The directivity of the microphone determines how much off-axis sound the microphone picks up
. The directivity is determined by design. A small pressure microphone (a microphone where the sound can only reach the diaphragm from one side) has a perfect omnidirectional characteristic, meaning it accepts sounds from all directions at all frequencies. Pressure-gradient microphones
exhibit various degrees of directionality. The actual characteristic may also depend on the placement of the unit. Enhanced directional features can also be obtained by the aid of so-called interference tubes in front of the diaphragm (“shotgun” microphones).
Microphones arranged in arrays can further improve the directionality. However, this also requires some signal processing. Nowadays, smart-phones often contain more than one microphone for improvement of speech over background noise.
Using more than one microphone also provides the possibility of calculating the direction of a sound source, for instance for shot-spotting purposes.
7. Physical environment
Security systems are usually installed to work for many years and it takes robust construction to survive so long in some hostile environments. Hence, microphones must be designed to function well within the relevant application. It is vital that environmental factors like humidity, temperature, barometric pressure, EMC, etc., do not degrade the functionality of the microphone.
When it comes to the placing of microphones, acoustic rules apply. Primarily, the sound must reach the microphone. However, the sound field around the microphone determines the quality of the captured sound. The way the mic is mounted may change both directivity and frequency response.
DPA microphones are easy to work with. Miniature Microphones leave a small footprint and there are many accessories to ensure optimum placement. There are even accessories for the concealment or disguisement of the microphone.
The microphone must be connected to an input, a preamplifier, that can properly handle the signal from the microphone. Also, the preamplifier must deliver a voltage to power the microphone. DPA microphones do not need much current. So battery-driven devices can feed the microphones for extended periods of time.
Installations must be designed to avoid EMC-problems. When “digging” in security or surveillance recordings, nothing but the acoustical sound should be on the tracks. DPA Microphones provides efficient preamplifiers for a variety of solutions – both analog and digital.
10. Examiners’ requirements
For security applications and audio forensics, many kinds of signal processing may apply. To make the signal processing perform at it’s best, the input signals provided must also be the best. Sometimes signals are subtracted from each other; at other times they are multiplied. Errors or deviations in microphones’ performance, like frequency range, phase response, linearity, dynamic range and distortion, automatically causes degradation of the final result.
So: Optimum processing requires optimum microphone performance. This is what DPA microphones are designed for.