help with 2 woofer, compound, vented sub

[rhizomaticon]

Folks--

I have a pair of used, older Peerless 831758 woofers I would like to re-use in a relatively small subwoofer. In hoping to keep the box small, I'd like to do a compound woofer alignment. In hoping to keep the design simple, I'd like to mount the woofers front to back and vent the rear woofer using the cabinet architecture. Something like this:
_____________
| | |
| / /
| | |
| \ \
| _____|___|_
|_____________

I've been trying to do port calculations using the cross-section area of the cabinet port and the lengths are coming out really long for even a very short port (right now working with a 10" interior dimension), or the tuning frequency is coming out too high. I suppose I could narrow the port to shorten the length/lower the tuning frequency, but I thought I'd ask before I go down my own little rabbit hole whether this entire design idea is really the best way to get the deepest base extension from these woofers in the smallest box possible? So any suggestions on meeting that goal are welcome.

TIA

[planet10]

By using a compound woofer you halve the Vas, and when you tune a small box low you get a big port. What do your sims look like?

dave

[rhizomaticon]

Thanks for the reply.

My attempt at an ASCII diagram failed miserably, but if you add some spaces you might get my intent.

I roughly understood the relationship between Vas, small box, and port, but the numbers I'm getting are crazy (5 foot vent length tuning to 25 Hz?). I wanted to make sure my calculations weren't off-- sounds like all the benefits of halving the Vas and box size get lost in a ported design because you have to make the port so big.

If by sims you mean software simulations, I have none. This is hand calculated (really, Excel) out of Dickason's Cookbook.

I'm thinking of switching up and just going sealed. This will allow it to be really small, and tight. Since it's really mostly for music in a little sub/satellite system, I might as well.

Thanks

[bjorno]

Originally Posted by rhizomaticon

Thanks for the reply.

My attempt at an ASCII diagram failed miserably, but if you add some spaces you might get my intent.

I roughly understood the relationship between Vas, small box, and port, but the numbers I'm getting are crazy (5 foot vent length tuning to 25 Hz?). I wanted to make sure my calculations weren't off-- sounds like all the benefits of halving the Vas and box size get lost in a ported design because you have to make the port so big.

If by sims you mean software simulations, I have none. This is hand calculated (really, Excel) out of Dickason's Cookbook.

I'm thinking of switching up and just going sealed. This will allow it to be really small, and tight. Since it's really mostly for music in a little sub/satellite system, I might as well.

Thanks

Hi,

Port size solved.Suggestion:Build a multi-folded 42L T-TQWT with series connected coils and Vas= Vas/2.

I doesn't get smaller than this, tall if single folded but more compact if multi-folded.

b

[planet10]

Sealed, Q=0.7 (20 litres net), 0.58 (34 litres net), 0.5 (58 litres net)

I did a vented alighment, 55 liter, tuned to 25 Hz, 4" vent needs 62cm long port.

dave

[picowallspeaker]

Hey!I was half sleepy and half awake this morning ...in the twilight
And I was thinking : is it possible that with all the big amount of woofers that all the DIYers have in hands ,nobody uses them in "compound" ??
Is it push-pull ,right ? Or I'm mistaken That's what are my boxes currently . And I was thinking also ...dreaming...of inductors and the Mystery Of BSC (and sensitivity ,you know ) ...because after more than twenty years of little study and practice around cabinets without any aid ,little by little I'm getting into it .
I'm using two 6.5" in p-p in a very little box with a very little port ,and they're doing fine until distortion arise , etc. The problem is to find a driver to tame the enormous BSC /low cut ,in fact I used to call them "a sub+a tweeter" but now it's 3 way (3" closed mid ,0.75" tw this being filtered 3rd order ,the others 1st order)

[rhizomaticon]

Originally Posted by bjorno

Hi,

Port size solved.Suggestion:Build a multi-folded 42L T-TQWT with series connected coils and Vas= Vas/2.

I doesn't get smaller than this, tall if single folded but more compact if multi-folded.

b

Bjorno-Tak sa mycket (sp?). A lot of the technical stuff and the T-TQWT acronym are lost on me, but FYI these woofers were originally used in a simple transmission line tower I built about 12 years ago and they produced unreal bass (but didn't ever real move enough air). Thanks for the diagrams and analysis runs-- I'll try to make sense of it and see if I can do, as you suggest, a small footprint, though maybe tall, t-line sub. I'm still leaning toward the simple compound sealed box, because it will be tiny. I have sats right now to go with it, but they will eventually move back to another room/system, at which time I might try to do some tiny coaxials or full range sats and see how small I can go

Thanks