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Useful
Information For Soundproofing
Noise
pollution is not easily defined. Part of the difficulty lies
in the fact that in some ways it is different from other
forms of pollution.
Understanding
Frequency & Acoustic Performance information
125hz
Low
Frequency (eg.bass sound from a speaker)
250hz
Low
Frequency (eg.bass sound associated with beat noise)
500hz
Low/Mid
Frequency (e.g sound of a car door closing)
1k
Mid
Frequency (e.g vocal noise)
2k
Mid/High
Frequency (e.g. vocal noise)
4k
High
Frequency (e.g. screaming)
Terminology
used in sound proofing:
Acoustic
barrier
Solid
walls or partitions, solid fences, earth mounds, earth berms,
buildings, etc used to reduce noise, without eliminating it.
Air-borne
noise
This
refers to noise which is fundamentally transmitted by way of
the air and can be attenuated by the use of barriers and walls
placed physically between the noise and receiver.
Ambient
sound
The
totally encompassing sound in a given situation at a given
time, usually composed of sound from all sources near and far.
Assessment
period
The
period in a day over which assessments are made.
Assessment
point
A
point at which noise measurements are taken or estimated.
Audible
range
The
limits of frequency which are audible or heard as sound. The
normal ear in young adults detects sound having frequencies
in the region 20 Hz to 20 kHz, although it is possible for
some people to detect frequencies outside these limits.
Background
noise
Background
noise is the term used to describe the noise measured in the
absence of the noise under investigation. It is described as
the average of the minimum noise levels measured on a sound
level meter and is measured statistically as the A-weighted
noise level exceeded for ninety percent of a sample period.
This is represented as the L90 noise level (see below).
Barrier
See "Acoustic
barrier", a solid object used to attenuate sound.
Character,
acoustic
The
total of the qualities making up the individuality of the noise.
The pitch or shape of a sound's frequency content (spectrum)
dictate a sound's character.
Decibel
[dB]
The
level of noise is measured objectively using a Sound Level
Meter. This instrument has been specifically developed to mimic
the operation of the human ear. The human ear responds to minute
pressure variations in the air. These pressure variations can
be likened to the ripples on the surface of water but of course
cannot be seen. The pressure variations in the air cause the
eardrum to vibrate and this is heard as sound in the brain.
The stronger the pressure variations, the louder the sound
is heard.
The
range of pressure variations associated with everyday living
may span over a range of a million to one. On the top range
may be the sound of a jet engine and on the bottom of the
range may be the sound of a pin dropping.
Instead
of expressing pressure in units ranging from a million
to one, it is found convenient to condense this range to
a scale 0 to 120 and give it the units of decibels. The
following are examples of the decibel readings of every
day sounds;
dB(A):
A-weighted decibels
The
ear is not as effective in hearing low frequency sounds as
it is hearing high frequency sounds. That is, low frequency
sounds of the same dB level are not heard as loud as high frequency
sounds. The sound level meter replicates the human response
of the ear by using an electronic filter which is called the "A" filter.
A sound level measured with this filter switched on is denoted
as dB(A). Practically all noise is measured using the A filter.
The sound pressure level in dB(A) gives a close indication
of the subjective loudness of the noise.
Diffraction
The
distortion around solid obstacles of waves traveling past.
Fluctuating
noise
Noise
that varies continuously and to an appreciable extent over
the period of observation. It can also include intermittent
noise. As a guide, when the level varies noticeably by more
than 5 dB over a period of less than one minute, the noise
is considered to be fluctuating.
Frequency
Frequency
is synonymous to pitch. Sounds have a pitch which is peculiar
to the nature of the sound generator. For example, the sound
of a tiny bell has a high pitch and the sound of a bass drum
has a low pitch. Frequency or pitch can be measured on a scale
in units of Hertz or Hz.
Heavy
vehicle
Heavy
vehicles are assumed to be buses, rigid trucks and semi trailer
trucks with a tare weight greater than 3 tonnes. Also heavy
vehicles can be defined in terms of length as buses, or trucks
with a length exceeding 5.25 meters.
Impulsive
noise
Having
a high peak of short duration or a sequence of such peaks.
A sequence of impulses in rapid succession is termed repetitive
impulsive noise.
Intermittent
noise
The
level suddenly drops to that of the background noise several
times during the period of observation. The time during which
the noise remains at levels different from that of the ambient
is one second or more.
Lnn
noise descriptors
Because
noise varies with time, a single noise value cannot adequately
define the noise ambient. For this reason, the acoustic environment
is described using a number of noise level descriptors as follows;
L1
The
sound pressure level that is exceeded for 1% of the time for
which the given sound is measured.
L10
The
sound pressure level that is exceeded for 10% of the time for
which the given sound is measured.
L10(18hr)
The
arithmetic average of the L10(1hr) levels for the 18 hour period
between 6am and 12 midnight on a normal working day. It was
a common traffic noise descriptor. For traffic noise it is
usually about 3dB(A) higher than Leq (24 hours).
L90
The
level of noise exceeded for 90% of the time. The bottom 10%
of the sample is the L90 noise level expressed in units of
dB(A).
Leq
Equivalent
sound pressure level - the steady sound level that, over a
specified period of time, would produce the same energy equivalence
as the fluctuating sound level actually occurring.
Leq(1hr)
The
Leq noise level for a specific one-hour period.
Leq(8hr)
The
continuous noise level during any one hour period between 10pm
and 6am.
Leq(9hr)
The
Leq noise level for the period 10pm to 7am.
Leq(15hr)
The
Leq noise level for the period 7am to 10pm.
Leq
(24hr)
The
equivalent continuous noise level during a 24 hour period,
usually from midnight to midnight.
Loudness
A
rise of 10 dB in sound level corresponds approximately to a
doubling of subjective loudness. That is, a sound of 85 dB
is twice as loud as a sound of 75 dB which is twice as loud
as a sound of 65 dB and so on. That is, the sound of 85 dB
is 400% times the loudness of a sound of 65 dB.
Low-frequency
noise
Containing
major components within the low frequency range (20Hz - 250Hz)
of the frequency spectrum.
Nature,
acoustic
The
innate or essential quality of the noise. That which makes
one noise distinguishable from another (e.g. the spoken voice
from the sound of a dog barking, a telephone ringing from the
sound of a gun).
Reflection
Sound
wave changed in direction of propagation due to a solid object
obscuring its path.
Sound
absorption
The
ability of a material to absorb sound energy through its conversion
into thermal energy.
Sound
level meter
An
instrument consisting of a microphone, amplifier and indicating
device, having a declared performance and designed to measure
sound pressure levels.
Sound
pressure level
The
level of noise, usually expressed in decibels, as measured
by a standard sound level meter with a microphone.
Sound
power level
Ten
times the logarithm to the base 10 of the ratio of the sound
power of the source to the reference sound power.
STC
Sound
Transmission Class. This is a measure of the extent of sound
reduction of noise going through a building element, presented
as a rating or class. It denotes the sound attenuation properties
of walls, floors and ceilings used to construct building spaces.
The higher the STC the better the sound reducing performance
of the construction.
Structure-borne
noise
This
refers to noise which is generated by vibrations induced in
the ground and/or structure. These vibrations excite walls
and slabs in buildings and cause them to radiate noise. This
type of noise can not be attenuated by barriers or walls but
requires the interposition of a resilient (neoprene, springs
etc.) break between the source and the receiver.
Tonal
noise
Containing
a prominent frequency and characterized by a definite pitch.
Products
DFB - Dense Fibre Block
Dense Fibre Block, is a type of mineral glass wool fiber products, it can be used in many applications for soundproofing. Please be aware that the lower the density of this product the less effective in soundproofing and the more effective in heat retention. Anything under 80kg density is not recomended.
Acoustic Wall Panels
Used
directly surface-mounted to wall or ideally in conjunction
with DFB
Acoustic Ceiling Panels
Used
directly surface-mounted to ceiling or ideally in conjunction
with DFB
NSSS Noise
Stop Systems Singapore
NoiseStop Systems is the generic name given to a certain
range of product