1. Architectural Acoustics of Closed Spaces
PHYS 536: Introduction to Acoustics
University of Washington, Fall Pankaj Karna
Introduce, Topic

2. Objective: Explain architectural acoustics by comparing different
sample cases of closed space
Agenda
Introduction/background
Cases:
Auditorium (sound enhancement)
Library (sound suppression)
Factory Interior (high noise environment)
Summary
Questions
My objective here is to explain architectural acoustics by comparing different types of closed spaces. My three cases are an auditorium where we need to enhance sound. A library where we need to suppress sound and a more challenging case , a factory interior which is a high noise environment in itself. So lets have a quick look at the outline and then we can go into the details. First, I will explain a little background of architectural acoustics. Then we will look at the three cases in detail. Finally I will summarize everything and open the floor for questions.

3. Introduction/Background
Definition : The science and engineering of achieving good sound within a building. It involves broad range of technics and materials. History: Greeks and Romans were pioneers. First recorded mention of architectural acoustics is in De Architectura by Roman Architect Marcus Vitruvius Pollio (1st Century BC).
Architectural Acoustics as the name suggests is the science and engineering of achieving good sound within a building. It involves broad range of techniques, materials and design features. Greeks and Romans were pioneers. First recorded mention of architectural acoustics is in De Architectura by Roman Architect Marcus Vitruvius Pollio (1st Century BC). He talked about layout, construction, materials and orientation of a theaters.
One of Vitruvius geometrical lay out of the Greek theatre
Image credit: ancient.eu

4. How did we get to closed spaces
Since the theme of our presentation is closed spaces, lets see how did we got to closed spaces in first place. Early gathering or performance spaces were mostly open. The Greeks had a wide open theater with uphill seating which helped with some reflection and distribution of sound. The romans went one step further and added huge back walls, arches and canopy like awnings. As we see, the romans were just one step away, all they needed is a roof. So it gradually moved from open to closed spaces. Then of course, we have the modern day theaters which are all enclosed and furnished with sophisticated materials and techniques.
Ancient Greek Theater
- Mostly open
- Uphill seating
Ancient Roman Theater
- Greek Theater +
- Back Walls +
- Arches +
- Awnings
Modern day theater
All enclosed with sophisticated materials and techniques
Image credits: Britannica encyclopedia

5. Cases/Types of Closed Spaces
Auditorium
Designed to Enhance sound
(music, Speech)
Library
Designed to
Suppress Noise
(background noise, Speech)
Factory Interior
Designed to
Suppress higher noise
Environment
(machinery, industrial processes )
We will focus on Indoor Spaces today. Let us look at the architectural acoustics of these three types of closed spaces with different acoustical needs and discuss their acoustical solutions. Lets look at them individually.
Image credits: Construct Canada

6. Case 1: Concert Hall/Auditorium
Aim/requirements
The audience must clearly hear all of the music
The performers must hear each other.
Reverberation should be appropriate to the style of the music.
Extraneous sounds must be inaudible in the concert space.
Important Considerations for architects:
Reverberation
Envelopment
Clarity
Shape and size
The purpose of a concert hall or auditorium is to enhance sound or music. The basic requirements are that audience and performers must clearly hear all of the music and sound, performers obviously need to hear each other to stay in sync. Reverberation and reflections that occur should be helpful, not detrimental. They should be appropriate to the style of the music. Lastly we want to shield any external noise, to meet these requirements any architect pays special attention to some acoustical phenomena like reverberation, envelopment, clarity, Shape and size. There are many other factors but we will focus on these main ones today.

7. Concert Hall: Reverberation and Envelopment
Image source: Penn State Physics Website
3 sources of sounds Direct , Early reflection and Late reverberation
Reverbarance: collection of reflected sounds from surfaces of an enclosure
Envelopment: perception of being surrounded by sound for the listener.
Achieve right frequency response and reverberation time
Use elements that we can quantify to improve perception of sound.
There are three sources of sound in a closed hall, direct sound from the source , early reflections and late reverberation at eventually die out. We use all these to create the perception of being surrounded by sound all around the listener. In other words create envelopment . It’s not just the big spaces, musicians play under bridges , arches or subways to obtain envelopment. Mathematically, the aim is to achieve right frequency response and reverberation time. We have already seen the calculation of reverberation time in class so I will not repeat it. In other words , we are trying use elements that we can quantify such as speed and frequency to improve perception of sound for the audience.

8. Concert Hall: Clarity vs Fullness
Fullness generally implies a long reverberation time
A fuller sound is generally required of Romantic music or performances by larger groups
Clarity implies a shorter reverberation time. It is the opposite of fullness, can be achieved by reducing the amplitude of the reverberant sound.
Clarity would be desirable for faster music and speech(for example classroom)
An ideal auditorium would be the one that can switch both modes by adjusting curtains, reflectors and diffusers.
Another design criteria to consider for architects is Clarity vs Fullness. Fullness generally implies a long reverberation time. A fuller sound is generally required of romantic music or performances by larger groups. On the other hand Clarity is the opposite of fullness. It is achieved by reducing the amplitude of the reverberant sound. Clarity would be desirable for faster music and speech (for example classroom).

9. Concert Hall: Components
Some important components of a concert hall are: Reflectors: Sound reflects off flat, large hard surfaces like walls or ceilings Absorbers: Soft or porous surfaces that can absorb sound like linings Diffusers: A rough surface, a diffuser, disperses sound in all directions.
Now since we have discussed important design criteria, let us see how do we achieve the. For a concert hall, some important components are reflectors, diffusers and absorbers.
Reflectors: Sound reflects off flat, large hard surfaces like walls and ceiling. Unplanned concave, convex or parallel hard surfaces can result in unwanted reflections
Absorbers: Soft or porous surfaces that can absorb sound. Absorption is usually avoided in concert halls because it eliminates desired sound. Listeners and cushion seating arrangements cause most absorptions in an auditorium.
Diffusers. A diffuser is a rough surface that disperses sound in all directions. Diffusers have many uses. For example they can remove detrimental echoes caused by surfaces such as the rear wall behind the audience.

10. Concert Hall: Some design considerations
Image source: USCS music website
Reflectors and absorbers should be strategically placed using sound ray mapping
Small design considerations like sound ray mapping can make a lot of difference. Reflectors should be strategically placed. For example, for a long room reflectors should be closer to the speaker to enable uniform distribution of sound. Also, the back celling and wall should have absorbers to prevent echo.

11. Concert Hall: Considering shape and Size and positioning
Mean distance between source and listener is an important factor to consider.
Flutter echoes are produced by sound traveling quickly between two parallel reflective surfaces, they can be avoided by shifting source position
For a relatively smaller room flutter echoes are produced by sound traveling quickly between two parallel reflective surfaces. For example, a shoe box style hall can produce flutter echoes. We can avoid them by shifting the position of source.
Image credits: IIT Kharagpur website

12. Concert Hall: Design process
Requirements > Important factors > components, materials
Designed for
sound Enhancement
(music, speech)
Reverberation
Envelopment
Clarity
Size and Shape
Reflectors
Absorbers
Diffusers
So this is sort of the general design process for an auditorium. First we look at the requirements then consider important factors to meet those requirements. Then finally execute it with right techniques and materials. People who design them take it very seriously. Here is an example of a table top miniature concert hall someone built. It is fitted with all the features and sensors for measurements. My original plan was to built one of those for demo, time did not allow.
Image credits: Rensselaer Architecture

13. Closed room : with and without acoustical treatment
Difference between with and without acoustical treatment. Same instrument
Same beat
same room
Here we have a demonstration of difference between with and without acoustical treatment. The sounds are from the same instrument, same beat in the same room.

14. Acoustics of a library
Requirement: Suppress sound to enable quieter environment Solution: A = Absorb B = Block C = Cover-up D = Diffuse
The acoustical goal of a library is to suppress sound, mostly coming from background noise like HVACs and some human speech. It can be achieved by the following.
A = Absorb (via drapes, carpets, ceiling tiles, etc.). Extreme version of this absorption would be the Anechoic Chamber which is already discussed.
B = Block (via panels, walls, floors, ceilings and layout)
C = Cover-up (via sound masking noisy surfaces)
D = Diffuse (Enable the sound energy to spread by radiating in many directions)
Example book racks can act as both absorbers and blockers.
Image credit: University of Wisconsin-Madison

15. Local example: Kane Hall vs Suzallo Library study Hall
Lets look at a Suzallo Library vs Kane Hall. To an general person both might look like a nice architectural design but to an acoustically aware person the features are clearly visible. The study hall has features to suppress noise, high ceilings, absorptive surfaces, On the other hand good old Kane Hall has the acoustical features needed for sound enhancement like reflectors and diffusers. To make a confession, I was that general person before taking this course, now I am a little more acoustically aware. When it comes to indoor noise control library is not a great example. Nobody Expects Library to have too much artificial noise. Lets look at a more challenging case. Lets look at a factory interior and see.
Image credits: University of Washington
Suzallo Library
Designed to suppress noise
-absorbing materials
-high ceiling to avoid reflections
-book shelfs on the side
Kane Hall
Designed to enhance sound
-less absorbing materials
- Strategically placed reflector
- Hard reflecting walls

16. Factory Interior Noise Control
Factory interior is a high noise environment by default
Main Sources are
Machinery and
Industrial processes
Solution
Reducing noise at source
Insulation (factory walls and machine interiors)
Isolation
Nobody Expects Library to have too much artificial noise. Lets look at a more challenging example. A factory interior, factory interior is a high noise environment by default. The main obvious sources are machinery and industrial processes. Here we will discuss the common methods or controlling these noises inside closed factory spaces, first is to reduce the noise at source itself, then insulating the noise source and finally isolation. Lets look at the them individually.
Image credits: Oscar Acoustics

17. Controlling factory noise at source
Common culprits: generators, compressors, motors, air blowers, turbines etc.
The most economical and efficient way to control noise is at the source.
Important that we understand:
amount of noise radiated from a machine surface depends on the
amplitude of the vibration and
surface area of the radiating surface.
Amplitude is determined by the resistance of the surface to oscillatory motion
Solutions:
By reducing the amount of energy communicated to the vibrating surface
By reducing the geometrical surface area itself.
One of the basic principles of noise control is that noise should be reduced as near the source as possible. The greatest number of people are protected from the noise by this means, and moreover, the noise control treatment is less expensive. The noise that is likely to be produced should be considered at the very beginning of the planning of a factory, even before the orders are placed for machines and tools. The machines and process used for production determines the level of noise on factory floor. We can control them by reducing the amount of energy communicated to the vibrating surface and by reducing the geometrical surface area of the radiating surface itself.

18. Factory Noise control: Insulation
Image credit: Jaladi Muda Industrial Acoustics
Once the noise is already produced the next line of noise control is to insulate.
Insulation is next method for noise control
At Macro Scale:
Entire Factory walls, doors, windows
At micro Scale:
Insulate interior of the machine : absorptive lining, foam etc.
Insulate it from outside: enclosures
Once the noise is already produced the next line of control is to insulate. At Macro Scale we can insulate the entire factory walls, doors, windows. We see some insulation at residential buildings to but industrial grade insulation is much absorptive. At micro scale we can insulate interior of the machine using absorptive lining foam. In some cases lining the machine internally is not possible , so use external enclosures like the one in the picture. There are professionals companies that specialize in just building such enclosures.

19. Factory Noise control: Isolation
Problem:
Vibration can be conducted along a mechanically rigid path for long distance inside a factory. It is worse in case of multi floor factories
Solution:
Geographically/physically isolate noise/vibration generating elements
Pneumatic suspension can be added to added to avoid transmittal of vibration.
Use resilient material to absorb vibration in the path
The reduction achieved depends on the ratio of the driving frequency of the source to the natural frequency of the resilient material.
The higher the ratio between the two frequencies, the greater the noise reduction.
If both the noise cannot be contained at the source by reduction or insulation. The next line of defense is to isolate the source of that noise. Vibration gets transmitted for long distances in a factory through mechanically rigid path like walls or floors .It is worse in case of multi floor factories because it can cause surround effect. The solution to this problem is to physically isolate the source, use suspensions or use resilient material to absorb vibration in the path. The reduction of vibration obtained from this method depends on the ratio of the driving frequency of the source to the natural frequency of the resiliently supported system. The natural frequency depends on the stiffness of the system. The higher the ratio between the two frequencies, the greater the noise reduction we can achieve.

20. Background : From open to closed Spaces
Summary
Background : From open to closed Spaces
Comparing three sample cases of Closed Spaces
Auditorium
Designed for
sound Enhancement (music, Speech)
Factors
Reverberance
Envelopment
Clarity
Size and Shape
Components
Reflectors
Absorbers
Diffusers
Library
Designed to
Suppress Noise
(music, Speech)
A = Absorb
B = Block
C = Cover-up
D = Diffuse
Factory Interior
Suppress higher noise
Environment
Reducing noise at Source
Insulation (Building and machines )
Isolation
That was a lot of information so I will quickly summarize it. We started with a little intro /background about architectural acoustics. We saw how we went from wide open spaces to enclosed spaces from a historical perspective. Then we looked at the three cases of closed spaces and discussed some techniques to create the right acoustical environment for these cases. A library where we need to suppress sound and a more challenging case, a factory interior which is a high noise environment in itself.

21. Bibliography
1. Designing interior architecture concept, typology, material, construction Sylvia Leydecker; 2013 Basel : Birkhäuser
Citation: Leydecker, S. (2013). Designing interior architecture concept, typology, material, construction. Basel: Birkhäuser.
2. Acoustic echoes reveal room shape
Citation: Dokmanic, Ivan ; Parhizkar, Reza ; Walther, Andreas ; Lu, Yue M ; Vetterli, Martin
Proceedings of the National Academy of Sciences of the United States of America, 23 July 2013, Vol.110(30), pp
3. Analysing Sound Environment and Architectural Characteristics of Libraries through IndoorSoundscape Framework
Dokmeci Yorukoglu, Papatya Nur ; Kang, Jian
Archives of Acoustics, 06/1/2016, Vol.41(2), pp
Citation: Dokmeci Yorukoglu, P., & Kang, J. (2016). Analysing Sound Environment and Architectural Characteristics of Libraries through Indoor Soundscape Framework. Archives of Acoustics,41(2),
4. In the place of sound : architecture, music, acoustics
Colin Ripley; Marco (Marco L.) Polo; Arthur Wrigglesworth;Ryerson University.;
2007 Newcastle, UK : Cambridge Scholars Pub.
Citation: Ripley, C., Polo, Marco, Wrigglesworth, Arthur, & Ryerson University. (2007). In the place of sound : Architecture, music, acoustics. Newcastle, UK: Cambridge Scholars Pub.
Some of the sources that I used

22. Bibliography (..continued)
5. Guide for industrial noise control
Paul N. Cheremisinoff Fred Ellerbusch
©1982 Ann Arbor, Mich. : Ann Arbor Science
Citation: Cheremisinoff, P., & Ellerbusch, Fred. (1982). Guide for industrial noise control. Ann Arbor, Mich.: Ann Arbor Science.
Some images are credited individually

23. Architectural Acoustics of Closed Spaces
Questions ?