One of the disadvantages of living in the city is the noise. There are reasons why people go out into the country for some time off; and one of those is that they want some peace and quiet. Even the suburbs can be noisy, especially for those who live alongside a major thoroughfare.
Yet most of us find it difficult to come by the time we want to get away to somewhere quieter. Rather, we put up with the noise around us, trying as best we can to do whatever we can to ignore it. But that can be challenging. Likewise, it can be challenging to ensure that the noise we create doesn’t disturb other family members or neighbors.
Architects and interior designers utilize the services of acoustic engineers when designing commercial buildings. Since many of those have extensive “hard” surfaces, acoustically speaking, along with a lot of people working and making noise, something is needed, so people can concentrate and work.
Obviously the services of an acoustic engineer are something that the average homeowner can afford. Yet we deal with the same problem in our homes, especially now that more homes are being built with wood, composite or tile floors, rather than carpeting. That makes our homes become the same acoustically hard environments as commercial office buildings. Yet we’re on our own for dealing with that problem.
Understanding the Basics of Sound Suppression
Sound is literally vibrations. The air around us is constantly vibrating, even though it might seem to be still. Wind carries vibrations as well, overlaid onto the general movement of the air. Ultimately, these vibrations reach our eardrums, causing them to vibrate. This causes the cells in the inner ear to recognize that as sound and transmit it via nerve impulses to the brain.
On the most simple level, we can stop that sound from reaching our ears by wearing ear plugs or earmuffs, blocking the sound waves and keeping them from reaching our eardrum. While the vibration of the sound in the air can cause the ear plugs and/or muffs to vibrate slightly, allowing some of the sound to pass through, the materials those are made of are selected for their ability to block the sound and keep that from happening. So only a minimal amount actually gets though. Even so, it’s not always convenient to wear ear protect; we often need to be able to hear what’s going on around us.
That means dealing with the sound before it gets to us. There are four basic strategies for this:
- Absorption – acoustically “soft” materials, like fabrics and insulation can absorb sound, essentially eliminating at least some of it in the process. Absorption is actually the most common means of dealing with excessive sound levels in a room or building. A variety of materials are used for absorption, but open-cell foam rubber is the best.
- Reflection – Sound waves which hit a hard surface they can’t be absorbed into will reflect the sound off in another direction. This direction can be calculated, allowing reflection to be used as a means of sound suppression. The main thing to avoid is allowing the sound to reflect back to where it came from.
- Blocking – As mentioned earlier, ear plugs can block sound. Other materials can do this too, even if they can’t absorb it. thick, heavy materials can do this, such as concrete and wood. But some other, lighter materials can do so as well, such as rubber. Rubber blocks sounds by not vibrating well, preventing the sound from being carried through the material.
- Baffles – Sound that is traveling through the air can be blocked by denying it a clear pathway from one room to another. This is used in recording studios, where cables need to go from the recording room to the sound booth. Those cables pass through a passageway where the openings are staggered, blocking sound from traveling through easily.
- Hiding – The use of white noise, music and other background noise is intended to hide sound by giving our brain something else to hear. This only works to a certain extent though, as it adds to the sound in a space, rather than eliminating it.
- Canceling – Relatively new technological breakthroughs have allowed engineers to design devices which mimic sound waves, “out of phase” and play that sound through speakers. Being out of phase means that it is the exact opposite sound, so the two separate sound waves combine together into something that has the effect of eliminating itself.
Absorption is actually the easiest of these methods to use. Many of the things we put in our homes, like furniture, carpeting, draperies and even people will all absorb sound. Lowering the overall sound level, whether that sound is being produced inside out homes or outside. It can help us keep from bothering our neighbors, as well as keeping their noise from bothering us.
Acoustic panels are merely decorative panels to hang on the wall, with this purpose. They are easy to make, attractive, lightweight, don’t take up a lot of room and most importantly… they are effective. Adding acoustic panels to any room is worthwhile, especially to those who want their peace and quiet.
Sound Blocking Construction
One of the best ways of blocking sound is to eliminate the means for the sound to be transmitted. Sound travels best through solid materials, rather than through air. That’s actually how we hear things going on outdoors. The sound is traveling through the solid part of the wall, specifically the 2”x 4”s, and not through the insulation in the wall.
We can eliminate this pathway for the sound by building a double wall, with the studs offset from each other. Sound passing halfway through the wall from one direction runs into insulation for the other half of the wall thickness, deadening the sound.
Obviously, this is a rather expensive method of construction, normally used only in building recording studios. Nevertheless, it’s a very effective method, especially when combined with other sound blocking and absorbing methods.
Are Acoustic Panels the Only Option?
While acoustic panels are an effective means of lowering the overall sound level, they are not the only option we have. There are a number of other things we can do, both to block outside sound from bothering us and to keep excessive sound we are making from bothering others.
- Carpeting – As I hinted at a moment ago, adding carpeting, especially thick carpeting can help to absorb sound.
- Draperies – Thick draperies, especially insulated ones, will absorb at least some of the sound coming through windows.
- Window Plugs – A more aggressive step for cutting down the amount of sound coming through windows is to install window plugs. The basic idea is to fill the window opening in the wall with a foam rubber mat, allowing it to absorb sound.
- Seal Leaks – Many rooms may have air leaks, such as the space below the door or areas that need to be caulked around the window. If air can get through those gaps, so can sound. Sealing them will help to reduce excess noise.
- Installing Acoustic Windows – Multi-pane acoustic windows are designed specifically for blocking the noise of heavy trucks driving down the road. They also help to insulate the home better from losing heat.
- Hang a Fabric Drape – Draping fabric on the ceiling works to absorb sound, just like carpeting does. If you’ve ever seen parachute fabric hanging from a ceiling, that’s the purpose.
- Add Background Noise – Investing in a white noise generator or a stereo playing soft music can help to hide unwanted noise.
- Install a Second Layer of Drywall – While not the most sound-absorbing material around, drywall actually is fairly good at blocking it. If you don’t believe me, just try communicating with your spouse, while you are in different rooms. The sound of the two speaking doesn’t pass well through the wall.
- Acoustic Panels – These hang on the wall, absorbing sound. They are especially good at blocking echoes and booming sounds within a room.
Generally speaking, it’s a good idea to incorporate a number of different ideas into the acoustic plan for a room, if it needs to be made a quiet space. The more of these ideas that are incorporated together, the lower the sound level will be.
Making Homemade Acoustic Panels
Acoustic panels are actually one of the easier steps that can be taken to reduce the sound level in any room. Churches, theatres and other auditoriums commonly hang acoustic panels on the walls, as part of the overall plan to control the sound level in the room. The same thing works just as well in smaller spaces, such as those in our homes.
These acoustic panels can be made from a variety of materials, although they are usually made of acoustic insulation and fabric. Acoustic insulation may look like other insulation and be made of many of the same materials, but is generally designed to reduce noise, rather than to hold in heat. While they will work to hold in heat, just like regular home insulation can work to reduce noise, these types of insulation are specifically designed for sound absorption, making them a superior choice.
Acoustic insulation normally comes in pieces designed to fit between the studs on walls which are framed with the studs on 24” inch centers. The pieces are four feet long, giving us a two foot by four foot panel. That works out to be a nice size for acoustic panels in the home.
Building the Frame
The basic frame for an acoustic panel can be made out of standard 1”x 4” dimensional lumber. High grade lumber is not needed, as the wood will not be visible and is not carrying a heavy load.
Before starting, open the insulation package and measure the size of a piece of the insulation. The dimensions given below may need to be altered to fit the actual size of the insulation being used.
Cut the 1”x 4’s to make pieces for the sides that are 47” long and pieces for the top and bottom that are 24.5” long. These four pieces can then be screwed together with 2” wood or drywall screws, making the perimeter of the frame, with the top and bottom overlapping the side pieces. Pilot holes should be drilled to prevent the wood from splitting and the heads of the screws should be sunk to flush or just below flush.
When choosing a pilot drill, the ideal drill size is the same size as the “root diameter” of the screw. This is also known as the “minor diameter” of the screw thread. It’s the thinnest dimension for the main part of the screw’s thread. If no calipers are available to measure this dimension, hold a screw up in front of and behind the drill bit. When the screw is in front, the drill bit shouldn’t be visible on either side. When the drill bit is in front, the screw body should not be seen, although the threads should be visible.
It’s a good idea to use a corner clamp whenever making a frame, even one as simple as this. It’s very easy to have parts slip while drilling the pilot hole, misaligning them in a mistake that is hard to get rid of. The few extra seconds taken to clamp the pieces together before drilling help ensure that the corner comes out right.
Countersinking may be necessary for normal wood screw, which are traditionally flat headed. drywall screws, on the other hand, have what’s known as a “bugle head” rather than a flat head. This means that the cross-section of the had is like the bell shape of the horn end of a bugle or trumpet. Bugle headed screws don’t need to have a countersink drilled as the screw will pull down flush with the wood’s surface when screwed in, especially on softwoods. This is why drywall screws are so popular for woodworking. Some wood screws are now being made with this same sort of head.
Even with all four corner of the frame screwed together, the frame will not be stable. squares and rectangles are not stable on their own; any side force can cause them to go out of square. So, some sort of bracing is needed, to help them stay square. To keep them from reducing the acoustic absorption of the panels, the bracing needs to be installed on the back side of the frame.
There are two basic ways of providing this bracing. One is to miter cut pieces of wood to go in the corner, bridging the two legs of each corner in a triangle. Triangles are one of the most structurally stable shapes, which is why they are so commonly used for trusses.
The other method is to cut pieces of 1”x 4” that will fit snug between the two sides of the frame. These can then be attached between the sides at either end, screw them to the sides and the ends. This also provides triangles, although they aren’t visible ones. Even so, they are almost identical to the angled braces, at least from a structural point of view.
Installing the Insulation and Cover
With the frame built, the insulation can be set in place. If the frame was built correctly, the insulation panel should fit neatly in the frame, without any gaps on the sides and without the insulation being scrunched up to fit.
Lay the fabric on the work surface or floor, face down, and smooth it out. Cut a rectangle that is 6” larger than the frame, all the way around. Slightly larger is not a problem, if that’s the way it works out; but avoid letting it be any smaller than that. If the fabric is wrinkled, take the time to iron it before proceeding.
After cutting and ironing, lay the fabric face down on the work area and smooth it out. Then lay the frame, with the insulation set into it, on the center of the fabric. Check that it is centered and straight by measuring the fabric sticking out around the frame.
The fabric is attached to the frame with staples from a staple gun. pretty much any length staples will do, from ¼” on up. Longer ones really don’t add anything to the strength of the panel and may not be driven in all the way by the staple gun.
Starting from the center of one long side, fold the fabric over the side and back of the frame and staple it to the back of the frame in the center. Add one staple on either side of it, about 2” away from the original one.
Going around to the other side of the table, pull the fabric taut, fold it over the side and the back of the frame. While maintaining enough pressure to keep the fabric taut, without being so much as to bend the frame, staple this side, just like the first side was stapled and directly across from it.
Repeat this procedure for both ends.
Going back to the first side, add additional staples on either side of the first set, pulling the fabric taut, but not so taut as to mess up the pattern. Follow the same order as used for the first set of staples, working around the frame again. Do this as many times as necessary, adding only two staples per side on each time around, until the fabric is stapled all the way to the corner on the short sides.
There will be a flap of “excess” fabric at each corner, which is the fabric that was originally the corners of the piece of fabric, while lying flat. This can be folded under the fabric on the long sides, making a triangle. Then staple the long side, all the way to the corner, being sure to maintain even tension on the fabric.
There will probably be some extra fabric sticking out in the inside of the frame on the back. This really isn’t a problem, but it can be cut off, so as to not have any problem with it sticking out around the edges of the panel, when the panel is hung.
Making a Better Acoustic Panel
No matter how good an acoustic insulation is, it can’t absorb all the sound that hits it; it will just absorb some percentage of it. Low pitched tones are worse, as the high pitched ones are more easily absorbed. What isn’t absorbed ends up being reflected away from the acoustic panel.
We can do something about how that sound is reflected away by the panel, by angling the face of the panel. If you look at the acoustic panels used in theatres, this is common. Rather than having a panel that is flat, reflecting the sound back where it came from, the panel is often angled, either because the wall it is mounted on is angled or because the panel has been made to be angled.
The reason for this is to prevent feedback, whether the kind that makes the sound system squeal or just the kind that hits our eardrums and confuses us as to where the sound is coming from. If the sound comes at us from opposite directions, it can be very confusing.
To make angled panels, all we need to do is change the material that’s used for the frame. Replace one side of the frame with a 1”x 8”, rather than a 1”x 4”. Then cut the top and bottom pieces at an angle, so that they ramp up from the 4” to 8” dimension. Do everything else the same and when the panel is hung on the wall, it will naturally be at an angle sufficient to reflect any sound it doesn’t absorb away from the source, regardless of where that source is located.
The one problem that might exist with an angled panel is that the insulation may try to fall down inside it, since there is more space inside the frame than what the insulation needs. The solution to this is to cut a piece of corrugated cardboard and install it behind the insulation, stapling it to the sides and ends.