Many times in the acoustical test and measurement world we will hear people talking about a “Type 1” microphone.
Microphone Type — What makes a Type 1 Mic?
In truth, there is no such thing as a Type 1 (or Class 1) microphone, only a Type 1 Sound Level Meter. According to both the US ANSI S1.43 specification, and the European counterpart, IEC 804, the entire system must be tested against the specification as a single unit.
In our case, that would include an iOS device running our AudioTools app, connected to one of hardware interfaces. It is be possible to have the entire system type-certified, at a testing lab. See this page for more information about certifying an iPrecisionMic.
AudioTools Standards Compliance
In our case, all of the algorithms, filters, and features of the SPL Meters meet or exceed the standard for Type 1. And, in the case of the RTA, the filters meet Class 1 of ANSI S1.11. So, if you use our software with a microphone that meets Type 1 or Type 2 specs you will in theory have a meter that meets these specs.
To be fully compliant, you would have to submit your microphone and iAudioInterface2 for calibration, to a designated calibration facility, and have a mic that meets all of the Type 1 specifications, which are summarized below.
Type 1 Standards Summary
Here is a summary (not intended to replace the specs) of some of the main features that a mic would have to meet, to be useful as the microphone in a Type 1 Sound Level Meter:
Frequency Response
This is probably what most people think about first.
- 20 Hz, +/- 2.5dB
- 25 Hz, +/- 2.0dB
- 31.5 and 40 Hz, +/- 1.5 dB
- 50 through 4000 Hz, +/- 1.0 dB
- 5000 Hz, +/- 1.5 dB
- 6300 Hz, +1.5, -2.0dB
- 8000 Hz, +1.5, -3.0 dB
- 10000 Hz, +2.0, -4.0 dB
- 12500 Hz, +3.0, -6.0 dB
- 16000 Hz, +3.0, -infinity (therefore not required)
- 20000 Hz, +3.0, -infinity “ “
That was the easy one, now for the more challenging ones to meet.
Linear Operating Range
Generally, 60 dB of operating range, with +/- 0.7 dB variability.
Free-Field vs Random Incidence
This is difficult to summarize, but there are strict limits (approx. +/-2.5 dB at 22 degrees) on how omnidirectional the microphone is, in actual use.
Environmental
In most cases, a plastic diaphragm mic cannot meet these specs.
Atmospheric pressure, no more than 0.3 dB change for a +/- 10% change in pressure.
Air temperature, no more than +/- 0.5dB change between 10 and 50 degrees C — or 50 to 122 degrees F.
Humidity, no more than 0.5 dB change from 30% to 90% humidity at 40 degrees C (104 degrees F).
