BU3 Module 2B and 3

• Sound absorption


  The rate at which sound is absorbed in a room is a prime factor in reducing noise and controlling reverberation
• Proper acoustical control often requires use of materials popularly known as "acoustical" materials
• It is always necessary to choose materials with proper acoustical characteristics but this is not enough. All other physical and decorative properties of the materials must be given proper attention
• Sound absorption


  Sound is absorbed by a mechanism that converts the sound into other forms of energy and ultimately into heat
• Porous materials


  • If the material is sufficiently porous, and of appropriate thickness, as much as 95% of energy of the incident sound wave may be absorbed
• Massive and stiff panels

  • The amount of acoustical energy converted into mechanical vibrations of the panel is exceedingly small
• Light and flexible panels

  • The amount of energy absorbed may be very large, especially at low frequency
• Nailing fiberboards and acoustical tiles to wood strips


  They can vibrate as panels and are much more absorptive at frequencies of 128 and 256 cycles
• Cementing or fastening fiberboards and acoustical tiles against a rigid surface


  They are less absorptive
• Porous materials


  • Absorption is large at high frequencies and small at low frequencies
• Panel vibration


  • Absorption is small at high frequencies but may be large at low frequencies
• Devices for sound absorption

  • Fibrous Materials
  • Panel Resonators
  • Volume Resonators
• Pre-fabricated acoustical units

  • Limitations for architectural treatment
  • Cost compared with other acoustical materials
• Types of pre-fabricated acoustical units

  • Tile, absorbent material covered by mechanically perforated units, and certain building boards and sheets
• Acoustical tile


  The tile is a factory made product; the absorptivity is relatively uniform from tile to tile of the same kind. This makes it foolproof, a highly desirable characteristics
• US Federal Specification SS-A-118a - Type I


  • Class A - All mineral units composed of small granular of finely divided particles with portland cement binder
  • Class B - All mineral units composed of small granular of finely divided particles with lime or gypsum binder
• US Federal Specification SS-A-118a - Type II


  • Class A - Units having a perforated surface that acts as a covering and support for the sound-absorbent material to be strong and durable and substantially rigid
  • Class B - Units having circular perforations extending into the sound-absorbent material
  • Class C - Units having slots or grooves extending into the sound absorbent material
• US Federal Specification SS-A-118a - Type III


  • Units having fissured surfaces
• US Federal Specification SS-A-118a - Type IV


  • Class A - Units composed of long wood fibers
  • Class B - Units composed of fine felted vegetable fiber or wood pulp
  • Class C - Units composed of mineral fibers
• Acoustical plaster and sprayed-on materials

  They can be used in most places where ordinary lime or gypsum plaster can be used without altering the architectural effect
• Acoustical plaster and sprayed-on materials

  • Deficiencies in regard to cleaning and decorating
  • Absorptivity is dependent on thickness, composition, application and drying
• US Federal Specification SS-A-118 - Types of acoustical plaster and sprayed-on materials


  • Type I - Acoustic plaster composed of cementitious material
  • Type II - Acoustic material other than acoustic plaster applied with a trowel
  • Type III - Fibrous materials combined with a binder agent and applied by spraying
• Acoustical blankets


  Made up chiefly of mineral or wood wool, glass fibers, kapok batts, and hair felt
• Mounting acoustical materials


  The manner of mounting can influence their absorptive properties. Certain materials may be unsatisfactory when applied directly against a rigid wall but satisfactory when mounted with an air space behind them
• Panel absorbers


  • Thin panels made of durable and flexible materials like pressed wood fiber or paper boards, plywood, or plastic boards can be used for ceilings, wainscoting, or walls to provide low frequency absorption
• Draperies


  • Generally not satisfactory for absorptive treatment of an auditorium as they are only slightly absorptive at low frequencies. Should be restricted to places like doorways or prosceniums. For maximum absorption, they should be made of heavy, lined and interlined velours
• Variable absorbers


  • Hinged panels, rotatable cylinders or movable draperies used to vary and control acoustical conditions in a room. Can control the magnitude and frequency shape of absorption, and the scattering/dispersion of sound
• Rotatable cylinders


  Convex surface made up of 3 different materials each extending the full length of the cylinder and 120 degrees around it. Fitted into openings so 120 degrees projects through a suspended plaster ceiling
• Rotatable panels


  One side is convex "treated hardboard" to control diffusion. Can be backed by an air space and an absorptive blanket. Controlled by push button
• Suspended absorbers


  Used in large enclosed spaces with extremely high ceilings where conventional absorption is difficult to apply
• Rotatable Panels


  • They differ from the cylinders in that their rotation generally changes the shape of the walls or ceiling
  • The rotation of panels has a pronounced influence on the diffusion as well as on the absorption of sound in the room
• Rotatable Panels


  This changes the total absorption of a room
• Rotatable Panels


  • One side of the panel is convex and is 'treated hardboard'
  • This panels control diffusion
  • They can be bucked by an air space and an absorptive blanket
  • This can be controlled by push button
• Suspended Absorbers


  • Relatively small prefabricated units of absorptive materials hung from the ceiling
  • Used in locations where it would be difficult or expensive to install a false ceiling because of pipes or other obstructions
  • Such treatment need not interfere with existing lighting or ventilating systems
• Ways to control sound

  • Absorb (Drapes, Carpets, Ceiling tiles)
  • Block (Panels, Walls, Floors, Ceiling and Layout)
  • Cover-up (Acoustic materials)
• Acoustic Membrane


  • Different types rated by dB reduction levels across differing Hz frequencies and available in different thicknesses
  • The thicknesses and weight will affect their application and effectiveness
• Acoustic Membrane


  • Ideal as a sound insulation membrane as it works well at reducing sound transference
  • Minimal depth to existing structures, easy to install, long lasting
  • Some are rather heavy with increased mass which in turn provides a contra effect
  • Some brands are more expensive but as the saying goes, you get what you pay for
• Acoustic Mineral Wool Cavity Insulation


  Mineral, rock or stone wool insulation, essentially open cell insulation materials which work very well at absorbing acoustic and thermal energies
• Acoustic Mineral Wool Cavity Insulation


  • Used to soundproof walls and ceilings, make acoustic panels and bass traps, and as soundproofing insulation
  • Affordable, natural material, fire and moisture resistant
  • Need a lot of depth of the material to be effective by itself
  • Protective breathing gear must be worn as cutting causes slivers which lodge in the skin, or may be inhaled and irritate the lungs
• Soundproof Drywall


  Combines several layers of gypsum boards, along with steel, to increase its density and mass to block sound effectively