How to Carry Out Octave Band Analysis of a Machine Using Noise Level Meters
There is only one way that you can carry out octave band analysis with a noise level meter, usually called a sound level meter: connect the auxiliary output of the meter to a computer running a real time analyzer (RTA) program, or to an existing stand-alone RTA microphone input. If you do not have an output on your meter, you'll have to get one that does. Sound pressure level meters (SPLM) are not frequency-selective and are therefore not capable of singling out parts of the spectrum: it's all or nothing. Machine octave analysis is always performed to isolate component behavior.
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Things You'll Need
- SPLM with AUX output
- RTA hardware with calibration mic input, or:
- Computer with mic input and RTA software
Instructions
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Set up your SPLM near the machine you plan to test, with the microphone end pointed toward the machine. Depending on the SLM you have, use an appropriate cable adapter to connect it to an analog microphone input on a freestanding RTA or computer sound card mic input. This may involve 3.5 mm plugs and jacks or RCA plugs and jacks -- it depends on your equipment, so the parts list does not mention specifics. Inspect the connectors on the equipment you're connecting, and adapt accordingly.
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Turn on your freestanding RTA (or your computer RTA software running on whatever computer platform you prefer, using either a sound card microphone input or a USB analog-to-digital audio interface device).
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Turn on all equipment, including the machinery you are testing. Keep in mind that if you are testing for infrasonics, a sound level meter is not appropriate; an infrasonic transducer is. The octave band that gives you the most energy corresponds to the machine component that is generating the noise. If acoustic analysis does not pinpoint your noise, use an electronic stethoscope held physically to machine areas with the appropriate connection cables, but that no longer involves an SPLM.
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References
- Photo Credit Adam Gault/Digital Vision/Getty Images
