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Old 28th January 2007, 04:08 PM   #1
cs is offline cs  United Kingdom
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Default Woofer advice sought

I am interested in building a 2-way sealed box speaker based on the Jordan JX92S to handle 100Hz to 20kHz, combined with a woofer to handle 30-100Hz.

However, most of the woofers I have seen have very low Q fundamental resonances, typically in the range 0.2 to 0.4. This would be fine for a reflex or TL enclosure, but I want to use sealed box, so really need a higher Q in the range 0.5 to 0.7.

Does anyone know of suitable units ?
Other preferred requirements would be :-
8, 10 or 12" dia.
88 to 90dB/W/m
100W power handling
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Old 28th January 2007, 04:43 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

c/o at 100Hz = sattelites + a subwoofer (or two).

Qts when not in a box does not = box Q.

A driver over Qts = 0.6 is generally difficult for any box loading.

/sreten.
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Old 28th January 2007, 05:10 PM   #3
cs is offline cs  United Kingdom
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Quote:
Originally posted by sreten
Hi,

Qts when not in a box does not = box Q.
A driver over Qts = 0.6 is generally difficult for any box loading.

Yes, I realise that, which is precisely my point.

If I want to achieve a flat and extended LF response, I need an overall system Q of between 0.5 and 0.7. But if I am starting with a woofer with a Qts of say 0.3, the necessary box loading (to flatten the response) would raise the overall system fs unacceptably.

So, the woofer Qts needs to be much closer to my overall target Q to begin with (or alternatively it needs a very much lower fs, of around 15Hz).
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Old 28th January 2007, 05:27 PM   #4
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by cs

Yes, I realise that, which is precisely my point.
Hi,

well not precise enough because you don't want a driver
with Qts= 0.7, whilst your original post implies you do.

You'll find plenty of subwoofers with the right sort of parameters.

/sreten.
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Old 28th January 2007, 07:58 PM   #5
infinia is offline infinia  United States
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Quote:
Originally posted by cs

So, the woofer Qts needs to be much closer to my overall target Q to begin with (or alternatively it needs a very much lower fs, of around 15Hz).

Hi your conclusions are correct, as per your critia of vented designs being ruled out.
As I see it, your 30Hz -3dB spec , is the difficulty and severely limits the availability for drivers used in sealed woofer designs.

IMO your choices are
1) Use Infinite baffle design.
2) Acoustic suspension box with higher cutoff. If you could settle for around 45 Hz -3dB this would open up choices for drivers.
3) Use a Linkwitz transform circuit with a variation of option 2).
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Old 28th January 2007, 11:39 PM   #6
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The Dayton Reference High Fidelity 10 and 12 subs give F3's of 40 Hz and 37 Hz respectively. The 10 requires about 1 cu ft and the 12 requires about 2 cu ft. I just looked at Parts Express and the 10 is on sale now too.
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Old 29th January 2007, 02:04 PM   #7
cs is offline cs  United Kingdom
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Found a good one from Scanspeak :-
http://www.tymphany.com/datasheet/printview.php?id=106

fs=20.5Hz
Qts=0.47
Vas=46 litres

Putting this into the MJK closed box worksheet gives system fs=30Hz and system Q=0.707, for a 1.25 cu. ft. box.

Not cheap at >200 however !
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Old 29th January 2007, 09:08 PM   #8
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check this one out
http://www.hifisound.de/oxid/oxid.ph...4---ALUMINIUM/
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