What is acoustics?

Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. The application of acoustics can be seen in almost all aspects of modern society with the most obvious being the audio and noise control industries.

Acoustics are also the influence that sound and resonance has on a room. For example, you've probably heard the phrase "this room has bad acoustics". It mwans that the properties of the room do not match the usage. For example, a concert hall has very different requirements than a lecture room.

We at the Acoustic Factory, use the following to design our solutions:
1   Room acoustics
2   Measurement techniques
3   Noise control and influence
     - Sound absorption
     - Soundproofing
4   Fundamentals
5   Music

Room acoustics

Room acoustics describes how sound behaves in an enclosed space.

The way that sound behaves in a room can be broken up into roughly four different frequency zones:

The first zone is below the frequency that has a wavelength of twice the longest length of the room. In this zone sound behaves very much like changes in static air pressure.
Above that zone, until the frequency is approximately 11,250(RT60/V)^1/2, wavelengths are comparable to the dimensions of the room, and so room resonances dominate.
The third region which extends approximately 2 octaves is a transition to the fourth zone.
In the fourth zone, sounds behave like rays of light bouncing around the room.

Measurement techniques

Sound level meters measure sound pressure level and are commonly used in noise pollution studies for the quantification of almost any noise, but especially for industrial, environmental and aircraft noise. However, the reading given by a sound level meter does not correlate well to human-perceived loudness; for this a loudness meter is needed.

Sound pressure level (SPL) or sound level $L p$ is a logarithmic measure of the effective sound pressure of a sound relative to a reference value. It is measured in decibels (dB) above a standard reference level.

$L_p=10 \log_{10}\left(\frac{{p_{\mathrm{{rms}}}}^2}{{p_{\mathrm{ref}}}^2}\right) =20 \log_{10}\left(\frac{p_{\mathrm{rms}}}{p_{\mathrm{ref}}}\right)\mbox{ dB} ,$

where $p ref$ is the reference sound pressure and $p rms$ is the rms sound pressure being measured.

Most sound level measurements will be made relative to this level, meaning 1 pascal will equal SPL of 94 dB. In other media, such as underwater, a reference level of 1 µPa is more often used.

For the sounds theat humans perceive, or to measure the total sound energy, the average (rms=root mean square) level over time is the most important. If sound is measured over time, the highest peak level gives the upper limit, the maximum is lower, and the average (rms) level is the lowest limit.

Noise control and influence
Sound absorption

Acoustical wall and ceiling panels can be constructed of many different materials and finishes. The ideal acoustical panels are those without a face or finish material that interferes with the acoustical infill or substrate. Fabric covered panels are one way to maximize the acoustical absorption. The finish material is used to cover over the acoustical substrate. Mineral fiber board, or Micore, is a commonly used acoustical substrate. Finish materials often consist of fabric, wood or metal. Fabric can be wrapped around substrates to create what is referred to as a "pre-fabricated panel" if laid onto a wall, and require no modifications. Such fabrics are generally acoustically 'transparent, meaning that they do not impede a sound wave. Prefabricated panels are limited to the size of the subas "on-site acoustical wall panels" This is constructed by "framing" the perimeter track into shape, infilling the acoustical substrate and then stretching and tucking the fabric into the perimeter frame system. On-site wall panels can be constructed to work around door frames, baseboard, or any other intrusion. Large panels (generally greater than 50 feet) can be created on walls and ceilings with this method.

Measurements
Absorption can be measured in two ways:
1. In a “standing wave tube” or “impedance tube”. This is a cheap method, for which a small piece of material is needed.
2. In a “reverberation chamber”. A bigger piece of material is need for this method. The measurements take place in a bigger laboratory. Method 1 only measures the perpendicular incidence of sound. This method measures the absorption of all angles at the same time.

Sound absorption with people
Absorption of sound is measured in (metric) sabin or in square meter (and in the USA in square foot). In case of a room with chairs, one can count/calculate per chair:

Frequency	250 Hz	1 kHz	4 kHz
Chair (uncovered)	0,018	0,036	0,028
Chair (covered)	0,26	0,46	0,41
Chair (occupied)	0,40	0,65	0,46

The sound absorption for (standing) people in a room in Sabin (please note, the data below are in m2 per person):

Frequency in Hz	125	250	500	1000	2000	4000
General people (avg)	0,19	0,28	0,37	0,46	0,46	0,37
Adults	0,23	0,33	0,39	0,43	0,46	0,47
Teenagers	0,20	0,28	0,35	0,39	0,42	0,42
Young children	0,17	0,21	0,26	0,30	0,33	0,33

From this number, one has to subtract the absorption of the floorspace which is occupied by people.

Soundproofing
Soundproofing is any means of reducing the sound pressure with respect to a specified sound source and receptor. There are several basic approaches to reducing sound: increasing the distance between source and receiver, using noise barriers to reflect or absorb the energy of the sound waves, using damping structures such as sound baffles, or using active antinoise sound generators.

Two distinct soundproofing problems may need to be considered when designing acoustic treatments - to improve the sound within a room (See anechoic chamber), and reduce sound leakage to/from adjacent rooms or outdoors. Acoustic quieting, noise mitigation, and noise control can be used to limit unwanted noise. Soundproofing can suppress unwanted indirect sound waves such as reflections that cause echoes and resonances that cause reverberation. Soundproofing can reduce the transmission of unwanted direct sound waves from the source to an involuntary listener through the use of distance and intervening objects in the sound path.

Fundamentals
- Soundwave
- Point source
- Line source
- Sound vibration
- Velocity of sound
- Sound pressure
- Sound level
- Sound intensity
- Loudness
- Volume (a poorly defined term)
- Decibel and dB , Day value, Lden
- Maximum sound pressure
- Weighting curves A and C
- Summing up sound levels
- Resonance
- Low frequency sound
- Infra sound
- Ultra sound
- Impedance- Soundwave
- Point source
- Line source
- Sound vibration
- Velocity of sound
- Sound pressure
- Sound level
- Sound intensity
- Loudness
- Volume (a poorly defined term)
- Decibel and dB, Lden
- Maximum sound pressure
- Weighting curves A and C
- Summing up sound levels
- Resonance
- Low frequency sound
- Infra sound
- Ultra sound
- Impedance

Music
Music is an art form whose medium is sound and silence. Its common elements are pitch (which governs melody and harmony), rhythm (and its associated concepts tempo, meter, and articulation), dynamics, and the sonic qualities of timbre and texture. The word derives from Greek μουσική (mousike; "art of the Muses").

Source = Wikipedia 2012

Akoestiekfabriek - Welkom bij de Akoestiekfabriek!

What is acoustics?