Problem with Wein AS-500 Air Purifier

# How to measure speaker impedance?

8 Solutions

Hello I am not an engineer and my skills in electronics are limited, so here goes: Is it possible to measure speaker impedance in an easy way???? Trying to remember what I learned at school I came up with this solution. What if I use two multimeters attached to my speakers. One in series measuring Amperes and one in parallel measuring Volts. Then playing pure Sinus tones at a fixed volume I simply read the two meters and calculate Impedance using Impedance = Volts/Amps. Plotting this in a graph and I'm home free???? Why doses this sound a little to easy even to me???? There has to do be something wrong here. Am I measuring the impedance to the speaker alone or to my entire system? Please help me. MVH Eirik Andreassen Do NOT Reply Remove the obvious for mail to:

## 8 Solutions

Why not be simple? Speakers typically come in specific flavors, 2ohm, 4ohm, 8ohm, 16ohm.

Measure the dc resistance with your cheapo radio-shack ohm-meter, and round up to the nearest reasonable value. if you measure 14ohms, that's a 16 ohm speaker. If you measure 3 ohms, that's a 4 ohm speaker.

An electrical engineer with access to a signal generator and the knowhow to set up a full accurate test bench isn't going to be asking how to measure speaking impedance on a diy website...

• Jeff This is true if you are only dealing with a very simple speaker circuit. This is not applicable if you are dealing with Paging System where a matching transformer is involved driving the speakers. Impedance value is the combination of inductance, capacitance and resistance reading in a circuit.

Feb 19, 2012

• Jeff This is true if you are only dealing with a simple speaker circuit only. This is not applicable if you are dealing with paging system where matching transformers are connected to each speaker. Impedance is the combination of inductance, capacitance and resistance in the circuit. The inductance meter introduces an AC signal while the regular multimeter introduces DC signal.

Feb 19, 2012

• steve_w_milt in other words, no. DC resistance is nothing like the actual impedance an amplifier will see. People who put together systems will use the DCR value, because the speaker will almost always present a load above the DC resistance value. This helps them keep the amplifier output stage safe from excessive current from driving too low an impedance.

Sep 29, 2012

• Geraldinex Reading all this (as far as solution 7) the true answer seems to be that it is virtually impossible for most people. I have been told that I risk damaging my new equipment unless I also buy matched speakers for it, unless my present speakers are 4 ohm. It looks as though I am never going to find out. So they will sell me new speakers (probably inferior ones of an inconvenient size) which I will be stuck with).

Mar 16, 2011

Really don't understand why people like to make simple things complex, I see so many examples.
1. of course you need sine wave because the impedance is a function of frequency. But the speaker shall have min power so that it is all most in sleep.
2. add a know resistor in series with the speaker, thus the resistor and impedance makes a voltage divider, Vo=Vi(R/(R+Z)), meaasure Vi,Vo and calculate Z.

In <6se5ku\$2i.net at 02:43 PM, "Eirik Andreassen" < Using your multimeter to measure the current and voltage may be a problem because very few multimeters have a frequency response that is good enough for audio work. Check the meter's specs. You may find that it is rated for 60 to 400 Hz. Always know the accuracy of your meter. Digital meter specs are interesting. There is a percentage and a digit spec. While you may have a 0.5% or better basic accuracy, they'll also throw in a "digit" spec. which says that the least significant digit can't be trusted within "n" digits. I've seen the digit spec. as high as seven -- which means that the last digit can't be trusted! In any case don't use a mutimeter to directly measure the current because you will be using a sweep of frequencies and you don't know the impedance of the meter. A standard trick for this measurement is to use a constant current source -- a resistor in series with the generator and the speaker. If you use a resistor value that is much larger than the expected speaker impedance, the current won't change enough over a range of frequencies to bother the measurement. Calculate a few typical values and satisfy yourself that this trick works. Pick a resistor value (don't use a wirewound resistor) and generator output that yields a convenient current -- 1 or 10 mA. Measure the voltage drop across the speaker, shift the decimal point, and you're done! Keep in mind that you don't need three or four digits of precision for your results. Also, since you will be dealing exclusively with a single frequency sine wave at each data point, you can use an RMS or average responding (but RMS calibrated) voltmeter. Conceptually it is possible to use your sound card and some programming to make the measurement. If you attempt the feat, be sure that your sound card has a decent frequency response at the frequencies of interest. (Barry Mann)

Just bought an LCR meter.... soooooooo simpleeeeeee

• Insert the probes of a digital multimeter in the correct sockets of the multimeter. There may be several different sockets for the probes depending on what parameters you're measuring. Look for the sockets marked "impedance" or displaying the ohm symbol. Different models and brands of multimeters will vary in their labeling, so check your multimeter's manual if you're not certain about which one to use.

• 2

Select the range for the multimeter. Since you'll be measuring fairly low resistance levels with a speaker, choose a range that will encompass readings in the 2-16 ohm range. It's extremely rare to find speakers that will have an impedance outside of that range.

• 3

Touch one probe to each of the speaker terminals and check the reading. This will be the impedance of the speaker. Record the measurement, and when you're done, turn off the multimeter to preserve the batteries for the next time you need the multimeter.

• sikcapri Dude did you read ANY of the above? O_o

Jun 11, 2012

Http://www.mitedu.freeserve.co.uk/Theory/inzoz.htm

I like innovation when you are designing quality assurance tests.
If you want a professional test you have the option of looking up ASTM tests which are developed by the engineering community or else using software - some is free like ARTA if you have a computer. I assume you want something handheld and accurate. The previous posts pointed out that it is harder to come by than you may think. I have found that low currents like speaker coil movement output (the actual output impedance, not the input impedance being assumed by other posts) is probably best approximated by vibrating the cone at 1000 herz (a standard) and using a handheld RF meter - I perfer UHF as digital has gone UHF instead of VHF. The new digital ones run about \$50 but the used coil needle older types run about \$20. The point is that that type of instrument is sensitive enough to pick up the speaker output.
Then there are other concers about quality. Thicker coil wire makes current stick to the inside of the wire because of shorter path length around the inside of the wire. The center of the coils also is worst because of coils next to it. But when doing engineering DIY - its ALWAYS best to start low cost and work up to better measurement equipment and quality methods.

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