Must Center Channels Always Have Two Woofers?

[annunaki]

This is probably more directed for the technically inclined. Why are almost all center channel designs in a MTM (D'Appolitio) configuration. Is there any technical reasoning behind not using a single woofer and tweeter in a two-way application? Is it done simply for visual symmetry? Wmax?

 

[jaxvon]

I'm not sure. If I recall correctly, a D'Appolito design is actually not the optimal design to use for a center channel. It creates lobing [I apologize if this is incorrect, but I remember that I read this]. This is why many center channels have an offset tweeter.

 

[jeffsg4mac]

I know one thing, I have a Paradigm CC370 and it stinks. Huge peak in the mid-bass region. I have since moved one of my mini monitors up front on a short stand. The cc370 is a D'Appolito design, but I am not sure if that is what is causing the huge mid-bass peak. The peak is not there with the mini.

 

[edwelly]

I know one thing, I have a Paradigm CC370 and it stinks. Huge peak in the mid-bass region. I have since moved one of my mini monitors up front on a short stand. The cc370 is a D'Appolito design, but I am not sure if that is what is causing the huge mid-bass peak. The peak is not there with the mini.

I have the same center channel and I am pleased with the performance. I haven't heard any peak that you are mentioning. Could it be an issue with placement and or surrounding issue(s)? Granted there are only so many places you can put a center channel

 

[jeffsg4mac]

I have the same center channel and I am pleased with the performance. I haven't heard any peak that you are mentioning. Could it be an issue with placement and or surrounding issue(s)? Granted there are only so many places you can put a center channel

Have you measured your center channels response with an RTA? you might be in for a surprise

 

[j_garcia]

I used to have the CC370 and I did not have a peak either. That is most likely your room and the placement of the speaker. Try putting the 370 on the stand. I thought the 370 was a pretty good center when I had it. In fact, the v3 was much better than the v2 because they changed the positioning of the tweeter from directly inline to slightly above, which I felt helped the sound noticably.

Annunaki, the main reason I can see for using dual drivers for the center is because you get a symmetric horizontal image and because the additional driver gives you greater sensitivity, which theoretically should help with dialogue.

M&K are one of the few manufacturers who do not use a MTM, but rather their same conventional TMM array (which is identical to the mains), including the slight angle to the tweeter. I felt this center sounded just as good as any other, but it still uses dual drivers. I don't think that answered your question though...

 

[jeffsg4mac]

I used to have the CC370 and I did not have a peak either. That is most likely your room and the placement of the speaker. Try putting the 370 on the stand. I thought the 370 was a pretty good center when I had it.

Annunaki, the main reason I can see for using dual drivers for the center is because you get a symmetric horizontal image and because the additional driver gives you greater sensitivity, which theoretically should help with dialogue.

M&K are one of the few manufacturers who do not use a MTM, but rather their same conventional TMM array (which is identical to the mains), including the slight angle to the tweeter. I felt this center sounded just as good as any other, but it still uses dual drivers. I don't think that answered your question though...

I have had the CC370 in two different houses and in 3 different rooms with the basically the same response. I have had it above the tv and below the tv and with the same results. From about 100 to 160 hertz it has a large peak in the response of about 15 db or so. Like I said I measured it. If it was the room then the mini monitor would have a similar response, but It does not.

 

[annunaki]

Sorry guys, that information is not really helping. I would appreciate it if we could keep it on topic. Thanks. Hopefully you can work out those issues you are having with your center.

 

[edwelly]

I am not doubting what you hear or your RTA displays. I am simply stating that I am not hearing any peaks. I have not used an RTA in my room nor do I want to (I would probably just cry after seeing the results) but I have used an SPL meter with a varing sine wave starting at 20hz going to 400hz and I didn't not see any peaks, at least not a 15db peak.

 

[jeffsg4mac]

Sorry guys, that information is not really helping. I would appreciate it if we could keep it on topic. Thanks. Hopefully you can work out those issues you are having with your center.

Yes, I did. I thew it away

You have a good question though, I would like an answer too. In a true D'Appolito configuration one of the benefits was controlled vertical dispersion. If you turn this speaker on its side then I guess you have controlled horizontal dispersion. Seems like you would be then creating a sweet spot for the center. So why are all center designed this way? I would like to know. Laying a DAppolito on its side seems like the wrong approach.

 

[annunaki]

I am possibly going to do a complete DIY Home theater set-up. If I do not have to buy an extra woofer and make the cabinet, for the center, any larger if I do not have to. That is partly why I am asking this. I am looking at using the Vifa XT25SC30 and the Vifa XT18WO09-8.

 

[j_garcia]

A conventional T-M speaker has a horizontal AND vertical image it outputs. Vertically oriented, that image may slant upwards or downwards, which in turn would mean it would favor one side or the other off axis when laid on it's side. Adding the second midbass makes the off axis response the same, and actually creates a sort of comb filter that reduces response off axis in nearly all cases, which may not always be a good thing. What you may need to do is experiment with the placement of the drivers on the front baffle to get a good image with a single midbass, but I do think it can be done.

 

[jeffsg4mac]

Annunaki, read a little of this article. http://www.hometheaterhifi.com/volume_8_3/diy-13-audax-center-channel-speaker-9-2001.html

 

[WmAx]

This is probably more directed for the technically inclined. Why are almost all center channel designs in a MTM (D'Appolitio) configuration. Is there any technical reasoning behind not using a single woofer and tweeter in a two-way application? Is it done simply for visual symmetry? Wmax?

I do not care to speculate as to why so many are MTM configurations. However, it does not serve any technical benefit over a MT system other than allowing use of two smaller diameter drivers to produce the same SPL as a larger diameter driver. Use of two smaller drivers, of course, allows for the sleeker looking cabinet, as opposed to a more boxed style that would occur using a larger driver. The MTM is actually technically inferior so far as dispersion. In the plane that the two drivers exist aligned with each other, the distance between two radiation sources becomes signifcant in relation to the upper bandwidth wavelengths(in air) of these transducers. Result is destructive interference interaction as the two drivers begin to operate out of phase with each other as the vector angle is increased off axis. The result, basicly, is a more limited horiztonal dispersion when the speaker is set so that the two drivers align in the horiztonal plane.

-Chris

 

[WmAx]

I'm not sure. If I recall correctly, a D'Appolito design is actually not the optimal design to use for a center channel. It creates lobing [I apologize if this is incorrect, but I remember that I read this]. This is why many center channels have an offset tweeter.

Actually, the lobing is minimized with a MTM design.

-Chris

 

[annunaki]

Jeff,

Thanks for the link. It was a good read. However, it really did not address my question. I am familiar with Lobing issues and the like. Thanks for your time, I appreciate it.

 

[annunaki]

I do not care to speculate as to why so many are MTM configurations. However, it does not serve any technical benefit over a MT system other than allowing use of two smaller diameter drivers to produce the same SPL as a larger diameter driver. Use of two smaller drivers, of course, allows for the sleeker looking cabinet, as opposed to a more boxed style that would occur using a larger driver. The MTM is actually technically inferior so far as dispersion. In the plane that the two drivers exist aligned with each other, the distance between two radiation sources becomes signifcant in relation to the upper bandwidth wavelengths(in air) of these transducers. Result is destructive interference interaction as the two drivers begin to operate out of phase with each other as the vector angle is increased off axis. The result, basicly, is a more limited horiztonal dispersion when the speaker is set so that the two drivers align in the horiztonal plane.

-Chris

Chris,

Thanks! So if I were to align the tweeter and the woofer horizontally (TM), there should be no real negative effect, or did I misunderstand that? It should not matter what side of the woofer the tweeter would be on then either, correct? If neccessary I can align them verically (TM) I guess.

 

[jeffsg4mac]

Is there any technical reasoning behind not using a single woofer and tweeter in a two-way application? Is it done simply for visual symmetry? Wmax?

Hmm, I must have missed something. Between the first part of that article and what Wmax said I think your answer to your first question is No!

I think you would want to mount them vertically for better dispersion.

 

[annunaki]

Correct me if I am wrong, but the first part of the article seems to be referring specifically to MTM designs placed horizontally, not TM designs.

 

[jeffsg4mac]

Correct me if I am wrong, but the first part of the article seems to be referring specifically to MTM designs placed horizontally, not TM designs.

Right, "MTMs were designed to be vertically oriented because their main strength is good horizontal dispersion. When laid on its side, you get good vertical dispersion, but what good does that do when your sitting off axis, unless you happen to be on the ceiling or you’re lying on the floor! Sitting out as little as 30° off the primary listening position (“sweet spot”), can cause a loss (dip) in the midrange frequencies."

So you would not want to use the MTM design. Also, laying a TM on its side would not be desirable either. This may explain why I am loving the mini-monitor up front compared to the cc370. Unless you do some fancy xover work and offset the tweeter and/or make it a 3way, a standard MTM is not desirable for a center channel.