Erling Nilsson

Decay processes in rooms with non-diffuse sound fields Part I: Ceiling treatment with absorbing material

The decay process in rooms with non-diffuse sound fields was the subject of this investigation. A rectangular room with high absorption at the ceiling and low absorption at the walls and floor constituted the basic configuration for the study. Several alterations of the room were carried out, including changes of room dimensions and the type of ceiling absorber, also additional treatment with absorbent material. The effects of these alterations on the decay curves were analysed. In order to predict the gross features of the decay curves, a two-system Statistical Energy Analysis model was developed. The sound field was subdivided into a grazing and nongrazing part. The grazing part comprised modes with propagation direction almost parallel to the ‘principal’ surface (generally the absorbent ceiling). The nongrazing part comprised the oblique modes, of importance for the decay process. The angle dependent absorbent properties of the principal surface were taken into account when subdividing the sound field into a grazing and nongrazing part. Measured and calculated decay curves for different room configurations were compared.

Decay processes in rooms with non-diffuse sound fields Part II: Effect of irregularities

The effect of sound scattering objects in a rectangular room with high absorption at the ceiling and low absorption at the walls and floor was investigated. In Part I of this paper a two-system Statistical Energy Analysis (SEA) model was developed in order to predict the gross features of the decay process. The sound field is subdivided into a grazing and nongrazing part. The main effect of introducing irregularities is to divert some of the energy in the grazing group into the nongrazing group. The energy transfer between the groups is taken into account by introducing a coupling loss factor. In order to quantify the effect of scattering objects and other irregularities, a measure called equivalent scattering area is introduced. The model demonstrates how the equivalent scattering area can be determined from measurements.

Room acoustical measures for open plan spaces

In an ongoing Nordic cooperation project the acoustical conditions in open‐plan spaces are investigated. Of special interest is to find suitable acoustical parameters that reveal the acoustical conditions in these spaces and also are of importance for the subjective perceived acoustics. Measurements have so far been carried out in five open plan offices accompanied with an inquiry gathering the subjective judgments by the staff. A program for the acoustical measurements was designed specifying how to perform the measurements, which type of parameters to measure and how to report the results. The acoustical parameters included in the measurements are Reverberation time T20, Early Decay Time (EDT), Deutlichkeit (D50), Speech transmission index (STI), Speech intelligibility index (SII), Privacy Index (PI), Rate of spatial decay of sound pressure levels per distance doubling (DL2), Excess of sound pressure level with respect to a reference curve (DLf), background noise levels in occupied and unoccupied office...

On subjective impact sound insulation classes

The possibility to divide impact sound annoyance into classes is investigated. The experiments, based on human perception, are done in a laboratory environment where various floor structures have been included to produce impact noise. These tests are correlated to studies pertained to real‐life situations for tenants. The statistical tool to test the significant differences between the classes is Rou–Kupper. Real footsteps are used as a noise source. In addition, airborne sound insulation is treated in a similar manner, whereby one may conclude that there are some difficulties finding classes with statistical significant differences. [Work supported by the Swedish Council of Building Research.]

Speakers comfort and voice use in different environments and babble-noise. What are the effects on effort and cognition?

Teachers often report voice problems related to the occupational environment, and voice problems are more prevalent in teaching than in other occupations. Relationships between objectively measurable acoustical parameters and voice use have been shown. Speakers have been shown to be able to predict the speaker-comfort of an environment. Teachers with voice problems use the room differently than their voice-healthy controls. The aim of this study was to investigate what vocal changes speakers do in different acoustical environments and noise conditions. Nine female speakers, voice patients, and voice-healthy were exposed to four controlled, acoustical “environments” mounted in the same room: 1. stripped; 2. wall- and ceiling mounted absorbents; 3-4 as 2 but with extra ceiling absorbents and in two positions. The speakers were recorded with voice-accumulator and simultaneous voice recordings and spoke freely for 3-5 min in three noise conditions in each setting: silence, classroom noise (60 dBA), and day-ca...

The effect of different acoustical treatment in a classroom

A common room acoustic measure in classrooms and other common public spaces is a suspended sound absorbing ceiling. However, the acoustical condition in the classroom not only depends on the suspended ceiling. The size and shape of the room as well as the properties of building material and the interior fittings and furniture will also affect the room acoustical conditions. Another circumstance is the non-fulfillment of the conditions for the classic diffuse field theory in rooms with absorbent ceiling treatment due to the non-uniform distribution of the absorbing material. This makes the calculation of room acoustic parameters more complex. This paper addresses the effect of different factors that are of importance for the acoustical conditions in a classroom. Outgoing from the unfurnished classroom without suspended ceiling the effect of introducing a suspended ceiling, adding furniture, adding wall panels, as well as extra low frequency absorption will be exemplified based on measurements in a full sca...

Acoustic Design for Open Plan Spaces

In an ongoing Nordic cooperation project (Nordic Innovation Center ‐ Sound Design of Open‐Plan Offices) the acoustical conditions in open‐plan spaces are investigated (see also the adjacent paper Room Acoustical Measures for Open Plan Spaces). The projects starting point is that acoustic qualities in terms of communication, orientation, comfort and privacy are crucial for open‐plan spaces. Therefore, beside acoustic parameters, the aim is to develop methodologies in order to measure and specify such qualities. Beside site analyses, one major methodological tool concerns the development of a questionnaire, intended to be utilized as a compliment to acoustic measurements, and thereby function as a tool for design measures of large open‐plan offices. Its purpose is to aid acousticians as well as architects and designers to identify different types of acoustic design criteria. The questionnaire covers not only the perception of the sound environment, but also psychosocial criteria, architectural design and t...

Evaluation of Drum Sound with ISO Tapping Machine

A branch norm, EPLF NORM 021029-3,1 has been established for measuring drum sound on laminate floor coverings. ‘Drum sound’ refers to the sound occurring when an object, e.g. a foot, strikes the flooring in the room in which the receiving ear is located. The norm evaluates the subjective perception of the drum sounds loudness using the ISO tapping machine. A round-robin study of the norm is reported along with the results of a paired comparison listening test using the same floor coverings. The article discusses general aspects of evaluation measures, tapping machines, test environments, etc., that need to be considered when measuring drum sound on various floor coverings, such as linoleum, wood parquet and laminate. It is concluded that loudness as measured according to ISO 532B correlates the best with the subjective perception of the drum sounds loudness. The tapping machine can be used to excite hard floor coverings to produce the drum sound, but should be used with caution in studying low-level drum sounds due to the tapping machines inherent mechanical noise.

A closed formulation of sound fields in front of periodical absorbents

Periodic resonant absorbers are known to give excessive back scattering for frequencies above a limit which is governed by the geometric proportions of the periodicity. One way to model this phenomenon is to transform the geometry into the wave number domain and solve the corresponding equation with respect to the pressure field. A drawback is that the equation matrix consists of an infinite (but relatively fast converging) set of harmonic components and therefore has to be truncated in order to be solved. However, it is possible to make use of the Poisson sum formula and obtain a closed formulation which can be solved in the wave domain without truncation. Furthermore, it is possible to transform the exact solution back to the spatial domain. This will yield an infinite series consisting of components which can be designated a physical interpretation. These components, i.e., partial pressures related to corresponding geometry, which constitute an exact solution, can then be truncated in a controlled and ...

A simple device for flow resistance measurements

A simple device for static measurements of flow resistance on thin porous materials is developed and evaluated. The device consists of a duct with a piston which is driven at a steady low speed. This generates a flow of air with constant volume velocity. The duct ends with a cavity with an interface to the outside where the sample is mounted. The differential pressure between the cavity and the outside is measured. In order to prevent nonlinear effects, the speed of the piston is kept so low that the constant velocity of the air is of the same order of magnitude at the sample as the rms velocity of sound waves at approximately 100 dB SPL. The device is so constructed that it is possible to measure samples of standard dimensions, e.g., cloth mounted at different perforated frames, if the speed of the moving piston is accordingly adjusted to match the open area. The performance of the device is tested and discussed.