Microphone standards. How well do you understand them?

Insights from the PCB Piezotronics Microphone Handbook

Modal Shop Precision Acoustic Calibration Workstation Model 9350C_from John Morris Industrial

Important Applicable Standards

Before picking out a microphone or other acoustic test hardware, consumers need to work out whether there are specific standards that the product must comply with for the application in which that product will be used. Whether for legal purposes, or for quality assurance programs, these standards will help determine the quality, accuracy and consistency of the products. Standards have been set for Sound Level Meters (SLMs), calibrators, microphones, and other related measurement components. There are numerous standards that correspond to the performance requirements, dimensions and characteristics of acoustical components. The most popular organisations for establishing these standards are the American National Standards Institute (ANSI) and the International Electrotechnical Commission (IEC.)Precision Acoustic Calibration Workstation Model 9350C_from John Morris Industrial

IEC 61094 deals specifically with the condenser microphone. It establishes specifications on the mechanical dimensions and certain electroacoustic characteristics for working standard microphones which are to be used as laboratory reference microphones. These condenser microphones require the highest accuracy, because these units will determine the accuracy of other microphones in primary calibrations by the reciprocity method.

IEC 61094 defines both dimensional sizes and tolerances along with electroacoustic specifications for the most common selection criteria: sensitivity, frequency range, dynamic range and more. Defining the dimensional sizes and tolerances ensures interchangeability between acoustic manufacturers microphones. The IEC 61094 types include WS1P/F/D, WS2P/F/D and WS3P/F/D, where the WS1 pertains to 1” (25mm) diameter microphones,while the WS2 is for the most common 1/2” (12mm) diameter models, and theWS3 is for the 1/4” (6mm) models. The P/F/D represents the field response type, where “P” is for Pressure, “F” is for Free-Field and “D” is for Diffuse Field (commonly referred to as Random Incidence.)

ANSI S1.4 is the ANSI standard for Sound Level Meters. It deals with the specifications for these products, and was originally written in 1983 and later amended to S1.4A in 1995, and is currently used today. ANSI S1.43 established in 1997 deals with setting a standard for compliance for Integrating-Average Sound Level Meters.

IEC 60942 was created with the specifications on sound calibrators in mind. There are three classes concerned with the standards of sound calibrators. The most stringent is the Laboratory Standard (LS). The LS class has the tightest tolerances and is designated for calibrators that will be used only in the laboratory. Both Class 1 and Class 2 instruments are considered for field usage applications. A Class 1 calibrator is intended to be used with a Class 1 sound level meter, while a Class 2 calibrator is designed to be used with a Class 2 sound level meter.

IEC 61672 was instituted to replace IEC 60651 and IEC 60804. IEC 61672 provides electroacoustic performance standards for Sound Level Meters. There are standards that range from the simplest integrated sound level meter which measures sound exposure levels, to SLMs that measure time-average sound levels, to conventional sound level meters that measure exponential time-weighted sound levels. A sound level meter can have one, all, or a combination of the previously mentioned measurements. There are several classes for the sound level meters. The standards are based around the same design characteristics, but differ in the tolerance limits and operational temperature specifications. To conform to a certain class, a specified frequency response for sound incident on the microphone in a free field or diffuse field must meet the IEC standards. Class two tolerances are more liberal, compared to class one standards.

There are certain classifications that are commonly referenced. Types ranging from Type 0 through Type 2 dictate the tolerance and accuracy of the system. These standards were created for SLMs, and get commonly referred to when mentioning components of the system, such as the microphone cartridge and the preamplifier. Type 0 refers to Laboratory reference. It is not required to satisfy the environmental requirements for field instruments, but must be extremely accurate, since this is what other sound level meters will be judged against or tested to. Type 1 is a working class standard for both laboratory use and for use in the field. The Type 1 standard is extremely accurate and durable. It is designed to take the challenges of the environment and still compile highly accurate and reliable acoustic measurements. This is a very popular type for research and design engineers. Type 2 sound level meters have standards that are more relaxed.

The Type 2 is a general-purpose type. These microphones do not have the high-frequency response, low cartridge thermal noise levels, or accuracy as the first two types, but offer a less expensive alternative for when the measurement accuracy is not as critical.

Some manufacturers will designate their microphone, preamp or filter as a certain type or to meet a particular standard. In order to conform you must look at the complete system. The whole system must meet the standard, not just one specific component. PCB designs each individual component to exceed the specifications, so that when installed it meets the Type 1 specifications, even after the accumulation of tolerances of each component is taken into consideration. For more information on these standards, please contact the above organisations. They can answer questions directly and forward you documentation on the specific standards that you’re interested in.

Got more questions about Modal Shop acoustic products?
Ourt Industrial team would love to hear from you
Phone free call AUS 1800 251 799 and free call NZ 0800 651 700

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