Capacitor value for tweeter protection with active crossover

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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?
 
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!
 
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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.
 
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...p-tweeters-in-systems-with-active-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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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.
 
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 "it´s 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, don´t overthink it.

Personally I don´t 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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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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If your tweeter is actively crossed at 2600hz then I would use a capacitor good enough for 1th order at 1300hz to 2600hz. So for 4 ohms the capacitor I would use would be at least 15uf and less than 30uf. You actually could go up to n uf but is useless and you will not be able to find a quality polypropylene cap in such higher values.
 
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:.....
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.

Hi Chopperbuilder,
I have gone through queries and answers in this thread and you said nothing of the AMP you're using for your precious tweeter: which model?
It should be an high class product as well as DM810 and speaker itself, I guess.

I did check the DM-810 manual and i.m.m.o. this one is the typical incredible hi-tech product as just only AudioControl could have engineered at date...other overseas renowned brand should take it as reference on their engineering boards.

So, this said, you have in your hands a "toy" it can.. "make coffee" for a number of people asking for different tastes at once!!
I agree with Perry as I do not see any way your tweeter would be damaged by amp freq. output and power with a 24db/oct 2,6kHz hi-pass, especially if your amp is driving just the PX concept ones, and being your choice not on a very poor one...
You maybe would apply more care about good sound matching with midrange speakers, not for dc protection against amp output blown.
Pls consider the following as of my modest knowledge:
- declared x-over freq. of a device indicates a -3db point in freq. response;
- 24db/oct slope meaning that lower octave of 1,3kHz is reproduced with at least 8times halving of the nominal amp power output (roughly 0,375W by 100W amp);
- a speaker's ohmic curve (impedance module) arounf its Fs freq. is always higher than remaining usable frequency range, that is meaning even a lower output than the up-written in this range region;
- inserting a passive component will change phase module response...;

Many many years ago (eighties...) when amplifiers were really weak and easy for them to output dc voltage (along with current of course) even if NOT blowing but just only badly clipping (!) I was used to suggest installers inserting a glass FUSE just at the tweeter positive terminal ! (I began an artisan diy production of those parts) and this after tenths of horn and poly-dome tweeters blown nonetheless typical 3,3 or 4,7 uF 63v and even 100v non-polar electrolytic caps in them.

Hope have given some useful hints for you to have more clear ideas on your issue.
 
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