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Old 16th June 2009, 02:08 PM   #1
stuman is offline stuman  United Kingdom
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Default jl 8w7 home design.

ok, i plan on using this driver in a home subwoofer powered with an o-audio plate amp with 500 Watt RMS of bash power into 4-ohm.

using the theil parameters on the JL website plugged into winISD. it looks as tho in a 65 liter box tuned to 22HZ it will reach flat to 20Hz. however i emailed JL audio asking what they thought and i got a very automated response quoting the box from their website.

"65 litters is too big of an enclosure for the 8w7. You need no more than 32 litters with a port 15sq” by 26.75” long." is what i got. this would mean -3db at about 32Hz.

if i don't need stupid amounts of spl would this sub work in the 65L ported box and produce up to 100db at the 20Hz mark? or am i missing something?

if not what would you guys recommend?

Also, has anybody from the UK used o-audio bash plate amps? price seems good?

Stuart.
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Old 16th June 2009, 06:13 PM   #2
stuman is offline stuman  United Kingdom
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ok, just realized,

guessing that the size is limited by the resonant frequency of the driver and its a bad idea to go below? over excursion?

if so would a sealed enclosure equalized down to 20hz work better?

Stu
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Old 16th June 2009, 08:48 PM   #3
GM is offline GM  United States
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Qts dominates its size, hence a box considerably larger than its tiny Vas, but did you notice how big/long the vent needs to be to tune it? This driver wants to 'feel' a TL or TH variant to 'be all it can be'.

GM
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Old 16th June 2009, 09:01 PM   #4
stuman is offline stuman  United Kingdom
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it wanted to be about 22" long but 10" wide and an inch high off the top of my head. would you then say that using the sub in the box recommended by JL would be the way to go? or keep it sealed like their fathom range and give it a 12dB/octave boost down to 25Hz?

Stu
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Old 17th June 2009, 08:42 PM   #5
GM is offline GM  United States
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Hmm, that's too small for a low compression vent. It's more like ~21.24"^2 x 41" long to get down to a 5% mach speed and why it want's to 'feel' a TL or TH variant.

GM
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Old 17th June 2009, 08:58 PM   #6
stuman is offline stuman  United Kingdom
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ok, in which case would a driver like this work well in an enclosure of about 30L sealed with a linkwitz transform circuit and about 500W RMS of power? i don't need mortar destroying SPL just a very clean low end in a small enclosure.
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Old 17th June 2009, 09:07 PM   #7
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Without at least +6 dB of room gain/20 Hz I seriously doubt it as the average peak SPL up higher will only be in the mid 90s, so unless you watch movies at below average HT SPLs it won't be able to keep up with the mains. Obviously, only one way to know for sure though.

GM
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Old 17th June 2009, 09:15 PM   #8
stuman is offline stuman  United Kingdom
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yeah makes sense. so back to the original idea then, 65Liter box tuned to 22Hz would this be able to produce what winISD says it will? or should i just go with a bigger driver? something like the dayton reference SQ 12" ?
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Old 17th June 2009, 11:42 PM   #9
GM is offline GM  United States
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Well, BIB (bigger is better) rules in speaker design, but if the specs are accurate and it doesn't compress too much at high power it should do it with the caveat that it probably has a high Le since it's not published, ergo it will have a rising response, peaking around 100 Hz, so still may not have enough dynamic headroom to EQ it flat unless the room helps out. Again, only one way to know for sure.

The Dayton OTOH has what I call a near ideal set of specs in that Vb = Vas, Fb = Fs will work fine and it has a known low Le, so lacking any other details and no personal experience with either, I'd go with the Dayton in a MLTL or similar to reduce the vent length requirement a bit as well as wind up with a somewhat more acoustically damped alignment.

GM
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Old 18th June 2009, 12:14 AM   #10
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Hi stuman,

If my T/S parameters used are in the ballpark for the JL8W7 driver and if the missed Le parameter is corrected , I'm suggesting you making/testing your own version of this folded Tapped-TQWT using HR.

As Gm wrote:'ergo it will have a rising response, peaking around 100 Hz ' a sharp cut-off LP-filter at about 80 Hz or lower is probably needed for this driver, for good SQ reasons.

b

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