Revision of ISO Standards on field sound insulation testing. Carl Hopkins

Transcription

1 Revision of ISO Standards on field sound insulation testing Carl Hopkins COST FP0702 & TU0901 meeting, EMPA, November 2011

2 Why revise the field testing Standards? Editorial reasons Introduction of the new ISO 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

3 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

4 Why revise the field testing Standards? Technical reasons In dwellings, many habitable rooms have small volumes Strong modal room responses typically occur in volumes < 25m 3 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

5 Introduction of manual scanning Problem with walking and scanning is that it results in non-uniform scanning speeds and walking noise

6 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 0.7 m 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, N eq

7 Introduction of manual scanning N eq =5 N eq =5 N eq =5

8 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 29m 3 source room 34m 3 receiving room

9 Low-frequency measurements Modal response in small rooms Many habitable rooms (particularly bedrooms) in dwellings and hotels have small volumes Strong modal room responses typically occur in volumes <25m 3 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 db 18m 3 receiving room 80Hz one-third octave band

10 Low-frequency measurements SPL measurements in the central zone 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 Normative part for Hz requires minimum distances from boundaries > 0.5m ISO Informative Annex D for the lowfrequency range below 100Hz proposes minimum distances of m

11 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 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

12 Normalized sound pressure level (db) Error (db) 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 One-third-octave frequency band (Hz) 29m 3 Source room 18m 3 Receiving room Mean (Receiving 95% limits (Receiving Mean (Source 95% limits (Source One-third-octave frequency band (Hz) Mean (Receiving 95% limits (Receiving Mean (Source 95% limits (Source

13 Low-frequency measurements Improvement due to corner positions Normalized sound pressure level (db) Error (db) 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 m 3 Source room 34m 3 Receiving room Mean (Receiving Mean (Receiving % limits (Receiving % limits (Receiving Mean (Source Mean (Source % limits (Source % limits (Source One-third-octave frequency band (Hz) One-third-octave frequency band (Hz)

14 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 m 3

15 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 % 33 % % 57 % % 86 % Octave band centre frequency (Hz) % satisfying BT > 8 criterion Using individual decay curves Using ensemble average decay curves % 100 %

16 Number Low-frequency measurements Implications Difference in the airborne sound insulation (D nt ) using the low-frequency method instead of ISO field tests in lightweight constructions Hz 63Hz 80Hz Low-frequency method ISO 140 (db)

17 Number Low-frequency measurements Implications Difference in the airborne sound insulation (D nt ) using the low-frequency method instead of ISO field tests in lightweight constructions Low-frequency method ISO (db) D nt,w +C DnTw+C D nt,w +C tr, DnTw+Ctr,

18 Impact sound insulation The rubber ball will be included as a normative option in ISO 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

19 Summary Field sound insulation Standards are currently under revision Main changes proposed are Introduction of manual scanning New low-frequency measurement procedure for rooms <25m 3 in the 50, 63 and 80Hz one-third octave bands Introduction of ISO Rubber ball (as well as the ISO tapping machine)

20 Timescales ISO : Airborne sound insulation CD registration: DIS registration: FDIS registration: Publication: ISO : Impact sound insulation ISO : Facade sound insulation CD registration: (indicative date) DIS registration: FDIS registration: Publication: