sub box construction

Hi all,

         I am after some info about building a dual speaker sub box. All the info I can find is for one speaker not two! I have heard that with the two speakers in the one "Sealed" or "Ported/Vented" box sizeis reduced by 50%. Is this true??? Also, if i decide to build a ported/vented box, do i need two ports or just the one?? The speakers will be in the one chamber. Not individual chamers! 

The subs i will be using are Blaupunkt, velocity, vcs12

I have all the data for the subs from the manual but it dose not say anything about two speakers in the one box.

thanks for all your help. 

More than likely the information from Blaupunkt is for each sub. So, if you make it twice as large as it would be for 1 sub, and add another identical port, it will be fine.

Or you could build 2 identical boxes ;)

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Thanks jmelton86 for the info,

I was thinking that with just doubling the size with the extra port but was not to sure.

Does any one know about the box size being smaller with the secon speaker? (insted of just doubling the size) I think it has something to do with the different pressures in the box with the second speaker which allows it to be smaller??? Is this true or just crap???

It's not that simple.  You need to calculate the correct size for the performance you want.  Putting two speakers into one enclosure is not always just doubling the specs for one, and it NEVER involves doubling the specified port!  For a very rough idea of what you need, go HERE and enter the data from your woofer's spec sheet.

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You can half the size of the required enclosure by using two speakers, but overall performance will suffer. It is called an isobaric configuration. The key to making it work is one speaker has to be wired out of phase of the other. You can then build an enclosure half the size that would be required for one speaker. The drawback is you'll need twice as much power (you need to power both subs with identical power) and the output will roughly equal the output of one sub.

The important thing about ports is port volume. You can use one port as long as the one port has the same volume as what the two ports would provide.

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Kevin Pierson

And to steal a saying from another person on another site...... minimum space = minimum bass.

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KPierson wrote:

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You can half the size of the required enclosure by using two speakers, but overall performance will suffer. It is called an isobaric configuration. The key to making it work is one speaker has to be wired out of phase of the other. You can then build an enclosure half the size that would be required for one speaker. The drawback is you'll need twice as much power (you need to power both subs with identical power) and the output will roughly equal the output of one sub.

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I suppose it depends on your definition of "suffering".

1: Half the volume for the same extension, frequency response, and total system Q. Bonus.
2: DRAMATICALLY improved linearity, perhaps the greatest BENEFIT to an iso-loading. Bonus.

Those aren't detractions to me...

Certainly, there are detractions...

1: Expense. You have to buy twice the drivers...
2: ...and that's all I got...

Big fan of iso loads!

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Sorry, that wasn't very clear. By "suffer" I meant you will not get the output of two subs in an isobaric configuration.

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Kevin Pierson

Why not just build a box twice the size of what they recommend for one sub and add .75" to the length(provided you're using .75" MDF) then in the direct middle, put a divider the size of the your sides of the box so it acts like it is 2 separate boxes, but it looks like one box and will sound great too.

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BP