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Multimeter and Speaker Output?

12595 Views 16 Replies 7 Participants Last post by stevensctt, Aug 17, 2011

stevensctt

Discussion Starter · Aug 16, 2011

Picked up two B&W DM610i and two DM640i for $100 (all 4) this morning, without hearing them but the seller did say one or two of the tweeters may not be working.

All four tweeters (same tweeter for all) are not functioning. Swapped tweeters between speakers with no change.

Before I decide to replace the tweeters, I need to get an inexpensive multimeter and test the tweeter wire connections. What type of meter do I need and what type of output should I be looking for? Speakers are 4 ohm.

Gotta believe that all tweeters are blown as it seems very unlikely that the same internal issues (crossover?) are common to each speaker.

Guessing someone used an 8ohm only receiver, and cranked the volumes.

Thinking this multimeter will measure what I need, but what settings and what should I expect to see if the speakers (crossovers) are working properly?

1 - 17 of 17 Posts

walbert

· #2 · Aug 16, 2011

What are you intending to do as a test?

If you put the multimeter across the individual driver leads, it should show some (low) resistance (it may not reflect the nominal impedance of the speaker system or whatever is printed on the driver, but it should show resistance/continuity), if it shows open you've got a problem.

The same goes if you put the meter across the terminal inputs on the back of the speaker - it should show continuity (some resistance, ideally not something insane like one megaohm), if it shows open you've got a problem.

If you want to test if the actual wire leads are good, put the meter across the wire's connection on the crossover and the bare lead that connects to the driver - it should show 0ohms or something very close to 0ohms.

Testing the crossovers or the drivers more extensively requires different equipment, more time, knowledge, etc.

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stevensctt

Discussion Starter · #3 · Aug 16, 2011

Quote:
Originally Posted by walbert /forum/post/20826900

What are you intending to do as a test?

If you put the multimeter across the individual driver leads, it should show some (low) resistance (it may not reflect the nominal impedance of the speaker system or whatever is printed on the driver, but it should show resistance/continuity), if it shows open you've got a problem.

The same goes if you put the meter across the terminal inputs on the back of the speaker - it should show continuity (some resistance, ideally not something insane like one megaohm), if it shows open you've got a problem.

If you want to test if the actual wire leads are good, put the meter across the wire's connection on the crossover and the bare lead that connects to the driver - it should show 0ohms or something very close to 0ohms.

Testing the crossovers or the drivers more extensively requires different equipment, more time, knowledge, etc.

Thanks for the reply. Only to see if there is a signal (output) to the two tweeter leads (wires).

DonH50

· #4 · Aug 16, 2011

Are the jumpers in place across the speaker terminals?

stevensctt

Discussion Starter · #5 · Aug 16, 2011

Quote:
Originally Posted by DonH50 /forum/post/20826953

Are the jumpers in place across the speaker terminals?

Yes they are. Thanks for pointing this out.

walbert

· #6 · Aug 16, 2011

In addition to checking for the jumpers (if you don't have jumpers, you can use bits of between the terminals, make sure you don't short them out though), in order to measure what you're interested in, you're looking for AC across the leads in question; it will need an input signal.

I'm sure there's a more scientific manner in which to conduct such a quick check, but normally I ensure the amplifier isn't set to some absurd output level, and don't leave the testing rig set-up for an extended period of time (I just don't see the need). If you were using a scope you could get more information, but for what you want, you should not need a scope.

stevensctt

Discussion Starter · #7 · Aug 16, 2011

Quote:
Originally Posted by walbert /forum/post/20827089

In addition to checking for the jumpers (if you don't have jumpers, you can use bits of between the terminals, make sure you don't short them out though), in order to measure what you're interested in, you're looking for AC across the leads in question; it will need an input signal.

I'm sure there's a more scientific manner in which to conduct such a quick check, but normally I ensure the amplifier isn't set to some absurd output level, and don't leave the testing rig set-up for an extended period of time (I just don't see the need). If you were using a scope you could get more information, but for what you want, you should not need a scope.

Thanks, I only want to determine if a signal is passed to the tweeter leads before I get new tweeters.

For the meter linked in my first post, I should provide a normal audio input signal and do this:

AC voltage measurement

* Connect the red lead to "VOmA" jack and the black test lead to the

"COM" jack.

* Set the rotary switch at the desired V~ position.

* Connect the test leads across the source or load being you want to

measure and read the voltage value on the LCD display.

What V~ position should be used?

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amirm

· #8 · Aug 16, 2011

A multimeter is not the tool of choice in measuring what signal is arriving at the tweeter. A typical tool is an oscilloscope which unfortunately is going to cost significant dollars.

You can pick a test tone and using that, attempt to measure the AC voltage. What range you use depends on how high the level is on your amplifier. If you have the levels very low then a range below 10 volts should work.

I would get the multimeter and test the drivers and all the interconnects as suggested first before worrying about above. My suggestion is to get half decent meter. Those $4 have really poor leads often showing no reading due to them not making a good connection. Opt for a $20 and they tend to be much better in this regard and some even have autoranging which solves the issue of what setting to use.

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walbert

· #9 · Aug 16, 2011

Quote:
Originally Posted by amirm /forum/post/20827140

A multimeter is not the tool of choice in measuring what signal is arriving at the tweeter. A typical tool is an oscilloscope which unfortunately is going to cost significant dollars.

You can pick a test tone and using that, attempt to measure the AC voltage. What range you use depends on how high the level is on your amplifier. If you have the levels very low then a range below 10 volts should work.

I would get the multimeter and test the drivers and all the interconnects as suggested first before worrying about above. My suggestion is to get half decent meter. Those $4 have really poor leads often showing no reading due to them not making a good connection. Opt for a $20 and they tend to be much better in this regard and some even have autoranging which solves the issue of what setting to use.

I agree with everything said here.

Radio Shack used to (still does?) sell a few meters, I'd personally pick one with a digital readout, but that's preference. If you want to get fancier, automotive shops sometimes have good deals on meters that have interchangeable leads (and sometimes they include packaged sets with multiple leads), beyond that I'd look at investing in a Fluke meter.

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A9X-308

· #10 · Aug 16, 2011

Take the tweeters out of the enclosures, and with them not connected to anything else, place the multimater, set on resistance, across the terminals of the tweeter. You should get a few ohms, somewhere between 60 and 80% of the nominal resistance of the driver. If it is an 8 oohm unit, somewhere between 5 and 7 ohms, but the actual value is not important; this test is to show if the coil has been burnt out. The wire is very fine and prone to acting like a fuse.

If you get a measurement, it's likely good and you can start looking for other reasons for them to fail. However, if you are careful and sensible, connect the tweeter to the output of a power amp (no xover), bare wire touching the terminals will do. Use a test tone in the range of the driver, ie above it's xover frequency - a small speaker like this will be about 2kHz (check manufacturer specs) so 3-4kHz will do. Safest way is to use a free tone generator to record a .wav onto a CD, and starting with the volume at minimum, bring it up slowly with the tone playing and your ear near the driver. this will confirm the driver is working or not. Of course, be sensible when you're doing it.

If it is look at the xover inside each and look for broken, burnt or otherwise wrong components. As it is the same fault, it might be an undersized resistor that has burnt out for example because of a design fault. That at least gets you started and makes sure you are heading in the right direction.

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stevensctt

Discussion Starter · #11 · Aug 16, 2011

Quote:
Originally Posted by A9X-308 /forum/post/20827327

Take the tweeters out of the enclosures, and with them not connected to anything else, place the multimater, set on resistance, across the terminals of the tweeter. You should get a few ohms, somewhere between 60 and 80% of the nominal resistance of the driver. If it is an 8 oohm unit, somewhere between 5 and 7 ohms, but the actual value is not important; this test is to show if the coil has been burnt out. The wire is very fine and prone to acting like a fuse.

If you get a measurement, it's likely good and you can start looking for other reasons for them to fail. However, if you are careful and sensible, connect the tweeter to the output of a power amp (no xover), bare wire touching the terminals will do. Use a test tone in the range of the driver, ie above it's xover frequency - a small speaker like this will be about 2kHz (check manufacturer specs) so 3-4kHz will do. Safest way is to use a free tone generator to record a .wav onto a CD, and starting with the volume at minimum, bring it up slowly with the tone playing and your ear near the driver. this will confirm the driver is working or not. Of course, be sensible when you're doing it.

If it is look at the xover inside each and look for broken, burnt or otherwise wrong components. As it is the same fault, it might be an undersized resistor that has burnt out for example because of a design fault. That at least gets you started and makes sure you are heading in the right direction.

Thanks, testing the tweeter individually with an ohm meter seems to be the easiest 1st step.

Isn't it most likely or probable that with four similar speaker (2 each identical) all with the same non-functioning tweeters, that the speakers were driven hard by an under-powered amp, resulting in clipping, a very common cause of blown tweeters?

A9X-308

· #12 · Aug 16, 2011

Quote:
Originally Posted by stevensctt /forum/post/20828332

Thanks, testing the tweeter individually with an ohm meter seems to be the easiest 1st step.

Isn't it most likely or probable that with four similar speaker (2 each identical) all with the same non-functioning tweeters, that the speakers were driven hard by an under-powered amp, resulting in clipping, a very common cause of blown tweeters?

It's a strong possibility, but testing will determine what the actual fault is. If you are incorrect and it is say a burnt resistor, are you going to be happy having bought 4 new tweeters that you don't need? It costs you nothing but a bit of time to test, so why not?

DonH50

· #13 · Aug 16, 2011

The meter probably has a listing of the AC frequency response; make sure it extends high enough (some are designed for power lines and don't go much over 60 Hz).

If you are really wanting to run sound through the crossovers and such, there are a couple of things you can try:

1. Use the test tones in your AVR, or download a set of tone files or pink noise.

2. Connect the tweeter direct to the AVR (or whatever you wish, e.g. the headphone jack on your PC) using appropriate adapters/clip wires. See if any sound comes out the tweeter. Keep the volume low!

3. Use a known-good speaker, or headphones, or even the woofer in the enclosure, and tie (clip leads again) to the tweeter output of the crossover. Again hook the speaker to the AVR and run pink noise or test tones through; any sound?

You could also run the crossover output via an attenuator (or watch the volume) into your sound card's line input to record/playback and see if sound gets through the crossover. Or find one of the apps that turns it into a 'scope.

HTH - Don

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Brian B

· #14 · Aug 16, 2011

I realize that it is not the preferred method, but it is usually easy enough to just hook up the tweeter directly to the output of the amplifier and see if there is any sound.

You'll want to make sure the volume is set very low and if you have a test disc to just output HF material this would be best (rather than finding a specific piece without a lot of low bass).

I've done this on multiple occasions without any incident, although I'm sure others will point out the possibility of damage.

The good part is you don't need to invest in anything $$.

Good luck,

Brian

PS I'm sure you know that if the parts are still available you can order them directly from the B&W support site.

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A9X-308

· #15 · Aug 16, 2011

Didn't I already suggest that?

Kal Rubinson

· #16 · Aug 16, 2011

Go to parts express and buy http://www.parts-express.com/pe/show...number=299-965

or eBay and buy the cheapest 4-8-16ohm tweeter you can find.

Connect it to each speaker's tweeter leads and see if it works. If so, the crossover is OK.

Then buy direct replacements from http://bwgroup-support.com/partscenter.html

stevensctt

Discussion Starter · #17 · Aug 17, 2011

Thanks for all the suggestions. I like the idea of buying a cheap 4ohm tweeter and did so off eBay. Should have it in the next couple of days.

In the meantime, I picked up 15-Range Digital Multimeter from Radio Shack and found the following:

Each individual tweeter measured Open Line with 200 ohm setting.

Both DM610i (4 ohm, 2-way 2nd order closed-box digital monitor) tweeter leads measured 0.5 ohms (200 ohm setting) with no input, not connected.

Both DM640i (4 ohm, 3-way 4th order variable port, base reflex digital monitor) tweeter leads measured Open Line (200 ohm setting) with no input, not connected. Influence of the crossover?

Measured ACV 200V with all speakers playing a jazz vocal with a strong trumpet lead in. Played same channel, same 20 second sample track through all speakers and each speaker measured a peak of ~1.6

Feel confident the issue is blown tweeters only.

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