I am trying to find tranducers that can be attached to a musical instrument (the Japanese koto). In addition I need some kind of signal output (as a complex number) device that I can analyze off line.
The purpose of this request is to measue, as a function of acoustic frequency (say 30 Hz to 3000Hz but the range is arbitrary for now), the damping of the wood fom which the instrument is made, ideally in each
direction (x, y, z).prefered method for wood damping .
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Hi Eric.
Mostly the acoustic transducers the average person comes across are called microphones.
I assume you want to measure the actual movement of the actual wood in 3 directions. I don’t know iff accelerometers would be sensitive enough for this but all you can do is try.
Someone else may have a better idea of what you are trying to do and have some other ideas but that is the only idea I have without knowing a bit more detail on what you are trying to do.
Cheers Bob
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Hi Bob. Thanks for your response.
Here is the back story that may help you understand what we are trying to do. My wife has recently retired as a professor of music at Adelaide University. She had been working on finite element analysis of musical instruments. I help in the background when I can.
Recently she has a paper accepted and published in the ” Journal of the Acoustical Society of America”. The link is here if you care to read it: https://asa.scitation.org/doi/full/10.1121/10.0002427
The response has been very positive. The only comment was from a senior member of the profession that said that her use of Raleigh damping was its only weakness and he was, unusually, helpful and still wanted the paper published without changes. She is planning another paper and we want to get it right this time.
We can do all the measurements he suggested but we no longer have access to the university instrumentation and need to work up something else.
The reviewer suggested that there were three basic methods of obtaining damping data. It all comes down to generating an acoustic signal at one end of the instrument (it is nearly 2 meters long ) over a wide range of frequencies and measuring the response at the other end of the instrument. We have a reasonable array of microphones so that in itself is not the problem - it is getting a usable signal from the microphone that is the problem. The method depends on having a “complex” signal allowing us to plot the Real part of the returning signal over the Imaginary part. We don’t know how to do that as we cannot make “wav” files split into the two components. I had tried this using a microphone but just get a useless wav file. We have been led to believe that the only way to do what we need is to have a transducer, plus a recorder, capable of measuring the incoming signal and split it into its Real and Imaginary components. That is where we are stuck.
Any insights would be helpful.
Thank you for your reply and hope this long-winded explanation of what we are trying to do helps.
Cheers
Eric
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As you are interested in the real and imaginary parts separately, I assume you want to measure mean energy flow (real) and local oscillatory transport of energy (imaginary). This device can do that, but as they advertise that it is the only device that can, I would guess that replicating the functionality with easily available components will be difficult.
MPU-6050 is I2C only, so you are limited to a data rate of about 2.5KHz - not nearly enough. The MPU6000 supports SPI which can run at a clock speed of 1 MHz but that’s still probably not fast enough, and in any case I am not aware of modules that use the 6000. MEMS devices can measure vibration in the audio range, so you may be able to find a module that incorporates a device with a data transfer rate high enough to support acoustic measurement, but it would be a specialised device not commonly used in the hobbyist space.
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Hi Eric
I think I get a better understanding of what you are trying to do.
My concept of a Transducer is something that converts electrical energy into mechanical movement and vice versa. A speaker would be such a device. The electrical energy is converted into cone movement which then causes changes in air pressure. A speaker will work in the reverse sense when you speak into it etc.
My interpretation of your description is I think you want to excite the timber (or whatever) at one point and measure the level of excitation at another point or the reflected signal and you are having trouble separating the incident signal from the reflected signal. This is done at radio frequencies with a device called a reflectometer but I have never heard of it at audio frequencies. It may be possible I just don’t know.
A common example of measuring echo is the vehicle parking sensor where a transmit unit sends a signal and a receiver unit receives an echo from a target. Also a marine echo sounder but in this case it is the same transducer. In both these cases the transducers are resonant at the excitation frequency and in the case of the echo sounder the connecting cable usually forms part of the tuned circuit. Also the important measurement here is time, and to be of any use the speed of sound has to be known in the medium of concern (air, water etc) and because of this the incident signal is pulsed.
The only way I can see you separating the 2 signals is to use the echo sounder technique. That is to pulse the incident signal and measure that and then measure the echo signal while the incident signal is off. If you are doing this over a range of frequencies any transducer resonances may have to be considered. The reason the above transducers are excited at their resonant frequency is to get maximum excitation of the air or water or whatever with the excitation power available.
I feel that I am only scratching around at the surface here and the fact is I just don’t know how you would do this. Even with university instrumentation. I think people at my level tended to let the boffins worry about these complicated bits. Don’t get me wrong. I think all this is quite important as this sort of thing would have much influence on how an acoustic musical instrument would sound at the end of the day.
Jeff,
That is an impressive bit of measurement gear. A bit up market on the handkerchief most DJs hold in front of their Woofers to see how much air they are blowing. That looks hilarious to the un initiated.
Cheers Bob
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Thank you both, Bob and Jeff. You insights are much apppreciated.
Eric
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