Improvement of the Facade of Dwellings and More
On a regular basis the acoustician is required to make a submission for a study on the improvement of the fagade sound insulation of condominiums. Most of the time the offer to perform a diagnosis of the sound insulation between flats, while assessing the performance of the existing fagade, is turned down. And usually 2 years later those clients come back, requiring a new submission, as they are now complaining of annoyance between flats much more than before.
The reader probably guessed it: The intrusion of noise from the exterior used to cover whatever noise came from the flats around. When the fagade was upgraded, there was less masking noise from the exterior, and the intrusion of noise from other parts of the building became more noticeable.
Lesson Learned: Always make an inventory of all the noise sources before attempting to set acoustic objectives.
Envelope Made of an Absorptive Material
In the 1970s the French Ministry of Culture launched a concept named “zenith” to try to reduce the cost of pop concert facilities. The original concept, by architect Chaix & Morel, called for a thick, absorptive material between two canvas layers that could be mounted like a circus tent.
Of course, while it provided significant sound reduction in the high-frequency range, it did not provide any in the low-frequency range. The concept was later evolved into a heavier (and more permanent) complex.
Designing, Building, and Commissioning
A building project was initially designed using 20 cm thick concrete walls. While this was accepted at the design stage, the structural engineer admitted that 20 cm thick plain concrete blocks with a concrete finish could also be used. Next, the client found it more expedient to use hollow concrete blocks of the same thickness, as they were cheaper and structurally acceptable. However, the sound reduction index was now down by more than 5 dB. Eventually, the contractor also managed a simplification of his own by replacing the concrete finish by a glued plasterboard, which resulted in a further 4 dB missing due to the resonance frequency introduced by the small gap between the plasterboard and concrete blocks and the unchecked porosity of the concrete blocks.
Lesson Learned: Always check with the acoustician before substituting a material for another.