Sound Insulation Measurements Research Articles

Evaluating standard airborne sound insulation measures in terms of annoyance, loudness, and audibility ratings

This paper reports the results of an evaluation of the merits of standard airborne sound insulation measures with respect to subjective ratings of the annoyance and loudness of transmitted sounds. Subjects listened to speech and music sounds modified to represent transmission through 20 different walls with sound transmission class (STC) ratings from 34 to 58. A number of variations in the standard measures were also considered. These included variations in the 8-dB rule for the maximum allowed deficiency in the STC measure as well as variations in the standard 32-dB total allowed deficiency. Several spectrum adaptation terms were considered in combination with weighted sound reduction index (R(w)) values as well as modifications to the range of included frequencies in the standard rating contour. A STC measure without an 8-dB rule and an R(w) rating with a new spectrum adaptation term were better predictors of annoyance and loudness ratings of speech sounds. R(w) ratings with one of two modified C(tr) spectrum adaptation terms were better predictors of annoyance and loudness ratings of transmitted music sounds. Although some measures were much better predictors of responses to one type of sound than were the standard STC and R(w) values, no measure was remarkably improved for predicting annoyance and loudness ratings of both music and speech sounds.

Room requirements for laboratory measurement of transmission loss and impact sound insulation.

Laboratory measurement of transmission loss (ASTM E90) and impact sound insulation (ASTM E492) have one thing in common: measurement of the sound power radiated into the receive room by the specimen under test. In E90 the reported quantity, transmission loss (TL), is the difference between the incident and transmitted sound power, whereas for E492 the reported quantity, normalized impact sound pressure level (NISPL), is a direct measure of the radiated sound power of the floor. A derivation of the TL and NISPL equations using a statistical energy analysis (SEA) framework shows that the ASTM equations are based on the assumption of power balance and statistical sampling of the sound field. This SEA framework is used to define the acoustical conditions of the receive room (number of modes in each frequency band, the average loss factor in each band, and hence the modal overlap factor), which are then related to the physical properties such as room shape, volume, absorption, etc. The conditions necessary for...

Measurement uncertainties caused by tapping machines in floor sound insulation tests.

This paper illustrates how the parameters of the tapping machine may influence the measurement accuracy when testing the impact sound insulation of floors. The analysis connects the specifications for tapping machines given in ISO 140‐6 and ASTM E 492‐4 standards with the requirements for repeatability and reproducibility of the sound insulation measurements given in ISO 140‐2. The paper also discusses calibration and testability aspects for tapping machines and presents the method developed at Scantek for measuring the impact velocity of the hammers. The paper gives modeling equations, preliminary calculations for measurement uncertainties, and experimental results obtained at Scantek on calibrating the Norsonic tapping machine N‐211.

Evaluation of the acoustic performance of classrooms in public schools

This paper presents the results of an evaluation of acoustic comfort of classrooms built according to a standard design. Three constructive designs located in the metropolitan area of Curitiba (Brazil) have been evaluated, two schools built under each of these three designs, in a total of six schools. The acoustic quality of the classrooms have been analyzed based on measurements of the reverberation time, sound pressure level inside and outside the classrooms, and sound insulation. Measurements of ambient noise (external and internal) followed the Brazilian Standards NBR 10151 and NBR 10152. Measurement of reverberation time and sound insulation followed the international Standards ISO 140-4, ISO 140-5, ISO 717-1, and ISO 3382. Results (sound insulation and reverberation time) have been compared with reference values found in the Brazilian Standard NBR 1279, and in the Standards ANSI S12.60 and DIN 18041. Results reveal poor acoustical quality of the surveyed classrooms, for all 3 constructive designs studied. The surveyed designs do not meet the guidelines of either the Brazilian Standards or of the International Standards employed as references.

Soundproofing effect of nano particle reinforced polymer composites

In this paper, the effects of soundproofing by polymer and carbon-nanotube (CNT) composites were investigated. The specimens for sound insulation measurement were fabricated with Acrylonitrile Butadiene Styrene (ABS)/CNT composites. Tests showed that sound transmission loss of ABS/CNT 15 vol.% composite was higher by 21.7% (4.1 dB) than that of pure ABS specimen at a frequency of 3400 Hz. It was found that the principal factor influencing the improvement of sound insulations of ABS/CNT composites was increased stiffness by CNT additives. To demonstrate the practical applicability of polymer/CNT composites, tests were conducted for the reduction of operational noise from mechanical relay.

Acoustic and Luminous Performance Evaluations in Classrooms in Curitiba, Brazil

This study deals with a standardized project in public schools in the Brazilian State of Paraná and analyzes acoustic and luminous qualities in classrooms. The acoustic analysis, conducted by measurements of background noise, reverberation time, and sound insulation, reveals the poor acoustic quality of the classrooms. Acoustic simulation results suggest the need for perforated plywood underneath the ceiling to reduce reverberation time and increase the overall acoustic comfort of the classrooms. The luminous performance analysis is based on computational simulations with daylighting programs for different combinations of days, schedules, and solar orientation of the buildings. Results show daylighting levels for various positions of the building. This allows the designer to choose the best way of siting the building with respect to aspects of the locality and the resulting quality of the indoor space. Finally, shading elements are designed for each orientation in order to improve daylighting levels and the building's overall thermal performance.

Sound fields near building facades – comparison of finite and semi-infinite reflectors on a rigid ground plane

The sound field in front of, and close to a building facade is relevant to the measurement and prediction of environmental noise and sound insulation. For simplicity it is often assumed that the facade can be treated as a semi-infinite reflector, however in the low-frequency range (50–200 Hz) this is no longer appropriate as the wavelengths are similar or larger than the facade dimensions. Scale model measurements and predictions using integral equation methods have been used to investigate the effect of diffraction on the sound field in front of finite size reflectors. For the situation that is commonly encountered in front of building facades, the results indicate that diffraction effects are only likely to be significant in the low-frequency range (50–200 Hz) when the façade dimensions are less than 5 m. This assumes that there is a point source close to the ground and microphones at a height of 1.2 or 1.5 m, at a distance between 1 and 2 m in front of the façade.

Uncertainty evaluation in field measurements of airborne sound insulation

The Brazilian Committee of Civil Engineering presented a set of standards concerning the evaluation of the performance of several topics for buildings up to five floors. The acoustic performance is one of them. The standards are in approval process and measurements in real buildings will be necessary. Different professionals using different equipment will emit certificates establishing which levels of insulation a certain flat provides and its uncertainties. The expanded measurement uncertainty can provide the basis to compare different measurement results for a same building. The international Guide to the Expression of Uncertainty in Measurement, the ISO GUM, is the document that specifies how to determine and evaluate the uncertainty of a measurement result. The standards concerning sound insulation measurements are ISO 140 and ISO 18233. Uncertainty estimates are available only for the classical technique described in ISO 140, based in repeatability and reproducibility tests performed in laboratories. Field measurements present some characteristics that can contaminate the results, as time variance. Several independent measurements were carried out in a one flat building using ISO 18233 specifications and the ISO GUM was applied to obtain the uncertainty for measurement results of airborne sound insulation between rooms in situ.

An Application of Time‐Reversal Acoustics to Sound Insulation Measurements in Buildings

This paper considers the possible application of time reversal acoustics (TRA) to airborne sound insulation measurements in buildings. In TRA, an array of transducers is set up to form a time‐reversal 'mirror' or 'cavity'. Using this array, the sound radiated from an initial source is collected and refocused spatially and temporally, thereby being reproduced at the initial source position with high signal‐to‐noise ratio (S/N). Most previous studies of TRA have been conducted underwater with ultrasonic sound sources, with only a few in the audible range in real buildings. The technique is best suited to non‐dissipative systems, raising the question of whether any advantage could exist for transmission between rooms. This study applies TRA experimentally in the audible range using maximum length sequence signals for transmission between two rooms. Comparison is made between conventional measurements (with and without impulse response deconvolution) and TRA in terms of effective S/N and apparent level differ...

Survey on the insulation performance of acoustic louvres

Machinery such as compressors, boilers and generators require adequate ventilation and extract. To avoid excessive noise breakout, acoustic louvres are frequently used. These are usually made of tilted hollow metallic blades filled with absorptive materials and perforated at the inside face. This study investigates the important characteristics of common shaped acoustic louvres with regard to sound insulation. First, a market survey on 109 existing acoustic louvres of 24 producers worldwide is made. Second, laboratory measurements of sound insulation on 38 prototypes of 1 m2 acoustic louvres are compared. The influence of several parameters are studied such as louvre depth, blade angle, blade shape, blade thickness, blade spacing, kind of absorptive material, perforation degree, and edge filling.

Numerical study of sound transmission loss using an indirect boundary element method

The purpose of this study was to simulate transmission loss tests at the acoustic facilities of FG Wilson, Larne, UK. A hemi‐anechoic chamber adjoins a reverberation room via a transmission plug where canopy panel sections are mounted for testing. Boundary element methods in LMS Virtual.Lab are used in conjunction with a baffle model to simulate the test facilities for transmission loss. On one side of this wall the reverberation room is modelled as a diffuse field using a series of defined plane waves, and on the other the hemi‐anechoic chamber is represented as a free field. Experiments were carried out on a steel plate and lead sheet following the ISO 15186 standard for measurement of sound insulation using sound intensity. Source room sound pressure levels were recorded with a microphone, and an intensity probe was used to map the sound intensity field on the receiving side. Transmission loss for a frequency range was calculated as stated in the standard and compared with the results for the computational analysis. Comparison of the computational simulation with the experimental yielded a sufficient agreement.

Measurement of room‐to‐room airborne sound insulation with an access floor in a dwelling unit of condominium

It is preferred covering a wooden access floor on the concrete floor for condominium apartments in Japan. The access floor usually installed after every partition in each dwelling unit. If access floor and ceiling were done before partition, one can obtain accuracy of construction and reduce waste material. Therefore, one can provide building more green. But, there is concern that may deteriorate sound insulation because of flanking path through under the access floor. On the other hand, there is also another dominant flanking path irrespectively to these construction methods: via doors leading into hallway. A number of field measurements of sound insulation were done with opening/closing doors to evaluate the flanking transmission via the doors. These results show that the doors affect especially in high frequency, but not significant in low‐mid frequency. Next, the sound transmission performances of access floors and ceilings measured at laboratory are compared with direct sound transmission through wall itself. As a conclusion, field measurement results show that this construction method difference less affect to airborne sound insulation performance.

Diffuseness and sound field distribution at room boundaries

In the present work, a classical modal analysis is used up to medium frequencies to study the sound field distribution, and its diffuseness, particularly at boundaries. Due to intensification zones at boundaries, the diffuse field distribution at room boundaries can not be assimilated to the distribution inside the room. Moreover, diffuseness at room boundaries, that is of interest for sound insulation measurement, is usually only related to an incidence angle while inside the room volume several descriptors such as a correlation function and the spatial uniformity are necessary to characterize a diffuse field. In this paper, we present a new descriptor adapted to characterize the sound field diffusivity at boundaries. This descriptor is called Boundary Diffuse Field Index. Its averaged value over a specific surface can be related to a limit incidence angle, and its standard deviation can be related to the spatial distribution over the surface. Finally, thanks to this descriptor, Sabine's assumptions of diffuse sound field are also evaluated in this study.

Measuring Sound Insulation using Deconvolution Techniques

To compare the acoustic performance of a building element with the given sound insulation requirements, measurements need to be done. Generally, a broadband noise source is used according to international standards. This method does not always work in practice due to high sound insulation values or high background noise levels. It is very inconvenient from a practical point of view or even impossible to perform an accurate sound insulation measurement for all frequency bands. A solution to this problem can be found in deconvolution techniques using mls or sweep signals. It is possible to increase the signal to noise ratio with these techniques by averaging measurements and spreading out the spectral sound energy in time. As a result an efficient use of available sound power is possible. In a laboratory is investigated how to use mls or sweep signals as a source signal and deconvolution as a measurement technique to obtain the sound insulation under noisy conditions.

Technical Note: Airborne Sound Insulation of Hollow Brickwork

This paper reports on the uncertainty of in situ measurements of the airborne sound insulation of hollow-brick walls in different housing plans, with emphasis on the influence of expansion joints. The mean and standard deviation of multiple measurements are obtained, which show significant differences in insulation values despite the fact that the same construction was used in each case.

Sound Insulation in Timber Buildings: The Finnish Experience

In Finland timber multi-storey houses have been in development for ten years. During this period, the sound insulation of timber structures has been actively studied both in the laboratory and on site. One of the main tasks was to ascertain if the impact sound insulation requirements were being achieved. An early consideration was the use of additional mass to achieve acceptability. However, there has been relatively little practical experience of this type of floor. A pilot building project, to develop new concepts of timber multi-storey houses is described. The buildings were erected using double frame wooden walls between flats and wooden truss floors with an in situ cast concrete top layer. The preliminary sound insulation measurement results between flats surpassed the expectations and the official requirements. The success was mainly due to the proper detailing of both wall and floor connections and proper workmanship.

Objective and subjective evaluation of the acoustic comfort in classrooms

The acoustic comfort of classrooms in a Brazilian public school has been evaluated through interviews with 62 teachers and 464 pupils, measurements of background noise, reverberation time, and sound insulation. Acoustic measurements have revealed the poor acoustic quality of the classrooms. Results have shown that teachers and pupils consider the noise generated and the voice of the teacher in neighboring classrooms as the main sources of annoyance inside the classroom. Acoustic simulations resulted in the suggestion of placement of perforated plywood on the ceiling, for reduction in reverberation time and increase in the acoustic comfort of the classrooms.

Uncertainty of measured and calculated sound insulation in buildings - Results of a Round Robin Test

An inter-laboratory comparison has been made in situ with the participation of 8 laboratories. The operators measured airborne and impact sound insulation of 7 partitions according to the ISO 140 standards and some additional guidelines. Variations of sound insulation, and their components, have been analyzed. In addition, field measurements of sound insulation in 40 building cases were compared to calculations according to EN 12354 (-1, -2). Safety margins for predictions of 3 dB are recommended for calculation of heavy building partitions, with respect to an estimated risk of 5% being disapproved by a sample measurement in situ.

A standard way of measuring rainfall noise

About 10 years ago at an ISO TC 29 meeting, the concept of the measurement of rainfall noise was suggested. At the time it made no sense to me. Who cares about this? Not me, since I liked the sound of rain on my roof, and the louder the better. The concept was to evaluate roofs to assess the insulation capabilities from sound (vibration?) produced by rainfall. But in spite of my skepticism, wiser heads prevailed, and in the end, the approach was drafted into a work item, a draft, and a final draft standard. This paper is a summary of ISO FDIS 140‐18, ‘‘Acoustics—Measurement of sound insulation in buildings and of building elements—part 18: Laboratory measurement of sound generated by rainfall on building elements.’’ I discuss the equipment needed, the test method, and the uncertainty.

Laboratory Sound Insulation Measurements of Improved Timber Floor Constructions: A Parametric Survey

An extensive measurement survey of timber floor constructions has been carried out by the acoustics laboratory of the Belgian Building Research Institute [1]. The basis of this study was the airborne and structure-borne sound insulation measured on a bare joist floor with OSB (Oriented Strand Board) sub floor. By adding different floor toppings and gypsum board ceilings to the basic floor construction, gradual improvements were recorded. A large number of floors are evaluated in the laboratory and formed a database for parametric studies. Improvements due to cavity absorption, floating floors and suspended ceilings were quantified and ranked by effectiveness. Measurement results revealed remarkable differences between floating floor systems. In addition, sound insulation measurements have been performed on joist floors with concrete toppings. The so-called mixed concrete-timber floors provide a higher mechanical resistance. The effect of the bonding and topping type on the airborne and structure borne sound insulation has been examined in the laboratory. The results of this additional research are briefly compared to traditional floor systems and compared with the (future) Belgian standard values. An overall evaluation of the acoustic relevance of timber floor partitions in and between dwellings is also made.