FIGURE E-2 Type 2270 meter in use. Copyright © Brüel & Kjær.

FIGURE E-2 Type 2270 meter in use. Copyright © Brüel & Kjær.

  • report period: from 1 minute to 24 hours with 1-minute resolution

  • all broadband data and statistics stored at each reporting interval

  • all spectrum data stored at each reporting interval

  • spectral statistics stored at each reporting interval

  • logging time: from 1 second to 31 days with 1 second resolution or continuous

  • data are saved in separate projects for every 24 hours of logging


The sound-level meter market can be divided into three levels. The high end is the integrating analyzer with a tremendous amount of computing power. Some manufacturers use a laptop computer attached to the instrument for this category. At the lowest level, these instruments are meters that can merely report a sound level.

The Brüel & Kjær Type 3639 Noise Monitoring Terminal will be used as the example for this discussion. There are several competing products by other manufacturers with very similar capabilities. The Type 3639 is designed for use in all climate environments, as well as industrial, urban, and rural conditions. It can be left unattended as part of an environmental noise monitoring system for permanent, mobile, or semipermanent monitoring. The Noise Monitoring Terminal can be controlled by a remote PC. This unit is shown in Figure E-3.

Typical capabilities for these types of monitoring systems are summarized here:

  • logging of broadband and 1/3-octave parameters every second or half-second

FIGURE E-3 Type 3639 monitoring station. Copyright © Brüel & Kjær.

FIGURE E-3 Type 3639 monitoring station. Copyright © Brüel & Kjær.

  • postprocessing that can create periodic statistical reports down to 1 minute, including LN data

  • GPS support

  • sound recording

  • weather data monitoring

  • camera support

  • remote operation via LAN, public telephone lines, mobile phone, or General Packet Radio Service (GPRS)

The definition of the measurements that can be done with these types of monitoring stations is quite lengthy. A short summary is presented here of typical calculations.

Broadband values:

  • X = frequency weightings A and C, or A and Linear, or C and Linear (two weightings simultaneously)

  • Y = time weightings Fast, Slow and Impulse (all simultaneously)

  • LXeq, LXpeak, LXim, LXYinst, LXYmax/SPL, LXYmin

Spectrum values:

  • equivalent continuous level (Leq) and I-weighted value also selectable (LAIeq)

  • 1/3-octave frequency range: 12.5 to 20 kHz

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