“A good auditorium
will accomplish effective projection of the sound to the rear of the auditorium
so that those distant listeners will not experience the extreme loss of sound
level caused by the inverse
square law. That projection is normally achieved by having a
sufficiently long reverberation
time. Another significant contributor will be a high, reflective
ceiling to reflect sound to the back of the auditorium.”
Here are two great reports on the acoustics of architecture
and the math behind it:
Firstly, the description of how the ear works is important. “The
ear has three main parts: the outer ear (including the external auditory
canal), middle ear, and inner ear. The outer ear (the part you can see) opens
into the ear canal. The eardrum (tympanic membrane) separates the ear canal
from the middle ear. The middle ear contains three small bones, which help
amplify and transfer sound to the inner ear. The inner ear contains the
cochlea, which changes sound into neurological signals and the auditory
(hearing) nerve, which takes sound to the brain. Any source of sound sends
vibrations or sound waves into the air. These funnel through the ear opening,
down the external ear canal, and strike your eardrum, causing it to vibrate.
The vibrations are passed to the three small bones of the middle ear, which
transmit them to the cochlea. The cochlea contains tubes filled with fluid.
Inside one of the tubes, tiny hair cells pick up the vibrations and convert
them into nerve impulses. These impulses are delivered to the brain via the
hearing nerve. The brain interprets the impulses as sound (music, voice, a car
horn, etc.).” http://www.entnet.org/HealthInformation/earWorks.cfm
Acoustics is the interdisciplinary science that deals
with the study of all mechanical
waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound.
The study of acoustics revolves around the generation, propagation and
reception of mechanical waves and vibrations. Architectural acoustics (also
known as building acoustics) involves the scientific understanding of how to
achieve a good sound within a building. It typically involves the study of
speech intelligibility, speech privacy and music quality in the built
environment. This science analyzes noise transmission from building exterior
envelope to interior and vice versa. The main noise paths are roofs, eaves, walls, windows, door and penetrations.
Sufficient control ensures space functionality and is often required based on
building use and local municipal codes.
Here are the technical aspects:
Interior building surfaces can be constructed of many
different materials and finishes. Ideal
acoustical panels are those without a face or finish material that
interferes with the acoustical infill or substrate. Fabric covered
panels are one way to heighten acoustical absorption. Perforated shows also sound absorbing qualities. Mineral
fiberboard, or Micore, is a commonly used acoustical
substrate. Finish materials often consist of fabric, wood or acoustical tile.
Fabric can be wrapped around substrates to create what is referred to as a
"pre-fabricated panel" and often provides good noise absorption if
laid onto a wall.
Prefabricated panels are limited to the size of the
substrate ranging from 2 by 4 feet (0.61 m × 1.22 m) to 4 by 10
feet (1.2 m × 3.0 m). Fabric retained in a wall-mounted
perimeter track system, is referred to as "on-site acoustical wall
panels". This is constructed by framing the perimeter track into shape,
infilling the acoustical substrate and then stretching and tucking the fabric
into the perimeter frame system. On-site wall panels can be constructed to
accommodate doorframes, baseboard, or any other intrusion. Large panels
(generally, greater than 50 square feet (4.6 m2)) can be created on walls
and ceilings with
this method. Wood finishes can consist of punched or routed slots and provide a
natural look to the interior space, although acoustical absorption may not be
great.
There are three ways
to improve workplace acoustics and solve workplace sound problems – the ABCs.
A = Absorb (via
drapes, carpets, ceiling tiles, etc.)
B = Block (via
panels, walls, floors, ceilings and layout)
C = Cover-up (via
sound masking)
Acoustic metamaterials are artificially fabricated
materials designed to control, direct, and manipulate sound waves as
these might occur in gases, liquids, and solids. The hereditary line into acoustic metamaterials follows
from theory and research in negative index material. Furthermore, with
acoustic metamaterials controlling sonic waves can
now be extended to the negative refraction domain.
Control of the various forms of sound waves is mostly
accomplished through the bulk modulus β, mass density ρ,
and chirality. The density and bulk modulus are
analogies of the electromagnetic parameters, permittivity and permeability in
negative index materials. Related to this is the mechanics of wave propagation
in a lattice structure. Also materials
have mass,
and instrinsic degrees of stiffness. Together these form a resonant system,
and the mechanical (sonic) resonance may be excited by appropriate sonic
frequencies (for example pulses at audio frequencies).
Further nerdy facts can be found here: https://en.wikipedia.org/wiki/Acoustic_metamaterials
In terms of materials:
When we choose the materials that will make up the structure
of a building, we are making decisions that will affect the nature of sound
within the building. Masonry materials are great for sound isolation,
especially when used in floors and walls where the masonry material is quite
thick. Wood is much less dense than masonry, and provides much less in the
way of sound isolation for that reason. Steel is a quite dense material, but
because of its expense it is rarely used as a sound isolation material. Steel’s
density actually becomes a liability in structural uses where its dense nature
causes it to carry sound vibrations for long distances. Insulating
materials have little mass, so they have limited uses for sound
isolation.
Elbphilharmonie Hamburg
Philharmonie de Paris
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