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Old 8th February 2015, 05:40 PM   #1
marko13 is offline marko13  Croatia
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Default Custom subwoofer advice

It's my first post so hello everyone
I am building myself a custom subwoofer from a design I found on one of Croatian web pages.
I'm really low on budget so most(all) of the parts are what I manage to find around or trade for some other stuff.
It's pretty much complete now, but I have a problem with low bass.
Using tone generator and my ears I've determined that it's resonant freq is about 125Hz, what is waaay high and my low bass is weak.
Could anyone tell me if there's something I could change or build differently to get more linear response?

Specs are:
53 Liter ported enclosure
75mm port width, 170mm port length, made of hard plastic aprox 1.5mm thickness
10 inch, 4 ohm, Cort bass guitar amplifier driver
I've filled two thirds of the enclosure with pretty thick foam.
I'm sorry but getting any T/s data of the speaker is impossible and I don't have the instruments to measure it

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Old 9th February 2015, 05:54 PM   #2
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You'll need an equaliser - apply boost down to your port tuning, and then add a steep high-pass below that.

You can make one yourself, or pick up a 2nd hand Behringer or something.

Chris
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Old 9th February 2015, 06:44 PM   #3
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Remove all the foam.. I don't see it helping.
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Old 10th February 2015, 05:17 PM   #4
marko13 is offline marko13  Croatia
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Getting an eq would be a kind of a problem, since all the cheap ones are crap. I'm driving the woofer with a Pioneer GM-4000 car amplifier and signal comes from Phonic PCR2213 digital crossover, cutoff frequency is set to 140Hz and left and right signals are summed.

I tried taking the foam out, that makes the bass sound like its coming from a bathroom :/
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Old 10th February 2015, 09:00 PM   #5
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Guitar drivers rarely have a lot of "xmax", or travel. That's what you need for deeper bass. If you can find a driver from a car audio system, designed to be a sub, that may do you better.
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Old 10th February 2015, 09:21 PM   #6
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Guitar drivers often have a pitifully weak motor and high Q, although you said it was a BASS guitar driver. The dust cap does look teeny tiny though.

I calculated the tuning frequency in Hornresp to be 33-34 Hz WITHOUT THE FOAM. I'm not sure what the foam does - try removing it. It looks like you made a hole in the foam for the back of the driver? The air from the back of the driver needs to be free to move around the box and get the port resonating.

So yeah err.... remove the foam, although if you're using it as bass and mid-range you might want to line the walls with 1.5" of foam to dampen mid-range reflections, and stop it sounding umm.... like a bathroom!

Last edited by TimLewis; 10th February 2015 at 09:25 PM.
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Old 11th February 2015, 12:57 PM   #7
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If you are only using that driver for bass then why dont you chuck it into a 4th order bandpass box.
That will naturally give you an "acoustic" bandpass filter. Depending on your budget it might help to not have to try and get extra electronic filters on there.
Having a sealed chamber on the one side will help to limit the excursion of the driver.
It will also allow you to play it a bit louder due to you not hearing the distortion as easily.
Also if you dont have any parameters on the driver it is going to be very hard to model. Having a sealed chamber on the one side makes things a bit easier, you will just have to play around with your port lengths to see what sounds best.

Try a test box. The driver is 10 inches. So make the sealed side of the box 11x11x11. Make the ported side a bit larger. Try 11x11x15. Get a cheap PVC drainpipe that you can cut into different lengths to test and see which length you like the sound of more.
If you do decide to use fiberglass cloth inside then only put a bit in the ported box side.
If you are going to put a crossover on it then having extra dampening in there is pretty pointless.
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Old 11th February 2015, 01:12 PM   #8
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Guitar and PA speakers have too high resonance frequency to be subs for home use. You need to find a car sub driver.
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Old 11th February 2015, 01:12 PM   #9
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I scrolled up again.
I missed that you said you are cutting it at 140.
Are you sure that it is a low pass? If it is a high pass you not going to get much bass at all.
Also check another thing.
You are "summing" the left and right channels. Check that you are bridging your amp correctly. Just because you have sound it doesnt mean it is right.
Try one channel at a time with a good RCA cable from a good source.
Often a wonky cable will create a spacey sound without any "oompth" to it.

If you take the driver out of the box put your ear within the cone of the speaker. So quite close to the driver. On low power play some music through it.
If your "filter" on your amp and cables are working correctly, that should sound pretty sweet.
But if that basic test is lacking presence and warmth then something else is wrong.

Another test, borrow a friends woofer and see if it sounds any better than yours.
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Old 11th February 2015, 01:17 PM   #10
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Quote:
Originally Posted by richie00boy View Post
Guitar and PA speakers have too high resonance frequency to be subs for home use. You need to find a car sub driver.
Agreed

In a conventional ported box without extreme electronic filtering they cant really work.

Bandpass "might" be your only hope for some speakers where they are technically just air pumps resonating at the port frequencies.
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