Development and use of prediction models in Building ... - Webistem

Development and use of prediction models in Building Acoustics as in EN 12354 Eddy Gerretsen TNO Science and Industry, P.O. Box 155, NL-2600 AD Delft, The Netherlands, [email protected]

Improving the acoustic climate in buildings is an important social item, both for new and renovated buildings, that involves many aspects and many sound sources. To do so with changing design and construction methods makes it necessary to use appropriate prediction models to link acoustic product performance with building performance. The series of standards EN 12354 is being developed to meet this challenge. For airborne and impact sound insulation between rooms and sound reduction or radiation by facades the standards are now available for some time. Experience in using these parts have been gained, raising questions at the same time about the application in complex situations, the appropriate input data on products and the accuracy of predictions. The main item for these parts remains the application to lightweight elements and construction methods. For the reverberant sound in enclosed spaces the standard became available only last year. Though the main body covers well-known models, some experiences with the indicated approach for irregular spaces is more than welcome. The most challenging item left concerns the air-borne and structure-borne sound from service equipment in buildings. A very first draft is being circulated for comments recently. The general approach will be presented, highlighting the main remaining problems to be solved such as measurement methods for the production of structure-borne sound by equipment and installations parts. These items will be touched in this introduction and be addresses by other papers in this structured session.

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standardizing the sound reduction index of building elements [4]. The main discussions in the application of these models relates to light and/or highly damped building elements. Some aspects will be discussed here.

Introduction

Initiated by the requirements from the Construction Products Directive in 1989, CEN started to draft standards to relate the acoustic performance of buildings with the acoustic performance of the products from which these buildings are constructed. This resulted in six parts of the standard EN 12354 of which the last part has just been published in its first draft version. Experience with the parts already published [1] has indicated some aspects where improvements and adjustments are desirable and feasible; this will be addressed in the next sections. Then attention will be given to the approach and background for the fifth part on the sound levels due to service equipment in buildings [2].

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2.2 Lightweight single elements The flanking airborne sound reduction index Rij for transmission from element i to element j is given by [1].

Rij =

Here Ri, Rj are the in-situ values of the sound reduction indices, Si, Sj are the areas and ai, aj the equivalent absorption lengths of the elements i and j, lij the coupling length between those elements, Kij the vibration reduction index for the junction between those elements and Ss the area of the separating element. This relation is valid for the whole frequency range usually considered, but as stated in the standard the sound reduction indices should than relate to resonant transmission only. So in case measured values are used an error is introduced since below the critical frequency also forced transmission can be important or even dominant. For heavy elements such an error is usually small and could be neglected, but that is no longer the case for light elements with high critical frequencies. The standard addresses this problem but without specifying a solution. A solution could be to correct the measured sound reduction index Rmeas

EN 12354, part 1 & 2

2.1 Airborne transmission

and

impact

ai a j Ri R j S (1) + + K ij + 10 lg s + 10 lg 2 2 lij Si S j

sound

The prediction models for airborne and impact sound transmission in buildings as described in EN 12354 part 1 and part 2 are by now well established [1]. Since the publication in 2000 the application to homogeneous, relatively heavy building elements is tested and backed by various studies, f.i. in a careful comparison with an SEA-approach [3]. Practical questions for such applications are mainly related to appropriate input data and the most practical way of applying the structural reverberation time in

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below the critical frequency for forced transmission τforced, for instance in the same way as was proposed in [4]. For f ≤ 2 f c ≈ 88000 / m' it follows:

[

Rres = −10 lg 10 − Rmeas / 10 − τ forced

element. In that case the level difference between both leafs of an elements is also included in the vibration reduction index [5]. This is illustrated in figure 1.

]

2

§ 2 ρc · ¸¸ 2σ f τ forced = ¨¨ © 2πfm' ¹

I.

R

(2)

Kij

The only values needed for this correction are the mass m’ of the element and the radiation efficiency σf for forced waves, for which a fixed value will normally be adequate [3]. The estimation of the critical frequency is not very critical since the result will be dominated by resonant transmission around that frequency anyway.

II.

R Kij

2.3 Lightweight damped elements In case of highly damped, homogeneous or double, elements the standard states that the structural reverberation time is either independent of the situation or irrelevant and relation (1) reduces to:

Rij =

Ri R j S + + K ij + 10 lg s 2 2 lij

Figure 1: Illustration of two possible approaches for a junction with a double flanking element.

(3) Since also here only free vibrations have to be considered, approach I seems to be most appropriate for elements with rather uncoupled leafs, while approach II. is most logical for elements with coupled leafs.

The appearance is quite the same but the sound reduction indices now are no longer situation dependent, though still referred to resonant transmission, and the meaning of Kij is somewhat different. This relation does not follow from sound power or SEA considerations, but more directly from average velocities of the building elements, applying reciprocity and assuming identical radiation efficiency at both sides of an element. Kij is then defined on the basis of the average velocity level of a given area of the elements. Due to the element damping this value will be rather independent of the actual area of the element as long as the measurement areas (Si and Sj) are not too small:

K ij =

Dv ,ij 2

+

Dv, ji 2

+ 10 lg

lij Si S j

Since the vibration reduction index of junctions with light elements could include various damping effects, it could be useful to consider each of these reducing effects more or less separately in order to gather more generally applicable data. The variations in junction details for a given type of element could than be added in an appropriate way to the damping effect of the elements itself. These and other aspects are considered and worked out in more detail. This is relevant for the laboratory measurement methods as specified in EN 10848 [6] and for guidelines on the application of the data in the prediction models.

(4)

Various of the items connected with the application of these parts and especially the application to lightweight structures will be addressed in several contributions to this session [19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30].

In this way this quantity includes both the reduction effects at the actual junction as well as level reductions over the damped element. In case of double elements there are different possibilities to apply this prediction scheme. It should be realized that the sound reduction index of the elements is used to estimate the average velocity level of an element at the radiating side and the vibration reduction index should therefore be related to the same sides of an element. So in case of a double element either only the inside is considered, both for R and Kij, or the total element is considered and Kij is based on the velocity levels of the not excited leaf of the double

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EN 12354, part 3 & 4

EN 12354 parts 3 and 4 treat the sound transmission through a building façade from the outside to the inside (part 3) or from the inside to the outside (part 4). The theoretical base for these parts is rather well known, though the formulation is partly new in order to cover various situations adequately. Important items in

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relation to these parts are mainly the applicable input data and the determination of some new quantities like the sound reduction index of sealing.

so that the resulting sound pressure levels can be simply added. Besides the general description of the calculation models, the document gives guidelines for each type of service equipment on the application of these models and the bases for the appropriate input data.

However, in this paper these parts will not be addressed further.

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The current document is a very first draft for part 5, published at the beginning of 2005 to generate and collect comments and contributions, also from outside the responsible working group. Various aspects still to be solved are indicated and will be addressed also in this paper and this session.

EN 12354, part 6

Part 6 on the sound absorption or reverberant sound in enclosed spaces describes mainly the well-known Sabine relation. Since it was known that in various situations with deviating room shapes or irregular distributed absorption that relation is not really adequate, information is also given on a possible different approach in annex D of that document. At the moment no new experience is available on the accuracy of that approach, but some work is going on in this field. Such studies are more than welcome in order to indicate the accuracy and field of application and to assist future amendments to the standard.

5.2 Transmission through ducts The sound transmission through ventilation and heating ducts has been treated already for a long time in various handbooks, for instance in [8], [9] and [10]. The basic approach is to consider the sound power level LW of various sources, like the ventilator or the air flow, and to take into account the power reduction ∆LW by each element in the system between the source and the considered receiving room (see figure 2).

This part will not be discussed further in this paper or this session.

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EN 12354 for service equipment

1

element 2 3

element i

4

LW

5.1 Introduction Service equipment in buildings varies largely in type and dimensions. It concerns water supply and waste water systems, heating, ventilation and lift installations, rubbish shuts and various types of household equipment. The sound levels due to the equipment are caused by various sound sources and various transmission mechanisms, making a prediction scheme rather complex. Even the aim of the estimation is not very precisely defined. The sound levels in rooms due to service equipment have to be measured in accordance with EN ISO 16032 [7], but the measurement quantities allowed in this standard show a large variation, both in frequency weighting (A or C), time weighting (maxF, maxS or eq) as in normalisation (n or nT). Though this can be partly derived from the same predicted sound spectrum, the relevant time weighting will normally determine the appropriate source input data.

room a Aref

room b Aref

Figure 2: System of a duct with source, transmission elements and receiving rooms (a and b). This is presented in equation (5):

Ln ,d = LW − ¦ ∆LW ,i + 10 lg i

4 Aref

(5)

In the document the various relevant elements are considered and it is indicated how the available measurement quantities for that element are related to the sound power reduction. For some elements a measurement standard is available, for others such standards are still missing and only global indications can be given. Since the mentioned handbooks are not always in agreement with each other, the most consistent choice is made for the definitions of the quantities taking into account reciprocity relations where appropriate.

The main excitation and transmission mechanisms distinguished are the airborne sound transmission through ducts, the airborne sound transmission through the building construction and the structure-borne sound transmission through the building construction. For each of these mechanism the sound transmission for a source is described separately in general terms of sound power transmission. The contribution of each source or partial source is considered to be independent

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5.3 Air-borne transmission

SEA modelling are already given, but it could be useful to elaborate on this.

The sound power level LW, as determined by various existing standards, specifies the airborne sound radiation by sources. The properties of the source room determine the resulting sound pressure levels in that room. The airborne sound transmission through the building is treated already in EN 12354-1 so that it can be applied also here. This is illustrated in figure 3. In these situations it will not be self-evident to refer the flanking sound reduction index Rij to the area of a separation element, hence a reference area Sref = 10 m2 is used.

source building construction source room between source room element i and receiving room Asource LW element j Lsource near

Rij

5.4 Structure-borne transmission For most equipment the sound levels in rooms are mainly due to structure-borne sound transmission. This is the most complex aspect and yet the base for a practical calculation model is rather weak. Not so much for the transmission, which is essentially identical to the transmission of airborne sound, but due to lack of a practical characterization of actual sources as a source of structure-borne sound. To solve this problem and to keep the prediction model in this respect open for future developments, it was decided to draft a model where the source strength is specified by a new and general quantity, the characteristic structure-borne sound power level LW,sc as proposed by Moorhouse and Gibbs [12] combined with a coupling term DC. This is a quantity that has the potential to be general and practical, though no measurement method is available at the moment but for the time being it can be related directly with existing quantities like the source force level. In section 5 this source descriptor will be discussed in more detail.

receiving room Areceive Lij,receive

Figure 3: Airborne sound transmission from a source through a building via transmission path ij.

This source sound power level and the coupling term together give the sound power injected in the supporting building element. The transmission of this injected power could be described in various ways, for instance relating it to the impact sound transmission by the tapping machine as in EN 12354-2. However, it was thought that in combination with the air-borne sound transmission for equipment it would be more logical to apply exactly the same quantity to express the transmission, i.e. the flanking sound transmission index Rij. This prediction scheme is illustrated in figure 4.

The relation to be used for a given transmission path ij is given in equation (6).

Ln ,a ,ij = LW + Ds ,i − Rij ,ref − 10 lg

S i Aref S ref 4

(6)

The term Ds,i specifies the sound transmission to element i in the source room. In case of a diffuse sound field and a source in the centre area of the room, this follows directly from the sound absorption in that room (=10lg Si/As). But such conditions will often not occur in equipment rooms. Thus in estimating this term, account will have to be taken of non-diffuse sound fields, directivity of the sound radiation, direct and near fields of the source. These aspects will still have to be studied further in order to be able to give guidelines for the best practical approach.

supporting element i

LWsc

Another aspect to consider concerns the sound transmission. EN 12354-1 considers the transmission to adjacent rooms, but in case of equipment the relevant receiving room may be positioned further away from the considered source. Thus a relevant transmission path may involve more than one junction and the number of relevant paths may quickly increase. Some indications are given how to deal with this and for some building types a complete SEA modelling might be appropriate. For that purpose some relations between the typical quantities in EN 12354 and for

coupling term

building construction receiving between source room supporting building Areceive element i and receiving room element j Lij,receiv Rij

Figure 4: Structure-borne sound transmission from a source through a building via transmission path ij. The relation to be applied to each transmission path is specified by equation (7).

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Ln, s ,ij = LWsc + DC ,i − Dsa ,i − Rij ,ref − 10 lg

S i Aref S ref 4

(7)

LWinj = LWsc + DC ,i

This equation contains an additional adaptation term Dsa that expresses the equivalence between the injected structure-borne and the incident air-borne sound power. This quantity is determined by the properties of the supporting building element only and follows for a homogeneous, heavy building element from the mass m and the critical frequency fc by:

Dsa = 10 lg

6

400 f c 17,6 ⋅10 6 ≈ 10 lg mf 2 m2 f 2

Dc ,i = 10 lg

(8)

LW , sc = LF + 10 lg Ys = LF − 30 DC ,i = 10 lg{Yi } + 30

v sf } / Wref

vsf2 Wref

1 Re{Ys }

Examples of sources that could be considered as force source are appendages in water supply installations and wastewater installations. For these sources measurement standards are available, the results of which could be expressed in a characteristic structureborne sound power level. For elements in water supply installations the sound production is given as the sound pressure level Lap in accordance with ISO 3822 [13]. Using the properties of the facility this result can be translated into the power level by:

(8)

LWsc = Lap − 10 lg

(9a)

2

F Ys Wref

Re{Y }σ − 22 ωη m

(13)

≈ Lap + 35 + 10 lg(0,01 f + 0,5 f )

or

LWsc = 10 lg

(11)

LWinj = LWsc + DC ,i = LF + 10 lg Re{Yi } (12)

In a simple one-dimensional case this reduces to:

LWsc = 10 lg

(10)

Again the installed sound power follows from equation (10), which in this case simplifies to a well-known result:

For the general case LW,sc follows from the complex free velocity vsf and the source mobility’s Ys for each support of a multi-degree of freedom source by (8). * −1

Re{Ys }

In case a source could be considered essentially as a one-dimensional force source the source mobility in equation (9b) is very high; for the application in buildings a value of Ys = 10-3 s/kg could be used as reference value. This would than lead to:

A general characterisation of the sound production by a structure-borne source has to take into account the source mobility for all degrees of freedom and for all the contact points between source and supporting element. From several proposals the most practical seems to be the characteristic structure-borne sound power LW,sc, which is the power, injected by the source in its mirror image [12]. In this way this quantity is just depending on source properties. The injected power in a specific situation, the installed sound power, will still depend on the mobility properties of the source and of the supporting elements though. So source mobility’s will have to be measured, estimated and modelled in order to be able to perform predictions.

Ys

Ys + Yi

2

6.2 Examples

6.1 Source strength characterisation

*T

Ys

Characteristics of the mounting like resilient elements can be incorporated in this coupling term. So to be able to predict the injected sound power in a practical way, it will be necessary to derive adequate models for the specification of the coupling term.

Structure-borne sound sources

LWsc = 10 lg Re{v sf

The sound power level LWinj injected into the building structure with mobility Yi follows in those simple cases from this source power and the coupling term DC as:

For wastewater installations the sound production is given as the sound pressure level Lp,n,sc in accordance with EN 14366 [14]. This result can be translated into the power level by:

(9b)

This sound power could be measured and applied directly and is useful already for comparison between comparable products. General measurement methods will have to be developed and work is going on [16, 17, 18]. For some simple situations the characteristic structure-borne sound power level can be deduced from well-known quantities. Some examples will be given in the next section.

LWsc = L p ,n , sc − LSSR + 34,7 − 10 lg f 2 ≈ L p ,n , sc + 8 lg f + 23,5

(14)

For other sources for which the force level or equivalent force level is known or measured the method can also be applied, with or without taking into

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account the effective source mobility. Gerretsen [15] illustrated this for a washing machine and for the ISOtapping machine. For the last case the source mobility and force level follow directly from the specifications of the machine, simply leading to:

LWsc = LF − 5 − 10 lg f

7

During the last fifteen years prediction models have been specified for all relevant aspects in building acoustics: airborne and impact sound transmission between rooms, sound reduction and sound radiation by facades, reverberant sound in enclosed spaces and sound levels due to service equipment.

(15)

≈ 115 dB re 1 pW per 1/3 oct

The first have been used for several years now and this experience indicates aspects that need further study and elaboration. That is for instance the case for lightweight, damped building elements.

Finally, also velocity sources can be relevant since that would be the appropriate way to characterise machines that usually will be resiliently mounted. So assuming a low source mobility as reference, i.e. a high source impedance of Zs = 106 kg/s, the sound power would follow from velocity levels by:

LWsc = Lv ,eq + 10 lg Z s + 10 lg

2 vref

Wref

= Lv ,eq (16a)

And the corresponding coupling term for a resiliently mounted machine with the stiffness of the mountings given by km would follow from:

DC ,i

k m2 = 10 lg 2 Re{Yi } − 60 ω

Conclusions

For the last asepct a very first version of models was drafted and comments and ongoing research is welcomed to improve and extend that part in the near future.

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Acknowledgement

The author would like to acknowledge the discussions within the CEN working group responsible for the EN 12354 standards and the assistance of dr. Heinz-Martin Fisher (FTH-Stuttgart) and of dr. Michel Villot (CSTB-Grenoble) in organizing the structured session on prediction models in Building Acoustics at Forum Acusticum 2005.

(16b)

As an illustration figure 5 gives some data on the characteristic structure-borne sound power level of several sources, based on force and velocity measurements, directly or indirectly, and transferred by the appropriate relations just given.

References 140

[1] EN 12354:2000, Building Acoustics - Estimation of acoustic performance of buildings from the performance of elements1: Airborne sound insulation between rooms; 2: Impact sound insulation between rooms 3: Airborne sound insulation against outdoor noise 4: Transmission of indoor sound to the outside 6: Sound absorption in enclosed spaces, 2003.

drill; eq. D.2 130

automat; drying; eq. D.2 dishw asher; eq. D.2

LWsc [dB re 1 pW]

120

boiler; eq. D.2

110

f illing bath; eq. D.2 100

tapping machine; eq. D.3

[2] Draft-prEN 12354-5, Building Acoustics Estimation of acoustic performance of buildings from the performance of elements - Part 5: Sound levels due to service equipment in buildings, 2004.

lift machine, springs; eq. D.4

90

80

[3] Nightingale, T.R., I. Bosmans, Expressions for 1st order flanking paths in homogeneous isotropic and lightly damped buildings, Acta Acustica /Acustica 89 (2003)

70

60 31

63

125

250

500

1000 2000

frequency [Hz]

[4] Gerretsen, E., Using the structural reverberation time in standardizing laboratory measurements of the sound reduction index, Forum Acusticum 2002, Sevilla,

Figure 5: Examples of characteristic structure-borne sound power levels of some sources; derived from measurements of force or velocity.

[5] Gerretsen, E., Calculation of airborne and impact sound insulation between dwellings, Applied Acoustics 19 (1986), 245-264.

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[6] EN ISO 10848, Acoustics –Laboratory measurement of the flanking transmission of airborne and impact noise between adjoining rooms, Part 1…4, 2005

[22] Nightingale, T.R. e.a., On the distribution of transverse vibration in a periodic rib stiffened plate, Forum Acusticum Budapest, 2005. [23] Brunskog, J., Structural transmission loss in joistreinforced plate structures, Forum Acusticum Budapest, 2005.

[7] EN ISO 16032, Acoustics – Measurement of sound pressure level from service equipment in buildings – engineering method, 2003.

[24] Schoenwald, S. e.a., Propagation of structureborne sound in lightweight gypsum board walls, Forum Acusticum Budapest, 2005.

[8] VDI 2081, Sound production and reduction in ventilation systems, VDI, 2000. [9] ASHREA Handbook – Heating, ventilating and air-conditioning applications, chapter 47, Sound and vibration control, ASHREA, 2003

[25] Nightingale, T.R. e.a., On the importance of the direct field in structure-borne transmission in framed constructions, Forum Acusticum Budapest, 2005.

[10] ARI-Standard 885, Procedures for estimating occupied space sound levels in the application of air terminals and air outlets, 1998.

[26] Villot, M. e.a., Prediction method adapted to lightweight constructions and related laboratory characterizations, Forum Acusticum Budapest, 2005.

[11] Craik, R.J., Sound transmission through buildings using SEA, Gower Publishing Ltd, Hampshire, Vermont, 1996.

[27] Crispin, C. e.a., The vibration transmission loss at junctions including a column, Forum Acusticum Budapest, 2005.

[12] Moorhouse, A.T. & B.M. Gibbs, Relationship between the characteristic power of structureborne sound sources and their emission when installed, Proc. Euronoise ’98, Munich; 1998.

[28] Schreuder, M. e.a., Flanking transmission of masonry building elements with flexible interlayer, Forum Acusticum Budapest, 2005.

[13] ISO 3822, Acoustics- Laboratory test on noise emission from appliances and equipment used in water supply installations, Part 1…4, 1995-1997.

[29] Guigou-Carter, C. e.a., Analytical and experimental study of wood floorings, Forum Acusticum Budapest, 2005.

[14] EN 14366, Buildings Acoustics – Laboratory measurement of noise from wastewater installations, 2004.

[30] Simmons, C., Uncertainty of measured and calculated sound insulation in buildings - results of a round robin, Forum Acusticum Budapest, 2005.

[15] Gerretsen, E., Modelling structure-borne sound from equipment in buildings – current developments in EN 12354-5, ICA 2004, Kyoto [16] Späh, M. e.a, New laboratory for the measurements of structure-borne sound power of sanitary installations, Forum Acusticum Budapest, 2005. [17] Villot, M., Laboratory characterisation and field prediction of whirlpool bath noise, Forum Acusticum Budapest, 2005. [18] Alber, T. e.a., Approach to describe valves as sound sources for fluid- and structure-borne sound, Forum Acusticum Budapest, 2005. [19] Scheck, J. e.a., Approach for the characterisation of wooden staircases as structure-borne sound sources, Forum Acusticum Budapest, 2005. [20] Dechsler, A. e.a., Impact sound of lightweight stairs - actual results of a research program, Forum Acusticum Budapest, 2005. [21] Scholl, W., About a test facility for installation noise in wooden houses, Forum Acusticum Budapest, 2005.

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