t/s parameter related question

Moon3041

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Hello, this is my first post in this forum. So if I posted my question in inappropriate section, I apologize.
I have a pair of quite old 8 inch (4 ohm) car woofers (Megavos MGX 883) for which I no manufacturer's specification. Since I have zero experience in measuring t/s parameter, I followed an you tube video. I used a 67.75 ohm resistor as sense resistor, a 9.75 ohm resistor for calibration and PC sound card. for weighted measurement I used 73 gm (close approx.) and 277 gm (close approx.) in two passes. Now, the problem is that after calculating t/s value, I'm having hard time believing the Qms measurement. Therefore, I probably messed up somewhere along the way, but lack sufficient knowledge to troubleshoot the graph. I would really appreciate it If someone can shade some insight.
 

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I would say that the measurements you made have some problems especially related to the mass you used, in fact 73gm and 273gm are absolutely too high values and could give incorrect results. However, the measurement method with added mass is used to calculate the T / S parameter of the Vas while the other parameters are obtained from the impedance curve in free air and from the measurement of the electrical resistance in DC of the moving coil. If you don't need high accuracy on the VAS you can use the method with only 1 added mass which from my experience for an 8 inch speaker could be roughly 5 / 10gm no more. As for the impedance calibration, if you use an audio amplifier to drive the speaker the value of 67.75 ohms is too high and with the excessive weight you used it certainly leads to not having an optimal electrical signal level at the speaker, this is even more true if you don't use an amplifier.
The optimal value of the electrical resistance with power amplifier should be approximately between 20/40 ohm max.

Greetings Antonio
 

sm52

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For everything to work out well, you need to very accurately measure the mass of the weights. Ideally with two decimal places. The first mass should be 87-90% Mms. The second mass should be half of the first.
 
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Certainly the mass must be precise, I use an electronic precision scale with a maximum capacity of 50gm, but I never use the vas measurement with double mass.The Vas measurement is very variable because the ambient temperature and the working times of the vas also depend on many factors. The loudspeaker, in fact, the more it works, the more the suspension heats up and the compliance varies accordingly. I am satisfied with the measurement with only one mass added, I do not consider it a parameter that needs a very high precision.
 

Moon3041

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Thanks for the explanation, I'll be more mindful to the weight next time I measure the parameters again.
 
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