Isobaric 8” subs

[ODougbo]

You’re going to want to find a speaker design program to download. I still use my old Perfect Box. However there are much better programs out there, I’m sure some of the more knowable fellows on here can point you in the right direction.

Incase you missed an earlier thread; I do have a little trick for a slot port:

semi build the box, to the point where the front baffle board and “slot” (glued together like an “L”) can be slid up and down, which changes the port’s volume - using a generator and volt meter you can tune the box with certainly and then do the final glue up (you’ll need a good number of clamps).

To answer your question about this box, I started with 1 8” woofer in a 2cf cabinet and tuned it to 30hz; great low, house shaking bass, however it did have some problems with bottoming out with high volume during action scenes (explosions, etc).

I decided to but two speakers in one box, to help handle the power. The design - I simply cut the volume in half and added of volume for the tunnel and extra speaker.

Originally Posted by crazycody1993

So what's the chance that the isobarick design works by having the moving mass of double the woofer? But it still has the same suspension setups giving it a lower FS, but it also has double the motor, giving it the light cone mass of the eight, and the suspension work against both cones. I could go on, but it seems like an excellent design, and I would really like to build one. Would you mind if I asked how you calculated the volume and port for the subwoofers? I have a pair of old drivers I'd like to build in a box like this.

[ODougbo]

It was a bit of a story, a friend gave me 4 cabinets with the woofers. I had 4 chances to get something to work, so by trying 4 different combinations, tuning, seat-of-the-pants stuff, I came up with this. I did end up burning up and throwing away the other 3 boxes (I was on a roll).

Foster, that sounds familiar, I think I have a pair an old pair of 10” they’re 12 ohm right?

Originally Posted by planet10

To optimally take advantage of 4 woofers you need to take a few measures... i have a stereo pair of push-push pairs of push-pull Foster 12" in the works.

dave

[planet10]

Originally Posted by ODougbo

Foster, that sounds familiar, I think I have a pair an old pair of 10” they’re 12 ohm right?

Foster is one of the largest speaker manufacturers in the world. They have likely built 1000s of different 10" drivers. Their Fostex subsidury is likely more recognizable.

dave

[Cal Weldon]

Foster = OEM.
Fostex was started to sell direct to the public.

IIRC.

[crazycody1993]

Originally Posted by ODougbo

You’re going to want to find a speaker design program to download. I still use my old Perfect Box. However there are much better programs out there, I’m sure some of the more knowable fellows on here can point you in the right direction.

Incase you missed an earlier thread; I do have a little trick for a slot port:

semi build the box, to the point where the front baffle board and “slot” (glued together like an “L”) can be slid up and down, which changes the port’s volume - using a generator and volt meter you can tune the box with certainly and then do the final glue up (you’ll need a good number of clamps).

To answer your question about this box, I started with 1 8” woofer in a 2cf cabinet and tuned it to 30hz; great low, house shaking bass, however it did have some problems with bottoming out with high volume during action scenes (explosions, etc).

I decided to but two speakers in one box, to help handle the power. The design - I simply cut the volume in half and added of volume for the tunnel and extra speaker.

So you went from 2cf to 1? as well as adding the second 8, and it still preforms just as well?

[ODougbo]

Yes, that is the process, 2 speakers ~ face to face (clamshell) – Mag to Mag – front to back, you can make the cabinet half the size. Don’t forget to add some extra volume for the 2nd speaker and/or internal “tunnel”.

I’d like to know a little more about push pull, I have a few Rockford 8” P2s around here. I tried them for HT, but they only started sounding good at higher volume levels.

Originally Posted by crazycody1993

So you went from 2cf to 1? as well as adding the second 8, and it still preforms just as well?

[revboden]

Originally Posted by ODougbo

Incase you missed an earlier thread; I do have a little trick for a slot port:

semi build the box, to the point where the front baffle board and “slot” (glued together like an “L”) can be slid up and down, which changes the port’s volume - using a generator and volt meter you can tune the box with certainly and then do the final glue up (you’ll need a good number of clamps).

using this method, how do you calculate friction loss coefficients?

the .75/10 ratio is almost Aperiodic.

[ODougbo]

Sound engineer, ohh….but I knew that before I looked at your profile. I do understand your question, to a point.

The sliding baffle idea; AKA Odoubo’s no calculator method.

[This probably won’t make any sense to people that never tuned a bass reflex speaker]

As mentioned I had the frequency generator and volt meter hooked up early on, I tried different versions (port lengths) and my measure was the amount of port air noise (keeping the high and low voltage peaks the same for each version).

I made adjustments to the length of the port (on the table saw, speakers and all) and also the height, before the final glue up.

With the experimentation, I set the port at the edge of the “wind noise” being noticeable, at same time setting the voltage swings where they looked good.

To expand on construction, the front/port, top, back, bottom need to cut at the same time; 10” wide for this project. You’ll want them all to be exactly the same for an air tight fit. The 17” x 19” sides can be cut oversized and trimmed with a router or belt sander. WATCH THE PORT, easy to forget and gouge it with a flush cut router.

[cyclecamper]

If you are not going to mount isobaric drivers "clamshell" facing each other, you might want to consider shallow-profile drivers for the automotive market for mounting with a short tunnel. There are some that are flat and shallow yet achieve relatively extreme excursion. Some place the "motor" inside the cone, others place the voice coil at the surround, some have convoluted formers, etc. etc. but it's a new creative emerging area, ALL WONDERFUL FOR CLOSE-MOUNTING ISOBARICS. Mounting the drivers closer wastes less space, and can operate to higher frequencies.

Take two of these wonderful babies from JL Audio and isobaric them, and you could get away with a really small box, or perhaps scale it up with more isobaric drivers and/or more boxes:
JL Audio 13TW5 Subwoofers - Car Audio Subwoofers

If you can't afford that:
http://www.earthquakesound.com/sws.htm

The disadvantages nobody has mentioned is inefficiency and cost. Engineering is a compromise and if you are willing to buy big amps and spend money amazing things are possible.

[ODougbo]

Thanks, The JL speakers are tempting, hard to justify buying them unless you seen and heard them in a proven design. Always wanted to experiment with their 8” W7 line, $350 bucks each though.

I saw one fellow write, one is never enough; so that’s where I would probably end up, buying a second :-/

For this box, the tunnel is 5” x 7” and the magnet is so big (the front speaker) there is not much space left in there. I did think about making the 10” by 10” plates concentric, hour glass shaped, but didn’t. As mentioned earlier, I did build a couple of clamshell boxes (leave 5/8” to 3/4"space between woofers!), I do think they had a slight advantage over the front to back, but these are much easier to look at.

Big amp for these??? naaaaaa. I had them hooked up to a 60watt Rotel, tons of bass (car crossover set at 50hz), pounded the whole workshop.

Rockford has a new shallow woofer also. For those that don’t know, Rockford has a great web site for DIY, the box wizard is very handy.