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Old 24th January 2008, 21:08   #1
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Question Bandpass enclosure for JBL GT4-12

Hey Gurus,

I would like you opinion on the same as I am confused. I am planning to put in a subwoofer in a Lancer. I already have a JBL GT4-12 with me and I find that the JBL GT4-12 has got a Qts factor of .43 which is quite ok for to create a fourth order band pass box with a steady response curve between 37 and 90 Hz. But my confusion is how this thing is going to behave in the trunk. I am looking for clean deep bass as with just one Gt4-12 I am not looking much into the SPL.

Last edited by Rehaan : 25th January 2008 at 00:28. Reason: Text formatting tags removed
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Old 24th January 2008, 23:26   #2
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The GT4-12 does perform beautifully in a 4th order BP. A good choice.
With adequate power, it will deliver deep bass in the trunk.
It will also have an excellent transient response, delivering some pretty accurate bass.
Make sure you have lots of power.

Here you go. Enjoy.



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Old 25th January 2008, 00:06   #3
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Thats gonna be a BIG box.

And this is why I hate custom boxes. Too much specs to take care-of .

Sam, how much RMS would he need?
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Old 25th January 2008, 00:22   #4
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With which amp are you gonna run this sub ?
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Old 25th January 2008, 14:22   #5
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Hi Sam,

Thanks for the design. Just to clarify, do you really need it that big? Because I am able to achieve an f3 low at 30 and f3 high at around 90 (in theory) with a chamber lesser in size.

V rear 27.98 L
V front 24.5 L
Port 3.5 in
Length 8 in

Not sure if this is a good design since I am not sure about the Group delay and the vent air velocity.

Could you help me with the group delay and vent velocity factors as well?
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Old 25th January 2008, 14:34   #6
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Quote:
Originally Posted by low_bass_makker View Post
With which amp are you gonna run this sub ?
Hey LBM,

I am planning on the JBL GTO301.1. I was told it would cost me around 9000 Rs. Can you help me with choices within the price range. I would love it to be a Class D Amp.
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Old 25th January 2008, 16:04   #7
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Thats right grey price for GTO 301.1 also have a look at GTO1260BR its 60th annirversary edition available for 5500.May be you can push off your GT4-12.
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Old 25th January 2008, 16:43   #8
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Quote:
Originally Posted by Ajaybiz View Post
Thats right grey price for GTO 301.1 also have a look at GTO1260BR its 60th annirversary edition available for 5500.May be you can push off your GT4-12.
Is that a bandpass enclosure? I guess it is a bass reflex, aka vented. Was the car you installed these, a hatchback or a sedan ? Any idea how much a GTO1204BP would cost ?
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Old 25th January 2008, 19:07   #9
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Its Bass Reflex but low frequency responce is too good just check its features.
Mine is Hatchback(Swift) still that woofer and amp is waiting for suitable day to get loaded in my car(no time man) :(.
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Old 25th January 2008, 19:31   #10
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Quote:
Originally Posted by Ajaybiz View Post
Its Bass Reflex but low frequency responce is too good just check its features.
Mine is Hatchback(Swift) still that woofer and amp is waiting for suitable day to get loaded in my car(no time man) :(.

IMHO ported and even bandpass enclosures for that matter, give good results in hatchbacks... hope we get to see the installation pictures soon
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Old 26th January 2008, 12:14   #11
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Quote:
Originally Posted by Xmax View Post
Hi Sam,

Thanks for the design. Just to clarify, do you really need it that big? Because I am able to achieve an f3 low at 30 and f3 high at around 90 (in theory) with a chamber lesser in size.

V rear 27.98 L
V front 24.5 L
Port 3.5 in
Length 8 in

Not sure if this is a good design since I am not sure about the Group delay and the vent air velocity.

Could you help me with the group delay and vent velocity factors as well?

How did you calculate the sizes ??
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Old 26th January 2008, 14:05   #12
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@Sam: Why do you have polyfill on the port side of the design? What's the need to increase the virtual volume there?

@Xmax: 301.1 is a class AB. Under 10k I think Pioneer D510 (500x1@2) is the only class D mono.
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Old 26th January 2008, 20:20   #13
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Quote:
Originally Posted by low_bass_makker View Post
How did you calculate the sizes ??

I did it in a trial and error method using Bass Box pro. As i told earlier I have not done one before and therefore its all theory for me.

It would be great if i could get some info on how these measurements might behave in the actual environment based on your experience.

My requirement is to achieve the best possible flat response between 35Hz and 90Hz with minimal vent air velocity. I am ok with high group delays if they are beyond my required response curve.
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Old 26th January 2008, 23:33   #14
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Thanks for the update determinus.... I find the pioneer model to be outdated. Is it still available for purchase ?
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Old 27th January 2008, 13:07   #15
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Quote:
Originally Posted by determinus View Post
@Sam: Why do you have polyfill on the port side of the design? What's the need to increase the virtual volume there?
I was wondering the same. Esp. With 2 cu.ft. In the Ported section.

Is it intended more to reduce the velocity of the air exiting the port, and so to reduce port whistle?
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