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Is there a rule of thumb (or better) for baffle width vs. low frequency cutoff?

I have a 12" bass driver in a sealed box, decent on bass, but of course I want to limit it's upper range. It is great at 100Hz, not so good at 500Hz.

How wide a baffle do I need to get close to 100Hz. I'd be happy even with 200-250Hz.

Assume the baffle is atop the 12" driver box, ~39" AFF, and over 24" off of the rear wall.

Several different drivers to use.......


BTW: I know the bass box is too small. Switched drivers. Theoretically ~0.5dB bump @ 92Hz, -3dB @ 46Hz. Made it 39" tall so I could place my experimental OB drivers at seated ear level on top of it.

Picture shows bass box in question with an unfortunate choice of drivers on top. Hey, I'm experimenting and learning!

There are some rules of thumb, but they don't necessarily translate well into the real world.

That said, as an example from the real world, the Basszilla crosses over at 150hz, and uses an 18" wide baffle.... Some people think they sound OK

Roscoe

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I can explain it to you, but I can’t understand it for you.

Just a correction. The 18" wide baffle on the Basszilla corresponds to a 250Hz crossover point. The Lowther version extends the height and adds wings on the sides to extend the baffle size. I seem to recall a graph on optimum baffle size, there also should be a baffle size calculator on the web someplace.

David

That seems to contradict the information posted here: http://www.blackdahlia.com/html/tip_43.html

Roscoe

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I can explain it to you, but I can’t understand it for you.

Thanks, while (according to Roscoe's link) the BassZilla does have a HP filter for the Fostex @ 150Hz, I didn't read much about the LF extension due to baffle dimensions alone, only that the driver is filtered to >150Hz.

So, assuming that David McGown is correct (and heck, he owns them), then 18" buys me about 250Hz. That should work out nicely.

The Room Equalization Wizard software and my UMM-6 mike will let me measure and see if it works out that way.

I'm going to measure the drivers outside and inside. The more I learn, the less I know.

REW: http://www.roomeqwizard.com/

UMM-6: http://www.parts-express.com/dayton-audio-umm-6-usb-measurement-microphone--390-808