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Old 8th November 2011, 07:54 PM   #1
sheep is offline sheep  Canada
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Default 2 x woofers alignment questions

I've never tried to build a multispeaker sub before.

I want to use 2 8" woofers in a subwoofer box. That makes for a speedier output than 1 bigger, heavier cone driver.
If the box is closed, do I need to use double the volume as for a single woofer?
For a bass reflex alignment, do I need to change box or tuning if adding an additional woofer? If so, how would I do that?
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Old 8th November 2011, 08:05 PM   #2
Boscoe is offline Boscoe  United Kingdom
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Whether it be closed or vented double everything except port length.
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Old 8th November 2011, 08:33 PM   #3
taloyd is offline taloyd  United States
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Quote:
Originally Posted by sheep View Post
I've never tried to build a multispeaker sub before.
I want to use 2 8" woofers in a subwoofer box. That makes for a speedier output than 1 bigger, heavier cone driver.
This is not true. The larger driver will likely have more swept area, and so will require less excursion for the same output, reducing distortion considerable.

However, if you are hung up on two drivers, use a configuration that maximizes that application, like a PPSL, or mounted on opposite sides of the enclosure, for force cancellation. If you DO put them on the same side, at least invert one for even-order distortion reduction.

In regards to your question - yes, two of the same driver will require double the box volume. Download Unibox and play with the tuning. Again, if you are hung up on two 8" woofers, look around carefully - most are woofers, not subwoofers. The Fs (natural resonance) of the driver will give it away - an Fs <40 Hz. is most likely a subwoofer.

The best advice? Follow an established plan design for a subwoofer. Then it'll definitely be successful!

cheers,
-Tal
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Old 8th November 2011, 08:35 PM   #4
sheep is offline sheep  Canada
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For a bass reflex, do I also need to change the vent area?

What are the pros/cons of a single chamber vs separate chamber for each speaker?
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Old 8th November 2011, 09:41 PM   #5
Boscoe is offline Boscoe  United Kingdom
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Quote:
Originally Posted by taloyd View Post
This is not true. The larger driver will likely have more swept area, and so will require less excursion for the same output, reducing distortion considerable.

However, if you are hung up on two drivers, use a configuration that maximizes that application, like a PPSL, or mounted on opposite sides of the enclosure, for force cancellation. If you DO put them on the same side, at least invert one for even-order distortion reduction.

In regards to your question - yes, two of the same driver will require double the box volume. Download Unibox and play with the tuning. Again, if you are hung up on two 8" woofers, look around carefully - most are woofers, not subwoofers. The Fs (natural resonance) of the driver will give it away - an Fs <40 Hz. is most likely a subwoofer.

The best advice? Follow an established plan design for a subwoofer. Then it'll definitely be successful!

cheers,
-Tal
Two drivers = higher sensitivity? You double VAS so you don't really gain anything I guess.

Two drivers? Why not? 2 x 8" = 12" surface area wise so it really dosen't matter. Just keep an eye out for the parameters you won't get good results with a woofer like taloyd said.

Yes you also double to vent area but not the length. Imagine joining two boxes together.

Two separate enclosures? I guess the only positive is one slightly weaker driver won't get pushed by the other but this wouldn't be noticeable especially in a vented box, two different boxes is just more work and more materials.
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Old 8th November 2011, 09:50 PM   #6
sheep is offline sheep  Canada
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I have downloaded Unibox 4.08. What does PPSL stand for?
The sub would cover up to say 140 Hz so maybe its really a 2 x woofer system for each side.
Anyways I have some 8" EPI woofers and I believe free air resonance is 20Hz.
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Old 8th November 2011, 10:36 PM   #7
Boscoe is offline Boscoe  United Kingdom
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Quote:
Originally Posted by sheep View Post
I have downloaded Unibox 4.08. What does PPSL stand for?
The sub would cover up to say 140 Hz so maybe its really a 2 x woofer system for each side.
Anyways I have some 8" EPI woofers and I believe free air resonance is 20Hz.
Yep that seems good and would be something I would go for, so you have 4 8" woofers in total?

PPSL is Push Pull something or other! Basically 2 drivers in a vented dox firing into a cavity which boosts performance.

There's a thread.
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Old 9th November 2011, 05:18 PM   #8
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Quote:
Originally Posted by sheep View Post
That makes for a speedier output than 1 bigger, heavier cone driver.
No! Subwoofer drivers move incredibly slowly - at 50Hz, 10mm p/p travel gives an average speed for one stroke of 1m/s. This cone movement is slow. The speeds become much higher in the hundreds of Hz, where 10mm p/p at 500Hz needs 10m/s cone speed - a heavier cone will lag then overshoot etc.

I'd almost always take a larger driver than a bunch of smaller ones of equivalent cone area: a decent 10" subwoofer driver will move 1" without much problem. A 5" driver will have a lot of trouble matching this. 4 of them, while having the same cone area, will still be moving way too much for their size, and therefore go into distortion much earlier than the 10".

Chris
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Old 9th November 2011, 05:19 PM   #9
sheep is offline sheep  Canada
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I have several EPI 8" woofers from speaker units.
I may try others with glass composite or even aluminum cones.
I believe 8" is more dynamic than to use a larger, heavier 12" woofer.
Even a 10" cone sounds slower.
Thanks for all the help.
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