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Sound Design
Sound Design
Most have us have been in a wonderful home with a great room with high dramatic ceilings. The problem is it feels like we are in a gymnasium. Or we have seen open floor plans with little sound isolation between rooms or between floors. A little understanding of the nature of sound can go a long way to integrating open or dramatic spaces with a sense of intimacy.
We need to approach our sound environment in two ways. One, to control undesirable sound. The other, to enhance the quality of desired sound. Let’s look at each…
Undesirable Sound
Unwanted sound can come from either outside or inside. Many log homes are in rural locations, without a lot of typical urban noise to contend with. In fact, the sound of nature is often desirable. Even if other homes are close, the mass of the log walls keep most sound out. While windows are the weak link, shutters or heavy curtains can help. Roofs are generally massive and not a concern. However, metal roofing will transmit the sound of rain: some find this disturbing; others find it soothing.
Typically, we are more concerned with interior sound: from room to room and between floors. In either case, this can be divided into two types: airborne sound, such as the sound of speech, music, and equipment; and structure-borne sound, objects striking a surface such as people walking on a floor. Footfall noise is particularly a problem in log homes that use solid decking as a single floor and ceiling finish. The sound of footsteps is easily transmitted. Even airborne sound is only marginally reduced.
The ability of a material or combination of materials to reduce sound transmission can be complex as it four components. The most important of these is mass or density. Generally, the denser a material is, the more effective it is in reducing sound transmission. Absorption is another component. Harder, non-porous, materials such as wood or glass tend to absorb less sound than materials such as carpet or underlayment. Another component is how well successive materials are isolated from each other, eg. in a wall or floor assembly. Finally, how well a wall or floor assembly is sealed will effect the amount of sound transmitted. For example, cut outs for electrical outlets or heat registers, and gaps at the edge of materials have a cumulative effect in allowing sound to pass through. The construction of doors and trim also has an influence.
Use dense materials
So, the best ways to reduce the noise pollution of unwanted sound are to use dense materials and isolate them as much as possible from each other. For example, to cut sound transmission through a floor, you could install carpeting with a dense underlayment. This will reduce sounds due to vibration and help absorb sounds carried through the air. You also can install underlayment boards on top of the normal floor sheathing for greater reduction. Using a floor joists instead of solid decking isolates the materials better. Manufactured I-joists do a better job than solid joists because there is less continuous material to transmit sound. For additional sound reduction, use a layer of sound deadening board and a layer of gypsum board for the ceiling, isolated from the underside of the joists with spacer bars (called resilient channel) running perpendicular to the joists. Concrete or liquid gypsum, used when installing radiant floor tubing, are very dense and therefore excellent sound reducers. Insulated Concrete Forms, or filled concrete block, can be used for sound walls in special situations. Ask your drywall or sheetrock contractor to put their scraps in the wall cavities during construction. It will contribute to sound reduction and reduce waste removal costs and environmental impact.
Use Absorptive Materials
There is a misconception that fiberglass insulation is good sound isolator. While it can absorb some frequencies, you need to use special fiber batts that are 3 to 4 times as dense to have a significant impact. Varying densities absorb sounds different wavelengths. For example, sound deadening board next to a layer of gypsum board will reduce more sound than two layers of gypsum board or two layers of sound deadening board.
Isolate Materials
The density of interior log walls can be very effective in reducing sound transmission, but you don’t have the benefit of isolating materials. If you need extra reduction, you will have to putting additional dense materials on at least one side of the log wall, or build another wall adjacent your log wall. For conventionally framed walls, use a 2 x 6 wall with wall studs staggered from side to side so there is no direct path from one side to the other except at the very bottom and top of the wall. For extra sound reduction, use a combination of sound deadening board and a layer of gypsum wallboard on at least one side. Isolating the wallboard from the studs with resilient channels goes even further. If you are modifying the thickness of walls to reduce sound remember this affects the thickness of doorjambs and the depth at which your electrical boxes must be set.
Seal the gaps
Breaks in your sound barriers, whether through floors or walls, can virtually eliminate any benefits of additional sound reduction techniques. Leaving a door open a crack is almost the same as having no wall at all. Similarly, hollow core doors, gaps around the doorjambs, and heating registers and electrical outlets can make all your hard work go to waste. So, use solid core doors, fill the cavity between the doorjamb and framing, seal all duct openings and electrical boxes and stagger electrical outlets on opposite sides of a wall by at least one stud cavity. You can put additional wallboard in behind the ductwork and electrical boxes. Use non-hardening acoustic sealant to reduce the cumulative effect of gaps around your flooring or wallboard.
Take steps to reduce mechanical noise in your home by choosing super quiet dishwashers and fans. Locate your furnace room away from living spaces and use the construction techniques outlined above. Sound resistant construction is also required around home theatres, as well. Insulate your ductwork and use appropriate isolators and sealants to reduce direct vibration. Plumbing pipes pose a particular challenge. Use cast iron pipes instead of plastic if your waste pipes from the upper floor pass next to a bedroom or primary living space. Install dense fiber batts or gypsum wallboard around the pipes.
Desirable Sound
Enhancing the quality of desired sound can be more of a challenge. With large spaces and high ceilings, such as in a great room, sound can be obscured in two ways. Firstly, reverberation causes a loss of sound clarity. Secondly, some of the sound will be ‘lost’ in the ceiling space, reducing the amount of original sound reaching your ear. This can make it difficult to hear a conversation or enjoy music or a video. This especially is a problem in a log home. Logs, having hard, non-porous surfaces, reflect far more sound than they absorb. Controlling the conversational distance may be the best way to confront this. Intimate furnishing arrangements ensure conversation reaches the intended recipient directly. To improve sound qualtiy, introduce absorptive materials to reduce the sense of being in a ‘gymnasium’. Carpets contribute significantly. If you have wood or stone floors, use area rugs generously. Consider more absorptive materials on adjacent interior walls. Paintings, bookshelves, and plants can help. On higher walls, tapestries can absorb some of the reverberated sound. Instead of wood ceilings, consider more absorptive materials such as gypsum board. It will highlight your roof beams much better, as well.
A good thing about logs is there shape. Round logs tends to diffuse sound well, resulting in fairly equal distribution of sound. Unusually shaped rooms or rooms with low ceilings can have dead spots. Generally, higher frequencies tend to diffuse better than lower frequencies. If you like to have music throughout your home, use enough absorptive materials to maintain sound clarity. Excessive absorption can distort the frequency distribution of sound. You can use individual audio systems in different rooms or a central system with speakers located as desired. If remote from the control center, provide volume controls at the speakers.
As you can see, controlling acoustics can be a challenge. You can start to intuitively understand the nature of sound by being aware of the acoustics in different rooms. Notice larger rooms that really work, whether for conversation or music. Note their construction and materials. Similarly, in rooms that are acoustically inadequate, note their construction and materials. While you can hire an acoustical consultant to help you ‘tune’ your primary rooms, incorporating a basic understanding of acoustics in the design process can make your home more enjoyable and livable.
© Murray Arnott
Monday, September 1, 2014
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