If I have double midwf + tw, better to make an d'appolito or a 2.5 way?
experiences regarding theory and also listening?
what are the advantages of the two types?
experiences regarding theory and also listening?
what are the advantages of the two types?
Notwithstanding losses, a 2 1/2 way inherently gives full baffle-step compensation (best away from walls as a result 😉 ). Depending on design details, it may (may) have a superior vertical polar response too. For a given main crossover frequency an MTM is likely to be more directional on the vertical axis. That may or may not be an advantage depending on what you happen to be doing. Crossover frequency and slope also come into this. If you don't mind the more uneven vertical polars and are willing to cross acoustically high, it may have reduced IM distortion.
I have been using a few different commercial MTM speakers, Berefoot, Focal, Lipinski, and currently JBL large with 18dB slope.
MTM can be very good, but the speakers has be placed at the right height, and the ceiling and floor has to be well considered. My room has serious acoustic ceiling treatment with 8" OC703 to avoid the ceiling reflection. You may want to have some kind of ceiling cloud at least, I think.
MTM can be very good, but the speakers has be placed at the right height, and the ceiling and floor has to be well considered. My room has serious acoustic ceiling treatment with 8" OC703 to avoid the ceiling reflection. You may want to have some kind of ceiling cloud at least, I think.
And, based on my subjective listening experience, I would say 2.5 can be better for casual listening, and MTM would be better for critical listening in general. 2.5 is more forgiven for its acoustic environment. If you are sitting far enough from the speakers, and/ or the speaker is small enough, I guess the difference would be minimized.
The "narrow directivity" of an MTM is usually presented as a benefit, but that narrow pattern is only going to be across a relatively small range of 1-2 octaves. I prefer to see at it as a hole in the vertical power response. And there is the unavoidable crossover lobing in the mix to deal with as well.
2.5 way makes the crossover design more complicated of course, especially if it is passive, but if you can't get the midwoofs and tweeter close enough (and usually you can't) I think it's the better arrangement. I'd rather have wider yet better matched vertical response from the 2.5 way.
P.S. many 2-ways also fail at this point because the tweeter polar "bloom" at its low end meeting the woofer's beamy upper register. The MTM struggle to cross the tweeter as low as possible can only worsen this, and also strain the tweeter - and this is usually happening in the critical vocal range. Using a waveguide or horn on the tweeter is a good idea, but that will push the CTC woofer distance apart even more and then a 2.5 becomes even more attractive.
2.5 way makes the crossover design more complicated of course, especially if it is passive, but if you can't get the midwoofs and tweeter close enough (and usually you can't) I think it's the better arrangement. I'd rather have wider yet better matched vertical response from the 2.5 way.
P.S. many 2-ways also fail at this point because the tweeter polar "bloom" at its low end meeting the woofer's beamy upper register. The MTM struggle to cross the tweeter as low as possible can only worsen this, and also strain the tweeter - and this is usually happening in the critical vocal range. Using a waveguide or horn on the tweeter is a good idea, but that will push the CTC woofer distance apart even more and then a 2.5 becomes even more attractive.
A paper from the mid 1990's exploring some pros and cons: Vertically Symmetric Two-Way Loudspeaker Arrays Reconsidered.
This is why MTM has been much more popular among professionals working in a controlled environment.
I always have to smile when I read the mostly hair brained Copy/Paste about MTM/2.5 or D'Appolito.
Fact is, that there is no "common denominator" even inside of single architecture like MTM. There are great and poor sounding examples in abundance. Even the posted advantages/disadvantages have little or nothing to do with reality - just bad copy/paste. Even if we take one brand name MTM speaker and put it in different rooms, or let it be set up by different people, the results will be all over the place.
How can I claim this, well I have a 6 year old project that exactly investigated it. My firsthand findings are not reflected by the mostly posting conjecture above.
So, what can I say about my research:
1) The MTM sounds NOTHING like a point source, it has little advantage in actual observed directionality. The specs look great, but the room performance is much different.
2) Large spacing acts like a line array. In a "big" MTM configuration, the"M"s (semi line array) reduce in volume by 3dB for every doubling of distance - the "T"s (no array) 6dB. Pick your listening difference carefully as well as control the early side reflections
3)2.5D with the woofers on the bottom - makes it easy to put the "T"s at listening height, a lot of grunt, floor reflections of both "M"s screw a lot up
4) D'Appolito is a VERY precise form of the MTM. I personally believe that it should only be used with REAL midranges and tweeters to keep the centers close together. In this use case, great results have been achieved. Check out John Dunlavys speakers.
5) my current object of test is a MTM configuration - 2x 12" woofers and a 26" Tractrix horn between them BUT with a 2.5 crossover. The crossover is at 120Hz and 500Hz. 1300mm high, 150 Liter volume. The top woofer is fFs to 500 Hz and the lower is the .5 with excellent floor coupling. Floor and ceiling bounce are no issue with the top midwoofer. Integration was very easy. None of the MTM or 2.5 warts.
6) Anal retentive attention to "phase alignment" between all drivers is needed for direct sound at the sweet spot. This is not so easy to do if you want to avoid diffraction/reflection of the "T"s.
I am not done yet. I am working on integrating a Karlson tweeter for everything above 8kHz.
Fact is, that there is no "common denominator" even inside of single architecture like MTM. There are great and poor sounding examples in abundance. Even the posted advantages/disadvantages have little or nothing to do with reality - just bad copy/paste. Even if we take one brand name MTM speaker and put it in different rooms, or let it be set up by different people, the results will be all over the place.
How can I claim this, well I have a 6 year old project that exactly investigated it. My firsthand findings are not reflected by the mostly posting conjecture above.
So, what can I say about my research:
1) The MTM sounds NOTHING like a point source, it has little advantage in actual observed directionality. The specs look great, but the room performance is much different.
2) Large spacing acts like a line array. In a "big" MTM configuration, the"M"s (semi line array) reduce in volume by 3dB for every doubling of distance - the "T"s (no array) 6dB. Pick your listening difference carefully as well as control the early side reflections
3)2.5D with the woofers on the bottom - makes it easy to put the "T"s at listening height, a lot of grunt, floor reflections of both "M"s screw a lot up
4) D'Appolito is a VERY precise form of the MTM. I personally believe that it should only be used with REAL midranges and tweeters to keep the centers close together. In this use case, great results have been achieved. Check out John Dunlavys speakers.
5) my current object of test is a MTM configuration - 2x 12" woofers and a 26" Tractrix horn between them BUT with a 2.5 crossover. The crossover is at 120Hz and 500Hz. 1300mm high, 150 Liter volume. The top woofer is fFs to 500 Hz and the lower is the .5 with excellent floor coupling. Floor and ceiling bounce are no issue with the top midwoofer. Integration was very easy. None of the MTM or 2.5 warts.
6) Anal retentive attention to "phase alignment" between all drivers is needed for direct sound at the sweet spot. This is not so easy to do if you want to avoid diffraction/reflection of the "T"s.
I am not done yet. I am working on integrating a Karlson tweeter for everything above 8kHz.