tswei Posted June 20, 2013 Share Posted June 20, 2013 I was advised by Mr. Crites that the way to test drivers is to test their impedence with a multimeter. Is there any special type I should get?? And how do I set it when I do the test?? The dial has a lot of settings. Are their other aspects to driver condition to know about?? The woofers in my 70s La Scalas look really pristine, but I don't know how to tell if the materials have worn at all. Quote Link to comment Share on other sites More sharing options...
babadono Posted June 20, 2013 Share Posted June 20, 2013 tswei, The meter will be used to test if the voice coil is intact. Set the meter to the lowest resistance (ohms) scale. I don't know the exact reading you should get but probably betweeen 4 and 8 ohms. The speaker needs to be disconnected from the crossover to make this measurement. If the voice coil reads open circuit the speaker is 'blown' as they say. This is not the only thing that can be wrong with cone speakers. The cone can be torn or seperated from the metal surround hence as you may have heard of a speaker being 'reconed'. I hope this helps. I also have a pair of circa mid 70's LaScalas and my woofers are still alive and well. babadono Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted June 20, 2013 Share Posted June 20, 2013 No special type and no need to spend gobs of money either. The ones I use at work and home cost less than $20.00 10 to 15 years ago. Figure $30.00 in todays money. I'v never had them let me down. Quote Link to comment Share on other sites More sharing options...
Mongo171 Posted June 20, 2013 Share Posted June 20, 2013 I use digital auto-ranging multimeters. No ranges to figure out. Just turn on to the Ohms setting and measure. Quote Link to comment Share on other sites More sharing options...
Islander Posted June 20, 2013 Share Posted June 20, 2013 I was advised by Mr. Crites that the way to test drivers is to test their impedence with a multimeter. Is there any special type I should get?? A multimeter usually can test three things: voltage (AC and DC), resistance, and amperage (volts-ohms-amps). It can not test impedance. I'm sure that Bob Crites knows the difference between impedance and resistance, so I suspect you may have misheard him. Impedance and resistance sometimes get confused because both are measured in ohms. The symbol of resistance is Omega. Resistance is a property of DC circuits, and is easily measured. The meter sends a small exact current into a circuit, and the reduction in the current when it returns is measured in ohms and shown on the meter. It's a single number. The symbol of impedance is Z. Impedance is a property of AC circuits and is much more complicated to measure than resistance. Readings have to be taken, and then calculations are made in order to determine the impedance. Impedance varies with the frequency of the current and is described with a graph, similar to a frequency response graph. The single resistance number that's used in the description of a speaker is a rough average of the various numbers in the graph. This will give you some idea of how complicated it is: https://en.wikipedia.org/wiki/Electrical_impedance Measuring the resistance of a speaker will tell you if it has a broken wire or bad connection. The resistance will be very high or infinite. It can also tell you if there's a short circuit. The resistance will be lower than normal or even near zero. The impedance gives some idea of the performance of the speaker and helps to determine what components will work properly with that speaker. Quote Link to comment Share on other sites More sharing options...
WMcD Posted June 20, 2013 Share Posted June 20, 2013 I'll be brave and tell you what to buy and how to use it. Smile. My first suggestion is http://www.parts-express.com/pe/showdetl.cfm?partnumber=391-062 Triplett is a good name and Parts Express has always been very good to me over the years. So that is $40. You don't get free shipping until you hit $100. A good thing is that it has test leads with screw-on alligator clips which can be added to the probes. Cheaper ones do not, and if you go out and buy probes with alligator clips it will cost about $15 or so. It also has auto off which means that you don't have to go to Walgreens and buy a new 9 volt battery for $5 when you don't turn it off. You say you don't need the temperature probe and function but you might have some fun with it. The next lower priced one I'd recommend is http://www.parts-express.com/pe/showdetl.cfm?partnumber=390-550 at $15. I have one and it works well. Except I wish it had alligator clips and I've croaked the battery. Smile. On the Parts Express website you can find an $8 no-name meter . . . but shipping starts equalizing prices and it might be getting to the junky stage, though workable. You''ll see that the Triplett and Vellerman look very much alike. In both cases you plug the leads into the center and right jacks. (The left jack is for high current, which you will not be using.) Set the pointer to 200 on the section of the dial marked in green with the Ω This is an upper case Greek omega which stands for d.c. (direct current) resistance in this case. The 200 means that it will give a good readout up to 200 ohms. So you must switch to a different setting if the resistance is higher to get a readout. It is not an "auto-ranging" meter, mentioned by others here. Technically you are measuring the impedance at zero Hertz frequency which is also called, d.c. which is what the meter, and its battery, puts out to examine the device to which you connect the leads. If you look at specifications for a driver, it is called Rdc or the like. (There is traffic about resistance and impedance by our forum friend. Impedance takes into account frequency, but at zero Hertz frequency, resistance and impedance are the same.) To go to specifics: A good speaker voice coil will give a reading of 3 to 20 ohms depending on the design. A bad = burned out voice coil of any design is always an open circuit or infinite ohms. Take note of what the display says when you don't have the leads attached to anything. It may be something like "OL". That is the equivalent of overload or off scale (lots of ohms) for the numbers. In the old moving pointer type meters there was actually an infinity sign at the end of the scale. I hope the above does not discourage you. I've been hitting some technical points. I'll also point out that sometimes a voice coil gets partially damaged and rubs up against the gap of the magnet structure in which it sits. In that case, an old style moving pointer ohm meter can be helpful because you can work the diaphragm and connected voice coil and see the resistance change as the pointer moves - easier than numbers changing. But this is not what you're into right now. WMcD Quote Link to comment Share on other sites More sharing options...
Quiet_Hollow Posted June 21, 2013 Share Posted June 21, 2013 See also: and I use digital auto-ranging multimeters. No ranges to figure out. Just turn on to the Ohms setting and measure. +1 [Y] Quote Link to comment Share on other sites More sharing options...
pzannucci Posted June 23, 2013 Share Posted June 23, 2013 If you want a multi-meter for other things also, get a good multi-meter (DMM). If you are exclusively looking for something to test speakers, get a WT-3 from Parts-express. It will give you accurate measurements of your speakers, not just DC resistance. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted June 23, 2013 Share Posted June 23, 2013 A LCR meter is nice thing to have for speaker projects as well. They can be had rather cheap... Quote Link to comment Share on other sites More sharing options...
Guest David H Posted June 30, 2013 Share Posted June 30, 2013 If you want a multi-meter for other things also, get a good multi-meter (DMM). If you are exclusively looking for something to test speakers, get a WT-3 from Parts-express. It will give you accurate measurements of your speakers, not just DC resistance. I agree, the WT3 is a great tool when used properly. If you decide to get this, follow the setup instructions exactly Quote Link to comment Share on other sites More sharing options...
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