How do I shrink and export SW impedance measurements?

[owdi]

I cannot figure out how to export impedance measurements from Speaker Workshop into a format that is usable by the FRD Consortium tools. I can export the impedance chart, but the resulting zma file is 4mb, causing Frequency Response Combiner to puke. My goal is to use the data in Passive Crossover Designer.

I've looked at several tutorials, but none seem to address this. I need to export the impedance measurement into a zma file with about 1000 data points. Is this possible?

If it's not possible, I'm stuck with taking a second set of measurements, and reducing my sample size. Seems a bit silly since I already have good measurements.

On a side note... the scale of my gated measurements in SW seems weird. The ungated near field and far field measurements are fine, but gated shows about 25db of baffle step.

Dan

[Dave Bullet]

Right click the dataset in question (FR or impedance)
Select properties
Select specifics tab
Select number of points radio button, then enter whatever you like. recommend somewhere between 256 and 1024 points resolution (so FRD tools don't get upset / take too long).
Click ok and the dataset will be truncated in SW
Export as per normal.

Hope that helps

David.

[Dave Bullet]

On a side note... the scale of my gated measurements in SW seems weird. The ungated near field and far field measurements are fine, but gated shows about 25db of baffle step.

what is your gate interval? (between markers).

In SW - resolution increases with increasing frequency. Divide the gate into 1000 and that is the lowest "usable" frequency. Anything below that is garbage. ie. a 4msec gate results in measurements down to 250 Hz (1000 / ) although the resolution is poor below about 500 Hz.

The only ways to increase the resolution of SW at lower frequencies i
a) nearfield measurements
b) longer gate (which means outside measurements or a very large room)
c) sound card with a higher sampling frequency ie. supprts 96kbps

Dave.

[owdi]

Hello Dave,

Thanks for the reply, I will try that tonight.

My gate is aprx. 5ms, and SW only displays the FR from 200hz and up. The difference between 200hz and 1200hz is 25db. Above that there is some ripple, which Arta measures at 2-3 db, but SW measures at 10-12db. It's weird, but I don't care too much, since I'm using the Arta FR measurements.

Dan

[Dave Bullet]

My gate is aprx. 5ms, and SW only displays the FR from 200hz and up

That's fine. 1000/5msec gate = 200Hz (lowest FR SW will measure at that gate interval).

I presume you have done all the calibration steps. Are you using an external amplifier for FR measurements? What Mic are you using?

I haven't experienced that problem before. Luckily for me my setup worked first time (quite a fluke really).

I am using an old PII/450 Windows PC - running Windows 98SE with a cheapo Soundblaster 128PCI sound card. Only capable of a 48kbps sampling rate. Event-1 pre-amp (includes +48v phantom power) with an ECM8000 mic and 10m balanced XLR cable. Hard wired jig between soundcard and pre-amp / voltage divider for impedance measurements. The only calibration step I didn't do was amplifier calibration. I am using a generic ECM8000 calibration file that gave a matching response to several published curves of the same tweeter (since the ECM8000 is more or less flat upto about 2KHz from where some rise, some don't etc....)

I've had weird measurements when I've forgotten to switch in the +48v phantom power, but that is the only scenario I can think of (especially if your nearfield and ungated farfield are ok).

Can you please publish a screen shot of your marker settings for the gated measurements?

David.