I want to detect only low frequencies, as from a diesel.
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |
I read in sci.electronics.design that Jeff wrote (in ) about 'infrasonic detector', on Thu, 22 Sep 2005:
Loudspeakers work quite well as microphones but you need a
**second-order** low-pass filter from very low frequencies to get a flat response. Peter Baxandall wrote an AES pre-print on the subject a long time ago, but it's probably still available.I read in sci.electronics.design that Jim Thompson wrote (in ) about 'infrasonic detector', on Thu, 22 Sep 2005:
You can buy them from the AES web site.
You may find it difficult if you don't have the pre-print number.
Loudspeakers as High-Quality Microphones It is established, using the reciprocity principle, that if a voltage-driven loudspeaker has a flat axial frequency-response, then such a response will also be obtained when it is used as a microphone, provided the associated amplifier has zero input impedance and a V out/I in response rising with frequency at 20dB/decade throughout the audio spectrum. The design of a suitable amplifier raises problems with regard to signal-to-noise ratio and the ability to handle the very large low-frequency input levels that are liable to be produced. Two different approaches are described, both leading to practical designs. In conclusion, consideration is given to the use of the technique for subjective loudspeaker quality assessment, and for the measurement of frequency response and absolute sensitivity. Preprint Number: 1593 Convention: 65 (January 1980) Author: Baxandall, Peter J. E-lib Location: (CD aes9) /pp7680/pp8002/1688.pdf downloadable electronic version PDF (1.0 MB) $5.00 AES Member | $20.00 Non-Member hard copy $5.00 AES Member | $20.00 Non-Member
I read in sci.electronics.design that Jim Thompson wrote (in ) about 'infrasonic detector', on Thu, 22 Sep 2005:
Don't blame me if it sounds funny, then. (;-)
so... what do you suggest ? Do I build this DIY sensor with my laptop microphone ?
oh yes... but it could be an idea... strange but perhaps good ... i'm going to do it with an AD822...
As long as nobody knows, what you want to detect and what kind of mircophone you want to use(even if you tell me the type of your laptop I don't know the mic)... Nobody knows...
Marte
Have something to add? Share your thoughts — no account required.
Ask the community — no account required