# MT vs MTM characteristics.



## Exocer (Apr 19, 2006)

I found a thread over on another forum regarding the differences between how these different driver arrangments (MT and MTM) can affect the sound we hear.

The original question reads (Hope the original poster doesn't mind).

Cool mr Steve asked
"What are the benefits of using two midwoofers as opposed to one, as in the MTM vs MT. Would I be correct in assuming that the MTM has noticeably better sound quality than the MT? Are there tradeoffs to the MTM, or to having more drivers in general?"

Here is an answer that I learned a lot from (thanks for providing lots of useful information)

Brian Walker
"1) The MTM will have better power handling and will play louder and be more dynamic.
2) The MTM will have a narrower vertical off axis response, meaning the sound will not spread vertically as much as an MT. This can be good or bad, depending on your application.
3) The MTM will likely cost more and require a bigger cabinet.
4) You can not assume that the MTM will have better sound quality. I would suggest that the sound quality will be the same, but the radiation pattern will be different, so depending on your application, one will likely work out better than the other.

Generally speaking an MTM is preferred for home theater because of the greater dynamics and narrow vertical response. This reduces floor and ceiling reflection and can improve the frequency response at the listeners position. But if you listen to music while standing or move around and don't just sit in the sweet spot, then you might like the response of the MT better. I'm sure others may have a slightly different opinion on this matter, so wait and see what others say."

Thought people considering DIY speakers should know some of the tradeoffs of the two designs.


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## F1 fan (Jul 6, 2006)

Another benifit the MTM (also known as the D'Appollito arrangement) is that it has a symmetrical vertical lobing pattern regardless of what type of crossover is used.


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## Exocer (Apr 19, 2006)

Sounds interesting F1 fan. But I don't understand what it is, or how its a good thing. Care to explain?:dontknow:


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## khellandros66 (Jun 7, 2006)

There tends to be a more balanced output of sound, meaning that the frequencies we hear from the tweeter (most importantly and noticeable) are no longer biased based on their position vertically on the cabinet.

I noticed immediately with my BP7006 towers that there was a greater sense of balance.

BP7006 is the following

M
T
W PR
PR

~Bob


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## F1 fan (Jul 6, 2006)

khellandros66 said:


> There tends to be a more balanced output of sound, meaning that the frequencies we hear from the tweeter (most importantly and noticeable) are no longer biased based on their position vertically on the cabinet.
> 
> Bob


Yes.

Some MT designs may exhibit lobing problems because of phase differences between the tweeter and woofer.The phase differences are a result of the crossover design and the relative horizontal offset of the drivers.Lobing means that the speaker will sound (and measure) differently above the tweeter axis than it does below it.So the ideal listening axis may be above or below the tweeter.The frequency range affected is around the crossover were the drivers overlap.Lobing will be worse with shallwer slope crossovers (1st order) because their is a bigger region of overlap but is less of a problem with steep 4th order crossovers.

The frequency response of an MTM will be the same above and below the tweeters axis even if there are phase differences between the drivers. The ideal listening axis will be directly in line with the tweeter. MTM,s do exhibit off axis nulls that can narrow it's vertical listening window or sweet spot somewhat .Thats why it may not be a good choice for horizontal placement as a centre channel.


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## Exocer (Apr 19, 2006)

Ah ha, interesting and very useful information guys.


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## khellandros66 (Jun 7, 2006)

i have yet to come across any issues with my Vifa MTM kit, same with my dad's Polk CS245i center.

IMO at HE2005 I was extremely impressed with Aperion's new center with the variable x-over.

~Bob


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## Exocer (Apr 19, 2006)

F1, didn't understand the vocabulary at first :duh: but now I do. This is about what I expected however the decrease in verticle dispersion of an MTM compared to that of an MT wasn't what I experienced in my room. That was really suprising because I always felt the Natalie P's sounded much better than the rest of my speakers (MT's) while standing up, but I guess that has a lot to do with my room's acoustic signature...for all I know the MT's could've been experiences more acoustic cancellation than the MTM's due to their dispersion behavior.

Glad you brought up the deficiencies of using an MTM center. I had been on the fence for a while debating whether or not to build CJD's Rs150 based center but always knew MTM's struggled in center channel duty. Now I know exactly why.

Correct me if I am wrong, but it is to my understanding that a center MTM mounted horizontally will suffer from horizontal dispersion deficiencies just as if it were standing vertically suffering from the vertical deficiencies mentioned earlier in this thread. This could limit spacial the size of the front soundstage.


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## F1 fan (Jul 6, 2006)

Exocer said:


> correct me if I am wrong, but it is to my understanding that a center MTM mounted horizontally will suffer from horizontal dispersion deficiencies just as if it were standing vertically suffering from the vertical deficiencies mentioned earlier in this thread. This could limit spacial the size of the front soundstage.


Correct Exo, but I would prefer to say it narrows the listening window not the soundstage they are different things.Some MTM's have greater off axis defficiencies than others depending on driver spacing (closer together is better)and the design of the crossover such as frequency and slope.


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## Exocer (Apr 19, 2006)

F1 fan, gotcha.:T


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## F1 fan (Jul 6, 2006)

For fun you could place one of your MTM's horizontal and hook it up as a centre channel.Then run some dialog through it as you listen at various horizontal angles and see how much the sound changes as you move away from the tweeters axis. Also if you happen to have a pink noise track play it as well, because it is a very good test for this.Ideally the character of the noise should change little as you listen from different angles.If there is noticable changes in the sound than there are some off axis nulls occuring.


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## Exocer (Apr 19, 2006)

F1 fan said:


> For fun you could place one of your MTM's horizontal and hook it up as a centre channel.Then run some dialog through it as you listen at various horizontal angles and see how much the sound changes as you move away from the tweeters axis. Also if you happen to have a pink noise track play it as well, because it is a very good test for this.Ideally the character of the noise should change little as you listen from different angles.If there is noticable changes in the sound than there are some off axis nulls occuring.


Cool idea. I am dying to try this right now but it is currently after 1am so i'll have to wait until I get out of work tomorrow.


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## khellandros66 (Jun 7, 2006)

Exocer you could build a TMM for the center and elimnate the horizontal projection problems.

I would talk to the designer of the NatPs see if you could use a matching setup in a WMTW array.

~Bob


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## Exocer (Apr 19, 2006)

Bob, thanks for the suggestion. How would a TMM evenly distribute output when placed horizontally though?
I am waiting for John Marsh to finalize the matching Natalie P center, which will incorporate a WTMW driver arrangment. Much more ideal for a center/horizontal placement...Lets just hope he designs a crossover without BSC as mine will need to be placed very close to other boundaries...for now on top of my Crt Tv :T


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## khellandros66 (Jun 7, 2006)

Exocer said:


> Bob, thanks for the suggestion. How would a TMM evenly distribute output when placed horizontally though?
> I am waiting for John Marsh to finalize the matching Natalie P center, which will incorporate a WTMW driver arrangment. Much more ideal for a center/horizontal placement...Lets just hope he designs a crossover without BSC as mine will need to be placed very close to other boundaries...for now on top of my Crt Tv :T


:mooooh: 

If you use an offset placement where the tweeter is centered in the room it will, but I could be mistaken. I know that M&K has done it for years..

Man just wait for that design, perfect match and its gonna be way better the TMM or MTM 

~Bob


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## Exocer (Apr 19, 2006)

Yeah Bob, I think thats what i'll do.

Didnt mean to sound like im putting down MTM centers or anything. I just wanna do it right the first time (i can be very nitpicky) and not have to go back to the drawing board.

Which brings up another question. Rumor has it that the matching natalie P center may not actually be designed around the Rs28a. Wouldn't this automatically throw off any hopes of having a complete and proper timbre match across the front soudnstage? Or is it not even that big of a deal, considering the center channel will play nothing but dialogue during movies most of the time?


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## Brian Bunge (Apr 21, 2006)

It's no rumor. The matching center won't use the RS28a. Jon is looking for a small faceplate tweeter so that the standard PE 1 ft^3 enclosures can be used, which would make the center 9" in height. IIRC, the other drivers will be the RS180's and the RS52 midrange. If you want to use the RS28a then you'll want to go with the bigger WMTM design using the RS225's, RS150 and RS28a. Of course this center is MUCH bigger. Hopefully I'll have mine done in a week or so!


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## Bent (May 24, 2006)

would anybody know if a pod on top of a horizontal array would work?
that would allow the PE boxes as well, plus a kinda B&W look to the speaker.


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## Exocer (Apr 19, 2006)

Brian Bunge said:


> It's no rumor. The matching center won't use the RS28a. Jon is looking for a small faceplate tweeter so that the standard PE 1 ft^3 enclosures can be used, which would make the center 9" in height. IIRC, the other drivers will be the RS180's and the RS52 midrange. If you want to use the RS28a then you'll want to go with the bigger WMTM design using the RS225's, RS150 and RS28a. Of course this center is MUCH bigger. Hopefully I'll have mine done in a week or so!


Brian, Glad to hear that it isn't a rumor. I'll never be able to fit the larger WTMW center in my listening space. I'll hold on to my extra rs28a for the Modula MT surrounds :T and build the new/slimmer WTMW center for the Natalie P's.

Bent, good question. I bet John could answer that for you.


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## Guest (Nov 16, 2006)

So it will use two RS180s and a RS52? Im about to make an order with PE and I might as well get the drivers now.

Which design will be a better match if using Modula MTs as mains? Natalie P as mains?


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## Exocer (Apr 19, 2006)

Yes Two rs180's and the Rs52 mid, I ordered the mid last night with the 1ft^3 gloss black box.they brought my total to right above $99 to qualify for the free shipping  The Vifa D26 will be the tweeter from what WillD tells me.


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