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Enclosure vibration measurements
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Old 14th January 2019, 10:16 PM   #31
George Schmermund is offline George Schmermund  United States
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I thought that it might be interesting to see what applying a simple bandpass filter would look like on a hammer tap using the same set up as described in post #28. These taps were done on the undamped panel. There was no averaging nor any attempt to reproduce the previous tests.


These 2 DSO images only show different taps with and w/o the filter. Channel 1 is unfiltered so that the force of the taps can be judged to be ~ equal. There was no attempt to be quantitative here, just a filter demo to show how a DSO measuring in the time domain can be used in these tests.
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File Type: jpg 2-DS0002.jpg (135.4 KB, 60 views)
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Old 19th January 2019, 02:56 AM   #32
George Schmermund is offline George Schmermund  United States
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This is a comparison of the 5th generation brass housing accelerometer along side of the previous 12L14 steel housing unit. The mass has dropped from 23 grams to 11 grams. The output signal levels are about the same, but the bandwidth on the new one is better.


The modal hammer is still being refined and everything still needs to be calibrated. When the designs have all pretty much stabilized I'll be able to offer up some real numbers about the capabilities and limitations of these 2 instruments.


Please excuse the focus. This camera seem to have a mind of it's own when it gets near my bourbon.
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Old 20th January 2019, 11:38 PM   #33
George Schmermund is offline George Schmermund  United States
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Now that I'm beginning to look at the modal hammer and accelerometer transducers more seriously it's time to start doing some measurements using charge amplifiers. These 2 DSO images are of the hammer tapping the same MDF panels as before.

The first image is of the hammer's signal going straight into the DSO's channel 2 input. As can be seen (and demonstrated in an earlier post) the half sine wave has been corrupted by the 1 megohm input resistance. The signal's amplitude is also attenuated. The signal has been averaged 4 times.

The second image is of the hammer having been passed through a very high impedance charge amplifier which allows the full signal from the hammer's force transducer to be collected and displayed undistorted by charge leakage. The charge amplifier has a low output impedance and can be adjusted to produce a calibrated force output signal to the DSO. This signal has also been averaged 4 times.
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Old 21st January 2019, 05:03 AM   #34
1audio is offline 1audio  United States
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Enclosure vibration measurements
Is it possible to miniaturze this enough to use on small objects like headphones? Please share some guidelines on building a system.
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Old 23rd January 2019, 12:40 AM   #35
George Schmermund is offline George Schmermund  United States
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I'm pretty sure that most things can be reduced in size by simply making them smaller. I have no plans at the moment to head in that direction. It's an open field, though.
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