An acoustic camera is the equivalent of a thermal camera for noise!
“It’s an imaging device used to locate sound sources and to characterize them. It consists of a (large) group of microphones, also called a microphone array, from which signals are simultaneously collected and processed to form a representation of the location of the sound sources.”(WiKi)
You point it at an area and the software (based on beamforming) will perform complex calculations from the info of the 128 channels to show the user where the loudest sound source is.
Imagine a refinery as here below in the picture, there are hundreds of sound sources causing noise nuisance, but with a sound level meter you will only be able to measure the overall sound pressure level in Decibel.
When we put the acoustic camera on some distance of the refinery, we will directly find the loudest sound source. If we need more detail, we can even see the sound level of only this sound source!! This is impossible with traditional sound level meters. The video here below will give you an idea how it works.
The acoustic camera has been around for some 10 years but is still not too well known to people who are not working in noise control or as acoustical engineers. The first acoustic cameras were setup with traditional condensor microphones which made it not so easy to setup (lots of cables) and expensive.
The newer generations of acoustic cameras are using MEMS microphones, these are digital microphones, they are very stable over time (accurate) and are cheap compared to traditional condensor microphones.
Here below an example of a traditional microphone (left) vs a MEMS microphone (right)
Condensor microphone as above with preamplifier, typically 30 – 100 mm long and diameter 1/2″, MEMS microphones on the right 3 x 3 mm.
The traditional condensor measurement microphone needs a preamplifier to be able to amplify and get the value to be read in a SLM (Sound Level Meter). There are many types of condensor microphones for various applications such as extremely low or extremely high noise levels, low or high frequencies etc. They are reliable, easy to calibrate and comply with measurement standards such as ISO (International Organization for Standardization).
MEMS microphones are still new in the classic physics domain of sound and vibration, and the ISO standards are not yet updated to allow MEMS microphones to be used in ISO sound and vibration measurements.
The accuracy of an acoustic camera is strongly depending on 2 main factors:
- the aperture size/dimension, the bigger the space between the 2 furthest located microphones is the lower the frequency that can be measured
- the number of microphones, the more microphones the higher the resolution will be hence the location of the sound sources will be more accurate, a now typical acoustic camera will have 128 microphones for normal usage and up to 384 for low frequency noise positioning
Here below an example of a typical acoustic camera as used by governmental noise enforcing agencies as well as acoustical consultants.
