HERRING STORER ACOUSTICS Suite 34, 11 Preston Street, Como, W.A. 6152 P.O. Box 219, Como, W.A. 6952 (08) 9367 6200 Telephone: (08) 9474 2579 Facsimile: Email: hsa@hsacoustics.com.au Acoustics: Back to basics Fundamentals of Acoustics Presented by Tim Reynolds Fundamentals To Cover Common Noise Sources Some Basic Definitions Basic Terminology Criteria Noise Sources and Typical Examples Basic Noise Controls Noise Source Decibel Level dB(A) Jet Takeoff (100m) 130 Live rock band 120 Chain Saw 110 Lawn Mower 100 Diesel Truck, food blender 090 Dishwasher 080 Freeway Traffic at 15m 070 Conversation 060 Quiet Suburb 050 Library, living room 040 Quiet rural area 030 020 010 Threshold of hearing 000 Definitions Decibel (dB) The human ear has a vast sound-sensitivity range of a thousand billion to one. The decibel is a logarithmic unit that allows this range to be compressed into a somewhat more comprehensible range. The decibel is ten times the logarithm of the ratio of a sound level to a reference sound level. Decibel noise levels cannot be added arithmetically since they are logarithmic numbers. dB(lin) Decibel measurement without any adjustment. dB(A) Decibel measurement according to the "A" weighted scale. The human ear does not respond equally to the same sound pressure at different frequencies. The "A" weighting has predetermined adjustments made at certain frequencies to make the measured sound level approximate to the response of the ear. Leq Equivalent Continuous Sound Level. The Leq measurement integrates these fluctuations in noise to give the equivalent continuous level containing an equal amount of energy over the time of measurement. LA1 Represents the A-weighted noise level which is exceeded for 1 per cent of the measurement period. LA10 Represents the A-weighted noise level which is exceeded for 10 per cent of the measurement period. LA90 Represents the A-weighted noise level which is exceeded for 90 per cent of the measurement period. Also often used to represent background noise level. Sound Pressure Level (SPL) The sound pressure level is the noise level of a sound measured at a point using a standard noise level meter relative to a standard noise level (2x10-5 N/m2). Sound Power Level (SWL) The sound power level of a source is the sound energy emitted by the source. The sound power level of a source cannot be measured directly, but is calculated based on measured sound pressure levels at a known distance (10-12W). Noise level measurements can be broken down into Octave or 1/3 Octave Bands, with the following centre frequencies. Measurement 1 - Time History Noise Level LA10 Overall LAEq Overall LA90 Overall 64 62 60 58 54 52 50 48 46 44 42 Time (Sec) 59 57 55 53 51 49 47 45 43 41 39 37 35 33 31 29 27 25 23 21 19 17 15 13 11 9 7 5 3 40 1 SPL (dBA) 56 Measurement 2 - Time History Noise Level LA10 Overall LAEq Overall LA90 Overall 60 58 56 54 50 48 46 44 42 Time (Sec) 55 53 51 49 47 45 43 41 39 37 35 33 31 29 27 25 23 21 19 17 15 13 11 9 7 5 3 40 1 SPL (dBA) 52 CRITERIA Environmental Noise Environmental Protection (Noise) Regulations 1997 Internal Noise Levels AS/NZ 2107:2000 Acoustics - Recommended design sound levels and reverberation times for building interiors Others Building Code of Australia (BCA) – Part F5 GreenStar ENVIRONNEMENTAL PROTECTION (NOISE) REGULATIONS 1997 The allowable or assigned noise level at the surrounding locales is prescribed by the Environmental Protection (Noise) Regulations 1997. Baseline Assigned Outdoor Noise Level Premises Receiving Noise Time of Day Assigned Level (dB) LAma LA10 LA1 x Noise sensitive premises 0700 - 1900 hours Monday to Saturday (Day) 0900 - 1900 hours Sunday and Public Holidays (Sunday / Public Holiday Day) 1900 - 2200 hours all days (Evening) Commercial premises 2200 hours on any day to 0700 hours Monday to Saturday and 0900 hours Sunday and Public Holidays (Night) All hours 45 + IF 55 + IF 65 + IF 40 + IF 50 + IF 65 + IF 40 + IF 50 + IF 55 + IF 35 + IF 45 + IF 55 + IF 60 75 80 The influencing factor is calculated for the usage of land within two circles, having radii of 100m and 450m from the premises of concern. Penalties are also applied for annoying characteristics. • Tonality • Modulating • Impulsiveness Tonality 45.0 40.0 30.0 25.0 20.0 15.0 10.0 5.0 1/3rd Octave Band Centre Frequency (Hz) Penalties Where tonality is present Where modulation is present Where impulsiveness is present +5 dB(A) +5 dB(A) +10 dB(A) 10 kHz 8 kHz 6.3 kHz 5 kHz 4 kHz 3.15 kHz 2.5 kHz 2 kHz 1.6 kHz 1.25 kHz 1 kHz 800 Hz 630 Hz 500 Hz 400 Hz 315 Hz 250 Hz 200 Hz 160 Hz 125 Hz 100 Hz 80 Hz 63 Hz 50 Hz 40 Hz 31.5 Hz 25 Hz 0.0 dB(A) Noise Level (dB(A)) 35.0 AS/NZ 2107:2000 AS2107 has the following recommended noise levels within an office building: Boardrooms and conference rooms Corridors and Lobbies General Office Areas Private Offices Reception Areas Tea Rooms Toilets Satisfactory Maximum 30 dB(A) 45 dB(A) 40 dB(A) 35 dB(A) 40 dB(A) 40 dB(A) 50 dB(A) 40 dB(A) 55 dB(A) 45 dB(A) 40 dB(A) 45 dB(A) 45 dB(A) 55 dB(A) Other Criteria Used are Noise Ratings (NR) Curves NR CURVES 160 140 120 NR 20 NR 30 Noise Level (dB) 100 NR 40 NR 50 NR 60 80 NR 70 NR 80 NR 90 60 NR 100 NR 110 40 NR 120 NR 130 20 0 31.5 62.5 125 250 500 1000 Octave Band Centre Frequency (Hz) 2000 4000 8000 160 140 120 NR 20 NR 30 NR 40 Noise Level (dB) 100 NR 50 NR 60 NR 70 80 NR 80 NR 90 60 NR 100 NR 110 NR 120 40 NR 130 Return Air 20 0 31.5 62.5 125 250 500 1000 Octave Band Centre Frequency (Hz) 2000 4000 8000 GREENSTAR For Example, under Office Design there are point available for Acoustics. Under IEQ-12 there are up to two points available where it is demonstrated that for 95% of the project’s NLA does not exceed the ‘Satisfactory’ ambient internal noise levels in accordance with AS/NZS 2107:2000. One point is awarded for building services design, where within the entire base building general office space, noise from the building services does not exceed 40 dB(A) Leq. One point is awarded for the overall building, where within the base building office space, the sound level does not exceed 40 dB(A) Leq (assuming open plan offices). Building Code Of Australia Part F5 of the BCA 2013 'Sound Transmission and Insulation'. Part F5 of the BCA 2013 details the requirements for sound transmission and insulation of residential type buildings. It is noted that Part F5 of the BCA 2013 is only applicable to the residential sections of the development. Basic Criteria Walls between Apartments Walls to corridor Floors Rw + Ctr not less than 50 Rw not less than 50 Rw +Ctr not less than 50 ENVIRONMENTAL NOISE Typical Example of Exhaust Fan Being 67 dB(A) at 3 metres (This is Sound Power of 87 dB(A)) Neighbour at 50 metres away Reduction for distance is 24 dB(A) Noise level at residence is 43 dB(A) However, with penalty of +5 dB(A) for tonality, assessable noise level would be 48 dB(A). Say Influencing Factor was 1 dB(A), then assigned noise level would be : Premises Receiving Noise Noise sensitive premises Assigned Level (dB) Time of Day LA 10 LA 1 LA max 0700 - 1900 hours Monday to Saturday 46 56 66 0900 - 1900 hours Sunday and Public Holidays 41 51 66 1900 - 2200 hours all days 41 51 56 2200 hours on any day to 0700 hours Monday to Saturday and 0900 hours Sunday and Public Holidays 36 46 56 Noise emissions from mechanical services are : - Steady state - Would operate for more than 10% of time Assessable Noise Level, dB(A) 48 Applicable Assigned LA10 Noise Level (dB) Exceedance to Assigned Noise Level (dB) 0700 - 1900 hours Monday to Saturday 46 +2 0900 - 1900 hours Sunday and Public Holidays 41 +7 1900 - 2200 hours all days 2200 hours on any day to 0700 hours Monday to Saturday and 0900 hours Sunday and Public Holidays 41 +7 36 +12 Applicable Times of Day Possible Noise Control : • • • • • • Barrier Enclose in plantroom Reduce speed Located equipment further away from neighbours Attenuators Acoustic Louvres Noise Reductions with Unpodded Silencers SWL (Linear) SWL (dB(A) Level at residence With 1D unpodded Silencer With 2D unpodded Silencer 100.0 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 8K 4K 2K 1K 500 250 125 63 dB(A) 0.0 Noise Reductions with Acoustic Louvres SWL (Linear) SWL (dB(A) Level at residence With 300mm Acoustic Louvre With 600mm Acoustic Louvre 100.0 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 8K 4K 2K 1K 500 250 125 63 dB(A) 0.0 NOISE PATHS Also need to consider regenerated noise. INTERNAL DESIGN TO CONTROL NOISE Supply Air Bends Internal Insulation Acoustic Type Flexible Ductwork Add attenuators Also consider : Air velocity Design to registers INSERTION LOSS OF FLEXIBLE DUCT 300 Diameter, 3m length Plain Flex Acoustic Flex 35 30 Insertion Loss dB 25 20 15 10 5 Octave Band Centre Frequency (Hz) 8K 4K 2K 1K 500 250 125 63 0 Noise Reductions with Flexible Duct SWL (Linear) SWL (dB(A) With Plain Flexible Duct With Acoustic Flexible Duct 95.0 90.0 85.0 80.0 75.0 70.0 65.0 60.0 55.0 50.0 45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 8K 4K 2K 1K 500 250 125 63 dB(A) 0.0 RETURN AIR Bends without Turning Vanes Return Air plenums Add attenuators Noise Reductions - Bends SWL (Linear) SWL (dB(A) With Turning Vanes Without Turning Vanes 8K 4K 2K 1K 500 250 125 63 dB(A) 95.0 90.0 85.0 80.0 75.0 70.0 65.0 60.0 55.0 50.0 45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.0 Breakout Need to consider : From flexible connections Flexible ductwork Also need to consider Regenerated Noise From Fantech Web Site