Speaker design myths revealed

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.

Thanks for the info Tom.

4' x 29 1/2" is what I am experimenting with using Birch ply, but the drivers are brand new and they need to be broken in. When I have about 250 hrs. on them I will do some in-room measurements to see exactly what type of bass response I am getting.

When I actually decide on the final dimensions of the baffle, I will be using .5 inch Lexan (stiff). I don't think it will flex!

Also I am going to try a unique baffle plan. I have an idea to make a wooden baffle like the Maple one pictured in the first link I posted. My baffle will be made from Koa, a beautiful wood native to Hawaii. But here's the unique part. Mounted between the driver and the wooden baffle, I am going to place a donut of 1/2" Lexan about 1/8" larger than the outside edge of the driver. So sandwiched between the driver and the Koa baffle, will be a 1/2" thick, Lexan donut. The big 4' x 29 1/2" Lexan baffle will have a hole cut about 1/16 larger than the Lexan "donut". (BTW, the Koa baffle will be 1/2" wider than the Lexan baffle around the sides and top so the 1/16" gap between the large Lexan baffle and the Lexan donut will have a backing.

When I am ready to listen, I can take the big Lexan baffles out of our coat closet, lean them against the smaller, wooden Koa baffle/driver, slipping the hole in the big baffles over the Lexan donut & driver for a really nice fit. This will be a removable baffle that is completely flush from the driver to the edge of the baffle. I suspect this may also reduce some resonance of the large Lexan baffle since there will be a 1/16 gap between the Lexan and the Lexan donut (which is sandwiched between the driver & Koa baffle.)

I plan on using an easily adjustable spike system underneath the "base" of the Koa baffle/driver to slightly raise or lower the Koa baffle/driver to perfectly fit the hole in the large Lexan baffles. The up & down adjustment will be from the top side of the "base" for convenience.

If everything was sitting directly on the hardwood floor, raising or lowering the Koa baffle/driver wouldn't be necessary, but since we have a 13 x 20 Persian rug (plus pad) which the speakers will be sitting on, there will be some settling of the Lexan baffle, as well as with the Koa baffle/driver.

When I am not listening, it will take less than a minute to remove the large Lexan baffles and place them in the closet for WAF. All that will be left in the room will be a rather small and neat 36" high x 15" wide Koa baffle/driver. (Plus subs)

To my knowledge this idea hasn't been tried, but I am pretty confident it will work pretty well (I mean the removable baffle). I simply need to break the drivers in and experiment with baffle size.

Thanks for your interest.

PS - and I apologize if my description is not clear, but it really is rather simple, just a little hard to describe on paper. If you look at the pic of the OB in the first link I posted with maple baffles it may help to visualize the removable baffle.