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Old 22nd February 2003, 01:27 PM   #1
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Question Simple variable subwoofer Crossover..

ive got my 1st real subwoofer from acouple of days and need to
build a good simple variable active crossover to be placed in my
car (working 0-12V) ,
all i need that it can be adjusted variably from about 10-150Hz
for a single JBL GT3-12 subwoofer and heres the parameters:

Diameter: 12"
RMS Power Handling:225W
Peak Power:1800W
Voice-Coil Diameter:50mm
Mounting Depth:155mm
Qes:0.6
Qms:5.53
Qts:0.54
Vas:100.45 ltr
Fs:28Hz
Sealed Enclosure (vol):40ltr
Frequency Response:35Hz - 3kHz
Sensitivity:89dB
Impedance:4 Ohms
Vented Enclosure (vol):50ltr

am going for SQ. and abit of SPL so igonna build a 60liters enclosure to give about Qtc of 0.88, and it gonna be powered with about 300watt rms. amp.

so ijust need a recommendations or guiding to agood one way
subwoofer crossover schematic..

thanks alot for any inputs..
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Old 22nd February 2003, 01:58 PM   #2
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A 6db/oct crossover is easy to make adjustable by adding a pot.

12db/oct can be made adjustable but it is more complicated.
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Old 22nd February 2003, 02:06 PM   #3
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Default in a car you won't worry that much about noise

there are two easy ways to do this -- you can use a a couple digital pots (as I pointed out on a previous post) and continuously adjust the f3db point. see the analog devices pdf on the AD8400 digital pots and use a Dallas device. Since you are only covering one octave you don't need to switch the capacitor.

You can also use the Linear LT1563 adjustable 4th order low pass filters. The f3 point is determined by 100X the desired frequency. So use an LM555 as a multivibrator, a flip flop to clean up the pulse and a pot in the RC element to control the frequency. The LT1563 has a bit of "clockthrough" noise but this shouldn't be noticeable at all in a subwoofer application.
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Old 22nd February 2003, 04:15 PM   #4
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Default Re: in a car you won't worry that much about noise

Quote:
Originally posted by jackinnj
there are two easy ways to do this -- you can use a a couple digital pots (as I pointed out on a previous post) and continuously adjust the f3db point. see the analog devices pdf on the AD8400 digital pots and use a Dallas device. Since you are only covering one octave you don't need to switch the capacitor.

You can also use the Linear LT1563 adjustable 4th order low pass filters. The f3 point is determined by 100X the desired frequency. So use an LM555 as a multivibrator, a flip flop to clean up the pulse and a pot in the RC element to control the frequency. The LT1563 has a bit of "clockthrough" noise but this shouldn't be noticeable at all in a subwoofer application.
unfortunately, idont understand chinese!!
comeon man, ireally didnt understand a word..

all ineed is a simple active sub. crossover with diff. freq. points
its ok if isee a schematic with a fixed freq. then ill attemp to make
it variable..

so any schematics??
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Old 23rd February 2003, 11:58 AM   #5
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hello...
where r u knowledgable guys?!
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Old 25th February 2003, 01:47 AM   #6
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Default I erred, it's the LT1063

not the LT1563 -- early dementia setting in.

One of the editors of AudioXpress did an article with a sinewave generator using the LT1063 as the low pass filter (I remember as they printed my correction) take a look at the product descriptor and you will get the idea.

Jack
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