Tweeter protection gizmo for active XO? - diyAudio
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Old 28th March 2009, 05:01 AM   #1
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Default Tweeter protection gizmo for active XO?

I have a current clamp that I can clamp on a wire so I can measure the current without interfering with the wire and it's signal. Is there a way I could detect LF in the HF signal path without actually interfering?
Im no EE so don't laugh, but could one not induce a tiny replica signal using a clamp on the tweeter speaker wire then trip a relay on detection of LF in the induced signal?
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Old 28th March 2009, 05:17 AM   #2
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yes you could.

the problems with such an approach are calibration - you have to calibrate the output signal for all frequencies, and processing such a signal without introducing noise, hum and other interfering signals.

You would need to amplify the signal and then filter it with an appropriate filter that matched the tweeter power handling capability. Then set up some kind of averaging circuit to convert the AC signal to a DC signal representing the envelope and then implement a comparator with the right threshold (from the earlier calibration)

You also need to consider false triggers and power up/ power down conditions.

All this assumes that the current clamp has a wide enough bandwidth to provide such information.
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Old 28th March 2009, 12:07 PM   #3
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The tweeter protection gizmo I use with active crossovers is a large capacitor in series with the tweeter. I usually go with 24+ uf depending on what is handy. That makes the cap induced high pass rolloff well below the active filter's. You can also make the cap smaller and use it as as one of the filter's poles.

Edit: So far the cap only failed to save just one tweeter - a ribbon when I turned off the crossover before the amp. Domes survived similar pops apparently undamaged.

A heck of a lot easier than what you're proposing, but probably not as much fun or educational. BTW, the relay might not activate fast enough to prevent tweeter destruction in a bad amp failure mode.
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Old 29th March 2009, 02:33 PM   #4
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Yes it's a complicated gizmo that I propose but it may be worth it the hassle, I have tweeters I really want to go active with but not at the risk of losing them.
It really seems a shame to have to put a passive cap on a tweeter so that you can go active. It's also tricky if the xo frequency is already very low.

The further we tweak and advance our gear, the more likely we are to use expensive tweeters and yet the more likely we are to want to take advantage of going active...

So getting a 'copy' of the tweeter signal is easy, there must be a clever little way of using it to trip.
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Old 29th March 2009, 03:22 PM   #5
CBS240 is offline CBS240  United States
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What about something like a frequency to voltage converter circuit that triggers above a set threshold? Then take the frequency controlled voltage and compare it to a reference to generate a signal to trigger the amplifier fault circuit. ......just thinking out loud.
All the trouble I've ever been in started out as fun......
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Old 31st March 2009, 08:18 AM   #6
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Default Why not a simple low pass?

While I was looking at frequency to voltage converter chips, (thanks CBS240) it dawned on me, why cant I simply apply a high order low pass filter set around 1K to my induced signal? Should something pass, it trips! A trim pot on the output should be enough for sensitivity adjustment for the trip stage.

Edit: I should say, Im using software XO and Im only concerned about a full range slipping through by mistake. Not so much for amp device failure or turn on thumps etc.
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