Easy ZMA and T/S Parameters Using The LIMP Module in ARTA - An Illustrated Guide

[johnnyrichards]

Setup>Measurement>Averaging>Linear>Max Averages 1 will do a single burst. At work so cannot confirm 100% this is correct, will double-check when I get home.

Great thread, by the way - home made jigs and free software are definitely in the spirit of DIY.

[hongrn]

Setup>Measurement>Averaging>Linear>Max Averages 1 will do a single burst. At work so cannot confirm 100% this is correct, will double-check when I get home.

Great thread, by the way - home made jigs and free software are definitely in the spirit of DIY.

Good memory for an old man! Yep, that's the setting! Thanks Johnny.

[donradick]

Thanks Hong
I've got to explore the pink noise option.

[Derekj]

Great write up Hong! How important is it to have an Intel chip? I run an AMD in my computer but the wife's laptop is an I3.

[johnnyrichards]

Great write up Hong! How important is it to have an Intel chip? I run an AMD in my computer but the wife's laptop is an I3.

ARTA is pretty much cpu independent so no worries.

[Derekj]

ARTA is pretty much cpu independent so no worries.

Thanks JR!

[Derekj]

So I built my jig and installed the software. Following the instructions I hooked a driver up to my jig and tried an impedance measurement. This is what I got, any ideas? I have a Creative x-fi titanium card. I tried to google the volume settings in windows for Limp but couldn't find anything.

[deschu]

Great guide! Thank you!

The following are all minor comments from my preferences.

Resistors are typically cheap and if you are already placing an order with one of the "other" electronics suppliers, you might want to specifically get a higher tolerance and specifically non-inductive resistor. For example, VIshay CPF3100R00BEE36 is about a dollar and is 0.1% 3W metal film (non-inductive), silicone coated and has a low temperature coefficient. So it should be darn near 100 Ohms darn near all the time. On the other hand you could get a 100 Ohm wirewound that has some impedance that impacts the measurement (but I haven't run a tolerance study --- an RS180-4 is about 0.45mH though). Some wirewounds have a special winding to make them non-inductive, but metal film resistors are typically the lowest inductance resistor flavor, and some piece of mind is never a bad thing.

If portability is key, one might consider flying cables to 3.5mm/RCA plugs and/or Pomona Mini-Grabber's (alas $$$) on the speaker side --- you can beat the size of the DATS-V2 this way and you can typically avoid the alligators inevitably snapping off the terminals if the grabbers can hook thru/onto the speaker's terminals. And you don't have to have a project box, just some creative soldering and heatshrinking should do it.

I was under the impression that the "reference" orientation for impedance testing was with the axis of the driver parallel to the ground, e.g. driver vertical, such that gravity was not acting in-line with the coil. It may not make much of a difference for most drivers (?), and the stated orientation in the tutorial is far easier for the added mass method and most importantly it's generally much harder to keep the driver stable when vertical and without a fixture.

This should be obvious, but in case it isn't to some newbies, but the testing should be done in a quiet location. Speakers are microphones after all.

Finally (and also obvious as above) it is often a good idea to repeat the same measurement (same serial number and test process) and understand the observed vs. expected variation.

[hongrn]

So I built my jig and installed the software. Following the instructions I hooked a driver up to my jig and tried an impedance measurement. This is what I got, any ideas? I have a Creative x-fi titanium card. I tried to google the volume settings in windows for Limp but couldn't find anything.

@Derekj,

Assuming that it is a full duplex card, I would check to make sure that the drivers are loaded correctly, and that they show up when you select "Audio Devices" under the "Setup" menu. Also, was the calibration successful? Check out section 4.2 of the LIMP manual, "Soundcard" Setup for more details. Good luck and let us know if you're able to resolve this issue.

http://artalabs.hr/download/LIMP-user-manual.pdf

[hongrn]

Great guide! Thank you!

The following are all minor comments from my preferences.

Resistors are typically cheap and if you are already placing an order with one of the "other" electronics suppliers, you might want to specifically get a higher tolerance and specifically non-inductive resistor. For example, VIshay CPF3100R00BEE36 is about a dollar and is 0.1% 3W metal film (non-inductive), silicone coated and has a low temperature coefficient. So it should be darn near 100 Ohms darn near all the time. On the other hand you could get a 100 Ohm wirewound that has some impedance that impacts the measurement (but I haven't run a tolerance study --- an RS180-4 is about 0.45mH though). Some wirewounds have a special winding to make them non-inductive, but metal film resistors are typically the lowest inductance resistor flavor, and some piece of mind is never a bad thing.

If portability is key, one might consider flying cables to 3.5mm/RCA plugs and/or Pomona Mini-Grabber's (alas $$$) on the speaker side --- you can beat the size of the DATS-V2 this way and you can typically avoid the alligators inevitably snapping off the terminals if the grabbers can hook thru/onto the speaker's terminals. And you don't have to have a project box, just some creative soldering and heatshrinking should do it.

I was under the impression that the "reference" orientation for impedance testing was with the axis of the driver parallel to the ground, e.g. driver vertical, such that gravity was not acting in-line with the coil. It may not make much of a difference for most drivers (?), and the stated orientation in the tutorial is far easier for the added mass method and most importantly it's generally much harder to keep the driver stable when vertical and without a fixture.

This should be obvious, but in case it isn't to some newbies, but the testing should be done in a quiet location. Speakers are microphones after all.

Finally (and also obvious as above) it is often a good idea to repeat the same measurement (same serial number and test process) and understand the observed vs. expected variation.

Derek, very valid points about the quality of the resistor. Thanks for your feedback.

Hong

[johnnyrichards]

One common error in LIMP jigs is not properly wiring said jig, Derekj

Take a few minutes and go through it again. After a few head scratching moments, I ended up re-drawing the schematic in a way that made it easier for me to understand:



Then, follow Hong's excellent advice. If you have more than one soundcard installed on the system LIMP will sometimes default to the wrong input/output. Also check to make sure LIMP did not select a mic input instead of a line input.

[MrSllez]

I also recently made a simple tool for impedance/TS parameter measurement with REW. 3D printed case with 100ohm resistor and switch for calibration. Connection with sound card is with 2 aux cables and the output has 2 alligator clips.

http://imgur.com/a/sgR06

[mattsk8]

Wow, hongrn , well done! This should definitely be a sticky.

[Derekj]

@Derekj,

Assuming that it is a full duplex card, I would check to make sure that the drivers are loaded correctly, and that they show up when you select "Audio Devices" under the "Setup" menu. Also, was the calibration successful? Check out section 4.2 of the LIMP manual, "Soundcard" Setup for more details. Good luck and let us know if you're able to resolve this issue.

http://artalabs.hr/download/LIMP-user-manual.pdf

When I run the Setup for audio devices it shows my Creative Sound card. The calibration runs successfully too. I followed the setup up procedure in the manual for setting up the card. Here are a few screenshots of the settings I used for speakers and recording. At first I was using the rca inputs on my sound card, then I tried the microphone input on the back of the sound card which is what the screenshot shows.

I checked the wiring for the jig as per JR's diagram and it seems ok. I checked all my connections with my meter when I put it together.

johnnyrichards where do you tell Limp which input you are using? Is it just in setup/audio devices?

[johnnyrichards]

When I run the Setup for audio devices it shows my Creative Sound card. The calibration runs successfully too. I followed the setup up procedure in the manual for setting up the card. Here are a few screenshots of the settings I used for speakers and recording. At first I was using the rca inputs on my sound card, then I tried the microphone input on the back of the sound card which is what the screenshot shows.

I checked the wiring for the jig as per JR's diagram and it seems ok. I checked all my connections with my meter when I put it together.

johnnyrichards where do you tell Limp which input you are using? Is it just in setup/audio devices?

Yessir