Acoustics Flashcards
Focusing
Sound is focused by concave surfaces and directed into a specific part of a room. Like at Union station or daap
Creep
Reflection of a sound along a curved surface such as a dome. Sound can be heard at points along the way but not across the room like with focusing.
Diffusion
Sound is scattered around a room by convex surfaces. Opposite of focusing.
Specular relfection
Reflection of sound of hard, polished surfaces
Buffer sound attenuation strategies
Solid sound barriers are effective when tall enough, close to either the source or receiver, and dense
Planting a combination of deciduous and evergreen trees and shrubs on a mound in large, deep groupings. The depth must be 100ft to be effective at blocking 10 dB (noticable difference).
Maximize distance between source and receiver
Avoid hard and parallel surfaces near receiver
Masking sounds like fountains help
Use solid balconies or laminated glass in the building
Ideal room absorption coefficient and effects of adding more
Between 0.20 and 0.50. Each doubling of absorption in a room reduces noise by 3 dB. Total should be tripled for a change of 5 dB.
Impact Insulation Class (IIC)
Code minimum for multi-family res: 50
Techniques: Mass, stiffness and decoupling hard surface from structure with acoustic underlayment, isolate ceiling with resilient clips or spring hangars
Complaints of footfall are more likely with concrete over wood floor construction because high frequency “clacks” are more audible with concrete.
Sound absorption in small v. large rooms
Celling treatment is better in large rooms
Wall treatment is better in small rooms
Reverberation time
The time it takes the sound level to decrease 60 dB after the source has stopped producing the sound. Each doubling of absorption in a room cuts this time by half.
NRC relationship to STC and absorption coefficient
High NRC = Low STC because porous materials are not good at blocking sound
High NRC = High Absorption Coefficient
Noise reduction
NR = Transmission Loss x 10log(Acoustical abosrption of receiving room / area of the barrier)
The difference in intensity levels between two rooms separated by a barrier given a transmission loss level.
Absorptive panels in receiving room help.
Transmission loss
Difference between sound power incident on a barrier in a source room on the opposite side of the barrier (typically a laboratory measurement). Double layer of gyp board helps.
Total absorption of a room
Coefficient of absorption (NRC) x area of each wall and element added up
Sound intensity in a room
Decreases 6 dB for each doubling of the distance between source and receiver
