7" sub? What to do?

[Carlp]

I have a generic 7" "subwoofer" that I got for almost nothing. I decided it was a good place to start playing around with subwoofers. I don't really need 20 or 30 Hz material as I'm more of a mid-bass and up kinda guy, so please humor me.

Dual voice coil (8 ohm, 4 per coil)
FS = 58 Hz
SPL = 88
Vas = 0.7 cu ft
Qts = 0.83
Xmax = 3.5 mm

Using my limited modeling abilities in a vented box I get a tuning frequency of 28.8 and cut-off of 19.6 with a 2" vent of 0.2 inches. Problem is, the box volume is over 6 cu ft! I'm not gonna build that. Forget WAF, the MAF (me acceptance factor) won't fly. Even a sealed enclosure would apparently be about 2.5 cu ft. Better, but still probably no go, at least for now.

I'm probably fine with a low end closer to 30 or 40 Hz. This project is likely to accompany a pair of 4.5" fullrange BD Pipes - a TL design - that I love but miss the low end on. Anyone care to suggest an approach that will nicely fill in the low end (maybe up to about 100-120 Hz) in a NON-Theater application?

Thanks!

[chris661]

ESP - The Linkwitz Transform Circuit

Pick your lower limit with care: I used a pair of 8" drivers in a fairly small room to attempt 28Hz. Did okay until turned up, movies nearly killed it (lots of gain to get it there, so any explosions and the coil hit the backplate).

40Hz would be a reasonable target, then add a high pass to stop the cones wobbling around on stupidly low stuff.

Chris

[mashaffer]

My first thought was a 40Hz horn or tapped horn but that Q is pretty high and might give you some trouble.

[revboden]

get a real driver...

example : SD270A-88 is 36$

[Carlp]

Thanks, all. The ESP page is worth a close look. It will at least help me learn a ton, though the power limits on this driver at 40 watts may be it's undoing. I had originally considered a tapped horn, but my guess (I didn't do any math) was that it too would be pretty big, a lot of work and I hadn't considered the high Qts. As for other drivers, I'm in the learning stage so want to work through this before spending any real $$. And for me right now, $36 plus shipping for the driver alone would be fairly real $$. But that driver looks good to a true el-cheapo-holic like me. Someday...

For now, I may just cob together a BIG experiment just to see what it can do. I recall one time seeing a sub built from a sonotube (was it Nelson Pass'?). Maybe I could do something like that for use in my barn.

Carl

[j.michael droke]

Originally Posted by Carlp

Thanks, all. .... I may just cob together a BIG experiment just to see what it can do. I recall one time seeing a sub built from a sonotube (was it Nelson Pass'?). Maybe I could do something like that for use in my barn. Carl

Yes, google-up El Pipeo, Nelson Pass's extream bass pipe experiment
....regards Michael

[chris661]

Originally Posted by Carlp

Thanks, all. The ESP page is worth a close look. It will at least help me learn a ton, though the power limits on this driver at 40 watts may be it's undoing. ......

Carl

40 watts is pretty loud.

You're likely to run into excursion troubles: in terms of subwoofers, 7" is small, so is 3.5mm Xmax.

Have you tried the driver in winISD? - this has the capability to add a Linkwitz Transform to a driver in a sealed box.

I'd advise aiming for a Q=0.5 (after eq) - this isn't as flat (in free space) as Q=0.707 (considered maximally flat), but once room gain and boundry loading have taken effect, it should be reasonably flat.

Chris

[CharlieLaub]

With the high Qts and Fs of the driver and the limited Xmax, you are really not talking subwoofer use here. You could try it in a 4th order bandpass enclosure. A very large vented box + series capacitor is another possibility. Both of these maximize the low Xmax of the driver while giving some low end extension, but be prepared for a box size that is probably several times Vas.

What is really limiting the low end is the high Fs near 60 Hz. A large vented box can be tuned below Fs, but this is really not an ideal driver for anything!

Good luck!

-Charlie

[mashaffer]

The more I look at it the more it looks like a cheapish car sub. Cabin gain would help. If you have a need for a car sub that might be worth a try. It does look more like a mid bass driver than a sub.

[DrDyna]

It's probably remarkably similar to the woofer that's in my Monsoon computer speaker's "sibwoofer" as I like to call it. It's a little box about 10 inches square with an anemic little OP amp plate in it.

It'll let you know if someone kicks a bass drum, but it won't tell you what it sounds like, if that makes any sense.

It looks like there are some good suggestions around here, but with the parameters of that driver, I wouldn't expect anything insane. It's probably best used like this one, for a little sib to be used for computer speakers, or in the door panel of your car.