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I have to measure the displacement of speaker cone with change in...
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Pamela Anne Trinidad
I have to measure the displacement of speaker cone with change in...
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'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?
To find the correct relationship between voice coil current and acceleration of the piston, you need to get both the signals in the same domain. So convert the current waveform sample from displacement to acceleration by differentiation in two stages using two operational amplifiers. This will get both of your signals in a form where they can be compared. Alternatively you can look at velocity, which could yield more useful data of what is happening? This would require one stage of differentiation for the current signal, and one stage of integration on the accelerometer signal. I hop that you understand what I'm getting at? Best regards, Mike.
To find the correct relationship between voice coil current and acceleration of the piston, you need to get both the signals in the same domain. So convert the current waveform sample from displacement to acceleration by differentiation in two stages using two operational amplifiers. This will get both of your signals in a form where they can be compared. Alternatively you can look at velocity, which could yield more useful data of what is happening? This would require one stage of differentiation for the current signal, and one stage of integration on the accelerometer signal. I hop that you understand what I'm getting at? Best regards, Mike.
The voice coil will try and follow the input waveform, but it is held back by the compliance of the speaker cone. The centre of the speaker cone can however be modelled as a piston following the current into the coil without too much error. However, at the edge where the cone meets the chassis there is little movement. So you cannot model the entire cone as a linear piston. depending on the speaker cone material, stiffness and suspension characteristics, the speaker cone is complex to model correctly. You will find that at certain frequencies the cone will distort, and be subject to axial and radial modal vibrations. Shining a laser will show deviation at different positions, but you will not see modes. A scanning laser may show how the cone is distorting, and yield better data. This has been done using laser holography to reveal actual displacements very well. So returning to your question, you need to deflect light so you do not add mass and therefore you will be able to see the try deflection. If you add mass comparable to the mass of the paper cone. you will get poor results. I hope this helps?
The voice coil will try and follow the input waveform, but it is held back by the compliance of the speaker cone. The centre of the speaker cone can however be modelled as a piston following the current into the coil without too much error. However, at the edge where the cone meets the chassis there is little movement. So you cannot model the entire cone as a linear piston. depending on the speaker cone material, stiffness and suspension characteristics, the speaker cone is complex to model correctly. You will find that at certain frequencies the cone will distort, and be subject to axial and radial modal vibrations. Shining a laser will show deviation at different positions, but you will not see modes. A scanning laser may show how the cone is distorting, and yield better data. This has been done using laser holography to reveal actual displacements very well. So returning to your question, you need to deflect light so you do not add mass and therefore you will be able to see the try deflection. If you add mass comparable to the mass of the paper cone. you will get poor results. I hope this helps?
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.
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.
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!
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'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?
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To find the correct relationship between voice coil current and acceleration of the piston, you need to get both the signals in the same domain. So convert the current waveform sample from displacement to acceleration by differentiation in two stages using two operational amplifiers. This will get both of your signals in a form where they can be compared.
Alternatively you can look at velocity, which could yield more useful data of what is happening? This would require one stage of differentiation for the current signal, and one stage of integration on the accelerometer signal.
I hop that you understand what I'm getting at? Best regards, Mike.
To find the correct relationship between voice coil current and acceleration of the piston, you need to get both the signals in the same domain. So convert the current waveform sample from displacement to acceleration by differentiation in two stages using two operational amplifiers. This will get both of your signals in a form where they can be compared.
Alternatively you can look at velocity, which could yield more useful data of what is happening? This would require one stage of differentiation for the current signal, and one stage of integration on the accelerometer signal.
I hop that you understand what I'm getting at? Best regards, Mike.
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VOTE
The voice coil will try and follow the input waveform, but it is held back by the compliance of the speaker cone. The centre of the speaker cone can however be modelled as a piston following the current into the coil without too much error. However, at the edge where the cone meets the chassis there is little movement. So you cannot model the entire cone as a linear piston. depending on the speaker cone material, stiffness and suspension characteristics, the speaker cone is complex to model correctly. You will find that at certain frequencies the cone will distort, and be subject to axial and radial modal vibrations. Shining a laser will show deviation at different positions, but you will not see modes. A scanning laser may show how the cone is distorting, and yield better data. This has been done using laser holography to reveal actual displacements very well. So returning to your question, you need to deflect light so you do not add mass and therefore you will be able to see the try deflection. If you add mass comparable to the mass of the paper cone. you will get poor results. I hope this helps?
The voice coil will try and follow the input waveform, but it is held back by the compliance of the speaker cone. The centre of the speaker cone can however be modelled as a piston following the current into the coil without too much error. However, at the edge where the cone meets the chassis there is little movement. So you cannot model the entire cone as a linear piston. depending on the speaker cone material, stiffness and suspension characteristics, the speaker cone is complex to model correctly. You will find that at certain frequencies the cone will distort, and be subject to axial and radial modal vibrations. Shining a laser will show deviation at different positions, but you will not see modes. A scanning laser may show how the cone is distorting, and yield better data. This has been done using laser holography to reveal actual displacements very well. So returning to your question, you need to deflect light so you do not add mass and therefore you will be able to see the try deflection. If you add mass comparable to the mass of the paper cone. you will get poor results. I hope this helps?
More
VOTE
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.
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.
More
VOTE
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!
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!
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