Manually-scanned level measurements are becoming increasingly popular for level measurements in field sound insulation surveys. Compared to measurements at fixed microphone positions, manually-scanning reduces the number of separate microphone positions required for a sound insulation survey and typically reduces the total survey time. It also eliminates the need to carry a tripod for the sound level meter. There is even evidence that manually-scanned measurements are more repeatable than measurements at fixed positions*, particularly at low frequencies.
Manually-scanned level measurements are explicitly supported in the ISO 16283 series of standards for field measurement of sound insulation in buildings, with specific requirements separate to those for fixed point and mechanically moved microphones. HBK 2255 and Building Acoustics Partner are optimized for manually-scanned measurements, meeting the requirements of ISO 16283 with maximum convenience and efficiency.
Manually-scanned measurements are made by moving the microphone through a predefined path with an outstretched arm. Each scan must be performed slowly and smoothly over a period of 30 seconds or more. For a typical airborne sound insulation test, a total of five scans are required: one for each source position in both the source and receiving rooms, plus one more for background noise in the receiving room. For a building survey covering 15 partitions, this adds up to more than half an hour of cumulative scanning time, slowly moving the sound level meter with an outstretched arm. Clearly, a lightweight sound level meter is desirable for this task. And at just 400 grams, HBK 2255 is one of the lightest sound level meters on the market, and more than 35% lighter than Type 2250.
HBK 2255 has another trick up its sleeve for manually-scanned measurements. ISO 16283 defines three scanning paths for use in normal rooms: circle, helix and cylindrical. Both the circle and helix paths require the user to adjust their body position partway through the scan, and the standard recommends that the user pauses measurement while repositioning to minimize operator noise.
No such repositioning is necessary for the cylindrical scan, but the standard requires the use of an extension rod to hold the microphone. With HBK 2255’s rigid microphone extension rod,
this requirement is met while keeping the sound level meter and microphone in one hand with easy access to the measurement control buttons.
Our Building Acoustics Partner app is also optimized for manually-scanned measurements.
When manually-scanned measurements are chosen in the project setup, the default number of measurement positions is adjusted to match, and the measurement time is switched from a preset duration to a free run, allowing you to stop the measurement when you’ve finished scanning, instead of the other way around. The app also has a ‘pocket mode’, allowing you to perform manual scanning measurements using HBK 2255’s interface, while still receiving workflow guidance pushed from the app to the sound level meter’s display. Every level measurement also includes a logging profile, allowing you to see how the level changes with time during your scan, helping you to spot any operator noise and refine your scanning technique.
For these reasons and more, we believe that HBK 2255 with Building Acoustics Partner is the best sound level meter in the world for manually-scanned building acoustics measurements.
* An empirical study of the effects of occupied test rooms and a moving microphone when measuring Airborne Sound Insulation
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