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Sep 24, 2023 279 likes •436 views

Airborne sound transmission across a hybrid heavyweight-lightweight timber floor: Initial modelling using Statistical Energy Analysis Claire Churchill, EMPA, Switzerland Carl Hopkins, University of Liverpool, UK Lubo Kraji, EMPA, Switzerland

SLIDE 1

Airborne sound transmission across a hybrid heavyweight-lightweight timber floor: Initial modelling using Statistical Energy Analysis

Claire Churchill, EMPA, Switzerland Carl Hopkins, University of Liverpool, UK Luboš Krajči, EMPA, Switzerland

SLIDE 2

Background

 In most European countries, timber floor

constructions are built from lightweight components such as timber and plasterboard

 In Switzerland and Canada, there are

hybrid lightweight-heavyweight floors which combine lightweight components with heavyweight components – a concrete base and a screed floating floor

 In Switzerland these are built in the factory

and transported to site

SLIDE 3

Aims

 For these hybrid floors it would be

beneficial to have a prediction model to determine the direct and flanking transmission in-situ

 The first stage in the research which

is reported in this presentation was to compare laboratory measurements of the airborne sound insulation with a prediction model based on Statistical Energy Analysis (SEA)

SLIDE 4

Hybrid lightweight-heavyweight timber floor

80mm mineral wool Suspended plasterboard ceiling using resilient hangars 260mm timber beams 70mm concrete on 12mm OSB

SLIDE 5

Airborne sound insulation:

Comparison of a basic timber joist floor with the hybrid lightweight-heavyweight timber floor

10 20 30 40 50 60 70 80 90 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000

Sound reduction index (dB) One-third-octave-band centre frequency (Hz) Hybrid lightweight-heavyweight floor Timber joist floor

SLIDE 6

SEA model for airborne sound insulation (Vertical transmission suite)

1.Source Room Win(1) Wd(1) 3.Cavities Wd(3) Non-resonant transmission Wd(2) 2.Concrete/ OSB 5.Receiving Room Wd(5) Wd(4) 4.Plasterboard 6.Joists Wd(6) Non-resonant transmission

70mm concrete on 12mm OSB 80mm mineral wool 260mm timber beams Suspended plasterboard ceiling using resilient hangars

SLIDE 7

SEA model – Simplifying assumptions

70mm concrete on 12mm OSB 80mm mineral wool 260mm timber beams Suspended plasterboard ceiling using resilient hangars



The screw and metal strip connections from the concrete/OSB into the beams can be modelled as rigid point connections from a composite plate representing the concrete and the OSB acting as a single plate



The mineral wool has negligible effect on the one-dimensional and two- dimensional sound fields in the cavity



The errors incurred in predicting the three-dimensional sound field in a cavity with one highly absorbent surface are negligible due to the strength of the structural transmission paths

SLIDE 8

SEA model – Inclusion of measured data

 Some properties of the floor

components were considered too complex to model in the early stages of the work

 Resilient hangars used for

the suspended ceiling

 52 connectors

 Reverberation times in the

floor cavities



The approach taken was to include measured data in the SEA model where needed and consider new theoretical models at a later stage

SLIDE 9

Measurement of the coupling loss factor between beams and plasterboard across the resilient hangars

 Laboratory mock-up  Excitation: Shaker on one

beam

 Response: Vibration levels

n beam (subsystem i) and

plasterboard (subsystem j)

 Coupling loss factor

estimated using

SLIDE 10

Excitation for 1D sound fields



Only axial modes exist at frequencies below 500Hz

 Loudspeaker was located at one end of

the cavity

 Decays were measured using MLS and

reverse-filter analysis with 4 microphone positions Excitation for 1D, 2D and 3D sound fields



At and above 500Hz there are axial, and tangential modes



At and above 800Hz there are axial, tangential and oblique modes

 Small loudspeaker was placed inside

the cavity

 Two source positions and four

microphone positions for each source postion

Measurement of the cavity reverberation time using a laboratory mock-up

SLIDE 11

Mode count in the cavity

2 4 6 8 10 12 14 16 50 63 80 100 125 160 200 250 315 400 500 630 800

Number of modes Third octave band centre frequency (Hz)

N (1D) N (2D) N (3D)

SLIDE 12

Measurements: Cavity reverberation time

0.1 0.2 0.3 0.4 0.5 0.6 0.7 50 500 5000

Reverberation time (s)

One-third octave band centre frequency (Hz)

Small speaker in cavity Large loudspeaker at one end



Very short reverberation times, on the verge of not being measurable in the low-frequencies even when using reverse-filter analysis



Reverberation times were used to calculate the total loss factors for the cavity

SLIDE 13

10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170

50 80 125 200 315 500 800 1250 2000 3150 5000

Sound reduction index (dB) One-third-octave-band centre frequency (Hz)

20 50 80 40 70 10 30 60

Measured SEA matrix solution

(1D sound field in cavity)

SEA matrix solution

(2D/3D sound field in cavity) 135 1345 1235 12345 12645

SEA transmission paths dotted lines = 1D sound field in cavity solid lines = 2D/3D sound field in cavity

Subsystem 1: Source room Subsystem 5: Receive room Subsystem 3: Cavity Subsystem 2: Chipboard Subsystem 6: Joist Subsystem 4: Plasterboard

10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240

50 80 125 200 315 500 800 1250 2000 3150 5000

Sound reduction index (dB) One-third-octave-band centre frequency (Hz)

20 50 80 40 70 10 30 60

Measured SEA matrix solution

(1D sound field in cavity)

SEA matrix solution

(2D/3D sound field in cavity) 135 1345 1235 12345 12645

SEA transmission paths dotted lines = 1D sound field in cavity solid lines = 2D/3D sound field in cavity

Subsystem 1: Source room Subsystem 5: Receive room Subsystem 3: Cavity Subsystem 6: Joist Subsystem 4: Plasterboard Subsystem 2: Concrete/OSB

100 110 120

SLIDE 14

Conclusions



Basic timber joist floor

 Good agreement between measurements and SEA in the frequency range

100Hz to 5kHz



Hybrid lightweight-heavyweight timber floor

 Good agreement between measurements and SEA up to 200Hz  SEA overestimates the sound transmission by approx. 10dB between 250Hz

and 5kHz

 Problem lies in modelling the coupling between the concrete/OSB and the beams

Airborne sound transmission across a hybrid heavyweight-lightweight timber floor: Initial modelling using Statistical Energy Analysis

Claire Churchill, EMPA, Switzerland Carl Hopkins, University of Liverpool, UK Luboš Krajči, EMPA, Switzerland

Background

 In most European countries, timber floor

constructions are built from lightweight components such as timber and plasterboard

 In Switzerland and Canada, there are

hybrid lightweight-heavyweight floors which combine lightweight components with heavyweight components – a concrete base and a screed floating floor

 In Switzerland these are built in the factory

and transported to site

Aims

 For these hybrid floors it would be

beneficial to have a prediction model to determine the direct and flanking transmission in-situ

 The first stage in the research which

is reported in this presentation was to compare laboratory measurements of the airborne sound insulation with a prediction model based on Statistical Energy Analysis (SEA)

Hybrid lightweight-heavyweight timber floor

80mm mineral wool Suspended plasterboard ceiling using resilient hangars 260mm timber beams 70mm concrete on 12mm OSB

Airborne sound insulation:

Comparison of a basic timber joist floor with the hybrid lightweight-heavyweight timber floor

Sound reduction index (dB) One-third-octave-band centre frequency (Hz) Hybrid lightweight-heavyweight floor Timber joist floor

SEA model for airborne sound insulation (Vertical transmission suite)

SEA model – Simplifying assumptions



The screw and metal strip connections from the concrete/OSB into the beams can be modelled as rigid point connections from a composite plate representing the concrete and the OSB acting as a single plate



The mineral wool has negligible effect on the one-dimensional and two- dimensional sound fields in the cavity



The errors incurred in predicting the three-dimensional sound field in a cavity with one highly absorbent surface are negligible due to the strength of the structural transmission paths

SEA model – Inclusion of measured data

 Some properties of the floor

components were considered too complex to model in the early stages of the work

 Resilient hangars used for

the suspended ceiling

 Reverberation times in the

floor cavities



The approach taken was to include measured data in the SEA model where needed and consider new theoretical models at a later stage

Measurement of the coupling loss factor between beams and plasterboard across the resilient hangars

 Laboratory mock-up  Excitation: Shaker on one

beam

 Response: Vibration levels

plasterboard (subsystem j)

 Coupling loss factor

estimated using

Excitation for 1D sound fields

Only axial modes exist at frequencies below 500Hz

the cavity

reverse-filter analysis with 4 microphone positions Excitation for 1D, 2D and 3D sound fields

At and above 500Hz there are axial, and tangential modes

At and above 800Hz there are axial, tangential and oblique modes

the cavity

microphone positions for each source postion

Measurement of the cavity reverberation time using a laboratory mock-up

Mode count in the cavity

2 4 6 8 10 12 14 16 50 63 80 100 125 160 200 250 315 400 500 630 800

Number of modes Third octave band centre frequency (Hz)

N (1D) N (2D) N (3D)

Measurements: Cavity reverberation time

0.1 0.2 0.3 0.4 0.5 0.6 0.7 50 500 5000

Reverberation time (s)

One-third octave band centre frequency (Hz)

Small speaker in cavity Large loudspeaker at one end

Very short reverberation times, on the verge of not being measurable in the low-frequencies even when using reverse-filter analysis

Reverberation times were used to calculate the total loss factors for the cavity

Conclusions



Basic timber joist floor

100Hz to 5kHz



Hybrid lightweight-heavyweight timber floor

and 5kHz



Future work

connections between the concrete/OSB and the beams

hangars

stiffness