A new handbook has been published by the Swedish National Board of Housing, Building and Planning. This handbook describes the building process from an acoustical point of view. It focuses on the conversion of functional requirements on the performance of the building to appropriate designs of a building. This type of requirement allows all kinds of solutions to be applied, but is also requires coordination of acoustic issues between the parties involved during the entire building process. Hence, the handbook addresses detailed information to each party. Functional requirements and acoustic issues are complex by nature, because they affect many building elements, they are handled by several parties and they must be considered during several phases of the building process. Typical errors come from building designs (floor plans), product designs (input data of elements), calculation models, quality of workmanship (during the construction phase) and uncertainties in field measurements. The aim is to help the commissioner manage the responsibility for these issues. The handbook also covers a large field of practical applications to support the acoustic expertise. It is expected that this handbook will encourage developers and contractors to deal with acoustic issues more efficiently. If the noise environment is not considered in the design process for new residential areas and other building facilities, the satisfaction of tenants, the health costs for the society and the building values will be affected. If verifications are made only at a late stage of the building process, errors are normally discovered too late. They are then expensive to correct for and it is difficult to find out who is responsible. When the verifications are made effectively during the process, costs are minimized.
A pilot project has been performed with a round robin comparison (inter-laboratory test), where a modified heavy-duty washing machine has been circulated for tests among 6 laboratories. The main goal of this pilot project was to find out whether a simple substitution method could be applied to estimate the structure-borne sound pressure level of some typical building service equipments. First, the vibration levels of a heavy low mobility test floor are measured when a machine with high internal mobility operates on this floor. Then, the vibration levels are measured at the same positions on the same floor when a standardized tapping machine (ISO 140-7) operates in the same positions as the test machine. The differences between the vibration level are then calculated. The difference may be used to compare the performance of different machines at one site or to estimate the sound pressure level in other buildings with heavy floors. In its simplest form, this can be made in the same way as for floorings, i.e., first calculating the normalized impact sound pressure level (EN 12354-2) and then subtracting the vibration level difference of the actual machine compared to the tapping machine. It remains to apply this method in the field and to compare estimated sound pressure levels with measured.
It has for long been debated whether 50 or 100 Hz is the proper lower frequency limit when evaluating airborne sound insulation between dwellings. Although 100 Hz is the lowest third-octave band within most regulations, there is an ongoing interest in paying more attention to lower frequencies. In Sweden, evaluation from 50 Hz became mandatory already in 1999 wherefore unique experiences are available by now. In this paper, extensive data in terms of field measurements and questionnaire surveys from in total 46 building objects of various constructions have been compiled. A number of single number quantities, standardized by ISO as well as alternatives, are compared concerning their correlation against the subjectively rated annoyance responded by the residents. The statistical evidence for a 50 Hz limit was found to be small considering the total database but when the lightweight buildings were analyzed by their own, the importance of frequencies below 100 Hz became clearer. The overall recommendation is to include frequencies from 50 Hz in order to achieve good sound protection against a broad variety of sound sources, including music and other possible items generating low frequencies.
Traditionally, multi-family houses have been constructed using heavy, homogenous materials like concrete and masonry. But as a consequence of the progress of lightweight building systems during the last decades, it has been questioned whether standardized sound insulation evaluation methods still are appropriate.An extensive measurement template has been applied in a field survey where several vibrational and acoustical parameters were determined in ten Swedish buildings of various constructions. In the same buildings, the occupants were asked to rate the perceived annoyance from a variety of natural sound sources. The highest annoyance score concerned impact sounds, mainly in the buildings with lightweight floors.Statistical analyses between the measured parameters and the subjective ratings revealed a useful correlation between the rated airborne sound insulation and Rw′+C50–3150 while the correlation between the rated impact sound insulation and Ln,w′+CI,50–2500 was weak. The latter correlation was considerably improved when the spectrum adaptation term with an extended frequency range starting from 20 Hz was applied. This suggests that frequencies below 50 Hz should be considered when evaluating impact sound in lightweight buildings.
Various research aspects on sound and vibrations in lightweight buildings are covered by the Swedish research programme AkuLite. One of the most important topics has been to find out to what extent objective measured parameters correlate with subjective opinions from people living in multifamily houses. Typical questions to be pointed out are: Do existing ratings like R'w (+C50-1350) and L'n,w (+CI,50-2500) correlate well enough to the tenants' perception? Can other measureable parameters be found that show better agreement? Are the often used frequency limits of 100Hz or 50Hz low enough? Can any significant differences be seen when comparing lightweight buildings with concrete buildings? Extensive sound and vibration measurements have been performed in numerous buildings of varying construction including lightweight timber or steel based framing, cross laminated timber and concrete. In general frequencies from 20 Hz have been covered. Questionnaires have been distributed to the tenants where they were asked to give their opinion on a number of adequate questions related to sound and/or vibration perception. The results from the measurements and from the questionnaires have then been compiled, followed by a comprehensive statistical analysis in order to see the degree of correlation between them.
A previous Swedish research project indicated the potential need for evaluating impact sound insulation from 20 Hz in buildings with lightweight constructions. This is a discrepancy compared to the commonly used frequency intervals starting from 50 or 100 Hz. The statistical significance of this groundbreaking suggestion was however not satisfactorily strong since the result was based upon a limited number of building objects.
The scope of the present paper is to secure the previous study by adding additional objects to the underlying database, thereby increasing the confidence of the results. The methodology is to perform impact sound insulation measurements in apartment buildings of various construction types and to perform questionnaire surveys among the residents. The measured sound insulation is compared to the subjective rating by the occupants in order to find the parameter giving the highest correlation with respect to frequency range and weighting.
The highest correlation was found when the impact sound insulation was evaluated from 25 Hz using a flat frequency-weighting factor. Frequencies below 50 Hz are of great importance when evaluating impact sound insulation in lightweight constructions.
In order to reduce costly downtime, adequate condition monitoring of the automatic transmission components in heavy duty construction equipment is necessary. The transmission in such equipment enables to change the gear ratio automatically. Further, the bearings in an automatic transmission provide low friction support to its rotating parts and act as an interface separating stationary from rotating components. Wear or other bearing faults may lead to an increase in energy consumption as well as failure of other related components in the automatic transmission, and thus costly downtime. In this study, different sensor data (particularly vibration) was collected on the automatic transmission during controlled test cycles in an automatic transmission test rig to enable adequate condition monitoring.
An analysis of the measured vibration data was carried out using signal processing methods. The results indicate that predictive maintenance information related to the automatic transmission bearings may be extracted from vibrations measured on an automatic transmission. This information may be used for early fault detection, thus improving uptime and availability of heavy duty construction equipment.
The relevance of performing reverberation time measurements at very low frequencies became an issue in Sweden when the national standard recommended that impact sound insulation should be evaluated from 20 Hz for sound classes above the minimum requirement. Even though the standard states that L'n,T is not to be normalized with respect of reverberation time for frequencies below 50 Hz, it could be argued to include such a correction term to handle any possible variation in the absorption properties of the room. But this can be done only if the reverberation time can be accomplished with reasonable accuracy. The present paper presents an empirical study where reverberation time has been measured from 20 Hz in two different bedrooms with more than 100 microphone positions in each in order to determine the spatial variation. A comparison is made between the uncertainty as a function of frequency and it is indicated that the standard deviation is larger for the lowest frequencies, below 50 Hz, compared to higher. From an engineering point of view, this can be compensated by adding additional positions to the already existing ISO measurement procedure
Measuring reverberation time is normally one of the steps within the procedure of determining sound insulation in dwellings where 100 or 50 Hz usually serves as the lower frequency limit. However, even lower frequencies have become a matter of interest as research in the field recently indicated that the range 20-50 Hz seems to be of great importance when it comes to the perception of impact sound in lightweight buildings. A major issue in this context is then whether it is appropriate to measure and evaluate reverberation time at such low frequencies. This paper presents an empirical study of reverberation time measurements made in two rooms using more than 100 microphone positions in each. The measurement uncertainty with respect to microphone position and combinations of positions are compared for the frequency bands from 16 to 1600 Hz. Furthermore, it is analyzed how many microphone positions are needed in order to, with a reasonable probability, end up with an uncertainty in the related standardized impact sound level insulation L′n,T within ±1 dB
The thesis summarizes results of research on the uncertainty of standardized methods applied in the field of building acoustics, with respect to calculations as well as to measurements. Eight published papers are appended to the thesis. It also gives references to relevant research that has been published in this field of interest, to give the reader a wider outlook. The EN 12354 series of standards on calculation methods, published in 2000-2009, have facilitated the management of building acoustics issues during the building process. To allow for lean designs of building structures, the uncertainty of the calculation methods (compared to measurement results) must be known, as the measurement results in finalized buildings are typically used to prove fulfillment of formal requirements. The standards facilitate a structured comparison of calculations (made during the design work) to the results of measurements. These comparisons have been used to estimate the combined uncertainty of the standardized methods and to derive safety margins to be observed during design work (i.e. to be added to calculated values). The combined uncertainty is estimated from the differences between field measurements of the performance of buildings (made according to international standards) and the corresponding theoretical estimations of each case (according to standardized calculation methods). There are several factors that complicate such comparisons, e.g. uncertainty of the input data of building elements, applicability of the calculation methods to the real building construction, effect of poor workmanship and uncertainty of the field measurement methods. Some studies address the uncertainty of the field measurement methods specifically. A separate section discusses management issues, which serve to reduce uncertainties pertaining to unclear definitions of requirements, poor building construction documentation and responsibility to be taken during each phase of the building process.
A draft standard was presented by a working group within ISO in April 2011. It describes six methods to simplify the measurement of a spatially averaged sound pressure level in a room, in order to determine an airborne sound insulation between two rooms. The draft standard is intended to replace ISO 140 part 4. The proposed methods are based on various spatial sampling techniques, where a microphone is moved continuously or kept steady at ?xed positions in differ¬ent parts of the room. The uncertainty of the average is to a large extent related to the ability of the sampling method to sample sound pressure levels uniformly from all parts of the room. The uncertainties of the simpli?ed methods of the draft standard have been estimated empirically by means of measurements made in ?ve rooms with different acoustic conditions. The result of each type of simpli?ed method is compared to an average of sound pressures recorded in a dense mesh of microphone positions throughout the permitted space in the same room. Some results that may be useful when an averaging method is to be decided: • the standard deviations may actually be higher above 100 Hz than below, the 160 and 200 Hz third octave bands may even contain the most uncer¬tain results • the ?xed positions method is practical and may be used in all types of room • the special corner method gave higher average sound pressure levels and lower uncertainties compared to the other methods • moving microphone methods are dif?cult to apply in small furnished rooms where there is not enough space to complete several indepen¬dent microphone paths • moving microphone methods may be sensitive to operator generated background noise • microphone positions should be spread over the entire room volume. This study has not estimated the uncertainty of the sound pressure level differ¬ence between two adjacent rooms, used for sound reduction index estimates.
Impact sounds at very low frequencies as well as floor vibrations may bother occupants in high riseapartment buildings where floors and walls are supported by timber (or steel) frames. Disturbing impactsounds at medium and high frequency may occur in buildings with conrete floors. A weighted singlenumber should preferably handle both types of sounds such that it is neutral with respect to buildingmaterials. This paper presents a brief overview of some main findings of the Swedish ‘AkuLite’ jointresearch project and discuss two single numbers for impact sound evaluated in the frequency range 20-5000Hz as well as a deflection criterion. These single numbers were based on results from field surveys wherethe occupants have rated the performance of their buildings as well as physical measurements in these. In acompanion paper by Ljunggren et al, the airborne and impact sound single numbers are evaluated by meansof correlation analyses. In listening tests by Thorsson, walking impact sounds were recorded on differenttypes of floor and played back to test subjects by means of paired comparisons. Jarnerö made a survey onfloor vibrations. Their results support the hypothesis, that an extension of the frequency range down to 20Hz as well as introducing a stricter deflection criterion could improve the correlation of physical parametersto occupants’ rating of annoyance from impact sounds.