== Isolation and Well Being ==
Acoustical Noise reduction through acoustical isolation is necessary for well being at all times. It is extremely important in a live-aboard boat to keep noise within a comfortable range. We experience sound in terms of a frequency range measured in Hertz (Hz) and air pressure measured in decibels (dB). The ear has a very wide non-linear response to the intensity of sound, so each 10 dB increase is ten times louder. Thus a 20 dB increase is 100 times more intense. Duration is also important. Constant noise over 85 dB will damage hearing.
For reference, the ambient noise level in most homes is 30-35 dB. Car interiors are around 40 dB. A normal conversation is around 60 dB. A diesel engine room is around 125 dB (wear ear protectors!}. A jet plane taking off is around 140 dB. For bedrooms, to get a good restful sleep, the [http://www.who.int/ World Health Organization] recommends 30 dB with no single noise event exceeding 45 dB.
== Eliminate Source ==
* Floor, ceiling and walls of the engine room
* Bulkheads and doors in living spaces
** [[HullInterior#Interior Fittings|Isolating all wall panels ]] from structural boat walls]]
In addition to the noise of combustion, there are several considerations in designing acoustical-isolation systems for an engine room. These are drive-train vibration, especially from the propeller, the peak frequencies generated by large noise generators such as the engine, and the range of noise to which the ear is most sensitive.
The human ear responds to sounds in the range of 20 Hz to 20 kHz but is most sensitive in the 1,000-5,000 Hz band with a peak around 4,000 Hz. The auditory canal alone has a closed-tube resonance of 2,000-5,000 Hz.
For a production boat it’s feasible to do a spectrum analysis and design suitable sound attenuation and test it. For a bespoke boat this is unlikely to be feasible. Thus a good cost-effective approach is to focus on reducing sound transmission in a target range such as 1,000-2,500 Hz (wavelengths of 13.5 to 5.4-in or 34.3 to 13.72 cm).
== Methods of Isolation ==
* Decoupling surfaces
Reflecting sound within a room causes sound to lose energy, reducing the amount of sound radiation outside the room. A common method of achieving this is to have reflective material on the outside surface of insulation. However the room shape and size can also have a major impact. The best shape for noise cancellation is a cube. The next best is a room where all dimensions are a multiple of the height, e.g., an engine a room that is 7 x 14 x 14 ft.
Dampening sound is achieved by absorbing it in insulation. The depth of insulation should be calculated to absorb the desired wavelengths (e.g.see above, 6-14 in for engine noise). Unless you want to listen to every noise from your neighbour or the adjacent head, make the cabin Cabins can be quietened with hollow walls hollow, and insulate them doors filled with acoustic dense fibre matting (DFM ) mineral wool or an aerogel sheet<ref>Aspen Aerogel Inc., http://www.aerogel.com/</ref> or use [[HullInteriors#Structural Insulated Panels|structural insulated panels ]] (SIP). Aerogel is also an excellent thermal insulator, with a value of around R22 per inch.
Sound waves can be converted to heat energy by adding mass to surfacesDFM mineral wool is non-flammable and chemically inert. Vibrating a mass absorbs more A random arrangement of fibres ensures no water penetration in any direction. It is rot proof, non-[https://en.wikipedia.org/wiki/Hygroscopy hygroscopic] and will not encourage the sound energygrowth of fungi, moulds or bacteria.
Decoupling is achieved Sound waves can be converted to heat energy by using viscoelastic dampers between adding mass to surfaces, and air gaps to prevent direct conduction. Air gaps need especial attention because they Vibrating a mass absorbs more of the sound energy. Mass can resonate, especially at the lower frequency (1000be added by marine-400 Hz) wavelengths of 13grade plywood panels or lead surfaces on insulation.5 to 33.76 in Medium-density fiberboard (34.3-85.75 cmMDF)is not as hard as plywood and can sag under heavy weight. Resonance will transfer acoustical energy across the gapMDF doesn't handle moisture very well, either.
=== Decoupling is achieved by using [https://en.wikipedia.org/wiki/Viscoelasticity viscoelastic] dampers between surfaces, and air gaps to prevent direct conduction. Air gaps need especial attention because they can resonate, especially at the lower frequency (1000-400 Hz) wavelengths of 13.50 to 33.76 in (34.3-85.75 cm). [http://www.physicsclassroom.com/class/sound/Lesson-5/Resonance Resonance] will transfer acoustical energy across the gap. An Example ===ideal space of 100-200 mm (3.9-7.9 in) is recommended in building construction.<ref>http://www.build.com.au/window-acoustics-and-noise-control</ref>
These techniques are applied in === Isolating the following hypothetical example where a saloon is located above an engine room, and cabins are adjacent to engine-room bulkheads.Engine Room ===
In a saloon above the Design an engine room, sound can entrance that has a double door. The inside door should be attenuated in the design of the sole watertight (with a view port) and the engine-room ceiling below thatoutside one should be air tight. For acoustic isolation The space in the sole build up a layered floor consisting of (starting at the bottom) a sub-sole, viscoelastic glue as between would make a damper, an underlayment of acoustic mat made of dense rubber (similar good place to the mat used in horse stalls), then cement board hang ear protectors and flooringother safety equipment. Both doors should have significant solid mass to absorb sound.
In With a saloon above the engine room design the ceiling to provide attachment points for a drop ceiling. Apply composite insulation such as lead-fibreglass with the fibreglass rated at, say, R13. Since we are dealing with wavelengths of, say, 5- to 14-sound can be attenuated in, the thickness design of the insulation should be in sole and the same range. Install a decoupled drop engine-room ceiling consisting of two layers of non-combustible panels bound with viscoelastic glue. Several marine-approved panel materials are availablebelow that.
Use spring ceiling hangers or other means to attach For acoustic isolation in the panels to sole build up a layered floor consisting of (starting at the attachment points in bottom) a decoupled way. In sub-sole, viscoelastic glue as a capsize the spring hangers should be able to withstand high accelerations damper, an underlayment of mass acoustic mat made of dense rubber (similar to avoid detaching the ceiling. There should be an air gap between the insulation mat used in horse stalls), then cement board and the panels. Where the drop ceiling meets the walls, prevent flanking noise leaking through using a flexible acoustic sealerflooring.
A In the engine room an ideal ceiling of this type, combining mass, decoupling, resilient would provide attachment points for a drop ceiling. This would require spring hangers (or even rubber engine mounts and insulation is ) capable of attenuating noise 60-75 dB over 1000-5000 Hzwithstanding high accelerations of mass to avoid detaching the ceiling in a capsize.<ref>The Green Glue Company, http://wwwattachment points should be 100-200mm long.greengluecompanyAttach two layers of non-combustible panels bound with viscoelastic glue. Several marine-approved panel materials are available.com</ref>
Similar techniques could be used on Where the bulkheads where feasible. Consider alternate arrangements to simplify construction. For examplecomposite panel meets the walls, in prevent flanking noise leaking through using a flexible acoustic strip such as neoprene. On the engine room use a viscoelastic glue side, apply to stick a non-combustible panel on the bulkhead, then attach the composite panel composite insulationsuch as lead-fibreglass with the fibreglass rated at, say, R13. In Since we are dealing with wavelengths of, say, 5 to 14 in, the living space on thickness of the other side attach furring strips using neoprene rubberinsulation should be in the same range. If more isolation is needed incorporate rubber mat or more A ceiling of this type, combining mass, decoupling, resilient mounts and insulationis capable of attenuating noise 60-75 dB over 1000-5000 Hz. Always leave an air gap to prevent conduction<ref>The Green Glue Company, http://www.greengluecompany.com</ref>
If there is ductwork originating in the engine room, use round lined ductwork (insulated on the inside). Round ducts transfer less sound than square ones. In the engine room coat the exterior of the duct with a viscoelastic material, and cover it with a soffit to prevent exposure to direct sound. Consider a 90 or 180 degree bend to force sound to interact with the duct liner. Where possible, use serpentine lengths of lined flex duct to create a more complex path for sound.
Design an Similar techniques could be used on the bulkheads. For example, in the engine room entrance that has use a double door. The inside door should be the watertight one (with viscoelastic glue to stick a view port)non-combustible panel on the bulkhead, and then attach the outside one should be air tightcomposite insulation. The In the living space in-between would make a good place to hang ear protectors, etcon the other side attach furring strips using neoprene rubber. Both doors should have significant solid massIf more isolation is needed incorporate rubber mat or more insulation. Always leave an air gap to prevent conduction.
== Some Cautions ==
** Start with a basic installation of isolation in the engine room. Run the engine and use a sound meter to measure the noise in adjacent cabin areas. Upgrade the isolation to reach your sound goal.
** Or, build a small test box with a logging sound meter inside. Add test isolation externally. Evaluate the performance of your choices by suspending the test box in the engine room and running the engine.
== Links ==
http://www.audioholics.com/room-acoustics/a-guide-to-sound-isolation-and-noise-control
http://www.audiology.org/sites/default/files/journal/JAAA_09_06_02.pdf
== References ==
[[Category:HullGeneral]]