Sealed subwoofer for ESL-63

There actually are dipole subwoofers---the OB/Dipole Gradient offered in the 1980’s for the QUAD 63, and the OB/Dipole now offered by Rythmik/GR Research. It consists of a pair of 12" OB-specific woofers mounted on an H- or W-frame---an open baffle, dipole sub with the Rythmik Servo-Feedback system, the only such sub in the world.

Ya’ll know Duke is a subwoofer expert, and his statement that dipole subs have smoother in-room bass than monopoles is, contrary to shadorne’s claim that "at these low frequencies they behave as an omnidirectional source"---an incorrect and mistaken notion, absolutely and incontrovertibly true.

A dipole sub has a null to either side (just like dipole speakers), propagating bass and bass-loading the room in one less dimension than an omni---not the width of the room. Consequently, fewer room modes are excited---less bass boom. That is an advantage inherent in dipole subs, and dipole speakers as well.

An OB-type dipole sub has one additional benefit---no sealed or ported enclosure to itself be a source of resonance or boom. As I described above, an OB sub has it's woofers are mounted on an open baffle, not in an enclosure. Lean, clean, and pristine!

Let me offer some clarification to my earlier post.

My statement that a dipole has smoother in-room bass is based on a paper written by James M. Kates and published in the Journal of the Audio Engineering Society in 2002.

It takes the ear a long time to hear low frequencies, relatively speaking. We cannot detect the presence of bass energy from less than one wavelength, and we must hear several cycles (several wavelengths) before we can detect pitch. If you stop and think about how long these wavelengths are, you’ll see that by the time we can hear low frequencies, they have already bounced around our little rooms quite a bit. So the room’s effects are all over the sub’s output by the time we hear it. In other words, perceptually we cannot separate the subwoofer(s) from the room - they form a system, for all practical purposes.

The idea with a distributed multisub system is, each sub inevitably generates a nasty room-interaction peak-and-dip pattern. But because the subs are intelligently scattered, these peak-and-dip patterns are all significantly different. The sum of these multiple dissimilar peak-and-dip patterns is pretty darn smooth, assuming we started out with four subs. This smoothness holds up pretty much throughout the room because at any location within the room, we have the summing of four dissimilar peak-and-dip patterns. And since smooth bass is fast bass (both literally and perceptually), the net result blends very well with dipoles.

Duke