ambient noise
TRANSCRIPT
Contents
• Basic characteristics• Quantification• Standard representation of noise• Noise Rating curve [NRC]• Room Criteria [RC]• Standard Transmission Class [STC]
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.
What is noise?• Unpleasant, unwanted, disturbing sound is
generally considered as noise that produces purely subjective feeling.
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.
Am
plitu
de (d
B) 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.
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.
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.
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.
Weighting Characteristics
A-weighting: 40Phon equal loudness level contour
C-weighting: 90Phon equal loudness level contour
D-weighting for Aircraft Noise
Octave Filters
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.
NR curve ApplicationNR 25 Concert halls, broadcasting and recording
studios, churchesNR 30 Private dwellings, hospitals, theatres, cinemas,
conference rooms
NR 35Libraries, 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 machinesNR 60 Light engineering worksNR 70 Foundries, heavy engineering works
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.
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
Type of Room - Space Type Recommended RC Level, RC Curve Equivalent Sound Level, dBA
Apartments 25-35 (N)1) 35-45Assembly Halls 25-30 (N) 35-40
Churches 30-35 (N) 40-45Courtrooms 30-40 (N) 40-50
Factories 40-65 (N) 50-75Hotels/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) 50-55Hospitals 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) 40-45Libraries 35-40 (N) 40-50
Legitimate theaters 20-25 (N) 30-65Private Residences 25-35 (N) 35-45
Restaurants 40-45 (N) 50-55TV Broadcast studies 15-25 (N) 25-35
Recording Studios 15-20 (N) 25-30Concert and recital halls 15-20 (N) 25-30
Sport Coliseums 45-55 (N) 55-65Recording studios 15-20 (N) 25-30
Sound transmission class [STC]
Sound TransmissionBarriers reduce sound transmission to reduce noise intrusion
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).
Sound Paths, Air-structure-Borne
Sound Transmission ClassSound Transmission Class (STC): defines overall transmission loss across center band frequencies
Barrier STC Descriptor/ ApplicationRanking
25 Poor/1 Space divider30 Fair/2 Room divider35 Very Good/4 Offices near quiet space42-45 Excellent/5 Party walls46-50 Total Privacy/6 Quiet next to noisy
Thank you