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post #1 of 15 Old 07-31-2014, 09:13 PM - Thread Starter
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Measuring speakers ohms

When I measure my back speakers from their speaker post's I'm getting a reading in the M ohms but when I open the speaker up and measure across the tweeters and woofers I get the correct reading of just over 4 ohms. Does this mean I may have an open in the cross-over or I'm just unable to get a true reading from the speaker wire post's.

Equipment List: Benq W6000, Darbee DVP-5000 Video Processor, JKP Affinity 100 inch 16x9 .9 gain reference screen, Onkyo 818 receiver, 3-Marantz Ma700 and 2-Ma6100 mono blocks, 9.2 set-up, B&W Nautilus 805 front speakers, B&W Nautilus HTM2 center speaker, Infinity ( soon to be replaced by B&W ) bookshelf Height Speakers, Mirage HDT-R side speakers, Jamo THX surround one rear speakers, Dual PSA XS30se subs, Richard Grey, Monster Power, and Panamax powerline conditioning/surge protection.
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post #2 of 15 Old 07-31-2014, 09:23 PM
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You can't measure a speaker's impedance with a DMM. You're measuring DC resistance, not impedance. Still, the DC resistance is usually a few ohms at most. Are the speakers working?
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post #3 of 15 Old 07-31-2014, 09:23 PM
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A speaker systems rated impedance is just that, a nominal figure, meaning it doesn't dip much below the rated impedance at any given frequency. If you mare measuring in meg's at the terminal, something sounds wrong. Either your measuring technique of the speaker or the speaker has serious issues. I'd expect it not to play at all it truly measeses in megs.
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post #4 of 15 Old 07-31-2014, 09:24 PM
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Quote:
Originally Posted by skriefal View Post
You can't measure a speaker's impedance with a DMM. You're measuring DC resistance, not impedance.
That is true, but it still shouldn't measure in megs at the terminal.
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post #5 of 15 Old 07-31-2014, 09:27 PM
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Originally Posted by 89grand View Post
That is true, but it still shouldn't measure in megs at the terminal.
Yup. Was in the middle of adding that to my post.
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post #6 of 15 Old 07-31-2014, 09:53 PM - Thread Starter
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The speakers I'm measuring are Mirage HDT-R, here is their descrition: The HDT-R surround speaker is said to be an Omnipolar design, meaning it is designed to radiate sound in all directions. At the demonstration I attended in Vancouver, Paisley described the speaker’s dispersion pattern as actually being more like half of a grapefruit (presumably when the speaker is mounted on a wall). The HDT-R is trapezoidal in shape with two 5.5" bass drivers on the front baffle that are slightly smaller than those utilized in the HDT-F and which fire directly into the room. Each side baffle, which is directed at an angle into the room, has the same PTH midrange driver and tweeter as the HDT-F, for a total of six drivers. Frequency response is rated from 80 to 20,000Hz with a sensitivity of 90dB and 6-ohm impedance. The HDT-R is also bi-wirable and bi-ampable like the HDT-F with the same high-quality binding posts. It, too, is an acoustic-suspension design and is available in black or white finishes.

This is the story behind me taking measurements, I was using a Marantz SR-18 receiver as a 5-channel amp to power my surrounds and back speakers, 1 of my surrounds were bi-amp. The surrounds are Mirage 6-ohm speakers and the backs are Jamo 4 ohm speakers, to make a long story one of the amp channel in the Marantz blew which cause all the channels to stop outputting ( safety feature ) so it went in the shop and I was told 1 of the channels blew and I was told I either have a short or an open somewhere or that the low impedance speakers caught up the the 15 year old Marantz. So I decided to take my meter out and start measuring all my speakers, first from the end of the cables leading into my rack area and then from the speaker posts, all my speakers measure perfect except the Mirages, I get a reading of 1-2 M ohms which to me seems very high. I opened 1 of the Mirage speakers up and measured from the inside of the speaker posts and I still get the high measurement but if I measure across each individual tweeter and woofer I get the correct 4-5 ohm reading. I called Mirage and I was told not to measure from the speaker post, if that is true then why I'm I getting the correct reading from my other speakers?

Equipment List: Benq W6000, Darbee DVP-5000 Video Processor, JKP Affinity 100 inch 16x9 .9 gain reference screen, Onkyo 818 receiver, 3-Marantz Ma700 and 2-Ma6100 mono blocks, 9.2 set-up, B&W Nautilus 805 front speakers, B&W Nautilus HTM2 center speaker, Infinity ( soon to be replaced by B&W ) bookshelf Height Speakers, Mirage HDT-R side speakers, Jamo THX surround one rear speakers, Dual PSA XS30se subs, Richard Grey, Monster Power, and Panamax powerline conditioning/surge protection.
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post #7 of 15 Old 07-31-2014, 09:55 PM - Thread Starter
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Quote:
Originally Posted by skriefal View Post
You can't measure a speaker's impedance with a DMM. You're measuring DC resistance, not impedance. Still, the DC resistance is usually a few ohms at most. Are the speakers working?
Yes the speakers work fine and when I run Odyssey XT32 they set their trim levels around -2, if there was truly very high impedance then I sure the trim levels would be pegged at +15 with very little sound coming out.

Equipment List: Benq W6000, Darbee DVP-5000 Video Processor, JKP Affinity 100 inch 16x9 .9 gain reference screen, Onkyo 818 receiver, 3-Marantz Ma700 and 2-Ma6100 mono blocks, 9.2 set-up, B&W Nautilus 805 front speakers, B&W Nautilus HTM2 center speaker, Infinity ( soon to be replaced by B&W ) bookshelf Height Speakers, Mirage HDT-R side speakers, Jamo THX surround one rear speakers, Dual PSA XS30se subs, Richard Grey, Monster Power, and Panamax powerline conditioning/surge protection.
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post #8 of 15 Old 07-31-2014, 10:03 PM - Thread Starter
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I've been out of the electronic game for a while and I'm a little rusty with impedance vs resistance so I just did a little reading to freshen up, I'm still a little concernd with my reading of the Mirage from the speaker post compared to the other speakers.

Equipment List: Benq W6000, Darbee DVP-5000 Video Processor, JKP Affinity 100 inch 16x9 .9 gain reference screen, Onkyo 818 receiver, 3-Marantz Ma700 and 2-Ma6100 mono blocks, 9.2 set-up, B&W Nautilus 805 front speakers, B&W Nautilus HTM2 center speaker, Infinity ( soon to be replaced by B&W ) bookshelf Height Speakers, Mirage HDT-R side speakers, Jamo THX surround one rear speakers, Dual PSA XS30se subs, Richard Grey, Monster Power, and Panamax powerline conditioning/surge protection.
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post #9 of 15 Old 08-01-2014, 05:16 AM
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If the speakers work but you're getting a high reading chances are there is a high pass capacitor in the circuit. Meters use DC to take a resistance measurement, capacitors block the passage of DC.

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post #10 of 15 Old 08-01-2014, 05:51 AM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post
If the speakers work but you're getting a high reading chances are there is a high pass capacitor in the circuit. Meters use DC to take a resistance measurement, capacitors block the passage of DC.
I was thinking the same thing but I wanted to make sure, thanks for the info.

Equipment List: Benq W6000, Darbee DVP-5000 Video Processor, JKP Affinity 100 inch 16x9 .9 gain reference screen, Onkyo 818 receiver, 3-Marantz Ma700 and 2-Ma6100 mono blocks, 9.2 set-up, B&W Nautilus 805 front speakers, B&W Nautilus HTM2 center speaker, Infinity ( soon to be replaced by B&W ) bookshelf Height Speakers, Mirage HDT-R side speakers, Jamo THX surround one rear speakers, Dual PSA XS30se subs, Richard Grey, Monster Power, and Panamax powerline conditioning/surge protection.
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post #11 of 15 Old 08-01-2014, 06:09 AM
 
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Quote:
Originally Posted by Mike Butny View Post
When I measure my back speakers from their speaker post's I'm getting a reading in the M ohms but when I open the speaker up and measure across the tweeters and woofers I get the correct reading of just over 4 ohms. Does this mean I may have an open in the cross-over or I'm just unable to get a true reading from the speaker wire post's.
The first question is: "Does the speaker work normally when hooked up by simpler means?".

The second question is: "Does another speaker known to be good work normally at that location?"

If you put a 9 volt battery across the speaker terminals, does it click?

There is a way to design a speaker with a large electrolytic capacitor in series with it chosen in such a way that it extends the bass response, as counter-intuitive as it may seem. But that would only apply if the speaker appeared to be working normally. That would make the impedance of the speaker measure very high with an ohm meter.
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post #12 of 15 Old 08-01-2014, 06:11 AM
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Anytime I measured a capacitor it would start at a lower reading then increase as the capacitor charged from the voltmeter's applied voltage. Of course it would depend on the working voltage of the cap. Still readings in the meg ohm range is unusual.
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post #13 of 15 Old 08-01-2014, 07:49 AM
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Originally Posted by kjfalls View Post
Anytime I measured a capacitor it would start at a lower reading then increase as the capacitor charged from the voltmeter's applied voltage.
The time frame that it takes for a cap to charge depends on its value. With a few thousand uF power supply cap that can take from a few seconds to perhaps a minute. With a low value filter cap it can be almost instantaneous.

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post #14 of 15 Old 08-01-2014, 01:32 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post
The time frame that it takes for a cap to charge depends on its value. With a few thousand uF power supply cap that can take from a few seconds to perhaps a minute. With a low value filter cap it can be almost instantaneous.
I know it takes five time constants 5T depending on the capacitance and resistance in the circuit.
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post #15 of 15 Old 08-01-2014, 01:57 PM
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Five time constants to what? How long it takes depends upon how far you want it to settle, and what the meter looks like. They are sometimes current sources, sort of, when measuring resistance so follow I = C*dV/dt rather than an RC time constant (exponential related to e^(-t/RC) ). When I want to measure a capacitor I use a capacitor meter, or cap function on a DMM, or (usually since I deal with HF circuits) a VNA.

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