acoustics fundamentals
DESCRIPTION
Basic Fundamental of acousticsTRANSCRIPT
Acoustics Fundamentals
Environmental Technology IV
Professor Tango & Parker Spring 2009
Acoustics is usually very broadly defined as "the science of sound."
Room Acoustics The shaping and equipping of an enclosed space to obtain the best possible conditions for faithful hearing of wanted sound and the direction and the reduction of unwanted sound.
Room Acoustics deal primarily with the control of sound which originates within a single enclosure, rather than its transmission between rooms.
The balance of keeping
wanted sounds
and eliminating
unwanted sounds
Sound Waves
What is a wave?http://www.kettering.edu/~drussell/Demos/waves-intro/waves-intro.html
frequency; vibration cycles per second
wave length:distance between identical points on a wave
amplitude
http://www.surendranath.org/Applets.html
• Amplitude and Frequency– Applet Menu >Waves > Transverse Waves
http://www.surendranath.org/Applets.html
The human ear can detect sounds between 20 HZ and 20,000 HZ. Most sensitive in the range of 100HZ to 5000HZ
Hear it: http://www.surendranath.org/Applets.html , then select: menu/ new applets/new menu/ waves/ hear the beats.
Speakerdiameter
(cm)Frequencies
(Hz)cutoff ka
Woofer 30 20-2,000 5.5
mid-range
12 2,000-5,000 5.5
tweeter 6 5,000-10,000
5.5
super-tweeter
3 10,000-20,000
5.5
20 HZ – 56 ½ feet
20,000 HZ - 11/16”
The length of a sound wave
Velocity Rate at which sound travels through a conductor
Air:
Wood:
Steel:
Velocity Rate at which sound travels through a conductor
Air:
Wood:
Steel:
1128 feet per second
11,700 feet per second
18,000 feet per second
Sound Pressure/Amplitude
Sound Pressure/Amplitude vs. Frequency
Complex Waves
http://www.surendranath.org/Applets.html
• Multiple TonesApplet Menu >Waves > Transverse Waves > Adding Transverse Waves (continuous)
The Mobility of Sound
Direct Sound
Since sound travels in all directions from the source, each listener will hear just the segment if the overall sound wave that is traveling in a direct line to his hear (in a space free from reflecting surfaces). As the distance from the source increases, the sound pressure at the listener's ear will decrease proportionately.
(Example: good Headphones)
Reflection
Diffusion
Diffraction: The Sound Squeezes Through
Sound waves are not always reflected or absorbed. When an obstacle is the same size as the wavelength or less, the sound can bend around obstacles or flow through small openings, and continue onward. This is called diffraction. This action is more likely for deeper sounds (of low frequency, and this with longer waveforms).
ReverberationReverberationThe perpetuation of reflected sound within a space after The perpetuation of reflected sound within a space after the source has ceased is called the source has ceased is called reverberationreverberation. The time . The time interval between reflections is usually so short that interval between reflections is usually so short that distinct echoes are not heard. Instead, this series of distinct echoes are not heard. Instead, this series of reflections will blend with the direct sound to add reflections will blend with the direct sound to add "depth". Reverberation is a basic acoustic property of a "depth". Reverberation is a basic acoustic property of a room. It can enrich speech and music in all areas -- or it room. It can enrich speech and music in all areas -- or it can slur speech and generate higher noise levels can slur speech and generate higher noise levels throughout a room, depending upon the room volume, throughout a room, depending upon the room volume, timing, and absorption.timing, and absorption.
Room Acoustics
Shape
Volume
Materials
Room Acoustics
Room Acoustics
Sound re-enforcement
Reflect
Absorb
The shape of a space determines the sound path within the space
Room Acoustics
AA
BC
Reverberation
A
Parallel reflective surfaces generates unwanted reverberation
Reverberation time must match room function•Pure speech requires short reverberation time
•Symphony blends notes with long reverberation time
The lower part of the band is best for rooms intended primarily for speech, the upper part is better for music rooms, and the middle portion is recommended for general purpose rooms.
Studies based on the audibility of speech and music reveal that the most desirable reverberation times generally fall within the ranges shown below. These values are based on a sound frequency of 500 Hz (approximate pitch of male speech). Reverberation time in secondsSpeech Small offices 0.50 to 0.75Classrooms/lecture rooms 0.75 to 1.00Work rooms 1.00 to 2.00
MusicRehearsal rooms 0.80 to 1.00Chamber music 1.00 to 1.50Orchestral/Choral/Average church music 1.50 to 2.00Large organ/liturgical choir 2.00 to 2.25
Live!
DEAD
A classification of typical rooms by acoustical environments
"Dead" : Very Absorptive
"Live“: Highly Reflective
Absorbing Materials•Carpet
•Soft ceiling tile
•Rigid foam
•people
Reflecting Materials•Masonry
•Wood – smooth panels
•Smooth concrete
•Glass
LiveAuditoriums, theaters(for music)Obtain proper reverberation time to enhance musical quality.Provide reflective surfaces near source to reinforce sound; absorptive surfaces toward rear.
Medium LiveConference and board roomsNormal speech must be heard over distances up to about 35 ft.Allow middle section of ceiling to act as a reinforcing sound-reflector. Apply absorbent to periphery of ceiling or to wall surfaces (not both). Additional treatment will contribute little to noise reduction.
Medium
Cafeterias (school or office)Reduce overall noise level.Use highly sound-absorptive ceiling; also use quiet equipment such as rubberized dish trays.
GymnasiumsInstructor must be heard over background noiseUse acoustical material over entire ceiling to reduce noise; walls remain untreated to permit some reflected sound.
Medium Dead
Elementary-grade classroomsTeacher must be heard distinctly; reduce noise level produced by children.Acoustical ceiling essential. Supplementary acoustical space units on upper rear and side walls are desirable.
Music rehearsal roomsUnlike music hall, instructor must hear individual notes distinctly; minimum reverberation desired.Entire ceiling, sidewalls, and wall facing musicians would be treated; wall behind musicians may be left sound-reflective for proper hearing. Room should be located away from normal use rooms.
Dead
KindergartenMaximum noise reduction.Maximum acoustical treatment on ceiling; space units on available wall surfaces.
Vocational classrooms and shopsMaximum noise reduction.Acoustical tile or lay-in panel ceiling, plus acoustical treatment of available upper wall areas; locate away from normal use rooms.
Reverberation time (in seconds) =
.05 x volume of room______________________________
sabins
Sabin
The amount of sound absorbed is measured in sabins. One sabin is equal to the sound absorption of one square foot of perfectly absorptive surface. The sound absorption equivalent to an open window of one square foot. (theoretical, since no such surface exists).
Measuring Absorption:Sound Absorption Coefficient
The fraction of the energy absorbed (at a specific frequency) during each reflection is represented by the sound absorption coefficient of the reflecting/absorbing surface. In the building industry, this is a meaningful and widely accepted quantitative measuring of sound absorption, and applies to all surfaces -- whether they be of reflective or absorptive materials.
Reflective Surfaces
Hard, massive, non-porous surfaces, such as plaster, masonry, glass and concrete, absorb generally less than 5% of the energy of striking sound waves and reflect the rest. Such materials heaver absorption coefficients of .05 or less.
Absorptive Surfaces:
Porous materials such as acoustical tile, carpets, draperies and furniture are
primarily absorptive. They permit the penetration of sound waves and are capable of absorbing most of the sound energy. These materials may have absorption coefficients approaching 1.00 (one sabin per sq. ft.).
Poor acoustical characteristics in this lecture room.
Reflective surfaces near the speaker. In lecture rooms more than 40 feet long, the rear wall should be absorptive to prevent echoes.
Why Sound Conditioning??
The objective of sound-conditioning is to create a haven for the occupant, shielded from annoyance and distractions. With such an environment, individuals show increased productivity, tenants complain less, turnovers and vacancies are reduced, and property values rise.
Structure borne sound Steel Frame
Plumbing Pipe
SourcePath
Receiver
Isolation Of Equipment
Isolation Of Equipment
Low-end RTUs (roof top units) are typically loud …. No isolation springs / poorly balanced
Background Noise
Acceptable Background Noise Levels
As a rule, we can tolerate, and even welcome, a certain amount of continuous sound before it becomes noise. An "acceptable" level neither disturbs room occupants nor interferes with the communication of wanted sound.
Recommended category classification and suggested noise criteria range for steady background noise as heard in various indoor functional activity areas as indicated in the
Preferred Noise Criterion (PNC)Curves.
Type of Space (and acoustical requirements)PNC curve
Concert halls, opera houses, and recital halls (for listening to faint musical sounds)
10 to 20 dbLarge auditoriums, large drama theaters, and churches (for
excellent listening conditions)Not to exceed 20 db
Broadcast, television, and recording studios (close microphone pickup only)
Not to exceed 25 db Small auditoriums, small theaters, small churches, musical rehearsal rooms, large meeting and conference rooms (for
good listening), or executive offices and conference rooms for 50 people (no amplification)
Not to exceed 35 db Bedrooms, sleeping quarters, hospitals, residences,
apartments, hotels, motels, etc. (for sleeping resting, relaxing)25 to 40 db
Private or semiprivate offices, small conference rooms, classrooms, libraries, etc. (for good listening conditions)
30 to 40 db
Type of Space (and acoustical requirements)PNC curve
Living rooms and similar spaces in dwellings (for conversing or listening to radio and TV)
30 to 40 db Large offices, reception areas, retail shops and stores,
cafeterias, restaurants, etc. (for moderately good listening conditions)35 to 45 db
Lobbies, laboratory work spaces, drafting and engineering rooms, general secretarial areas (for fair listening
conditions)40 to 50 db
Light maintenance shops, office and computer equipment rooms, kitchens and laundries (for moderately fair listening
conditions)45 to 55 db
Levels above PNC-60 are not recommended for any office or communication situation.
Minimize Background Noise Level - Overall noise levels which may interfere with wanted communication should always be anticipated and corrected. To provide maximum quiet, typical methods include the following: 1. Elimination of outside noise by sound attenuation in walls, ceilings, and floor
2. Use of quiet mechanical equipment wherever possible.
3 .Control of remaining noise by absorption -- carpeting, upholstery, and acoustical treatment placed above and behind audience.
4. Individual handling of unusual noise sources -- for example, isolation of a noisy movie projector.
5. Electronic amplification of the wanted sound level above the background noise level -- usually done as a last resort.
Masking:
Creating Background "Noise“
When an undesirable background sound can't be reduced or eliminated, it can sometimes be masked (made less objectionable by introducing a different sound). For example, piped-in music in restaurants can mask the din of dish clatter and multiple conversation.At the other extreme, a masking sound may be introduced to correct an oppressively quiet room. For example, a telephone ring or a slight cough can be distracting in a very "dead" room, and speech privacy would be impossible. In many cases the heating and air conditioning systems will provide a sufficient amount of masking noise.
white noise
pink noise
Sound Isolation
The control of intruding sound ideally begins with the initial building concept and continues to be a consideration through the life of the building. Total sound conditioning affects
1. site selection2. building orientation on the site3. room orientation within the building4. design, detailing, specification5. construction6. inspection.
Predictable sound attenuation can be achieved by careful attention to detail during all phases of planning and construction.
Site Selection for Sound Control
Orientation
Room Arrangement
1. What is the STC rating of the outside kitchen exterior wall?
sound barrier
Sound BarriersIf the noise source is intense and no natural sound barrier exists, a man-made sound barrier should be considered as part of the design. A solid fence-type barrier may remove from 10 to 20 db from the noise level. High-frequency sounds will be reduce more than low frequency sounds. The cost of an outside barrier may be less than the cost of reducing the sound transmission in the construction.This type of sound barrier must completely shield the building from the noise source. It should be placed as close to the sound source as possible to obtain the greatest sound-shadow angle. If a fence or wall is used, no louvers or openings should be permitted.
Acoustical Zoning
Airborne Sound Airborne sound includes conversation, outdoor noises, music and machine noises (machines usually also produce impact sound). It is the major source of intruding sound from rooms on the same floor and from the outdoors. It is controlled by:1. Mass (weight), 2. Isolation (decoupling), 3. Absorption 4. Limpness of Construction. These must be combined with airtight sealing and the elimination of flanking paths (routes by which the sound travels around a partition rather than being stopped by it).
Mass
Impact Sound
Impact IsolationIf the surface receiving the impact, such as a floor, can be isolated from the structure, the impact sound will not be transmitted. Likewise, if the structure can be isolated from the ceiling below, the impact sound will be restricted from traveling into the room below.Isolation of the ceiling of the receiving room can be accomplished with resilient mounting of the drywall panels or lath. This still allows some sound from above to enter the structure and travel to other rooms. Resilient subflooring materials such as insulation board and underlayment compounds are effective, as is heavy carpet over thick under pad. A combination of these methods is necessary to produce ideal attenuation of impact noise.Other sources of structure-borne sound, such as motors, flushing toilets, dishwashers, garbage disposals, blowers, and plumbing, can be isolated from the structure by resilient mounting procedures.
Isolation (Decoupling)
staggered 2x3 studs on a single sill plate, with alternate studs connected to opposite diaphragms
double row of studs on separate sill plates
2x4 studs with one diaphragm attached through sound deadening board.
2x4 studs with one diaphragm attached by means of resilient channels
Resilient Channel 1/2”
AbsorptionThe amount of sound energy dissipated depends on the thickness of the material, its density (which determines the amount of difficulty that the sound encounters in traveling through), and it's resiliency (flexibility with the ability to spring back to its original shape). Mineral wool insulation because of its porous yet dense character, is highly effective in this application. Sound attenuation blankets are manufactured with higher density than thermal insulating blankets to obtain optimum attenuation. Mineral fiber sound attenuation blankets, placed between the studs in a resilient partition with resilient channels, retard movement of the air column and convert considerable sound energy into heat. However, if the diaphragms are directly connected to rigid studs, the partition will act as a single diaphragm, rendering the wool ineffective in dissipating sound energy.
Effective mass is contributed by the gypsum panels or plaster. A common wood-stud partition with 5/8-in. SHEETROCK FIRECODE "C" Gypsum Panels on each side will test STC 34. Using double-layer panels on each side will increase the rating to STC 41,an improvement, but certainly not optimum. Increasing the mass beyond this point is of little value since other, less expensive methods of achieving better performance are available. Gypsum panels decoupled on one side with RC-1 SHEETROCK Resilient Channels, will have sound attenuation of STC 49; STC 59 with the addition of 3-in. THERMAFIBER Insulating Blankets.The performance of an assembly can vary as much as 15 STC points with the quality of the workmanship
The performance level being sought will usually fall in the STC range of 45 to 60. The partitions used in most single-family dwellings today would test about STC 35 (although the actual performance is often even less due to leaks and flanking paths). On the other end of the scale, STC-60 partitions are found increasingly in luxury multi-family dwellings, and other quality buildings. Partition performance of STC 60 will, for practical purposes, reduce an 85 db noise level (the maximum normally encountered in a residence) to a 25 db background sound (comparable to a night-time rural sound level) -- near ideal for sleeping rooms.
Noise Reduction Coefficient (NRC)The average amount of sound energy absorbed over a range of frequencies between 250 Hz and 2,000 Hz.
NORMAL SPEECH RANGE
What is CAC? A: CAC, or Ceiling Attenuation Class, is a measure of the sound transmission loss as noise travels between rooms. Essentially, it is the ability of a ceiling panel to block sound between rooms.
Q: What spaces require CAC values? A: CAC values are essential in interior spaces that require physical separation from other areas such as conference and board rooms, private offices, bathrooms, and corridors.
Q: Is CAC important in open plan offices? A: Actually, CAC is important to assure privacy for areas outside or adjoining an open plan such as private offices or conference rooms.
Details, Specifications and Construction
Some of the most common flanking paths are supplied by plumbing pipes, air ducts and electrical conduit rigidly connected between the floor and ceiling.
Continuous walls between floors, columns or any other continuous structural elements will act as flanking paths for impact sound. In fact, any rigid connection between the two diaphragms will effectively transmit impact sound.
Flanking Paths
Flanking Paths
Flanking PathsFlanking PathsHVAC
Good
Sound Control
• Negative impacts• ‘Flanking Paths’
– Electrical Boxes• Especially back-to-back
– HVAC
– Perimeter Seals
– Doors
– Other penetrations
50 STC
Example: Back-to-backelectrical boxes
Flanking Paths
BestBetter
CUTOUTS
Flanking Paths
Cabinet
Eliminating a flanking path with a non-resilent material
STC 53
STC 29 Unsealed
SoundSound SealSeal
2 Layers5/8” Gypsum Board
Insulation
Sound Path
STC 53
SoundSound SealSeal
AcousticalSealant
STC 29 Unsealed
2 Layers5/8” Gypsum Board
Insulation
Sound Path
STC 53
2 Layers5/8” Gypsum Board
Insulation
SoundSound SealSeal
Sealed
AcousticalSealant
Sealing
figure 50A. 29 STCUnsealed
figure 50B. 53 STCBoth Base layers sealed.No relief on face layers.
figure 50C. 53 STCSealant applied to runnertrack and board.
figure 50D. 53 STCSealant beneath and on edgeof runner track. Base layer not relieved. Face layer relieved and sealed.
Sound Control• How to achieve Sound
AttenuationIncrease STC by:
65 dB 15 dB
50 STC
Isolation
De-coupling
Absorption
Mass
Usually the Dimension of theFraming – 3 5/8”
RC-1 or resilient channelInsulation – either SAFBor fiberglass to absorbsound energy
Drywall or engineered panel
Improving Sound TransmissionLoss
• Doubling Partition Width = 5 dB Transmission Loss Improvement
• Doubling MASS = 5 dB Transmission Loss Improvement
Rules of Thumb
STC 48
Improving STCImproving STC
STC 54 STC 61
STC 43 - 25 ga. Steel stud STC 40 - 20 ga. Steel stud
ISOLATION
MASSDECOUPLINGRC-1 Resilient Channel
STC 37 - Wood stud
ABSORPTION3 1/2” Insulation
STC 43 - 25 ga. Steel stud
Doors & Door FramesHigh STC PartitionsHigh STC Partitions
Fill
Solid Core
Gasket
Assignment 11
Room sabin absorption calculations and
reverberation
last Environmental Tech class : - (
Next Thursday: Dave Duda With Newcomb Boyd Security Design
thenFinal Exam Review