Sound Level Meters

GO BACK  Previous: Octave Filters  Next: Limiting Test     

 

The CoCo can be uses as a sound level meter and includes calculations and displays for all standard sound level metrics.

	Sound Level Meter display shows all standard metrics in bar chart and digital readout format.

 

In CoCo, time weighted sound level is the output of frequency-weighting and then time weighting filters. Time weighting serves an exponential averaging operator. The computation is illustrated below.

Time weighting sound level computation and storage against RPM or Time

The table below shows the symbols for the time-weighted sound level.

Symbol used for time weighted value		Frequency Weighting
		Z	A	B	C
Time Weighting	F(Fast)	LZF	LAF	LBF	LCF
	S(Slow)	LZS	LAS	LBS	LCS
	I(Impulse)	LZI	LAI	LBI	LCI
	Custom	LZC	LAC	LBC	LCC

 

In CoCo, time averaged sound level is the output of frequency-weighting and then time average operation. Time average serves a linear averaging operator. Figure 44 illustrates the computation.

Time averaged sound level computation.

SLM includes traces of the native time streams and the time weighted sound levels,

Native or time weighted sound levels can be viewed in a time trace.

SLM also includes a display called Analysis Results.  The Analysis Results display is similar to a typical sound level meter display and shows the numerical values for the measures and a bar meter for the time and frequency weighted level and equivalent level. 

SLM Analysis Results display.

Metrics can also be viewed with large digital display as shown below.

Numerical display for SLM.

It shows the Leq values of each of the four input channels.

Another common display for SLM measurements is a histogram which shows a statistical distribution of the frequency of occurrence versus amplitude.

Linear-Normalized histogram display for SLM measurements.

The histogram can also be viewed in cumulative format by selecting Select View Mode for Current Trace from the Traces Button and choosing Cumulative.

Cumulative histogram display for SLM measurements.

RPM Based SLM measurements can be made by selecting an RPMTrace. The figure shows the sound level in dB vs. RPM.  This is one of the most popularly used measurement in automotive NVH application.

RPM based SLM measurement.