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Room Acoustics - The Problem

Room Acoustics - Research Room Acoustics - Solutions Room Acoustics - How it Worked Room Acoustics - Evaluation Calculation Table for Different Absorption Coefficients/Sabines
Instrument Acoustics- The Problem Instrument Acoustics -  Research Instrument Acoustics - Solutions Instrument Acoustics - Practical Designs Instrument Acoustics - How it Worked Instrument Acoustics - Evaluation

Dealing with Acoustic Room Treatment (Part 2)



As well as extensive research online we also placed a microphone in the room and played test tones (sine waves at different frequencies) and pink noise (a signal containing all frequencies) into it. Analysing this on Cool Edit Pro though proved inconclusive.


This could be down to the quality of the microphone used but is just as likely to be down to the poor quality of the available speakers, which were small and cheap meaning little likelihood of any significant bass end output and little likelihood of a flat frequency response across all other frequencies. This would result in a significantly coloured and flawed input signal to start with.


We were actually looking to do a spectral analysis to identify problem frequencies i.e. those which were emphasised or those which were deficient and possibly to identify any standing waves.


My online research indicated that various options could be tried to tame our reverb problem. Realigning walls was, as mention, impractical and would not solve the main problem anyway. Similarly, diffusers, while easy to construct, would not solve the long reverb time problem.


Rearranging the room so that monitors and microphones can be placed in the utmost positions was also not feasible as this is a television studio and visual considerations have to be taken into account. Microphones and monitors in shot is obviously, not acceptable.


We therefore concentrated our efforts on absorbers. Several different options can be seen in the enclosed printouts. However the best all round solution seems to be a Helmholtz design.


This consists of an enclosed box with an aperture (or series of apertures) with absorbent material near the apertures and an air gap behind the material. Sound waves enter through the apertures where the sound is absorbed by this material. The air gap is designed to keep catch the sound waves before they hit the hard surface behind. When they hit this surface their velocity becomes zero and so little will be trapped. By catching them before they hit this surface they are caught while still moving and can therefore be absorbed better.


The size of this air gap can also be used to change the frequencies which will be most affected by the absorber. This is because a sound wave is at its fastest at a distance of one quarter of its wavelength. Therefore the frequency which corresponds to a wavelength of four times the air gap will be that which is most affected.

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