I searched for a post of this question and couldn't find it. I'm sending a frequency generator to an amplifier, and the output of the amplifier to the speaker. How do I test the speaker's resistance using a multimeter? I've included a picture of the digital multimeter that I am using, which I assume is fairly standard. I'm looking for the frequency with the least resistance so that I know the tuning of my ported cabinet. Thanks ya'll.
Hi,
First, you need a known resistor in series with the speaker load,
then you need to accurately measure the voltage going to the speaker from the amp. You then you need to measure the voltage drop across the speaker terminals.
Rod Elliot's ESP site has an article describing the procedure, with a diagram and a handy spreadsheet to put the values in. It's here
First, you need a known resistor in series with the speaker load,
then you need to accurately measure the voltage going to the speaker from the amp. You then you need to measure the voltage drop across the speaker terminals.
Rod Elliot's ESP site has an article describing the procedure, with a diagram and a handy spreadsheet to put the values in. It's here
Thanks John. Are you sure the resistor is needed for this test though? This is just to see the resistance fluctuation between 30 and 100hz. http://www.diysubwoofers.org/faq.htm section 1.03 gives a brief explanation saying that the resistor is more accurate but not necessary. Also, I don't think my multimeter does millivolts. 
Gee, I didn't even look at your MM, but yeah, no mVAC scale. Looks like you are SOL, as the only way to determine the impedance is to measure the voltage drop , which will be AC and tiny.
The fixed resistor is needed to calculate the current draw. Without it, you need another MM to measure mA draw. A resistor is cheaper.
EDIT: Sorry, just looked at the Brian Steele link you posted. If all you need is the Fs, then that will work ok. mA AC measurements on these cheaper DMM are not very accurate though.
Looks like you are SOL, as the only way to determine the impedance is to measure the voltage drop , which will be AC and tiny. The fixed resistor is needed to calculate the current draw. Without it, you need another MM to measure mA draw. A resistor is cheaper.
EDIT: Sorry, just looked at the Brian Steele link you posted. If all you need is the Fs, then that will work ok. mA AC measurements on these cheaper DMM are not very accurate though.
Thanks again John. I found a good site with diagrams as well. It's here:
http://www.bcae1.com/spboxad3.htm
http://www.bcae1.com/spboxad3.htm
Hi,
for an approximate answer measure the DC resistance of the speaker at the input terminals. Add about 25% to that DC figure to get impedance.
If you require a more accurate impedance value you need to send audio band pink noise to the speaker and need special instrumentation to measure the full audio bandwidth of the signal across the speaker and the resistor.
But probably easier to open the speaker and read off the impedance printed on the driver labels.
for an approximate answer measure the DC resistance of the speaker at the input terminals. Add about 25% to that DC figure to get impedance.
If you require a more accurate impedance value you need to send audio band pink noise to the speaker and need special instrumentation to measure the full audio bandwidth of the signal across the speaker and the resistor.
But probably easier to open the speaker and read off the impedance printed on the driver labels.
With a small amount of thought capital and some inexpensive cables to your computer soundcard, you could use the free software called "speaker workshop" to measure and plot the impedance.
The benefit of this method is that you will already be on the learning curve should you decide that you want to make acoustic measurements later on.
The software is available here:
http://www.speakerworkshop.com/
A comprehensive tutorial on how to use this software is here:
http://www.claudionegro.com/
A tutorial of the cables you will need to setup is here:
http://www.claudionegro.com/swsetup/cables/cables.html
Regards,
David
The benefit of this method is that you will already be on the learning curve should you decide that you want to make acoustic measurements later on.
The software is available here:
http://www.speakerworkshop.com/
A comprehensive tutorial on how to use this software is here:
http://www.claudionegro.com/
A tutorial of the cables you will need to setup is here:
http://www.claudionegro.com/swsetup/cables/cables.html
Regards,
David
Hi, you will never do it with that meter I'm afraid. Going from memory if you put 600 ohms in series with the speaker and feed this from 6 volts R.M.S. you can read off in mv the impedance of the speaker at any frequency (hope I have remembered correctly, have to get the calculator out) by measuring the voltage directly across the speaker terminals. For e.g. 30mv would be 30 ohms. Easy to check if values correct, substitute the speaker for a fixed resistor, 10 ohms say and check you get 10 mv reading. It is a technique that works really well. Get a better meter if poss and if your signal generator won't go to 6v rms, use a power amp to feed the network. Doug Self described this technique many moons ago, during his articles on Class B amplifiers.
Hope it helps,
Regards Karl (and get a better meter )
Hope it helps,
Regards Karl (and get a better meter
)
Use the computer!
For example you can download Tone and RTSect from my homepage http://www.tolvan.com/products/ use Tone as a tone generator, and measure the amplitude over the loudspeaker with RTSect. Connect a series resistance as described by the others.
All you need is a computer with a soundcard, the software is free.
For example you can download Tone and RTSect from my homepage http://www.tolvan.com/products/ use Tone as a tone generator, and measure the amplitude over the loudspeaker with RTSect. Connect a series resistance as described by the others.
All you need is a computer with a soundcard, the software is free.
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