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Old 30th August 2002, 06:33 PM   #1
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Default THD, Intermodulation, S/N

Can someone indicate me god articles, websites , etc, teaching how to measure and calculate these kind of distortions...
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Old 30th August 2002, 06:55 PM   #2
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Another question, its obvious that a resistive load is quite different of real loudspeakers, I would like to build a test circuit wich has the same caracteristics of a real load. Where can I get such schematics?
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Old 30th August 2002, 08:43 PM   #3
skaara is offline skaara  Slovenia
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Why bother with making circuits.. Buy a loudspeaker?!
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Old 30th August 2002, 09:28 PM   #4
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Buy a cheap speaker and use that. It'll cost less and be easier than trying to do it on your own. If you really wanted to have something to test with, you could mimick a speaker pretty well with a coil that has a matched inductance to your speaker.
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Old 30th August 2002, 09:44 PM   #5
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Well the first question is for myself, but the load simular circuit is for lab tests, my boss (professor) told me to make one, so I have to find out how................
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Old 30th August 2002, 09:50 PM   #6
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Hello,
There's a nice piece of freeware called Speaker Workshop that allows you to make THD measurements using the sound card in your PC. I'm not totally convinced that the figures are accurate but it might give you a guide.

It also measures impedance, passive values, freq resp (with a mic), xover optimisation (rather primitive) and box calculation.

Check out www.speakerworkshop.com

Regards,
David
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Old 3rd September 2002, 07:10 PM   #7
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The only way you can entirely accurately test an amp is to use the load you will be listening through. As the load is a complex thing to model why go to all the bother?

If you wanted an accurate "dummy load" it would have to mimic so many varying factors - complex impedance curves created by the interaction of the crossover network and the voice coils, not to mention resonances and their associated harmonics and how this effects the impedance and load characteristics.
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Old 3rd September 2002, 07:11 PM   #8
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...I thnk that last post was a bit extreme somehow, but you get the idea.

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Old 3rd September 2002, 07:38 PM   #9
Dirk is offline Dirk  Belgium
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Hi,

I think there are several very good reasons to use a dummy load instead of a speaker (cheap or not):

* Sine wave testing at high power will fry your ears and your speaker. A dummy load is (almost) silent!

* A suitable dummy load can easily be reproduced by others, and can therefore serve as a standard. This makes comparison of measurements possible.

* Simulating a speaker using a dummy load is not that strange; it's just what Thiele and Small did, no?

Regards, Dirk
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Old 3rd September 2002, 07:42 PM   #10
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Do you have a model of a Dummy load for me Dirck?
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