides is outstanding, not to mention very useful. With all that is going on within, I am continually amazed by how transparent and polished the sound remains. In her usual patient way, my wife helped me move some things around, to where it's possible to effectively once again use the rear channels of the Lex. I will also be able to use the La Scala with the Altec mid-horn (also sent by Shawn), since the TeeVee is no longer using it as a throne.

Erik

[Al Klappenberger]

Shawn,

"Those different methods combine *different* information into the resulting channel. Don't you see that? The mini-box does L+R, the method using the 4ohm taps on the amplifier results in a L-R signal. What information ends up in that resulting channel isn't the same... one is a sum the other is a difference signal. "

I'm surprised at this statement. I have always been impressed by how well you do you homework. This time however you have missed the boat completely! Nobody is perfect I suppose. Every center derivation technique that has been described here is a L+R sumation. Look carefully at the scheme I posted. One channel has been inverted such that on a mono program, when one channel is going + the other is going -. If you bridge across these you have L+R! If you switch your preamp to mono the center channel will play nicely. If both L and R power amp outputs were in phase (no phase inversion) bridging across them would give no potential difference. That would be L-R. This is why one channel is inverted and the speaker connect to that channel is inverted again to bring the Left and Right acoustic output back in phase. I have actually used this scheme except that I had to build a small inverter amp using an op-amp IC to invert one channel since I didn't have the nice balanced XLR cables of the new Mc275 and C2200 that can easily by cris-cross wired. If it was L-R, switching to mono would give no output from the center speaker. This does not happen. Furthmore, I have actually used L-R connection before I built the little inverter amp by bridging in the same way. Under these conditions, mono produces no output from the center, BUT, when you are listening to a normal stereo program there is often considerable L-R component in the stereo signal and the center actually works when connected L-R! It just does noting on a centerally located mono source, like the DJ on a FM radio station.

Al K.

[sfogg]

Al,

"This time however you have missed the boat completely! Nobody is

perfect I suppose. Every center derivation technique that has been

described here is a L+R sumation."

I suggest you re-read the paper from Klipsch you referenced. It shows a

L-R difference signal as being connected to the center channel. It

further suggests that that setup offered better performance then the

mini-box. The L-R connection to the center is a wacky suggestion for

the reasons given numerous times already.

"Under these conditions, mono produces no output from the center, BUT,

when you are listening to a normal stereo program there is often

considerable L-R component in the stereo signal and the center actually

works when connected L-R"

Just because you get output at the center doesn't mean it is working in any sort of a logical way.

Connect a center channel in parallel with R and you get output too. So

what.. the object isn't to just get output from the speaker it is to

get material in the center speaker that belongs in the center

speaker.... IOW... material that would image to the center in normal

two channel listening.

A L-R difference signal doesn't image to the center. Routing that

information to a center speaker makes no sense as Klipsch suggested in

that paper you referenced.

" It just does noting on a centerally located mono source, like the DJ on a FM radio station."

Which makes no sense since a centrally located mono source is going to

image from the center. That is when the center speaker should be most

active, not doing nothing.

IME an optimal situation would be the center speaker alone reproducing

the centrally located mono source. That eliminates all the comb

filtering between multiple speakers and will firmly lock the central

image in place for off center listeners. You can't do that with the

passive method of deriving a center... but you can with the active

methods. (Or with the 3 channel discrete sources)

Read the various papers and works of Schreiber, Fosgate, Dolby, Gerzon

and Griesinger. They all have differing methods and alternate ways of

expanding two channel recordings out to more speakers and some of the

psychoacoustic effects of that. They all differ in their effectiveness

and 'sound' on playback.

Some light reading might include....

http://world.std.com/~griesngr/sur.pdf

http://world.std.com/~griesngr/pan_laws.pdf

http://world.std.com/~griesngr/surround_from_stereo2.ppt (be

ready for serious information overload in this presentation.. it

describes some of what is at work behind the method both Erik and

myself use)

http://www.audiosignal.co.uk/Resources/Three_channels_A4.pdf (this is

the basis for Gezron's 'Trifield' which is a considered a passive (

meaning non-steered) method of deriving out one or more speakers up

front)

http://www.audiosignal.co.uk/Resources/Surround_sound_from_2-channel_stereo_A4.pdf

For those who haven't experienced these methods and haven't looked into

them before they might find it rather shocking how they work and the

research that has gone into them.

Shawn