Car Audio & Crossovers

Kryten

Old Cow.
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Dec 22, 2003
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Alright folks, heres one for you.

One of my rear speakers popped in my car a while ago, and I've been messing about with kit I've got lying around. I've not a penny to my name, so going out and buying stuff like amps and active crossovers is a no-go.

But, being electronically minded and an obsessive tinkerer, I'd like to have a go at wiring things up myself.

Basically, I've replaced both the 8" fullrange units in the back with a pair of 2" tweeter/midrange units from an old pair of Tannoy monitor/studio speakers - which despite the size are far superior in quality and volume.

Now, the same units had a pair of mid-woofers in, and this has gotten me thinking a little - perhaps it'd be worth slapping those in elsewhere in the boot (out the way and not intrusively sounding/looking). Therefore I'd need some form of crossover system - basically to delegate highrange/tweeter functions to the 2" drivers, and low range/sub frequencies to the woofers.

I'm not after chavvy-town-neighbour-annoying-badger-buggering in car systems, I'm just after some semi-decent audio levels and separation for literally no money.

It doesn't look like it'd be too difficult to make an in-line passive crossover system - it appeared my old Renault Megane had one built in, each speaker had a capacitor attached which filtered the signal to tweeter/midrange.

Problem is, I don't know where to start on doing this. I can get hold of capacitors and coils easily - obviously the values I'd need I don't know. Googling around shows up endless sites with a "simple walkthrough" you need a PHd in Bullshit to understand.

So, is this anything someone here has done, or would be able to advise on?
 

Tom

I am a FH squatter
Joined
Dec 22, 2003
Messages
17,179
I don't suppose you have any graphs of frequency response for each driver? Probably not, in which case its going to be hard for you to design a crossover that will work effectively on your two drivers because you won't know at which point on the two response curves both drivers meet. Unless you have a microphone, tone generator with speaker, and oscilloscope, you're not going to get that information any time soon. If you have access to a Lindos test set that will help things, as they can plot graphs easily.

The important thing is that you don't feed LF signals to the tweeter because you'll just damage it.

You also need to know the impedance of the finished circuit - get it too low and you could blow the output transistor of the amplifier.

Have a read of section 5 here:

Passive Crossover Network Design

It gives practical examples with which you can experiment. You could do it on veroboard, or just hard wire the circuit, but again, without accurate response curves for your drivers, you're going to struggle.
 

Kryten

Old Cow.
Moderator
Joined
Dec 22, 2003
Messages
3,351
Cripes, this is what I mean.
I thought it was gonna be as simple as "slap an inline cap here, here and here and bob's yer uncle".

I'll probably find a cheap one on Ebay ;)

Cheers anyhow
 

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