SYSTEM NOTES FOR ACOUSTICAL CONSULTANTS

Supportive Data

Though Grozier system are often used to qualify sound emissions according to simple metrics, there is also the need for supportive data to help solve the sound emission problem in general.

For example:
The local regulation says that 1 hour Leq sound levels at the property line shall not exceed 65 dBA. A Grozier system can do this readily, however a report that shows that levels have been exceeded does not go far toward the solution of the problem. Tabulated below are additional system features of increasing complexity and usefulness.

1. A simple histogram of the 1 sec Leq distribution every minute, shows information about time and level that result in the 1 hour Leq being exceeded.

2. An audio sample triggered and stored every time a level is exceeded helps determine aurally the source of the offending sound.

3. Live synchronous audio and video recording allow the consultant in his office assess the situation immediately at the remote site.

So in summary, before you close out the specification for the Grozier system, think about the data you may need for the next phase of the project.

Security of Data

Grozier systems built around either Linux or Windows operating systems. For those clients who need the flexibility and familiarity, Windows is preferred. They often already know how to network the Grozier system, access directories, download files to flash drive and make their own notes on Notepad. So even though access to parts of the system can be restricted by passwords, we need to pay attention to security of the data itself. This issue is compounded when the user is policing itself in under the direction of a local ordinance or court order.

For these reasons reports can be validated by a checksum appended to a report. This checksum is a string of characters that is unique to the prior data in the report. If there is a question about the veracity of the data, you can run a separate program which reads the data file verifying the checksum that had been previously appended to the report. This result can be attested in court.

Crowd Sound Detection

Sometimes local regulations allow the crown sound not to be included in the facility sound emissions. We have employed several ways to separate music and crowd sounds. The first to do this was our system at Great Woods Amphitheater 20 years ago. Here an operator was at hand to press a button when the crowd sound was judged to be dominant. This pressing diverted the sound level data into a separate record file for crowd only. In addition a mark was automatically applied to the graphical record of the event.

Alternatively, Grozier has used the fact that crowd sound contain little energy at low frequency. So by monitoring the sound in the 63 Hz octave band, only the contribution of the bass music is detected. In situations where the bass has been found to be the offending characteristic of the sound, this is an acceptable way to specify sound level limits. i.e. Leq 63Hz octave.

Where this choice is not acceptable, the electrical feed to the house loudspeaker system can continuously monitored on a separate data channel so that system "knows" when the the speakers are active. When "quiet" is detected from the speakers, then the microphone sound is considered to be crowd sound. This "crowd only" data is stored separately.

***** Copyright 2009 *****