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Is using two center channel speakers advisable ?


markooo

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Putting the two speakers together won't be like an RC 64.  Klipsch engineers looked at factor in placing the drivers in the 64 and designed the XO for that arrangement.  It most likely won't be super terrible but, in principle, it is not necessary and if there is a problem with hearing dialogue, other factors need to be looked at. 

 

Maybe everyone should start running two of everything and take the 7.1 to 14.2?:wacko:

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I run two identical speakers as centers in parallel and I don't experience ANY audible moire pattern... in either music or theater.

I don't need to run two speakers, but I have two heresys and it would be a shame to use only one.

 

It might be a measurable phenomenon, but an audible one... not on my system.

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2 hours ago, derrickdj1 said:

Maybe everyone should start running two of everything and take the 7.1 to 14.2?:wacko:

I like the way you think!

 

Will you help me hoist one 175 pound Khorn on top of another?  :D

+++

 

The one issue I haven't heard addressed is how impedance will be affected.  Wouldn't the amp have to pull a lot of juice to power two speakers when it was only designed for one?

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20 minutes ago, wvu80 said:

I like the way you think!

 

Will you help me hoist one 175 pound Khorn on top of another?  :D

+++

 

The one issue I haven't heard addressed is how impedance will be affected.  Wouldn't the amp have to pull a lot of juice to power two speakers when it was only designed for one?

 

Depends how its wired.

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On 12/22/2015 at 8:06 AM, matt scarlett said:
If it's good enough for Sonus Faber .... 

 

 

 

 

 

 

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this is a very simplistic statement and the implication is that side by side tweeters do not in fact have issues when they do. Sonus Faber have designed the speaker system to work and I expect they have a very complex crossover as a result. You can run multiple speakers but there will be acoustic interference and the load will be more complex for the amplifier. Some people do this and they don't care or they don't notice the problems. People are free to do what they want. From a performance point of view though it is not a good idea so it is not wise to recommend. I am not attempting to argue that using two speakers as a combined centre channel will not work or that it cannot be done rather that there are reasons why this is not a standard practice and that it is not advisable. Past that be happy and welcome aboard. moray james.

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21 minutes ago, moray james said:

but there will be acoustic interference and the load will be more complex for the amplifier. Some people do this and they don't care or they don't notice the problems.

I use two amps.  So I guess I fit in the don't know / don't care box...

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there can be a lot of variables and in systems and rooms which all factor in to how things sound. An easy way for you to determine what the interaction of the two tweeters sound like is to cover one tweeter so its radiation is effectively eliminated from the system say with a plastic cup with some damping inside held in place with some duct tape. Easy to compare back and forth. This is not ideal but it should permit you to hear what sounds are being affected by the interaction between the two tweeters. You will want to do listening evaluations from both the centre position as well as from either end of the couch. In any event you will get the least amount of interaction with the two tweeters as physically close to each other as possible.  If you were to build a box with a new baffle and you mounted the tweeters in the same plane one above the other they would act much more like a single point source driver than two separate ones, the usual problem in doing this is the magnet size setting the spacing at a larger gap than what would be considered ideal. 

   In any event your can as suggested cover one tweeter and listen to the difference in the stage and image of instruments/female voices. You can listen to the sound of instruments or voices at the crossover point of the tweeter (at a guess this will likely be around 2200 -2500Hz.). Find some music with and instrument or voice which traverses up and down from below to above this range. Listen to the instrument in both configurations and you should be able to here differences in the timbre of the instrument. Interference's will cause the voice or instrument to take on a sudden shift in sound quality (texture or tone) and or shifts in the stage or image point of the voice/instrument, it will seem to shift or move back and forth between two physical locations in the space in which the recording took place. So you will be able to hear this best with a good quality recording with the minimum of production manipulations. Simple voice or piano recordings would make these differences easier to pick out. Once you identify these differences it will be easier for you notice them in more complex recordings. This is a great exercise for honing your listening skills. You can experiment with inserting a thin section of felt or high density fiberglass (or even a section of cardboard) in between the two speakers positioned on their sides and end to end. If the felt or fiberglass extend 3-4 inches past the plane of the baffle they the two tweeters will each be in the shadow of the other. This will prevent or diminish the high frequency interaction between the two tweeters. You could also experiment with the speakers on their sides and end to end then angle the two cabinets so the tweeters are both firing at the central seating location. You may well find some  angle which gets the two tweeters working together with a minimum of negative interaction. What you will find is that "fixes" like this will be location dependent. In other words they will work when listening from one location but not so much or at all from another seating location. remember that your surround system is designed to work with loudspeakers which attempt to behave as a point source. Departing from that principal and things start to slide out of the operating parameters in which the system was intended to work at its best. I hope that you do experiment with your speakers and see for yourself what things sound like.

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16 hours ago, Schu said:

What physics is causing the higher frequency to interfere and not lower frequencies if they are all waves of energy that radiate and interact?

The physics of acoustic waves.

 

Placing two speakers side by side is a compromise. It is the practice of robbing Peter to pay Paul. It's not simply a matter of placing two cabinets together. It requires some consideration.

 

I use two La Scala side-by-side as a center channel for two reasons:

 

1. Controlled Dispersion. When watching movies, and negating the subwoofer channel for the sake of this conversation, the remaining majority of sound power comes out of the center....ie, almost all of it. I don't like spraying all that energy across the room at reference levels, especially the mids. I don't have the luxury of peppering my room with absorbers/diffusers.  Side-by-side tightens up the mid range horizontal dispersion pattern considerably. It parks all the energy on the center listening area which really clears up dialogue...particularly male voices. It also has the side effect of keeping the neighbor's happy, even at stupid loud levels. The couch can be ground zero at war volume, yet in the kitchen you can still comfortably hold a conversation.

 

Beyond this desire, and the fact that I don't have a projection screen to hide a pile of speakers behind, there is no reason not to stack vertically. :emotion-55:

 

2. Boundary effects / mutual coupling. A single La Scala placed along a wall will suffer some comparative loss in bass performance. As a pair however, the horns couple and dramatically improve their response. Horns behave differently than direct radiators in this regard. The results don't directly translate between designs. This is where knowing the performance envelope of the speakers helps considerably. Paying attention to the design's Directivity Index, Toe-in to minimize interference, but no so much that the tweeters are bouncing directly off the opposite baffles at crossover. However, toe-in creates a cavity between the rear of the cabinets and the wall, and a nice split along the lower baffle that acts like a port, which all has to be effectively sealed off to prevent interference. So you have to run a thick foam gasket between the two baffles and place a cover across the top with a rigid board that extends over the entire cavity and all the way up to the rear wall, then mass load it with something substantial (like a TV). Otherwise, it sounds like sh*t. Finally, you have to be aware of the 1/4 wavelength distance that the pair is from the L&R main channels and set your global high pass filter cutoff point high enough that front three channels aren't stepping all over one another.

 

Can you still hear the interference in the treble range? Sure, but it's subtle compared to the dramatic improvement in the mids and bass. Once again, a compromise...and it all depends on what your priorities are. If I sit directly on-axis while listening to some treble material, and translate my head evenly from left to right and back, I can hear the comb filtering. It's not offensive in any way, and it's not like the performance drops into the abyss either. Off-axis, I can't even detect it. The fact that most center channel program material is largely mono, plays into to this as well. Others have pointed out that the tonal shift isn't as bad as it is on paper, and I agree, but I'm also smart enough not to bother trying this with my left and right channels either.

 

In summary, #2 is why I use a pair for my center channel, #1 is why they are situated side-by-side.

 

So...yes, I use two center channel speakers without much issue, but the setup is not a benign process.     ...and no, not like the Sonos....not even close. :lol:

 

 

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I realize you said you wanted to do this for fun, but why?  Coming from a cinema perspective, multiple centers are sometimes used, but only in the most massive theaters to help people hear the dialog when they're seated off-axis.  Sony's SDDS format and IMAX have used multiple centers for panning, but essentially gave up on that as the extra mixing wasn't really worth the effort and SDDS died off as a format.  Atmos and DTS:X use extra center speakers in some cinemas purely for effects, but the home version (at least for Atmos, not sure about DTS:X) doesn't include those channels.

 

Unless your room is incredibly huge and you have massive screen as well, it seems a bit pointless to use more than on center speaker.  Center speakers are designed for broad dispersion, but even stereo speakers should have plenty of dispersion. The center channel was intended primarily for dialog so voices coming from multiple speakers are likely to sound odd as your brain is able to distinguish the point source in that frequency range.

 

OTOH if you just want to have fun trying it out and have speakers and amps to spare, why not?

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Off axis is the one consideration I thought was a positive when I decided to do it. My room is NOT IDEAL for non-listening position seating and widening the center disbursement was better in my circumstance.

For music, not having a pin point Center doesn't seem to bother me as much as the idea that there might be some sonic moire pattern occuring... but I don't hear a thing. Cancelation, who knows but perhaps the output offsets that phenomenon.

Less than optimal... who cares. I am slightly perturbed to think I need to live in a mind set where nothing less than perfection is thought of as being less then human. :P

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All technical talk aside, I have a RP-450 on a stand under the screen and a RP-250 behind the acoustically transparent screen about half way up. The smaller center makes it easier to hear dialog on the back row since the 450 is pointed right at the front row. Nobody even knows there are two centers unless I show them the one behind the screen. I'm glad I decided to try it and have stuck with it. It's worked great for me. I have them run in series.  

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On 2/13/2017 at 10:39 PM, Darqman said:

All technical talk aside, I have a RP-450 on a stand under the screen and a RP-250 behind the acoustically transparent screen about half way up. The smaller center makes it easier to hear dialog on the back row since the 450 is pointed right at the front row. Nobody even knows there are two centers unless I show them the one behind the screen. I'm glad I decided to try it and have stuck with it. It's worked great for me. I have them run in series.  

Do you have elevated rows? If so, I can see that working well as you say.  From all I've read, the home theater center speakers are usually designed for broad horizontal distribution, and less so for vertical distribution (Klipsch horn tweeters aside...), so that would make sense.  Also, out of curiosity, how far apart are the two speakers? 

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Yes, my second and third row is on a 12" riser.   The two center speakers are about 3 feet apart.  If you're sitting in the middle row and there are people sitting in the front row you can't see the center speaker below the screen. I've always heard that you should be able to see the speaker or else it won't sound as good. 

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  • 2 weeks later...
On 8.2.2017 at 4:04 PM, wvu80 said:

 

Welcome to the Klipsch forum, Leo. Your first ever post is a good one.  :)  :emotion-19: 

 

How did you wire your center speakers?  I assume they were wired in parallel so if they were 8 Ohm speakers the amp would see a 4 Ohm load, ie  each speaker would get their own +/-  from the amp.  If you wired them in series that would produce a 16 Ohm load.


Thanx Dave :)
Yes, I wired the speakers parallell. My front and center are all dual 8ohm speakers. If you look closer at the picture you'll see that the fronts are dual speakers, the upper one flipped upside-down, tweeter-to-tweeter, to keep the directional part of the sound coming from one place. My goal was to make the horizontal line through FL-C-FR as flat as possible. I've been running this setup for about 6 months now and I'm quite happy with it. I have to admit that my setup is a low-cost and not completely finished in terms of making it look good and such. It's in my basement living room, kind of a man cave and work-in-progress.

A week ago I went to my local hifi-shop and tested their demo room. It was a nice $8'000ish setup, 11.1 Atmos. It all sounded VERY good, BUT... Voices sounded like the actors laid on the floor. FL and FR were on the wall nicely placed at the horisontal center line of the screen, center was just under. The test movie was Unbroken (2014). When the camera turned and sounds moved from speaker to speaker, it was just irritating when I could hear the sound coming from a much lower place, then jumping up again when the sound was panned across the three front channels. I tested with the same movie sequence at home and the center channel sounds MUCH more natural. If I ever change the TV for a projector I'll use a sound transparent screen and place the center behind it, but for now I feel I've found something that works.

The dual center is something I've been thinking about for a long time, I tried to read up on it, but most of what I could find didn't agree with "my theory" so I just had to try it out and make up my own opinion. Most people who seems to know a bit (or it all...) are worried about canceling out (in lack of correct english terms, I'm norwegian...), but not mentioning speakers with two tweeters or how mono sound appears with a headset on. Yes, there's many things that can work less than optimal, but with some things like sound you just might have to try for your self. And that's the beauty with a cheap setup, I got a used identical center speaker for about $20, I'm not at all worried about the amp (Yamaha RX-V661) and so on, I could just throw it all together and listen to it. That's what I did, just to try it out. Now it stays that way :)

Of course, what turned out great in my basement don't have to sound that great everywhere else, but would wish many more tried out their own ideas and DIY's, there's not gold under every rock, but absolutely under some of them :)

IMG_1515_1.jpg

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  • 2 years later...

Just to be pedantic, the problem described in other posts is the creation of an interference pattern, not comb filtering. The two concepts are very closely related, but not quite the same. Interference means a change in frequency response at different locations in space, while comb filtering means a change in frequency response of a single signal as a result of combining it with a delayed version of itself. So an interference pattern is the result of an infinite number of comb filters.

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  • 3 months later...
On 10/24/2014 at 8:38 AM, psg said:

 

Not a silly question.  If the wavelength of the sound being created is longer than the speaker-driver separation, then the two point sources work as one (basically projecting the same wave).  Woofers in a single speaker are usually spaced next to each other, so not an issue. Since wavelength gets smaller with higher frequency, it's mostly a tweeter issue in 2-way systems.  A wavelength of 1m is 340 Hz, and 1 foot is about 1 KHz.  Some people actually disconnect one of the tweeters.  So if you lay them on their side, keep the tweeters closer together in the middle.  It should be fine.  I would be more worried about the orientation of the horn and its dispersion pattern.

 

Awesome thread...   Thank you for the knowledge in this forum.  I have a Left Center Right...  the Center is comprised of (4)  6 inch 8 ohm 2 way  in wall speakers wired series/parallel to give my amp an 8ohm resistance.  I am about to install as my remodel is almost complete.  Based on what I have read and my understand, I won't have any issues.  I did like the post from PSG that suggests removing the tweeters as they are more prone to combing and interference pattern issues because of the higher freq... If necessary I will remove 3 of the 4 tweeters if I find they mess with each other. I will let you know how it all works out.  

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Tried it with some KV-2's ... and do not recommend it.  The treble range seemed (???) very slightly distorted, but mids and base was improved. So; yes ... a very little bit better, but would advise going to a bigger/better SINGLE speaker. I switched to a Heresy center and was very pleased with a REAL improvement :D 

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