Effects Of Acoustic Treatment Research Articles

The effectiveness of acoustic treatments in general hospital wards in China

The aim of this study was to quantitatively determine the effect of various acoustic treatments in hospital wards on reverberation time, noise levels and users' subjective evaluation during normal operations by installing a sound absorptive ceiling and soundproof door and windows. Patient rooms, corridors and nurse stations in two general wards in a Chinese hospital were chosen as the study sites. The quantitative measurements showed that the reverberation time of 500 Hz–1 kHz decreased by 13∼53% to approximately 0.3 s in the patient rooms, corridors and nurse stations after the acoustic treatment. Noise levels in the corridors and nurse stations decreased significantly by 5∼11 dB(A) (p < 0.01). Smaller differences were found in the patient rooms with noise levels decreasing after application of the acoustic treatment by 2∼4 dB(A) (p < 0.01) during the daytime and 5–6 dB(A) (p < 0.01) during the nighttime. Questionnaires indicated that acoustic treatment could significantly decrease the negative impacts of noise on patients’ conversations (p < 0.01) and emotional state (p < 0.01) and extend the quiet period during the night-time for sleep. Meanwhile, staff members reported that they could take advantage of speaking with a lower voice and having a higher working efficiency at the nurse station after changing the ceiling material to an absorptive one.

Effect of acoustic treatment on fan flutter stability

This paper presents an investigation of the effect of acoustically treated wall on fan flutter stability. The analysis is based on a three-dimensional analytical model which captures the aerodynamic coupling between oscillating annular rotor and finite-length liner in subsonic flow. With the response function of the entire system constructed as a whole, the perturbed duct field in modal description is determined by a simultaneous solution of the rotor and liner responses. Whether or not the aeroelastic instability occurs under a given wall impedance condition is evaluated through the energy method. Numerical experiments are conducted in the parametric space of inter-blade phase angle, liner distribution and acoustic impedance. The results show that under different conditions the acoustically treated wall can take diverse effects on the fan flutter stability. In the presented cases where the rotor stability is considerably affected, it is found that the aerodynamic interaction between the rotor and the lined section modify the overall distribution of the aerodynamic loadings on blade surface rather than change their magnitudes significantly. Moreover, the aeroelastic response of the oscillating blades turns out to be very susceptive to the reactance variation when the resistance is small, further indicating the important role of the reflections on the liner surface in such aerodynamic interaction. The analysis in general implies that the actual impact of a lined wall on the fan flutter stability depends on the aerodynamic excitation condition mutually determined by duct geometry, rotor state and configurations of liner.

Does acoustic environment modify boldness and related life-history traits in field cricket nymphs?

Between-individual differences in personality and life-history traits can arise from both genetic and environmental factors, with the latter possibly reflecting contrasting individual experiences during ontogeny. It is yet unclear how the acoustic environment may affect the development of boldness and related life-history traits such as growth rate, maturation age and longevity in species that normally rely on acoustic cues to adjust their behaviours. We studied if long-term exposure of field cricket Gryllus integer nymphs to traffic noise or acoustic conspecific signalling would affect the level or repeatability of boldness or life history traits. An integrative boldness score was statistically significantly repeatable in control and cricket sound groups, but not in the traffic noise group. However, our data did not show any effect of acoustic treatment on individual boldness. Acoustic treatments had no effects on life-history traits, either. Future studies are needed to confirm whether the acoustic environment could affect the development of personality and behavioural consistency.

Effects of Acoustic Treatment on Music Teachers' Exposure to Sound

Abstract In this study, music teachers' exposure to sound was tested by measuring the A-weighted equivalent sound pressure level (SPL), the A-weighted maximum SPL and the C-weighted peak SPL. Measurements were taken prior to and after acoustic treatment in four rooms during classes of trumpet, saxophone, French horn, trombone and percussion instruments. Results showed that acoustic treatment affects the exposure of music teachers to sound. Daily noise exposure levels (LEX, 8 h) for all teachers exceeded a limit of 85 dB while teaching music lessons prior to room treatment. It was found that the LEX, 8 h values ranged from 85.8 to 91.6 dB. The highest A-weighted maximum SPL and C-weighted peak SPL that music teachers were exposed to were observed with percussion instruments (LAmax = 110.4 dB and LCpeak = 138.0 dB). After the treatments, daily noise exposure level decreased by an average of 5.8, 3.2, 3.0, 4.2 and 4.5 dB, respectively, for the classes of trumpet, saxophone, French horn, trombone and drums, and did not exceed 85 dB in any case.

Computation of Fan Noise Radiation through an Engine Exhaust Geometry with Flow

This paper outlines a computational model of noise radiation from a realistic engine exhaust geometry with flow. The computational model described allows acoustic waves, propagating inside the bypass duct of a generic aircraft engine, to be admitted into a computational domain that includes the aft duct section, the exit plane of the duct, and the jet flow immediately downstream. The method has three parts: a matching process to admit acoustic waves into the induct propagation region; near field propagation inside the duct and diffraction at the lip of the exhaust duct; and an integral surface for far field directivity. In this model the near field propagation is determined by a numerical solution of a 2.5D form of the linearised Euler equations. The mean flow about which the equations are linearised is assumed to be axisymmetric. The proposed method is illustrated through a case study on the radiation of a typical fan assembly generated acoustic wave from a generic engine bypass duct. Inside the duct, an acoustic wave of circumferential order m = −13 and comprising five radial modes ( n = 1 – 5) is admitted into the model as inputs on the boundary of the computation domain. The radiation of the acoustic wave through the exhaust geometry and mean flow is determined, with the effect of acoustic treatment through the inclusion of lined duct sections also examined.

Effect of Sound-Absorbing Treatment on Speech Discrimination in Rooms

Noise and reverberation in a room affect speech discrimination. Sound-absorbing materials are used to shorten reverberation times. To find out the effect of acoustic treatment on speech discrimination, an acoustic refitting was carried out in a classroom and in a multipurpose hall. The normal-hearing test subjects perceived the word material (sentences, words and nonsense words) binaurally from the loudspeaker. The tests were repeated after the acoustic refitting of the rooms. The sound-absorbing treatment improved speech discrimination. In quiet, the improvement in discrimination was minimal or absent, but was well documented in a noisy environment. In rooms where speech communication takes place, attention should be paid to acoustic conditions: acoustic treatment can improve the quality of communication.

Effects of acoustic treatment on the interior noise of a twin-enginepropeller airplane

A study of the cabin acoustics of a Fairchild Merlin IVC twin-engine propeller airplane is described^ The sound field was measured at six locations inside both an untreated green airplane and a completely finished airplane. Several flight conditions were tested, including different altitudes, engine power settings, and cabin pressures. The overall sound pressure level for each test condition and microphone position was computed from a one-third octave band analysis of the data. The blade passage frequency and its integral multiples, which dominate the low-frequency noise spectrum, were examined using a narrowband analysis of the data. The insertion loss due to the added acoustical treatment was determined by comparing the narrowband results from the two airplanes. These insertion loss values varied widely, depending on many factors, such as position in the cabin, multiple of blade passage frequency, cabin pressure, and engine torque. The space-averaged sound pressure levels corresponding to specific tests of the treated airplane were found to be in good agreement with predictions from the Propeller Aircraft Interior Noise (PAIN) computer program.