The GRAS 47AC is a 1/2" CCP precision condenser microphone set for infra-sound measurements in open acoustic fields.
As a free-field microphone, 47AC is designed essentially to measure the sound pressure as it would appear if the microphone were not present, the sound field pointing towards the microphone.
At low frequencies, the disturbing effects of its presence in the sound field are minimal because the wavelengths are large compared to the size of the microphone.
The 47AC is especially designed for infra-sound measurements and can measure down to 0.09 Hz. To make this possible, it is furnished with an integrated low frequency adapter with a specially designed pressure equalization system and a dedicated preamplifier.
47AC专为声音测量而设计，可测量低至0.09 Hz。 为了实现这一目标，它配备了一个集成的低频适配器，配有专门设计的压力均衡系统和专用前置放大器。
To make it possible for the microphone to measure sound with very long wavelengths, the pressure equalization system has a long settling time. It is therefore important that the 47AC is allowed sufficient time to settle in conditions with varying ambient pressure. How long depends on the specific circumstances, but about half a minute after the ambient pressure has stabilized is sufficient in most cases.
为了使麦克风能够测量具有非常长波长的声音，压力均衡系统具有长的建立时间。 因此，重要的是允许47AC足够的时间在具有变化的环境压力的条件下沉降。 多长时间取决于具体情况，但在大多数情况下，在环境压力稳定后约半分钟就足够了。
The preamplifier has TEDS for automatic sensor identification and reading of calibration data.
Typical applications and use 典型应用和使用
The low-frequency property combined with its high sensitivity and robust design make 47AC the obvious choice for infra-sound measurements - a fast growing discipline following the need for monitoring and reducing low-frequency noise from, for example, power and production plants and wind turbines.
低频特性与其高灵敏度和强大的设计相结合，使47AC成为声音测量的明显选择 - 这是一个快速发展的学科，需要监测和减少来自电力和生产工厂和风的低频噪声涡轮机。
With a lower limit below 0.1 Hz 47AC is also well suited for realistic measurements of supersonic booms which requires a microphone with a high bandwidth and the ability to capture steep low-frequency pressure variations.
Freq range 频率范围: 0.09 Hz to 20 kHz
Dyn range 动态范围 : 20 dB(A) to 148 dB
Sensitivity灵敏度 : 8 mV/Pa
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