Microphones

Measurement Microphones
The key components that determines the accuracy of a sound level meter is the measurement microphone and its associated preamplifier. The effectiveness of these components in converting the acoustic signal into an electrical analogue set the maximum accuracy that can be achieved by the ensuing signal processing. Norsonic have a carefully balanced range of measurement microphones to suite a wide range of applications that complement modern instrumentation yet maintain traditional values.

All microphones are designed to meet the IEC 61094-4 standard for specifications for working standard microphones and are therefore suitable for use with both Norsonic and other leading makes of measurement preamplifiers for making precision acoustic measurements.

Full use has been made of modern materials which when coupled with traditional engineering skills produces microphones that meet all the requirements of the precision measurement standards yet are robust and resistant to corrosion. These microphones are used in conjunction with the Norsonic range of preamplifiers that closely couple to them and ensure perfect matching to the associated instrument with minimum disturbance to the acoustic field. The preamplifiers have the necessary signal handling capability and low self noise to allow full use to be made of the wide dynamic range of the microphones.

Calibration of all Norsonic microphones is directly traceable to National and International Standards with particular attention being paid in the design to ensuring long term stability. Each microphone is delivered with an individual certificate of calibration giving all the key information relating to its performance. This includes the nominal sensitivity and frequency response along with the environmental data that relates to the calibration.

Summary of Applications
The Norsonic programme includes both traditional and new generation types of microphones. It is the materials that constitute the essential difference between them. The new generation devices are constructed with the recently introduced advanced stainless steels; this gives them improved mechanical strength, higher operating temperatures and excellent resistance to corrosion. High electrical insulation is obtained by using synthetic sapphire for the insulators and to ensure low noise connections the contacts are all gold-plated German silver.

The new generation microphones are indicated in this set of articles by the symbol NG. The traditional design, constructed from brass with nickel for the diaphragm, have been proven over many years. The construction methods used for these traditional designs have been continually refined over the past forty years and to ensure stability the aging process is extended to a period of three months. Traditional devices are identified by TR in this set of articles.

The Norsonic range of microphones consists of free-field microphones, pressure microphones and random incidence microphones. They are all rear-vented.

Free-field Microphones
A free field microphone is designed to measure the sound pressure in the sound field, compensating for the influence of the presence of the microphone in the sound field. In effect, the microphone measures the sound pressure as it existed before the microphone was introduced in the sound field, i.e. free field conditions. Applicable standard is IEC60651. The free field microphone should be pointed towards the sound source at a 0° angle of incidence.

Pressure Response Microphones
A pressure microphone is designed to measure the sound pressure that actually exists in the front of the diaphragm. This means that no compensation is made for the microphone's influence on the sound field. The pressure microphone is typically used in coupler measurements or when the microphone is, for example, mounted flush in a wall to measure the sound pressure there and then.

Random Incidence Microphones
A random incidence microphone, also named diffuse field microphone is designed to essentially measure the sound pressure as it existed before the microphone was introduced into a diffuse sound field. At higher frequencies the presence of the microphone itself in the sound field will change the sound pressure. In general the sound pressure around the microphone cartridge will increase due to reflections and diffractions. This pressure increase is different for different incidence directions. The random incidence microphone is designed so that the frequency characteristics compensates for this pressure increase, assuming that the sound waves arrive at random from all directions. Applicable standard is ANSI S1.4. and IEC 1183.

Selection chart for microphone types

 
Microphone Cartridges