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Bruel and Kjaer EMS Inc.
4182 - Probe Microphone
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Uses
• Near-field measurement of loudspeakers
• Investigation of sound distribution inside:
• Telephone equipment
• Hi-Fi headphones
• Musical instruments
• Measurement of noise radiation from intricate machinery
• Measurement of attenuation in hearing protectors
• Acoustic impedance measurements
• Smooth frequency response characteristic between 1 Hz and 20 kHz
• Small size and lightweight (only 45 g (1.47 oz.))
• Selection of interchangeable stiff and flexible probe tubes
• Probe-tip can withstand temperatures up to 700°C (1292°F)
• High acoustic impedance
• Pressure equalization with the measurement site
Features
• Smooth frequency response characteristic between 1Hz and 20 kHz
• Small size and lightweight (only 45 g (1.47 oz))
• Selection of interchangeable stiff and flexible probe tubes
• Probe-tip can withstand temperatures up to 700°C (1292°F)
• High acoustic impedance
• Pressure equalization with the measurement site
Вesigned for sound pressure measurements to be made in small or awkward places or in harsh environments where a conventional microphone would be unsuitable. The probe microphone has a smooth frequency response from 1Hz to 20kHz, with a very smooth high-frequency roll-off.
Physically, it is very small and lightweight and has a durable construction. Measurements can be performed extremely close to the sound source due to its small size. Measurement points can be closely spaced when it is necessary to have high spatial resolution.
The high impedance of the narrow probe tip enables measurements in very small volumes – as small as 1cm3 with only minor effects due to acoustic loading. Interchangeable stiff and flexible probe tubes, of various lengths, make the probe microphone very adaptable for measurements in awkward places (for safety reasons Probe Microphone Type 4182 is not suitable for measurements on the human body).
The static pressure inside the probe microphone can be equalised to that of the measurement site.
Specifications
Using the probe microphone allows you to make measurements in very harsh conditions. The tips of the 100 mm and 200 mm stiff probe tubes can withstand temperatures of up to 700°C.
The probe microphone can also be used as a reference microphone with the Brüel & Kjær Spatial Transformation of Sound Fields (STSF) System. This uses near-field sound measurements to predict far-field behaviour. With its small size, it is easy to get close to the near-field using the probe microphone.
When you are using the probe microphone for exhaust system measurements, water may condense inside the probe tube system. To avoid damage to the built-in microphone use the 200 mm probe tube and make sure the pressure at the measurement point is not greater than 10 000 Pa (0.1 bar).
Specifications
Construction
You can make measurements in high-pressure environments by connecting a tube from the external vent into the measurement environment to equalize the static pressure.
The narrow probe tubes provide the probe microphone with a very high acoustic impedance (approx. 8 ° 108 Ns/m5). Above 50 Hz, there is negligible acoustic loading to volumes of 1 cm3 or greater.
Frequency Response
Using the probe microphone allows you to make measurements in very harsh conditions. The tips of the 100 mm and 200 mm stiff probe tubes can withstand temperatures of up to 700°C.
Examples of Use
The probe microphone can also be used as a reference microphone with the Brüel & Kjær Spatial Transformation of Sound Fields (STSF) System. This uses near-field sound measurements to predict far-field behaviour. With its small size, it is easy to get close to the near-field using the probe microphone.
Measurements on Exhaust Systems
When you are using the probe microphone for exhaust system measurements, water may condense inside the probe tube system. To avoid damage to the built-in microphone use the 200 mm probe tube and make sure the pressure at the measurement point is not greater than 10 000 Pa (0.1 bar).
In large systems, a metal waveguide tube is inserted through the wall of the exhaust channel. The waveguide uses a long flexible hose to provide proper acoustic termination. The end of the hose is sealed to prevent exhaust gas flow in the waveguide. If the attenuation in the waveguide is taken into account, the sound pressure in the waveguide is equal to the sound pressure in the exhaust channel. The probe microphone can then be used to measure in the waveguide. For good results, the internal area of the waveguide should be greater than 13.25 mm2 (dia. 4.1 mm).
The waveguide’s internal area should also be 25 times smaller that the exhaust channel’s internal area. An equalisation tube connects the microphone pressure equalization vent to the tube. You can also measure the attenuation across filters in the exhaust channel.
