Applications of Architectural AcousticsTufts University – ME 93September 10, 2015

Outline• Sound Proofing vs. Acoustical Treatment• Concerns addressed through acoustical treatment• Materials used in acoustical treatment• Measurement tools in acoustic analysis• Considerations in small recording spaces• Next steps

Sound ProofingReducing sound transmission between spaces

Source: Dan Russell, Penn State Mass = A+ sound proofingAir Between Two Decoupled Walls = B sound proofing

Sound ProofingAchieved with:• Mass, Isolated Construction and Tight Closures• Cinder blocks for speaker stands, heavy doors• Room-within-a-room construction• Door, window and wall seals

• See White: Chapter 18 for more information

Acoustical TreatmentDesigned for correction

Acoustical TreatmentDesigned for a particular purpose and character

Acoustical TreatmentDesigned for recording instruments & ensembles

Acoustical TreatmentDesigned for critical listening and assessment

Reflections• Any hard surface will likely reflect sound• Any hard flat surface that is larger than the

wavelength of a particular frequency will likely reflect energy at that frequency and above

Frequency1 kHz

Wavelength1 foot

Period1 ms

λ= Vf

Reflections• Echoes are distinct reflections where we can pick

out the individual occurrences.• We start hearing distinct delays around 20 ms

• Reflections of less than 20 ms can result in comb filtering

Comb filter caused by two signals generated1 ms apart

Frequency Specific IssuesModes or Standing Waves• Can be calculated

and mitigated

• Types of room modes:• Axial = 2 surfaces• Tangential = 3 surfaces• Oblique = 4 or more surfaces

Calculating Axial Modes

f = n(c / 2D)

Frequency of the mode

Dimension between the

two boundary surfaces

Speed of Sound(1130 ft/second)

Positive Integer

LENGTH WIDTH HEIGHT

1st Mode

2nd Mode

3rd Mode

4th Mode

Frequency Specific IssuesNodes• Hard to prevent; move your groove thing

Treatment Materials• Absorbers• Diffusors• Reflectors

Absorbers• Convert acoustical energy into heat• The amount of heat generated is marginal

• Common absorbers• Foam• Carpet• Draperies• Soft furniture• Large Mammals

Absorption Coefficients

• Measured across the spectrum• 0 = perfect reflector 1 = perfect absorber• Noise Reduction Coefficient = average of four octaves

(250, 500, 1k, 2k)• We generally want to absorb equally across the spectrum• White pg. 169 has coefficients for common materials

Decay time

Calculating decay time

0.049Vf

SA

0.161Vm

SA

RT60 =

RT60 =

Sabine’s Equation:V = volume of the space

(in cubic feet or meters)

S = absorbing surface area

(in ft2or m2)

A = absorption coefficient(in Sabins)

Measuring decay time

Anechoic SpacesUsed for measurement

DiffusorsBlackbird Studio,Nashville

Diffusors Quadratic Fractal

Frequency and scatter patterns depend on size/shape

Reflectors• Parallel Walls• Offset/non-parallel designed walls to redirect

sound• Domes & curves

Intentional ReflectorsAcoustic shells

Kennedy Center – before & after acoustic shell

Measurement tools• EASE• SMAART• REW • Faber Acoustical

Building a small studio

Speaker placement

6 ft.

6 ft.

6 ft.

Use heavy cinder block speaker stands to decouple from the floor

Mix Position

6 ft.

6 ft.

6 ft.

Major reflection issues

6 ft.

6 ft.

6 ft.

BOOKS

BOOKS

RA

CK

OF

CLO

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Grow more hair

Beware of desk reflections

Isolation & sound proofingWhat sounds don’t we want in the recording space?

What sounds don’t we want in the control room?

Recording Acoustic Instruments• Special Concerns• Sound proofing• Room volume

• Does the sound have time to develop?

• Ambient noise floor• HVAC• Computers and noisy devices

• Sonic character

Safety and Aesthetics• Fireproofing is a thing• Aesthetics are also a thing• If it sounds good, is it good?

Work with what you have• Check low-end in good quality headphones• Look for drastic gestures in your work• Just do something and learn

Next Steps• Fields of acoustics• Architectural Acoustics Graduate Programs• Internships related to Architectural and Musical

Acoustics• Job descriptions for careers related to Acoustics• Play with free toys, check out additional resources• What can you do to optimize your own space?