Someone emailed me about a box design they saw online.
So I thought I'd put in some time to show what I think it's doing.
In a nutshell, you can combine vented and bandpass enclosures and achieve some interesting results.
Here's a sim that shows the combination of a bandpass box and a vented box. The woofers are the same, an Alpine SWS-10D2.
In the frequency response, you can see that the response curve of the two boxes are comparable. If their phase is identical they'll sum constructively.
Because one is vented and one is bandpass, you might think that the phase response would vary. But with some juggling of the parameters, you can get it fairly close. These two boxes have a group delay curve that's basically the same, down to 35Hz, so they WILL combine constructively.
Below 35Hz, the phase of the two boxes varies quite a bit. This is because the vented box sees 180 degrees of phase shift at it's tuning frequency. At 35Hz, the two boxes are 135 degrees out of phase.
This situation can be addressed fairly easily. For instance, you might use a steep high pass on the bandpass box, so that it's output is reduced below 35Hz. The bandpass box is already radiating 3dB less output than the vented box at 35Hz, so attenuating it another 6dB probably wouldn't be a big deal.
Another option might be to manipulate the phase using FIR filters, all-pass filters, or just plain ol' active filters.
To me, the most interesting aspect of the design, by far, is that the impedance of ONE subwoofer is very high when the OTHER one is LOW, and vice versa. This really has the potential to increase your maximum output, if the two subs share the same amplifier. For instance, at 51Hz the bandpass box is receiving 500% more power than the vented box. At 30Hz, the vented box is receiving over 200% more power than the bandpass box.
So this becomes a "yin yang" thing, for the amplifier, where one sub is drawing a ton of power at a frequency, while the other is not.
In my old home theater, I had a tapped horn, a vented box, and a bandpass box, all at the same time. That worked really nicely, and operates on the same principle.
This thread was inspired by a discussion here:
https://www.diyaudio.com/forums/subwoofers/359383-active-compliance-management.html
So I thought I'd put in some time to show what I think it's doing.
In a nutshell, you can combine vented and bandpass enclosures and achieve some interesting results.
Here's a sim that shows the combination of a bandpass box and a vented box. The woofers are the same, an Alpine SWS-10D2.
In the frequency response, you can see that the response curve of the two boxes are comparable. If their phase is identical they'll sum constructively.
Because one is vented and one is bandpass, you might think that the phase response would vary. But with some juggling of the parameters, you can get it fairly close. These two boxes have a group delay curve that's basically the same, down to 35Hz, so they WILL combine constructively.
Below 35Hz, the phase of the two boxes varies quite a bit. This is because the vented box sees 180 degrees of phase shift at it's tuning frequency. At 35Hz, the two boxes are 135 degrees out of phase.
This situation can be addressed fairly easily. For instance, you might use a steep high pass on the bandpass box, so that it's output is reduced below 35Hz. The bandpass box is already radiating 3dB less output than the vented box at 35Hz, so attenuating it another 6dB probably wouldn't be a big deal.
Another option might be to manipulate the phase using FIR filters, all-pass filters, or just plain ol' active filters.
To me, the most interesting aspect of the design, by far, is that the impedance of ONE subwoofer is very high when the OTHER one is LOW, and vice versa. This really has the potential to increase your maximum output, if the two subs share the same amplifier. For instance, at 51Hz the bandpass box is receiving 500% more power than the vented box. At 30Hz, the vented box is receiving over 200% more power than the bandpass box.
So this becomes a "yin yang" thing, for the amplifier, where one sub is drawing a ton of power at a frequency, while the other is not.
In my old home theater, I had a tapped horn, a vented box, and a bandpass box, all at the same time. That worked really nicely, and operates on the same principle.
This thread was inspired by a discussion here:
https://www.diyaudio.com/forums/subwoofers/359383-active-compliance-management.html
The animated GIF from vueaudio, and it's patent and it's literature seems to imply that you can make a loudspeaker box behave as if it's larger, by putting two drivers in the box that are 90 degrees out of phase.
IE, if you have two woofers in a box and they're in phase, both woofers are compressing the air in the box at the same time. If you phase shift one driver by 90 degrees, then when one driver has it's voice coil centered, the other driver is at it's maximum excursion.
Similar to how standing waves work.
But I think the patent is bogus; if it was true, it would violate Hoffman's Iron Law.
Here's how that looks.
The top picture is the combination of the vented and bandpass wired in phase.
The second picture is the combination of the vented and bandpass wired OUT of phase.
And then I overlaid the two on each other.
For instance, the output at 40Hz goes up nearly five dB when the two subs are wired out of phase.
At very low frequency (20Hz) the design with the subs out-of-phase is attenuated by 7dB, due to them, well, being out of phase.
Of course, the interesting thing here, would be to put them ninety degrees out of phase. That would give you the best of both worlds.
Of course, you might ask, why go to all this hassle?
I'd argue:
1) it's a marketing gimmick
2) If the two woofers share an amplifier (or a dual channel amp with one power supply) then this system will probably get louder, because it's an easier load to drive.
I think this design has a lot of potential, especially if you can tweak the delay between the two woofers, ideally with a frequency dependent delay. You could do that with FIR filters, or even conventional filters, with a little experimentation.
The thing that's interesting to me, is that the LOW frequency output is basically maximized when the two subs are OUT of phase!
In the gif, drivers share back chamber. So pressure in this chamber change is function of the mixed phase effect of both drivers, that is what make a bit sense for their naming "compliance management". It should be easy to simulate with our old school akabak, but i have way too much stuff going on ^^
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