scholarly journals Sound absorption of acoustical draperies used to provide variable reverberation time in concert halls

1980 ◽  
Vol 67 (S1) ◽  
pp. S83-S83
Author(s):  
Theodore J. Schultz
Keyword(s):  
Sound Absorption ◽  
Reverberation Time ◽  
Concert Halls

scholarly journals A Revised Sound Energy Theory Based on a New Formula for the Reverberation Radius in Rooms with Non-Diffuse Sound Field

2015 ◽  
Vol 40 (1) ◽  
pp. 33-40 ◽  
Author(s):  
Higini Arau-Puchades ◽  
Umberto Berardi
Keyword(s):  
Sound Absorption ◽  
Sound Field ◽  
Critical Distance ◽  
Sound Level ◽  
Reverberation Time ◽  
Sound Energy ◽  
Sound Fields ◽  
Energy Theory ◽  
New Interpretation ◽  
New Formula

Abstract This paper discusses the concept of the reverberation radius, also known as critical distance, in rooms with non-uniformly distributed sound absorption. The reverberation radius is the distance from a sound source at which the direct sound level equals the reflected sound level. The currently used formulas to calculate the reverberation radius have been derived by the classic theories of Sabine or Eyring. However, these theories are only valid in perfectly diffused sound fields; thus, only when the energy density is constant throughout a room. Nevertheless, the generally used formulas for the reverberation radius have been used in any circumstance. Starting from theories for determining the reverberation time in non- diffuse sound fields, this paper firstly proposes a new formula to calculate the reverberation radius in rooms with non-uniformly distributed sound absorption. Then, a comparison between the classic formulas and the new one is performed in some rectangular rooms with non-uniformly distributed sound absorption. Finally, this paper introduces a new interpretation of the reverberation radius in non-diffuse sound fields. According to this interpretation, the time corresponding to the sound to travel a reverberation radius should be assumed as the lower limit of integration of the diffuse sound energy

scholarly journals EFFECT OF A RESONANT SUSPENDED CEILING ON THE ACOUSTIC PROPERTIES OF A HALL/REZONANSINIŲ KABAMŲJŲ LUBŲ ĮTAKA SALĖS AKUSTINIAMS RODIKLIAMS

1996 ◽  
Vol 2 (7) ◽  
pp. 64-69
Author(s):  
Vytautas Stauskis
Keyword(s):  
Sound Source ◽  
Sound Absorption ◽  
Acoustic Properties ◽  
Subjective Perception ◽  
Technical Equipment ◽  
Analog To Digital Converter ◽  
Digital Converter ◽  
Reverberation Time ◽  
Analog To Digital ◽  
Hard Surface

The article covers the experimental research into basic acoustic properties of a hall using a new type resonant suspended ceiling with large area cross-shaped apertures between surfaces. The research was carried out at a physical simulator of a hall. Geometric parameters, frequency range of the simulator and availability of technical equipment were taken into consideration while selecting the scale of the simulator. A recording hall of the Lithuanian radio and TV's Grand Symphonic Orchestra was chosen for the purposes of research. The dimensions of the hall are 34×22×12.7 m. The scale of a simulator for such a large hall was established as 1:25. All the wall and floor surfaces of the simulator are made of textolite. Its coefficient of sound absorption at 10 kHz is equal to 0.15. The suspended ceiling is made of 6 mm thick plywood whereof all the contours had been lacquered 3 times. The orchestra's raised platform of 116 m2 floorspace was covered with 5–6 mm thick flannel which has coefficient of absorption of about 0.5–0.6. In this case the absorption of sound in the air and characteristics of materials are of no importance, as all the research results are relative. A block diagram was used for recording of sound signals at the simulator which diagram comprised a sound source, microphone, microphone's amplifier and analog-to-digital converter. A spark impulse was used as a sound source which impulse was formed by our made spark generator with preset necessary technical parameters. The research was carried out using a 1/4” microphone. An analog-to-digital converter had been manufactured according to preset characteristics. It was designed for changing analog signals into digital form for their further processing. The number of input channels can be set up from 1 through 8. The nominal level of the input signal is ± 1 V. The converter's discrimination is equal to 12 bits. Time of conversion is 2 μs. The quantization time is equal to 5 μs, whereas the quantization frequency is 200 kHz. The experimental simulator of a hall allows to determine the dependence of basic acoustic characteristics on the form of the apertures in the suspended ceiling, their surface, distance to the hard surface, absorbing material used in side and end walls and over the suspended ceiling, as well as on the distance from the source to the microphone. The research covered by this article determines the effect produced upon the acoustic coefficient by the distance between the suspended ceiling and the hard surface while the area of the cross-shaped aperture is not changed. During the research a measurement point was chosen near the sound source. The influence of the height of the suspended resonant ceiling upon the reverberation time is expressed only up to 160 Hz, however, a more expressive dependence has not been noticed. The decrease in the reverberation time at this range reaches 0.4–0.6 s. At frequencies of 200 and 250 Hz an expressly noticeable resonance is formed at which resonance the reverberation time is reduced even by 1.1 s., which is a large figure. Under further increase in the frequency the decrease is stable and reaches about 0.4 s. Such a decrease in the reverberation time with the expressive resonance at 200–250 Hz is dependent only on the crossshaped apertures in the suspended ceiling. This indicates that they have effect on the hall's acoustics. The decrease in the early reverberation time is most expressive at very low frequency up to 100 Hz and it reaches even 1–7 s. Resonance occurs again at 200 Hz, at which resonance the reverberation is decreased by up to 2.5 s and is not dependent on the height of the suspended ceiling. The early damping period of the sound field is basically dependent on the early sound reflections. They are of crucial importance while forming the subjective perception of a sound. The coefficient of the sound absorption depends on the height of the suspended ceiling and it is higher when the height of the ceiling is reduced. In all cases this coefficient has a resonant importance at 200–250 Hz. The coefficients of the absolute absorption are reduced because there is an increased reverberation time of the entire hall and surface area. The sound absorption is expressly increased only when the distance between the height of the suspended ceiling and the hard surface is 100 cm. At resonant frequencies of 200 and 250 Hz it is equal to 60 m2. The fidelity index of music is changeable from −14 dB at lower frequencies up to 0 dB at higher frequencies. The increase in the height of the suspended ceiling begins to have effect only from 200 Hz.

Effect of orchestra absorption on the reverberation time in concert halls

2017 ◽  
Vol 141 (5) ◽  
pp. 3599-3599
Author(s):  
Sung Min Kim ◽  
Hyung Suk Jang ◽  
Jin Yong Jeon
Keyword(s):  
Reverberation Time ◽  
Concert Halls

scholarly journals The influence of the distribution of sound absorbing materials on the estimation of reverberation time in rooms

2018 ◽  
Vol 49 ◽  
pp. 00078
Author(s):  
Marcelina Olechowska ◽  
Artur Nowoświat ◽  
Jan Ślusarek ◽  
Mateusz Latawiec
Keyword(s):  
Absorption Coefficient ◽  
Acoustic Field ◽  
Sound Absorption ◽  
Sound Field ◽  
Reverberation Time ◽  
Type D ◽  
Absorbing Materials ◽  
Absorbing Material ◽  
Different Dimensions ◽  
Materials Used

Reverberation time in rooms depends on many factors, e.g. cubature, surface of envelopes, sound absorption coefficient of materials used for the construction of the envelopes, geometry of rooms or the distribution of sound absorbing materials. The arrangement of sound absorbing materials in rooms has an impact on the dispersion of acoustic field, yet theoretical calculation models do not take into account this impact. According to these models, regardless of the arrangement of sound absorbing materials, the reverberation time in a room will remain unchanged. The present paper investigates the above problem by means of computer simulations. For the needs of the simulation, three rooms with different dimensions were adopted, i.e. type 'p' - a cuboidal room with a square base, type 'd' - a cuboidal room (with one side of the 'p' room lengthened), type 'w' - a cuboidal room (with the height of the room lengthened 'p'). During the simulation, the way of acoustic field dispersion was being changed and its influence on the reverberation time in the rooms was being determined. The authors investigated two situations. The first one involved a non-dampened room, in which the sound absorbing material was being arranged differently. The second one involved a welldampened room, and the dispersion of sound field was analyzed depending on the location of the reflecting material.

Measurement of sound absorption coefficient in a reverberant room using probability density function of damping constant

2021 ◽  
Vol 263 (4) ◽  
pp. 2940-2948
Author(s):  
Kosuke Goto ◽  
Takehiko Nakagawa ◽  
Yoshinari Yamada
Keyword(s):  
Probability Density Function ◽  
Absorption Coefficient ◽  
Spatial Variability ◽  
Measurement Method ◽  
Sound Absorption ◽  
Measurement Accuracy ◽  
Sound Absorption Coefficient ◽  
Reverberation Time ◽  
Low Frequencies ◽  
Sinusoidal Input

The measurement method of the sound absorption coefficient in a reverberation room is standardized in ISO 354. However, the measurement accuracy often deteriorates at low frequencies. This paper proposes a method that improves the measurement accuracy of the sound absorption coefficient at low frequencies. It calculates the sound absorption coefficient using reverberation time (RT) that is derived from the distribution of a damping constant for a sinusoidal input. The measured values by the proposed method were compared with those by the ISO 354 method. As a result, the proposed method reduces the spatial variability of RT and gives a better agreement with the statistical absorption coefficient that is calculated by a transfer matrix model at low frequencies.

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