Eminence Lab12, ported box

[chris661]

What he said.
Another idea is to make a speaker where the drivers are at opposite sides of the box, both in phase. The result is that the box doesn't vibrate (provided you brace it properly), so colouration is kept to a minimal. You could port this design if you wish.

Chris

[sangram]

Thanks - but wouldn't I get the same gain in output level if I use 2 separate boxes twice the size of the Isobaric box? I also was thinking two subs would be significantly easier to place than a single humongous one. I do get the fact about the net cancellation of forces within the box with opposed dirvers, though, just wondering which approach will work better.

[PB2]

Originally Posted by sangram

Hi there, first post in subwoofers

http://www.diyaudio.com/forums/showp...96&postcount=3

I'm looking at building two smallish efficient subs for home use, mainly music. I'm not a basshead, but I think the L18 boxes I'm building will not be able to take too much juice and was thinking of crossing them over at the low end. The Lab12 is locally available unlike the Dayton woofers (those cost over $350 after adding shipping and customs ), as are some of the JBL pro sub drivers.

I don't have very much power (LM4780 BPA, ~150-180 watts max) so I need efficiency over extension/xmax, though I'd like to hit about 25-30Hz in-room. I don't need it to be very loud either, just enough to take the load off the L18 woofers at the very bottom (<60Hz).

My boxes came out a bit different from sreten's calculations in the linked post - 3.5cuft (not small but not too big) with a single 4x3 port, tuned to 26Hz, -3dB at 26 Hz, 111 dB SPL with 180 watts and well within the driver's excursion limits. Room is 22x18x12 ft, and two of these will be used in a stereo configuration (budgets permitting).

Does this look good to go or am I missing something? I've never built a sub before, or even needed one so I'm not sure if this is the right way to go.

TIA for your help

That is a big box, but given your limited power it will provide more sensitivity around Fb. I would consider a 20 or even 18 Hz tuning given the size of the box and Xmax capability of the driver. You'll get a more gradual rolloff that should match room gain with better power handling down low. Also, be sure to have enough port area to avoid compression due to turbulance. Multiple ports make sense here. This is the idea:
http://www.svsound.com/products-sub-box-pb13ultra.cfm

Yes to your most recent question, two boxes that allow you to position them more favorably with your mains.

[sangram]

Thanks, that's very reassuring

Re. ports, would you think a 4x3 square port will do the job? It's already pretty long this way, a bigger port will become bigger than the length of the box itself And wouldn't more ports also become pretty long? I seem to get 2-3x the length of a single a port when I add more (keeping port diameter the same, and I don't want to drop to 2 inch ports with a sub this big even given that I'm not pushing too much air)...

I suppose a downfiring port allows a slightly shorter length - in which case, how much of the floor volume should I lump with the port volume? Half? More? Less?

[danielm]

Art over on the PSW Lab sub forum has much experience with this driver in small(ish) cabinets.

[sangram]

Thanks for that Daniel, guess I should go stalk him there

[ashok]

The Lab12 has a foam surround. Eminence says that it's compressed from a large chunk of foam material. Foam typically rots in our hot humid climate . However they have not had any complaints. Does this version of foam really manage to stay without deterioration ? ( Bangalore isn't quite as hot or humid as other parts of the country !)

[sangram]

I don't know about that. I have a set of four locally made woofers with foam surrounds, which had been in storage for the last five years (and are about seven years old). The storage conditions were abysmal - they were wrapped in newspaper and left in a very hot attic, and the humidity in Calcutta hits 95% at times.

They seem to be fine, with no cracks or other damage at all, and the woofers seem to be working just as well as they did when I put them away. I think foam rot may be long-term issue, like 15 years maybe. I have not yet encountered it myself.

[ashok]

Yes, all foam surrounds are not the same. I have seen some rot within 18 months ! Some do last very much longer. It's possible that the material used nowadays is also quite different or treated some way. But it always worries me. Rubber surrounds are much better here . At least they don't fall apart with time.

[danielm]

Originally Posted by ashok

The Lab12 has a foam surround. Eminence says that it's compressed from a large chunk of foam material. Foam typically rots in our hot humid climate . However they have not had any complaints. Does this version of foam really manage to stay without deterioration ? ( Bangalore isn't quite as hot or humid as other parts of the country !)

I built four Lab subs way back when the project was first started on PSW.
I don't recall how long it has been... maybe nine years. They still perform well after being stored pratically outdoors in Texas all this time.
They will be part of an outdoor festival rig next weekend.