Speaker design myths revealed

Johnk: "OB drivers" = open baffle drivers??? If so, disabuse yourself. There no such thing as an "open baffle driver" (although certain drive units' T/S parametres may indicate good performance on an open baffle...). Cheers

Fiddler: what Twl notes above about diametres is a (unfortunate maybe) necessity. The links you give refer to ("quasi quasars") actually show baffles that should be ~0,5m wide (~20,5"). Good luck, the Phy is a beautiful unit!

Nzera, do you have a link for Nelson Pass' comparision of the Jordan driver? I can't find it at 6moons archive

Fiddler, basically the baffle size requirement is directly related to the bass "wraparound" cancellation that is inherent in open baffle speakers. If you use subwoofers with these systems, then the baffles can be much smaller, depending upon how high you want to cross-in the subs.

For example, if you want the OB mains to only go down to 128Hz, then the quarter-wave formula would show a baffle dimension of 2' square.

"this info is mostly for jordans only or other OB drivers, OB drivers need much help to produce any kind of range.Other drivers wouldnt perform well in theses type of designs."

Johnk, if you are referring to the PHY driver, then sorry to disagree. Qt primarily determines whether a driver is suitable in OBs.

The manufacturer recommends the PHY KM 30 SAG for open baffle designs. For OBs, one just has to accept a compromise between bass response vs. baffle size. With subs, baffle size options can more real-world.

Thanks Twl, I am starting with a baffle about twice that size (but rectangular, not square) with the driver mounted off-center. In my earlier post, when I said smaller baffles, I didn't mean "reeeeal" small, I just meant in the four foot range with a plan to use subs crossed-over where the PHY rolls off.

Fiddler, that's cool.

If you keep the basic quarter-wave formula in mind, then you'll have something to lean on when deciding on baffle-related issues.

Slightly off-center driver will be a bit smoother, as would a slightly curved panel.

I wouldn't recommend going "wildly" off center for driver mounting, because as you get nearer any edge of the baffle, there could be exacerbated cancellation issues.

Assuming a four foot height rectangle, which may be (what?) around 3 feet wide? You may expect to have a decent protection against wraparound cancellation(and have bass frequency boundary reinforcement) down to around 80-90Hz.

Remember that this baffle must be rigid enough to properly allow the driver to do its thing, without flexing and causing doppler and info loss, and also must be rigid enough to not flex from the SPL which it is being directly subjected to. If you are using Lexan or plexi, make sure the thickness is good enough, and that it is somewhat braced so that it doesn't act as a "secondary radiator". It can do this, because it has a large surface area, and if it is flexing with the music, it is re-radiating the soundwaves out of phase, and will cause smear and possibly other unwanted issues. Strong is good.

Basic numbers:

For quarter-wave reinforcement above the stated freq.

Frequency / Wavelength / 1/4wavelength / Baffle size
32Hz 32' 8' 8'
48Hz 24' 6' 6'
64Hz 16' 4' 4'
96Hz 12' 3' 3'
128Hz 8' 2' 2'

If you want to use a certain frequency between these numbers, you can interpolate.