Speaker Asylum

Dipole cancellation

4.242.60.29

In Reply to: RE: ...open baffle speakers harsh on classical mucic? posted by layman on May 04, 2008 at 07:44:00

"Consider that the lack of a baffle can lead to phase cancellations at bass and lower mid-range frequencies. At lower mid-range frequencies where the wavelength gets longer than a foot, the out of phase front and back wave of the speaker will wrap around the baffle and cancel.

This would tend to emphasize higher frequencies leading to the "harshness" that you describe.

I think that the open baffle of the design would have to be large in order that these phase cancellations not effect the lower mid-range and upper bass (robbing the music of warmth in the way that you have described)."

Well, yes and no. Dipole phase cancellation is a well-understood phenomenon, with a 6dB/octave highpass function, and any competent designer will take it into account in the crossover. In an actively crossed, multi-amped design like the Linkwitz Orions (which use dipole woofers as well as mids), line-level EQ is applied to flatten the response well down into the bass. Carver's Amazings used some very high-Qts woofers, which increased in output with dropping frequency, to precisely compensate for the dipole phase cancellation. (I believe most planars employ a similar strategy). Many designs using open-back cone mids add shallow sides to the baffle, to push the cancellation lower in frequency, and to push the 90 degree off-axis null zone further behind the baffle plane. (Too deep sides, though, will produce cavity resonances which can color the sound as they reflect back into the room).

ALL speakers are sensitive to room acoustics, dipoles far more so than conventional boxes. They have little output to the sides, as a result of the phase cancellation, and can thus be placed closer to side walls than most speakers. But they need plenty of open air behind them, and the front wall needs to have a combination of absorbtive and refractive treatments so that the out-of-phase rear wave reflects back into the room at much-reduced amplitude but without grossly distorted frequency response.

I haven't yet had the pleasure of hearing the Orions, but I doubt if they sound the least bit harsh with classical music. Sigfried Linkwitz is a lifelong subscriber to the San Francisco Symphony, has engineered many classical recordings, and used primarily classical music in voicing the speakers.

Follow Ups:

Post a Followup:

FAQ

Post a Message!

Forgot Password?

Moniker (Username):
Password (Optional):
	Remember my Moniker & Password (What's this?) Eat Me
E-Mail (Optional):
Subject:

Message:	(Posts are subject to Content Rules)

Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:	Automagically notify you when someone responds.

To view your new posting or follow-up, click on the RELOAD or REFRESH button on your browser.