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hello: new here and I saw some talk about Ripole designs. There is a thread on Ripole driver selection at diyaydio.com in the subwoofer section. I would invite those with interest to have a look and welcome you to participate as well. Thanks and regards Moray James.
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Driver considerations are the same as for a normal open baffle. Therefore high surface area (think of 12, 15 or 18 inch) low fs, highish qts (>0.4), and preferably high xmax with a lot of power or high efficiency + reasonable xmax (8 mm).
The only addition a ripole yields is that the baffle is more or less folded and the chamber behind and in front of the woofer generates a lower fs of the complete system.
When some parameters are off spec (say a low qts of a typical PA woofer) you need more eq in the filter. In my case (Visaton BGS 40) I wasted the efficiency of two times 98 dB/w/m resulting in a inroom efficiency of about 93.
In addition I've to say that the room dictates the lower threshold of the FR response as shown in one of the papers on the website of JohnK.
By the way, I forgot to mention the ripole resonance, this needs atleast a parallel LCR circuit in combination with a >3rd order electrical filter. The resonance is typically in the 200-300 Hz range so a lot of uF and mH are in order (typically >10 mH and >300 uF). The design can only be finalized when you atleast can measure the impedance (resonance is easily recognizable in the impedance curve) but IMHO to be able to design a proper loudspeaker you also need to measure the FR.
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