Just a quick update on this project. It's been moved to the back burner while I focus on some other stuff that I need to get ready for Burning Amp. In the meantime I've made some progress with other stuff, namely my Raspberry Pi powered active speakers and streaming audio implementation. I'm now planning to use just a single Raspberry Pi 2 to implement the crossover for the sub and the satellites - that's a 6 or 7 output crossover. What these powerful little Pis can do is amazing.
Ah, finally I have been able to put this thing into play, er sort of. I managed to feed one channel, low passed, from my crossover system to a outboard amp and connect up the sub. Wow, not the high sensitivity beast I was expecting... but once I added some gain and played around a little bit I do have some low, low bass. Luckily the entire first floor of my home has an open floor plan, so even though this is a dipole sub I get pretty extended response.
It's been a couple of years since I built this sub, and someone asked me to post an update so I will share the final info on it.
The sub has been dismantled (I moved >2000 miles to a new home). It was one of my early attempts at a large dipole sub, and it did have good low bass. The main problem was the line resonances (there were at least two or three). These resulted from the depth, with and height dimensions of the cavities in front and rear. Together they made the sub sound "boomy" and were difficult to EQ out or otherwise correct. The problem was the way I constructed the enclosure generated lots of different cavities of different sizes, and these all created various and sundry internal resonances at or below 100Hz.
What I have evolved to now is a large H-frame design with a single large driver. By "large" I mean the opening is on the order of 24"x24" (60cmx60cm) and the depth (front to back including both from and rear cavities) is also about 24", give or take. I employ an 18" sub with Qts>=0.4 (higher is better) and as high an efficiency as possible (e.g. using prosound drivers). This works pretty well, and there is only a single resonance from the identically sized front and rear cavities of the H-frame. I can just EQ it out as part of the low pass filter, e.g. around 100-150Hz or so, depending on where the resonance peak is located.
Because the H-frame is relatively wide and deep, I can still get good dipole bass from this system. The challenge is to reduce vibration to a minimum, which I do by making it very heavy. Sand-filled side panels are helpful in this regard, and something weighing well over 100lbs is needed if the driver's moving mass (e.g. Mms) is more than a few hundred grams.
I will eventually post about my latest efforts in this area. I'm not yet up and running after my move but maybe by springtime 2019.
The sub has been dismantled (I moved >2000 miles to a new home). It was one of my early attempts at a large dipole sub, and it did have good low bass. The main problem was the line resonances (there were at least two or three). These resulted from the depth, with and height dimensions of the cavities in front and rear. Together they made the sub sound "boomy" and were difficult to EQ out or otherwise correct. The problem was the way I constructed the enclosure generated lots of different cavities of different sizes, and these all created various and sundry internal resonances at or below 100Hz.
What I have evolved to now is a large H-frame design with a single large driver. By "large" I mean the opening is on the order of 24"x24" (60cmx60cm) and the depth (front to back including both from and rear cavities) is also about 24", give or take. I employ an 18" sub with Qts>=0.4 (higher is better) and as high an efficiency as possible (e.g. using prosound drivers). This works pretty well, and there is only a single resonance from the identically sized front and rear cavities of the H-frame. I can just EQ it out as part of the low pass filter, e.g. around 100-150Hz or so, depending on where the resonance peak is located.
Because the H-frame is relatively wide and deep, I can still get good dipole bass from this system. The challenge is to reduce vibration to a minimum, which I do by making it very heavy. Sand-filled side panels are helpful in this regard, and something weighing well over 100lbs is needed if the driver's moving mass (e.g. Mms) is more than a few hundred grams.
I will eventually post about my latest efforts in this area. I'm not yet up and running after my move but maybe by springtime 2019.
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Yes on the idea of 4 12" drivers in a H-frame about 24x24 (or just large enough to fit them).
But I don't see how you will get any force cancellation... all the diaphragms must move in the same direction at the same time. You will probably get some even order distortion reduction with two of the drivers mounted "backwards".
The only way to mount the drivers to reduce vibration is for two pairs of two to face each other. This can't really be done in an H-frame. You have to resort to what I did for the 12 driver system, and that resulted in all of the resonance issues I mentioned. I would stick to the regular H-frame geometry.
Want to use two of these subwoofers in a home tv/stereo cabinet, which i custom make.
Is that a good idea, adding the subs into a home/tv stereo cabinet?
Really like the space i will save. Already put these specs into
Subwoofer Box for 12 inch subwoofer | Ported Box | Slot
to see what i get with the dimensions i put in. It does seem to fit, with a tuning Fs of 33Hz. So, is this a good idea?
Is that a good idea, adding the subs into a home/tv stereo cabinet?
Really like the space i will save. Already put these specs into
Subwoofer Box for 12 inch subwoofer | Ported Box | Slot
to see what i get with the dimensions i put in. It does seem to fit, with a tuning Fs of 33Hz. So, is this a good idea?
If the driver you are intending to use is the GRS 12SW-4 that I used in the 12-driver dipole sub, that would not work well at all. The Qts value is way too high for a ported/vented/PR application. You should look for a driver with a low Fs (<30Hz) and Qts around 0.35, no higher than Qts=0.4. Use a modeling program to see the response of the driver in your box.
The GRS 12SW-4 is best used in an infinite baffle or open baffle application.
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