No.3 Various measurement instrument: Sensors for sound measurement
In this column, I will introduce the sensors (detectors) for sound measurement.
When you hear “the detectors for sound”, what you come to mind is a microphone.
There are various types of microphones, such as those for karaoke, conferences, smartphones, and noise measurement. This time, I will explain about the measurement microphone as examples.
The "measurement microphone" is required to have the accuracy to measure from quiet to loud sounds and the stable performance to measure a wide range from low to high sounds.
Structure of measurement microphones
The measurement microphone has a diaphragm protected by a grid (microphone cap) that receives sound pressure and vibrates to detect sound. The amplitude of the diaphragm is output as an electric signal through a preamplifier. The output signal is converted to Pa (Pascal), which is a unit of sound pressure. The unit dB (decibel), which is often used for noise, will be explained later.
Loudness of sound/ Pitch of sound
Pa (Pascal) or dB (decibel) is used as a unit to express sound.
The range of loudness that humans can hear is very wide from 0.00002 Pa to 20 Pa, that is, a range of one million times. In the unit of “Pa“, there are concerns about misreading and miscopying of digits, thus, a unit called dB (decibel) using a logarithmic scale has been used (0.00002 Pa-20 Pa →
0 dB-120 dB).
Another reason why the dB unit is often used is that auditory sense is said to be close to the logarithm scale. This means that the human can easily perceive slight differences for small sounds, but not for some loud sounds.
The unit of sound pitch uses the unit of frequency called Hz (hertz). The audible sound range that humans can hear is from 20 Hz to 20 kHz.
Types of measurement microphones
I will introduce our products as examples. Our products are lined up according to the microphone performance and purpose of application.
High performance under harsh measurement environment (MI-1271)
Suitable for high-frequency measurement more than 20 kHz (MI-1531)
For general purpose (MI-1235/MI-1433)
Other than measurement microphones, we provide the microphones for specific purposes.
For measurement even in limited spaces with ultra compact & super lightweight (MB-2200M10)
A sharp directivity that detects intended sound clearly (MI-8100)
Visualizing sound source using only 4 microphones & a camera with wider viewing angle (MI-5420)
Sound level meters
Many of you know the term “Sound level meter (Souonkei in Japanese)” as a sound measurement instrument. The sound level meter is an instrument that integrates a measurement microphone (microphone & preamplifier) and a display device, and displays in dB (decibel) as described above. The term of "Sound level meter" is specified in the JIS standard (IEC standard). As for “Souonkei” is specified in the "Measurement Law" and is verified as a specified measuring instrument.
In sound measurement, not only noise level measurement but also sound source probing and sound quality evaluation for sound countermeasures are required. In recent years, sound level meters (LA-7000 series, our product) that meet the above requirement have become more popular. The LA-7000 series is equipped with the listening function that allows you to measure while listening to sound as standard, the sound probing function that you can search for a sound source in the field, and the simulation function that you can listen to the sound after countermeasures by increasing or decreasing the pitch of a specific sound, and take effect before taking measures. You can use it for various applications.
Please take a look at our website.
Measurement instrument standards
JIS C1509-1 (IEC61672-1) is required as the standard for measurement instruments in the sound measurement method and measurement manual. In JIS C1509-1 (sound level meter), it is specified by class 1 and class 2. In addition, various items such as level linearity error in the frequency range are specified. JIS C1509-1 is a Japanese Industrial Standard based on IEC 61672-1 (International standards).
The specification of measurement microphones is sometimes described as class 1 and class 2, which often refers to class 1 and class 2 of JIS C 1509-1 (IEC61672-1). There are other standards such as IEC 61094-4 (for measurement microphones).
（KH2）
【Microphone & Amp】
https://www.onosokki.co.jp/English/hp_e/products/category/sound.html#t1
【High performance Sound Level Meter
LA-7000 series】
https://www.onosokki.co.jp/English/hp_e/products/keisoku/s_v/la7000.htm