3 channel question

[steve]

Shawn

since the Klipschorns were designed to have a center channel originially, there has to be a simple way of deriving that center channel..I really feel like I have a hole in the middle with the KHorns properly positioned in the corners. If I toe them out, the imaging is much better, but I lose some of the low end. I'd really like to have a center. (plus it's too late to turn back, I have a Belle on the way!)

Steve

edit: I'm taking Al's advice and making the SET my center channel..I just have to rewire it as a monoblock..hey, it'll double the power!

[sfogg]

"since the Klipschorns were designed to have a center channel originially,"

They were designed in the mono days.

"there has to be a simple way of deriving that center channel.."

There is, it is listed here. But it is not without its pros and cons.

There are also other approaches to deriving a center channel. They all have pros and cons too.

" I'd really like to have a center. (plus it's too late to turn back, I have a Belle on the way!)"

A center can be a huge improvement on music. I've been doing that for a long time too.

Shawn

[Al Klappenberger]

Shawn,

I don't buy that argument about bass boost in a center channel. Energy from two sources adding together wouldn't happen in 3 channels any more than with 2 channels. It would be a function of phasing between two cources. That is, the distance between speakers no matter if it was between left and center or left and right in a room half the size! I have been doing the 3 channel thing for years in three different living room situations and have run into nothing like that! With highs or lows from multiple sources, it's a matter of the phase between the sources. In other words, it's the room acoustics, not the number of speakers you have!

On the matter of separation, if you analyze the center channel output under hard left or hard right signals, you will see that the center level drops by 6 db on a single left or right signal compared to mono from both left and right. The center channel is also run at a low level compared to the flanks. If you turn the preamp balance control fully to one side you virtually hear just one speaker. There is virtually no loss of separation. It just removes the hole in the middle! If you have the center cranked up too high the separation will be reduced, but you will realize very quickly that it's too loud! It will be very obvious.

Al K.

[PrestonTom]

Regarding Shawn's comment about my comment (it gets confusing)

""The summing was done early in the circuit of the "center" pre-amp and all the L&R's were tied together and "went back" to the "stereo" pre-amp. The stereo separation was lost."

.........

Any of these passive approaches reduce stereo seperation and placement. You no longer have the ability to reproduce hard right and hard left in a mix... it will be reproduced as right and center or left and center. "

I was referring to to folks inadvertently summing all the inputs with y-cords & sometimes multiple preamps (can easily be checked with a VOM meter).

The issue of decreasing the stereo seperation with a passive device should not be all that problematic. I built the Klipsch-version, the seperation is still about 30 dB (measured at the output of the box). This is plenty to get the full stereo spread. This of course will be decreased if the volume on the Center channel is turned up too much. It should be a few to several dB down from the L& R speakers.

Good Luck,

-Tom

[steve]

This is all great info, and certainly encouraging. Now if I can just get Tom M to build me one..

Thanx all

Steve

[sfogg]

Al,

"Energy from two sources adding together wouldn't happen in 3 channels any more than with 2 channels."

Of course it would. The distance between the speakers is reduced with

three speakers compared against two. When you get closer then around

1/4 of a wavelength apart the drivers will sum more then at frequencies

above that point.

"It would be a function of phasing between two cources. That is, the

distance between speakers no matter if it was between left and center

or left and right in a room half the size!"

Exactly. And take any size room you want and add a third speaker

between L and R and you just in effect brought three sources of energy

closer together then when you only had two.

"I have been doing the 3 channel thing for years in three different living room situations and have run into nothing like that!"

Aren't you summing everything below 70hz to a subwoofer? You likely

wouldn't run into the situation since you don't have three sources

reproducing bass... you have one. Also worth noting that K'Horns go

deeper the Belles.

"If you have the center cranked up too high the separation will be

reduced, but you will realize very quickly that it's too loud! It will

be very obvious"

That is the point. With the passive approach you can only use the

center as a lower level fill, it can't be played back at the same level

as L/R as it sounds lousy doing that.

With other approaches that isn't the case.. the center doesn't have to

be turned down to keep from being a distraction (from the reducing in

separation and bass bloat)... the center is balanced to run at the same

level as the L/Rs and material is steered between them. Something hard

left stays hard left and vice versa on the other side. Something dead

center goes mainly to the center...etc..etc...

Shawn

[Hardhead]

Bass bloat? I've been doing the derived center channel thing for 32 years in 9 very different rooms in 3 states, and I've never heard any kind of bass bloat, although it simply may not show up in those 3 states. I suspect that if there were a real problem with bass bloat, Bell Labs would have noticed it back in the 1930's when they were doing their experiments with 3 channels. I've also tried turning off the center speaker to hear the differences, and the only difference I could hear was the sweet spot became much narrower with the center speaker off.

As to the level of the center speaker, it can be tricky since it's a psychoacoustic effect. If the volume is too loud, the stereo effect disappears; when it's too soft, the effect of the center speaker is lost. PWK recommended a -6dB setting, and I found that -7dB works best for me. I figured out how to make a voltage divider to set the volume at: http://www.troester.org/ls/lpad.html . It works very well. Use the single resistor value. You can even figure it out to the tenth of a dB, and, interestingly enough, I could make a distinction between a 1dB difference. I tried it with a few values of cheap resistors before I bought a pair of excellent ones. I suggest resistors with a 1% tolerence if you really want to get anal.

I didn't want to install a volume control to avoid degrading the sound with any volume control I could afford and because I wanted to keep the box simple and comparatively cheap. Besides, with volume controls you still have to get the impedance right or the sound can really suffer. Perhaps that's where bass bloat comes from.

[Erik Mandaville]

Al:

"Where did you get this from? There is no exaggerated bass created by a center channel!"

From my own experience. It was immediately repaired with the suggestion from Shawn to try an in-line filter. The balance was much better with that addition in the minibox.

Erik

[Al Klappenberger]

Shawn,

I still don't buy it! The size of your room and the distance between speakers just as random from one listeners home to the next no matter if it's two speakers or three. Imagine 25 speakers all in a row across your listening room wall. All are in phase all the time. They will all add together the same way. The kicker is that they will NOT always be in phase. I don't care how many you have, 1, 2, or 25, the phasing (which changes with frequency) is still random and a function of the room and spacing between them, not how may you have! How many you have is just another random factor in the phasing

Yes, I am using a sub right now, but I have only had it for a couple years. I was using the combination of 2 Belles and a Cornwall center for years before that. In fact, I considered the Cornwall to be a subwoofer of sorts. I only got the LF-10 sub AFTER I got the 3rd Belle to replace the Cornwall. What you suggest about exaguratioon of the bass is the same thing as moving a subwoofer around the room to get the best bass performance. It depends on where you put it even with only ONE source! Another point: Steve will have two Khorns which go down to 35 Hz or so. The center Belle starts to poop out at 70 and is really only putting out good bass down to about 50 Hz. There will be only the original 2 sources making bass below 50 Hz, so there will be no "third speaker bass boost" below 50 Hz even if it was a real thing.

Al K.

[Al Klappenberger]

Erik,

What kind of "in-line filter"? Describe it. Show me a schematic..

Al K.

[Erik Mandaville]

"Bass bloat? I've been doing the derived center channel thing for 32 years in 9 very different rooms in 3 states, and I've never heard any kind of bass bloat, although it simply may not show up in those 3 states."

This is not my imagination. Very likley this response anomoly was related to room acoustics, which in our case is amplified by the fact that we have our system on socond story suspended floor. It is not an ideal listening room by any means, but with some work -- and indeed an inline filter in the minibox when I was using a passive derived center channel -- we have gotten some good sound here.

With the Lexicon processor, which IMO is quite a step up from the minibox, I have experienced nothing in the way of bass heaviness from the center, which is also rolled off at 120Hz, similar to the use of the crossover in the minibox.

My feeling is that the 25K potentiometer had very little if nothing to do with this bloated bass response.

Erik

[Erik Mandaville]

I think it's possible to experiment with this. The minibox is simple enough to where the addition of a filter can be tried if there seems to be an imbalance in frequency response -- and it can be clipped out if there isn't. If I turned the center channel up just a small amount beyond a certain point, the bass seemed very much out of proportion. I used the passive center/minibox in a very subtle way, which in my case means it was completely 'invisible'...............unless it was turned off.

As I said, the problem was very likely much more associated with peculiar room modes, and many may not experience what we did. The wonderful flexibility of the Lexicon has enabled very detailed adjustments with the 7 speakers we now use, and there is no bass emphasis to speak of. The room itself is still a bit more 'live' than I would like, and that's still kind of a work in progress.

Erik

[Erik Mandaville]

Al:

You don't have to 'buy' anything.

You asked, "What kind of "in-line filter"? Describe it. Show me a schematic.."

I don't have a schematic, however if you look a few responses up, you'll see the diagrams for the miniboxes. Add the appropriate device on the output, and that's what this is. Very simple. I bought it from the autosound dept. at Best Buy.

Erik

edit: Al: If you want, I can try to draw this up and get a picture of it somehow. I tried it a couple of different ways in relation to the minibox, including using the cap in series with the driver. These things are commonly used to prevent low frequencies from damaging mid or HF drivers, and in this case were used simply to roll off the response at higher frequency to help tame the bass heaviness.

[Al Klappenberger]

Guys,

Here is a poor-mans scheme for a center channel that I came up with years ago. I requires no box or third amp. I actually wrote a letter about it to Klipsch. The letter was answered (indirectly by PWK himself). PWK suggested that the power amp I had (also a McIntosh) would simply allow me to get into it and reverse the transformer leads rather than inverting the phase of the input of one channel.

Anyhow..

If your peramp and power amp both have XLR connectors (ballanced) all you need to do is invert the phase of one channel. To compensate, you ALSO need to invert the speaker cable to THAT channel. This allows anything bridged across the left and right output to sum up (L+R). By puting an adjustable L-pad in the line with the center you will have a controlable level center chanel. You will need to establish the phasing of the center by trial and error. Just pick the phase for the best bass. I used this method for a while before I got a third amp. It WORKS!

Al K.

[D-MAN]

Along the same lines, Dynaco applied for a patent on the derived-third channel scheme.

[D-MAN]

page 2 of 2.

[sfogg]

"The size of your room and the distance between speakers just as random

from one listeners home to the next no matter if it's two speakers or

three."

And in every case if you put a center channel between the L/R you have reduced the distance between the sources.

"The kicker is that they will NOT always be in phase. I don't care how

many you have, 1, 2, or 25, the phasing (which changes with

frequency) is still random and a function of the room and spacing

between them, not how may you have! How many you have is just another

random factor in the phasing"

It is not random at all which will be in phase or not... all the

derived speakers are receiving is a mono mix of the L+R. In that case

what will be in phase is based on the distance between speakers and the

wavelength of sound they are reproducing. If they are within about 1/4

of a wavelength apart they will be in phase. In the mini-box it is not

steering individual sounds to all those extra speakers, not the same

thing as having three discrete channels of information.

"There will be only the original 2 sources making bass below 50 Hz, so

there will be no "third speaker bass boost" below 50 Hz even if it was

a real thing."

No, but there would be bass boost between 50hz and the upper limit of the coupling between speakers.

"What you suggest about exaguratioon of the bass is the same thing as

moving a subwoofer around the room to get the best bass performance. It

depends on where you put it even with only ONE source!"

Get a second sub (fed mono like the other) and experiment with what

happens when you move the subs closer and closer to each other. The

bottom end of their response starts getting boosted in SPL first. The

closer you get them together the higher up in frequency the SPL gains

will be. Same deal there as with multiple speakers reproducing the same

material.

It is a real thing in some situations wether you believe it or not. Why

do you think you have to run the center speaker at a lower volume then

L/R? With three discrete channels (what Bell Labs was doing) that isn't

the case... the center speaker is run at the same volume as the L and R

speakers.

Erik noticed it right off the bat after he went back to the mini-box

after spending time using a more advanced version of deriving a center

channel.

Shawn

[sfogg]

"I suspect that if there were a real problem with bass bloat, Bell Labs

would have noticed it back in the 1930's when they were doing their

experiments with 3 channels. "

As I recall Bell Labs was working with three discrete channels. Not two

channels and a duplication of them for the center. The problem Bell ran

into was they didn't have a delivery method available for three

channels available at the time. So they had to work with what was

available... two channel delivery.

And again.. I'm not saying a center is a bad thing. I'm just saying a

mixed mono center isn't the end all be all of deriving a center

channel. It is a start... not the end point IME.

Shawn

[sfogg]

"

Get a second sub (fed mono like the other) and experiment with what

happens when you move the subs closer and closer to each other. The

bottom end of their response starts getting boosted in SPL first. The

closer you get them together the higher up in frequency the SPL gains

will be. Same deal there as with multiple speakers reproducing the same

material."

Actually... even simpler then that.

Take another identical sub with its internal volume control configured exactly the same as your first sub.

Now add it to the system fed the exact same signal as your first sub.... guess what is going to happen....

Your system is going to experience bass bloat. Adding additional 'woofage' fed the same signal is going to cause it.

Shawn

[Al Klappenberger]

Dana,

I like that scheme for the center channel. Too bad I didn't think of it! All it needs is a simple pot connected across the center speaker to control the level.

Al K.