Quick Question, 2 Woofers in 1 Ported Enclosure

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LineSource

LineSource

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Joined 2003
When putting two identical woofers in a single ported box.

-Double the single-driver box volume.
-If your port has "sharp" ends on both sides, then you can just double the port tube length.
-If your port has rounded ends on one of both sides, then you should run a few calculations to get accurate construction details.
-The port resonance will increase, and this might become audible. You may want to change port diameter.
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With high-output woofers, a single volume with two woofers "might" generate angular rocking of the cones which "might" generate voice coil rubbing on the pole steel. Pro-woofer cabinets often use multiple ports in balanced-pressure baffle locations.
 
JShadzi

JShadzi

Member
Joined 2016
LineSource said:
When putting two identical woofers in a single ported box.

-Double the single-driver box volume.
-If your port has "sharp" ends on both sides, then you can just double the port tube length.
-If your port has rounded ends on one of both sides, then you should run a few calculations to get accurate construction details.
-The port resonance will increase, and this might become audible. You may want to change port diameter.
==========
With high-output woofers, a single volume with two woofers "might" generate angular rocking of the cones which "might" generate voice coil rubbing on the pole steel. Pro-woofer cabinets often use multiple ports in balanced-pressure baffle locations.
Click to expand...

Thanks for the responses everyone!

So to confirm, double port length as well? I am modeling two 6.5" drivers in a 28l box, when I model for 1 driver with a Vas of 35 it says make the 2.75" diameter port 8" long, when I double Vas the port length drops to 3.5", seems like it's compensating for the Vas change no?

Thanks!
 
system7

system7

Member
Joined 2008
You pretty much double everything with two drivers.

Two boxes, two ports, two crossovers.

Here's the thought experiment.
 

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system7

system7

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Joined 2008
JShadzi said:
Ok that's easy enough, so in that case you'd keep Vas the same and just double the enclosure volume as well as number of ports?
Click to expand...

Exactly. The crossover, however, depends on series or parallel wiring because of the relative loudness involved. There's also a slight complexity with a single tweeter.

But essentially, if you've got a good design for a single woofer and tweeter, you can easily convert it to an MTM or MTTM.

You then gain that PA type sound which projects well to the back of the room.
 
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JShadzi

JShadzi

Member
Joined 2016
Anyone have an issue with calculating the volume for one driver, then halving the enclosure size to calculate port size and length for a tuning resonance with 2 drivers?

So for example, say I want I run a calc for one driver a 2 cubic feet and I calculate a 3" port that is 8" long. Then I run the same calculation but for 1 cubic foot which now calls for an 11" long port.

Then I build a 2 cubic foot box with a 3x11 port and install both drivers in it.

Does that work?
 
JShadzi

JShadzi

Member
Joined 2016
john k... said:
The correct information is that you would double the volume of the single driver case and, if the port diameter remains constant you would reduce the port length by around 1/2 or more to keep the tuning frequency constant.
Click to expand...

Thanks guys for your input! I really want to understand this to be sure I do it right.

So in my example above, according to what you wrote, I calculate for a single driver, and run that driver in 2 cubic feet for 2 drivers vs 1 ft for one. Port length changes from 11" to 8" in the calc, does that sound correct?

Thanks for the help everyone!
 
J

jReave

Member
Joined 2012
Unibox
WinISD

Unibox suggests Vb=21.5L, Fb=43Hz and a port= 5cmx12.5cm per single driver.

For 2 drivers in the same box, Vb=43L, Fb=43Hz and the port=7.5cmx12cm (or 2 x (5cmx12.5cm).

But here's a thought - put each driver in a separate chamber with its own port. This has the added flexibility of allowing you to fine tune your speaker's LF response to your room by stuffing a single port if you find that the bass ends up on the boomy side.
 
JShadzi

JShadzi

Member
Joined 2016
jReave said:
Unibox
WinISD

Unibox suggests Vb=21.5L, Fb=43Hz and a port= 5cmx12.5cm per single driver.

For 2 drivers in the same box, Vb=43L, Fb=43Hz and the port=7.5cmx12cm (or 2 x (5cmx12.5cm).

But here's a thought - put each driver in a separate chamber with its own port. This has the added flexibility of allowing you to fine tune your speaker's LF response to your room by stuffing a single port if you find that the bass ends up on the boomy side.
Click to expand...

Thanks! That lines up exactly with what I calculated, I appreciate it. I'll think about the separate enclosures as well, definitely a good point.

Thanks everyone!
 
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