Measuring impedance& TS parameters using REW

Hi everyone. I have this new locally manufactured 8 inch mid-woofer driver(8 ohms). I m currently measuring this driver using REW(on mac) with a simple jig(attached the schematic which is from a arta limp manual) with 100ohm carbon resistor. Initially I calibrated the sound card (uca 202) with headphone right out looped back to right line in. The calibration process went on smoothly.

But when I clicked on measure module of the REW program I got this message(attached) that SPL meter is not calibrated. I don't understand this since I am not using spl meter to measure. Anyway I went ahead with the impedance measurement. Before that I had to calibrate the impedance jig with the resistor shorted out and the drivers removed. This step was successful. Then with the resistor connected and the driver load connected and the resistance value fed into the program I made a impedance measurement. The programs measurement has me little confused because the impedance values are above 100 ohms. where have I gone wrong here. Is it something to do with the SPL calibration?. Any advice in this regard will be appreciated. Thanks in advance!.

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^:up: it also says the following

Tony.

Thanks a lot!. It works now after swapping the left right channels. But whenever i select the measure option I get this message "spl meter not calibrated".I have calibrated the sound card with the headphone right looping into the right input channel. Is calibrating SPL necessary for impedance and TS measurements?. Will the results be inaccurate if I don't do so?. Kindly advise.
 

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AS for measuring TS parameters I made two impedance sweeps, the second one with mass added. I was prompted by the software to enter a lower DCR value a couple of times while I clicked the calculate button. The measured DCR was 5.46 Ohms(voltage divider method with a resistance in series)....finally ended up entering 4 ohms after which I did not get the warning message. I am not sure about the measurements particularly of le in blocked impedance parameters which is 19,698,092.277 mH. Is something wrong here and wrong with the the overall procedure I am following?. Please advise.
 

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wintermute

Administrator
Paid Member
2003-08-03 11:43 am
Sydney
It's been a while since I did any impedance measurements with REW, but I did get sensible results for all the T/S params... there is definitely something screwy going on with your measrements the Le should be realistic.

edit: how accurately did you measure your added mass, and how well attached to the cone was it? I usually use bluetack rolled out and placed around the dust cap. It needs to be firmly attached and not moving around.

Tony.
 
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