sound_isolation and noise control in home theatres

Sound isolation, also known as soundproofing, refers to the process of blocking or significantly reducing sound transmission between spaces. This can be achieved through various methods and materials that absorb, dampen, or reflect sound waves, preventing unwanted noise from entering or leaving a particular area. The effectiveness of sound isolation depends on factors like the type of materials used, the density of barriers, the construction techniques, and the nature of the spaces involved.

There are several key strategies employed in sound isolation:

1. **Adding Mass**: Increasing the mass of walls, floors, and ceilings can help block sound transmission. Heavier materials are typically better at dampening vibrations.

2. **Damping**: This involves the use of materials or techniques that dissipate vibrational energy. Special acoustic panels, soundproofing foams, or layers of drywall with viscoelastic compounds can reduce the amplitude of sound waves.

3. **Decoupling**: This technique separates two sides of a wall or structure to interrupt the path of the sound waves. For example, using staggered studs in walls or floating floors can significantly reduce sound transmission.

4. **Absorption**: This involves using soft materials that absorb sound energy rather than reflecting it. Materials such as fibrous insulation and specialized acoustic tiles can help

1. Sound Isolation and Noise Control in Home Theaters by Floyd E. Toole This is a supplement to Sound Reproduction, 3 rd Edition, Focal Press, 2018

2. Home theaters vs. listening rooms Quality listening experiences in multichannel movies or stereo music have the same fundamental needs in terms of sound isolation and noise control. The cost and difficulty of achieving high levels of isolation and low levels of background noise are reasons for serious thought before embarking on a project. If you are an installer/contractor you need to discuss this with the customer, determining what is and is not likely to be acceptable. Some things cannot be changed after the fact.

3. Sound travels both ways: in and out Noises from outdoors or other parts of the house are distractions while listening to music or watching movies or TV. Constant background hums, rumbles and hisses from HVAC are annoying. Rumbles, booms and crashes emanating from the theater can be disruptive to someone elsewhere in the house who is trying to work, relax or sleep. The main problem: The bass sounds that are so impressive in movies and music are very difficult to isolate.

4. Sound isolation is a hidden virtue Sound isolation in a home theater or listening room needs to be designed in from the beginning; retrofitting is much more difficult and often less satisfactory. If it is well done, nobody is likely to notice − a good thing! If it is inadequate, listeners are repeatedly reminded of the fact. Clattering dishes in the kitchen, toilet flushes, door slams, and screaming children at play can break the carefully crafted “spell” of music and movies. That is not good!

5. Measurements vs. perceptions Sound level measurements are related to human reaction to sounds, but it is a very imperfect correlation. One reason is that we react to more than simple loudness, especially if the sound has information content. Annoyance can be very personal and situation-dependent. For example: Voices or some kinds of music when you are trying to concentrate. Merely hearing these sounds faintly in the background can be distracting to some people. Sounds of violence, as in many movies, are more distressing than neutral sounds at the same sound level; loud bass sounds can be particularly bothersome to some.

6. Limitations of measurements Given the complexity of sounds in movies and music, it is no surprise that a single-number rating is imperfect, even for simple loudness. Nevertheless, single-number ratings exist for sound levels, sound absorption and sound transmission loss. Their usefulness is limited because of their simplicity, and because some of them were created only to address matters related to speech intelligibility and privacy. The frequency range of speech does not include the abundant, easily transmitted, and annoying low bass sounds in movies and music.

7. Factors in home theater location Most situations offer few or no options for the location of the listening room, but if there is a choice, here are some factors to consider: Door closing thumps, garage door rumbles, toilet flushes that travel through frame construction, HVAC rumbles (fan vibration and combustion noise) and hisses (turbulence at the vents), TV and games in nearby rooms, footfalls upstairs, Traffic, aircraft, etc.

8. Factors in home theater location Identify those areas of the home that need to be protected from sounds leaking from the theater: bedrooms, study and office/working areas. Can the theater space be isolated by sound attenuating walls, ceiling and floor, doors, etc.? If not, can a better location for the theater be found? If not, is the customer willing to accept the noise?

9. Factors in home theater location Noises that interfere with enjoying movies and music: sources within the theater space—cooling fans on the projector and other equipment, hard drives, transformer hum, HVAC vent noise, etc. sources outside the theater space—traffic, aircraft flyovers, household noises such as toilets, kitchen appliances, vacuums, furnace fan and combustion noise, garage doors, etc.

10. Factors in home theater location Beware of flanking paths—sound that leaks in or out through acoustical or mechanical connections: HVAC ducts, plumbing and electrical services Structural coupling to sources of vibration, e.g. garage door openers, roof- or attic-mounted AC, furnace fan, drainage and sewage lift pumps, etc. Sound communicated through a shared attic, basement or crawl space.

11. Factors in home theater location Access to the theater, toilet, refreshments, etc. Is there a convenient gathering/talking/socializing space close by? Is one necessary? Is there a need for handicapped access? Any stairs or ramps need to be lighted, and elderly or unsteady people will benefit from hand rails—the interior decorator will simply have to consider it an additional challenge!

12. Factors in home theater location Light In multipurpose rooms, are there light sources that will wash out a projected image or be reflected from the glass of a direct view display? Can they be controlled with moveable or motorized curtains, shades or screens? Can the display be positioned to minimize the effect? Projection screens with gain discriminate against light arriving from the sides. In dedicated theaters, will an open door spill light on the screen?

13. Factors in home theater location Windows From the perspective of interior room acoustics, double-glazed windows are very similar to a single layer of drywall. If windows are to be preserved, sound attenuation can be much improved by the addition of a second window, physically separated by several inches. Special products exist with damped multiple laminations. If they are to be closed off, use an opaque coating or closed shutters to preserve a good outside appearance and cover the interior surface with a wall.

14. We need some acoustical terminology To describe background sound levels that are acceptable for the activities in the room. To describe the amount by which sounds are reduced in travelling through various materials, wall, ceiling and floor constructions. To describe the proportion of incident sound that is absorbed by acoustical materials.

15. What happens when sound hits a wall? Some of the sound is reflected. Some of the sound is absorbed by the surface or what is on the surface. Some of the sound travels through the wall to the adjacent space.

16. Sound absorption The absorption coefficient describes the percentage of sound energy that is reflected back into the room. 100% absorption suggests that nothing should be reflected back into the room. Problem: this specification assumes a diffuse sound field. In small listening rooms the sound field is not diffuse. The spec is misleading.

17. Sound transmission loss Transmission loss defines the amount of attenuation experienced by sound as it passes through a room boundary. The amount of loss is very frequency dependent. In home theaters attenuation of bass frequencies is very important—and difficult to achieve.

18. Sound absorption vs. transmission loss Materials that provide effective absorption often provide little or no sound transmission loss. They are very different mechanisms. The acoustical performances of materials and structural methods used in home theater construction need to be specified as a function of frequency so that we can absorb or isolate the right sounds. At present, there is no single-number rating that is reliably useful for our purposes.

19. Sound absorption specifications: Sound absorption coefficient—measured at several frequencies in a diffuse sound field— useful in large reverberant spaces, but less reliable in small acoustically well-damped rooms. Directional absorption data is needed to address individual reflections. Noise Reduction Coefficient (NRC)—a single number applying to speech frequencies only— use only as a rough guide

20. Sound attenuation specifications Sound attenuation through floors and walls: Impact Insulation Class (IIC)—floors only—a measure of impact noise transmission from the floor above. Useful for “ high heels on hardwood, ” but useless for anything else. Sound Transmission Loss—real measurements at many frequencies—this is the “ truth. ” Sound Transmission Class (STC)—speech frequencies only—use only as a rough guide! Weighted sound reduction index ( Rw )—speech frequencies only—use only as a rough guide!

21. Background noise specification Noise Criterion curves (NC)—the “ traditional ” measure created for evaluation of speech interference. There is no evaluation of the quality of the background noise. A background noise that perfectly fits an NC curve will sound boomy and hissy. The “adjacency” rating method allows background noises that can be irritating. Some judgment is required to ensure that there are no prominent spectral peaks.

22. The new NC contours Figure 4.8 in Sound Reproduction , 3 rd ed. 2018 Reprinted from ANSI/ASA S12.2:2008 American National Standard on Criteria for Evaluating Room Noise, © 2008, with the permission of the Acoustical Society of America, 1305 Walt Whitman Road, Suite 300, Melville, NY 11747. The new NC contours showing a measured spectrum registering NC-51 according to the tangency criterion. The NC rating of a spectrum is designated as the value of the highest NC curve “touched” by the measured octave-band spectrum.

23. Some examples of NC ratings: Recording & broadcast studios: distant microphone pickup NC-5 to NC-10 close microphone pickup NC-15 to NC-25 Concert halls and other live performance spaces NC-15 to NC-20 Home theaters, suburban homes NC-15 to NC-25 Movie theaters NC-30 to NC 35 Urban residences and apartments NC-30 to NC-40

24. A practical example

25. Observations:

26. More observations:

27. How much sound transmission loss is needed for different room boundaries? Standard construction (STC=34): OK for non-critical situations. Examples: garage, storage room, hallway. Level 1 (STC=52): noise outside HT is moderate and/or the adjacent space is moderately noise sensitive. Examples: kitchen, casual dining area. Level 2 (STC=60): significant noise outside HT and/or the adjacent space is significantly noise sensitive. Examples: living room, dining room, office, library. Level 3 (STC=70): high noise levels outside HT and/or the adjacent space is very noise sensitive. Examples: bedrooms, noisy areas like gaming room, playroom, and outdoor noises from heavy traffic, aircraft flyovers, trains, etc.

28. The idealized acoustical goal

29. Being practical:

30. More details

31. Understanding sound transmission through walls

32. Increasing transmission loss:

33. Fundamentals of sound isolation Poor at all frequencies Better at mid & high frequencies. Small air volume is stiff at low frequencies though. Slightly better, but the mechanical connection dominates Even better at mid & high frequencies. Some isolation at low frequencies now. Little change at mid & high frequencies. More isolation at low frequencies. Fibrous material: fiberglass, mineral wool, etc.

34. Fundamentals of sound isolation Adding more layers of drywall (mass) improves everything. Adding damping ( visco -elastic compound, sheets or pads) between the layers, or using prefabricated multilayer products improves things even more, including low frequencies, which is good.

35. Fundamentals of sound isolation No caulking: STC 14 Caulking only under floor plate: STC 30 Caulking at edges of floor plate and at edges of gypsum board: STC 50 Caulking eliminates a sound leak

36. Fundamentals of sound isolation Soft pads eliminate a sound leak e.g. ISO-SILL™ from acoustiguard.com or GenieMat FIS® from pliteq.com

37. Practical Problems with Retrofits: When adding a theater to an existing building, there is much less flexibility: Existing walls usually must stay. During construction new interior walls may only be accessible from one side only. There may be space or weight limitations. E.g. adding thickness to a wall outside a theater may violate a corridor width regulation. Many layers of drywall may exceed the load rating for building structure—seek advice from a structural engineer. Flanking paths often cannot be treated in the most effective ways.

38. Techniques for retrofits or where space is limited Plan view Elevation view Multiple layers of gypsum board mounted on Resilient Channel or Resilient Sound Isolation Clips (RSICs) plus fiberglass make huge mid/high frequency improvements. Resilient mounting also reduces structure-borne flanking path leakage. Adding more d amping compound or sheets between layers can be beneficial. Poor at all frequencies

39. Resilient Channel-1 RC-1 Plan view Elevation view Intended for ceilings or walls Caution: drywall screws must NOT contact the studs, short-circuiting the mechanical isolation!

40. Resilient Channel-2 RC-2 Intended for ceilings Caution: drywall screws must NOT contact the studs, short-circuiting the mechanical isolation!

41. Resilient sound isolation clips Resilient sound isolation clip RSIC-1 Drywall furring “ hat ” channel, or “ hat track ” Wall Ceiling Illustrations from: www.pac-intel.com Supports up to 2 layers of 5/8 ” drywall for substantial gains in sound isolation

42. Resilient Sound Isolation Clips RSIC-1-SI (spring isolation) Illustrations from: www.pac-intel.com

43. Sound transmission losses of some real walls

44. How much transmission loss do we need? Assume that the sound source is pop music at an average listening level of about 85 dB—a good “ foreground ” listening level. These are the sound levels that would appear on the other side of various walls. The standard wall fails. A Level 1 wall is OK, except at bass frequencies.

45. Crescendo sound levels are problems! If the sound inside the HT is music or a movie at peak crescendo level of about 105 dB: Even a Level 3 wall will have problems with bass, but all others are in serious trouble. Lesson: even elaborate walls cannot isolate all sounds .

46. Sound leakage and structure-borne sound Sound propagates through structures in parallel—flanking—paths compromising the performance of even the best walls. In some instances it can be true that an overdesigned wall is a waste of space and money. A total design must consider all possible paths sound can take on its way from the source to the listener ’ s ears.

47. Flanking paths This is why ground floors and basements are attractive locations for noisy home theaters! And, why the most expensive and acoustically effective wall, floor or ceiling may not completely solve a problem.

48. Flanking paths reduce effectiveness of walls Different construction styles of the floor connecting two spaces makes a difference.

49. All of this and more is in: The National Research Council of Canada “ Guide for Sound Insulation in Wood Frame Construction, ” by Quirt, Nightingale and King, 2006. Publication RR219 Available at no cost at: http:// nparc.cisti-icist.nrc-cnrc.gc.ca / eng /search/?q=rr219&m=1

50. Concrete Floor on Grade - Simple The risk? That the weight of the walls will cause the floor to sink and break.

51. Concrete Floor on Grade—Better This may require removing part of the floor and splicing in new concrete with footings

52. Some sample walls It is important to remember that in all of the following examples significant variations can occur, depending on the details of materials and construction. Note also that equivalent acoustical performance is possible using a number of different designs. NO allowance for flanking sound has been made!

53. Single-stud walls STC 34 STC 57 Manufactured laminated internally damped panels

54. Walls used in some of the examples Manufactured laminated internally damped panels

55. Other variations

56. Concrete options

57. Some retrofit ideas Level 2 example for +

58. Room-within-a-room options: A basic add-on interior wall is good enough for many situations.

59. Room-within-a-room options: Simple ways to push the acoustical isolation of a retrofit wall to a much higher level.

60. Room-within-a-room options: A serious assault on sound isolation in a retrofit situation. The resilient mounting adds wall isolation and attacks flanking path vibration.

61. Ceilings

62. Floors There are two considerations Preventing sound from escaping to a lower floor. Allowing the floor surface to vibrate in response to the bass, giving listeners a tactile sense of bass energy. In this case the floor must be very well mechanically damped to avoid embarrassing “one note” vibrations.

63. Floors, continued For maximum isolation use a poured concrete slab for the floating floor. Alternative: layers of gypsum board sandwiched between ¾ ” plywood sheets, joints staggered. If floor vibrations are desired for aesthetic effect, add a decorative floor on compliant sleepers (e.g. strips of rigid fiberglass board or iso mounts) above the floating floor.

64. Floors, continued The kind and distribution density of the isolation mounts depends on the total mass they must support. Consult a manufacturer (e.g. www.kineticsnoise.com ). If sound isolation is not an issue—e.g. the structural floor is a ground level concrete slab—and some bass “ feel ” in the floor is desired, just use the decorative floor.

65. Putting it all together ... Individual walls, the floor and ceiling can only be effective if they are carefully mated at the corner junctions. Interior and exterior wall structures must be kept mechanically separate from each other, cracks must be filled with acoustical (i.e. non-hardening) caulk, or strips of compliant material. This requires a knowledgeable builder and/or very careful supervision.

66. Doors and windows These are usually the “ weak links ” in any well-designed home theater. Acoustical upgrades to conventional solid-core doors (added mass, weatherstripping , drop seals) improve things. Inner and outer doors are a good idea. Sound rated doors are very effective, but expensive. Eliminate windows if possible. But there are ways to upgrade the acoustical performance when they must remain.

67. Improving the transmission loss of windows Data from: www.soundproofwindows.com Original single or double pane: STC 26-32 With spaced sound-attenuating glass added: STC 48-54

68. How soundproof doors work Sold as a pre-hung system. Demanding circumstances may require and inner and outer doors in separated frames or, better, separated by a small chamber or room. It is possible to create functional do-it-yourself versions, but acoustical performance is not assured.

69. Commercial sound-rated doors There are numerous manufacturers of custom doors accessible through the Internet—e.g. search “soundproof doors”. There are also several guides for do-it-yourself improvements to readily available doors and companies selling some of the components shown in the previous slide. Always check carefully for properly conducted sound attenuation measurements.

70. Isolating projector noise Ceiling Remotely located quiet (centrifugal) fan ¾ ” plywood box with 2 ” fiberglass Ensure that air flow is in the same direction as that of the projector

71. Reducing HVAC noise in ducts Force air through 90 º or 180º turns in a duct lined with not less than 2 ” (50 mm) fiberglass duct liner (coated to prevent fiber loss). Manufactured duct silencers are available. These devices and long runs of lined duct are useful to isolate middle and high frequency sounds. Bass is not effectively isolated so a dedicated HVAC system for the home theater is recommended.

72. Reducing HVAC noise at the vents Calculate the air flow necessary to support human life, and to remove heat generated in the HT. Use industry charts to determine appropriate duct size and diffuser—keeping the face velocity low to prevent turbulence. The ASHRAE handbook, for example, has such information.

73. Quieting garage door openers Vibration isolating the opener motor . . . . . . and the track So that sound is not communicated by the house frame. Illustrations from: www.pac-intl.com

74. A simple A/C isolation Outdoor A/C unit Rubber puck or block Concrete slab on grade When the supporting surface or structure weighs much more than the vibrating unit, isolation is simple. Energy that is transferred to the structure generates very little motion, and little or no noise.

75. Complicated rubber “pucks” These are much more effective than the traditional solid rubber pucks and blocks. They are designed to support specific load ranges, so be sure to pick the right one for your needs. From: www.mason-industries.com

76. A more complicated situation: Outdoor A/C unit Spring with the right amount of stiffness for the supported mass. The manufacturer of the isolator has this information Typical roof construction on a frame building When the supporting surface or structure weighs less than the vibrating unit, isolation is more difficult. The optimum amount of compliance (springiness) is necessary to minimize vibration transfer. It is a more complicated “ tuned ” system.

77. Attic installations Indoor A/C/furnace/fan unit Another situation in which the supporting surface or structure weighs less than the vibrating unit. Maximum isolation requires that the springs be matched to the load being supported

78. Sophisticated hangers Rubber bushings reduce high frequency vibrations while springs take care of low-frequency rumbles and shakes. Units are designed to tolerate a certain amount of movement, but seismic restraints are necessary. Be sure that they do not couple vibrations to the structure of the house. Available for specific load ranges, pick the right one! From: www.mason-industries.com

79. Recommended reading An excellent comprehensive textbook on room acoustics and noise control: Architectural Acoustics , Marshall Long, Elsevier Academic Press, 2006. A good introductory book: Master Handbook of Acoustics, 5 th Edition, Everest and Pohlmann , McGraw-Hill, 2009.

80. Recommended reading Sound Transmission Loss measurements on many wall and floor constructions, and papers on fundamental research can be found at: http://nparc.cisti-icist.nrc-cnrc.gc.ca/eng/search/?q=sound+transmission+loss&s=sc&ps=25&m=1 The following are more specific: http://nparc.cisti-icist.nrc-cnrc.gc.ca/eng/view/fulltext/?id=57dbff41-7b93-4621-bd17-ae2c6ab6c7e0 http:// nparc.cisti-icist.nrc-cnrc.gc.ca / eng /view/object/?id=04ac8069-a5d2-4038-8787-da064b073e7f No cost.

81. Recommended reading—Internet Searches on specific topics yield many sources of information. Good information on vibration and sound isolation products and techniques at: www.mason-ind.com www.pac-intl.com www.kineticsnoise.com www.asc-soundproof.com And others ...