The eight inch peerless 850137 ?

[sagamotto]

Has anyone used this driver for a paasive sub ?
I am currently working on a pair of open baffle and in need of some low end.
The driver i am using is consist of 8" coax fullrange and a peerless 830685 (6.5 midbass) and dayton ND20FB-4. All wrap up in 1st order 6 db at 220-1325 hz and 1325-9000. So far it sounded alright, very open sound. I am thinking doing something with the Peerless 850137 for the low end but could find very much info on the web. What would be an ideal box size for about 20 hz tunning?

thks

[charlielaub]

Although I could not find a datasheet for this driver, I did find one for the 8 ohm version, the 850136, which probably has similar T/S parameters. It looks like this is an older Peerless CSX woofer. This is not really a subwoofer, as it only has about a 4mm Xmax and is an 8" driver.

First of all, I would not ever, ever use a single 8" driver to 20 Hz even if some design program indicated that the driver would have F3=20Hz. You can expect problems from harmonic distortion at higher bass frequencies when the poor little 8" driver tries its best to woof out 20 Hz. Output at that frequency will be very limited because the total displacement (Sd*Xmax) is not sufficient for much output. In short, the driver will barely be able to generate enough SPL at 20Hz to be heard (as a pure tone) and all you will hear is the harmonic distortion products. Finally, specific to this driver, the Fs for the 850136 is only 28 Hz and it has a low-ish Q so I assume the 850137 is similar. If so, ina vented box you probably cannot get flat response to 20 Hz without getting a large peak in the response around box resonance and that would require a large Vb/Vas so it might not be all that practical.

This driver would probably be great to 40 Hz or maybe 35 Hz. That gives good bass, although not the lowest octave. The benefits of trying to reproduce sound below 30 Hz are few unless you want to really get serious about it (e.g. with a bigger and more suitable driver).

Also, you might think about factoring in room gain. Sometimes you don't need flat (anechoic) response to 20 Hz to get relatively flat in-room response to 20 Hz via a combination of driver output and room gain. Smaller rooms work in your favor here, although they would not work in the favor of an open baffle type speaker. You can estimate room gain using Jeff Bagby's Baffle Diffraction and Boundary Simulator. IIRC some combination of a closed box speaker with low Q and the room gain of a small-to-medium sized room can give you flat extension to 0 Hz, so this approach does have its merits!

You might consider purchasing one of the Dayton 12" or 15" RSS drivers (subs) and put it to use as a single subwoofer to give you the low end that you are craving. These drivers are first rate and have relatively low distortion.

There is another approach - a near field subwoofer! That's right. Make a subwoofer that you sit on, preferably firing up in to the seat of your chair. This requires much less output because you are only at most 3 feet away from the driver, plus you get extra good vibrations thru the chair. This also does an end around any room response irregularities because of the properties of the near field.

Have fun! (but don't use an 8" driver to 20 Hz! )

-Charlie