Repurposing existing sealed box to ported? - diyAudio
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Old 11th October 2011, 01:55 PM   #1
Kahooli is offline Kahooli  Abu Dhabi
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Location: Cincinnati, OH
Default Repurposing existing sealed box to ported?

Question: Is there any practical reason to prevent one from having the majority of a pvc port OUTSIDE of the enclosure( meaning maybe 7" inside, and the rest outside) beside cosmetics?

Background:
I acquired two 2.6cuft sealed subwoofer Cabinet from a guy from work and am considering converting them to ported boxes for my "party room".

They are actually ceramic chimney flu liners surrounded by and bonded to two sheets of 3/4 in MDF on each side, with the baffle side and "plate amp" side being just braced mdf (no flu liner ). They are lined with rigid fibreglass. with the rear stuffed with fibrefill (unknown amount).
They are massive for a sealed 12" woofer box. He originally used them with a pair of Dayton titanic MkIIs back in their heyday, with a final Q of 0.50000

I have no real desire to use them as a sealed box, I have no subwoofers that would work well in that size enclosure, nor do I desire to buy them.

Goal:
Use a pair of subs I have in my basement, design a ported enclosure with V<= 2.6cuft; if the port is external, as low tuned as possible with external tubing, maximizing response to 19Hz (+0-3db to 20Hz), port velocity <19m/s at max power, never reaching the excursion limit of the driver (23mm lin one way xmax).

Note: If I could cut through flu liner I would just use some new css PRs, but alas I cannot!
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Old 11th October 2011, 03:21 PM   #2
johnr66 is offline johnr66  United States
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Other than looking odd, no reason you can't extend the port outside the box. 2.6cu/ft is fine for a decent twelve. I wouldn't tune them so low. Hoffman's iron law. I'd use bigger drivers and boxes for better efficiency for those low frequencies. Human hearing rolls off quite a bit, so you need more SPL to hear those low frequencies with any real impact. Tuning so low also squanders the efficiency of the woofers for higher bass 30hz on up where it has real impact. I'd tune such boxes in the mid 30Hz range, but no lower than 30Hz, If for HT, build bigger boxes.
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Old 11th October 2011, 03:29 PM   #3
bbggg is offline bbggg  United States
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Quote:
Originally Posted by Kahooli View Post
Question: Is there any practical reason to prevent one from having the majority of a pvc port OUTSIDE of the enclosure
None, a port can be inside, outside, or any proportion thereof.
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Old 11th October 2011, 05:57 PM   #4
Kahooli is offline Kahooli  Abu Dhabi
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Space considerations in the room prevent anything larger than this pair of boxes, unfortunately. I would prefer to make a giant LLT style pair with a different driver but right now, 2 subs I already have and a pair of sealed boxes for $35/pair was all I could swing to this project.
So many projects, so little time.
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Old 11th October 2011, 11:27 PM   #5
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considering a driver with the excursion you quote, you're going to have a tough time tuning down that low in a box that small. if you don't have the TS specs for the drivers, i'd start with a 6" pipe 34" long and see how it goes, should tune to about 28Hz.
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Old 12th October 2011, 01:08 PM   #6
Kahooli is offline Kahooli  Abu Dhabi
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Fs 25.21 Hz
Qms 4.748
Vas 41.71 L
Cms 121.9 umN
Mms 326.8 g
Rms 10.91 mohms
Xmax 23 mm
Xmec 32 mm
Dia 25 cm
Sd 491 sq. cm.
Vd 1.129 L
Qes 0.383
Re 3.6 ohms
Le 1.319 mH
Z 4 ohms
BL 22.07 NA Tm
Pe 1000w (up to)
Qts 0.354
no 0.169
SPL 84.3 1W1m
SPL 87.89 2.8V1m
Attached Files
File Type: zip DIYMA REF12.zip (721 Bytes, 4 views)
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Old 12th October 2011, 01:29 PM   #7
Kahooli is offline Kahooli  Abu Dhabi
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A quick sim puts me at 17m/s port velocity @ 25Hz @ 600watts

2.4 cuft box with 5x47.6in vent @21hz
Attached Images
File Type: png conex.PNG (38.8 KB, 33 views)
File Type: png magresp.PNG (39.6 KB, 33 views)
File Type: png portvel.PNG (37.7 KB, 33 views)
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Old 12th October 2011, 10:29 PM   #8
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5"x47.6" vent has pipe resonance of 147Hz. unless you are going to cross very low that's bad. I try to stay below 34" for vent lengths so they keep resonance above ~200Hz.
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