Many thanks for all your help guys. I recently replaced the MiniDSP with a Onkyo Receiver that has a digital crossover built in. It has the option for 0 or 180 degree phase for the tweeter and the woofer. Since the capacitor introduces 90 degree shift, should I add an inductor in order to make a second order crossover shifted to 180 degree and then use the Onkyo 180 switch in order to bring it back to 0? The passive crossver would be at about 600Hz and should not interfere with the active crossover, am i correct?
Hey, figured I'd revive this one rather than start a new thread, I'm using active crossovers for a new set up, I'm wondering if there's any issue in using an MLCC (class 2 ceramic) cap as a protection cap. The corner frequency of the cap would be around 1000Hz with the active crossover set to 2800Hz (4th order L-R).
Should I expect any issues with this?
Should I expect any issues with this?
@j2020 - yes, that's way too close to the crossover frequency. It's basically adding another first order HP filter, which will rotate the phase another 90 degrees.
When adding a capacitor for "protection", aim for a corner frequency that is 5-10 times lower than the crossover corner frequency when used in combination with the tweeter's impedance.
Since this subject has been re-opened, it seems to be not too clear that a capacitor does NOT offer protection for large transient events or an amp failure where DC (e.g. rail voltage) is connected to the driver. Why? Because a cap will only "block DC" under steady state conditions and will pass other transient events just like an audio signal that is high passed. Given a big enough "pop", your tweeter will be seeing a lot of energy. When the amplifier fails and the DC level goes from zero to rail voltage the cap will pass the step change at first, just as if it were a high frequency square wave. What you get after the cap is the step response of the highpass filter formed by the cap and the driver. If you look a this, it will be a large pulse of energy with amplitude reaching the new DC level before decaying back to zero (as you reach the new steady state condition). For a brief moment the full DC rail voltage will be applied to the little tweeter and that can certainly damage it if the DC is high enough.
When adding a capacitor for "protection", aim for a corner frequency that is 5-10 times lower than the crossover corner frequency when used in combination with the tweeter's impedance.
Since this subject has been re-opened, it seems to be not too clear that a capacitor does NOT offer protection for large transient events or an amp failure where DC (e.g. rail voltage) is connected to the driver. Why? Because a cap will only "block DC" under steady state conditions and will pass other transient events just like an audio signal that is high passed. Given a big enough "pop", your tweeter will be seeing a lot of energy. When the amplifier fails and the DC level goes from zero to rail voltage the cap will pass the step change at first, just as if it were a high frequency square wave. What you get after the cap is the step response of the highpass filter formed by the cap and the driver. If you look a this, it will be a large pulse of energy with amplitude reaching the new DC level before decaying back to zero (as you reach the new steady state condition). For a brief moment the full DC rail voltage will be applied to the little tweeter and that can certainly damage it if the DC is high enough.
Large value capacitors are even worse "protection," in my opinion. Charging/discharging during normal thumps/transients is not effectively minimized due to the longer time constant. A capacitor is much closer to a short-circuit than it is a full-proof protection device in this instance. 
I would suggest, if feeling the need to use a series capacitor, select a value specifically to incorporate it into the desired crossover slope. That way you'll be using a much smaller value and the "protection" aspect will be somewhat improved.
Dave.
I would suggest, if feeling the need to use a series capacitor, select a value specifically to incorporate it into the desired crossover slope. That way you'll be using a much smaller value and the "protection" aspect will be somewhat improved.
Dave.
Here's a nice write-up on the subject: BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 2
I'm using 68uF Mundorf MCaps in series with my Morel ST 728 Supreme 1-1/8" Soft Dome Tweeters.
I'm using 68uF Mundorf MCaps in series with my Morel ST 728 Supreme 1-1/8" Soft Dome Tweeters.
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Using the tweeter protection cap as the last stage of the active filter seems to be the best way to go, in terms of cost at least. And it would offer the best protection from transients.
Any idea what it would do to the properties of the filter if not selected correctly? Would additional components be required?
I've never understood going active then putting a cap in the circuit. And no, I don't believe the size of the cap has some magical effect of disappearing sonically just because it is big.
I've also never seen a quality amp thump on power cycling, the issue is almost always power cycling on the upstream active crossover, miniDSP being notorious for this. My solution was to put the miniDSP and AVR on UPS power. No thumps, even when I stupidly listen to music in thunderstorms.
Since then this has been introduced: https://www.madisoundspeakerstore.com/digital-signal-processors-dsp/minidsp-minidc-isolator/ I still like my electronics on UPS though.
I've also never seen a quality amp thump on power cycling, the issue is almost always power cycling on the upstream active crossover, miniDSP being notorious for this. My solution was to put the miniDSP and AVR on UPS power. No thumps, even when I stupidly listen to music in thunderstorms.
Since then this has been introduced: https://www.madisoundspeakerstore.com/digital-signal-processors-dsp/minidsp-minidc-isolator/ I still like my electronics on UPS though.
I don't use a cap either. My amp is rated 125W RMS. The CD is rated 450W peak. That is actually worst case unless the amp spec is conservative. Its already survived a couple of really good thumps.
I think a passive attenuator would make it pretty much bullet proof. I could move 10 db of the cut I have in the DSP XO into a couple of resistors and not have to worry about it anymore. It would also lift the CD output up 10 db higher than the noise floor.
I think a passive attenuator would make it pretty much bullet proof. I could move 10 db of the cut I have in the DSP XO into a couple of resistors and not have to worry about it anymore. It would also lift the CD output up 10 db higher than the noise floor.
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