No, as said a piezo-buzzer is very non-flat and very limited in BW. OTOH you could probably excite the tonearm/cart low frequency resonance with one.
I think a DC voltage causes the disk to flex in a DC sense as in the excitation on a microphone collapses the diaphragm.
My guess is that people use test LPs to check cartridge frequency response as this is the cheapest most convenient way to do it. To get another transducer which is sufficiently flat in frequency response and sufficiently robust etc might cost quite a lot. It may also be the case that the frequency response is affected by whatever is at the end of the stylus so you want vinyl there - to test an item it often makes sense to put it in something like the working environment it was designed for.
Thinking like mad scientist so hope no one laughs 
...if we take another cartridge and harden the cantilever suspension and somehow couple it to measuring cartridge's cantilever and supply low voltage frequency sweep to the first cartridge's terminals....
1) would the cantilever move ?
2) if it moves, would it accurately transfer the vibrations to the measuring cartridge ?
Regards.
...if we take another cartridge and harden the cantilever suspension and somehow couple it to measuring cartridge's cantilever and supply low voltage frequency sweep to the first cartridge's terminals....
1) would the cantilever move ?
2) if it moves, would it accurately transfer the vibrations to the measuring cartridge ?
Regards.
It is quite a challenge since reciprocity is very difficult to achieve with mechanical coupling unlike condenser microphones which can be calibrated to fractions of a dB this way.
Perhaps (I didn’t test it), having the cartridge fall on a record and recording the generated signal after the MM (or MC) preamp with a program like ARTA (or any other that can work with external signal excitation) would give you some insight regarding the response. I would imagine that this would produce something close to an impulse response to the cartridge coils. Else, there are some test disks with pink noise.
Yes, Peter Moncrieff used to do this. He never demonstrated that it correlated well with the measured frequency response
from a test record, though.
That can be normalized out. The rest of your post I agree with. The main issue with test records is that frequency responses from one test record to another don't seem to be terribly consistent. The cutter? The vinyl? The pressing? Who knows, the medium itself is full of uncontrollable variables.
Since a buzzer is resonant in the band of interest makeing the loop stable is challenging as well as the problem that you want constant velocity not displacement (I think?). Possibly a tiny SMT accelerometer glued to one would work and give a piece of "plastic" to sit the stylus on. In either case probably calibrating at several frequencies is better than trying to close the loop.
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OTOH as the library of congress and others have proven, you can take a photo of the record and get the information off that way You Can Play the Record, but Don't Touch : NPR . Can't be too long before some DIYs that, possibly not to this standard but enough to get the response curve off the vinyl?
For the well heeled there is of course the Finial. Someone must have one of those somewhere...
How about using Hard Drive read/write head (if it can be controlled by a circuit) Magnetic field on HD surface is 10 nM* which is equal to 0.01 micron. Minimum Vinyl groove modulations is 0.1* micron, so we make a small hole resting place in which stylus diamond can be placed and we move HD head on all frequency range at particular speed. Would that simulate proper frequency response on cartridge output terminals ?
Regards.
* All data from the net.
Regards.
* All data from the net.
My concern was that it is easy to get into the problem of subtracting big numbers to get a result with lots of digits but few significant figures. If you are measuring something which is supposed to be approximately flat it helps if the measuring device is similarly flat, then errors don't accumulate too much.SY said:
Apart from the coupling problem which Scott raised, I think you could in theory do this with three transducers, measuring them in pairs. A similar trick can be done with radio antennas. I suspect that real life is not so simple.
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