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In Reply to: RE: AudioKinesis SWARM: The Ideal Sub System? posted by triamp on March 22, 2009 at 01:53:58:
Triamp, I agree with your overall observation about planar bass, but not with the reason you give.Stretched membranes (which describes most planars) usually have a significant drum-head resonance characteristic in the bass region. Planar designers use this resonance to extend the bass considerably deeper than it would normally go for a dipole of that size without bass boost, but they also have to control it so that it doesn't dominate the bass presentation. For example Magnepan uses the little hockey pucks, SoundLab and Martin Logan use distributed resonance, and Apogee used a trapezoidal bass diaphragm.
My understanding is that the superior pitch definition of planars does not come from superior low-frequency transient response, which they demonstrably do not have. Rather, the superior pitch definition of a dipole arises from its superior room interaction characteristics. James M. Kates documented that dipoles have superior in-room bass smoothness in an AES paper entitled "Dipole loudspeaker response in listening rooms".
There is another way to get smooth in-room bass response, and that is with distributed multiple monopole sources (Todd Welti et al, "In-room low frequency optimization"). I think there is some common ground shared by these two approaches: You see, a dipole can be modelled as two monopoles, one in reverse polarity, separated by an acoustic path length. So, two dipoles are in effect a special case of four distributed monopoles.
Here's a bit more on that common ground theme: What is acoustically and psychoacoustically desirable at low frequencies is a de-correlated sound field. In the midrange and treble region, the in-room reflections are spaced so close together that they combine into a semi-randomized, de-correlated sound field. In the bass region, the reflections and room modes are typically spaced far enough apart and distinct enough ("well-correlated" enough) to create large, audible peaks and valleys. Dipole bass sources are one effective way of de-correlating the low frequency soundfield. Scattered monopole multisubs are another. They are two non-obviously related roads-less-travelled that both lead to the acoustic promised land.
Duke
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.
Edits: 03/24/09 03/24/09
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Follow Ups
- My understanding of planar transient behavior in the bass region is a bit different - Duke 22:34:58 03/24/09 (0)
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