This paper proposes a new approach for calculating the impulse response of room acoustics. Impulse response provides unique characterization of any discrete lineartime invariant (LTI) systems. We assume that the room is a linear time-invariant system and the impulse response is calculated simply by sending a Dirac Impulse into the system as input and getting the response from the output. Then, the output of the system is represented as a sum of time-shifted weighted impulse responses. Both mathematical justifications for the proposed method and results from simulation software developed to evaluate the proposed approach are presented in detail.
In recent years we have interviewed members of the audience after musical performances and asked them to evaluate the acoustics of the concert halls. A group of ‘music lovers’ (with a high level of musical training and experience) and ‘acousticians’ (with a wide knowledge of the physical characteristics of sound transmission) also attended each performance and answered the same questions as the general public. This group thereby served as a control group when evaluating surveys of the general public. In this paper, the results obtained when analyzing these control group surveys are presented. This analysis shows that a common vocabulary exists between music lovers and acousticians when rating a hall, although the grouping of the questions for each factor depends on the training of the respondents.
The purpose of the study was to compare auditory judgments of sound clarity of music examples recorded in a concert hall with predictions of clarity made from the impulse response signal recorded in the same hall. Auditory judgments were made with the use of two methods: by rating sound clarity on a numerical scale with two endpoints, and by absolute magnitude estimation. Results obtained by both methods were then compared against the values of clarity indices, C80 and C50, determined from the impulse response of the concert hall, measured in places in which the microphone was located during recording of music examples. Results show that auditory judgments of sound clarity and predictions made from the C80 index yield a similar rank order of data, but the relation between the C80 scale and perceived sound clarity is nonlinear. The data also show that the values of C80 and C50 indices are in very close agreement.
Acoustic parameters were analysed in nine auditoria and multi-purpose conference rooms in the University of Extremadura. Parameters related to the reverberation time, background noise, and intelligibility (both physical measurements of different parameters [Definition (D-50) and STI] and speech tests used to study the subjective response of listeners) were studied. The measurements were compared with some recommendations from the literature and, considering that speech was the main use of the studied rooms, with the intelligibility results. Some different recommendations for reverberation times taken from the literature were analysed. The intelligibility results obtained from the measurements were also compared with the intelligibility results that were determined by the speech tests.
Blank handgun shots, party balloon bursts, and a pneumatic compressor with a small-diameter nozzle were used as sources of sound in the assessments of reverberation time, T. The two first sources were of impulse type, while the third one resembled a noise signal source. In this work, 532 values of T were experimentally obtained in four rooms of different volumes and compared. The T values for 1/3 octave frequency bands were found to be independent of the sound source. Reverberation times for the A-frequency-weighting filtered signals were close to one another for the shots and balloon bursts, while those obtained using the compressor nozzle were significantly shorter. The latter effect can be attributed to the relatively high share of high frequency waves in the sound generated by the nozzle. The results show that balloon bursts can be used as handgun shot substitutes in the assessments of reverberation times. While the nozzle noise is rather unsuitable for this purpose, it can be applied in the assessments of T for high frequency waves, up to the ultrasound range. Such acoustic climate information may be useful in designing spaces for high frequency sound-sensitive individuals, e.g. animal shelters.
Reflecting structures placed over the stage in auditoria and concert halls should provide sound reflection in a way that enhances sound emission from the stage without causing acoustic defects in the interior. Model studies conducted by the authors were used to determine the relative level of sound reflection by reflecting structures as a function of frequency for a number of geometric configurations and materials. Analysis of the results allowed drawing conclusions about the effect of modifications of the ceiling over the reflecting panels on the quality of the sound reflected from them. It was shown that modification of the ceiling over the reflecting panels by employing highly sound absorbing materials significantly improved the characteristics of the reflected sound. Also, certain configurations of elements located in the space under the ceiling should be avoided, as the experiments indicated the occurrence of adverse acoustic effects.
Large venues and auditoriums are commonly associated with their astounding architecture. Their acoustic quality is an essential factor in its qualification as a great and functional, or a badly designed place. However, acoustics is often overlooked during the design stage of a building due to the complexity and high cost of the measurements involved. For this reason, it is important to explore more accessible ways to implement acoustics evaluations. The aim of this work is to compare typical experimental measuring methods and the use of mobile devices to assess the acoustic quality of a room. These measurements are contrasted with the software simulation of the same acoustical space. The results show that the mobile system can be used for professional measurements with low restrictions in the frequency range of interest of this study (90 Hz to 4000 Hz).
This paper presents the results of measurements of the sound absorption coefficient of auditorium seats carried out in the laboratory using two methods. In the first one, small blocks of seats in various arrangements were studied in a reverberation chamber to determine the absorption coefficient of an auditorium of infinite dimensions. The results were compared to the values of the absorption coefficient measured using the second method, which involved samples enclosed within a frame screening the side surfaces of other auditorium blocks. The results of both methods allowed for the assessment of the sound absorption coefficient of an auditorium of any dimensions while taking into account the sound absorption by the side surfaces. The method developed by the authors will simplify the currently known measurement procedures.
The church of Santa Ana in Moratalaz, Madrid, Spain (1965-1971), is an emblematic work of the architect Miguel Fisac. In his long career include interventions in the religious field, constituting one of the most important contributions to Spanish religious architecture of the last century. This church is a singular place of worship and architecturally significant, in which the acoustics played an important role in the configuration of the spatiality of the church. This paper studies the acoustic behaviour of the church and its relationship with its unique structural, spatial and coating material characteristics. The analysis of the current acoustic conditions, with high reverberation times (up to 6 seconds) and poor intelligibility on the audience, serve as the basis for making an acoustic rehabilitation proposal that contributes to improving the sound conditions of the building for the intended use, without distorting the spatial, formal and material aspects with which the architect conceived the project.
Several authors have proposed indices to synthesize the acoustics of a space, especially of concert halls. Meanwhile, a few studies have focused on the acoustics of worship spaces. The peculiarities of these last ones have shown distinctive characteristics. The increasing interest for the acoustics of worship spaces justifies the formulation of indices to synthesize the results of acoustic studies in these buildings too. This paper proposes a double synthetic index to evaluate the acoustics of a church. The index is obtained combining the average values of seven parameters generally considered in studies of architectural acoustics. The differences between requirements for music and speech in churches suggest to consider different optimal values of the selected parameters for different kinds of sound. A double synthetic index has been defined to synthesize the acoustical properties related to the music and to the speech separately. The validity of this double index is then assessed, comparing its values with subjective preferences captured through listening tests. The index, which is proposed and validated in this paper, aims to be an instrument to show synthetically the acoustical characteristics of a church to people with low knowledge in acoustics.
Ray tracing simulation of sound field in rooms is a common tool in room acoustic design for predicting impulse response. There are numerous commercial engineering tools utilising ray tracing simulation. A specific problem in the simulation is the modelling of diffuse reflections when contribution of individual surface is prevailing. The paper introduces modelling of scattering which is interesting when the whole impulse response of a room is not a goal but contribution of certain surface. The main goal of the project is to shape directivity characteristics of scattered reflection. Also, an innovative approach is suggested for converting the energy histogram information obtained by ray tracing into an “equivalent impulse response”. The proposed algorithm is tested by comparing the results with measurements in a real sound field, realised in a scaled model where a diffusing surface is hardware-implemented.
Sound and vibrations are often perceived via the auditory and tactile senses simultaneously, e.g., in a car or train. During a rock concert, the body vibrates with the rhythm of the music. Even in a concert hall or a church, sound can excite vibrations in the ground or seats. These vibrations might not be perceived separately because they integrate with the other sensory modalities into one multi-modal perception.
This paper discusses the relation between sound and vibration for frequencies up to 1 kHz in an opera house and a church. Therefore, the transfer function between sound pressure and acceleration was measured at different exemplary listening positions. A dodecahedron loudspeaker on the stage was used as a sound source. Accelerometers on the ground, seat and arm rest measured the resulting vibrations. It was found that vibrations were excited over a broad frequency range via airborne sound. The transfer function was measured using various sound pressure levels. Thereby, no dependence on level was found. The acceleration level at the seat corresponds approximately to the sound pressure level and is independent of the receiver position. Stronger differences were measured for vibrations on the ground.
Reverberant responses are widely used to characterize acoustic properties of rooms, such as the early decay time (EDT) and the reverberation times T20 and T30. However, in real conditions a sound decay is often deformed by background noise, thus a precise evaluation of decay times from noisy room responses is the main problem. In this paper this issue is examined by means of numerical method where the decay times are estimated from the decay function that has been determined by nonlinear polynomial regression from a pressure envelope obtained via the discrete Hilbert transform. In numerical experiment the room responses were obtained from simulations of a sound decay for two-room coupled system. Calculation results have shown that background noise slightly affects the evaluation of reverberation times T20 and T30 as long as the signal-to-noise ratio (SNR) is not smaller than about 25 and 35 dB, respectively. However, when the SNR is close to about 20 and 30 dB, high overestimation of these times may occur as a result of bending up of the decay curve during the late decay.
49th Winter School on Wave and Quantum Acoustics constituted platforms for sharing the results and achievements obtained in different branches of physical acoustics, as molecular acoustics, quantum acoustics, acousto-optics, magnetoacoustics, photoacoustics, acoustics of solid state, acoustic emission, and others. Moreover, researches in some selected topics related to those mentioned above (e.g. optoelectronics, relaxation processes) were presented during the school.
The conference consisted of the 16th Workshop on Acoustoelectronics and the 16th Workshop on Molecular Acoustics, Relaxation and Calorimetric Methods. However, the organizers are opened to organizing workshops on other subjects in future. We would like to invite scientific centers and other professional groups to cooperate in organizing workshops on the subjects of their interests.
XLVIIIth Winter School on Environmental Acoustics and Vibroacoustics was a forum for all environmental and vibroacoustics fields. Particularly it was concerned with traffic noise, vibroacoustics of machines, room acoustics, building acoustics, noise protection and similar problems. During the Conference, seminars on “Measurement of noise and vibration at the workplace” and Environmental noise monitoring”, combined with measurement workshops, were organised in association with SVANTEK.
The Conferences began with the special, joined session dedicated to celebration of the 15th Jubilee Conference Integrated Optics – Sensors, Sensing Structures and Methods. In summary, 48 people participated in Conferences and seminars, presenting 37 lectures, reports and posters. In this issue one can find abstracts of some lectures and posters, which were presented during the Conferences.
Virtual or active acoustics refers to the generation of a simulated room response by means of electroacoustics and digital signal processing. An artificial room response may include sound reflections and reverberation as well as other acoustic features mimicking the actual room. They will cause the listener to have an impression of being immersed in virtual acoustics of another simulated room that coexists with the actual physical room. Using low-latency broadband multi-channel convolution and carefully measured room data, optimized transducers for rendering of sound fields, and an intuitive touch control user interface, it is possible to achieve a very high perceived quality of active acoustics, with a straightforward adjustability. The electroacoustically coupled room resulting from such optimization does not merely produce an equivalent of a back-door reverberation chamber, but rather a fully functional complete room superimposed on the physical room, yet with highly selectable and adjustable acoustic response. The utility of such active system for music recording and performance is discussed and supported with examples.