In this way, you will be able to determine how much the recorded sound is attenuated in any off-axis direction. Each shift between emphasized circles indicates a 5 dB step typically, unless stated otherwise. It means that even if the microphone’s sensitivity may be different at different frequencies (uneven frequency response), at 0°, they align at 0 dB (the level of the graph is raised or lowered to obtain this alignment of the curves). The 0° indicates the on-axis direction of the microphone.Īll measured data are normalized at 0°. A reference point, marked as 0°, is defined at the top of the outer circle. Each circle represents a dB level, usually starting with 0 dB at the outer circle. The polar plot is based on a grid of concentric circles. One feature of microphones is the directionality, which can be expressed by the help of a polar plot.
The directional pattern is a graphic way to show the acceptance angle of a microphone. This absolute value applies, for instance, to the specification of microphones’ sensitivity. Describing the level of sound pressure “ dB re 20 μPa” also can be written as “dB SPL” (Sound Pressure Level).įor electrical measurements, another reference is 1 Volt, written as “0 dBV” or “0 dB re 1 Volt”. Now 0 dB means that sound pressure is present, and it is 20 μPa (approximately the threshold of hearing at mid-frequencies). You can make dB an absolute scale by applying a reference - for instance, the sound pressure level, the reference being 20 μPa. Any negative dB number indicates a negative change (the value now is lower than before). Any positive dB number indicates a positive change (the value now is higher than before). The largest dB number you will find in real life is <200 dB, meaning, if the dB number has three digits, the first always being “1”. By and large, each step on the scale is perceived as equal in size. 10 dB is subjectively perceived as a doubling or a halving. The advantage of this scale is that 1 dB is about the smallest change of level you can hear. or ratio 2, the units are: 1-2-4-8-16, etc.) This logarithmic scaling applies to many of the electrical or acoustical measures, which specify microphones (i.e. Using a logarithmic scale means that there is a fixed ratio between each unit of the scale (e.g., ratio 10, the units are: 1-1, etc. The dB scale is logarithmic and applied because most human senses - including hearing - are close to being logarithmic.
The basis for most microphone specifications is the decibel scale. Thus the scale is logarithmic, which provides the perception of equal-sized increment. The decibel scale is related to the way humans hear. With a focus on the DPA microphone specification sheet, this article is designed to help evaluate specs in a meaningful way. In addition, when comparing specifications, the same technical term sometimes is interpreted differently from brand to brand.
In most cases, the specifications can be measured or calculated in various ways, although the standard IEC 60.268-4 is the common ground for this. When you read microphone specifications, you must understand how to interpret them.