First Name: Dzhambulat
Last Name: Khadashev
Student ID №: 12023830
Module: Acoustics (BE0850)
Teacher: Lawrence Hughes
Submission date: 01/05/2014 by 4pm
4. Manual calculations and results
Reverberation time is the primary descriptor of an acoustic environment. A space with a long reverberation time is referred to as a "live" environment. When sound dies out quickly within a space it is referred to as being an acoustically "dead" environment. But the time for reverberation to completely die away will depend upon how loud the sound was to begin with, and will also depend upon the acuity of the hearing of the observer. An optimum reverberation time depends highly on the use of the space. For example, speech is best understood within a "dead" environment. Music can be enhanced within a "live" environment as the notes blend together. (Acoustics.com, 2004)
In order to provide a reproducible parameter, a standard reverberation time has been defined as the time for the sound to die away to a level 60 dB below its original level (called RT60). Reverberation time is defined for wide band signals. When talking about the decay of an individual frequency, the term decay time is used. (Nave, 2012)
Basic factors that affect a room's reverberation time include the size and shape of the enclosure as well as the materials used in the construction of the room. Every object placed within the enclosure can also affect this reverberation time, including people and their belongings. (Peoples, 2009)
The aim of this laboratory exercise is to demonstrate how Reverberation time can be measured using an integrating Sound Level Meter and eventually how to conduct manual calculations with collected data regarding the spaces. Key elements of use of a modern sound level meter with building acoustic analysis and its terminology will be also demonstrated in this lab. (Hughes, 2014)
Multi-directional Speaker with Power amplifier (picture 1) - is a very suitable instrument for building acoustic measurements. The output acoustic power is a pink noise, which frequency range can be selected by user.
Portable sound level Meter (picture 2) – is a measurement instruments that has been designed to measure sound and noise levels
Measurement equipment (B&K 2260)
Sound level calibrator - is a hand-held device that emits an audible tone of very accurate level and frequency. Before making noise measurements the Calibrator is fitted over the meter's microphone and the reading is either checked manually by the user or automatically by the meter.
Materials to create impulse sound field (Party Balloons)
Laser measure (picture 3) – is a distance measuring device.
The reverberation time is perceived as the time for the sound to die away after the sound source ceases, but that of course depends upon the intensity of the sound. To have a reproducible parameter to characterize an auditorium which is independent of the intensity of the test sound, it is necessary to define a standard reverberation time in terms of the drop in intensity from the original level, i.e., to define it in terms of relative intensity (D. J. MacKenzie, 1999).
It is difficult in practise to measure the time it takes for the level to decay 60 dB, so 20 dB and 30 dB decays (also known as T20 and T30 decays) were used and extrapolated to find the 60 dB decay. (Hughes, 2014)
The experiment was carried out in Room 310 in the Wayne Jones building, Northumbria University. In order to allow for spatial variations of reverberation decay, a series of measurements were made at different positions in the room as shown below.
The experiment was done with two different sound sources. The first one was Multi-directional Speaker and this method is called Interrupted Noise Method. The second sound