My two Rythmik non-ported direct servo subs are lined with GR Research "No Rez" damping+foam material and use Swiss Digital Fuse Box units. Both mods make a big difference in output and sound quality. No Rez has an effect equivalent to both increasing enclosure inner air space and damping enclosure vibrations so you aren't listening to the enclosure resonance any more. The SDFB with a copper slug sounds like a much more powerful amp. CC: @bdp24 , @lewinskih01 , @rhg3
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@deep_333 No need for anything expensive under a sub for isolation. Just use a $25-$30 set of four spring feet with at least half of the springs damped with closed cell foam earplugs. Can do the same under components, optimizing tone with 50-75% of springs foam damped. More damping means more bass and low mids.
I don't think it's the size of the cone that's the big issue. I think it's the spider, the length of the voice coil and a careful choice of suspension elements, that helps prevent the pistonic motion loss in woofers. FWIW, I have 15'' and 18'' woofers from the same manufacturer in my two channel stereo system and the only difference between the two woofers is the 18'' has higher horsepower, longer voice coil length and higher efficiency. Both woofers exhibit no dynamic offset. 😎 See below:
Woofer dynamic offset is a problem long known about but seldom discussed or treated. With high input power at low frequencies, many woofers tend to shift their mean displacement forward or backward until the coil is nearly out of the gap. This is most likely to happen just above each low frequency impedance peak of a system. The result is a high level of second harmonic distortion and subjectively a bass character that loses its tightness at high acoustical output levels . The cure for offset, as shown by T, H. Wiik , is a restoring spring force that increases in stiffness at high displacement in an amount that counterbalances the reduced B field at the extremes of voice coil travel. Such a nonlinear spider will in fact reduce distortion and eliminate the tendency to offset.
(4) M. R. Gander, "Moving-Coil Loudspeaker Topology as an Indicator of Linear Excursion Capability," J. Audio Eng..Soc., vol. 29, pp 10-26 (Jan./Feb. 1981).
(6) T. ti. Wiik, "Transient Distortion Caused by Nonlinearities in Driving Force and Suspension of a Loudspeaker," Presented at the S6th Convention of the Audio Eng. Soc., Preprint No. 1205 (C-6), _lareh 1977).
The new DEQX units which will be along shortly are insanely more user friendly and considerably more expensive. They will not require an expert to set up. Their build quality has gone up significantly. The Pre 8 has a 4 way crossover with 8 DAC channels! It will retail for $10,995.00.
I watched a 21" driver under a strobe doing a snake dance at relatively small excursions. A good 18" driver should be OK. The problem is the size of the enclosure needed to house the thing. I would like to be able to see my screen!
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