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Old 18th March 2017, 12:31 PM   #1
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Default HELP LIMP ARTA Measure Impedance and Fs

Hello I have 8 Inch driver that doesn't have any specification, and I plan to measure Free Air Resonance and Actual Impedance, Then I search and find LIMP Software.

I did use JIG with 100 Ohm Resistor, Use soundblaster audio card, short cable, but I confused because the impedance after measurement in LIMP is lower than DCR with multimeter.

And with another driver that have specification sheet and rated 8 ohm, there's lower result (around 5 ohm) when I measure use limp.

Second question, is it the peak at LIMP measurement is free air resonant frequency?

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Old 18th March 2017, 02:48 PM   #2
DUG is online now DUG  Canada
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Have you used it to measure a known resistor?

i.e. 10R
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Old 18th March 2017, 03:40 PM   #3
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If you use 10 ohms resistor you have to see more or less like this:

Click the image to open in full size.
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Old 19th March 2017, 06:19 AM   #4
Crashpc is offline Crashpc  Czech Republic
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Hello. Your questions seem to be quite chaotic.
If you have lower impedance measured than DCR of the driver, you have done poor measurement. Firstly, check the multimeter. Meaure shorted leads of the multimeter to check if there is not parasitic resistance somewhere in your measurement tool. If yes, then you can calibrate it, or deduct the base (shorted measurement) value off your speaker measurement. Then measure the 100Ohm tool, if it is right. Measure on the cables, not on the resistor. Then you can check with Arta/limp with switched channels, if it also sees 100Ohm of your tool as real 100Ohm. Only after checking this, you are mostly sure, the HW is okay.

Another "geg" I encountered with exactly your issue is, that you might mistype the separator sign. Not sure if it is dot, or the other symbol. If the program measures lets say 5,6, and you write 5.8, it might see it like 5, because it didn't see the number behind separator.

After you checked all this, it must work. There is no other way.
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Old 20th March 2017, 08:16 PM   #5
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This may help: Easy ZMA and T/S Parameters Using The LIMP Module in ARTA - An Illustrated Guide.

http://techtalk.parts-express.com/fo...ustrated-guide
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Old 21st April 2017, 07:23 AM   #6
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Quote:
Originally Posted by DUG View Post
Have you used it to measure a known resistor?

i.e. 10R
Quote:
Originally Posted by merlin el mago View Post
If you use 10 ohms resistor you have to see more or less like this:

Click the image to open in full size.
Quote:
Originally Posted by Crashpc View Post
Hello. Your questions seem to be quite chaotic.
If you have lower impedance measured than DCR of the driver, you have done poor measurement. Firstly, check the multimeter. Meaure shorted leads of the multimeter to check if there is not parasitic resistance somewhere in your measurement tool. If yes, then you can calibrate it, or deduct the base (shorted measurement) value off your speaker measurement. Then measure the 100Ohm tool, if it is right. Measure on the cables, not on the resistor. Then you can check with Arta/limp with switched channels, if it also sees 100Ohm of your tool as real 100Ohm. Only after checking this, you are mostly sure, the HW is okay.

Another "geg" I encountered with exactly your issue is, that you might mistype the separator sign. Not sure if it is dot, or the other symbol. If the program measures lets say 5,6, and you write 5.8, it might see it like 5, because it didn't see the number behind separator.

After you checked all this, it must work. There is no other way.
Quote:
Originally Posted by ernperkins View Post
This may help: Easy ZMA and T/S Parameters Using The LIMP Module in ARTA - An Illustrated Guide.

Easy ZMA and T/S Parameters Using The LIMP Module in ARTA - An Illustrated Guide - Techtalk Speaker Building, Audio, Video Discussion Forum
I've done repeatly do that, and lucky me I've better measurement now Thanks for all the sugestion, you're rock!
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Old 21st April 2017, 07:31 AM   #7
Crashpc is offline Crashpc  Czech Republic
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ayokzone:
Hey. Thatīs awesome. Hope you enjoy and use your new gained skill for further scientific research :-)
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Old 21st April 2017, 07:48 AM   #8
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Quote:
Originally Posted by ayokzone View Post
I did use JIG with 100 Ohm Resistor, Use soundblaster audio card, short cable, but I confused because the impedance after measurement in LIMP is lower than DCR with multimeter.
The multimeter gives DC resistance of the voice coil. The impedance measurement reflects AC. While unlikely, I wouldn't be surprised if there are speakers that exhibit impedance that is slightly lower at some frequencies than at DC. I'd still check your measurement, though. The suggested test using a dummy resistor with known resistance is good.

Quote:
Originally Posted by ayokzone View Post
And with another driver that have specification sheet and rated 8 ohm, there's lower result (around 5 ohm) when I measure use limp.
The "impedance specification" is just that, a specification. There are some rules saying that the impedance of a "8 Ohm driver" must never be lower than some value. I can't remember the exact number, but it is certainly a bit less than 8 Ohm. I'd say your 5 Ohm minimum might be just about consistent with the 8 Ohm specification.

Quote:
Originally Posted by ayokzone View Post
Second question, is it the peak at LIMP measurement is free air resonant frequency?
Probably. Many drivers exhibit more than just one peak. There's usually one larger peak (the "free air resonance", if measured in free air), plus some smaller wiggles relating to other (often undesired) mechanical resonances in the driver (for instance spider or membrane resonances).

Overall, I'd recommend you to read a good text about speaker testing. I like the good old "Testing Loudspeakers" book by Joseph d'Appolito.
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Old 21st April 2017, 10:00 AM   #9
Crashpc is offline Crashpc  Czech Republic
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How is that possible to measure lower impedance on dynamic driver (with voice coil) to measure lower impedance?
Havenīt seen single occasion yet.
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