COST FP0702 & TU0901 meeting, EMPA, November 2011

Revision of ISO Standards on field sound insulation testing

Carl Hopkins

• Editorial reasons

– Introduction of the new ISO 10140 series left the ISO 140 series of Standards with many gaps in the numbering system

– ISO 140 Parts 4, 7 and 14 were at their five year review point

– A need to improve the text, remove ambiguities in the English language versions, and make the text consistent in style with ISO 10140

Why revise the field testing Standards?

• Technical reasons

– National Building Regulations require repeatable and reproducible measurements

• To allow quick measurements on noisy building sites, acoustic consultants were interested in using manual scanning in an engineering method

(a) To reduce the equipment and cabling that is needed for field measurements

(b) To reduce measurement times

(c) To allow operators to be inside the receiving room to monitor the background noise

Note that ISO 140 Parts 4 and 7 do not specifically allow or forbid the presence of an operator in the room; hence clarification was needed

Why revise the field testing Standards?

• Technical reasons – In dwellings, many habitable rooms have small volumes

• Strong modal room responses typically occur in volumes < 25m3 where there are often less than five room modes below 100Hz

– Current measurement procedures are prone to poor repeatability and reproducibility at low frequencies

• ISO 140 Parts 4 and 7 have Informative Annexes giving ‘Guidance for measurements in low frequency bands’ which is sometimes impossible to satisfy in small room volumes

– The need for improved accuracy for measurements of sound insulation at low-frequencies in lightweight framed-buildings - highlighted in EU COST project FP0702

Why revise the field testing Standards?

Introduction of manual scanning

• Problem with walking and scanning is that it results in non-uniform scanning speeds and walking noise

Introduction of manual scanning

Two main types of scanning path were considered:

1) Paths which can be carried out from a standing position

– Ideal for furnished rooms with limited space to move

2) Paths which can be carried out by rotating the body about a fixed point

For sound fields with a known spatial correlation coefficient it is possible to calculate the efficacy of any manual scan with defined geometry by calculating an equivalent number of discrete, uncorrelated positions for each path, Neq

0.7 m

Introduction of manual scanning

Neq=5 Neq=5

Neq=5

Low-frequency measurements

• In typical rooms the spatial variation in the sound pressure level increases at low-frequencies which increases the uncertainty in the spatial-average sound pressure level

34m3 receiving room 29m3 source room

Low-frequency measurements Modal response in small rooms

18m3 receiving room 80Hz one-third octave band

• Many habitable rooms (particularly bedrooms) in dwellings and hotels have small volumes

• Strong modal room responses typically occur in volumes <25m3 where there are often less than five room modes below 100Hz

• Maximum differences between the lowest level in the central zone of the room and the highest level that is ≈0.5m from the room boundaries can be 17 – 28 dB

Low-frequency measurements SPL measurements in the central zone

• Normative part for 100–5000Hz requires minimum distances from boundaries > 0.5m

• ISO 140-4 Informative Annex D for the low-frequency range below 100Hz proposes minimum distances of 1.0 – 1.2m

• Problem: Central measurement zone occupies nodal planes at mid-height in the room hence sound insulation can be over- or under-estimated, and be irrelevant to occupants

Low-frequency measurements Incorporating corner positions

• Repeatability is improved by making use of additional microphone positions to sample sound pressure in the corners of rooms below 100Hz – Similar approach is used in ISO 10052 for

low-frequency noise measurements from service equipment in buildings

• Aim is to use the central zone SPL measurement and the corner SPL to estimate the average SPL for the entire room volume

• This can be achieved using an empirical weighting according to

-5

-4

-3

-2

-1

0

1

2

3

4

5

20 25 31 40 50 63 80 100

Err

or

(dB

)

One-third-octave frequency band (Hz)

Mean (Receiving Room)

95% limits (Receiving Room)

Mean (Source Room)

95% limits (Source Room)-5

-4

-3

-2

-1

0

1

2

3

4

5

20 31 50 80 125 200 315 500

No

rma

lize

d s

ou

nd

pre

ssu

re le

ve

l (d

B)

One-third-octave frequency band (Hz)

Mean (Receiving Room)

95% limits (Receiving Room)

Mean (Source Room)

95% limits (Source Room)

Low-frequency measurements Improvement due to corner positions

• For frequency bands with a mode count, N < 5 (typically below 100Hz)

– mean error is approximately 0dB when using the low-frequency method to estimate the average SPL over the entire room volume

– 95% confidence intervals for the low-frequency method are similar to those in the central zone for different sets of stationary microphone positions between 100 and 500 Hz measured according to ISO 140-4

29m3 Source room 18m3 Receiving room

Low-frequency measurements Improvement due to corner positions

39m3 Source room 34m3 Receiving room

-5

-4

-3

-2

-1

0

1

2

3

4

5

50 63 80 100 125 160 200 250 315 400 500

No

rma

lize

d s

ou

nd

pre

ssu

re le

ve

l (d

B)

One-third-octave frequency band (Hz)

Mean (Receiving Room)

95% limits (Receiving Room)

Mean (Source Room)

95% limits (Source Room)

-5

-4

-3

-2

-1

0

1

2

3

4

5

50 63 80 100

Err

or

(dB

)

One-third-octave frequency band (Hz)

Mean (Receiving Room)

95% limits (Receiving Room)

Mean (Source Room)

95% limits (Source Room)

• For frequency bands with a mode count, N < 5 (typically below 100Hz)

– mean error is approximately 0dB when using the low-frequency method to estimate the average SPL over the entire room volume

– 95% confidence intervals for the low-frequency method are similar to those in the central zone for different sets of stationary microphone positions between 100 and 500 Hz measured according to ISO 140-4

Low-frequency measurements Reverberation times

• Reverberation times can be difficult to measure accurately in one-third octave bands below 100Hz due to a lack of modes or because the decays are fast

– This results in signal processing errors primarily from the filtering or errors when evaluating decay curves

• Compared to heavyweight buildings, rooms in lightweight buildings often have short reverberation times in the low-frequency range

– Typically 0.3s < T < 0.8s for volumes of 20 – 60 m3

Low-frequency measurements Reverberation times

• 250 individual RT measurements using forward filter analysis with interrupted noise in unfurnished timber and steel frame buildings

One-third-octave band centre

frequency (Hz)

% satisfying BT > 8 criterion

Using individual decay curves

Using ensemble average decay curves

50 37 % 33 %

63 48 % 57 %

80 87 % 86 %

Octave band centre frequency (Hz)

% satisfying BT > 8 criterion

Using individual decay curves

Using ensemble average decay curves

63 98.8 % 100 %

Low-frequency measurements Implications

• Difference in the airborne sound insulation (DnT) using the low-frequency method instead of ISO 140-4

• 37 field tests in lightweight constructions

0

2

4

6

8

10

12

14

-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7

Nu

mb

er

Low-frequency method – ISO 140 (dB)

50Hz

63Hz

80Hz

Low-frequency measurements Implications

• Difference in the airborne sound insulation (DnT) using the low-frequency method instead of ISO 140-4

• 37 field tests in lightweight constructions

0

2

4

6

8

10

12

14

16

18

20

-4 -3 -2 -1 0 1 2 3 4

Nu

mb

er

Low-frequency method – ISO 140-4 (dB)

DnTw+C50-3150

DnTw+Ctr,50-3150

DnT,w+C50-3150

DnT,w+Ctr,50-3150

Impact sound insulation

• The rubber ball will be included as a normative option in ISO 16283-2 – Primarily for Japan and South

Korea

• If needed, National Standards can have a foreword to emphasize that National Regulations require use of the ISO tapping machine, or the ISO rubber ball, or both in their National Regulations

Summary

• Field sound insulation Standards are currently under revision

• Main changes proposed are

– Introduction of manual scanning

– New low-frequency measurement procedure for rooms <25m3 in the 50, 63 and 80Hz one-third octave bands

– Introduction of ISO Rubber ball (as well as the ISO tapping machine)

Timescales

• ISO 16283-1 : Airborne sound insulation – CD registration: 2011-03-09 – DIS registration: 2012-03-09 – FDIS registration: 2013-09-09 – Publication: 2014-03-09

• ISO 16283-2 : Impact sound insulation • ISO 16283-3 : Facade sound insulation

– CD registration: 2012-10-21 (indicative date) – DIS registration: 2013-10-21 – FDIS registration: 2015-04-21 – Publication: 2015-10-21