Hi!
I am in the process of building my first project. I plan to post it here later, as there will be some result. It's a long story.
Almost all components have already been purchased.
But I again had the idea of MTM, although I had already abandoned this idea, as I thought that in the active version, MTM has fewer advantages + a limited budget.
My drivers set: 12" + 4.5" + ribbon tweeter
Makes sense MTM: 12" + 4.5" + Ribbon Tweeter + 4.5 "(as close as possible)?
4.5" from 250-300 Hz to 2500-3000, Tweeter can from 2500 Hz without distortion
Will a large effective area Sd be more useful than negative from interference?
Thank you
I am in the process of building my first project. I plan to post it here later, as there will be some result. It's a long story.
Almost all components have already been purchased.
But I again had the idea of MTM, although I had already abandoned this idea, as I thought that in the active version, MTM has fewer advantages + a limited budget.
My drivers set: 12" + 4.5" + ribbon tweeter
Makes sense MTM: 12" + 4.5" + Ribbon Tweeter + 4.5 "(as close as possible)?
4.5" from 250-300 Hz to 2500-3000, Tweeter can from 2500 Hz without distortion
Will a large effective area Sd be more useful than negative from interference?
Thank you
4.5" is very large if you want to cross over at 2500 Hz. There will be considerable beaming and you will never get the power response right. If you need more Sd at the low end, you can use two mid drivers in an MTM setup, but it would be wise to put one of the two drivers on a 6dB/octave down slope almost from the low crossover point upwards.
This ribbon in extreme cases (with still low distortion) can play up to 2 kHz, but I think that 2.5 kHz would be better for it. I will definitely try both. Thank you
You can probably surmise that you'll get a reasonably good result doing what you're proposing, considering the number of examples of those who have done it successfully before.
If you want some definite answers you might be struggling considering this is a first project. There are so many directivity turnover points in a boxed MTM design, not necessarily working together. It's just that you'd need to do some fancy measuring and simming to get one at its best.
You can and should still measure at least in the usual way.. and build and also tweak by ear. Unless you want to postpone and do some deeper analysis, this usually flows better the more experience you can put with it.
If you want some definite answers you might be struggling considering this is a first project. There are so many directivity turnover points in a boxed MTM design, not necessarily working together. It's just that you'd need to do some fancy measuring and simming to get one at its best.
You can and should still measure at least in the usual way.. and build and also tweak by ear. Unless you want to postpone and do some deeper analysis, this usually flows better the more experience you can put with it.
Dreg, that is not what I meant. My point was that the two mid drivers in an MTM should not be fed with the same signal. One has to be limited for high frequencies. Regardless of the crossover point to the tweeter. Going down from 2.5kHz to 2kHz for the crossover point to the tweeter is not going to do much.
It sounds like 3.5-way. This option does not suit me, only 3-way.
I don’t really understand why I can’t give the same signal?
I am with vacuphile on this one.
Your described MTM setup will result in beaming with the crossover point that you are aiming for. It will work, sure, however expecially the off axxis response will show the typical effects. 2500Hz is pretty low for a ribbon... granted. Even a quite powerful viawave ribbon cannot easily go down to 2k and if pushed volumewise it will distort. My 2 cents... pseudo d'appolito systems do work. However if you understand a bit of what floyd toole and his spinorama and whatnot tried to find out then it will be abundantly clear to you that such MTM configs with high xover points do have some problems.
Your described MTM setup will result in beaming with the crossover point that you are aiming for. It will work, sure, however expecially the off axxis response will show the typical effects. 2500Hz is pretty low for a ribbon... granted. Even a quite powerful viawave ribbon cannot easily go down to 2k and if pushed volumewise it will distort. My 2 cents... pseudo d'appolito systems do work. However if you understand a bit of what floyd toole and his spinorama and whatnot tried to find out then it will be abundantly clear to you that such MTM configs with high xover points do have some problems.
Yes, Viawave SRT-7 in my project.
So this problem occurs due to interference?
Then the question is, will the pluses outweigh the minuses?
I disagree...based on the data from most drivers, 10" starts beaming at ~1900Hz, 8" starts beaming at ~ 2800Hz, 6" can be used up to 3kHz easily, 5" up to 4kHz (I used AC130F1 up to 5kHz no issues), 4.5" can easily be crossed at 5kHz, depending on its breakups. AC130F1 has minor breakups, so no issue crossing it high to ribbon.
here I crossed 6" fullrange (modified) to ribbon at ~8kHz, no beaming whatsoever
betsy wow and ribbon
Hi adason, others,
it depends how you define beaming. For crossover work and power response consideration, if the drivers have different directivity at crossover there is going to be dip in the power response so one would want to match the high and low transducer directivity at the crossover (over some bandwidth).
If the high transducer is smaller than the low transducer they both transition from omni to "beaming" over different bandwidth so it is not possible to make the crossover on this transition region and get them aligned, since they do not overlap. Directivities align only where they both are "omni" (in the beaming frequencies the low transducer is not probably pistonic anymore and has pretty wild directivity and other problems so not good idea to cross that high).
I think the definition for "omni" is when wavenumber (ka) is less than 1 and narrowing starts when ka > 1.
ka is calculated ka = driver circumference / wavelength = ( pi * d ) / wl, so for 10" driver ka = 1 roughly at wl = (pi * 10") / 1 = 31" ~ 430Hz!
Often beaming is approximated using driver diameter as wavelength, this would make 10" beaming at ~1350Hz. If one uses -6db at 90 degrees off axis as definition for beaming then 10" beams at ~1900Hz. This would yield a dip in the power response though, if the high transducer is not -6db at 90 degrees.
Cool chart here: So, up to what frequency are drivers REALLY omnidirectional?
it depends how you define beaming. For crossover work and power response consideration, if the drivers have different directivity at crossover there is going to be dip in the power response so one would want to match the high and low transducer directivity at the crossover (over some bandwidth).
If the high transducer is smaller than the low transducer they both transition from omni to "beaming" over different bandwidth so it is not possible to make the crossover on this transition region and get them aligned, since they do not overlap. Directivities align only where they both are "omni" (in the beaming frequencies the low transducer is not probably pistonic anymore and has pretty wild directivity and other problems so not good idea to cross that high).
I think the definition for "omni" is when wavenumber (ka) is less than 1 and narrowing starts when ka > 1.
ka is calculated ka = driver circumference / wavelength = ( pi * d ) / wl, so for 10" driver ka = 1 roughly at wl = (pi * 10") / 1 = 31" ~ 430Hz!
Often beaming is approximated using driver diameter as wavelength, this would make 10" beaming at ~1350Hz. If one uses -6db at 90 degrees off axis as definition for beaming then 10" beams at ~1900Hz. This would yield a dip in the power response though, if the high transducer is not -6db at 90 degrees.
Cool chart here: So, up to what frequency are drivers REALLY omnidirectional?
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Because otherwise on the high end, the two midranges will start to beam like crazy. This might not seem to be much of a problem if you can tune the speaker flat on axis, but it is, and not just because it limits your listening position to a small horizontal band.
The major problem with this is power response. I cannot explain without writing an essay, so please do your own research.
Beaming starts when the wavelength of the sound reproduced becomes smaller than the circumference of the driver. It is pretty much the same for all drivers, cone shape has little impact. A 10" gets out of its piston band around 450 Hz. The math is unforgiving.
For that reason, all modern two ways use a wave guide on the tweeter in order to mimic the dispersion (read beaming) of the midwoofer around the crossover frequency.
"As a rule of thumb, speaker drivers will start beaming a frequency having a wavelength equal to the diameter of the radiating cone. Just a few comments here to illustrate the problem as I've had to explain this many times from mails coming in.
Having an 8" driver with a cone diameter of 17 cm, beaming will start at 34400/17 = 2023 Hz (speed of sound in cm/diameter in cm). This may prove an 8" well suited for a 2-way with a point of crossover around 2 kHz, but it's not as simple as that. As can be seen from the graphs below, an 8" starts losing off-axis response already at 1 kHz being some 7-8 dB down on 60 deg off-axis compared to on-axis response, the Discovery being 8 dB down. Despite differences in cone geometry, this figures are fairly constant. Cone geometry may to some extent impact dispersion, but it's not a major factor in overcoming the problem. Some old-time soft-cones may be less prone to beaming as only the part of the cone around the voice coil will generate sound in upper-mid/lower treble as the cone breaks up and the outer part of the cone not generate high frequencies at all. Manufacturers have called this "controlled" break-up to cover the fact the cones break up and smear detail as different parts of the cone move in opposite direction and cause phase shifts, which sometimes can seriously distress the ear and cause listening fatigue at loud levels. I rush to say that at moderate levels this can be very good indeed like the old Vifa C17 cone having a fairly soft and thin coated paper cone."
Having an 8" driver with a cone diameter of 17 cm, beaming will start at 34400/17 = 2023 Hz (speed of sound in cm/diameter in cm). This may prove an 8" well suited for a 2-way with a point of crossover around 2 kHz, but it's not as simple as that. As can be seen from the graphs below, an 8" starts losing off-axis response already at 1 kHz being some 7-8 dB down on 60 deg off-axis compared to on-axis response, the Discovery being 8 dB down. Despite differences in cone geometry, this figures are fairly constant. Cone geometry may to some extent impact dispersion, but it's not a major factor in overcoming the problem. Some old-time soft-cones may be less prone to beaming as only the part of the cone around the voice coil will generate sound in upper-mid/lower treble as the cone breaks up and the outer part of the cone not generate high frequencies at all. Manufacturers have called this "controlled" break-up to cover the fact the cones break up and smear detail as different parts of the cone move in opposite direction and cause phase shifts, which sometimes can seriously distress the ear and cause listening fatigue at loud levels. I rush to say that at moderate levels this can be very good indeed like the old Vifa C17 cone having a fairly soft and thin coated paper cone."