ACOUSTICAL CONTROL IN BUILDINGS Flashcards
present in all buildings and affects people in a space.
Sound
Controlling all aspects of sound entering or leaving a room or building space is the essence of
good acoustical design
- frequency
- wavelength
- amplitude
Sound Generation:
Sound has been observed to travel in oscillating waves that radiate out from the source.
FREQUENCY
The time it takes to complete that one cycle of a sound wave is measured in ____.
hertz
equal to a frequency of one cycle per second.
One Hz
The human ear can typically hear frequencies or sound “pitch” between about_______ up to around _____ if the person is fairly young; older adults may hear frequencies up to about ________
20 Hz; 20,000 Hz
15,000 Hz.
distance between the start and end of a sound wave cycle or the distance between two successive sound wave pressure peaks.
wavelength of a sound wave
equal to the speed of sound in the material, such as air divided by the frequency of the sound wave.
wavelength of a sound wave
height from bottom to top, but is in fact indicative of the strength of the energy in that wave.
amplitude of a sound wave
amplitude is measured in
is measured in
common range of db;
human speech
0-130db
50 to 65 dB
The most widely used sound level filter is the
expressed as dBA
Using this filter, a sound level meter is less sensitive to very high and very low frequencies.
A scale
A fundamental measurement of the ability of a material or building assembly to block or reduce the amount of sound passing through it.
It is measured in decibels at different frequencies to determine how much sound transmission is lost at each measured frequency.
Generally speaking, a TL of 10 means that the sound is 10 dB quieter on the listening side compared to the sound-originating side.
TRANSMISSION LOSS
Determined by ASTM E90 test methods to measure airborne transmission loss specifically in interior walls and ceiling/floor assemblies. Sound generated on one side of a wall will energize the wall structure and set it in motion, much like a diaphragm. The wall itself becomes the transmitter of the sound energy, which can be heard on the opposite side of the wall by the listener.Hence, the ASTM test methods used to determine STC ratings have focused on this direct transmission process, although this testing has changed over the years, meaning that STC results posted before 1999 may not produce the same results today.
Currently, the STC number is derived from sound values tested at 16 standard frequencies from 125 Hz to 4,000 Hz. The STC measurement is accurate for speech sounds but less so for amplified music, mechanical equipment noise, transportation noise, or any sound with substantial low-frequency energy below 125 Hz. Nonetheless, since this is fundamentally a measure of TL, the derived STC number generally reflects how many decibels quieter the receiving side of a wall is compared to the sound-originating side (e.g. In terms of people’s perception of sound, a general rule of thumb is that each 10-point increase in STC value will decrease the perceived noise by one half of the starting point.
SOUND TRANSMISSION CLASS
A standard method used to rate the amount of transmission loss in an exterior wall setting, such as determining how much traffic noise an exterior wall can stop.
The OITC covers a lower or broader frequency range from 80 Hz to 4,000 Hz, where most aircraft, rail, and vehicular traffic sounds would be found.
OUTDOOR INDOOR TRANSMISSION CLASS
A measure of the ability of a floor-ceiling assembly to absorb or deflect sound from impacts (such as people walking or objects dropping) and keep it from being transmitted to the space below.
Test data obtained in accordance with ASTM E492: Standard Test Method for Laboratory Measurement of Impact Sound Transmission Through Floor/Ceiling Assemblies Using the Tapping Machine, is used to determine the IIC rating of a floor.
IMPACT INSULATION CLASS
A measure for rating the performance of a ceiling system as a barrier to airborne sound transmission through a common plenum between adjacent closed spaces, such as offices.
CAC for ceilings is similar to an STC rating for walls, but is specific to suspended ceiling conditions where a dividing wall is constructed only to the ceiling height, thus allowing sound to pass through a plenum space above the ceiling.
As an ASTM E1414 tested measurement, it is a ‘two pass’ test in that the sound is looked at as it transmits up through the ceiling in one space, across the ceiling plenum, and back down through the ceiling in an adjacent space.
CEILING ATTENUATION CLASS
With an understanding of the principles of sound generation and sound transmission, we can focus on the impact of sound and noise on the indoor environment. We have all likely experienced situations where unwanted background noise has interfered with normal activities in a room or space. The response, if we are talking, is typically to speak louder. In fact, it is generally accepted that most people would need to speak at least 15 decibels (dBA) louder than the background noise level in order to be heard at all.
This observation and others has led to the development of national standards, such as ANSI Standard S12.60: Acoustical Performance Criteria, Design Requirements and Guidelines for Schools, which establishes some very stringent thresholds for background noise. Specifically, for core learning spaces of 20,000 cubic feet or less, the one-hour steady-state background noise levels should not exceed 35 dB, while those more than 20,000 cubic feet should not exceed 40 dB. This is the same low level of sound that one would experience in a quiet office.
SOUND AND INDOOR ENVIRONMENTAL QUALITY
talking, is typically to speak louder. In fact, it is generally accepted that most people would need to speak at least __________ louder than the background noise level in order to be heard at all.
15 decibels (dBA)
establishes some very stringent thresholds for background noise. Specifically, for core learning spaces of 20,000 cubic feet or less, the one-hour steady-state background noise levels should not exceed 35 dB, while those more than 20,000 cubic feet should not exceed 40 dB. This is the same low level of sound that one would experience in a quiet office.
ANSI Standard S12.60: Acoustical Performance Criteria, Design Requirements and Guidelines for Schools
variety of foams, fabrics, metals, etc. used to quiet workplaces, homes, automobiles, and so forth to increase the comfort and safety of their inhabitants by reducing noise generated both inside and outside of those spaces.
Acoustical materials
Noise generated from
outside a given space
is blocked from entering
the space.
SOUNDPROOFING
Noise generated within a space
is reduced inside the space
itself.
SOUND ABSORBING
Use of soundproofing
BLOCKING
Converting sound energy to heat.
DIFFUSION
Scatter sound without deadening a room.
ABSORPTION
Placing a compressor on isolation mounts of the
noise itself.
ISOLATING
defined as the portion of sound energy incident on a material’s surface that is not reflected.
The absorption coefficient, or sound absorption coefficient
the product of a material’s density and its acoustic velocity. The effectiveness of acoustic material to absorb sound energy depends upon the frequency of the sound, with the mid-to-high ranges being more effectively muted by most materials than the lower frequencies.
SPECIFIC ACOUSTIC IMPEDANCE
establishes a material’s average absorption coefficient at frequencies of 250, 500, 1000, and 2000 Hz., and is useful for comparing a material’s effectiveness at absorbing noise in general. In special applications, such as recording studios, the noise reduction coefficient is less useful because it does not cover the lower base range frequencies which tend to present the biggest problem.
In these situations, using the absorption coefficient at the frequency in question can make a better determination of a material’s effectiveness; unfortunately, noise reduction coefficients for various commercial materials are often published whereas the absorption coefficients generally are not.
NOISE REDUCTION COEFFICIENT
Materials used for soundproofing are given an STC, or Sound Transmission Class, a rating which quantifies how well a material blocks transmission at frequencies associated with speech. Like the Noise Reduction Coefficient associated with absorptive materials, the STC rating does not give a good indication of a material’s effectiveness at blocking low- or high-frequency sounds, such as mechanical noise or music.
SOUND TRANSMISSION CLASS
Sound for human-occupied environments is measured by an A-weighted sound level scale, which reduces the impact of high and low frequencies to better match the human ear’s response to the middle ranges. This scale, with units of dBA, is sometimes referred to as noise level and is a selectable feature of most sound meters. The dB refers to decibels, which is logarithmic versus linear scale.
A-WEIGHTED SOUND LEVEL SCALE
Commercially available soundproof drywall, or pre-damped drywall, achieves its reduction in sound transmission by sandwiching a layer of viscous damping glue between two sheets of usually dissimilar materials of unequal thickness. Acoustic caulk or other forms of sound dampening sealants, marketed under a number of trade names, are available for this purpose. Other forms of materials can be applied to help deaden or dampen sound including Liquid Applied Sound Deadeners (LASD) or sound dampening liquid coatings.
SOUNDPROOFING
provide a mechanical means of decoupling inside walls from exterior structures. Usually consisting of rubber-fitted mounts that hold nailing strips, these clips provide a convenient method of isolating a room from external noises. As with any of these soundproofing methods, clips are designed only to work on airborne sound. Noise coming through structures, plumbing, etc. will remain unmuffled by their use.
Sound isolation clips
A generic term for several commercial products which use heavy vinyl sheeting installed behind sheetrock as a means of blocking sound transmission. By being loosely draped between stud attachments, the material flexes as sound waves impinge upon it, prohibiting the transfer of their energy to the more-rigid interior walls.
MASS LOADED VINYL
also referred to as acoustic or acoustical lead, which, given the material’s high density, proves an effective method of reducing sound transmission through walls. In many applications, the lead is bonded to foam on both sides and then adhered to sheetrock.
LEAD SHEET
Sound absorption materials
come in a variety of styles allowing them to integrate aesthetically to indoor offices and the like. They are also available in special laminated versions for industrial applications such as machinery enclosures, automobile headliners, etc.
usually of the open cell variety as closed-cell structures tend to reflect sound rather than absorb it.
Acoustic foam
can be flat or topological—the familiar “egg-crate” pattern being representative of the form.
Foam surfaces
does not block sound. It is used in sound absorption applications such as gymnasiums to reduce reverberations as noise travels and bounces off reflective surfaces.
Acoustic foam
available both as hanging acoustical baffles and as sound dampening room dividers. Sometimes referred to as sound abatement panels, these come in an array of designs and constructions to complement the décor of the spaces in which they are installed. They can be flat, permanently installed dividers or moveable, soundproof accordion room dividers.
ACOUSTICAL ABSORBERS
expressed in units of phons to provide a qualitative measure, a phon being defined as the pressure level in dB of a 1000 Hz. tone against which a person compares another pure or complex tone.
Another measure, the sone, is defined as the loudness of a 1000 Hz., 40 dB tone. A relationship can be plotted between phons and sones.
Loudness
Loudness is expressed in units of
phons
subjective measure of the pleasantness or unpleasantness of sound which can make sounds of the same loudness appear more or less disturbing.
Quality
determined mainly by frequency, then intensity and wave shape
Pitch
determined mainly by frequency, then intensity and wave shape
timbre
