Adu Building Utilities 3 Sound

3

is a physical wave, or a mechanical vibration or simply a series of pressure variations in an elastic medium. For airborne sound, the medium is air. For structure-borne sound, the medium is concrete, steel, wood, glass and combinations of all the three.

Sound

The science that studies the waves that are conducted through matter due to the motion of the matter. Usually, air is the material that most people think of when it comes to acoustic waves. But acoustic waves exist in all matter.

Acoustics

Pressure fluctuations in the air that are heard when an acoustic wave passes by. They are usually caused by objects in the air that quickly change position or a stream of air that quickly changes position.

Sound (waves)

The measure of the strength of sound. Units are decibels (dB) and usually measured with a dB meter. The threshold of quiet sound is zero dB and the onset of painful sound is 100 db.

Sound Level

The apparent strength of the sound to the listener. A change in 1 dB is just barely noticed as a change in loudness. Something twice as loud is actually 10 dB stronger, (10 times stronger). Something half as loud is 10 dB weaker, (1/10th as strong).

Loudness

The part of a sound wave that travels directly along the line-of-sight path between the speaker or sound source and the listener. The dry or actual sound.

Direct Sound (direct signal)

Sound waves that strike a surface and bounce off are reflected sounds. They bounce off the wall, changing directions but keeping the same angle off the wall as they had when they approached the wall.

Reflections

Reflections that are heard within 1/20 of a second of the direct sound are called early reflections. Early reflections cannot be distinguished from direct signals, they merge with the direct sound to form one composite sound. This combining effect can cause the sound of the direct signal to change in tonal characteristics and apparent direction.

Early Reflections

A distinct reflection that arrives at the listener later than 1/20th of a second after the direct sound is heard. The listener can identify from where an echo comes. An echo does not change the tonal characteristics of the direct sound.

Late reflections (Echoes)

This type of echo is most easily heard as one clap their hands out in front of them, while standing in a hallway. The sound "zings" and its tone depend on how many times a second the reflection passes by the listener's head. In a hall 8' wide, the clap will expand out, hit the wall and return 143 times a second and the zing will sound like a 143 Hz buzzy tone. Not a real sound, just a pseudo-tone.

Flutter Echo

For sound in a large room, reverberation begins at about 1/5 second following the direct sound. It is due to the accumulation of many reflections, compounding one upon the other, so much that the sound no longer seems composed of echoes but rather just a sound of noise, a din of chaos that has no discrete direction and no discrete timing.

Reverberation

Reflections off of a non-flat surface that causes the sound wave to become more quickly disorganized than if off a flat surface is a diffusive surface. Diffusion decreases the time it takes for echoes to become converted to reverberation. The beautiful gothic churches of the old world have very diffusive or sound scattering surfaces. That is part of the sonic beauty of those spaces.

Diffusion

The dying out of sound. Usually referring to the steady decline in the loudness of the reverberation.

Decay

The time (in seconds) it takes for reverberation to change from very loud to imperceptibly quiet, a total sound level difference of 60 db. For a living room the RT-60 might be 1 second but, in a gym, it might be 4 seconds.

Decay Rate (RT-60)

The loss of sound energy that occurs when the sound wave strikes a fibrous surface. The fibers provide acoustic friction for the sound wave. The wave does not slow down due to the friction, it keeps its same speed but it does lose energy and get quieter.

Absorption

A rating for absorption. It gives the % efficiency for a surface to absorb sound. If a surface is 30% absorptive, then only 70% of the incident sound is reflected back into the room.

NRC Rating (Noise Reduction Coefficient)

The unwanted, undesirable and usually interfering sounds present in a listening space, typically due to an air conditioner or other conversations.

Noise (Background Noise)

The strength of the background noise, measured in db. It is difficult to understand what is being said in a room with a high noise floor.

Noise Floor

The difference in sound level (dB) between the desired sound and the noise floor.

Signal-to-Noise Ratio (S/N ratio)

The clarity of a sound, particularly a message conveyed by sound, such that it can be easily and completely understood.

Articulation

A measure of the clarity of sound based on the comprehension of the message being conveyed by sound. A "cat, bat, tat, rat... type of recognition test. The conversational version of Articulation.

Intelligibility

The condition of sound in which there is an abundance of treble range reflections giving the feeling of "brightness" or "liveliness" to the sound. Sound in a tile bathroom or kitchen is bright. Too much can seem harsh and irritating.

Bright/Lively

The condition of sound in a room when there is a lack of reflections and a lack of reverberance. Too much can seem lack-luster and uneasy feeling.

Dark/Dead

The condition of sound in a room when the lower frequencies, particularly the male voice range are excessively reverberant.

Boomy

The study and science of how the human comprehends and makes sense out of the sounds they hear. The difference between an early reflection and a late (echo) reflection, is an example of psychoacoustics. The blending of the early reflections with the direct sound is another.

Psychoacoustics

The science and practice of amplifying or otherwise improving how well a person hears sound.

Audiology

A single sound pulse as from a fire cracker has sound energy but no tone. Tones are sounds that come from voices or instruments which have a repetitive pressure pulse characteristic. The number of repeat times per second that a sound has is called its frequency. It's unit of measurement is cycles per second (cps) also called Hz (Hertz). Similar to pitch in musical terms.

Frequency (Hertz, Hz, cps)

The sound level measured at different frequencies. Most tones are composed of more than one frequency, a combination of frequencies, as in a musical chord. The sound spectrum would measure the strength of each frequency and display that graph as a plot of Sound Level vs. Frequency, also known as a sound spectrum. The "color" of sound is used as emphasis in the spectrum.

Sound Spectrum

The shift in emphasis of a complex sound within its spectral range. A neutral color is the preferred natural sound but sometimes sound can have a warm color, an emphasis on lower frequencies or a cold color, an emphasis on higher frequencies or a nasal color, an emphasis on midrange frequencies.

Sonic Color

Sound whose frequency range is above that of human hearing, above 20,000 Hz.

Ultrasonics

Sound whose frequency range is below that of human hearing, below 20 Hz.

Infrasonic

Sound that exists within a limited frequency range, between a lower set frequency and a set upper frequency. The difference between the lower and upper frequency is specified to be equal to the lower frequency. The octave sequence for the note "C" starts at 31 Hz and continues thru 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1k Hz, 2k Hz, 4k Hz, 8k Hz and ends at 16k Hz. (k = thousand)

Octave

The process of defining the desirable condition of sound in an acoustic space. It integrates the direct, early and late reflections with the reverberation, including a sense of timing and direction for each into an appropriate and desirable acoustic condition for the listener.

Voicing

An acoustical engineer who is trained and experienced in voicing rooms.

Acoustician

One formally educated, experienced in the science and practice of acoustics.

Acoustical Engineer

Someone trained in setting up microphones and speakers.

Sound Engineer

Someone trained and experienced in installing acoustic tiles and wall panels.

Acoustic Contractor

Someone, not formally trained, experienced in providing acoustical services.

Acoustic Consultant

Someone, not formally trained, who prepares blueprints for acoustic projects.

Acoustic Designer

One who envisions and directs the way sound plays out of a stage.

Sound Designer