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Old 19th March 2004, 08:57 PM   #1
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Default subwoofer enclosure design questions

I've been given a couple of subs, JL Audio 12W0-4. The only problem being that they came in a tiny sealed enclosure that looks like an off-the-shelf acquisition with no regard for T/S parameters. In any case, I'm trying to come up with and build a new enclosure for these and would appreciate the opinions of those more experienced than I am. I've built subs in the past, but they were for car audio applications in the 80s and we mostly used sealed boxes and did all of our calculations by hand. Now, I'm modeling these in WinISD and I am concerned about actual performance in terms of fidelity not correlating with expectations.

I intend to mount both subs in an enclosure and use them in my home and for portable sound reinforcement in open spaces. The EBP for the subs is 49 indicating that they'd work best in a sealed enclosure, but the low-frequency extension just doesn't seem adequate for home theater LFE (-3dB at 37Hz). Modeling a vented enclosure yields a quite satisfactory low-frequency extension (-3dB at 20Hz). However, I'm concerned about this design as the recommended volume (362L for both subs) is a great deal larger than what is recommended by JL Audio(140L). I've read that when the simulator recommends a very large enclosure volume for a ported system that the driver just isn't appropriate for a ported application. I wonder what the negative effects could be? I expect poor transient response and distortion. A nice compromise would be a 4th order bandpass enclosure which has good low-frequency extension (-3dB at 23Hz) and a very small enclosure volume in an isobaric configuration. The problem is that I've never built a 4th order bandpass system, nor have I ever done an isobaric configuration. I wonder if there are any shortcomings that I'm unaware of. I'm also concerned about doing an isobaric setup and it's potential drawbacks. Will the power handling capability be the same? Advice or opinions are appreciated




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Old 22nd March 2004, 11:34 AM   #2
sreten is offline sreten  United Kingdom
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Useful alignments for home space use and open air use are quite different.

Personally don't like bandpass designs.

Isobaric loading will soak up as much juice as parallel loading,
but for the same input level produces -6dB bass, which is what
to expect from a box a quarter of the size of normal loading.

Its quite normal for the volume required for reflex loading
to be twice that of the reccommended sealed box volume.

Personally I think a reflex box, around 250L tuned to around
20Hz, would work well at home will the port stuffed and OK
in open air with the port open.

But low bass in open air ?, won't get very far.

How tiny is the sealed enclosure ?
Isobaric sealed volume useable is 35L to 70L.

sreten.
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Old 23rd March 2004, 10:45 AM   #3
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Useful alignments for home space use and open air use are quite different.

Obviously that's the case. At the risk of being long-winded, I should've been more specific. Primarily, my intention is to use these in my home and only occasionally in open air. I don't expect to be doing serious sound reinforcement, mostly just for small gatherings with very low SPL.

I've given up on doing an isobaric setup, the only real benefit seems to be a smaller enclosure, which is not something I need in this case. However, I'm still vascillating on the bandpass enclosure. With such a low bandpass at 20-60hz, I believe it would be difficult to get the mids to match the system. A ported enclosure of 250L tuned to 20hz shows good LFE in WinISD.

Personally don't like bandpass designs.

Why is that? I'm not familiar with the shortcomings of this type of enclosure. I'm mainly interested because the frequency response in WinISD looks very flat and I've never built one before.
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Old 23rd March 2004, 02:18 PM   #4
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by halbritt

Personally don't like bandpass designs.

Why is that? I'm not familiar with the shortcomings of this type of enclosure. I'm mainly interested because the frequency response in WinISD looks very flat and I've never built one before. [/B]
First off you have to consider room gain, flat to 20Hz
usually sounds completely overblown in most rooms.

All the bandpass designs I've heard have been slow sounding
boom boxes, which is enough to put me off building one.

You also need to use the SPL display, not gain to see whats
going on with your bandpass design, as you also say its low
high frequency cutoff could cause integration problems.

I get 4dB lower efficiency and much higher volumes
than you for the bandpass, 150L and 50L.

Bandpasses are useful in domestic products for increasing
upper bass powerhandling and setting the sub cutoff point.

They are also useful in PA type applications for maximising
power handling as well.

But IMO in domestic situations with decent drivers not needed.

sreten.
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