1. Applications of Architectural Acoustics
Tufts University – ES65 September 07, 2017

2. 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

3. Sound Proofing Reducing sound transmission between spaces
Source: Dan Russell, Penn State
Mass = A+ sound proofing
Air Between Two Decoupled Walls = B sound proofing
Click 1 – Animation
Click 2 – Wall Added
Click 3 – Wall + Air added
Click 4 – Mass & Air

4. Sound Proofing Achieved 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

5. Acoustical Treatment Designed for correction

6. Acoustical Treatment
Designed for a particular purpose and character

7. Acoustical Treatment
Designed for recording instruments & ensembles

8. Acoustical Treatment
Designed for critical listening and assessment

9. Reflections V λ= f Hard flat surfaces will reflect sound like a mirror
Any hard flat surface that is larger than the wavelength of a particular frequency will likely reflect energy at that frequency and above
Frequency 1 kHz
Wavelength 1 foot λ= V f
Period 1 ms
FLUTTER ECHOS
FOCUSES
Wavelength = Period / Frequency??? (look this up)

10. 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
Flutter echos are a concern for small rooms and studios.  These occur when high-frequencies are reflected multiple times.
Reflections of less that 20 ms can result in comb filtering
Desks
Play examples of a microphone on a desk stand
Music stands
Have them speak into a music stand, then add foam
Hard surfaces around speakers
Take a portable studio monitor, set it up in a corner, then move it away
Control room glass

11. Frequency Specific Issues
Modes or Standing Waves
Can be calculated
and mitigated
Types of room modes:
Axial = 2 surfaces
Tangential = 3 surfaces
Oblique = 4 or more surfaces

12. Calculating Axial Modes
Speed of Sound (1130 ft/second)
Dimension between the two boundary surfaces
Frequency of the mode
f = n(c / 2D)
Positive Integer
LENGTH
WIDTH
HEIGHT
1st Mode
2nd Mode
3rd Mode
4th Mode

13. Frequency Specific Issues
Nodes
Hard to prevent; move your groove thing

14. Treatment Materials
Absorbers
Diffusors
Reflectors

15. Absorbers Convert acoustical energy into heat Common absorbers Foam
The amount of heat generated is marginal
Common absorbers
Foam
Carpet
Draperies
Soft furniture
Large Mammals
Absorbers attenuate sound

16. 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

17. Decay time

18. Calculating decay time
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)
0.049Vf SA
RT60 =
0.161Vm SA
RT60 =
This would have to be totaled for different absorption coefficients at different frequencies, and different absorptive materials throughout a space. You can imagine how insane that could get with a space like Distler… There are more expansive versions of this formula to address further complexities of actual spaces. This is only a very rough estimate.

19. Measuring decay time

20. Anechoic Spaces Used for measurement
Measurement of sound, antennas, vibration. Equal absorption across the spectrum
Also radically low noise floor
Some people claim they cause hallucinations
Because they absorb so much energy, and require a great deal of energy to move air molecules inside of them

21. Diffusors
Blackbird Studio, Nashville
Diffusion SCATTERs sound

22. Diffusors Quadratic Fractal
Quadratic, Fractal, phase grating, formulas depend on what part of the spectrum you aim to diffuse.  Free construction plans at
Book cases and interrupted walls without large parallel surfaces help
Frequency and scatter patterns depend on size/shape

23. Reflectors Parallel Walls
Offset/non-parallel designed walls to redirect sound
Domes & curves

24. Intentional Reflectors
Acoustic shells
Kennedy Center – before & after acoustic shell

25. Measurement tools
EASE
SMAART
REW
Faber Acoustical

26. Building a small studio
Recording or critical listening/voice?

27. Speaker placement
Use heavy cinder block speaker stands to decouple from the floor
6 ft.

28. Mix Position 6 ft. Node? Especially in the center of a room
Area of optimal reflections
Too few reflections from the side can affect imaging

29. Major reflection issuesB O K S
Beware of desk reflections
6 ft.
RACK OF CLOTHES B O K S
Grow
more
hair
Flutter echoes
Will make you crazy
Modes
Could just be an awareness or EQ correction

30. Isolation & sound proofing
What sounds don’t we want in the recording space? What sounds don’t we want in the control room?
Computer noise
Refrigerators
Cell phones
Cats
All of the above
Transferred energy from the recording space(s)

31. 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

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

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

34. 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?