CANVAS requires information regarding background details including source, whether voices, music, or mechanical noise. The destination table indicates the actual losses at the receiving end, the human ear. These are the tables or numbers normally represented. The graph on the right indicates both the origin as a line indicating the amplitude of sound level and a dotted line which indicates the sound level at the destination. The difference between these two lines is exactly the loss of sound transmission through the partition as calculated by CANVAS®.
So, each frequency is depicted along the horizontal axis of the graph while the vertical axis indicates the decibel sound level in A-scale reading. Each graph, for purposes of this narrative, identifies the types of adjacency spaces and the sources of noise present used in the calculation.
An additional feature depicted is a banded area in the region of the destination (sometimes also within the source area). The “noise criterion” (NC) class is depicted here. The NC class is an established basis of design for setting acoustical standards acceptable in the receiving room. In other words, if every frequency falls within the banded NC area as programmed for the space, the sound pressure level meets minimum acceptable standards.
In our experience, sometimes a frequency falls outside the band or the accepted region for noise control. This may indicate failure of the partition to perform, or it may indicate a costly situation unfeasible to correct. Having all frequencies fall within the band guarantees compliance to minimum standards. However, a specific frequency outside the band may not be economically justifiable to correct to achieve compliance across the entire frequency spectrum.
The second type of graph is the Fitzroy Calculation which is used to analyze the reverberation time for spaces small, medium, or large. Fitzroy is a complicated equation based on logarithmic expressions, exponential powers, and division within a three coordinate space to emulate a three-dimensional calculation of acoustical response within a room. Although complicated, the Fitzroy equation renders a far more accurate result in defining reverberation time of rooms ranging in size from small to large. While simpler calculations provide basic reverberation time, they are often inaccurate when materials are not homogeneously applied to all walls.
The Fitzroy equation accounts for location of absorbent materials within all planes of a three-dimensional space. The “Fitzroy Calculation” graph demonstrates typical CANVAS® output graphics as follows:
- Room size: Noted in order to calculate volume and surface area within the room.
- Surfaces are input, whether hard reflective or absorbent.
- Reverberation time at different frequencies.
- Average reverberation time calculated per ANSI standards.
- Expected reverberation time at respective frequencies. Frequencies are shown on the X coordinate, while reverberation time is appears on the Y coordinate. CANVAS® readily calculates the reverberation time throughout the audible spectrum in an easily understood format.
On the CANVAS® output is a band indicating the acceptable level of reverberation for the size and use of a room. The band shows the acceptable range for reverberation within the space. Through experimental results dating as early as the 1920’s, acceptable reverberation ranges have been established and later amended, giving Acoustical designers a target area. The upper level of the band indicates acceptable reverberation times for musical venue while the lower portion of the band indicates reverberation time acceptable for speech. Seldom is the case where applied materials and calculations indicate reverberation level within a space 100% compliant within the range of acceptable reverberation times.
The CANVAS® acoustics software program was developed by and is the sole property of Professional Systems Engineering, LLC.