Corrected Statistical Energy Analysis Model in a Non-Reverberant Acoustic Space

Statistical Energy Analysis(SEA)is a well-known method to analyze the flow of acoustic and vibration energy in a complex structure.This study investigates the application of the corrected SEA model in a non-reverberant acoustic space where the direct field component from the sound source dominates the total sound field rather than a diffuse field in a reverberant space which the classical SEA model assumption is based on.A corrected SEA model is proposed where the direct field component in the energy is removed and the power injected in the subsystem considers only the remaining power after the loss at first reflection.Measurement was conducted in a box divided into two rooms separated by a partition with an opening where the condition of reverberant and non-reverberant can conveniently be controlled.In the case of a non-reverberant space where acoustic material was installed inside the wall of the experimental box,the signals are corrected by eliminating the direct field component in the measured impulse response.Using the corrected SEA model,comparison of the coupling loss factor(CLF)and damping loss factor(DLF)with the theory shows good agreement.

Acoustic Characteristics Analysis of Industrial Premises with Process Equipment

Process equipment placing in industrial premises leads to essential change of room acoustic characteristics: mean length of sound rays’ free runs, reverberation time and mean absorption factor in a room. The changes influence distribution of the reflected sound energy in premise volume. Failure to take account of the given circumstance results in errors at definition of sound pressure levels and an estimation of efficiency of building-acoustic measures of noise abatement. In the paper the results of computer modeling of acoustic processes in premises with the process equipment are considered and influence of the equipment on a sound absorption indoors is analyzed. The computer simulation is carried out on the basis of the ray tracing method with taking into account rays’ energy distribution in a room. It is shown that such approach allows determining objectively the integral acoustic characteristics of industrial premises, takes into account influencing to them the room parameters, the presence and scattering characteristics of the equipment and makes more accurate the equations putting into engineering practice.

Preliminary Archaeoacoustic Study of Kanheri Caves in Mumbai(Maharashtra,India)

Here we report first ever study on acoustical evaluation of Kanheri Caves located in Sanjay Gandhi National Park,Mumbai(Maharashtra,India).These caves are dated to a period between 2nd century BCE to 7th century CE.In this study we used an ambisonic recorder to capture Impulse Response,which carries acoustic signature of the place.Out of total 109 caves 41 were surveyed in available time.Out of those reverberant environment was noted in 12 caves.Measurements were made only in 3 caves(Cave Nos.1,3,11)which are important.In the beginning we carried out an FFT analysis.We then studied room acoustic parameters like Reverberation Time,Early Decay Time,Clarity,Definition,etc.,based on the measurement of Impulse response.Cave No.3 have high value of reverberation time,compared to other.Therefore it also have lower clarity compared to others.It is properties needs to be compared with similar structures(chaityas)in Maharashtra(at Ajanta,Ellora,Nashik,Junnar,etc.)and elsewhere in India.It is worthwhile to carry out further research in Cave No.3 with more sophisticated instruments as well as 3D modeling.Since the experiment was performed with receiver at only one position,we also suggest to carry out experiment with receiver at multiple positions and then comparing them.

Loudness criteria in auditorium acoustics

Loudness, one of the distinguishing characteristics in auditorium acoustics, has received less attention by acoustical consultants than other parameters up to the present. Due to the lack of an appropriate paramcter, neither measurements in auditorium on this subject is practicable, nor prediction could be made during the design process. The frequently applied method is by means of the summation of the direct sound and the reverberant sound as the total sound level over the audience area. In fact, this is only suitable for predicting the sound level from a steady sound source and in the reverberant field, apparently not appropriate in practice either for acoustic design or for on-site measurement. Strength index G (Starkemass in Germany) (dB), proposed by Lehmann, as loudness criteria, might be a proper parameter. But,as the primary results from our investigation and from others as well, showed that the early reflections presented the main contribution to the perccived loudness, it is more reasonable to set a limit to the integrating time of index G, say 50 ms for speech and 80 ms for music, which have been commonly recognized as useful portion in 'definition' and 'clarity', instead of the infinitive integrating time as Lehmann proposed. Therefore, G50 and G80 are highly recommendedto be used as loudness criteria for speech and music in auditorium acoustics respectfully.

Steady-state sound field in enclosures

The classical normal-mode theory expresses the steady-state sound field in an enclosure produced by a sound source as a series of normal modes of vibration. Experimental facts are not often explained by this theory, and it was conjectured that the normal-mode expression is not the complete solution of the wave equation in the enclosure, but only the reverberant part of it, and there should be an additional term representing the direct spherical radiation to make the solution complete. The problem is examined by critically reviewing the derivation of the normal-mode expression, and by theoretical analysis of the steady-state sound field in the room and experimental measurements therein. The conjecture is thus confirmed, and it is definitely shown that the sound field should contain the direct wave as well as the standing waves (normal modes) formed by the confinement of the boundary surfaces. Relevant mathematical expressions are derived.