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Discussion Starter #1
I have 2 JBL JT5-12 subwoofers ( http://manuals.harman.com/JBL/CAR/Boxes and Parameters/GT512Tech_050108.pdf ), that I wanted to make into a music subwoofer, both driver's in 1 box. I modelled the driver in Win isd but I must be doing something wrong?. I wanted to drive the sub's with a Jaycar 600 watt module (AA-0509). The response in a sealed box is better but no extension. Ported is all over the shop.
Any help would be great. Thanks
 

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The JBL JT5-12 appears to be a single 4 ohm sub, 2 will have to be wired in series for a 8 ohm load. The AA-0509 amp will produce 300 watts at that load. A 2 ohm load is not possible as the amp won't handle it. The modeling assumes a HPF at 18 hz. To maintain a Q of 707 it's going to take a large sealed box of 18 cu.ft. Ported is a lot smaller at 10 cu.ft.

JBL JT5.JPG
 

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The red graph looks a lot better to me. What about excursion?
 

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A stronger amp would do a better job for sure...
 

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Discussion Starter #6
Was hoping for alot smaller box, that is huge. Please help me to understand the graph's more if I was to put these sub's into a 110 lt box tuned to 34 hz, as the manufacturer recommends. I modelled it and its not a very flat response, but if your only playing music with not much sound below 30 hz why do you still need a hpf.
 

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I was to put these sub's into a 110 lt box tuned to 34 hz, as the manufacturer recommends.
That recommendation is for car audio. Home applications are different. Here is a SPL graph of 3 models. All are in 110 liters and with 300 watts input.

White - tuned to 34 hz, big hump in the response. It would take two 4 inch ports 12 inches long to keep the air speed down.
Green - tuned to 20 hz, much better response. One 4 inch port 18.75 inches long. Air speed is good until 18 hz, then it gets too high.
Yellow - sealed but the Q is .885. I have no idea how that would sound. I'll ask Josh to join in here.

JBL JT5 Comparison.JPG
 

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The sealed having a Q of .885 may be a bit ringy, or not. It sort of depends on the driver's used. JBL's are usually at-least decent even on their lower lines so they'd probably still sound quite good. It doesn't look like the response will be peaked up so that is a good sign and with the limited xmax on these it would help control the excursion a bit. I don't think that it would be very noticeably different until you get the Q even higher like 1.0.
 

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Discussion Starter #10
I will give the white the go, I'll keep the box and port's so I can adjust the tuning. Unfortunatly i've never been a fan of a sealed box, but saying that, I've never listened to one with a huge amount of power driving it. I thinks for music, this will surely be the way to go.

And so it begin's. 110 litre's, 34 hz tuning and 2 X 4" port's, 12" long.

Thanks Heaps.
 
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