Best use of these 8" Seas drivers? - diyAudio
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Old 8th April 2006, 04:27 PM   #1
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Join Date: Feb 2005
Location: Boston, MA
Default Best use of these 8" Seas drivers?

So, I pulled a pair of Seas CA21RE drivers from the car (they wanted a bigger enclosure than I had room for) and decided to augment my home setup: AR-XA table, NAD 3020 amp, Boston A60 speakers.

I was looking at straight push-pull designs until I stumbled on all the sonotube hype. Went to Home Depot and got a 5' length of 8" quickrete tube, stuffed it and mounted one driver. Pretty cool. Cut off 1" and made a mounting ring for driver #2, out of phase. Much cleaner, faster, a bit less SPL.

System is passive with an old Allison sub x-over (not exactly sure of the freq., it's 200Hz at 4Ohm, all speakers are 8Ohm. 5mH coils and 110uf caps, 12db 2-way. Speaker Workshop seems to still have it around 200Hz).

I don't fully understand the relationship between Vas and Vb, but according to Shultz's calcs I need an Sd of 10.25" -- a 10" tube should be pretty close.

So, should I mount both drivers push-pull in a single 10" tube, single 8" tube, or separate them into dual 8" tubes like Pass recommends? Either way I plan to put a 3/4" MDF box around the whole thing for looks and rigidty, and I may eventually use something like that nice MCM buyout plate amp, but it will stay passive with this x-over for a bit.

Relevant specs are:
Qts: 0.48
Vas: 81.3l/2.871ft^3
SPL: 91db
Xmax: 6mm

I have the rest if need be.

Thanks to all in advance!
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Old 9th April 2006, 01:04 AM   #2
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Duh, driver Fs is 31Hz too. The length and stuffing seems to tune to 37.5Hz. And I didn't mean Sd above, I meant the CSA. Thx!
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Old 17th April 2006, 03:47 PM   #3
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I can't believe no one has an opinion?

When I went from an 8" to a 10" tube, the bass definitely got lower although I lost some punch in the midbass range -- this is consistent with what I've read. I'm still confused about stuffing density and Vb though.

I realized that I had gotten 4' tubes and not 5'! The 10" tube gives me a Vb of 2.181ft^3, the driver's published Vas is 2.871ft^3 and I'm using 2 in a push-pull if it matters. I plan to add another 6" by building a box, giving a Vb of 2.454ft^3, but it's still below the Vas. What can I expect from a 12" tube?

Also, the quarter-wavelength at 4' is 70.625Hz -- how low will the stuffing get it? I've heard that stuffing can "effectively double" the line length, reduce the SoS to 2/3 (for a tuning freq. of 47.08333Hz?), or reduce the SoS to .7-.9 (and yes I realize this is an apparent rather than actual reduction). Shultz's charts say I should shoot for 1.5lbs/cubic foot! Can anyone explain this stuff or point me in the right direction?

Finally, John Risch suggests tuning for lower than Fs with a moderate-to-high-Q driver -- the Seas' .48 seems to fit that bill. I could possibly get pretty close with a stuffed folded line using my 2 tubes or the 10" and a 12". Everywhere else I've seen tunings higher than Fs, so I would be OK between 38-43Hz...Help!

TIA
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Old 18th April 2006, 12:05 AM   #4
simon5 is offline simon5  Canada
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Location: Québec, Québec
Not much users here built TLs in their life, but maybe GM or someone else will step in this thread and help you.
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Old 22nd April 2006, 04:36 PM   #5
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Join Date: Feb 2005
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Or maybe I'm asking the wrong questions?!?

I saw GM recommend to someone else to do 2 tubes with the SLS-10...starting to rethink the wonders of push-pull. I suppose I can try my 10" tube on one side, 8" on the other and compare with the fader, since I have them.
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Old 24th April 2006, 06:00 AM   #6
simon5 is offline simon5  Canada
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Or maybe GM don't look into threads that don't have TL in the topic line hehe!

Maybe reply in the SLS thread and ask help to the folks in there...

Look at this website for a bit of help :
http://www.quarter-wave.com/
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