Thiele-Small Parameters measurement using dual added mass method.

miniDSP and AV Nirvana

jcandy​

Hello. There is a question how to fix the driver during the measurement of parameters. The driver must be positioned vertically in the air. The question is how to fix it correctly? Intuitively, it seems that the driver should be fixed through the holes in the basket that the manufacturer made for this, to some kind of structure that can hold the driver so that there are no obstacles around the driver. But on your videos and pictures, the driver is fixed by a magnet. In some cases, there are solutions when the driver is fixed to the housing by a magnet, and the basket is fixed in the hole by pressing. But in most cases, the drivers are fixed to the case through holes around the circumference of the basket. So how to properly fix the driver so that there are no parasitic vibrations during the measurement?
 

John Mulcahy​

I measured a driver that has very low sensitivity. About 80 dB. During measurements, the sweep was very quiet. It's usually louder. Can the measurements be trusted in this case? Should there be a dependence of the level of the measuring signal on the sensitivity of the driver being measured?
 
Dual added mass measurements include a Bℓ curve, it should be close to horizontal around the resonant frequency if the measurements are good.
 
Thank you. The parameters include Lp. In my case it is 80.24 dB (1W/1m). The help doesn't describe what it shows. I couldn't find a description of it on the Internet. Does it have anything to do with driver sensitivity?
 
It is the calculated power sensitivity, but it is generally better to use the manufacturer's figure.
 
To answer your question in post 77 about measurement level, the usual advice is to say that for good comparison with linear theory, the level needs to be high enough to have a good S/N ratio, but low enough to avoid nonlinearity. Practically this means something between 10mV and 500mV for 3in-8in drivers. For larger drivers and for modeling high-power applications, you will of course want higher voltages. Is there a specific question about Speakerbench?
 

John Mulcahy,​

Does it matter at what signal level I calibrate the equipment before measuring the impedance? If I plan to measure impedance at levels of 100-700 mV, at what level should I calibrate? And if at the levels of 1.4-3 V, at what level should the calibration be done?
 
Thank you. The picture shows two tables of TS parameters created based on the same data. Left from REW, right from Speakerbench. I highlighted a small discrepancy in blue, and a large discrepancy in red. Is there anything that can be done to ensure that the parameters marked in red match closely?
 

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A lot of parameters have significantly more resolution than seems appropriate. Some measured parameters likely have a significant accuracy tolerance, depending on how the measurement was taken, and with what means, and whether the measurement was done at an appropriate location (eg. the voice coil resistance). It almost suggests the need to use a monte carlo simulation to appreciate what range a calculated parameter could end up with.
 
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