Thiele Small Question

Hello everyone!

I'm doing some tests with REW to get T&S parameters and I had a question about a accuracy of my measure. I think that my audio interface doesn't have the necessary gain to get a perfect curve because if I use -12 dBFS I get a curve with a lot of peaks and when I use 0 dBFS the response is quite better.

I don't have a amplifier to use in the middle (I accept suggestions).

So I will add some images of my tests:

1 - My Audio Interface, M-Audio M-Track https://www.m-audio.com/legacy/m-track.html


2 - Speaker I'm measuring, JBL 62V2A 6 inches https://www.jbl.com.br/on/demandwar...BL_62V2A_-_par_28085151_manual_portuguese.pdf


3- Soundcard levels:


4- Soundcard calibration:


5- Open Circuit Calibration:


6- Short Circuit Calibration:


7- Reference Calibration (456 Ohms):


8- First measuring using -12dBFS:


9- Second measure using 0dBFS:


10- Measure 0dBFS with added 14g mass:


11- TS result:


12- REW result side-by-side with factory measurement:


My mainly question about the measure I got is:
Is it reliable?

Thank you.

Doesn't look very reliable. You can find tips on measurement setup in the Speakerbench manual. Use a resistor closer to the range of impedances you expect to measure for the reference calibration step. The measurements are suffering from mains hum pickup and noise, rearranging the positions and layout of the test leads may reduce that. The interface headphone output may have better drive capability.

If as a result you have received almost factory TS parameters of your drivers, this confirms the correct measurement. The obstacles visible on the graphs are the result of poor contacts and network interference. The resistance of a short circuit should be much less, 0.5 om or less. But this does not cancel the result. In the factory parameters there is SD = 137 cm sq. You indicated 152 cm sq.

Hello guys.
Just to update. I've bought a 100ohm 1% resistor and made my calibration with 12ohm 1% resistor (I will test with some value closer to 4ohm) and now the response is quite better.

Looking to this amplitude I think that is so low, could you please help me to understand if is necessary to have a amplifier to be more precise?

Looks good as it is.

Thank you for reply.
It's good to know that is a good measurement. I just don't understand why the T&S parameters is so different of the speaker's manual.

brunohydra said:

I just don't understand why the T&S parameters is so different of the speaker's manual.

Click to expand...

This is so for several reasons. First. You do not know at what voltage the manufacturer received the parameters. Different data are obtained at different voltages. Second. You did not choose the added mass well. Third. The double added mass method is more precise than the method of one added mass. Fourth. If the driver was in a horizontal position during the measurement, as in the picture, then this is incorrect. Fifth. To obtain accurate results, you need to bring the driver into a linear state.