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Old 15th May 2009, 01:55 PM   #1
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Question Tweeter damping resistor. Why?

What is the purpose of adding a largish value of resistor in parallel with the tweeter coil? Is it just for current limiting, and can it safely be done away with?
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Old 15th May 2009, 02:17 PM   #2
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to provide a more resistive and predictable load for the crossover and thus better define the roll off frequency and roll off slope.

It can also reduce the apparent sensitivity of the treble driver in comparison to the bass/mid driver.

A cross over that is loaded with a frequency variable load, does not achieve the theoretical slope and frequency predicted by the R & L & C values used in the crossover.
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Old 15th May 2009, 03:47 PM   #3
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Thanks Andrew,

Can it safely be removed without fear of damaging the tweeter?

Regards

Chris.
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Old 15th May 2009, 04:03 PM   #4
AndrewT is offline AndrewT  Scotland
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without seeing the crossover, it's impossible to offer a guarantee, but I suspect no damage will occur.

However, it's removal will completely alter the frequency response of the speaker. All the other components will need to be re-selected to try to bring back the response and may never sound as good again.
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Old 15th May 2009, 06:46 PM   #5
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I'm with Andrew on this one. Best to leave it in place. Removing it will cahnge how the high pass filter works and may do things you won't like.

If you do try, turn it up slowly.
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Old 15th May 2009, 08:11 PM   #6
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No can do, for the reasons Andrew pointed out.
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Old 15th May 2009, 08:36 PM   #7
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I haven't heard it yet. I'm in the process of building it. I was given the design by someone else. I think I will leave it in the design.
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Old 16th May 2009, 12:09 AM   #8
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there are 2 ways to pad down a tweeter - the standard way is to use a L-pad i.e. a resistor in series with the tweeter and another in parallel - as noted above, this keeps the impedance constant for the crossover.

another way is to use a single resistor in series, but if this is tweaked, freq response of the xover will change because of the changing impedance. To avoid this, the resistor can be placed before the crossover components.

This calculator will show you how it works:
http://www.sengpielaudio.com/calculator-Lpad.htm

This page may be help you with how xovers work:
http://sound.westhost.com/lr-passive.htm
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 16th May 2009, 10:59 PM   #9
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Old 17th May 2009, 10:43 PM   #10
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if you're using a non-ferrofluid damped tweeter, then use the L pad method, otherwise either method is OK.

The reason the guys in the linked thread had problems is because they're using voodoo rather than appropriatly calculated crossovers for the job - crossovers are neither good nor evil, they're just a tool to get a job done...
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