Open baffles?


2001-12-26 9:04 pm
Hi all. I've been at this (speaker and amplifier DIY) for all of 2 weeks now... I just came across an open baffle speaker on Does anyone have opinions on this? From what I've read, the enclosure design has a LOT to do with the way the speaker sounds. Is it possible to design an audiophile quality speaker with an open baffle???


Depending on how you look at it, open baffle speakers (bipolar or dipolar, depending on your inclination) have been around forever. Nearly every electrostatic speaker is open in back (I believe the old Beveridges were closed. Bryan, you'd have liked 'em, the cabinet was tubular, like your subs.) The planar speakers (e.g. Magnepan) are open in back.
And, yes, dynamic drivers have been used in open baffles for years. Coincidentally, I was looking for something the other day and ran across an old piece of sales literature for the Enigma subwoofer (yes, you read that right <i>sub</i>woofer). It was about the size and appearance of a Dalquist DQ-10 and used four 15" (maybe 12", I forget) drivers in an open baffle. Naturally, the response rolled off once the wavelength got long enough in relation to the panel width, but they compensated for this by boosting the output at low frequencies. An amp and driver circuit were included. The amp looked suspiciously like a Hafler DH-200 with different silk screen on the front. Whatever works...
Anyway, the thing to watch is damping. With no cabinet, the driver tends to get floppy fast, so you'll need a fairly stiff suspension on your driver if you want anything like tight bass, or mid range for that matter. (Although I've thought about the idea of a servo on the driver to tighten things up a bit...)
Bryan's observation is correct, getting rid of the cabinet is a useful thing to do. The link Geoff suggested is the only open baffle design I've seen in years; Linkwitz is a pretty smart cookie, so I imagine it sounds good.

The Legacy Whispers run free-air compound load 15"s as woofers.

We kloned them for fun. The way they load into the room is interesting, more like a planar than a conventional box. The output dies below 100Hz. Legacy supplies a bass boost box. But the one's I heard still needed a sub. Our Whisper klones are bi-amped at 100Hz to a small IB sub.

I have a open baffle prototype that uses the B&G RD-75 with a line array of 8-8" Eton woofers in free-air. They sound pretty good, but are still very much a work-in-progress.

As others have noted it's necessary to have lots of displacement so the drivers aren't overworked.