Elements of Acoustics Flashcards
____ is how the energy is generated; in other words, the source of the sound.
A. Production B. Propagation C. Control D. Interaction E. Reception
A. Production
____ is the pathway of the energy.
A. Production B. Propagation C. Control D. Interaction E. Reception
B. Propagation
____ is how (sound) energy is generated and subsequently propagated.
A. Production B. Propagation C. Control D. Interaction E. Reception
C. Control
____ is how material responds to the sound energy imposed upon it.
A. Production B. Propagation C. Control D. Interaction E. Reception
D. Interaction
____ is how hearers’ ears and brains will respond to the stimuli placed upon them.
A. Production B. Propagation C. Control D. Interaction E. Reception
E. Reception
_____ is the distance between two corresponding points of two consecutive cycles.
Wavelength
The speed of sound in air is ____ft per second.
1,130 ft (344 m)
Wavelength formula
λ = v/f
where:
• λ is the wavelength measured in feet or meters.
• v is the speed of sound in feet (meters) per second.
• f is the frequency in hertz.
divide the speed of sound by frequency
As frequency increases, the wavelength ____.
decreases
The unit for sound power is _____.
watts per square meter (W/m2)
_____ is the distance of a particle’s movement from its equilibrium position in a medium as it transmits a sound wave.
Particle Displacement
_____ is sound that arrives directly from the source to the listener.
Direct sound
____ is sound that arrives to the listener after the direct sound as reflected energy.
reflections
____ reflections bounce directly off a surface like light bouncing off a mirror. Like light, the incoming angle (the angle of incidence) will equal the outgoing angle (the angle of reflection).
Direct (or specular)
____ is the scattering or random redistribution of a sound wave from a surface. It occurs when surfaces are at least as long as the sound wavelengths but not more than four times as long.
Diffusion
For reflecting surfaces to function as diffusers, they must be heavily textured and irregular—the dimensions of irregularities should be _____ to the wavelength of sound.
nearly equal
A _____ is a series of reflections that continue to bounce back and forth between parallel hard surfaces, such as large walls, ceilings, windows, and floors.
flutter echo
A ____ is the amount of energy at fixed positions within a room. They significantly affect the perceived low-frequency performance in smaller rooms, such as boardrooms, conference rooms, classrooms, home theaters, music practice rooms, and small studios—really, any relatively small room.
mode (or standing wave or room resonance)
A _____ occurs when a sound wave travels between two reflecting surfaces, such as two parallel walls.
standing wave
_____is the sound that persists in a room after the energy that created it is stopped.
Reverberation
The _____ of a space (Figure 11-8) is said to be the number of seconds it takes for the sound to decay to one-thousandth of its original level, or 60 dB.
reverberation time
Reverberation time is also referred to as _____.
RT 60
The _____ takes an average of the four middle test frequencies (250, 500, 1000, and 2000).
noise reduction coefficient (NRC)
Generally speaking, NRC values smaller than ___ are considered to be reflective, while values greater than ___ are considered to be absorptive.
0.20 / 0.40
The _____ is a single-number rating that is the average, rounded off to the nearest 0.01, of the sound absorption coefficients of a material for the 12 one-third octave bands from 200 through 2500 Hz.
sound absorption average (SAA)
Acoustic Mass Law formula
TL = 20 * log (m * f ) – 47.2
where:
• TL is the transmission loss in dB.
• m is the mass in kg/m2.
• f is the frequency in Hz.
_____rates transmission loss at speech frequencies from 125 to 4000 Hz plotted against a standard contour as the reference.
Sound transmission class (STC)
STC does not evaluate performance at frequencies below ___ Hz, where music and mechanical equipment noise levels can be high.
125
Speech Privacy
No privacy. Voices clearly heard between rooms.
A. 0-20 STC
B. 20-40 STC
C. 40-55 STC
D. 55-65 STC
A. 0-20 STC
Speech Privacy
Some privacy. Voices will be heard.
A. 0-20 STC
B. 20-40 STC
C. 40-55 STC
D. 55-65 STC
B. 20-40 STC
Speech Privacy
Adequate privacy. Only raised voices will be heard.
A. 0-20 STC
B. 20-40 STC
C. 40-55 STC
D. 55-65 STC
C. 40-55 STC
Speech Privacy
Complete privacy. Only high level noise will be heard. Note that the term complete may not be adequate for some secure facilities.
A. 0-20 STC
B. 20-40 STC
C. 40-55 STC
D. 55-65 STC
D. 55-65 STC
____ is a rating used to quantify impact sound absorption. It is an average of the attenuation in decibels that occurs at frequencies ranging from 100 to 3150 Hz.
Impact insulation class (IIC)
The ____ the IIC rating is, the better insulation from impact noise the material provides.
higher
Within certain time frames, our ear/brain system processes direct and reflected energy as one sound event, known as the _____.
integration process
Our brain uses the comparison between direct and reflected sound to determine the direction of the sound’s origin, a psychoacoustic effect called _____.
precedence effect
First notch frequency formula
F = 1 / 2t
where:
- F is the frequency.
- t is the time in seconds.
_____ is the background noise that originates from all sources other than the desired source.
Ambient noise
An important unseen effect is an increase in loudness, which occurs when the reflected sound is within what is colloquially called the _____ —about 30 ms for speech and 50 ms for music, depending on the temporal structure of the sound.
integration interval
