Push-pull sealed subwoofer

[Roland Gama]

Design: Sealed push-pull (non-isobarik) using a 90 litre box with a pair of Eminence Lab 12.
Design reminiscent of M&K. Bass Box Pro simulated F3 to be around 45Hz with 107 dB at 20hz full power.

How would this design work with actively equalizing the sub to flatter response.

Any suggestions???

[Geoff St. Germain]

Is there a particular reason that you want to use a pair of Lab 12s in a sealed box that small? I think that there are better drivers for the money and if you're using the Lab 12s because you already have them, then I think a larger box would be better. The smallest I would go with a pair of Lab 12s would be 105 L (.707 Qtc).

Also, I don't see how you're going to get 107 dB/1m @ 20 Hz out of a pair of Lab 12s in a sealed enclosure. They're excursion limited to about 103 dB/1m.

[Blaser]

I agree with you Goeff.

Roland,

Why do you chose such a configutration? Are you limited with space?

[Roland Gama]

Yes, I have a pair of Lab 12s.
Bass Box Pro simulation gave me the figures. Infact with typical stuffing in a 90 litre box the QTC is under .7
Space is not a definite factor but subwoofer choice is a big problem here in India.
JBL Pro are available. Do they have any you would suggest even if I have to go ported?

I constructed a rough prototype of the push pull design I had in mind. It sounds loud but I have not yet done any RTA on it yet. Photo attached.

Thanks for your reply.

[mdrake]

I agree with the other dudes. You might want to consider a larger box or put the woofers in an isobaric configuration, which would then require half the enclosure volume.

Matt

[sparky77]

In the push pull configuration you could actually go a bit smaller with a 60L enclosure and have pretty flat response depending on your room. I have a garage full of lab12's and have done quite a few experiments, and an isobaric configuration would be a waste fo the available cone area, stick with push pull you put together, and maybe try a few different sizes between 40 and 90L. That is unless you want to go larger and use a long slot port where you can easily dig down to less than 16hz in room response.

[thxgoon]

Isobaric would also limit output compared to a push pull setup. I lived with an MK sub for years and I can confidently say that I've never heard it's equal for sound quality. I ultimately gave it up when I started to crave massive sub 20hz output and initially considered a large push pull design, I ended up going LLT. Since you already have the drivers I'd say go push pull if max output is not your primary concern. I'd take that 107db at 20hz with a grain of salt.

[Roland Gama]

Thank you all for the supportive replies.
A pair of these would improve things in the 20 hz range by about 6dB.

I will try simulating the push pull design in LLT. The Labs are not a great choice and I may end up with a box too big as compromise.

[Roland Gama]

Hello Sparky,
The box could go smaller than 90 litres and more liberal use of polyfill. However, I have noticed that in the simulations there is a slight drop in SPL in direct proportion to the amount of fill.
What does this imply?
In your opinion what size of box did you prefer?
Thank you.

[sparky77]

For a sealed enclosure I would go with the 60L stuffed about 1/3 of the way with polyfill, for a ported enclosure it would be 290L so I would probably expect you to stick with the sealed unless you have the room. What do you plan to power this with, you'll need an amp thats either two channeled or stable to 2 ohms.

[Roland Gama]

You are spot on Sparky!
Since a pair of Lab12 in parallel will present a 3ohm load an amplifier with 2 ohms load is desired.
And since I am considering building a pair of boxes (total of 4 Lab12's) I am considering an amplifier capable of 1000watts per channel at 2ohms stability.
Harman Pro group do market their stuff here and I would probably find something from the Crown stable.