11. marzo 2021

Checking a PA’s frequency response and uniformity of coverage with the XL2

Checking a PA’s frequency response and uniformity of coverage with the XL2

Do you have testing specifications calling out frequency response limits for a public address (PA) or paging system? An XL2 with the Spectral Limits Option gives you the answer quickly and on-site.

Public address and paging systems are meant to be understandable. Besides a Speech Intelligibility test, there is often a frequency response test. Here is a typical example:

Measure acoustically at typical listener’s ear level in contiguous one/third octave bands: within plus or minus 2 decibels of flat from 100 to 2,000 Hertz, then rolling off at 3 decibels per octave to 10,000 Hertz.

An XL2 with the Spectral Limits Option, allows you to create PASS/FAIL spectral masks with the specified limits. The XL2’s built-in LED will show the result with an easy-to-understand green or red light. The display indicates which frequencies failed with a solid bar above the spectrum.

XL2 showing Spectral Limits

Nobody wants to make a second visit to commission a system.

An immediate answer on-site lets you know you passed. If there is a problem, you will know immediately and can remeasure or adjust the system to compensate for the room or speakers’ variance.

The XL2’s “Fast Frequency Response Measurement”, part of the Spectral Limits Option, makes it fast and easy to survey a space to find the best measurement location. A running measurement settles within 1 second as you survey the room.


Coverage testing

Since sound typically varies within a space as a function of position, a coverage test (variation of level throughout listening areas) is sometimes specified. Here is a typical example:

Make measurements at multiple locations, either fixed locations or a continuous scan of each acoustically distinguishable space (ADS). The maximum and the minimum should be within plus or minus 6 decibels from 1000 to 4000 Hertz.

The coverage test measures both the running maximum minus the running minimum spectrum as you either:

  • walk the listening area, or
  • take discrete measurements, pausing the measurement between locations.

Of course, the minimum will never be greater than the maximum, so +/- 6 becomes 0-12 dB.

XL2 showing band-limited Spectral Limits 

Again, a green light means you can go home knowing the system passed. A red light indicates a problem. You might need to adjust the volume of individual speakers or add additional speakers (hopefully not) to pass a coverage test.

If you are interested in learning more about frequency response and coverage testing with the XL2 contact us at NTi Audio.