I have toyed with the idea of making a smaller basshorn for quite some time. When I designed the 12π, I planned to build a scaled down version with higher cutoff. I've always had a philosophical problem with undersized basshorns, those that display peaks and dips in response. However, there is some merit in the idea of making a basshorn that is designed to be used in groups in order to get the desired performance.

The idea occured to me that I could pretty much just cut a 12π in half, and each side would be much easier to carry than one large box. A half a 12π is called a 10π, which can be used individually but is designed to be used in pairs. Of course, this means that there is actually a 10π-A and a 10π-B, with the "A" version having the cone facing the front chamber and the "B" version having the magnet facing the front chamber. The cooling plugs and heat plate access panels are also on different sides, so that a pair of 10π basshorns can be stood together to form the equivalent of a 12π basshorn subwoofer.

I would recommend the original 12π be used where possible, because the cancellation of harmonic distortion in the combined throat will be better than the cancellation that occurs from summing at the mouth. I cannot tell how much better the distortion of the 12π basshorn is compared to a pair of 10π basshorns from simulations, because I don't have software tools that can model this sort of thing. That will have to be determined by measurements. A single 10π horn, without a complementary pair, becomes a traditional basshorn. When a complementary pair is used, it gains the benefit of push-pull drive. I plan to assemble a pair of 10π prototypes by the 2007 Prosound Shootout.

Can you achieve similar benefits in a ported box with two woofers, one facing the normal way and one reversed (presumably then connected in opposite phase so they drive the external wavefront in phase)?

Have you had any thoughts about using push-pull in other designs - for example a dual-woofer corner horn with one facing into the box and one facing out? Could two cheaper woofers perform as well as or better than one expensive woofer in such a configuration?

• push-pull drive for π cornerhorn

tim

When I considered push-pull for seven π cornerhorns, I realized that the top of the line model already has a mechanism for reducing distortion caused by flux modulation, so push-pull drive wouldn't be as effective for it. The woofer used in the Professional Series seven π uses a shorting ring that is effective down to below 100Hz. Shorting rings begin to lose effectiveness at subwoofer frequencies, so I'm not sure they make sense for dedicated subwoofers but for the bass bin of a cornerhorn, flux-stabilized woofers are perfect.

• ...charts like p2 of this Selenium driver data sheet

• Distortion conversion chart - decibels to percentage

tim