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-   -   Need some help designing a low pass filter. (http://www.diyaudio.com/forums/subwoofers/170866-need-some-help-designing-low-pass-filter.html)

Boscoe 26th July 2010 08:29 PM

Need some help designing a low pass filter.
 
Basically I'm desgining a low budget sub. I am going to use THIS driver and assuming that if it has two coils could I out left and right through it? I don't quite understand that tbh! Anyway I need an active low pass filter for the sub for sub 150Hz into 8ohm for this driver. Can someone give me a hand?

Thanks
Boscoe

cbj591 27th July 2010 06:00 AM

Good morning -

By looking at the sub, it is a dual voice coil driver. Each voice coil is 8 ohms. You may use one for 8 ohms, or both in series for 16 ohm, or both in parallel for 4 ohms.

An active crossover is an electronic crossover that is inline with the signal before amplification. The speakers parameters do not have anything to do with the design of the crossover.

Design link - Sub-Woofer Controller

A passive crossover is a crossover that filters a full range signal (using chokes and capacitors) from the amplifier and limits the frequencies going to the driver. See the following link for design calculators. 1 - 4th order = 6db, 12db, 18db, and 24db roll off.

Just enter the frequency (150hz) and ohm rating that you will be running the speaker at and it will calculate the correct values for you. Since you will not be using the high pass part of the calculator, just enter the same ohm value and click calculate.

Just disregard the high pass info and use the lowpass.

ERSE - Crossover Calculator - First Order 2 Way
ERSE - Crossover Calculator - Second Order 2 Way
ERSE - Crossover Calculator - Third Order 2 Way
ERSE - Crossover Calculator - Fourth Order 2 Way

Good luck
Brian

Boscoe 27th July 2010 08:52 AM

Thanks a lot, so can I put two different channels into each voice coil? If not how can I combine the two channels in the sub without making everything else mono?

rikvancoolwijk 27th July 2010 09:37 AM

when you put a right and a left signal in the diferen vc's and the signal is is stereo (diferent per chanel) you will rip the woofer apart.

Greets Rik

Boscoe 27th July 2010 10:10 AM

Okay then how do I combine the left and right channels for it?

rikvancoolwijk 27th July 2010 10:18 AM

as Brian stated you van drive them with a mono amp series 16 ohm or 4 ohm paralel, you can also combine the stereo signal into a mono signal with a active lp filter and than feeding the left and right chanel with the same signal.
you'll need to make sure the signal is the same.
its better using a mono amp

rikvancoolwijk 27th July 2010 10:30 AM

or do you already have an amp you’re going to use for the project, if you are what kind of amp? some amps you can use as mono amp in btm (bridge tight mode)

AndrewT 27th July 2010 10:34 AM

Quote:

Originally Posted by Boscoe (Post 2255074)
Thanks a lot, so can I put two different channels into each voice coil? If not how can I combine the two channels in the sub without making everything else mono?

use a sumer (adder) circuit. An opamp wired for inverting mode ADDs the two inputs to give one output.

Repeat the input resistor for as many inputs that you want to ADD/SUM

If you use an MFB filter as your low pass then it uses the same inverting topology and you can combine the summing function with the filter function in one opamp. You get a 2pole active rolloff and sumer.

Be wary of using Left and Right into a dual VC driver. If the signals are not in phase the VC cooling will be reduced and you could burn out the driver.

cbj591 27th July 2010 12:49 PM

You can hook up the left side to one voice coil and the right side to the other. That was the initial intent behind the dual voice coil speaker design.

You just need to make sure that the voice coils are hooked together in phase.


Brian

Boscoe 27th July 2010 01:50 PM

So you can do it. That makes things a lot easier and things in phase is just making the wires are the right way round as I am using the same amps and filters on each channel.


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