 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Natural Science Forum / Physics / Acoustics / October 2004Microphone spiking 450Hz?
Microphone spiking 450Hz? Hi, I'm planning to do measurements with microphone in the frequency range of 380-510 Hz. Sound, in the question, is low amplitude sine wave and is surrounded of lots of noise. I thought first step is to find a microphone which is specially designed to this frequency range. So, that the mechanical resonance frequency is close by. Do you know where to buy, or how to build one? Or is there any? If you have tips to give, please do, I have not done sound measurements before. */Tomi > Microphone spiking 450Hz? > [quoted text clipped - 12 lines] > measurements before. > */Tomi A tuned microphone can be easily constructed by attaching a tube of appropriate length and diameter to a Panasonic electret mic capsule to form a Helmholtz resonator (acoustic mass of tube resonating with equivalent volume of mic capsule). However, using a tuned microphone is not the proper way to make the measurement that you propose. The proper approach would be to measure the sound with a broadband microphone and to perform a narrow-band FFT analysis on the broadband sound. Thank you for pointing out Helmholz resonators! "The proper approach would be to measure the sound with a broadband microphone and to perform a narrow-band FFT analysis on the broadband sound." I'm planning to do narrow-band FFT to the signal recorded using tuned microphone. I have an idea that if works better that way. But well, I'm not sure at all this works, it should though? */Tomi > > Microphone spiking 450Hz? > > [quoted text clipped - 20 lines] > would be to measure the sound with a broadband microphone and to perform a > narrow-band FFT analysis on the broadband sound. > Thank you for pointing out Helmholz resonators! snip....snip > I'm planning to do narrow-band FFT to the signal recorded using tuned > microphone. I have an idea that if works better that way. But well, > I'm not sure at all this works, it should though? If, as you previously stated, you have a low amplitude sine wave burried in broadband external noise, it is unlikely that a tuned microphone is going to provide better S/N than a broadband microphone. The only case in which a tuned microphone would help is if the external noise as a spectral dip at the same frequency of the sinusoid you are trying to measure AND if the level of the sinusoid you are trying to measure is below the spectral level of the electrical noise floor of the microphone for the particular FFT analysis bandwidth that you are using. > > Thank you for pointing out Helmholz resonators! > > [quoted text clipped - 12 lines] > of the electrical noise floor of the microphone for the particular FFT > analysis bandwidth that you are using. A tuned system will help reduce out of band noise but (as noted above) you still have in band noise to deal with. However, synchronous detection techniques can do wonders with SNR. Don't know if this would be practical with your source. Maybe check some of the NASA tech briefs and papers on satellite communications. Later... Ron Capik NJ Pinelands Cultural Society -- > Microphone spiking 450Hz? > Hi, [quoted text clipped - 8 lines] > > */Tomi I'm not sure that see the need for eliminating the frequencies below 380Hz and above 510Hz at the measurement stage, rather these regions can be ignored at the analysis stage. HAve you considered a band pass filter after the microphone. "Low amplitude sine wave" suggests that you are looking for a tone of consistent amplitude (with time), in a random "noise background". FFT across the restricted band width and look at the average energy levels over an extended time period. What is the source of the "sine wave"? I have dealt with this type of situation previously in a number of industrial applications (one of which is currently under patent). |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2009 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.