I need to protect a very expensive Focal Be tweeter in an active crossover setup with a MiniDsp 2x8 digital crossover. The crossover frequency is 2200Hz. What is the absolute best capacitor for this purpose and what is the value that you guys would recommend. I am new to this hoby and would really appreciate your help.
Thanks in advance,
Chris
Thanks in advance,
Chris
Try this link here.
The point is to protect the tweeter from DC, pops, or really low frequencies that usually come from equipment turning on or off.
First, you need to select a frequency for the capacitor that is below your intended crossover point for the active crossover. Since caps can vary as much as 20% for their stated value, you should account for any tolerances in that selection point. Check the specs for the capacitor you select.
At or above the tweeter's lowest usable frequency is a good point for the protection cap. Going lower is probably not going to matter since there should not be any program material down there anyway.
Second the quality of the cap is not really going to be super critical, so don't go wild, but do select a good one and do not use electrolytic caps.
Madisound sells some good caps and Parts-Express is another source.
The point is to protect the tweeter from DC, pops, or really low frequencies that usually come from equipment turning on or off.
First, you need to select a frequency for the capacitor that is below your intended crossover point for the active crossover. Since caps can vary as much as 20% for their stated value, you should account for any tolerances in that selection point. Check the specs for the capacitor you select.
At or above the tweeter's lowest usable frequency is a good point for the protection cap. Going lower is probably not going to matter since there should not be any program material down there anyway.
Second the quality of the cap is not really going to be super critical, so don't go wild, but do select a good one and do not use electrolytic caps.
Madisound sells some good caps and Parts-Express is another source.
This is the tweeter I am using:
Focal Grande Utopia technologies: tweeter Beryllium IAL2 generation.
From what I understand, the lowest safe operating frequency is 528Hz. The operating crossover setting is going to be 2200Hz. I don't know the impedance of the tweeter though, in order to calculate the capacitor value. How can I measure it?
Focal Grande Utopia technologies: tweeter Beryllium IAL2 generation.
From what I understand, the lowest safe operating frequency is 528Hz. The operating crossover setting is going to be 2200Hz. I don't know the impedance of the tweeter though, in order to calculate the capacitor value. How can I measure it?
On my last big loudspeaker project, I was running totally active. On the Altec compression driver I was using, I had a Solen 51uF cap on the drivers for a 400Hz point. The driver was actively crossed at 600Hz, 4th order. I just had the cap there for any possible turn on/off thump the amp might have put out, though it never did.
To put a cap in an active setup is going backwards.
Test the amps with the actual drivers and squarewave at a low level-this should reveal any amp instablities with that driver.
Use a protection circuit with a delay at switch-on and fast turn off as psu falls - mine also incorporates dc detection.
Test the amps with the actual drivers and squarewave at a low level-this should reveal any amp instablities with that driver.
Use a protection circuit with a delay at switch-on and fast turn off as psu falls - mine also incorporates dc detection.
It sure is! That is why capacitors are used with active amplification for safety purposes. Safety means it will ALWAYS work! Fuses always work--over current sensors don't.
I was in medical equipment for 25 years--the safety stuff was almost always mechanical in nature. Philips built a mammography machine with an automatic compression paddle--it was computer controlled hydraulic entertainment. GE made one that used the same computer controller but used air for the compression paddle. The air lines would physically blow off when they hit 35 PSI. The Philips had a massive recall when the computer controlled stuff failed and ripped the breasts off a patient with a hydraulic crusher paddle. The hydraulic paddle broke and then bent the frame of the unit. That one cost Philips 20 million dollars (here is a blank check)
Fuses and capacitors for active systems make sense. Everything fails eventually so throwing a poly cap that will outlast the electronics makes sense. Not exotic by any means but neither are fuses, mechanical stops, bumpers and seat belt pendulums... but they work!
Throw a cap on that tweeter and don't worry about it.
That will not protect you if something goes wrong with a cable on the input side of the amp or the crossover has a pop or worse yet, fails. I had the latter happen with an Ashley that produced a loud pop. This was after the unit was running for a time.
That would require you to use some form of tester to get the impedance of the driver and care must be taken to not damage it.
The alternative is to try to get the manufacture to give you that data at maybe 1 kHz.
ALWAYS put a cap on a Tweeter, its the proper way to protect it. A 35uF cap should work just fine, heck since you are wanting a > 2KHz XO any 25uF to 35uF cap (in series on the positive wire) is going to work 100% as a protection circuit. To post that "its going backwards" in an active setup is just silly opinion. Protect your tweeter and leave silly banter to those who never spend any $$$ on anything 
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I take it my earlier question about HF oscillation was a stupid one.
But if I understand it correctly, a series cap will provides failsafe protection against DC and low frequency, and no protection against high frequency overload. Using a DSP-based active crossover, a software glitch could result in a full scale output at ultrasonic frequencies that fries the tweeter.
Just sayin'...
But if I understand it correctly, a series cap will provides failsafe protection against DC and low frequency, and no protection against high frequency overload. Using a DSP-based active crossover, a software glitch could result in a full scale output at ultrasonic frequencies that fries the tweeter.
Just sayin'...
Probably not stupid at all if its true but never read much about that or ever had that problem (7 years of active XO design). Do you have any links on how it happens? Is it specific to certain DSPs?
Right now DC is definitely important to protect against, I always have a cap to protect the tweeter.
Right now DC is definitely important to protect against, I always have a cap to protect the tweeter.
If you're implementing an active crossover properly then this implies you've actually measured the loudspeaker drive units to design a decent crossover. Adding a capacitor in series with the tweeter isn't a problem, even if it's quite small in value, say 10uf and has a large effect on the frequency response. This doesn't matter of course, because you add the cap before you measure, so the modified frequency response is designed around.
If you can't measure then your best bet is to use a very large cap. Focal say don't use the tweeter below 528Hz, that's fine, the active xover in there is make sure nothing low gets to the tweeter. If you want to block from turn on thumps then a 100u cap or a 100000000u cap will do. If you want to protect the driver from the possibility of a failure somewhere, where a bang, or a pop could be sent, then using a cap of say 10u would prevent more nasties from reaching the tweeter.
If you can't measure then your best bet is to use a very large cap. Focal say don't use the tweeter below 528Hz, that's fine, the active xover in there is make sure nothing low gets to the tweeter. If you want to block from turn on thumps then a 100u cap or a 100000000u cap will do. If you want to protect the driver from the possibility of a failure somewhere, where a bang, or a pop could be sent, then using a cap of say 10u would prevent more nasties from reaching the tweeter.
I'd highly doubt that this would happen. The DSP is only one part of a chain with the DAC coming after it. The DAC by design cannot produce anything above 1/2 of the sampling frequency and it will contain a low pass on the output. So unless we're moving on to, if you're DAC explodes, then I wouldn't worry about a *what if* of that nature.
If high frequency stuff is something to worry about I'd expect the amplifier to oscillate before the DSP gives you anything to worry about. Hopefully the frequency will be so high that the tweeters own inductance will protect it. Failing that you could use a series cap and a series inductor if you're that worried about frying your tweeter.
There's usually no high end roll off applied for the tweeter so it's running flat out at higher frequencies anyway. The real problem would be if the filter "reset" itself and sent full level bass to the tweeter. A suitable cap tuned for one octave below the crossover frequency will also protect against this.
I'm sure you're right, but as a DSP dabbler myself I could conceive of an unintentional loop sending alternating large +ve and -ve values to the output, and even more likely, pseudo-random full scale noise. Not likely in a tried and tested product, but if the intention is to experiment it's nice to think there's protection against all eventualities, including a dodgy amp. (I'm a bit paranoid after I destroyed a tweeter with an oscillating amplifier.)
I was thinking along the lines of an HF protection crowbar - which certainly would be easier to design for after a series capacitor. You could conceive of a fairly simple circuit that trips a relay if a combination of frequency and amplitude moves outside a certain envelope; shorting the terminals if you don't like series contacts, or in series with the output if you don't like the idea of shorting them.
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