MTM sound characteristics

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I think the difference to MTM vs TM, distills down to what kind of vertical pattern control do you want. If narrower, MTM.

Otherwise, if properly done, horizontal control, as well as the sound of the two outdoors, should be near identical.
This is assuming using the same drivers, same spacing, same tuning etc etc.
And very importantly, adherence to 1/4 WL spacing between any drivers providing summed response....something not always so easy to do...hence alot of easier TM designs....
 
Thank you everyone for this discussion. I was considering building a prototype MTM, perhaps using a pair of SB15CAC30's. I was going to see if I liked it better than my existing build which is a single SB17CAC35... but after reviewing the data and the many opinions here, I am going to skip this experiment.
 
My interest in the format was piqued by the fact that several manufacturers have flagship products that use MTM archetecture: Wilson, Focal Utopia, Eggleston Viginti, to name a few. However there are many more highly regarded direct radiator speakers which use a single mid driver with a single tweeter.

I have no doubt that MTMW can sound great. But I do not believe that an MTMW format is inherently superior to a TMW format.

I want to limit my explorations to those features and formats that are very likely to be better than what I have.
 
I used perform a test with WTW speakers switching on/off the top woofer to compare WT and WTW (with level compensation). In my impression, WTW sounds more dynamic and analytical, but less intimate. For home audio, I would choose WT, and for critical listening WTW.
That's not really a fair comparison as by turning off one woofer you're modifying both the frequency response and directivity.

Not only this, but a TM speaker is optimal with a linkwitz-riley alignment while MTM is optimal with a butterworth alignment. Converting from one to the other requires completely redesigning all crossover filters.
 
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I find the polar comments interesting. Yes MTM's have nulls in the vertical polar response if the CTC distance is too great (or crossover point too high) which in reality is almost always. Theoretically you can use this to your advantage if the nulls are positioned to hit the ceiling and floor with respect to the listening position.

Horizontal polar response is not affected and will depend on the speakers used.

If the primary use will be seated listening just design so that the tweeters are at ear height when seated and enjoy :)

My MTM's I've been very happy with. Yes they do loose some top end if I am standing, but they still sound good.

There are always those that say they are horrible due to all of the problems... The only way to find out if they are horrible for you is to try them :)

Building speakers is all about compromizes. I've long believed that different people have different things that they find annoying with speakers, and you need to find out for yourself which are the things you can live with and which are the ones that you can't and then try to design such that you minimize the ones that you can't live with. That's going to be different for different people :)

Tony.
 

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You forget that you also listening to the off-axis. It will never be linear which results in a non-linear power response. This means that a MTM speaker will never sound linear as a listener will not be exposed to all the power in all frequency bands that the recording contained. It doesn't mean that all MTM are horrible of course. It doesn't mean that one can't be happy with such design... If you need more sound pressure, e.g. more drivers, it is one way to go.

//
 
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If we take that approach then you could say the same about room treatments :) If you absorb the sound at certain places to reduce some of the reflections you don't want, is that any different?

Is there any real difference someone putting some absorption on the ceiling and thick rug on the floor compared to tayloring the lobe pattern of an MTM to do the same?

Note that I haven't tryed to optimize mine to achieve this, and I don't have any ceiling treatment, but it is something I have considered for a future experiment.

Tony.
 
Thank you everyone for this discussion. I was considering building a prototype MTM, perhaps using a pair of SB15CAC30's. I was going to see if I liked it better than my existing build which is a single SB17CAC35... but after reviewing the data and the many opinions here, I am going to skip this experiment.

If I would build speaker with SB ceramic, MTM would be my choice, because in my experience, metal cone MTM (Amphion) can sound really impressive, and if I use SB ceramic tweeter, I probably can cross lower than usual which is good for MTM as Scottmoose said.
 
That's not really a fair comparison as by turning off one woofer you're modifying both the frequency response and directivity.

Not only this, but a TM speaker is optimal with a linkwitz-riley alignment while MTM is optimal with a butterworth alignment. Converting from one to the other requires completely redesigning all crossover filters.

You may think I don't use active crossover and measurement rig, but that's wrong. :)
 
One thing I forgot to say about MTM. As I said before, I think MTM is suitable for critical listening, because MTM tends to insist you to sit down at the same height, visually and audibly. And this MTM's character makes the sound from MTM more consistent over time, which is really good for monitoring and critical listening.
 
One thing I forgot to say about MTM. As I said before, I think MTM is suitable for critical listening, because MTM tends to insist you to sit down at the same height, visually and audibly. And this MTM's character makes the sound from MTM more consistent over time, which is really good for monitoring and critical listening.

I am not sure that is correct, at least it is not for me. When i tried mtm i was at first very impressed by the projection or focus of it, it was a bit like wearing enormous headphones, but as soon i left the tiny sweet spot the sound became very phasey, i could not stand it. But if you listen at a much greater distance then the phase troubles becames smaller. So far, to me, the only way to minimize the phasey problems is to use coaxial drivers, and to get the focused sound i think it should be combined with slightly larger driver
 
I am not sure that is correct, at least it is not for me. When i tried mtm i was at first very impressed by the projection or focus of it, it was a bit like wearing enormous headphones, but as soon i left the tiny sweet spot the sound became very phasey, i could not stand it. But if you listen at a much greater distance then the phase troubles becames smaller. So far, to me, the only way to minimize the phasey problems is to use coaxial drivers, and to get the focused sound i think it should be combined with slightly larger driver

Many of us might not be as sensitive as you about phase issue of MTM, but basically, that's what I was saying. MTM tells you where to listen to, so that it can give you more consistent listening experience. I too like coax, but it is more challenging to make it flat as MTM due to diffraction.
 
Well, the different phase angles is what causes said, so it amounts to more or less the same thing. The issue becomes worse with higher crossover frequencies for a given spacing of the midbass drivers, which is why, if the speaker is to be used by more than one person, they really need to be crossed as low as possible, as that reduces the issue. If they're only likely to be listened to by one person, and you can set them up accordingly to a given listening position, you've more freedom in this regard.
 
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You may think I don't use active crossover and measurement rig, but that's wrong. :)

Not sure what you are using, but assuming you digital xo in active system...do you happen to use Acourate to generate filters? I ask because Acourate includes Horbach-Keele type filters that seem like a perfect match for MTM. I think their approach tends to add more active channels (4 or 5-way), but they achieve very consistent vertical dispersion. The size and location of the drivers, together with their xo are the key.

Here's a link to their papers. I posted on a thread of mine. I'm also exploring MTMs, and H-K is one approach I'd like to try. Attached to post #12.
https://www.diyaudio.com/forums/multi-way/355704-lobing-mtm-tpl-150h-8pe21-2.html#post6240525

Hope it helps. Interesting read to me.
 
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