Provides basic characteristics of ambient noise

1. AMBIENT NOISE
R.Narasimha Swamy
Senior consultant
narasimhaswamy@yahoo.com

2. Contents
• Basic characteristics
• Quantification
• Standard representation of noise
• Noise Rating curve [NRC]
• Room Criteria [RC]
• Standard Transmission Class [STC]

3. Motivation
• To introduce the basic concepts, importance and
causes of noise, vibration and harshness
engineering practices (NVH) and solution for its
mitigation as applicable to Sound recording and
Broadcasting Studios.
• Demonstrate methods for the control of noise and
vibration to help its reduction, if not total
elimination.
• Indicate methods by which the designer can
control vibration and noise to create an equitable
environment.

4. What is noise?
• Unpleasant, unwanted, disturbing sound is
generally considered as noise that produces
purely subjective feeling.

5. Nature
• Noise is, to a great extent, a purely subjective
personal phenomena.
• Noise does, however, have two basic
characteristics.
– Physical phenomenon which can be measured,
quantified, specified and used as a proof of initiating
the measures for improvement.
– Psycho acoustical characteristic which attempts to
judge the effect of noise on human beings.

6. Amplitude(dB)
A1
f1 Frequency (Hz)
Characteristics
 Mainly because of noise generated by reciprocating and rotating
machinery, human activities etc.
 Characterized by random and complex temporal and spectrum
components.
No discrete tones, but consists of broad band of frequency components.
 Their strength is normally expressed in frequency bands i.e octaves or
some times in 1/3 of it, for standard comparison.

7. Noise measurement
• Quantifies the noise in the standard and
objective technical parameters for comparison.
• Permit precise, scientific analysis and efforts in
understanding the nature of noise.
• Helps in noise reduction measures for class
rooms, Recording studios, auditorium, airports,
hospitals, highways, etc.
• Helps in estimation of damage to hearing.

10. Quantifying noise [1/2]
• The method used to quantify environmental noise that
closely reflects the human auditory perception to
frequencies is called "A" weighting. The noise
measured with such weighting is called the A-weighted
noise level (dBA).
• To describe the time-varying character of
environmental noise, the statistical noise descriptors,
L01, L10, L50, and L90, are commonly used. They are
the A-weighted noise levels equalled or exceeded
during 1, 10, 50, and 90 percent of a stated time
period.
• The Leq the average A-weighted noise level during a
stated period of time that generates equivalent
acoustical energy to the time varying ambient levels.

11. Quantifying noise [2/2]
• DNL, Ldn are the average A-weighted noise level during a
24-hour day, obtained after addition of 10 decibels to
levels measured in the night between 10:00 pm and
7:00 am.
• Lmax, Lmin are the maximum and minimum A-weighted
noise level during the measurement period.
• CNEL – Community noise equivalent level is the 24-
hour, A-weighted average noise level from midnight to
midnight, obtained after the addition of five dBs to
sound levels occurring in the evening from 7-10PM and
after the addition of 10 dBs to sound levels occurring
in the night time between 10PM -7AM.

12. Weighting Characteristics
A-weighting: 40Phon equal loudness level contour
C-weighting: 90Phon equal loudness level contour
D-weighting for Aircraft Noise

14. Octave Filters

15. Noise Rating curves [NR]
• The NR curves are developed by the ISO to
determine the acceptable noise in indoor
environment for hearing preservation, speech
communication and annoyance.
• The NR curves are originally produced to develop a
procedure to determine whether noise from factories
heard in adjacent apartments and houses is
acceptable.
• In US, similar rating is done using NC (noise
criterion) curves. NC-25 is approximately 30 dBA
and NR-25 is 35 dBA.

17. NR curve Application
NR 25
Concert halls, broadcasting and recording
studios, churches
NR 30
Private dwellings, hospitals, theatres, cinemas,
conference rooms
NR 35
Libraries, museums, court rooms, schools,
hospitals operating theaters and wards, flats,
hotels, executive offices
NR 40
Halls, corridors, cloakrooms, restaurants, night
clubs, offices, shops
NR 45
Department stores, supermarkets, canteens,
general offices
NR 50 Typing pools, offices with business machines
NR 60 Light engineering works
NR 70 Foundries, heavy engineering works

18. Room criteria [RC]
• RC - measures the background noise in a building over
the frequency range 16 Hz to 4000 Hz.
• This rating system requires determination of the mid-
frequency average level and determining the perceived
balance between high and low frequency sound.
• NC curves are not defined in LF range (16 and 31.5 Hz
octave bands) and are also generally regarded as
allowing too much noise in the HF region (>= 2kHz).
• Defined for NC frequencies plus extremely low
frequencies (~16 and 31.5 Hz). RC is fast replacing NC
curves.

19. Room criteria (RC) curves are similar to NC curves in
that provide a rating for SPL in indoor environments.
Steps to determine RC rating are as follows: -
1)Plot the octave-band sound-pressure levels on the RC
chart.
2) Determine the speech interference level = arithmetic
average of the sound pressure levels in the 500, 1k and 2K
octave bands.
Perceptible vibration : The sound level in the octave
bands between 16 Hz and 63 Hz regions (A and B).
Region A: High probability that noise-induced vibration
levels in lightweight wall and ceiling constructions.
Anticipate audible rattles in light fixtures, doors, windows.
Region B: Noise-induced vibration levels in lightweight wall
and ceiling constructions may be felt. Slight possibility of
rattles in light fixtures, doors, windows.
Room Criteria Curves

20. Type of Room - Space Type Recommended RC Level, RC Curve Equivalent Sound Level, dBA
Apartments 25-35 (N)1) 35-45
Assembly Halls 25-30 (N) 35-40
Churches 30-35 (N) 40-45
Courtrooms 30-40 (N) 40-50
Factories 40-65 (N) 50-75
Hotels/Motels
- Individual rooms or suites 30-35 (N) 35-45
- Meeting or banquet rooms 25-35 (N) 35-45
- Service and Support Areas 40-45 (N) 45-50
- Halls, corridors, lobbies 35-40 (N) 50-55
- Conference rooms 25-30 (N) 35-40
- Private 30-35 (N) 40-45
- Open-plan areas 35-40 (N) 45-50
- Business machines/computers 40-45 (N) 50-55
Hospitals and Clinics
- Private rooms 25-30 (N) 35-40
- Operating rooms 25-30 (N) 35-40
- Wards 30-35 (N) 40-45
- Laboratories 35-40 (N) 45-50
- Corridors 30-35 (N) 40-45
- Public areas 35-40 (N) 45-50
- Lecture and classrooms 25-30 (N) 35-40
- Open-plan classrooms 30-40 (N) 45-50
Movie motion picture theaters 30-35 (N) 40-45
Libraries 35-40 (N) 40-50
Legitimate theaters 20-25 (N) 30-65
Private Residences 25-35 (N) 35-45
Restaurants 40-45 (N) 50-55
TV Broadcast studies 15-25 (N) 25-35
Recording Studios 15-20 (N) 25-30
Concert and recital halls 15-20 (N) 25-30
Sport Coliseums 45-55 (N) 55-65
Recording studios 15-20 (N) 25-30

21. Sound transmission class [STC]

22. Sound Transmission
Barriers reduce sound transmission to reduce noise intrusion

23. Sound transmission class
• Sound Transmission Class (STC) is an integer rating to indicate
how well the building partition attenuates the airborne noise in the
band of 125 to 4000 Hz. It is widely used to rate the interior
partitions, ceilings/floors, doors, windows and exterior wall
configurations.
• STC is highly dependant on the construction of the partition. A
partition's STC can be increased by:
– Adding mass
– Increasing or adding air space
– Adding absorptive material within the partition.
• Even with a high STC rating, any penetration, air-gap, or
"flanking" path can seriously degrade the isolation quality of a
wall.
• It is defined in the series of standards - ISO 140(parts 1-14).

24. Sound Paths, Air-structure-Borne

25. Sound Transmission Class
Sound Transmission Class (STC): defines overall
transmission loss across center band frequencies
Barrier STC Descriptor/ Application
Ranking
25 Poor/1 Space divider
30 Fair/2 Room divider
35 Very Good/4 Offices near quiet space
42-45 Excellent/5 Party walls
46-50 Total Privacy/6 Quiet next to noisy

26. Thank you