How to Measure Audible Hzby Jennifer Lyons
Sound is a mechanical vibration carried through a liquid, gas or solid medium through which energy moves away from the source in waves. The number of waves per second is called the frequency and is measured in hertz, or Hz. Human ears can detect frequencies between 20 Hz and 20,000 Hz. Pressure variations with frequencies that are lower than 20 Hz are called infrasound, and frequencies higher than 20,000 Hz, written as 20 kHz, are called ultrasound.
Choose your microphone. You will need a very sensitive microphone selected based on the kind of sound you intend to measure. For low sound levels, you will need a high sensitivity microphone. For high levels, low sensitivity microphones are used. Based on the type of acoustic field you will be measuring, you can choose either a free or diffuse microphone. A diffuse field microphone is used for measuring ambient sound levels such as city traffic. Free field microphones will measure a specific sound emitted from one source such as a stereo. The size of the microphone is determined by the frequency of sound. A small microphone is desirable for a wide range of frequencies, but they are often less sensitive and therefore less reliable than a larger microphone.
Select a sound level meter. There are four types of sound level meters which differ by precision. Type 0 and type 1 should be used for a laboratory setting where the acoustic environment is controlled and there is a lack of ambient sound. The type 2 sound level meter is best for measuring general frequencies in non-laboratory environments. The type 3 sound level meter is best used for measuring field sound.
Set up the microphone and sound level meter. Plug your microphone cord into your sound level meter. Point the microphone directly at the sound source. If you are trying to measure a free field, you can place women's panty hose over the microphone to block out ambient noise. If you are measuring a diffuse field of noise, you may need a wind shield placed around the microphone so that the sound levels are not affected.
Turn on your sound level meter. The meter will measure the amount of frequencies per second and display the results on the screen. This is the number of Hz of audible sound.