Sound Level Meter

The golden standard for sound noise level measurement reimagined with the Dewesoft approach, priding on certified compliance with international standards, ensuring maximum accuracy. No matter the acoustics measurement, a sound level solution is always at the heart of the sound measurement. Extra care was devoted making it your trusted partner in the acoustic analysis.

Sound pressure
Sound pressure

Main Features

  • SUPPORTED STANDARD: IEC 61672 Class 1 sound level meter
  • UNMATCHED FLEXIBILITY: SLM supports measurements in either air or water and can be combined with all other physical measurement parameters, vehicle bus systems, video, GPS and other math to build a thorough image of your entire measurement.
  • HIGH DYNAMIC RANGE: our top-of-the-class data acquisition hardware with 160 dB dynamic range in time and frequency domain allows direct input of IEPE compatible microphones with support for TEDS automatic recognition. Data acquisition system can be scaled for any number of microphones, microphones can be effortlessly calibrated with a calibrator
  • ADVANCED MATH - ALL AT THE SAME TIME: predefined standard frequency weighting  A, B, C, D, and Z), time weighting (Fast, Slow or Impulse), sound pressure level, equivalent, peak, minimum & maximum sound pressure levels, sound energy, impulsivity of sound, statistical noise level (LAF1, 5, 10, 50, 90, 95 and 99 % classes of values) are all available at the same time
  • RICH VISUALIZATION: flexible displays offering digital meters, analog bars, time domain recorders, narrow band FFT and octave analyzers can be freely combined to show your SLM data in real time as well as in post-processing

Class 1 Sound Level Meter

Class 1 sound level meter is designed to meet the requirements of IEC 61672. This standard specifies two levels of performance, Class 1 and Class 2, with Class 1 being effectively more accurate.

Within the standard are a set of performance criteria that an instrument must meet and each of these has a tolerance associated with it.

Real-time Sound Analysis

Real-time octave and third-octave filters analyze a signal and measure energy at the output to give frequency data. The  Octave Analysis option provides time-based realtime octave band and 1/3 octave band measurements. Additionally, 1/n octaves can be post processed for requirements that need 1/6 octave, 1/12 octave, and 1/24 octave band spectral analysis.

Microphone Calibration

In order to make a scientific measurement with a microphone, we must know its precise sensitivity. Microphone calibration will enable confidence in the performed measurements. Since this may change over the lifetime of the device, it is necessary to regularly calibrate the measurement microphone. A microphone can be calibrated into several different ways in DEWESoft:

  • with TEDS  (the sensitivity of the microphone is written on TEDS chip, the software will read it)
  • with a calibrator (calibrate the microphone with the calibrator directly in DEWESoft)
  • with calibration certificate (simply enter the sensitivity into the channel setup of the microphone)

Frequency Weighting

Frequency weighted noise measurements offer convenient ways to measure sound, and we use each of these frequency weightings for different types of measurements.

  • A-weighting is applied to measured sound levels in an effort to account for the relative loudness perceived by the human ear. The human ear is less sensitive to low and high audio frequencies.
  • B-weighting is the best weighting to use for music listening purposes.
  • C-weighting is used for high-level noise measurements.
  • D-weighting was specifically designed for use when measuring high-level aircraft noise in accordance with the IEC 537 measurement standard. The large peak in the D-weighting curve reflects the fact that humans hear random noise differently from pure tones, an effect that is particularly pronounced around 6 kHz.
  • Z-weighting is linear at all frequencies and it has the same effect on all measured values.


Time Weighting

Sound level measurements using any grade of a sound level meter can be fast, slow, or impulse time-weighted. These weightings date back to the time when sound level meters had analog meters and defined the speed at which the meter moved.

  • Fast - the needle would move fast to show quickly varying noise. Fast corresponds to a 125 ms time constant.
  • Slow - the needle would be damped to smooth the noise out to be easier to read. Slow corresponds to a 1-second time constant.
  • Impulse - The Impulse time weighting is about four times faster than Fast, with a short rising time constant but a slow falling constant. Impulse has a rise time constant of 35 ms and fall time constant of 1,5 s.


Calculated Parameters

Sound level meter calculates several parameters and channels in real time, during the measurement:

  • Lp (SPL) - time and frequency-weighted sound pressure level (SPL) already scaled to dB (decibel) 
  • Lpk value, which shows the current maximum value of the sound levels
  • Frequency weighted raw value shows the frequency weighted time curve of sound in Pa (Pascal).
  • frequency-weighted Leq value, which is equivalent continuous sound level
  • Lim tells the impulsivity of sound and is the impulse-weighted equivalent
  • LE which is the frequency-weighted sound energy

True Peak Level

True peak level shows the real peak value of the input signal in dB. The sound pressure level always contains a time weighting filter, which has an influence on the peak value.

 The SPL does not reach that high values, no matter if we select F, S or I time weighting. The LCpk, however, shows the “true peak”. 

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