Acoustic Bulletin the place for the latest news on indoor acoustic environment

Are you going to Internoise 2013 in Austria?


Starting on Sunday the 15-18th September, INTER-NOISE 2013, the 42nd International Congress and Exposition on Noise Control Engineering, will be held at the International Congress Centre in Innsbruck, Austria. The theme of the congress is Noise Control for Quality of Life and it is sponsored by the International Institute of Noise Control Engineering (I-INCE), and is being organized by the Austrian Noise Abatement Association (Österreichischer Arbeitsring für Lärmbekämpfung) (ÖAL).

Ecophon will participate in several sessions (more info below) and we hope to see you there and look forward to more room acoustic discussions!

On Tuesday in the Educational Settings session Jonas Christensson will present “Speech Intelligibility in Swedish Forests an Example of Good Classroom Acoustics”.
For thousands of years we have developed our hearing in an outdoor environment full of natural sounds, as babbling brooks, wind from trees, bird songs and human voices. The problem is that students and teachers spend a major part of their time indoors, in a sound environment with very few natural sounds. The effect is problem for students to understand what the teacher is saying and voice problems for teachers. It is important that teaching places provide good speech intelligibility for listeners and good speech comfort for speakers. Being able to listen without effort is important for good learning and we know that incorrect room acoustics is a burden that impedes learning. An interesting teaching place is the Swedish forests, where we can talk to each other over long distances without having to raise our voice. I have made several listening tests in the forest and also measured the forest “room acoustics”.
In the Classroom Acoustics session Colin Campbell will present “Classroom acoustic research findings on speech behaviour of teachers and students”.
Looking at three extensive acoustic field measurement investigations carried out over the last 15 years, we can see that with improved room acoustic treatment the speech and activity sound levels in classrooms are reduced much more than would be theoretically expected. It is interesting and vital to understand how these benefits affect the core teaching and learning processes and how we in turn need to look beyond single number room evaluations and rather focus on how we can have a better interpretation of the complete room acoustic responses. Looking at the subjective speech behaviour in connection with sound level measurements and the corresponding questionnaires and post occupancy evaluations we can understand more about the vocal load, sound levels and listening conditions in different classroom acoustic conditions.
Also in the Classroom Acoustics session, Erling Nilsson will present “Calculations and measurements of Reverberation Time, sound strength, clarity, in classrooms with absorbing ceilings”.
The acoustic evaluation of classrooms is very much focused on the reverberation time as the main room acoustic parameter. Although room acoustic research since many years noticed its shortcomings and also presented several more relevant descriptors, very little of this knowledge have been used in practice. In many ordinary rooms like classrooms, the typical acoustic solution is a suspended absorbing ceiling. The non-uniform distribution of the absorbing material leads to a non-diffuse sound decay and to a low correlation between reverberation time and parameters related to sound strength and speech clarity. Measurement of reverberation time T20, sound strength G, and speech clarity C50 has been carried out in 14 classrooms. Two different ceiling absorbers have been tested in each classroom, making a total of 28 configurations. Measured results are compared with estimations based on classical diffuse field assumptions and formulas taking non-diffusivity into account. It is concluded that in typical classrooms where the main absorption is situated in the ceiling there will be an improvement in the correspondence between measurements and calculations if the degeneration of the diffusivity during the sound decay is taken into account.
In another Room Acoustics session Yoan Le Muet will present “Thermally activated cooling technology (TABS) and high acoustic demand: Acoustic and thermal results from field measurements”.
New office buildings use thermal capacity of the structure mass to provide thermal comfort. This technique provides stable thermal conditions and is perceived to be a long-term energy efficient solution. This kind of technique is not compatible with traditional suspended ceilings, covering a room from wall to wall. This is due to the fact that the ceiling, positioned between the soffit and the users, would then be a mask for radiation and would stop convection . How then can we quantify their acoustic and thermal impact? In order to investigate the subject we performed dynamic measurements in the summer period of June to August 2012 in the Woopa building located in Lyon, France. The aim of this research was to quantify the reduction of the cooling capacity due to a glass wool suspended ceiling by measuring the temp erature increase in the room. The purpose of this paper is to show the acoustic and thermal tests that have been conducted, the set-up used, the measurement methods, as well as to present examples of projects and give data to encourage dialogue and coordination between the acoustician and other building engineering disciplines.
Finally in the Prediction Methods for Buildings and Room Acoustics, Gerd Marbjerg working on a joint PhD with Saint-Gobain Ecophon and the Technical University of Denmark (DTU) presented “Development of a pressure based room acoustic model using impedance descriptions of surfaces”.
If a simulation tool is to be used for the optimization of absorbent ceilings, it is important that the simulation tool includes a good description of the surface. This study therefore aims at developing a model which can describe surfaces by their impedance values and not just by their statistical absorption coefficient, thus retaining the phase and the angle dependence. The approach of the proposed model will be to calculate the pressure impulse response using a combination of the image source method and acoustic radiosity. The image source method will account for the specular reflections and acoustic radiosity will account for the diffuse reflections. This paper presents the motivation for the new model in the form of results in literature, which show the importance of retaining the angle dependence and phase information in reflections along with simple examples of angle dependent reflection from a porous absorber.

Acoustics miscellaneous 220

Related Blog Posts