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Capacitor value for tweeter protection with active crossover
Capacitor value for tweeter protection with active crossover
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Old 5th June 2019, 05:43 PM   #1
Chopperbuilder is offline Chopperbuilder  United States
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Default Capacitor value for tweeter protection with active crossover

In the event something should ever fail in my system I would like to have a capacitor in place in series with my tweeter to protect it from receiving a full range of frequency. I have done a lot of research on this yet I haven't been able to find a definitive answer as to what capacitor value I should use for how I have my system set.

I'm using:
Audicontrol DM-810 - crossover set at 2600k Hz Linkwitz–Riley 24dB/octave slope.
A/D/S PX Concept tweeters 4 Ohm.


I have found a number of calculators on line but the ones for a single in series capacitor are for a 6 dB/octave slope. Those that I've found for a 24dB/octave slope are for building a passive crossover.

Anyone have any suggestions on what value capacitor I should use?
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Old 5th June 2019, 06:09 PM   #2
academia50 is offline academia50  Argentina
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The value of the tweeter capacitor is chosen according to the crossover with the mid range, (overlap in Db) and depends on the frequency response and the sensitivity of both transducers, to achieve a reusable as flat as possible.

A typical value would be between 5 and 10 uF. for a crossing at 5000 hertz, but that does not say much, and make sure you have good isolation in volts, 100 volts minimum!

Last edited by academia50; 5th June 2019 at 06:16 PM.
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Old 5th June 2019, 06:21 PM   #3
Perry Babin is offline Perry Babin  United States
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There is virtually nothing that could happen to cause the crossover to receive a full range signal. The benefit that you will get with an inline capacitor is blocking any DC from the tweeter if the amp fails.

I'm not sure what you meant by 2600kHz.

A single cap will only be 6dB but that will block DC. Any value capacitor will do that. Choose one that would be a bit below the crossover frequency of your electronic crossover for a 4 ohm tweeter.
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Old 5th June 2019, 06:33 PM   #4
rayma is offline rayma  United States
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Quote:
Originally Posted by Chopperbuilder View Post
any suggestions on what value capacitor I should use?
Around 100uF bipolar will be ok for protection. Much smaller will affect the crossover response.
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Old 5th June 2019, 06:39 PM   #5
Chopperbuilder is offline Chopperbuilder  United States
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The active crossover point for my mid range and tweeters is 2600 hertz. I initially chose a 17uF 100v capacitor for this but then I ran across an article talking about this subject saying that the dB/octave slope needs to be taken into account in determining the value of the capacitor: https://www.audiofrog.com/community/...ve-crossovers/

In fact the 24dB/octave slope, crossover point (2500 hertz) and tweeter resistance (4 Ohm) he was using in the article are almost identical to how I have my system set. He chose a 68uf 100v capacitor for this. With such a large value difference between the capacitor I have and the one he was using, it had me second guessing my choice. With further research I could find nothing to confirm or discredit using a 68uF capacitor as the correct capacitor for this application.
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Last edited by Chopperbuilder; 5th June 2019 at 06:45 PM.
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Old 5th June 2019, 06:49 PM   #6
rayma is offline rayma  United States
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Quote:
Originally Posted by Chopperbuilder View Post
The crossover point for my mid range and tweeters is 2600 hertz. I initially chose
a 17uF 100v capacitor for this but then I ran across an article talking about this
subject saying that the dB/octave slope needs to be taken into account in
determining the value of the capacitor:
Not really. The idea is for the high pass formed by the protection C with
the 4 ohm tweeter to be a decade lower than the actual crossover frequency,
2600Hz/10 = 260Hz. Then C = 1/ (2Pi x 4 x 260) = 150uF.
This keeps the effect on the crossover small, while keeping C to an acceptable size.
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Old 5th June 2019, 07:45 PM   #7
JMFahey is offline JMFahey  Argentina
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You might solve it two ways, both valid.

1) add a capacitor calculated to be an extra pole added based on your current active crossover.
You now a next higher slope Xover or you might use one less in the active one to leave "everything the same"
A "grammar nazi" might complain "itīs not an active crossover any more but a mix of active and passive"
He may "technically" be right but anyway .... no big deal.

2) make the protection capacitor large enough to work 2 octaves below (my choice) or a decade below (almost same thing) so it does little if at all.

In any case, donīt overthink it.

Personally I donīt worry about any input signal problem but the feared blown power amp which applies brutal DC to very weak tweeter voice coil.
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Old 8th June 2019, 03:15 AM   #8
Chopperbuilder is offline Chopperbuilder  United States
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Thanks everyone for your advice.
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Old 8th June 2019, 06:51 AM   #9
jan.didden is online now jan.didden  Europe
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You do realize that there already is a series cap as part of the crossover, which blocks DC and attenuates low frequencies reaching the tweeter?
So you are putting another one in series if you do this.

Then you have two choices:
a) make it much larger than the cap already there so as not to impact on the xover frequency, but that has no impact on the protection issue;
b) make it much smaller than the cap already there which tightens the protection but messes up the xover frequency.

The only way to avoid all this and keep the existing protection, including the DC blocking, is to do nothing.
A rare case where spending money would actually do either noting or do harm to your sound.

Jan
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Last edited by jan.didden; 8th June 2019 at 06:57 AM.
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Old 10th June 2019, 01:16 AM   #10
Chopperbuilder is offline Chopperbuilder  United States
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That would be true of a passive crossover. I am running an active crossover an AudioControl Dm-810 processor. The crossover is done pre-amp so there is nothing between the amp and the tweeter to protect it from any failure that could possibly damage it.
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