I appreciate any thoughts. More things to try. Ultimately I don't use this above 100hz, it was never meant for use above that. The cavity size for the slots were sized to keep the resonance above my operating bandwidth. Eventually when I pick up some rockwool, I will try stuffing the rear chamber heavily with it and see what happens there.
Very best,
@MalVeauX --
Fantastic project, experiments, end results & writeup! 👍😎🙂
Esp the work on the slot width, cavity dimensions, and sorting out what was happening on both sides of the driver cones. 👍👍
One thing I didn't see here or in your avsforum posts was how much the volume on the back side of the woofers could be reduced without hurting performance. Did you study that and/or post this somewhere?
I ask because I'm pondering a similar but scaled down build with dual 12"s (or 4x 8" or 10") and would like to get the overall width down to maybe 14~15" if possible. I guess that might put me into Nelson Pass ripole territory?
Fantastic project, experiments, end results & writeup! 👍😎🙂
Esp the work on the slot width, cavity dimensions, and sorting out what was happening on both sides of the driver cones. 👍👍
One thing I didn't see here or in your avsforum posts was how much the volume on the back side of the woofers could be reduced without hurting performance. Did you study that and/or post this somewhere?
I ask because I'm pondering a similar but scaled down build with dual 12"s (or 4x 8" or 10") and would like to get the overall width down to maybe 14~15" if possible. I guess that might put me into Nelson Pass ripole territory?
I tried stuffing the back chamber different ways, but not enough to dramatically reduce volume. My understanding was that if I reduced the volume of the back chambers too much, this would do similar to the slot loading and the result would be higher air velocity and more energy from the rear chambers, so the cancellation effect would meet closer to 90 degree's off axis instead of slightly off from that, and would in theory increase cancellation earlier in bandpass at a higher frequency. So I didn't reduce the chambers in the back heavily from that perspective--which may not be correct, it was the thought at the time. I did however try to make the chambers smaller, to avoid having a bunch of wasted volume back there, but I also didn't want it so tight that I couldn't install the drivers easily. This is why I installed the drivers and had the wings (sides) able to be removed, so I could put in the drivers and then close the sides. Otherwise, it was so difficult to install the drivers in a tight space like that from one side even with a right angle screw driver. Just something to think about. Small volume space is really hard to install in, if it has sides. So I minimized it but left enough to install the drivers.
If you look at ripoles, the magnets are even sticking out the sides to reduce the chamber size. You can certainly reduce the rear chamber more. I would suggest doing it with higher excursion drivers if doing so few (2~4 drivers).
When I stuffed the rear chamber and left it unstuffed, I didn't measure a difference to matter, so I only left the lining on the side panels there for air velocity purposes from the vent poles behind each driver.
Very best,
Yeah, I get that. Built 3 pairs of up/down W-frames so far & had to make the top panel removable to access/install the top driver.
Thank you for the other details.
I'm considering dual SBA SB34SWNRX-S75-6, mainly. The best price/performance for me. In a standard larger volume W-frame with those 12"s, I'm getting 180~200 Hz cavity peak of 10 dB. Not happy with the low freq. of that peak. Want to push it up closer to 300Hz.
The peak of the cavity will increase its bandpass if you reduce the width of the slot. Delicate balance between slot width relative to mass loading the drivers relative to bandpass below the slot cavity peak resonance. I had to do physical models with my drivers to find that info for mine. With other drivers, I'd probably do small physical models to get an idea of that behavior.
If your goal is 300hz though for the slot cavity resonance, that's 1.14 meter as a full wavelength, so as a quarter wavelength that's 0.286 meters. That doesn't leave much room for the size of your drivers and to have any slot width. Even if your slot depth was 250mm, the cone width of your drivers roughly, that leaves 35mm as half the slot width, or 70mm as the total slot width. That's as large as you could go, to keep the peak resonance 300hz.
That may work. Or not. Not sure, without building a physical model to see how the two drivers behave when mass loading in a slot that is 70mm wide by 250mm depth and 250mm height to get that 300hz peak resonance.
Very best,
300 Hz would be ideal. I use DSP/active crossover so can use steep crossovers & notch filters, but I would prefer not to apply as much digital correction.
Currently, in the aforementioned system, the cavity between the drivers is 14" deep & wide, 10" tall. The SBA 12"s have an oversize frame -- 346mm or 13.6" diameter. Should have made the height 7~8" which would at least push the cavity peak to >200Hz.
Currently, in the aforementioned system, the cavity between the drivers is 14" deep & wide, 10" tall. The SBA 12"s have an oversize frame -- 346mm or 13.6" diameter. Should have made the height 7~8" which would at least push the cavity peak to >200Hz.
To keep it 200hz or above, the minimum would be 343/200hz=1.715m, 1.715m / 4 = 0.429m = 16.89 inches as our quarter wavelength.
If your cavity is 14" deep, the remainder is 16.89" - 14" = 2.89" as half the width of your slot. So the slot would be 5.78 inches wide.
5.78" wide slot, with 14" depth into the cavity will give you 200hz peak resonance from the cavity and above. You could crossover (low pass) around 100hz~150hz and be fine.
That's a lot more realistic for drivers with high excursion to have a slot wide of 5.8" like that.
Very best,