Upload
dokhuong
View
224
Download
1
Embed Size (px)
Citation preview
ACOUSTICS PRESENTATION
OWNERS CORPORATION NETWORK SEMINAR
What is Sound ?
Sound is vibration is air or materials (ie a buildings structure).
Sound is a cyclic change of pressure.
The amount the pressure fluctuates determines the loudness of the sound.
Sound propagates through the air, liquids or solids as waves, similar to a stone dropped in a pool of water. Naturally we cannot see these waves, but our ears sense the change in air pressure and we are able to perceive these as sound having loudness and a pitch.
Loudness Scales
Human hearing does not perceive the loudness of low frequency sound evenly across the range of human hearing.
Loudness of the sound in terms of a number output ‐ complex relationship between loudness/frequency/human perception.
Weighting scales to convert the loudness and frequency measured by a sound level meter into a single number rating. The most common is dB(A) or A‐weighted level.
Structure Borne Noise
The structure is directly vibrated and the vibration is transmitted through the structure in all directions where this energy vibrates a surface in an space. The surface radiates the vibration as audible noise in the same way that a loudspeaker cone converts movement of the cone to audible sound.
Examples:Railway vibration, plant vibration, Demolition activitiesImpact noise, or foot fall noise.
Airborne Noise
Sound that is transmitted via the air. Sound generated in one room reaches the wall or floor, vibrates that surface and then is re‐radiated by the surface on the other side of the wall or floor to the adjacent room.
Examples:TV’s and musicPeople talking
Rating Walls and Floors for Sound Transmission
Impact Noise RatingIIC – Measure of hard floor impact isolation. IIC 35 bare concrete, IIC 50‐55 tile or timber floor with underlay, IIC 75 carpet.Lntw + C1 – Impact noise level used in current BCA. 75 ‐ bare concrete, 55‐60 tile or timber floor with underlay, 45 carpet
Airborne Noise RatingSound Transmission Class (STC) (USA standard) – Old BCA criteria and some councils (ie Sydney City Couuncil).RW ‐Weighted Sound Reduction Index (ISO standard) – Similar to STC –Used in current BCACtr – Traffic noise spectrum adaptation term – used in current BCA to correlate partition performance to low frequency noise sources such as home theatre.
Floor Requirements –Minimum Criteria
Descriptor
Legislation Sound TransmissionAir Borne noise
Impact RequirementStructure Borne Nosie
BCA Rw + Ctr 50 Ln,w + C1 < 62
Strata Management Schemes Act Refers to the BCA IIC 50
Sydney City Council FSTC 50-55 IIC 50
Body Corporate Crieria As detailed in By-Laws
As detailed in By-Laws
Typical floor constructions
5mm Vibramat or equipment
150mm thick concrete slab
Ceramic tile flooring. Screed.
Stop wall and floor tiles 2-3mm short of edges and fill with resilient caulking compound
Wall.
Vibra pad150mm thick concrete slab
Strip timber flooring.
Stop floor 5mm short of edges and fill with resilient caulking compound.
Skirting board 2-3mm above floor
Timber Battens
Wall.
5mm Vibramat or similar
150mm thick concrete slab
Floating timber floor
Stop floor 2-3mm short of edges and fill with resilient caulkingcompound
Skirting board 2-3mm above floor
Wall.
Testing Walls and Floors for Sound Transmission
Tapping Testing
Noise is generated by placing a standardised “tapping machine” on the floor and measuring the sound pressure levels are measured in the room under at several different frequencies. The sound levels are corrected to account for the acoustical properties of the receiving room.
Tapping machine
Flooring system
Main Factors Affecting Impact Noise Performance
Mass of floor‐ This may be an issue for older buildings with light weight constructions (ie timber framed buildings).
Flanking paths – eg load bearing walls. Apparent performance of underlays in load bearing structure less than non‐load bearing.
Type of underlay used. Generally the softer the underlay the better the performance but this is limited by effect of entrained air and the need to maintain a solid substrate for tiles.
Installation errors such as nails through underlay, bridging of the perimeter gap, incorrect underlay etc.
Criteria –Issues with By‐Laws
By‐Laws of buildings can specify a criteria over and above BCA or council DCP requirements. These criteria may in event render hard floorsimpractical as compliance is impossible, ie
Timber floor with a rating of IIC 55‐60 or greaterTiled floors with a IIC of 55 or greater
Some buildings By‐Laws indicate that replacing carpet floors with a hard floor finish is not possible. An acoustic engineer can not help with this issue!
Installing a hard floor in lieu of carpet, even with acoustic underlay, will not result is a similar performance to carpet.
Some buildings By‐Laws will require an acoustic report prior to installation and/or testing on completion of the hard floor.
Hard Floors ‐ Tenant Activities‐ Expectations
A tenants use of their apartment will contribute to the noise impact to the neighbour below especially where had floors have been installed. That is an ‘extraneous’ activity will generate a noise level which is likely to cause complaints below, ie
Scraping of chairs and tables over hard floors.Children playing with balls, marbles, running, remote controlled cars etc.
Designated hard floor treatments will not mitigate noise from extraneous events.
Installing a hard floor in lieu of carpet, even with acoustic underlay, will not result is a similar performance to carpet.
Noise generated from hard floors is one of the greatest sources of complaint within residential apartments…..
T H E E N D