PDA

View Full Version : multimeter ohm setting



midlife
02-04-2010, 01:31 PM
to test a 035ti tweeter for dcr, what should I have the ohms setting at on the meter dial? thanks

midlife
02-04-2010, 01:56 PM
to test a 035ti tweeter for dcr, what should I have the ohms setting at on the meter dial? thanks
Maybe I figured it out & have it on 200. On the 035ti the best I can get is 4.6ohms. I found the specs and they read 3.5-4.2, deal or no deal?

rdgrimes
02-04-2010, 02:06 PM
It's usually +/- 10%.

midlife
02-04-2010, 02:12 PM
It's usually +/- 10%.
So as dcr increases the speaker is in trouble ? thanks

jcrobso
02-04-2010, 02:30 PM
Digital of analog? I assume digital these days, but they also have an accuracy rating. Thus 4.6 ohms reading from a $200 Fluke is going to more accurate than a $30 Radio shack meter.

midlife
02-04-2010, 03:32 PM
Digital of analog? I assume digital these days, but they also have an accuracy rating. Thus 4.6 ohms reading from a $200 Fluke is going to more accurate than a $30 Radio shack meter.
Its a GB meter, not to cheap-average?, when dcr approaches it highest stated value of a speaker that indicates its nearly at the end of its proper performance??

rdgrimes
02-04-2010, 03:35 PM
Its a GB meter, not to cheap-average?, when dcr approaches it highest stated value of a speaker that indicates its nearly at the end of its proper performance??
Not reliably. But if it's 1000x rating, yes. Or, if it's "0". ;)

I've had them read normal and not work at all. The main issue I can see is that when they are out of spec, the XO will not perform as designed and the whole system could sound wonky. (technical term). Also best to have 2 that measure near equal.

midlife
02-04-2010, 04:27 PM
Not reliably. But if it's 1000x rating, yes. Or, if it's "0". ;)

I've had them read normal and not work at all. The main issue I can see is that when they are out of spec, the XO will not perform as designed and the whole system could sound wonky. (technical term). Also best to have 2 that measure near equal.
Sorry gotta ask, when do you rely on dcr numbers?

Beowulf57
02-04-2010, 07:25 PM
Why are you testing the DCR in the first place? Do you hear some audible anomaly during listening? Keep in mind that DCR can be affected by the contact integrity of the multimeter probe with the measurement point. Oxidation can reduce this contact integrity. I don't know that this is affecting your measurements...but unless you can hear a problem, why worry?

toddalin
02-04-2010, 07:38 PM
to test a 035ti tweeter for dcr, what should I have the ohms setting at on the meter dial? thanks

To answer you question as posted, use whatever the minimum setting that your meter goes to. For example, if you have a 1-100 ohm scale use that as opposed to the 10-1,000 or 100-10,000 ohm scale (or such). The dcr for most any home-use speaker (be it woofer, mid, or tweeter) will be less than 16 ohms, and as low as just a couple ohms. Car speakers can be down around 1-2 ohms in extreme cases.

scott fitlin
02-04-2010, 08:16 PM
system could sound wonky. (technical term). :applaud:

NEW WORD! I Absolutely must remember this one!

:bouncy:

SMKSoundPro
02-04-2010, 10:21 PM
when dcr approaches it highest stated value of a speaker that indicates its nearly at the end of its proper performance??

No, that's not how this works. DC resistance that your measuring is showing continuity only, not how it sounds, or fatigue or age.

Remember that a speaker voil coil is a winding of wire that will have a DCR that is directly related to the length and thickness of wire wound around the voice coil former. As manufacturing continues, the DCR will vary by a little bit, hence the DCR window of 3.5 - 4.2 ohms.

So, please don't just use the Ohms scale as a way to judge a speaker, except to know whether the voice winding has continuity or is burned open, like a filament in a Edison lightbulb.

Also, the coil of wire on the coil gets hot as you turn the volume up louder, and starts to melt the enamel coating on the magnet wire on the coil. The voice coil then starts to blister and because of JBL's signature tight tolerances, starts to become bound up in the magnetic gap and sounds scratchy. Remember that the wire used in a tweeter winding is very small! It can't take allot of heat or abuse before it pops open.

I hope this helps.

Keep the faith, here. You're asking the right questions in the right forum for your 035 tweeters.

Scotty.

Beowulf57
02-05-2010, 05:38 AM
:applaud:

NEW WORD! I Absolutely must remember this one!

:bouncy:

Wonky = Super white honky = opposite of dark, veiled and a cousin of squawker. Occurs when the dog barks at a bird, as in the woofer frightened the tweeter. :D

Beowulf57
02-05-2010, 05:45 AM
Also: Play your speaker at high levels for a while and then measure the resistance again. If your meter is sensitive enough you will note that the resistance of the voice coil is higher, i.e., the temperature coefficient of copper is positive. With an old carbon resistor, the resistance is lower as carbon has a negative temperature coefficient.

Mr. Widget
02-05-2010, 08:59 AM
No, that's not how this works. DC resistance that your measuring is showing continuity only, not how it sounds, or fatigue or age.:yes:

There seems to be a widely held misconception that DCR values are really important. Other than to show that the coil isn't burned out, an open circuit, the DCR values posted on eBay and elsewhere are there simply because that is the only piece of test gear most people own.

Frequency response and impedance plots on the other hand can be extremely valuable in letting you know if a driver is still up to spec. Unfortunately few have calibrated test gear to measure these.


Widget