Z. Maekawa

Noise reduction by screens

Abstract This paper presents experimental data on the diffraction of sound round a semi-infinite plane screen in a free field and describes a method for calculating the shielding effect of a real screen employed for the purpose of noise reduction, with the assistance of a single graph and without the aid of a computer.

Noise control by barriers—Part 2: Noise reduction by an absorptive barrier☆

This paper presents a method of estimating the excess attenuation of a noise by an absorptive barrier covered with sound-absorbing materials. The approximate theory of diffraction by the absorptive barrier is derived from rigorous theory for a hard barrier. A single chart, which may be very convenient for the rapid estimation of the effect of absorption (the increase of the excess attenuation caused by the absorbing treatment of the barrier) in the practice of noise control, is presented. The validity of the method developed in this paper is confirmed by comparing estimated with measured values.

Noise reduction by distance from sources of various shapes

Abstract This paper presents a review of the geometrical method for calculating the sound level distribution caused by noise sources of various shapes, i.e. a point source, a line source, and a plane source. It is useful for practical noise control in the incoherent sound fields.

Noise control by barriers—Part 1: Noise reduction by a thick barrier

Abstract This paper presents a method of estimating the excess attenuation of noise by a thick barrier. In this method, the excess attenuation of noise by a thick barrier is assumed to be composed of two parts, one being the effect of a virtual thin barrier with the same height and the other the effect of thickness. A single chart for estimating this thickness effect is offered under conditions which only permit an error of a few decibels. The validity of the method presented here is verified by comparing the estimated with the measured values. Consequently, this method may be useful for the purpose of estimating the excess attenuation of a band of noise by the barrier whose thickness is larger than half a wavelength.

Interpretation of long term data measured continuously on long range sound propagation over sea surfaces

Abstract In order to obtain the data for environmental impact assessment of a new planned airport on an artificial offshore island, long term (14 months) continuous measurement of long range (5 km) sound propagation over a sea surface was carried out with the MLS correlation method. The measured noise reduction data were analyzed statistically to explore any relationships with meteorological conditions observed simultaneously. Although clear results could not be found between these relationships, useful statistical data of excess attenuation for propagation of estimated aircraft noise was obtained.

Long time measurement of long range sound propagation over an ocean surface

Abstract In order to obtain data for environmental impact assessment of noise from an airport under development, an MLS test-signal was emitted from a fixed point at the site on the sea and received on the seacoast about 5 km from the source. The measuring system was operated automatically, and the measurements were carried out at every hour and continued for 14 months. The MLS correlation method was applied in order not to annoy the people near the site, since the method succeeded in sound propagation measurements with signal levels lower than the background noise level. During the measurements, some meteorological conditions were also observed simultaneously.

A simple chart for the estimation of the attenuation by a wedge diffraction

Abstract A simple method of estimating the effect of wedge angle on the sound attenuation achieved by diffraction with a wedge is described. The effect is defined as the difference between the attenuation brought about by the wedge and that due to a virtual thin barrier with the same Fresnel number, related to the source-receiver geometry. A single, reasonably accurate chart is derived from the exact solution by means of parametric studies, carried out with the aid of a computer under restricted conditions.

Analysis of the structure-borne sound in an existing building by the SEA method

Abstract By using the SEA method, the characteristics of structure-borne sound propagation in an existing building are analyzed. The calculated results of the sound-pressure level in the room are compared with measured values. An analytical model that simplifies the building is a group of rectangular rooms. For a certain type of building, the structure-borne sound propagation may be obtained by the use of a reduced two-dimensional model. It is found that the sound-pressure level in each room shows a linear attenuation with a room-location factor that is defined by the number of unit rectangular rooms and the regression coefficient relating to room dimensions. In this calculation, effects of the main structural wall and the blocking mass at each junction are taken into consideration.

Preference test of seven European concert halls

Preference tests of seven European concert halls using musical motifs recorded through a dummy head were performed. Test signals were reproduced binaurally. Eighty‐eight students served as subjects. The results show that (1) there was no significant difference between preference scores for these halls when averaged over all subjects, and (2) subjects could be divided into several groups with respect to preference. In conclusion, even though each subject was free to prefer hall A to hall B, the acoustical quality of a certain hall could not be solely evaluated using the preference score. [Work supported, in part, by The Kajima Foundation.]

A design principle for the sound reinforcement system of an open‐field stage

If loudspeakers radiate sound from images which lie behind the imaginary walls of an open‐field auditorium, the audience can hear sounds in a simulated indoor auditorium. This principle was applied to an open‐field stage in Hyogo Prefecture, Japan. In order to supply simulated reflections over all of the audience seats, four positions for the loudspeakers were selected, two on each side of the stage symmetrically. Two poles 18 m in height were built close to the stage, and two other 12 m high poles were kept at some distance from the stage. Two loudspeakers were installed at each position, one for the seats near the stage, and the other for the more distant seats so that everyone in the audience would be able to receive at least one simulated reflection within a suitable delay‐time after arrival of the direct sound from the stage. In order to arrange delay‐time for each loudspeaker, four channels of digital delay‐machines were used. The suitable delay‐times were determined by psychoacoustical experiments ...