Laboratory measurements of building acoustics at low frequencies: a modal approach

The current international request to extend standard laboratory measurements of building acoustics (airborne and impact sound insulation and reverberation time) to frequencies below 100 Hz requires a deep study on the involved physical phenomenon and a proper procedure in order to get repeatable and reproducible results. In typical laboratory volumes (50-80 m$^3$) and at low frequencies (50-100 Hz), the acoustic field is non-diffuse due to the presence of standing waves or resonant modes in the small laboratory rooms. In space and frequency domains, the sound field is characterized by large fluctuations of sound pressure levels, different from diffuse field condition, characterized by uniform sound field in both domains and is assumed from 100 Hz on in laboratory standard procedures. Under such conditions, standard sound insulation measurements and reverberation time descriptors are not adequate to correctly characterize the insulating property of partitions or flooring systems or the reverberation times of laboratory (or ordinary dwelling) rooms. For this reason, a new measurement approach based on resonant frequencies, or room modes, the so-called modal approach, is introduced. Resonant modes provide deterministic quantities in non-diffuse field and are responsible of most annoyance. For airborne sound insulation, the standard sound reduction index is not representative of sound insulation as it is based on sound power measurements, which is still undefined for non-diffuse acoustic field. In the coupled system room-partition-room, in addition to natural resonant modes of each system component, the transmission of modes from the source to the receiving room is observed. The modal approach allows to evaluate the sound insulation by the determination of the sound transmission loss of a single source room mode passing into the receiving room through the partition. Such characteristic is the base of the new descriptor: the modal sound insulation. It is defined as the difference between the maximum sound pressure levels (evaluated in the corners of rectangular rooms) of source room modes that occur in both source and receiving rooms. Starting from the classical modal theory, a proper normalization term, corresponding to receiving room volume, is also introduced and presented together with a new method, based on the envelope of room frequency responses, to extend the results to the whole low frequency range, due to the discrete nature of modal sound insulation. Furthermore, the uncertainty budget is analysed. From scale model measurements, normalization term results to be negligible and problems due to source and receiving room modal match, cause of sound insulation underestimation, has to be solved in the future with a proper weighting procedure, based on the increase of modal sound insulation as function of modal overlap degree (Kohlrausch-Williams-Watts function), experimentally evaluated in the scale model. The modal approach is also applied to impact sound insulation and impact noise reduction measurement: new procedure and descriptors are introduced and first experimental tests on three different mass-spring systems are shown. Results agree with theoretical basis and validate such approach. In the end, the modal approach is used for the measurement of reverberation time in small rooms, in terms of modal reverberation time. Two different methods are evaluated on the base of their mathematical relation: the direct and indirect methods. The first is based on the measurement of the direct modal sound decay, whereas the second evaluates the modal decay starting from the measurement of the half bandwidth of the resonant peak. For both methods, different sound signals are compared and suitable procedures are applied. First experimental tests show a good agreement between the two methods and their mathematical relation is confirmed

Towards a sustainable approach for sound absorption assessment of building materials: Validation of small-scale reverberation room measurement

The research and development phase of sound absorptive building materials by designers, engineers, acoustic consultants and architects need tools for fast, inexpensive preliminary comparison tests on products or acoustic systems. The existing methods exhibit some drawbacks: the impedance tube (IT) is not suitable for 3D systems, while the full-scale reverberation room (FSRR) requires test samples of large dimensions. To overcome these limitations, this work aims to explore the capabilities of small-scale reverberation rooms (SSRR) of about 3 m3 located at Politecnico di Torino in evaluating the randomincidence sound absorption coefficient. In order to define the range of application and reliability of the method, the considered factors are the sample area and its orientation on the room floor. Four different materials have been tested by applying IT, FSRR and SSRR. The absorption coefficients data obtained with SSRR are compatible with the FSRR benchmarking in the 400–5000 Hz frequency range for three porous materials, and in the range 1000–5000 Hz for the thin rigid material. Therefore, the SSRR can be considered as a reliable alternative for the sound absorption characterization in these ranges for this kind of materials, leading to several benefits. Among them, samples with reduced size can be evaluated with a cheaper equipment in a short time, increasing the overall economical sustainability of the measurement process; in turn, this can encourage designers and architects to perform acoustical measurements since the very early research and development phase, leading to an overall reduction of design costs and improved product quality

Sound Insulation of Building Elements at Low Frequency: A Modal Approach

In typical laboratory volumes (50-80 m(3)) and at low frequencies (50-100 Hz), the acoustic field is non-diffuse due to the presence of source and receiving room modes. Under such conditions, standard sound insulation measurements and descriptors are not adequate to correctly characterize the insulating property of partitions or flooring systems. The "modal approach" allows to evaluate the airborne sound insulation by the determination of modal transmission loss, or modal sound insulation, of a single mode passing through the partition. Proper normalization terms and an extension method to one-third octave bands are also introduced. The same approach is applied to impact sound insulation measurement. (C) 2015 The Authors. Published by Elsevier Ltd

Sophy project: evidences intimate hygiene

The importance of intimate hygiene, pH and vaginal flora in keeping the vaginal ecosystem in good balance is known and widely described. No systematic, nation-wide, current study is up to now available, on the correlation between vaginal pH and intimate hygiene in the different ages and condition of the woman, mainly considering the modified hygienic and clothing habits. A project aimed to collect systematically data related to intimate hygiene, in a representative sample of the Italian gynaecological population has been realised, helped by a specific website to insert the data. Lifestyle, vaginal pH, intimate hygiene compliance, presence of symptoms, gynaecological treatment stratified in different subgroups (prepubertal, fertile, pregnant, lactating, pre-menopause and menopause) have been recorded up to now on 119t women. The Study on pH and Hygiene (SOPHY) provides a strong educational impact, pushing doctors and women in considering pH and intimate hygiene an important moment of their professional and daily life. Each natural plant extract used in intimate hygiene (Sage, Thyme and Chamomile) confirmed its clinical activity on protecting against bacteria, mycoses and inflammation

Streamlining Microdata for the Analysis of ICT, Innovation and Performance

This report portrays the outcomes of the workshop Bridging microeconomic data sources for the analysis of ICT, innovation and performance organised by IPTS on the state of art in international micro-founded analyses on Information Communication Technologies (ICTs), R&D, innovation, and economic performance. Micro-level statistics allow to elicit the internal variability of productive systems. For this reason, they can be extremely useful for understanding industry and macro dynamics, as well as for policy design and monitoring. Nonetheless, large-scale application of these statistics is still limited for different reasons, mostly related to the availability of information. Against this background, the workshop aimed to provide a broad overview of completed and ongoing analyses at National, European and OECD levels, and also to share experiences and discuss proposals to address current issues and fully deploy the potential of micro-data. The studies presented covered the whole techno-economic paradigm related to ICTs, innovation and performance, including: factors determining the intensity and sophistication of ICT usage; its relationships with patterns of innovation and performance at firm and macroeconomic levels; the determinants of the EU-US gap in research and knowledge intensive activities; the role of entrepreneurship, and the capability of firms to grow. To this end, the studies used a number of sources in different combinations. Methodological issues addressed in the presentations and debate included: problems encountered when trying to enhance the potential of bridging micro-sources and possible solutions, interactions with macro data, complementary and non-official statistical sources; measurement of ICT-related activities and R&D across the economy, and the reconciliation of company information to BERD (business expenditure in R&D) statistics; the building of composite indicators and their effectiveness, etc. The report summarises experiences and views gathered and shared on these topics.JRC.DDG.J.4-Information Societ

Reverberation time measurements in non-diffuse acoustic field by the modal reverberation time

partially_open3mixedPrato, A.; Casassa, F.; Schiavi, A.Prato, A.; Casassa, F.; Schiavi, Alessandr

A MODAL APPROACH FORREVERBERATION TIME MEASUREMENTS IN NON-DIFFUSE SOUND FIELD

In recent years the extension of reverberation time measurements to frequencies below 100 Hz is becoming more and more important due to the increase of low frequency sources. In ordinary rooms with volumes smaller than 200 m3the low frequency sound field is non-diffuse due to the presence of modes, which are also the main cause of bad quality of listening in terms of clarity and rumble effects. Since standard measurements according to ISO 3382 fail to achieve accurate and precise values in third octave bands due to non-linear decays of room modes, a new ap-proach based on reverberation time measurements of single resonant frequencies (the modal re-verberation time) is introduced. Two measurementmethods based on the relation between mod-al decays and resonant half bandwidths are proposed: the direct method, based on the direct evaluation of modal sound decays with interrupted source signals, and the indirect method based on half bandwidth measurements. Proper measurement procedures, with microphones placed at rectangular room corners and anti-resonant sine waves and sweep source signals for direct and indirect measurement methods respectively, are proposed. Comparison between direct and indi-rect methods shows good and significant agreement. Comparing modal reverberation times with standard ones, the inadequacy of standard procedure to get accurate and precise values at low frequencies with respect to the modal approach becomes evident. In the future, further investi-gations are necessary in more rooms toimprove uncertainty evaluation

Correction of squareness measurements of Vickers indenters due to the tilt of the pyramid axis

In Vickers hardness measurements, ISO 6507-2 and 6507-3 Standards require to verify that the quadrilateral of the pyramid indenter base has angles of 90° ± 0.2°. Such measurement is usuallyperformed through optical measuring systems, which, rotating the diamond indenter, allowsto evaluate the angles between two consecutive faces with high accuracy. These angles correspond to the angles of the quadrilateral base when the axis of the pyramidis perfectly perpendicularto the seating surface. Nevertheless, when the pyramid axis is tilted, the angles between two consecutive faces are different from the corresponding angles on the quadrilateral base, thus a correction is required. In this work, a method to correct squareness measurements, based on a geometrical model, is presented

Traceability of gravity acceleration measurement in calibration laboratories

Primary measurements of force, torque and pressureare directly influenced by local gravityacceleration,g. At present, gmeasurementin calibration laboratoriesisevaluated through absolute or relative measurementsor through theoretical/empiricalrelations. Except forsome absolute measurements, other methods are not traceable. As consequence, measurementsofthesequantities could behighly impacted by this lackin terms of accuracy and uncertainty.The Consultative Committee for Mass and related quantities (CCM) of CIPM and International Association of Geodesy (IAG) arecurrently working ona resolutionstrategy to ensure traceability to the SI for gravity measurementsthrough the establishment of a global absolute gravity reference system. Thisnetwork could becomea useful tool to transferthe gmeasurement to calibration laboratories at international level. However, as well any other measurements, thispossible solution should be established under the Quality Management system of accredited laboratories

A Bayesian statistical method for large-scale MEMS-based sensors calibration: a case study on 100 digital accelerometers

Low-cost sensors and in particular micro-electro-mechanical systems (MEMS) devices are widely used in many applications, including consumer electronics, healthcare, automotive, and industrial automation. Their large-scale production (typically in the order of millions per week in a single factory) would require the calibration of a huge number of devices that would be costly and time-consuming. A solution can be found in the use of statistical methods in order to (at least partially) substitute for the typical calibration procedures. In this work, we propose a Bayesian method to statistically calibrate large batches of sensors using probabilistic models and prior knowledge. The method involves experimentally calibrating only a small sample of sensors, then infer the number of reliable sensors in the entire batch and assign an appropriate uncertainty to all the sensors. Therefore, it can be considered as a statistical calibration of the batch. The Bayesian nature of this approach allows reducing the number of experimental calibrations by incorporating the prior knowledge coming from the previous calibration of a 'benchmark' batch, which is performed 'once and for all' and is representative of the whole production process. The application and validation of the method are performed through the calibration of 100 digital MEMS accelerometers. Validation results showed an acceptable agreement between experimental-based bootstrap and theoretical values, with relative differences within +/- 7%