Also sometimes referred to as articulation, intelligibility or definition, clarity is the quality of sound that supports the comprehension of detail and the distinct separation of individual sounds and articulations.
Clarity is generally achieved with strong, direct sound to listeners, with an abundance of quickly-arriving sound reflections (0.0 to 0.05 seconds after the direct sound). It depends on the size, shape and materials used in the architectural space, as well as the absence of noise. Rooms should be designed to project sound to the audience.
A relative unit of measurement, being equal to one-tenth of a Bel (named in honour of Alexander Graham Bell). Decibel increments are based on a logarithmic scale, and so increase exponentially. Therefore, an increase of 3dB corresponds to an approximate doubling of power, while tripling the power is only equal to about 4.7dB. While decibels are technically a dimensionless unit (being a fixed ratio rather than a finite measurement of value), they are most commonly used to measure the loudness of sound, using an 'A' weighted curve based upon the 40-phon loudness contour.
The overall quantity of sound, as perceived by a listener. Also referred to as volume or strength. The units used to measure loudness are the Phon and the Sone.
With regards to acoustic design, loudness is achieved through close proximity to a sound source and from an abundance of early and late-arriving sound reflections within a sound-reflective room. Materials such as plaster, concrete, and other non-porous, massive sound-reflecting materials assist in maximizing loudness. Room size and shape can also strongly influence the apparent loudness within a space.
A unit for measuring loudness, originally based upon research conducted by Fletcher and Munson in 1933. The phon scale is logarithmic, so increases exponentially in value for each increment of measurement. 0 phon represents the threshold of audibility (ie. what can just be heard by a person with normal hearing), with 120 phon representing the threshold of pain (ie. so loud it hurts). These days, the phon is less frequently used for measuring loudness, in favour of the decibel, which is also based upon a logarithmic scale.
Also referred to as reverberance, decay or lingering, reverberation is the perceived lingering of sound following the cessation of music or speech.
Reverberation is created by an abundance of late-arriving sound reflections (0.25 to 2.20 seconds after direct sound) that have traveled long distances within a room due to multiple sound reflections. Room size, geometry and material selections all affect reverberation.
As defined by W.C. Sabine, Reverberation Time (RT) is the time taken for a continuous sound within a room to decay by 60 dB after being abruptly switched off. Sabine carried out a considerable amount of research in this area and arrived at an empirical relationship between the volume of an auditorium, the amount of absorptive material within it and a quantity which he called the Reverberation Time.
The sone is an alternative unit for measuring perceived loudness, proposed by S. Smith Stevens in 1936. Unlike the Phon, the sone scale is directly proportional to loudness (ie. does not increase exponentially between each increment of measure). Therefore, 1 sone is equal to approximately 40 phon, but 2 sone is equal to 50 phon, and 4 sone equals 60 phon. According to the sone scale, 0 sone is the threshold of audibility, and around 676 sone is the threshold of pain.
Daylight refers to the diffuse natural light coming from the whole of the sky dome or reflected off clouds, the ground and other adjacent surfaces in the surrounding environment. Daylight specifically precludes that component of light coming directly from the sun and is a desirable light source as it is free and very efficient relative to the amount of heat generated per lumen of light available.
Illuminance is a measure of the amount of light actually falling on a patricular surface. Illuminance is measured in either lux (lumens/square meter) or Footcandles (lumens/square foot). One footcandle equals 10.76 lux, although for convenience 10 lux commonly is used as the equivalent.
Luminance is the measure of the amount of light being emitted or reflected off a particular surface. This is the photometric quantity that our eyes react to and therefore governs our perception of brightness. Luminance is measured in units of luminous intensity (candelas) per unit area (square feet or square meter).
Luminous Efficacy is the ratio between the amount of light that a source generates relative to its heat output. It is measured in lumens per watt (lm/W). A 150W incandescent bulb has a luminous efficacy of between 16-40 lm/W, while diffuse skylight is around 150 lm/W (ie. produces more than three times the light for each watt of heat generated).
Sunlight refers to the light coming directly from the sun itself, passing straight through the atmosphere without reflection, refraction or diffusion. Sunlight is therefore highly directional - coming obviously from the current position of the sun in the sky which varies both seasonally and diurnally. Additionally it is often obscured by clouds, trees and even other surrounding buildings, so its level can also change quite rapidly.
Solar radiation is radiant electromagnetic energy emitted by the sun. This radiant energy ranges from very high frequency gamma and cosmic rays right down to much lower frequency radio waves at the other end of the spectrum. The majority of this energy falls within the near infra-red and visible light freqency bands.
Shading coefficients rate windows and other transparent apertures based on the fraction of solar heat gain that passes through compared to either the incident solar radiation or the transmission of a reference glazing type. They are all given as a decimal value in the range 0-1, however there several different types, each using a different reference measure for comparison. These include the standard '''Shading Coefficient (SC)''', the '''Solar Heat Gain Coefficient (SHGC)''' and the '''G-Value (G)'''. In all case, the lower the shading coefficient, the less solar heat the object will transmit and the greater its overall shading ability. Thus, a higher coefficient is more effective at transmitting solar heat gains in winter whilst a low coefficient is more effective at reducing cooling loads during the summer by blocking heat gain from the sun. Therefore, what shading coefficient you need for a window, door, or skylight should be determined factors such as the climate, surface orientation and the nature of any external obstructions.