Bolserst's Complex Driver Inductance Calculator

[Ricci]

Bolserst is a long time contributing member over at DIYAudio forums. He has developed this spreadsheet that will take an impedance measurement and calculate the complex inductance of a driver. David McBean the author of HornResponse has added the capability to simulate using this data into HR. This is a much more accurate way to simulate and design speakers and subs.

In short if you are designing bass systems using modern, high power, long throw drivers and you are not accounting for complex inductance in your modeling; The models are probably not representative of what you would be building. Previously you would need to purchase costly software in order to derive and simulate using these parameters, or figure out a way to roll your own way.

The spreadsheet imports a text file of an impedance measurement and calculates the complex inductance specs. Additionally if you have an added mass or Vas (Known air volume) impedance measurement you can also import it and the spreadsheet will calculate all driver parameters needed for modeling. A driver file can then be exported for use in HR.

 

Semi-Le_Calc_V3.xlsm

[lilmike]

Thanks!  

Timing was just about perfect for my projects. I hope to get the sub designs finalized in the next couple weeks, then get some sawdust made before year end. Will drag out the measurement gear and get some impedance sweeps of my drivers as soon as I can, then see if the models still look OK. Neither driver has all that high of an inductance (Le/Re of 1.03 for the 15s and 0.47 for the 18s). 

[Samps]

Can the impedance sweep be done at low level, or does it need to be done with an amp?

[Ricci]

I would recommend using an amplifier for large high power woofers. However you don't need to run it as hard as you might think. 1 to 3 volts is plenty. The main thing is load invariance, linear response and freedom from clipping. If you cannot get an amp try to use a good quality headphone output these usually have a better result driving low impedance loads and a bit more current capability than a line level output. Things like the DATS can work in a pinch but the drive level is only a few milli-volts. It's not enough for accurate repeatable measurements on the types of drivers I usually test. IMHO.

[lilmike]

I'll add a second to Ricci's post. I typically measure big drivers at about a watt applied, so 2V for a 4R driver, 2.83V for an 8R driver.  My DATS and WT2 aren't quite enough for the big drivers, the Clio Pocket does OK though. The Clio manual recommends the lowest drive level that yields a clean signal. 

The headphone out on the UCA202 is almost enough power, but the crosstalk killed it as a contender, Pity, it was widely available and only $30. I haven't tried the headphone outs on the other Behringer USB interfaces I have. Maybe one of these days...

When I need an amp, I use an old single-channel amp I got from a buddy now, it is an old TOA. Overkill for the low level stuff and it weighs WAY too much to move around, but it was free and does the job.

Be sure to use a good meter and watch voltages when using an amp, it's way too easy to send more signal than the sound card can handle. Back to back Zener diodes and/or voltage dividers are a good idea. 

Yeah - my last post was ambitious... It has been damn near 6 months and I still haven't had the time to pull final specs and design final boxes. Worse yet, I am rapidly working my way through my stash of plywood building other projects.

[Ricci]

I hear that Mike...Way more ambition than time eh? I know that story.

I second the caution to watch the SC input level. It's easy to smoke one with an amp. I'm using an old Crest 8002 with a blown channel that it isn't worth it to fix. Does just fine with the 1 good channel sitting on a test bench though.