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  Acoustical Measurement Basics



Typical measurement setup to cover your requirements for measuring and analysing architectural and building acoustics.


An ideal closed acoustical space has:
  • a perfectly diffuse sound field
  • evenly spaced absorption
  • negligible single room modes
  • an exponential decay of sound vs. time
  • no background noise


Standard room acoustical parameters are based
on this ideal model.

A real closed acoustical space typically exhibits:
  • a mixed sound field of direct, reflected and diffuse sound (strong temporal variance)
  • unevenly spaced absorption (audience…)
  • strong single room modes at low frequencies
  • multiple decays
  • high levels of background noise


Background

To investigate the acoustical properties of a room, you can clap your hands and listen to the response of the room. Although it may not be easy to describe accurately what you hear, this method evidently gives you an impression of whether music would sound pleasant or speech would be intelligible in this room.

Impulse Responses

The mathematical impulse or Dirac delta function, named after the theoretical physicist Paul A.M. Dirac, is infinitely short and has unit energy. A system’s response to such an impulse contains all the information on the system, and as such, is convenient for analyis and storage.


Required Hardware

The minimum hardware required is a PC with a soundcard, an impulsive sound source, such as a blank pistol, and a microphone connected to the actual soundcard line input. Each of these three components can be varied, depending on the type of measurement to be performed.

Typical soundcard functions are a line input, a line output and gain controls. In case of a notebook or laptop PC, soundcard functions are integrated or otherwise can be attached as a PCMCIA or USB device.

Instead of an impulsive sound source, you can use a loudspeaker sound source. To measure room acoustical parameters in compliance with the ISO 3382 standard, an omni-directional sound source should be used. To simulate a real talker in speech intelligibility measurements according to the IEC 60268-16 standard, you can use a mouth simulator or a small loudspeaker. To measure the speech intelligibility through a sound reinforcement system, you can use the loudspeakers of that system.

At high sound–pressure levels, the signal from the microphone may be sufficient to perform impulse response measurements, when fed directly into the soundcard line input. However, additional amplification is usually required. In this instance, a sound level meter with a line output could be used.



Build a high quality measurement and recording microphone by Siegfried Linkwitz ( extern link )

Using the Panasonic WM61A as a Measurement Microphone ( extern link )

Recording and Measurement Microphones (Rod Elliott (ESP)) ( extern link )

The "Alice" Microphone ( extern link )



My Equipment




Bruel & Kjaer DIRAC Room Acoustic Software


Omni-directional microphon DBX RTA-M




Sound Pressure Level Meter MS 101


Toshiba Satellite


StageLine MPA-202



USB Soundblaster


Power Amplifier (120W Bridged)


Selfmade Omni Loudspeaker with Fostex Drivers