Soundproofing Solutions
Posted: Wed May 20, 2009 1:36 am
I am initiating this topic in response to Dave’s (NormaJean) interest in effective sound isolation (see discussion thread about slide-out rooms). And since Dave is ready to install a floor into his Eagle 15, it may be best to touch on the pitfalls and folly when one discards soundproofing, including the prevention of resonance and critical vibration.
Proper sound isolation is essential. For example, you may find a converted bus or RV parked next to you that has an impressively quiet generator set. You can even have a normal conversation with the proud owner only a few feet away from it. Yet, when you are invited to go inside the coach, you will more often than not feel vibration and hear an annoying rumble, droning, or other subliminal noises. This is because the coach builder has noticeably designed and assembled a proper enclosure for the generator set, but failed to pay attention to thoroughly sound isolating the coach and especially the floor.
There are many materials one can use for sound isolation, namely Plywood, Acoustical Deck, Acoustical Foam, Acoustical Plaster, Acoustical Tile, Fibrous Board, Fibrous Plank, Fibrous Spay, Insulation (Loose), Laminated Glass, Lead Sheet, Petal Pans, Mineral Fiber, Sealants, Slats and Grills, etc.
For the floor in our coach, we decided to use a three layer arrangement, a sandwich of two layers of ¾” marine plywood with a layer of lead in-between.
Corollary:
When sound travels through a medium, its intensity diminishes with distance. In idealized materials, sound pressure (signal amplitude) is only reduced by the spreading of the wave. Natural materials, however, all produce an effect which further weakens the sound. This further weakening results from scattering and absorption. Scattering is the reflection of the sound in directions other than its original direction of propagation. Absorption is the conversion of the sound energy to other forms of energy. The combined effect of scattering and absorption is called attenuation.
Plywood by itself is a laminate of several layers of wood veneer. It is commonly used as an underlayment of floors, as sheathing on studs or rafters, or as finished paneling on walls. Mainly because of its modest mass [approximately 0.6 kg/dm^3 (36 lb/ft^3)], specifically its mass per unit area, plywood is relatively ineffective as a sound attenuator. However, it is often adequate in combination with other materials or where high performance is not required. Thin plywood, if furred out from a solid wall, is a potent low frequency absorber. Specially detailed resonant absorbers, made of plywood, are sometimes used to “tune” special purpose rooms. At the higher frequencies, plywood is quite reflective.
Lead sheet, on the other hand, provides excellent attenuation per unit thickness because it is heavy [11.34 g/cm^3 (grams per cubic centimeter) or 0.40968 lb/in^3 (pounds per cubic inch)] or roughly 11kg/dm^3 or 700 lb/ft^3] and limp. Furthermore, lead is easily shaped to conform to irregularities, which avoid holes in barriers that must be tightly sealed.
In conclusion, the combination of plywood and lead sheet is widely used in high density housing, cruise ships, luxury yachts, sound studios and other noise-sensitive environments. Because of its high physical density, lead is the ideal material for reliable soundproofing solutions and that includes the floor of bus conversions!
Christian
Proper sound isolation is essential. For example, you may find a converted bus or RV parked next to you that has an impressively quiet generator set. You can even have a normal conversation with the proud owner only a few feet away from it. Yet, when you are invited to go inside the coach, you will more often than not feel vibration and hear an annoying rumble, droning, or other subliminal noises. This is because the coach builder has noticeably designed and assembled a proper enclosure for the generator set, but failed to pay attention to thoroughly sound isolating the coach and especially the floor.
There are many materials one can use for sound isolation, namely Plywood, Acoustical Deck, Acoustical Foam, Acoustical Plaster, Acoustical Tile, Fibrous Board, Fibrous Plank, Fibrous Spay, Insulation (Loose), Laminated Glass, Lead Sheet, Petal Pans, Mineral Fiber, Sealants, Slats and Grills, etc.
For the floor in our coach, we decided to use a three layer arrangement, a sandwich of two layers of ¾” marine plywood with a layer of lead in-between.
Corollary:
When sound travels through a medium, its intensity diminishes with distance. In idealized materials, sound pressure (signal amplitude) is only reduced by the spreading of the wave. Natural materials, however, all produce an effect which further weakens the sound. This further weakening results from scattering and absorption. Scattering is the reflection of the sound in directions other than its original direction of propagation. Absorption is the conversion of the sound energy to other forms of energy. The combined effect of scattering and absorption is called attenuation.
Plywood by itself is a laminate of several layers of wood veneer. It is commonly used as an underlayment of floors, as sheathing on studs or rafters, or as finished paneling on walls. Mainly because of its modest mass [approximately 0.6 kg/dm^3 (36 lb/ft^3)], specifically its mass per unit area, plywood is relatively ineffective as a sound attenuator. However, it is often adequate in combination with other materials or where high performance is not required. Thin plywood, if furred out from a solid wall, is a potent low frequency absorber. Specially detailed resonant absorbers, made of plywood, are sometimes used to “tune” special purpose rooms. At the higher frequencies, plywood is quite reflective.
Lead sheet, on the other hand, provides excellent attenuation per unit thickness because it is heavy [11.34 g/cm^3 (grams per cubic centimeter) or 0.40968 lb/in^3 (pounds per cubic inch)] or roughly 11kg/dm^3 or 700 lb/ft^3] and limp. Furthermore, lead is easily shaped to conform to irregularities, which avoid holes in barriers that must be tightly sealed.
In conclusion, the combination of plywood and lead sheet is widely used in high density housing, cruise ships, luxury yachts, sound studios and other noise-sensitive environments. Because of its high physical density, lead is the ideal material for reliable soundproofing solutions and that includes the floor of bus conversions!
Christian