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In Reply to: Re: Allison Effect posted by layman on January 06, 2002 at 12:14:43:
Sure. The interesting thing though is that a planar will have an essentially infinite number of "quarter wave lengths" since the bass frequencies are radiated over a continuous surface.It seems like the over-all effect would be a very slight reduction in a range of frquencies rather than a higher reduction confined to a single fequency.
Also, planars don't radiate from the sides so there wouldn't be the same interaction with the side walls.
And they radiate from the back so there is an additional sound source to factor in.
An interesting puzzle to solve!
Follow Ups:
“Sure. The interesting thing though is that a planar will have an essentially infinite number of "quarter wave lengths" since the bass frequencies are radiated over a continuous surface. It seems like the over-all effect would be a very slight reduction in a range of frequencies rather than a higher reduction confined to a single frequency. Also, planars don't radiate from the sides so there wouldn't be the same interaction with the sidewalls.”In every frequency response graph of planars that I have ever seen, I have spotted boundary effects in the bass (unless the speakers were measured in an an-echoic chamber). The dipolar nature of planar radiation does not change the fact that the bass that planars do produce behaves like all bass and radiates omni-directionally. Boundary interactions will still come into play in the bass then, even if they do not come into play in the mid-range and treble. Planars do radiate from the sides at bass frequencies, or rather, at those long wavelengths, the “side” cannot be distinguished from the “front” or “rear.” Planar produced bass will interact with boundaries just like that produced by moving coil drive units.
“And they radiate from the back so there is an additional sound source to factor in.”
The back-wave is the reason unenclosed planars do not delve very deep into the bass, as the back and front waves cancel each other out at low frequencies, but (big) planars can produce bass down to the 150 Hz to 200 Hz range, and this is where the majority of boundary induced suckouts occur.
Thanks for the info. Some of it makes sense to me.The back-wave is the reason unenclosed planars do not delve very deep into the bass, as the back and front waves cancel each other out at low frequencies, but (big) planars can produce bass down to the 150 Hz to 200 Hz range, and this is where the majority of boundary induced suckouts occur.
Maybe I'm confused but Magnepan rates their larger models into 20's for bass response. I have heard various maggies, and measured with an RTA and there is definately bass below 150.
Are you saying bass is not possible below 150 with planars or are you saying it is just more susceptable to being cancelled by the back wave?
All drivers are dipolar (planar or moving-coil). Bass drivers are no exception, and the only way to achieve (preserve) bass, is by preventing the out of phase back-wave cancelling the front wave.Low bass can be achieved using planar/electrostatic technology through several means. Firstly, you could enclose the bass driver, preventing the back-wave from interacting with the front-wave. Secondly, you could augment the bass with a conventional enclosed moving coil drive unit (hybrid designs like the Martin Logans). Moreover, big size helps. Big size prevents the back-wave working its way to the front (at least down to the upper bass), but at really low frequencies, you would need an infinite baffle (an enclosure) to prevent these destructive interactions.
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