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Soundscape Design for Outdoor Spaces

Apr 17, 2020
Video Length:  1:01:58
Presented By:  Alex Zahn

Sound has a proven and enormous impact on our perception and emotions. Even so, acoustic aesthetics have historically lagged far behind visual aesthetics as a point of focus in architectural design. Amid increasing noise pollution, careful consideration of the “soundscape” in landscape design and its effect on listeners has grown considerably since the 1960s and is currently more important than ever. We’ll give you some, ahem, sound advice on outdoor acoustics and provide some design techniques you can use to improve the soundscapes of the exterior spaces you design.

Webinar Contents:

Note: The following catalog of content covered in this webinar is time stamped to allow you to follow along or skip to sections of the video that are relevant to your questions. You can also search for content on this page using the FIND command in your browser (CTRL + F in Windows, Command + F in Mac OS.)

  • Intro/TOC
  • A Sound Foundation: The Basics of Acoustics
  • Enter the Soundscape
  • Establishing Design Objectives
  • Shaping the Soundscape: Design Techniques to Control Sound
  • Review

0:00 – 7:38: Intro/TOC

Why soundscape design? (4:00)

  • Societal value
  • Environmental value
  • Economic value

 

An example: courtyard sounds (5:22)

7:39 – 18:29: A Sound Foundation: The Basics of Acoustics

Light waves and sound waves (8:12):

  • Like light, sound waves radiate outward in three dimensions.
  • Like light, sound waves can reflect off of surfaces.

 

Example: Light applause, direct sound only vs. direct sound and reflections (9:17)

 

Concave vs. convex surfaces (10:14):

  • Concave surfaces focus sound to one area.
  • Convex surfaces disperse sound.

 

Smooth vs. rough surfaces (10:58):

  • Smooth surfaces reflect sounds at the angles from which they come.
  • Rough surfaces disperse sounds at various angles.

 

Example: Smooth, flat surroundings vs. rough, textured surroundings (12:03)

 

Visible light spectrum and audible sound spectrum (13:54)

 

Frequency (16:03):

  • High frequency = short wavelengths.
  • Low frequency = long wavelengths.
  • The longer the wavelength, the farther it will penetrate.
  • Low-frequency sounds:
    • Travel farther
    • Pass through materials more easily

 

Quick review (16:53):

  • Concave surfaces focus reflections.
  • Convex surfaces disperse reflections.
  • Smooth surfaces allow direct reflections.
  • Rough surfaces disperse and absorb.
  • Sound frequencies fall into a wide range, just like colors of light.
  • Low-frequency sound absorption requires dense, thick materials.

 

What about measurement? (17:34)

  • Our ears perceive loudness logarithmically (not linearly).
  • Loudness is measured in dB(A).

 

Sound Level Change

 0 db

-3 db

-10 db

-20 db

-30 db

-40 db

Relative Loudness

Reference

Perceptible change

Half as loud

1/4 as loud

1/8 as loud

1/16 as loud

18:30 – 22:07: Enter the Soundscape

Sound does not equal noise (19:12):

  • Noise is unwanted sound.
  • What's defined as "unwanted" will vary from project to project.
  • The soundscape is an accumulation of many distinct sounds. Only some of them are noise.
  • Overall loudness is a red herring. The importance lies in the actual content and significance of each sound.

 

Components of the soundscape (20:03):

  • Keynote sounds
    • The "background."
    • These set the tone and space.
  • Sound signals
    • The "foreground"
    • Convey information
  • Soundmarks
    • Audible landmarks

22:08 – 30:39: Establishing Design Objectives

What to consider (22:47):

  • Acoustic characteristics of the space
    • Size, surroundings, material, and shape of surfaces
  • Characteristics of each sound present
    • "Color," time, loudness, significance
  • The intended use of the space
    • Zoning, surrounding environment
  • The intended users of the space
    • Personal characteristics and sound preferences

 

Consider the area's intended use (24:12):

  • Is it a work area that requires quiet and speech privacy?
  • Is it a performance area that requires sound to go from stage to audience?
  • Are there nearby private residences or quiet areas?
  • How will wildlife be affected?
  • Will noise from a nearby highway or busy street pervade the space if not accounted for?
  • Will people use the space if that background noise is present?

 

Consider the space's intended users: (25:45)

 

  • There are significant differences in sound preferences across age groups. (25:45)
  • Examples:
    • Music from stores
    • Birdsong

 

  • There are significant differences in sound preferences across cultures. (27:40)
    • When asked how favorable they considered speech sounds in a public square, over 50% of Greeks rated them 'annoying,' while less than 1% of Germans rated them 'annoying,' and over 45% of Italians rated them 'favorite.'" (Yang & Kang, 2003)

 

Defining your soundscape objectives (28:34):

  • Focus on:
    • Site context
    • The information content of sounds
    • Relative loudness (i.e., the relation of sounds to each other)

 

Examples from Zion National Park:

  • "Natural sounds are audible and discernible, with common noise intrusions by visitors and park operators concentrated near roads and heavily developed areas."
  • "Noise levels that mask important auditory signals for wildlife should be uncommon and should be limited to locations near roads and heavily developed areas."
  • "Moving water should be the dominant sound heard."

30:40 – 50:12: Shaping the Soundscape: Design Techniques to Control Sound

Objective: Provide wanted sounds & reduce the level of unwanted sounds (31:03)

 

Provide wanted sounds (31:24):

  • Take advantage of existing water features, or add some, such as fountains.
    • Is a quiet, trickling fountain or a large, powerful fountain more appropriate for this space?
  • Choose plants that attract birds and wanted insects.
  • Include interactive features, or passive features like sound sculptures.

 

Examples (33:06):

  • Aeolian harp
  • Sea Organ, Croatia

 

Reduce the level of unwanted sounds (34:17):

  • Use appropriate forms, boundaries, and sound-absorbent materials.
    • Green walls, green roofs, dense hedges
    • Choose highly sound-absorbent plants where necessary.
  • Spacing
    • Consider seating arrangements at a café on a busy city street, compared with seating arrangements in a tranquil garden.
  • Mask them with wanted sounds.
    • The sound of rushing water from a fountain or waterfall can help cover up some noise such as traffic sounds.

 

Materials: stone gabion barrier vs. porous clay barrier (36:05)

 

Which plants are highly sound absorbent? (37:30)

  • Thick leaves, densely packed
  • Leaves with high surface area
  • Leaves that grow out from branches at larger angles

 

Examples:

  • Thuja plicata (western red cedar)
  • Hosta montana (plantain lily)

 

Example rendering, courtesy of Coleman & Associates (38:52)

 

Example: pedestrian area next to roadway (40:00):

  • Without abatement
  • With barrier and trees

 

More examples: bike/pedestrian path beneath a roadway or tramway (42:58)

 

One highly efficient noise treatment, or many less-effective treatments? (44:31)

It's generally more cost effective to use cheaper strategies and cover all noise sources, than to focus on just one noise source.

 

Example: Atlanta Botanical Garden amphitheater (47:04)

50:13 – end: Review

  • Concave and flat surfaces reflect sound and enhance the sense of space.
  • Convex and textured surfaces disperse and absorb sound.
  • Low-frequency sound absorption requires thicker materials.
  • Not all sounds are equal.
    • Consider keynote sounds, signal sounds, and soundmarks.
    • Consider your site's intended use, and intended users' preferences.
    • Determine which sounds are wanted and which are noise.
  • Design the space to provide wanted sounds and reduce unwanted sounds.
    • Use appropriate forms and spacing to shape the space acoustically.
    • Choose plants and planting areas wisely.
    • Don't put all your eggs into one basket – use noise-reduction techniques on as many noise sources as you can.

 

Many design choices can full two needs with one deed. (52:10)

Examples:

  • Plant choices that absorb noise, attract birds, and improve visual aesthetics
  • Using excess soil and stones from construction work to build noise-reducing berms

 

Additional resources:

 

Question: Are there cultural considerations to sound design like there are for color? (54:42)

Answer: Yes, the preferences of users by culture can vary. It's not so much the frequency of the sound to consider but the emotional significance of the sound, which will often vary between cultures. See research by Kang and Yang for more details.

 

Question: Is sound basically just line of sight? (55:36)

Answer: Not necessarily. Sound can reflect off of surfaces. Rather than looking at line of sight, it's important to pay attention to surroundings and which objects could potentially reflect sounds.

 

Question: Considering barriers, is it better to layer multiple barriers or focus on the material of a single barrier, and are you focused on the line of sight direction with barriers? (55:36)

Answer: When it comes to one noise source, it's generally best to install one treatment for that one source. If you apply multiple techniques to one sound without a close analysis of what they're actually doing, the combination of measures may either boost one or more of the frequencies or even cancel each other out.

 

Question: What about taking into account hearing loss for aging populations? (59:02)

Answer: It's difficult to characterize hearing loss because of all the different "colors" of sound across the spectrum. Each individual who has experienced hearing loss will have different challenges hearing specific portions of the spectrum.

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