OSIX Basic Principles and Technics
By dampening down its own resonance in the inaudible spectrum, the OSIX suspension strongly limits the low audible frequencies of the boom pole noises at the cost of allowing a certain increase in the infra-low frequencies. Therefore, it is imperative to use a low cut filter but there is no need to have a high frequency cut-off. Except for any subjective choices, the ideal is a filter 50-70 Hz steeply sloping (12 or 18 dB/oct). Attention should be given to the filters on the microphones themselves as they are sometimes quite "soft" (ie. they have weak slope) and have higher cut-off frequencies. It is advised to carry out some tests with an aim of preserving the "roundness" of the signal (voice) while limiting to the maximum "panics" (inaudible) of the modulation meters during the handling of the poles.
Remember: At the time of the first talking films, technical and artistic choices (lighting, direction, etc) during shootings were often regulated around the sound recording problems taking into account the technical limitations of the equipment. Today, the operators, their assistants and their equipment must constantly adapt to the new rules of the game: sensitive microphones, greater dynamics of recording, more mobility of the actors, the poles increasingly light and microphonic, etc... In this context, the mike suspension is an essential accessory allowing the assistant to concentrate on their work of sound recording without being constrained by the fear of a boom noise.
Apart from some other practical aspects, the quality of vibratory insulation is not the only criterion characterising a "good" suspension. There is a need, too for decoupling naturally which involves the best "softness" of the microphone mounting. On the other hand, the right function of the mounting itself prescribes a strengthening of the insulators. A good suspension, therefore, is one which offers the best compromise between a suitable vibratory insulation and sufficient firmness of the mounting. One of the major problems is the mechanical assymmetry belonging to many microphones. The front part is often longer than the back where it is held in position.
For all these reasons and taking into account the large diversity of standard microphones now available which are different in shape, size and weight, OSIX suspension are not universal; they have been designed for specific microphones which are widely used in the film industry. It is, therefore, not advisable to use them with microphones for which they have not been designed. Equally, it is not worth trying to adapt OSIX suspension into a windshield because the basket resonances involve a considerable degradation of anti-vibratory filtering.