Absorbing
sound with hard materials
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THIN AND LIGHT-WEIGHT: The
metal plates are under 1 millimetre in thickness and need
a few centimetres of space behind them to deaden the echoes
of bass and mid-range sounds, explained Ole-Christian Drage
(left) and Bjørn André Fløtre, here in NTNU's anechoic room.
Photo: Nina Tveter
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Sound-absorbing metal plates seem impossible
– but they are not.
Architects will love them. People with allergies
will find it easier to breathe. All of this because of an acoustic
improbability: Sound-absorbing plates that don’t contain the fibres
that cause allergy and asthma, and that can also be used as aesthetic
interior design elements.
PRACTICALLY
NO HOLES
Most sound-absorbing plates are made of porous materials.
De- Amp, a new Norwegian company founded by engineers from NTNU,
has taken the opposite approach, using hard materials such as metal,
plastics, glass and Plexiglas to muffle sound. The secret lies in
very fine micro fissures that have been burnt right through the
plates using a laser, combined with the design of the spacing between
the fissures. The metal plates are less than one millimetre thick
and are intended for indoor use, in ceilings or walls. The plates
have to have a space of a few centimetres behind them to muffle
the echo of bass and mid-range sounds, which are in the pitch of
the human voice.
Common, perforated sound-absorbing plates,
known as cavity absorbents, have a perforation rate of 10 to 30
per cent. The new, hard plates have a perforation rate of less than
1 per cent.
“They appear unbroken, and can be used creatively,
as signs, or even as part of a piece of art, because they can be
shaped", says Bjørn André Fløtre, product developer for DeAmp.
“The plates can also be wave-shaped, as long
as the cavity behind them has the exact same shape. That makes them
even more efficient as the absorbing surface gets even larger. The
sound-absorbing effect results when sound waves hit the plate and
cause the air in the fissures to vibrate. Energy is lost because
of the friction between the air and the walls of the fissures, and
the friction drains the sound of energy and absorbs it as heat.”
HEALTH BENEFITS
Microscopic fibres that escape from sound-absorbing materials
are a problem for people with respiratory problems. The Norwegian
Board of Health’s standards for indoor air quality state that “Exact
levels for the prevention of health effects are not yet known, but
free fibres in indoor air should not be permitted”. Nevertheless,
schools and offices often contain sound-absorbing materials that
produce fibres as they degrade. Thus, the sound-absorbing, fibre-free
plates could offer major health benefits. The plates are also quite
easy to clean, because they can be both washed and flushed with
water or other cleaners.
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MICRO FISSURES: DeAmp’s new, sound-absorbing
plates have continuous, laser-cut micro fissures measuring
0.2 millimetres. The fissures are cut in such a way that less
than 1 per cent of the plate is actually perforated.
Photo: Nina Tveter
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ORIGINATED
AT NTNU/SINTEF
The idea behind this product originated in the acoustic research
laboratories at NTNU and SINTEF. The use of micro-perforation with
holes as a technique for sound reduction is a well-known technology,
but over the last several years, Professor Emeritus Tor Erik Vigran
has developed this technology even further. He has developed a program
that can calculate the design criteria for sound absorbents and
has crafted a special version of the program that is used to make
sound-absorbing plates.
Professor Vigran and Odd Kr. Ø. Pettersen,
NTNU professor and Head of Research at SINTEF IKT, started this
work as a result of student projects in the autumn of 2003. The
results were so promising that Bjørn André Fløtre and two other
advanced engineers from NTNU, Pål Ove Henden and Ole-Christian Drage,
established DeAmp as a company and applied for a patent for the
technology, with the goal of commercialising the idea.
FOR PUBLIC
PLACES
Currently, the firm is trying to find partners that can manufacture
the plates at a large scale and for a reasonable price. Several
European companies in Germany, Italy and Slovakia are being considered.
A prototype will be ready this autumn, with the goal of having the
plates on the market in the spring.
So far, DeAmp has focused on aluminium and
steel as the materials of choice for their plates. The firm’s main
market will be businesses that have public spaces.
“Restaurants, conference rooms, offices and
hotels, places with special requirements for finish and decoration,
are target groups for us”, says Fløtre. “In the future, plates made
of plastics could be of interest in surgical settings, or in the
food industry where hygiene requirements are very strict. Several
types of plastic have been approved for medical use because they
can be sterilized”.
By Nina Tveter
Contact: Bjørn André Fløtre, DeAmp
Tel: +47 959 29 610, Email: flotre@deamp.com
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