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Old 2nd January 2005, 09:56 AM   #1
Allan is offline Allan  Australia
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Default Measureing Cable & Crossover Series Resistance

I'm using Speaker Workshop to determine the enclosure volume of a base reflex system. The volume calculation calls for the series resistance - its help file describes this parameter as follows;

"Include cable and crossover series resistance in this amount. Changing this will also change Box Volume and Port Length".

Is it possible to measure this using a multimeter, if so, how should this be done?

Thanks
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Old 2nd January 2005, 10:33 AM   #2
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I would think that just measuring across the two speaker connection terminals on the enclosure should be all you need to do.

How does the resistance alter box volume and port length?

Gary.
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Old 2nd January 2005, 07:06 PM   #3
Allan is offline Allan  Australia
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How or where it comes into the calculation for enclosure volume it changes I dont know, this resistance only effects ported enclosures, not sealed according to the Speaker Workshop program! I have the Loudspeaker Cookbook vol 4 & 5 and dont recall reading about this anywhere!

I have just read the example loudspeaker guide available at Speaker Workshops home page, they say this resistance is seen from the Inductors which are in series with the bass driver(s).
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Old 2nd January 2005, 09:07 PM   #4
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Series resistance changes Q and affects both vented and sealed enclosures.
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Old 2nd January 2005, 09:18 PM   #5
simon5 is offline simon5  Canada
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If you know the AWG of the wire you're using, you can look in a table to know what resistance it haves.

Resistance of an inductor is easy to measure with a multimeter, series resistance of a capacitor is harder, you need an oscilloscope.
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Old 2nd January 2005, 09:52 PM   #6
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capacitors have no part in this discussion.
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Old 2nd January 2005, 09:56 PM   #7
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Default Re: Measureing Cable & Crossover Series Resistance

Quote:
Originally posted by Allan

"Include cable and crossover series resistance in this amount. Changing this will also change Box Volume and Port Length".

Is it possible to measure this using a multimeter, if so, how should this be done?

Thanks
Multimeter will get you in the right ballpark, just remember to measure the resistance of the probes themselves and compensate.


Francois.
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Old 2nd January 2005, 10:17 PM   #8
simon5 is offline simon5  Canada
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Quote:
Originally posted by Bill Fitzpatrick
capacitors have no part in this discussion.
Why not? If he uses a rumble filter, a capacitor will be in the signal path... please explain.
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Old 2nd January 2005, 10:32 PM   #9
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The only resistance that matters is between the amp and speaker terminals. A rumble filter is located in a pre-amp.

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Old 2nd January 2005, 11:25 PM   #10
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Hi Allan,

Keeping in mind that your multimeter is probably not that accurate at low ohms, if you have the crossover built, put a short length of heavy gauge wire across the crosover output for the speaker and hook up your speaker cables then measure the the resistance across the amp end of the speaker cable.

As mentioned by DSP_Geek also check what the meter reads when shorting the probes together and subtract this amount. giving the series resistance of the leads/crossover......

I always find this a little odd, as you really need to check the freqency response of the driver before designing the crossover, and to do that properly it has to be in-box..... somewhat of a chicken and egg problem....

Also you might like to consider using something like winisd or Unibox for doing the box design, and only using speaker workshop for the measuring (and possibly crossover design)... Have you downloaded the speaker workshop manual? I think you will find it much better than the built in help files. http://www.audiodiycentral.com/ntutorials.shtml

Tony.
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