Multimeter to test ohms
 

Hi,
Can anyone recommend a multimeter that can test Ohms of a speaker? I need to test to see if a speaker/horn/tweeter is blown. I understand that if I connect a multimeter across the connections of the speaker I can tell by the reading if it is within range or not. The multimeter I have goes from 200 to 2k ohms. I am guessing I need one that will test lower than that since I am testing 8 ohm speakers. I can't find a meter online that goes lower than 200 ohms.
Thanks for any advice.

Any $20 one from a hardware store. I think the lowest range is 0 - 200 even though it is the 200 setting. I use mine to test sprinkler valves and they usually run between 40 - 60 ohms. I use the 200 setting for that. Try it first.

You can still take a reading. The decimal point may be in the wrong spot.

I got a good multipurpose one at Sears a few years ago. I can test batteries as well. Instructions will tell you which setting to use for different usues. Also remember, 8 ohms will not usually read exactly 8. Normally less, like 6.9 / 7.2 etc. :cool:

Meter resolution
 

Keep in mind that even a high quality meter -
like a Fluke 73--- will have limits in the lower range of DCR since it can "measure" 0 ohms to a couple of million ohms.

If you are looking to test a speaker, buy a cheap meter and test a known good 4 ohm and 8 ohm speaker.

You'll likely get a readin of 3 ohms and 6 ohms DCR not impedance (z). More accurate readings would require an device called and impedance bridge or an LCR meter.

Kind of off topic here, but can you use a multimeter to test pickups also ? If so, where do you set the multimeter ?

If you get an auto-ranging multimeter, then you just set it to Ohms and it figures out the range. It's a bit of a splurge, but I'm really happy with my Fluke 115.

Yes, you can use a multimeter to test pickups. The typical DC resistance is in the range 5K-9K ohms. Some ohm meters are auto ranging, all you need to do it turn it on and let it warm up. Otherwise, to have the most accuracy, pick a range on the meter just below that of the pickup. Zero the meter by shorting the leads as you turn it on or manually if the meter has a button or knob to do this. A good battery in the meter will make a difference. Don't touch the bare leads with your hands while measuring. It will affect the readings.

If the pickup is bad, it can read infinity (open circuit coil), or very low (short circuit coil). The DCR value will vary depending on the pickup's temperature. The reading will also be different when the pickup is installed in the instrument with the other parts soldered in place.

If you have an LC meter you can also measure inductance. Readings are often in the 1-10 Henry range. In general, the higher the inductance, the better the bass response and the output level. An LC meter is used the same way as an ohm meter.

Among other things, a useful measurement that a designer would look at is the pickup's frequency response. This allows you to see the impedance plotted against frequency and will also show the resonant frequency. The nice thing about this is you can see if the pickup has a low frequency bump. It can also tell you how different capacitors or pots in the circuit will affect the response. Bottom line is there are a number of things that will affect the performance of a pickup when plugged in.

Resistance in a DC circuit is called ohms. Impedance in an AC circuit is also called ohms. There is a big difference and most mutimeters can not measure impedance. That requires an LCR meter. What are you trying to accomplish with a meter? DC ohm meters will measure the DC resistance of a speaker or a pick-up but be aware that an impedance measurement will not be the same value as the DC resistance measurement done on the same device.

Example: an 8 ohm rated speaker will measure somewhere between 5 and 7 ohms DC resistance. The DC resistance value will be different from one manufacturer to another due to differences in the design and manufacture of speakers.

+1
 

Also, as previously stated, the accuracy of the meter when measuring below 10 ohms comes in to play.

A value of 6 ohms displayed on the meter is 6 ohms + or - some percentage. Look at the specs of the meter being used.

200 means the range goes UP TO 200, 2K Ohms means it will read UP TO 2K, etc.

You won't be able to read the tweeter's resistance if you measure from the jack, either- you'll need to remove it from the cabinet.

As previously said, most multimeters do not measure impedance (speaker ohms) you would need something like a minirator to do this. However, there is a way of measuring impedance using a tone generator and a multimeter, you can google this.

all agreed, and if you want something accurate, be aware that the accuracy is a % of full scale not % of the reading and also +/- one digit..

so an 8 ohm speaker being measured on a multimeter with 1% accuracy on a 200 Ohm range can indicate from 5.9 to 10.1 Ohms, the same on a 20 Ohm range could read 7.7 to 8.3 Ohms.

and for the sake of checking out a speaker... it doesnt matter, any $10 multimeter is good enough to see if its a 4 ohm (typically 3 ish) or 8 ohm (typically 5 ish)speaker and if there is a short or open circuit in the voice coil.

whoosh, back on topic > what the op has... a 200 ohm range on his meter, is more than adequate

Thanks all. As always, good advice:) I am actually testing a PA cab. It has two tweeters, a horn and a 15" speaker. I took out one tweeter and without disconnecting any of the wires, put the leads of my multimeter to the terminals and got a reading. Since it was still connected, I am assuming the reading was for the entire system. I disconnected the tweeter entirely, tested at the terminals and got no reading at all. I then moved on to the horn and did the same. Got a reading with the horn connected, but no reading with it not connected. I am wondering if they are bad, or my meter just can't detect the resistance.... As you can tell I am totally new to this. The speaker is over 20 years old and produces a loud buzzing noise at low frequencies. By putting my ear to it, it sounded like the noise was coming from the tweeter. I figured I had nothing to loose by tearing into it and seeing if I can isolate the problem and either bypass it or replace it.

Sounds like you got dead drivers - but run a full range sweep through the cab at a couple of volts and follow the sound through the drivers - or try touching speaker leads with a small battery with your ear hole at each driver in turn [9 volts should get you a nice thump/tick from every driver].

https://www.google.com/search?q=swee...rator+download

This is the cheapest hand-held impedance tester I know of http://www.parts-express.com/pe/show...number=390-825.
Otherwise an auto-ranging meter is easiest for checking DCR.

You can get a Minirator for that price.