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4x 8" Subwoofer experiment.
4x 8" Subwoofer experiment.
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Old 31st December 2018, 12:08 PM   #1
Dr1v3n is offline Dr1v3n  United States
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Default 4x 8" Subwoofer experiment.

Hello, first post here in the Subwoofer dep't.
I have had 2 of these sub's working for about a year using SB Acoustics SB23MFCL-4. I was running them all in parallel for a 1 ohm load, torturing my poor Audiosource Amp3. In fact I did finalyl destroy one of these fine Amps after cranking it up without a warm-up period...

Well now they're being individually powered by IRS2092S 380W class D amps each. 2 separate 500W SMPS's powers a pair of these IRS2092S amps. miniDIGI+miniDSP are on the front end for EQ and SPDIF optical is used. Warning: These China amps needed a mod to work properly...

I've found it runs best when the 2 top drivers are run inverted from the bottom 2. The top and bottom drivers are spaced about 1/2" away from the end of the tubes, so it can be considered a vented system. Inside the tubes the drivers are very tight. With 12AWG wiring to the input connectors going around the drivers, the PVC tube slides very tightly over the bottom 2 drivers. Same when mounting the top to drivers... The PVC tube is 5/8" thick and 4ft tall and about 8.82" ID, so about 2.2cuft.

My question is how to find out the the F3 and SPL on this setup? Thanks!
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Last edited by Dr1v3n; 31st December 2018 at 12:16 PM.
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Old 31st December 2018, 12:51 PM   #2
cspieker is offline cspieker
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Am I missing something? I've never seen anything like this before. It seems to me, if the inner drivers seal against the walls of the tube, that you have a sealed alignment for those two, although it probably leaks enough that it isn't technically sealed. The outer drivers, if they are spaced away from the tube end, are operating open baffle, which at 90 degrees off axis will mean that they provide essentially no output with the back wave out of phase with the front. I would guess that it would operate better without the two outer woofers connected at all and with just one woofer per end perfectly sealed and mounted flush. Of course first the driver parameters would have to be known and modeled to find out if the enclosure volume is appropriate. Perhaps I am not understanding the picture and description correctly. Can you explain why you did not use a conventional alignment and what you thought the benefits of this alignment would be? Btw, I love oddball experiments, it's just that they very seldom work out. . Craig
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Old 31st December 2018, 01:48 PM   #3
vallickad is offline vallickad  India
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Seems to be a double isobaric sealed. Check out the part picture of the complimentary, speaker on the right.
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Old 31st December 2018, 01:50 PM   #4
cspieker is offline cspieker
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At first glance I thought the same, except for this:

"The top and bottom drivers are spaced about 1/2" away from the end of the tubes... "
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Old 31st December 2018, 01:55 PM   #5
cspieker is offline cspieker
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I guess I never answered your question though. F3 and spl is determined a couple of ways. Use a signal generator app on your phone or laptop to feed varying frequencies to the amp inputs, then use an spl meter and measure. Or alternatively and vastly better, get a measurement microphone and REW. I like the UMIK. To eliminate the room effects measuring outdoors away from any structures is best, but in room can be okay for your purposes often.
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Old 31st December 2018, 01:56 PM   #6
Dr1v3n is offline Dr1v3n  United States
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Hey Craig and thanks for your thoughts!

The initial/simpler idea comes from an isobaric design where 2 identical drivers are in phase in a sealed enclosure. The idea was to use 1/2 volume to achieve the same F3 when compared to using a single driver... I realize nowadays, subwoofer drivers have come a long way and don't need as much volume as I have here, especially considering the # of drivers.

I might agree with you that 2 drivers may achieve the same result here, i.e. 1 on each side of the tube. I can come close to simulating this by muting either the inner or outer drivers, which could simulate sealed vs. unsealed with the unused driver acting as a passive radiator? But I think under high SPL the drivers will help each other out if they're all powered.

I'll post an updated pic late. Thanks!
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Old 31st December 2018, 02:08 PM   #7
cspieker is offline cspieker
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Is there really a space between the tube and the outer driver? Because that changes everything. Any air leakage anywhere changes things entirely.
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Old 31st December 2018, 02:17 PM   #8
Dr1v3n is offline Dr1v3n  United States
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Quote:
Originally Posted by cspieker View Post
Is there really a space between the tube and the outer driver? Because that changes everything. Any air leakage anywhere changes things entirely.
The inner drivers have a gap of about 2mm equal from the ID of the PVC tube.
The outer drivers do have a 1/2" gap due to the way I currently have them mounted...
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Old 31st December 2018, 04:50 PM   #9
cspieker is offline cspieker
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Measure what you have, then convert it to a well sealed design with one driver on each end with zero air leakage, then remeasure and listen. You will find it capable of much higher output and lower F3. What you have now is impossible to model and very unlikely to give good results. I think it's awesome that you just built it! But some modeling will give better results 99.999% of the time. Do have the TS parameters for the drivers? Get winisd and start playing around. Good luck! Craig
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Old 31st December 2018, 04:57 PM   #10
phivates is offline phivates  United States
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And you can make another sub with the liberated pair of lovely drivers...
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