Low pass filter

[zerocover]

Anyone ever try making a diy filter for there subs/speakers.

Im trying to make a filter that with a cutoff of around 100hz for my sub. But everything I hook it up it doesnt work. Im trying to use the basic RC design with the cap at 2.2 uF and the resistor at 1k.

I have had this circuit working on other applications but for some odd reason I cant get it to work in this scenerio. Is there some thing special about car amps that need minor tweeking. I think the main problem is that the - is not just a ground. Another thing is I think that I had it working for a couple minutes but now nothing.

I know I could probubly go to the store and pick up a passive xo. But I have all the parts right here, to come up with any frequency cutoff I want with any slope, and this is really pissin me off.

[blue LEDz]

passives are not generally used for car audio subs. too much power going through them. if you keep the power low (read under 200 watts), it can be done. but for a low pass of 100 hz, you'd need an inductor that is 9 mH and a capacitor that is about 281 uF.

http://www.partsexpress.com/resources/xover.html

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=260-221

[zerocover]

The main problem is that I cant get my hands on an inductor, radioshack doesnt have it and is it really worth the $5 shipping for a 10 cent part. Otherwise I would totaly go with the time tested and proven filters.

The RC I designed should be more then capable of handeling over 400watts and I could quadruple in a heartbeat. Its just that I cant even test it, so I have to reason to start soldering stuff if I dont know if it will work.

Now this had become a challenge, Ill probubly end up hooking the filter into the rca jacks.

How much damage would I do if I ran the sub without a filter, I know in sealed boxes the voice coils overheat from not being able to reproduce the mids. But I have a ported box so I would assume it would have better heat dissipation.

[blue LEDz]

as long as you aren't totally overpowering the subs, they should be ok. but both your hu and amp don't have low pass filter's? and what resistors are you using? the only ones i've hooked to my amp outputs where for power testing purposes and they were the 100 watt ones.

[zerocover]

The headunit has 4 preamp out puts but nothing sub specific. The amp doesnt have a filter but has >0.01 THD so I dont care.

Ill just give up and order some Fmods. THe reistors are the normal radio shack ones. Becuase of there high resistance (and low resistance of a sub) very little power is dissapated in them and just about eveything goes to the sub.

[blue LEDz]

THD = spec that doesn't mean ****, until you get over 1%

that and it's one of those great specs that many manufacturers pull out of thin air and publish