In converting a two-way sealed system to three way, I want to attach a 4 inch open- back midrange driver to the same baffle that a 12 inch woofer is mounted on. If possible, to cut down on the amount of work in making the conversion, I would like to avoid building a little box for the midrange.
The crossover frequency between the woofer and midrange is going to be 500 Hz. The free air resonance frequency of the midrange is about 60 Hz. So even if I back-load the midrange with a small box, the pass-band for the midrange is going to be well above the resonance frequency of the midrange. But as I plan a first order cross-over, it might be beneficial for the sys. resonance freq. of the midrange to be close to the free air resonance freq.. So that would be another reason not to give the mid its own sealed box.
I haven't read it explicitly stated anywhere, but my assumption is that separating the acoustic outputs of the drivers is maybe necessary because the back wave of the woofer potentially will distort the sound of the midrange if it isn't blocked from acting on the rear of the cone of the midrange.
How about if I give the sealed box a 100% fill (of damping material); do you think that that would prevent the rear wave of the woofer from driving the cone of the midrange?
Hey, this is one of my longer posts,
cT
The crossover frequency between the woofer and midrange is going to be 500 Hz. The free air resonance frequency of the midrange is about 60 Hz. So even if I back-load the midrange with a small box, the pass-band for the midrange is going to be well above the resonance frequency of the midrange. But as I plan a first order cross-over, it might be beneficial for the sys. resonance freq. of the midrange to be close to the free air resonance freq.. So that would be another reason not to give the mid its own sealed box.
I haven't read it explicitly stated anywhere, but my assumption is that separating the acoustic outputs of the drivers is maybe necessary because the back wave of the woofer potentially will distort the sound of the midrange if it isn't blocked from acting on the rear of the cone of the midrange.
How about if I give the sealed box a 100% fill (of damping material); do you think that that would prevent the rear wave of the woofer from driving the cone of the midrange?
Hey, this is one of my longer posts,
cT
Yes, it certainly will. You need a separate box for the midrange or the internal box pressure from the woofer will move it all over the place.
Dave.
In a passive-radiator system, at frequencies greater than the box resonance frequency, the system functions as a sealed system. That is, at those higher frequencies, the cone of the passive-radiator is essentially at a standstill.
For the passive radiator system, at frequencies less than the box resonance frequency, the cone of the passive radiator moves in concert with the pressure wave inside the box of the system.
So for a mid-range driver sharing the same sealed enclosure as the woofer, I think that the greatest difficulty might occur at frequencies below the resonance freq. of the mid-range. At those frequencies, I think that the potential is there that, as Dave says, the woofer would really push on the cone of the mid-range.
Also, the surface area of the cone of the 4 inch mid-range is about one-ninth of that of the 12 inch woofer. In terms of bass response, then, the affect of the exterior of the cone of the mid-range pushed out of phase with the exterior of the cone of the woofer is going to be small.
cT
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While I'm no expert won't the midrange be pushed more? The woofer pushes in X m^3 of air more than nominal, won't that mean that the midrange then will be pushed out by X m^3 air also? Which if I have my math correct means that 1 mm movement on the woofer equals 9 mm anti phase movement on the midrange if the cone are ratio is 1/9. In practice it's probably less since the midrange has an acoustical resistance but I think it's still more than the woofer excursion.
IMO this is a complicated question, and I'm most certainly not a physicist. What I was primarily addressing was that the mid-range that I'm adding to the system has half the Xmax of the woofer and cone area of the mid-range is about 1/9 that of the woofer. So the mid-range's acoustic output into the room in anti-phase to that of the woofer would I believe be relatively insignificant.
An alternate way to think about it would be from the point of view of the woofer compressing and decompressing the box. At peak compression the woofer causes X grams per cm^2. The force produced on the back-side of the cone of the mid-range would be 1/9 of the force that the woofer exerted to reach peak compression. Beyond that, I wouldn't know what to say about what the mid-range does.
Possibly I will try to determine what happens experimentally. That is, I'll mount the mid-range on the sealed enclosure for the woofer, drive the woofer with a sine wave signal of fixed voltage and variable frequency, and measure the output voltage of the mid-range functioning as a generator.
Thanks for the responses,
cT
Wouldn't the total force, xmax * cone area applied on the midrange be the same in anti phase as the woofer is in phase. Such that the midrange which has lesser cone area must be pushed more.
I'm thinking the water analog, if I have a watering can and I could somehow block the big hole and then push down and compress the water. If I'm not mistaken that would make the water shoot out from the funnel at ~ X times the velocity of the push where X is the ratio of area between the big hole and the funnel. Shouldn't the same principle be applied here?
You won't need to measure it. You'll see it.
And when you do, won't that answer your question?
Dave.
A separate enclosure for the mid-range is absolutely needed. Reproducing sine waves with the woofer and the coil of the mid-range open, both drivers sharing one enclosure, didn't provide much evidence of a lot wrong. But playing a (music) cd thru the partially assembled system caused extreme excursion of the mid-range's cone. In doing a proper experiment, I suppose that I should have used pink noise rather than a sine wave to test.
Thanks to all for the responses. I'll just have to live with a 5-10% smaller interior volume for the woofer as a result of the separate enclosure for the mid-range in there. That was an additional reason why I didn't want the separate enclosure for the mid-range. The woofer in the two-way system had a box volume about 1/3 larger than it will in the three-way system and had great bass response coupled to the larger box.
cT
Right now i have a little 3L 2 way system with 4" "woofer" and tweeter. Woofer is Dayton audio TCP115-4. Now i would like to test a 2 way consisting of the same woofer and some mid/full range 3" speaker, like visaton FRS8 M. The system is ported and i would like to do it to test a few things and learn.
I am wondering what would be an effect of using both woofer and midrange in the same enclosure. Would that destroy the midrange fast? What would be the effect on audio quality ?
I opened some cheap 3 way speakers and many of them use 1 enclosure for all the speakers, ported.
I am wondering what would be an effect of using both woofer and midrange in the same enclosure. Would that destroy the midrange fast? What would be the effect on audio quality ?
I opened some cheap 3 way speakers and many of them use 1 enclosure for all the speakers, ported.
I wondered why the Home Entertainment store demonstrated the Acoustic Research AR3 with Simon & Garfunkel? No bass in the demo track, no modulation of midrange by the bass in that sealed enclosure?
I heard the 3 way KLH5 at the same time, same track. I haven't heard many 3 ways with 3-6" midrange since 1973.
I didn't like them well enough to pay the $200 each premium over the two way LWEIII which I bought.
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The midrange will act as a leak. So your ported system becomes less effective. Depending on whether the coil is shorted at low frequencies (either by the amp or by a cross coil) or not, the mid cone will make big or small unwanted excursions and that introduces distortion. I don’t think the unit will be destroyed, but it’s a no-no brainer.
Yeah, i thought so. If i put FRS 8M in its own box, that means that much less volume for bass making woofer. What would be the smallest possible box for FRS 8M that will sound o.k., but eat as little space from the woofer ? Obviously i would like to keep as many lows from FRS 8M but that takes space. I would be totaly fine to get 500Hz and up from it. I hope the question isn't to dumb, i am a complete novice in this regard.
