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Ported box plans for JBL GT5 12"


Sweety

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After 16 years of use my old JBL GT3 sub has has gone into retirement & has been replaced with a brand new JBL GT5 12". I know JBL recommend a 1.75ft^3 ported enclosure with a 4" tube port 10" long but here in the UK i'm finding it very hard to get 4" pvc pipe unless it's thick walled drainage pipe which you can only get in a 10ft length & it's not cheap? so am thinking of maybe a slot port or using 2x 2.5" round ports which I have, the sub is being powered by a JBL amp pushing 220WRMS bridged at 4 ohm. I was wondering if someone could possibly give me a plan for an enclosure of something like 1.8-1.9ft^3 my max width is 35.5", hight of around 15" & with as least depth possible so I keep as much room in the trunk as I can 

 

Thiele-Small parameters

FS(Hz) 29
VAS(l.) 54
QTS 0.58
QMS 6.39
QES 0.61
BL(Tm) 15.2
CMS(mm/N) 135
RMS(kg/s) 6.359
LE(mH) 0
MMS(gr) 223
VD(l.) 0.753
SD(mm.2) 53000
X-Max(mm.) 14.2
X-Mech(mm.) 0
RE(Ohm) 4

General specifications

Max power(W.) 1100
RMS power(W.) 275
Number of coils 1
Impedance Z-Nom(Ohm) 4
Reference efficiency η0(%) 0
Sensitivity(dB) 1-W 85.2
Sensitivity(dB) 2.8-V

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To give you a port area to shoot for I think you need to provide a desired tuning frequency. At 35Hz you would need about a 17 square inch port, which is much larger than 2.5" tube. I used Triticums Port area calculator, which I recommend you get acquainted with. I just went with a slot port because I got tired of looking for tubing and didn't want 6' of it in my apartment.

I pulled 35hz out of my ass, not recommending that tuning.

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25 minutes ago, Bret said:

To give you a port area to shoot for I think you need to provide a desired tuning frequency. At 35Hz you would need about a 17 square inch port, which is much larger than 2.5" tube. I used Triticums Port area calculator, which I recommend you get acquainted with. I just went with a slot port because I got tired of looking for tubing and didn't want 6' of it in my apartment.

I pulled 35hz out of my ass, not recommending that tuning.

Thanks for your input Bret, I was looking at setting the tuning to 33-34hz, I may have tracked down some 4" pipe but at the moment can't find a 90' bend to fit it as I really need to keep the enclosure as shallow as I can for room in the truck. The car is a Ford Mondeo which is like the Ford Fusion sold in the US I was planing on having the sub rear firing along with the port but am now wondering if I had the port firing to the side if it would sound ok

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As long as you don't have anything obstructing the port , out the side is fine.

And the area of a 4" circle is 12.57. Someone else will have to chime in here, I don't know if that would give you port noise or not.

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