Research project (3 mounth)
Laboratoire d'Acoustique du Conservatoire National des Arts et Métiers, Paris, France
Modeling of a microphone stand shockmount for movie sound recording

This project was conducted for an industrial development by the VDB society which is specialised in the fabrication of sound recording equipment. This society has been created by a sound engineer named Van den Bergh who was unsatisfied with the equipment he was using. For ten years, VDB has manufactured sound recording booms (350 booms/year sold, 90% abroad). The necessity to attach a suspension led to this project.

During a shooting, the microphone requires a large mobility to follow the actors. So, it is essential to use a hand-boom and a directional microphone.

A microphone turns acoustic vibrations into electric variations. It is composed of a membrane which is also very sensitive to mechanic vibrations. This sensitivity to the solidian transmission is particularly significant since the microphone is directionnal. In this case, a suspension is necessary to limit noise picked up by the microphone corresponding to perturbations caused by mechanic excitations of the boom.

The aim of this project was to model and to design the geometric and mechanic configuration of the suspension. All the parameters which characterize the system of a mass suspended by springs (number of springs, rigidity, dispositions in relation to the microphone, etc.) had to be determined in order to optimize the microphone isolation and the sound recording.

A parametric study based on a numeric resolution of the Lagrange's equations using Matlab and Mathematica softwares allowed to conclude concerning the suspension improvement. Experimental manipulations have been performed, particularly transmissibility measurements, in order to check experimentally our predictions.

> back