Hong-Seok Yang

Quantifying scattered sound energy from a single tree by means of reverberation time

Trees in urban spaces surrounded by buildings may be effective in dispersing sound energy, and this could affect sound level distribution and street canyon reverberation. To quantify this effect of trees with a view to including it in numerical predictions, this paper examines sound scattering from a single tree in open field by means of reverberation time (RT). Five trees of different species and crown sizes were considered. The influence of ground condition, receiver height, crown size and shape, foliage condition, and source-receiver angle and distance has been assessed. The results show that RT20 is proportional to the tree crown size, which is the most important factor. The maximum RT20 measured was 0.28u2009s at 4000u2009Hz for the studied trees when in leaf (with foliage). The presence of leaves increased RT20 at high frequencies, typically by 0.08u2009s at 4000u2009Hz. It was also demonstrated that the source-receiver angle can affect the characteristics of decay curves significantly. With increasing source-receiver distance within 40u2009m, RT20 was slightly changed. It was shown that ground condition and receiver height affect the decay curves, especially at low and mid frequencies, where sound scattering is of relatively limited importance.

Acoustic characteristics of outdoor spaces in an apartment complex

Many apartment complexes in Korea feature underground car parks releasing more of the landscape for residents leisure, rest, or conversation. The acoustic characteristics of these outdoor spaces can therefore make a significant contribution to the overall quality of the environment. This experimental study investigated the acoustic characteristics of outdoor spaces surrounded by multi-storey apartment buildings. In-situ measurements in three positions were carried out to evaluate the acoustic parameters, including reverberation time (RT), early decay time (EDT), rapid speech transmission index (RASTI) and sound pressure level (SPL) distribution. The results show that RTwas generally rather long, over 4 sec at 500 Hz. On the other hand, RTat 125 Hz and 250 Hz was relatively short, about 0 to 3 sec. Above 500 Hz, RT increased with increasing source-receiver distance. EDT was longer than RT over a certain source-receiver distance at about 40 m. In terms of sound distribution, measured SPL was up to 8 dB higher compared to the semi-free field situation, indicating the effects of multiple reflections.

Characteristics of Sound Reduction Index through Small Sized Lightweight Panel

Recently, framed structure is increasingly being used as apartment structure due to the advantages during remodeling. Therefore, the use of lightweight panel as separating wall is increasing. To construct lightweight panel structures with sound insulation performance appropriate to the conditions of each field, measurement of sound reduction index(SRI) through panel structures should be performed. In this study, measurement of SRI through 46 kinds of panel structures was performed in the condition of various factors such as surface density, air space and absorber. The result showed that SRI of panel structures was generally higher by increasing of surface density. In the case of double panel with no absorber, SRI at below critical frequency was gradually increased according to rise of air space. Double panel with absorber make remarkable improvement in SRI at low frequency, but there is a little difference compared with SRI of double panel with no absorber over critical frequency.

Characteristics of Acoustic Indicators Evaluating Speech Intelligibility in Korean Elementary School Classrooms

ABSTRACT This study was carried out to examine characteristics of various acoustic indicators evaluating speech intelligibility such as reverberation time(T 30 ), D 50 , C 50 and speech transmission index(STI) in Korean elementary school classrooms. Results showed that mean T 30 at middle frequencies(500Hz to 2000Hz) measured in 9 classrooms was about 0.75s, which exceeds a regulation specified on American National Standards(ANSI); 0.60s. Mean D 50 , C 50 and STI were 60% to 66%, +2dB to +3dB, and 0.65, respectively. The maximum difference in D 50 and C 50 according to different receiver points in a classroom was 13% and 2.5dB, while the maximum difference in T 30 was 0.03s. Whereas STI measured in classrooms has relatively low correlation with other indicators, correlation between D 50 and C 50 was high, R 2 =.9964. In addition, T 30 and C 50 were fitted well as logarithmic regression curve with R 2 =.9610. It was +3.73dB in C 50 and 68% in D 50 which are the value corre-sponding to 0.60 s in T

In-situ characterization of hedges with a parametric acoustic transducer

This work reports on the results of outdoor measurements which were carried out using a highly directional parametric acoustic transducer and a 2-D array of microphones. The purpose of these measurements was to determine the frequency and angular dependence of the acoustic transmission loss of hedges (hedgerows). The experimental setup and procedure used in this work enabled us to simulate an approximately plane wave propagation regime and to reduce considerably the effect of ground on the recorded transmission loss data. The results show that a 1.5-2.5m thick hedge can provide a considerable (up to 20 dB) transmission loss which is comparable to that expected from an artificial noise barrier structure. The theory developed by Aylor (JASA 51(1), 197-205, 1972) is used to explain the observed dependencies as a function of the leaf density, size and hedge thickness. An alternative equivalent fluid theory for porous absorber (Horoshenkov et al, JASA 104(3), 1198-1209, 1998) is also used to explain the observ...