Developed an amplifier circuit to power up the speaker with a signal generated from function generator in the audio frequency range with manually changing amplitude and freq. of the signal. Now I have to find the speaker cone displacement using any method. I am currently looking at current sense circuit(Low side). But not able to understand the result! Can anyone tell me the feasible method to measure the exact displacement of speaker cone?
I also want some relationship with applied signal amplitude with displacement of speaker cone?
Please help.
Do you have access to an accelerometer (or a LASER vibrometer or anything similar) and can you generate harmonic signals at different frequencies?
With an accelerometer you will be able to measure the acceleration of the speaker cone at a given location, which, when divided by -w^2 (w is the angular frequency in rad/s), gives you the displacement.
a(t)=-w^2*x(t)
If you want to avoid affecting the frequency response due to the added mass, I would suggest using a miniature piezoelectric accelerometer (this can cost between 300 and 500 GBP) placed as close as possible to the centre of the piston (I would avoid placing it at the membrane).
I suppose that you can use a signal generator, but I am assuming that you do NOT have a spectrum analyser. In that case, what you need to do is to use a Stepped-Sine signal. This consists of applying harmonic signals (sine waves) at consecutive discrete frequencies. This can be a bit time consuming, depending on your frequency range, bandwidth and intended spectral resolution.
A transfer function could then be determined from the ratio between the amplitude of the response sine wave and the amplitude of the applied signal.
Assuming the system is linear, you can validate your results by repeating this process for different applied signal amplitudes.
Not sure this helps, as you will need to have some equipment available to measure the displacement of the cone (I am assuming it is a piston speaker).
Good luck!
Thank you for the answer. I'll try to use the concept as suggested.
I am using a function generator as a signal generator with a frequency range of 1-500Hz varying manually with signal amplitude. I am using a current sensing circuit by connecting sense resistor in series with speaker, calculating the load current in terms of voltage using op-amp. At this stage I am facing a problem such that not able correlate the current or voltage with applied signal amplitude or freq.!
Another method I am trying to use as a LASER sensor which is bit useful but costlier. That's why I moved towards circuit based measurement.
Can someone tell me how I can link (in terms of relation) the speaker cone displacement with applied signal amplitude/freq.? Is there any circuit that I can use here for the same?
Thank you for the answer.
I have attached a stud based shaft arrangement onto speaker cap at center. I am mounting an accelerometer on that shaft as a feedback. Now I need to find the displacement of the speaker by means of any circuit or assembly to measure the vibration amplitude generated by speaker. Laser assembly is a good option but cost is too high (Still looking for it). What if I connect a shunt resistor at loudspeaker end in series to calculate the current through speaker? But the issue is I am not able to understand the signal across the shunt resistor and how to relate it with amplitude of signal!
I am attaching a current sensing circuit which is similar to my circuit with system load as speaker.
Sorry if my questions look irrelevant.
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