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locost subwoofer problem.
smart51 - 20/8/09 at 07:35 PM

I've made an under seat subwoofer for my other car because the bass from the front speakers isn't very good and there's no space to improve them further. The idea was this: Car speaker in a very thin box that fits under the seats. Larger volume enclosure than the fronts will help the bass response, as will the reflex ports. A 6mH inductor acts as a 1st order low pass filter at 100 Hz so that it only adds to the bass. Even if the bass response is not appreciably lower, an extra 3dB from another pair of speaker will give some more lows.

It all works beautifully at very low volumes. At moderate volumes it distorts badly. shorting out the inductor kills the distortion and the whole thing can be turned right up cleanly.

I've used an inductor wound on a ferrite ring about 50mm in diameter, because I found some. Keeping junk is great isn't it.

Could it be the ferrite core that is causing the distortion? Would an air cored inductor be beteer? They aren't cheap and I don't want to buy a pair just as an experiment.

flak monkey - 20/8/09 at 07:40 PM

The other alternative is just buy a pair of crossovers? You know they will work and its less hassle?

http://www.maplin.co.uk/Module.aspx?ModuleNo=3389&C=SO&U=strat15

http://www.bluearan.co.uk/index.php?id=SKT900584&browsemode=category

smart51 - 20/8/09 at 07:50 PM

The maplins crossover is 1200Hz which is no good. I like the other link though. They are cheap! Sadly 8 ohm crosovers don't work with 4 ohm speakers. The values are all wrong and you get a very odd frequency response. A bargain at the price though.

oadamo - 20/8/09 at 08:05 PM

buy amp amp with a built in sub channel then you will get some nice bass.
adam

flak monkey - 20/8/09 at 08:07 PM

Damn, oh well worth a try

I also assume you have seen this reference chart for the values of the components?

http://www.the12volt.com/caraudio/cross4ohm.asp

David

Macbeast - 20/8/09 at 08:47 PM

Maybe the current at high levels is saturating the inductor core ?

MikeRJ - 20/8/09 at 09:57 PM

quote:
Originally posted by Macbeast
Maybe the current at high levels is saturating the inductor core ?


It's certainly possible. This is the reason why using random ferrite cores for inductors can cause problems, unless you are only using them for very low currents.

smart51 - 27/8/09 at 07:46 PM

An air cored inductor solved the problem. 300 turns rather than 70 is a lot of wire and a lot of winding but it works. Now to make another for the other side.