Cap value for piezo tweeter crossover

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=37116
Printed Date: May 19, 2024 at 10:21 AM

Topic: Cap value for piezo tweeter crossover

Posted By: zane9000
Subject: Cap value for piezo tweeter crossover
Date Posted: August 10, 2004 at 11:52 AM

I've got a set of piezo tweeter that i want to put a crossover on but I have no idea how to determine the cap value for the high pass filter. The piezo tweeters just say that their impeadance is high but gives no ohm rating, which from what I understand an ohm rating is nessacary for determining cap values.

Help?

-------------
I had Cheetos and wine for dinenr.

Replies:

Posted By: zane9000
Date Posted: August 10, 2004 at 11:52 AM

BTW I wanted to filter out all freq. below 2kHz.

Thanks

-------------
I had Cheetos and wine for dinenr.

Posted By: stevdart
Date Posted: August 10, 2004 at 7:12 PM

https://www.the12volt.com/caraudio/crosscalc.asp#ccc and have you measured the resistance across the tweeter with a DMM?

-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Posted By: zane9000
Date Posted: August 10, 2004 at 8:11 PM

thanks, i didnt know if the DC resistance measured by my meter would be the right value for that formula. thanks a bunch.

-------------
I had Cheetos and wine for dinenr.

Posted By: haemphyst
Date Posted: August 11, 2004 at 12:56 AM

Forget the DCR... piezo tweeters are highly capacitive devices, and they should measure essentially an open resistance (very high DCR - therefor an ineffective number will likely come out when you try to apply standard formulae to "figuring a crossover cap"). Piezo tweeters do not need a crossover, they are inherently "self-crossing" due to their high capacitance. If you want to crossover a tweeter that is a piezo type, the best way to do it is with an electronic crossover, however, you'd be better off just tossing them and getting a real tweeter. If you use the numbers you get with the calculator, you will not be getting the right value components, as you will be adding two capacitances together in series, which work mathematically the same as paralleling two resistors.

examples:
4 ohms in parallel with 4 ohms will give you 2 ohms 4/2=2
4 ohms in series with 4 ohms will give you 8 ohms 4+4=8

4 uF in parallel with 4 uF gives 8 uF 4+4=8
4 uF in series with 4 uF gives 2 uF 4/2=2

I know it seems weird, but this is the way it works.

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."