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Capacitor to filter low freq buzz?
Capacitor to filter low freq buzz?
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Old 9th January 2009, 03:30 PM   #1
steve71 is offline steve71  Australia
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Default Capacitor to filter low freq buzz?

I'm using a high powered crown amp on the high frequency channels of my actively crossed tri-amped speakers. Specifically it's an B&C DE10 compression driver (8 ohm) crossed at 7.2Khz.

The crown amp causes the compression driver to buzz. I'd like to use a cap across the speaker (or amp) terminals to filter this out. Filtering everything below 1-2 Khz should do the trick. How do I calculate the capacitance? Also which type of capacitor? I assume a 10 volt cap is OK since this is for home use and the driver isn't going to see more than 10watts max.
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Old 9th January 2009, 06:43 PM   #2
steve71 is offline steve71  Australia
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Well to answer my own question...

This is just a simple high pass filter

http://en.wikipedia.org/wiki/High-pass_filter

f (-3db point) = 1/(2pi*rc)

c = 1/(2pi*r*f) = 1/(2*3.14*8*1000)

so I'll need a 20uF cap which will go (in series) between the amp's +'ve terminal and the speakers +'ve terminal for a 1Khz hpf or a 10uF cap for a 2khz hpf

In my initial post I stated that the cap goes between the speakers/amp +'ve and -'ve terminals. THIS IS INCORRECT.

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Old 9th January 2009, 07:11 PM   #3
pedroskova is offline pedroskova
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On an active speaker, with a SS amp feeding the tweeter, it is normal practice to put a cap in series with the tweeter to protect it from any DC that the amp might leak. It's easy to burn a voice coil under those circumstances.
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Old 9th January 2009, 11:39 PM   #4
steve71 is offline steve71  Australia
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Yes, that's a good point and I should really put a cap on my midrange compression drivers for the same reason.

.... anyway the 10uf cap did reduce the buzz about 10db, which is still not enough. I really should buy a more suitable amp, but I'd rather work with what I have for now.

I might try a different cap which filters a little higher and see if that helps.
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Old 10th January 2009, 12:10 AM   #5
wakibaki is offline wakibaki  United Kingdom
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This is a 20W driver. What do you need the Crown amp for?

What kind of horn is it driving?

Something is seriously out of whack if you can hear anything low enough to be called a 'buzz' coming out of this unit. I'm surprised it hasn't self-destructed. I'd be very cautious about running it in these circumstances at all. Does it work normally otherwise?

w
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Old 10th January 2009, 02:39 AM   #6
steve71 is offline steve71  Australia
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Quote:
Originally posted by wakibaki
This is a 20W driver. What do you need the Crown amp for?

What kind of horn is it driving?

Something is seriously out of whack if you can hear anything low enough to be called a 'buzz' coming out of this unit. I'm surprised it hasn't self-destructed. I'd be very cautious about running it in these circumstances at all. Does it work normally otherwise?

w
I need the crown amp because my preamp goes to 11!

But seriously, I have a bunch of crowns lying around (xls 402Ds). The buzz is really only annoying when I'm sitting at my PC which is about 1.5 meters from the B&C DE10 (on an ME10 horn to answer your question). When I'm at the normal listening position (approx 3 meters) it's not much of an issue.

And yes, it functions as normal - crossed at 7.2Khz. I should sell the crown and get a t-amp.
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Old 10th January 2009, 03:56 AM   #7
g3dahl is offline g3dahl  United States
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Unfortunately, I think you're going to have to use another amp. Any noise that can be accurately described as a "buzz" contains high-frequency harmonics -- otherwise, it would be just a hum. These HF components are right in the operating range of the tweeter, so you can't filter them out without losing the highs in your program material.

Your filter's corner frequency (1-2 kHz) is right in the range of notes you can whistle. Most of the energy in the buzz that you are hearing is probably above 10 kHz.

Gary Dahl
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Old 10th January 2009, 04:07 AM   #8
M50SNIPER is offline M50SNIPER  United States
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Hmmm... I would say there is definitely something wrong here. But I have part of my system bi or tri-amped also and I sometimes have a problem like this (especially when running tv sound through amps). I just threw a resistor between the positive and negative and a 2200uF bipolar capacitor on the last line to the speakers (tweeters only I would recommend). Much better sound in my opinion.
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Old 11th January 2009, 01:56 AM   #9
wakibaki is offline wakibaki  United Kingdom
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Ah, you mean 'fizz'.

Yeah, get a T-amp. I'm listening to one right now. No complaints.

w
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Old 12th January 2009, 06:05 PM   #10
steve71 is offline steve71  Australia
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Quote:
Originally posted by g3dahl
Unfortunately, I think you're going to have to use another amp. Any noise that can be accurately described as a "buzz" contains high-frequency harmonics -- otherwise, it would be just a hum. These HF components are right in the operating range of the tweeter, so you can't filter them out without losing the highs in your program material.

Your filter's corner frequency (1-2 kHz) is right in the range of notes you can whistle. Most of the energy in the buzz that you are hearing is probably above 10 kHz.

Gary Dahl
Good point re the harmonics.

Quote:
Originally posted by wakibaki
Ah, you mean 'fizz'.

Yeah, get a T-amp. I'm listening to one right now. No complaints.

w
Yeah a Fizz or Buzz would describe the sound depending on your accent lol.

I have t-amp (TA-10.1) driving the Altec 288's on MR64 horns and I'd agree - no complains. It would be nice to try a SET amp one day or a class A amp, but that's probably not going to yeild a huge improvement for the cost.

For now I'm going to do some searching and see what people think of these

http://cgi.ebay.com/215-watt-4ohm-ta...ayphotohosting
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