The Rule of Two helps make spaces sound better
Researchers developed a new acoustic measurement technique in a room with
more acoustic combinations than there are ants on Earth

Date:
March 30, 2022
Source:
Aalto University
Summary:
Researchers developed a new acoustic measurement technique in a
room with more acoustic combinations than there are ants on Earth.



FULL STORY ========================================================================== Acoustics researchers of Aalto University have improved the most
common method for measuring the acoustics of a room, the sine sweep
technique. The new approach will make it easier and faster to design a
room so that the right sounds reach the right spots.


==========================================================================
In the sine sweep, a room's acoustics are tested by measuring the echoes
of a continuous whistle that changes frequency logarithmically from 20
Hz to 20,000 Hz, the full range of human hearing. The sweep lasts for
only a few seconds.

Using a longer sweep would feed more energy to the room and reduce the proportion of other noises affecting the measurement, but it would also increase the chance of other disturbances or changes in the environments, adding uncertainty to the measurements.

The new method, which the researchers call the Rule of Two, uses multiple measurements to get around the problem. By repeating the sine sweep
measurement until two runs pass the cleanliness criterion, automated measurements can reliably collect better data.

The Arni room at the Aalto Acoustics Lab in Otaniemi provided the tools to measure the thousands of combinations needed to develop this method. "The measurement techniques of acoustics and audio technology have developed
greatly over the years. In the early days, acousticians used to clap
their hands or use a starting pistol in a room and then listen to
how the echo decayed. Nowadays, measurements are done with a computer
and accurate calculations tell us precisely how sound reverberates in
different spaces," says Vesa Va"lima"ki, a professor of acoustics.

Karolina Prawda, a doctoral researcher, explains that "the name of our
method, Rule of Two (Ro2), comes from the requirement that reliability
calls for two clean measurements which correlate strongly. Later we
learned that, by coincidence, there is also a rule of two in Star
Wars. The acoustic measurement method has nothing to do with Star
Wars, except for the same term." The researchers believe that the
new measurement technique will replace the 20- year-old single sine
sweep method because the more reliable technique saves time in design
work. Acoustic measurements are commonly used in the design of any
interior spaces where speech, announcements or music have to be clearly audible, such as in movie theatres, metro stations, concert halls,
lecture rooms, churches, and congress centers.

"At Aalto University, we will immediately start using this method in
teaching.

I hope that the acoustics sector will notice its benefits as soon as
possible," Professor Va"lima"ki says.

Learning from endless echoes The walls of the Arni room are covered in
rotating panels. Each panel has a hard side and a soft side. The room can
be made reverberant by exposing the hard surfaces and attenuated using
the soft ones. A spherical loudspeaker plays sounds in all directions,
and the acoustic properties can be measured with several microphones
at the same time. By rotating the panels, researchers can modify the
acoustic environment in the room almost endlessly.

"The measurement method was discovered because of thousands of
measurements.

The walls can produce more combinations than there are ants in the world," explains Professor of Practice Sebastian Schlecht.

"The wall panels open and close when the software commands them. Our
task was to analyze the thousands of measurements and compare them with
each other," Prawda says.


========================================================================== Story Source: Materials provided by Aalto_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Karolina Prawda, Sebastian J. Schlecht, Vesa Va"lima"ki. Robust
selection
of clean swept-sine measurements in non-stationary noise. The
Journal of the Acoustical Society of America, 2022; 151 (3):
2117 DOI: 10.1121/ 10.0009915 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220330103202.htm

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