1!

First, a definition…

!  Acoustics

Definitions

"  the “science of sound” "  describes the behavior of

sound waves in a room

!!Acoustics: Reflection of Sound

!  Sound reflects off of surfaces at angle equal (and opposite) to angle of incidence

Reflection of Sound

!!Reflection of Sound

!  predictable result involving smooth, concave, and convex surfaces

Reflection of Sound

2!

!!Reflection of Sound

!  Multiple reflections & “buildup” (wall-floor intersections)

Reflection of Sound

Acoustics: Absorption of Sound

!  some sound energy “absorbed” by surface material

!  some sound energy “reflected” by surface material

!

Absorption of Sound

!!Acoustics: Diffusion of Sound !  scattering of sound in all

directions on reflection from a surface

Diffusion of Sound

Acoustics: Diffraction of Sound

!  spreads around barriers

!  bends through an opening!

Diffraction of Sound

3!

Room Treatment

Control Room Acoustical Treatment Improve room acoustics (control unwanted room reflections) using …

•  strategically placed absorbers, diffusers, and bass traps

Typical Studio Design

Control Room View

Studio View

Typical Studio Design

Typical Studio Design (Floor plan)

Control Room

Studio Isolation Booths

Sound lock

Room Shape

Room Shape

Control Room

(Listening)

Studio

(Recording) Isolation Booths

centerline

Asymmetrical

Symmetrical

4!

Noise

• “Noise” (unwanted sound) will disturb audio production

• comes from external (outside) & internal (inside) sources

• Noise Criteria (NC) is a rating system used by acousticians

Very

Quiet

Very

Noisy

Noisy Moderately

Noisy

Quiet

Noise

Isolation

Isolation

preventing sounds from studio ‘leaking’ into outside areas

preventing outside noises from transmitting into the studio via air, ground, structure

preventing sound from ‘leaking’ between areas

• Specialized construction techniques are used to improve “isolation” from outside sound & between adjacent rooms

Hearing is Binaural

First, a definition…

!  Psychoacoustics

"  human perception of acoustics

" our subjective response to the sound waves

Hearing is Binaural

5!

Perception of Direction = Spatial Localization !  need two ears to localize

sound source

!  called spatial or binaural

localization

!  three mechanisms

Spatial (Binaural) Localization 1. Arrival time differences

Perception of Direction = Spatial Localization

1. Inter-aural (between ear)

arrival-time differences

2. Intensity differences

Perception of Direction = Spatial Localization

2. Inter-aural (between ear) intensity differences

louder softer

3. Vertical localizing

3. The effect of the pinnae (reflection on an asymmetrical surface)

Perception of Direction = Spatial Localization

6!

!  need two ears to localize

sound source

!  three mechanisms "  arrival time "  intensity "  pinna reflection

!  better at localizing ‘forward’ (in front)

Spatial (Binaural) Localization

Perception of Direction = Spatial Localization

Acoustic Behavior of Sound in an Enclosed Room

!  ear and brain combine to

perceive the size and physical characteristics of an acoustic space

Perception of Space

Perception of Space

Perception of Space

“direct sound” " shortest path

" tells location, size, timbre

of source

!

!

Direct Sound

Perception of Space

“early reflections” " travel longer (<50 ms)!

" tell reflectivity, size, etc. of space

" elapsed time gives size info

!

Early Reflections

7!

!!

“temporal fusion”

" reflections w/i 30ms are suppressed and fused with direct

sound by the ear and brain >> ‘one source’

Temporal Fusion

Haas (“precedence”) effect "  apparent location of source when the sound is heard from

two sources but arriving at different times >> earliest & loudest!

Perception of Space

reverberation (‘late reflections’) "  reflections off of many boundaries

"  random, diminishing sound "  ratio of direct to reverberant sound

= distance from sound source

!

!Reverberation

!! “LIFECYCLE OF SOUND IN A SPACE”

Lifecycle of Sound in a Space

‘source’ ‘room’ ‘distance’

Neumann demo

!!Reverberation Time of Acoustic Spaces

Reverberation Time of Acoustic Spaces

• Reverb Time = amount of time for sound to ‘die away’ (-60dB)