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

[hongrn]

This modest contribution is for newcomers to this great hobby who have done kits, but wish to go deep (football pun intended) and design their own. We often read about budget constraints and especially about where to start. Well, here's one way to start determining the parameters of any speaker driver, and produce accurate ZMA files without breaking the bank. Here we go:

1. Download ARTA software (current version is 1.8.5) from http://artalabs.hr/download.htm.
Total cost: Free

2. Hardware Requirements:

a. Laptop or desktop running Windows 7 or 10.
b. Duplex soundcard – I suggest you experiment with your current duplex soundcard to see if there are incompatibilities before investing in a new card.
More info here: http://artalabs.hr/requirements.htm
c. Digital Multimeter (DMM).
d. Appropriate audio cables to connect jig, soundcard and speaker driver.
e. Weight for added mass method (explained below).
f. Double-sided scotch tape.

3. Measurement Jig Bill of Materials:

a. 6X3X2 project box:
http://www.parts-express.com/hammond...1-x-2--320-714

b. Dual binding post:
http://www.parts-express.com/parts-e...black--090-475

c. 2 pairs of RCA jacks:
http://www.parts-express.com/parts-e...-pair--090-278

d. One 100ohm resistor:
http://www.parts-express.com/100-ohm...rance--015-100

Total parts cost: $15.31

[hongrn]

4. Jig Construction -

[hongrn]

To generate a ZMA file from a speaker driver:

1. Connect the finished jig to the computer soundcard using the appropriate cables.

2. Start the LIMP module. Click Continue in Demo Mode. LIMP is fully functional in demo mode, except for the Save function.

3. Change the starting frequency to 10Hz, since the graphs of both PCD and WinPCD start at this same frequency.

[hongrn]

Right-click on the program to bring up the Graph Setup dialog box, change the Low frequency to 10Hz and click on Update. This will extend the graph from 20 to 10Hz (see lower left corner).

[hongrn]

Go to the Setup menu to select the drivers for your particular soundcard:



My soundcard is a Creative EMU 0204, so my setup looks like this:

[hongrn]

Next, calibrate the soundcard:

1. Click on the CAL icon to bring up the Calibrate Input Channels box.
2. Click on Calibrate in the Dialog Box to calibrate both channels. LIMP will alert if there’s a significant difference between the 2 channels. In the Status box, the channel difference is only 0.11dB, so the calibration process is successful.

Note: Do not connect your speaker driver to the jig during the calibration process.

[hongrn]

After the soundcard is successfully calibrated:

1. Position the driver on a hard, flat surface, while making sure the venting hole is not blocked, and connect the speaker driver to the jig.
2. Select Pink PN (Pink Periodic Noise) as the generator.
3. Select the M+P icon (magnitude and phase).
4. Click on the Record icon to start the measurement process, then click Stop once the waveform is displayed.

[hongrn]

You should see the following graph displayed:

[hongrn]

Under the File menu, select Export as Plain .ZMA file.

[hongrn]

Save the file on a hard drive location, and load into PCD to test. You should see the ZMA file appear on the driver impedance box as shown below. As you can see, PCD’s graphs start at 10Hz, so should the measurements in LIMP.

[hongrn]

To generate T/S Parameters for a speaker driver:

1. Save the graph as an overlay by selecting Set as overlay curve in the Overlay menu.

[hongrn]

2. Add about 20g of weight to the woofer and secure weight to the cone with double-sided tape. Four nickels can be used as each weighs about 5g, or enough weight to shift the resonance frequency (Fs) lower by at least 20% to 50%.

[hongrn]

3. Click Record again and click Stop when you see the graph below displayed. The first impedance graph (blue) is the original measurement, the second one (black) is with the added weight. Let's see if the added weight was sufficient.

[hongrn]

4. Next, click on the Analyze menu and select Loudspeaker parameters – Added mass method.

[jhollander]

Nice, thank you Hong