JBL w15gti MKii Best Ported Enclosure? - diyAudio
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Old 29th February 2012, 01:25 AM   #1
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Default JBL w15gti MKii Best Ported Enclosure?

I have a 15" JBL GTI sub that i want to use for my main room/TV/Music/Movies system. I'm modelling a box in the 8-9 cubic foot range with approximate exterior dimensions of 49" tall, 21" wide 19" deep. I like the winisd curve tuned at 25hz so far but would like any and all input.

I am considering casting concrete or using braced MDF. For MDF i can get 1.125" thick for $85 cut to my specs. My dimensions allow me to build this with only one sheet of MDF. Or i could use two .75" sheets for about the same cost.

I want this to by cheap, DIY, and great.

Concrete would be cheaper and the weight is not a problem.

Its currently powered by a 1400 watt jbl car amp, in a 4.7' box with two GTi subs. The box they came in is very poorly made (particle board) and i want to go down to just one sub as two is really too loud. I figure one sub in a great box with more power will be superior to the two subs in a junk box.
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Old 1st March 2012, 09:43 PM   #2
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Today i've been thinking about a curved slot port design and curved top. Walls would be MDF, top curved concrete. See crude MS paint design. I'm thinking i can use tempered hardboard to form the curves and fill with some concrete to make it very dead. Please comment and make recommendations.

Also if you think i should stick with a simple round port let me know.
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Old 1st March 2012, 11:35 PM   #3
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A 9 cubic foot box/225lt, tuned to 20Hz, with a 8" port, looks really good!

It will handle 1Kw, if you use a HPF at 19Hz, it seems to have a very flat response, and gives around 115db@ 20Hz.

I would leave out the concrete, 1" MDF well braced will be fine. Slot ports are great too, I just think round ones are easier and look better!

John.
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Old 2nd March 2012, 12:14 AM   #4
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I don't think i can fit an 20hz 8" round port in the space i have. Unless i made it a down firing port. What would be the cons of tuning a little higher, say 23-25hz? i could hit 120db tuned at 25hz.
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Old 2nd March 2012, 03:43 PM   #5
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8 cubic feet tuned to 23-25Hz is fine too, at 23Hz a 8" port only needs to be 26" long, so with the 8" clearance you should have around the port, you would need a dimension of around 34", either height or depth.

I only suggested 20Hz because its a nice round tuning for your needs,20-25Hz is perfect for this sub, and the box size you want. Will you use a power amp?
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Old 2nd March 2012, 06:42 PM   #6
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I have a JBL GTO 14001 car amp and a power supply to run it. The amp is rated to produce 1500 watts rms at 2 ohms and 1200 at 4 ohms. I have enough DC current to expect about 600 watts true rms. If that is not enough i can get another supply and a capacitor. The amp's frequency response is 20hz-330hz and has a highpass filter. Does that usually mean it won't play below 20hz at all or just a steep roll off?

I'm trying to fit two 6" ports now since i really want front facing ports. I'm going to have to make the box bigger.
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Old 2nd March 2012, 08:36 PM   #7
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Latest design:
49" tall, 24" wide, 26.25" deep. 1.125" MDF, a full sheet is used for the four walls. Top, bottom, and bracing will be .75 MDF.
14.122 internal volume, subtract 1.25 for the ports, .135 for the driver, and i have 12.737 cubes. I'm thinking two 6" ports 20" long. So depending on bracing volume the tuning will between 22.5hz to 23.25 hz.

This won't be too much cubic feet right?
WinISD says i'l have a max port velocity of 28.74 meters per second at 800 watts. By 30hz its only 10.5 meters per second. Will I likely hear any port noise out of dual 6" ports? I'm thinking not.
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Old 11th September 2012, 10:32 PM   #8
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it is rated down to 16 hz, how does calc look for an enclosure, and what are measurements?
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Old 11th September 2012, 11:17 PM   #9
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I would use birch plywood for for the box, much lighter and stiffer. Cheap 3/4" 5 ply birch. JMHO.
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Old 11th September 2012, 11:47 PM   #10
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Quote:
Originally Posted by turbodawg View Post
I would use birch plywood for for the box, much lighter and stiffer. Cheap 3/4" 5 ply birch. JMHO.
Err.. what??
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