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Old 14th June 2006, 11:15 AM   #1
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Default Factory Crossover Hacking

This is a repost from DIYMA, maybe someone here can point me in the right direction...

Help crossover gurus!

My car came with an OE component set, and I replaced the individual drivers. I like the sound but I'm wondering what the crossover is doing. It's 2-way with 2 coils (unknown value, smallish) and four caps (330ufd, 15ufd, 6ufd, 3.9ufd). Is this actually high-pass/band-pass to protect the 4" mids, or does each side have caps in parallel (or series)? Anyone want to take a stab at figuring it out?

I'd love to know where it's crossing over at 4 ohms, but my dirty secret here is I used 6 ohm replacements -- I assume I am getting some ugly overlap which might account for the upper mid harshness I hear? If this is the case, would it be possible (and cheaper) to replace the caps to align it right, or to buy new tweets (since I'm already planning on new mids)?

thanks a bundle in advance!
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Old 14th June 2006, 10:51 PM   #2
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A quick and dirty trick to figure out the curves is to use any of the freeware spectrum analyzer programs on a laptop that has a line input. Burn a CD of pink noise and play that through the speaker system. use a cable from the line input connected to a speaker driver and view the spectrum on the laptop. this will give a rough indication of the response curve into that driver. By superimposing all the curves, you can get an idea of the over lap. If you also keep the same volume level, you can get a rough idea of the level differences between drivers as well under real conditions.

This works pretty well. just make sure you dont clip the input to the laptop. 1Vrms is about max i would bet.


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Old 16th June 2006, 11:04 AM   #3
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Wow, cool! I will definitely try that soon. But doesn't using a 6 ohm driver in a x-over designed for 4 ohm drivers make a jagged frequency response?

I'm wondering if it's worth trying to ballpark (or measure) the inductor values and replace the caps? These tweets may find a home in my wife's car anyway...
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Old 17th June 2006, 02:01 AM   #4
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Quote:
Originally posted by GhettoSQ
Wow, cool! I will definitely try that soon. But doesn't using a 6 ohm driver in a x-over designed for 4 ohm drivers make a jagged frequency response?

I'm wondering if it's worth trying to ballpark (or measure) the inductor values and replace the caps? These tweets may find a home in my wife's car anyway...
It will change the crossover frequency and if the sensitivity of the driver is different, It will alter the frequency response.

But, by figuring out what the crossover is doing using the stock 4 ohm drivers, you can then create a proper crossover with the same specs for a 6 ohm driver. you then will have to try and match the sensitivity of the drivers. hopefully the new tweeter is louder then the old driver and you can then just pad it down to match.


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Old 20th June 2006, 03:47 AM   #5
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the 330uF will likely Indicate the HP(6db/oct) at 121Hz@4ohms or 80.4Hz at 6ohms. If I were to guess at the crossover by the component quantity I would guess a 12dB/oct LP on the woofer and a 18dB/oct on the tweeter. You would need to draw it out and measure the inductors to understand it properly.
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Old 20th June 2006, 10:29 AM   #6
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Yeah, I figured I couldn't do much without knowing the inductor values. Those 330uf hp values would explain why I wrecked my first set of 6 ohm mids and needed to add another cap. Ugh, what a mess. I may just put the 6 ohm tweets in my wife's taurus and buy myself some new 4 ohm drivers with reasonable tolerances. Still, when I have the time it would be fun to measure it.

Would I get any noticeable improvement replacing the 3 other caps with poly?
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Old 20th June 2006, 07:29 PM   #7
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poly caps will offer a bit more resolution overall,but the 15 uf cap would be very large,another option wich is less time consuming and less expensive would be to bypass those caps with smaller .01-.1uf poly caps ,just solder the leads on top of the originals ,and your good to go,if your going to reconfigure the whole crossover you might as well spend the money on dampening your doors properly,you would get more benefit than replacing all the caps
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Old 29th March 2010, 08:46 PM   #8
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Wish I'd had the brains to follow up on this years ago, but I'm finally getting around to it. I'm now using Dayton RS100 mids and the same 6 ohm tweets. From what I can tell the crossover is designed as above, 6db high pass at 120Hz, 12db low pass at 5000Hz, 18db high pass at 5000Hz at 4 ohms which results in a -3db point of closer to 3500Hz at 6 ohms -- nasty lobing. I want to replace the 6ufd and 15ufd caps with 3.3ufd and 10ufd, which should bring the point down to ~5300Hz. Not sure what dodgerblue is saying above - can I just solder these new caps on top of the leads of the old ones, and it will use them instead? Or was he talking about wiring in parallel and adding small values? Obviously, if that's the case I would have to replace them since I want to lower the capacitance.

The tweeters are a bit more sensitive than the mids, so I think I'll use an adjustable 8-ohm L-Pad to dial them in rather than play with resistors.
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