ESA ESTEC Noordwijk

Large European Acoustic Facility

This is the most powerful sound system in Europe – but no human being could survive hearing it at maximum output.

Engineer Kees van Zijtveldt is standing beside the largest sound horn of ESA’s Large European Acoustic Facility (LEAF), capable of subjecting satellites to the same noise a launcher produces as it takes off and flies through the atmosphere.

LEAF is an integral part of ESA’s ESTEC Test Centre in Noordwijk, the Netherlands, a collection of spaceflight simulation facilities under a single roof. One wall of the chamber – which stands 11 m wide by 9 m deep and 16.4 m high – is embedded with a set of enormous sound horns. Nitrogen shot through the horns can produce a range of noise up to more than 154 decibels, like standing close to multiple jets taking off.

As a safety feature, LEAF can operate only once all the doors are closed. Steel-reinforced concrete walls safely contain its noise, coated with epoxy resin to reflect noise to produce a uniform sound field within the chamber. The chamber itself is supported on rubber bearing pads to isolate it from its surroundings.

ESA’s Large European Acoustic Facility (LEAF) subjects satellites to an acoustic noise level which will be encountered by the satellite during the launch phase. The chamber’s noise generation system consists of four different sound horns with cut-off frequencies of 25Hz, 35Hz, 80Hz and 160Hz plus three high frequency generators, together allowing acoustic excitation in the frequency range from 25Hz to 10kHz to an overall noise level of more than 154 decibels.

While standard stereo speakers produce noise by the pushing and pulling of an electromagnet attached to a flexible cone, the LEAF’s acoustic noise is produced by a modulated flow of gaseous nitrogen blown through the sound horns, on the order of several kilograms per second during a typical 90 to 120 second test.

The LEAF’s surrounding walls are made of steel-reinforced concrete 0.5 m thick and are coated with a thick coating of epoxy resin to reduce noise absorption and increase internal reverberation, creating a homogeneous sound field throughout the 11 m by 9 m chamber.
During testing the LEAF’s 250-tonne door is fully closed with only the test satellite inside – certainly no people. 120 dB is usually the level at which noise becomes painful. LEAF can reproduce a sound pressure about 50 times higher. Harmful resonance vibrations would also be set up inside the human body. And because the LEAF is operated with gaseous nitrogen the absence of oxygen would be lethal as well…

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