Why do planars have poor bass extension?

Dipole panels have the same problem with bass as open baffle cone speakers. The technology is less relevant than basic acoutics. As an experiment, try 1' deep plywood "U-frames" on panel speakers.

Due to the energy lost into the acoustic short circuit between front and back surfaces in a domestically friendly 14.5" wide planer speaker or deep W/H frame you need 4X the displacement compared to a monopole and 12dB more raw output compared to the same speaker at 160Hz (so total excursion is 64X what it is at 160Hz).

It's better to roll-off the response than have the speaker encountering its mechanical limits.

If you want dipole bass (it couples differently to room modes, and sounds subjectively better with Siegfried Linkwitz hypothesizing it's due to preserving the bass signal's envelope better) with low extension and the ability to handle music at less than scale model levels in a spouse friendly package the only practical solution is W or H frame woofers with electronic boost at low frequencies.

The Orion designed by Siegfried Linkwitz (http://www.linkwitzlab.com) and sold by Wood Artistry (Starting at $14,750 - http://www.theorionspeakers.com/speakers-and-cabinets/release-orion-4.html) does this. Gradient sells the SW-63 sub-woofer for the classic Quad ESL 63. Martin Logan has a few speakers with physically opposed cone woofers that start out as dipoles and transition to monopoles as excursion becomes a problem and you're getting below the room's fundamental resonance where it's not buying you anything.

Thanks all! I'm particularly interested in the canceling effects inherent in the dipolar radiation pattern – could anyone point me to some more in-depth literature along the lines of Drew_eckhardt's response -

"Due to the energy lost into the acoustic short circuit between front and back surfaces in a domestically friendly 14.5" wide planer speaker or deep W/H frame you need 4X the displacement compared to a monopole and 12dB more raw output compared to the same speaker at 160Hz (so total excursion is 64X what it is at 160Hz)."

References are greatly appreciated!

At 40Hz (oops, omitted that). At 20Hz it's 8X more than the monopole, 18dB more raw output (64X) than at 160Hz, and 512 times the displacement.

04-15-12: Drew_eckhardt
>Due to the energy lost into the acoustic short circuit between front and back surfaces in a domestically friendly 14.5" wide planer speaker or deep W/H frame you need 4X the displacement compared to a monopole and 12dB more raw output compared to the same speaker at 160Hz (so total excursion is 64X what it is at 160Hz).

>04-16-12: Sideshowgabe
Thanks all! I'm particularly interested in the canceling effects inherent in the dipolar radiation pattern  could anyone point me to some more in-depth literature along the lines of Drew_eckhardt's response -

My comparison was at 40Hz (it's worse at low frequencies and better at high with equal output between dipole and monopole in the hypothetical 14.5" example around 160Hz); sorry for not proof reading that.

Siegfried Linkwitz

http://www.linkwitzlab.com/models.htm

and John Krevosky

http://www.musicanddesign.com/Dipoles_and_open_baffles.html

have written extensively on dipole speakers.

Their focus is open-baffles with cone bass and midrange drivers and dome or ribbon tweeters but the same principles apply to planar speakers especially at low frequencies.