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MY Open Baffle Dipole Sub Results

Posted by MarcL (A) on October 14, 2024 at 05:28:06

Yes, we have seen stories about these. I weighed options and decided to build a pair AND do a LOT of testing to understand what they do. 100% success!

Visceral Immediacy. I'm going with this description. It's not the chest slam of four 18" ported subs playing the opening scenes from Top Gun. It's the presence of articulate bass even at low listening levels. It's a startling transient from a piece of music you've heard 100 times, but not with that dynamic range.

Clarity ... room resonances are greatly reduced, and so then the masking of resonance peaks and long decays. Bass notes and percussion stand with better definition in the soundstage. And with two subs, each crossed over at 60Hz from their respective left and right channel 3.7/DWM pair, I can locate the source of fundamentals down to 30Hz (my wife was less sure of 30/40, but still good down to 50).

These are built with three 12" 16 ohm GR Research servo drivers and a Rythmik A370PEQ servo amp. I drove the speakers alone with a different amp to determine how they work without the servo and shelf filters. Then I drove them with the servo amp and tried all of the damping and bass extension settings. Final settings were Hi damping and 14Hz extension. Ground plane tests in the back yard verified flat response 3db down at 15Hz and smooth up over 200Hz. Distortion mostly under 1%, rising through 2% below 20Hz. p.s. DO NOT operate this amp without the servo coil connected! And DO NOT accidently reverse the polarity of the coil wires!

Testing in my untreated 11'x15'x8' den where they were built verified that side/side and top/bottom resonances are substantially cancelled. Aimed in the 15' direction that modal resonance at 37.5Hz was evident. Turning 90 degrees playing across the 11' width, the 37.5Hz went away and the 51Hz width resonance was evident. Neither case showed a 70Hz floor/ceiling resonance.

I did not hurt myself trying to HEAR the difference between Hi, Mid, Lo damping. Suffice to say the impulse responses confirmed damping beyond 8ms, with more difference between Mid and Lo than there was between Mid and Hi. I saw no reason not to use the Hi setting. And though the subs could clearly play below 10Hz, I have the Rumble filter on.

I did notice through measurements that when correctly (triple checked!) wired, the polarity was reversed. I verified myself and with a note to Rythmik that turning the Phase knob from 0 to 180 degrees is NOT the same as switching the wires. The Phase control is for fine tuning phase at the crossover point. I switched the wires and it all worked.

Glad to answer any questions and provide measurements.

Agilist, Musician, Photographer, Audiophile
7.1.4 Magneplanar: 3.7, CCR, LRS, MC1(4), DWM(2); Emotiva B1+; GR Research OB Dipole Subs (2x3); Emotiva XMC-2; Nord One NC500DM; Nord Three 1ET7040SA; VTV NC502MP; Crown XLi800;OPPO 205

Edits: 10/14/24

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