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

[hongrn]

5. In the Loudspeaker Parameters – Added Mass Method dialog box:

1. The frequency shift is 30% with the 20g, so within the recommended limit. Add or subtract weight as required to ensure the shift is correct and re-measure if necessary.
2. Use the DMM to measure the Voice Coil Resistance (Ω) of the speaker and enter the value in this box.
3. Enter the piston diameter in cm by measuring from mid-surround to mid-surround.
4. Enter the value of the mass used.
5. Click on Calculate Parameters.

[hongrn]

6. The complete parameters are now displayed. Select Copy to copy the parameters and paste into Notepad or a word processor to be saved, or enter the values into your favorite box design program to start calculating box volume.

[hongrn]

I hope you find this thread useful. Please let me know if there are errors. The forum does not let me upload a 2.5MB pdf, so if you wish to have this set of instructions on one document, please email me at hongrn AT sbcglobal DOT net. Thanks..

Hong

[wogg]

This is fantastic, thanks Hong! Sent from my SM-G920P using Tapatalk

[Millstonemike]

Very good write up and info. A question; how might the tolerance of the 100 ohm resistor effect the accuracy of results?

[hongrn]

Very good write up and info. A question; how might the tolerance of the 100 ohm resistor effect the accuracy of results?

It would be a good idea to pick one with the least tolerance. I had a whole bunch of 100 ohm resistors, so I picked the one that measured 99.96 ohms.

[Jeff B.]

Very nice.

[Neis]

Thank you!

[johnnyrichards]

The only thing I would add is it is worth tweaking what you enter for the resistance value based on LCR measurements. To get it accurate, you may have to change it a few ohms up or down. My LCR measurements using LIMP match my measurements using my DER EE LCR meter within 0.1%. With a correct setup and using pink noise, LIMP is as fast and accurate as any of the turn-key solutions out there. The "estimate DCR" feature, however, is hit or miss. I am going to investigate it further and see what can be done about that.

I use a Soundblaster X-Fi now - I had built a setup using a cheap soundcard but after some time I wanted more accuracy below 40Hz and the El-cheapo exhibited some drift down low. My next step was one of those Behringer Uphoria cards (forget the model number - 204 maybe?), but that thing was a noisy POS.

My only real complaint about LIMP is the lack of ability to store more than one overlay in memory. Otherwise, it is a very nice bit of software.

[donradick]

Excellent addition to the knowledge base Hong!

Couple of very minor nits:

when the test is running, I never click on "stop" - the prog stops automatically when it reaches 20Khz.
I've read that the drive needs to be in a horizontal position (magnet down, cone up) and securely fastened to the table or desk.
I've used clamps or made a little jig that I mount the driver into.
Won't your free weights on the cone bounce around too much for accuracy? I've always attached weights (nickels) to the cone using
blue tape or 3M blu tac putty.

Please forgive any implied criticism - you have contributed a very nice and useful guide.

regards

[skatz]

So very clear and concise, even I can follow it with no problem! Thanks.

[Chris Roemer]

If your weights "jump" (or even if the driver jumps, which a lighter driver w/a strong motor - like neo, WILL do - unless you hold it down somehow) you'll see it 'cause the Z-plot won't be smooth - it'll have "wiggles" in it. Sometimes I might add like 4 nickels around the dustcap - but the plot won't be smooth. Most of the time adding another nickel or 2 is all it takes to smooth it out. I usually just hold pressure down on the driver frame w/a free hand.

[hongrn]

Thanks everyone for your comments.

Don, please don't be so apologetic about chiming in. I love your feedback man! You don't have to click on Stop when you use the Stepped Sine generator. In my write up, I use the Pink Noise generator, which runs continuously, so you'd have to click on Stop. Another advantage of the continuous Pink Noise is that the signal is small, so it doesn't seem to make the weight jump and subsequently distort the plot. Here are the plots for the added weight (red line), and the same weight secured to the cone with double-sided tape (black line). Anyway, I'll add the tape suggestion to the write up just to be on the safe side. Thanks guys and please continue to post your comments.

[johnnyrichards]

You can set it to do a single burst of pink noise so you do not have to manually stop it, as well.

[hongrn]

You can set it to do a single burst of pink noise so you do not have to manually stop it, as well.

What's the setting? Thanks Johnny.