Program Description & Overview

SPMSoft is new measurement software developed by NRC-IRC to help consultants assess acoustical conditions and diagnose problems in open-plan offices. Better procedures for evaluating acoustical conditions and diagnosing the cause of problems are an important part of efforts to improve acoustical conditions for workers in open-plan offices.

 

The SPMSoft measurement/diagnostic tool is based on measuring impulse responses in offices. The user can measure ambient noise and speech privacy during occupied conditions with minimal disturbance to the occupants.

Such improved measurements and diagnostics make the systematic improvement of open-plan office acoustics a practical option. This is particularly important because acceptable conditions in open-plan offices require all of the details to be near optimum.

SPMSoft was developed with the support of PWGSC, Public Works and Government Services Canada.

SPMSoft Program Overview

The SPMSoft computer program makes it possible to conveniently measure speech privacy between locations in open-plan offices. The program outputs test signals and measures the response to them as well as measuring ambient noise levels. It is possible to do this in occupied offices with minimal disturbance to the occupants. From these data the program calculates objective measures of the speech privacy between the source and receiver locations. These include the Articulation Index (AI), the Speech Intelligibility Index (SII) and the Speech Transmission Index (STI).

The program requires a measurement microphone connected to the computer’s sound card input via a suitable signal amplifier. The output of the computer’s sound card must be connected to a power amplifier that is used to amplify the test signals for reproduction by a loudspeaker.

Ambient noise levels are measured in 1/3-octave bands but are displayed on the screen as octave band values to provide a simpler display that is compared with octave band rating contours.

The attenuation of sound from the source position to the receiver position is obtained by measuring the impulse response between the two points. Impulse responses are calculated by outputting a sine sweep test signal. The response to this signal is transformed into the impulse response between the source and receiver locations. The output of the sine sweep test signal is first calibrated by measuring it at a distance of 1 m in free field conditions. The attenuation of sound between the loudspeaker and microphone positions in an office is then determined from the difference between the measured test signal in the open-plan office and the previous free-field measurement of the same signal.

The user selects a speech source spectrum and the speech levels at the receiver are calculated by subtracting the measured attenuations from the 1/3-octave band levels of the speech source spectrum. The calculated speech levels at the receiver position and the measured ambient noise levels at this location are used to calculate values of the speech privacy measures. When representative ambient noise levels are not available, the user can select a preset noise spectrum for these calculations. This also permits comparisons of measurements at different locations in terms of only the attenuation differences.

Cross section through a workstation showing the source loudspeaker and a microphone with an inset plot of a measured impulse response. Red indicates the initial ceiling reflection, blue the initial diffracted path over the separating panel.

The software can estimate the arrival times of test sounds traveling via two key sound paths: the initial ceiling reflection path (red arrow in figure) and the initial path by which sound is diffracted over the separating partial height panel (blue arrow in figure). The user enters dimensions of the office design and the program draws boxes on the plotted impulse response to indicate the location of these events (see red and blue boxes on impulse response plot). This helps the user to estimate the relative importance of ceiling absorption and panel height for improving speech privacy conditions in the open-plan office.

Impulse responses are saved for possible further analysis. All measured and calculated values are saved in *.csv files for convenient further use with spreadsheet software.

SPMSoft complements the COPE-Calc open-plan office acoustical design software.