The Ways of a Punk
Assignment Title: The Polar Response of a Microphone Introduction The aim of this experiment is to evaluate the behaviour and characteristics of a number of varying types of microphones, produced by different manufacturers, through the use of the MLSSA system. MLSSA, or Maximum Length Sequence System Analyser, is a dedicated hardware and software measuring tool originally developed for the evaluation of room acoustics and loudspeakers. With the implementation of this system a maximum length sequence excitation signal can be generated and sent to a loud speaker unit whilst simultaneously measuring the input signal received back from the microphone in question. The difference seen between the MLS signal and the input signal of the microphone is impulse response, from which the frequency response can be obtained by Fourier Transformation. Apparatus The three microphones used in this experiment were: MBC omni-directional condenser microphone - this type of microphone operates by responding to air pressure changes on the outside of the case which contact and move a diaphragm. It can be said to be omni-directional (¡®omni¡¯ equating to ¡®all¡¯) because sounds that are emitted from the side or to the rear of the microphone diffract around the case and are picked up at the front. Ideally it would be constantly omni-directional at all frequencies. AKG cardioid condenser microphone - this type of microphone is a directional microphone. It functions by comparing the pressure differences seen on either side of the diaphragm. It therefore has an large aperture at the rear of the microphone, which when combined with an acoustic labyrinth, eliminates sound pick up from the back (or 180o). This is performed by sufficiently slowing down any backwards sound so that it takes the same amount of time to travel through the case as round it, therefore eradicating any diaphragm movement by cancelling out the unwanted rear sound. Rode large-diaphragm cardioid condenser microphone - this microphone has the same basic principle as the aforementioned AKG cardioid microphone with the addition of a larger diaphragm. Method The apparatus was first obtained and then set up as stipulated in the course handbook. Care was taken at this point to ensure that the loud speaker unit was positioned on the edge of a bench in an appropriate location so as to ensure that hard reflective surfaces, such as walls, cupboards and the floor, were as distant as possible.