While a case is open, the user can choose a noise metric (for baseline levels, noise limits, and calculated results) and enter the noise limit criteria for a local area. The user may edit the Lmax and L10 or Leq day, evening, and night noise limit criteria for a residential, commercial, or industrial area. Daytime, evening, and nighttime may represent any time periods the user wishes, but they are typically defined as 7 AM to 6 PM, 6 PM to 10 PM, and 10 PM to 7 AM, respectively. The criteria, used together with the baseline sound levels, define the noise limits for each receptor. CA/T Noise Limit Criteria are used as a default [1], but users may input their own criteria. The RCNM offers a metric pull-down menu and two or three command buttons to the right of the Receptor input dialogue box.
A pull-down menu allows the user to choose between the L10 or Leq metric, as in Figure 9. The chosen metric represents that used for the baseline levels, noise limits, and calculated results. For the noise limits and calculated results, Lmax values are also included.
Figure 9. Noise Metric pull-down menu
A pop-up dialogue box allows the user to specify Noise Limit Criteria information for an area being studied in a case, as in Figure 10. The flexibility of the Noise Limit Criteria allows RCNM users to incorporate criteria based on local noise ordinances and baseline levels measured for each receptor.
Figure 10. Noise Limit Criteria pop-up dialogue box
The user may populate this dialogue box with Noise Limit Criteria information derived from CA/T Construction Noise Control Spec. 721.560 [1] by clicking on the "Default" command button and clicking "Yes" when asked to load information from the default file, which is stored in the RCNM (see Table 2).
| Daytime (7 AM to 6PM) | Evening (6 PM to 10 PM) | Nighttime (10 PM to 7 AM) | ||||
|---|---|---|---|---|---|---|
| Land Use | L10 Limit (dBA) | Lmax Limit (dBA) | L10 Limit (dBA) | Lmax Limit (dBA) | L10 Limit (dBA) | Lmax Limit (dBA) |
| Residential | maximum of 75 and baseline + 5 for non-impact* and exempt for impact** | 85 for non-impact and 90 for impact | baseline + 5 | 85 | if baseline <70 then baseline +5; if baseline ≥70 then baseline + 3 | 80 |
| Commercial | maximum of 80 and baseline + 5 for non-impact and exempt for impact | N/A | N/A | N/A | N/A | N/A |
| Industrial | maximum of 85 and baseline+5 for non-impact and exempt for impact | N/A | N/A | N/A | N/A | N/A |
* Non-impact equipment is equipment that generates a constant noise level while in operation.
** Impact Equipment is equipment that generates impulsive noise. Impulse Noise is defined as noise produced by the periodic impact of a mass on a surface, of short duration (generally less than one second), high intensity, abrupt onset and rapid decay, and often rapidly changing spectral composition.
Otherwise, the user may clear any information present in the dialogue box and specify new data in each cell. Clicking on the "Clear" command button will prompt the user to set all the cells in the dialogue box to Not Applicable (N/A), as in Figure 11. By clicking "Yes," the user will populate all cells with N/A; by clicking "No," the dialogue box will return to the data present before the user clicked "Clear."
Figure 11. The Noise Limit Criteria "Clear" command button
