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
