Some further advise before you start buying drivers:
go for the smallest drivers for the MTM-part and mount them as closely together as you can. A 3" inch driver is still ok, 4" is already very challenging. Reason is beaming. Even with small midranges, spaced as closely together as possible, you need to opt for a lowish xover point, 2250 Hz or something, and use 24 dB/octave slope xovers.
As for the tweeter, the one you selected has a huge outside diameter for this purpose. Better go for one of those neodymium tweeters like this:
https://www.parts-express.com/cat/t...eca:matches(.,"P_Searchable","1")]&PortalID=1
Or even smaller. Like this:
https://www.parts-express.com/peerless-by-tymphany-ox20sc00-04-3-4-fabric-dome-tweeter--264-1002
go for the smallest drivers for the MTM-part and mount them as closely together as you can. A 3" inch driver is still ok, 4" is already very challenging. Reason is beaming. Even with small midranges, spaced as closely together as possible, you need to opt for a lowish xover point, 2250 Hz or something, and use 24 dB/octave slope xovers.
As for the tweeter, the one you selected has a huge outside diameter for this purpose. Better go for one of those neodymium tweeters like this:
https://www.parts-express.com/cat/t...eca:matches(.,"P_Searchable","1")]&PortalID=1
Or even smaller. Like this:
https://www.parts-express.com/peerless-by-tymphany-ox20sc00-04-3-4-fabric-dome-tweeter--264-1002
Lou Corragio had some good designs. This is a tangband 4 ohm 5" woofer WWMTM design:
Shtick MTMWW Speaker
A good point of departure, I think. I don't know what you will run into with that 6" bass.
Shtick MTMWW Speaker
A good point of departure, I think. I don't know what you will run into with that 6" bass.
I'd suggest the OP first to learn how to properly simulate the whole speaker project and then proceed with acquiring measurement system to do the same in reality. If one is blessed with a talent, that would still mean months of research. That's why I partly share Erik's view on that matter. The information is definitely all over the place in this forum, but it's there and for free.
Hummmm
I am totally aware on how challenging it is, I've been reading arround for mounths already
first off all, for the design, I am not really quite convinced of MTM I've read some good things about it, and I've understood that even when considering the physics, that design make good points specialy about sound directions etc ... however, looking at very very high end designs, most of them have a classic TM configuration a simple tweerter + medium and one to many bass drivers (considering that I'll never ever have more skills than their designers), now as I will not go further than 6,5 inchs, many suggest that little bass drivers have more dynamic bass as they have a less heavy mecanism and I ve seen high end designs using up to 3 bass drivers with only one medium (with same size)
so this is not definitive design actually so advices are welcome
I am also considering these config :
Tweeter Vifa XT25
medium Tang Band W5-1611SAF (or 2 x Tang Band W3-871B ???)
bass 2 x W5-1138SMF (considering this one goes only 45hz (15 deeper then the W5-1611SAF) ? what I find suspecious is that why 1611SAF have 11 litr vas the 1138SMF is only 4 litres ? Monacor SPH-165 could be better (vas 36 litres) ? or maybe 3x W5-1611SAF 1 for medium 2 for bass ??)
I am totally aware on how challenging it is, I've been reading arround for mounths already
first off all, for the design, I am not really quite convinced of MTM I've read some good things about it, and I've understood that even when considering the physics, that design make good points specialy about sound directions etc ... however, looking at very very high end designs, most of them have a classic TM configuration a simple tweerter + medium and one to many bass drivers (considering that I'll never ever have more skills than their designers), now as I will not go further than 6,5 inchs, many suggest that little bass drivers have more dynamic bass as they have a less heavy mecanism and I ve seen high end designs using up to 3 bass drivers with only one medium (with same size)
so this is not definitive design actually so advices are welcome
I am also considering these config :
Tweeter Vifa XT25
medium Tang Band W5-1611SAF (or 2 x Tang Band W3-871B ???)
bass 2 x W5-1138SMF (considering this one goes only 45hz (15 deeper then the W5-1611SAF) ? what I find suspecious is that why 1611SAF have 11 litr vas the 1138SMF is only 4 litres ? Monacor SPH-165 could be better (vas 36 litres) ? or maybe 3x W5-1611SAF 1 for medium 2 for bass ??)
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No, that's wrong. Doubling the membrane surface gives you only +3dB while double the loudness would be +10dB, to quadruple it, you'd need additional +10dB. If you were referring to the +3dB at the half impedance on parallel drivers, that is correct, at least partly. Because then the power also doubles and that means, the distortion rises the same.
system7 said: "...I like the idea of twin drivers. You get 4X the level for the same distortion."
You haven't thought about it. And you are confusing perceived loudness with power. Wire two 80dB 8 ohm MT speakers in parallel, and you now have a 86dB 4 ohm MTTM. Each speaker is working at exactly the same level and distortion but we have gained 6dB, which is 4 times the power. The series wired equivalent works the same way, but it's then an 80dB 16 ohm MTTM speaker. I rest my case.
Sorry mansa. That doesn't help you much here. I think you need a modelling program or a good 3 way design that you can maybe convert for doubled drivers. And series wired twin drivers is easier.
You haven't thought about it. And you are confusing perceived loudness with power. Wire two 80dB 8 ohm MT speakers in parallel, and you now have a 86dB 4 ohm MTTM. Each speaker is working at exactly the same level and distortion but we have gained 6dB, which is 4 times the power. The series wired equivalent works the same way, but it's then an 80dB 16 ohm MTTM speaker. I rest my case.
Sorry mansa. That doesn't help you much here. I think you need a modelling program or a good 3 way design that you can maybe convert for doubled drivers. And series wired twin drivers is easier.
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No, I don't, you obviously don't know that the dB is a logarithmic unit and you don't know Ohm's law.
No, that's exactly what's wrong. You do not get +6dB/W, you gain 6dB at the same voltage or in other words: instead of x dB/1W it's x+6dB/2W. These 6dB consist of +3dB gain for the double membrane surface and - because of the halved impedance - +3dB because of the higher (2x) power. Please use Ohm's law and check it for yourself, it is exactly the double power or - to make it understandable for you - it's the same power per driver. The same power means, each driver does x dB distortion (or calculate it in %), added up means not only the level gains +3dB, but the distortion also gains +3dB. Yes, you're rising in distortion the same you're gaining level, 3dB. So no, not 4x, only 2x regarding the distortion.
The series wired equivalent works the same way, but it's then an 80dB 16 ohm MTTM speaker. I rest my case.
Again, it's +3dB for doubling the cone surface and -3dB for doubling the impedance, therefore halving the power, meaning that's at only 0.5W. In essence: With double drivers you gain 3dB at the same power, no matter what impedance. If you look at it the other way and take a constant voltage, that gives you +6dB but at doubling the power. And yes, I rest my case too until you've learned the Ohm's law.
Simple exercise:
U=2,83 V
R=8 Ohm
P=U²xR
P=1 W
Now the two drivers in parallel:
U=2,83 V
R=4 Ohm
P=U²xR
P=2 W
Same goes for serial:
U=2,83 V
R=16 Ohm
P=U²xR
P=0,5 W
That's absolutely correct. But he claimed +6dB at the same distortion. And since the distortion is directly power related, that's definitely wrong.
You don't need 3 way system for 6,5 inch woofer. 6,5 inch drivers are perfect for 2 way.
1138SMF has lower Vas due to much lower efficiency, it has only 82dB at 1W/1m which is really poor.
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The lower Vas is result of a very high moving mass (Mms) and a stiff suspension. The low spl is caused by the high Mms and the motor, not the other way around.
In level, yes. In level in correlation with distortion - no. That then still only the +3dB of the double surface area. Think about it, same power per driver equals the same output per driver but also the distortion is the same. If the level is added, it's +3dB, but the same, the very same number goes to the distortion aswell, so you get also +3dB distortion! That said, you do NOT gain +6dB at the same distortion, instead you only gain +3dB while maintaining the same distortion. How hard is that to understand? Just because you've got two drivers, the distortion of one does not magically disappear! The level adds and the distortion ofcourse too!
More drivers equals higher maximum spl or lower distortion at the same spl. In the midrange there are other issues though because the distance between the mid drivers creates interferences. How significant they are depends on the crossover frequency and the geometrical distance of the center of the source of the sound between the drivers. That means also beaming vertically, that can be wanted or to be avoided, that depens very much on the situation, speakers and the room. For a MTM configuration the D'Appolito setup rules are very helpful.
Also, on a parallel setup most amps are able to deliver more power because of the lower impedance, which theoretically results in higher daynamics (but practically depending very much on the amp).
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