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Why do planars have poor bass extension?

I've been wondering about this. Is it because the excursion is limited because of the tension of the diaphragm & low BL limits its excursion?

On a related note, what techniques do companies like Magnepan use to get more bass out of their low-frequency drivers? Do they put bigger magnets in the grid than would be feasible for the midrange? Heavier diaphragms?

Finally if anyone knows a good reference for learning about the TS parameters of planars and if/how such calculations differ from dynamic speakers, that would be awesome!

Thanks all!
sideshowgabe
sideshowgabe OP
2 posts
 
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!
drew_eckhardt
394 posts
 
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).
drew_eckhardt
394 posts
 
>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.
ngjockey
1,042 posts
 
Aside from the Infinty IRS V and the Genesis 1,2 and 3 series, can't think of any other planar using either flat or folded "wings" and they all had sealed woofers and somewhat different bass expectations.

Getting beyond theoretical but...

http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf

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

There's also A,B,C,Dipole freeware.
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