Im considering building a pair of double or quadrouple (stacked) ripoles using the AE dipole 12.
Would this driver be considered suitable for a ripole construction?
Yes, the Dipole series of woofers would work quite well in this application. The parameters are ideal and the high excursion capability makes them good candidates for subwoofer use. Most of our customers use them on flat open baffles, but for subwoofer use the ripole construction allows you to get more output from a similarly sized front baffle.
I wouldn’t worry too much about the Qts of the Dipole12. Many people look for Qts of over 1.0 to get some boost in the low end. The Qts is still going to be lower than that. In reality I don’t think you need the slot loading, but could put more distance between them but still have them dual opposed to prevent vibration on the cabinet. If you do want a lower Qts, look at the LO12 which would give you that. http://www.aespeakers.com/drivers.php?driver_id=59
Many like to use Qts of .5 for more controlled bass. Others like to use Qts of 1.0 or higher for a bump in frequency response and more boost. Our Dipole woofers all fall between those two ranges. The big benefit to ours though is the underhung motor. This means that the Bl will stay roughly the same at all points in excursion. That means the Qts stays roughly the same as well. Other drivers like the Eminence Alpha15 that some people use have a higher Qts to start with, about 1.3. The short overhung coil though has a significant loss in Bl by only 3mm. Once it starts moving to that excursion, the loss in Bl actually increases the Qts to nearly 3.0! This is where things start to get boomy. This is not an issue with our woofers as the Bl does not significantly change with excursion within the +/-12mm range.
I asked Martin King his thoughts on ripoles. He has built and modeled many U and H frames but never a Ripole. Here was his comment:
“I have never looked in detail at Ripoles or any of the other folded frame concepts. I have never been able to think of any significant benefits that the added complexity might deliver.”
I have tried to build a ri-pol but it “drops dead” below 40Hz… It my ripol to big or is it not possible for the 12″ dipol speaker to reach below 40Hz?
I have also tried U-frame with same result.
Is there somebody here that have a design proposal for this driver to reach 20-25Hz?
I hade 4 of this drivers.
After looking more in depth at the “ripole” concept, there are some issues with this that I was not aware of 2 years ago. The design fires the woofer into a slot. This slot provides additional acoustic loading on the driver. It increases the apparent Qts of the driver. It lowers the upper end efficiency. This is the type of design used when trying to force a non-ideal, low Qts driver to work in an open baffle application. The decrease in upper end efficiency and increase in Qts give an apparent lower F3 point. It requires a lot of power though. It also causes additional resonances due to the slots.
The rolloff at 40hz is a function of three things. One is the “loading” effect on the woofer in the ripole. Two is the position in the room. Three is the baffle size. The Dipole12 itself has an F3 at about 30hz and is only 8dB down at 20hz. This requires a VERY large open baffle to get this though. The baffle also has to be placed appropriately in the room to avoid cancellation from the back wave reflecting off the wall behind and coming back out of phase with the front wave.
If you were to use the Dipole12 in a standard flat open baffle you will likely get better results. A U-baffle you would give even more distance between front and back wave, increasing the efficiency.
Kyron Audio achieves 32hz in the Kronos:
The Lotus Group Granada achieves 25Hz:
Both use 2x Dipole12, but have some processing to do this.
Additionally, open baffles, u-baffles, etc, typically all benefit from some EQ to correct the low end response.
The best option is to model the U baffle with something like ABC Dipole to know what to expect. http://www.musicanddesign.com/A_B_C_Dipole.html
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