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It’s all about sound or better yet about controlling it. So in your normal daily life, there are normal background sounds that break the silence without becoming annoyingly loud and to which you quickly get accustomed. They become normal to the point that even though you still hear them you no longer pay much attention to them.
But then again, there is sound and there is noise. It’s important to understand the distinction between the two. Sound is any vibration transmitted through a medium such as gas, liquid, or solid.
Noise, however, is a type of loud or unpleasant sound that you could define as unwanted and annoying. Noise comes from tones that make up background sounds or that pierce through and can be heard above the normal regular background sounds, commonly present and part of your daily environment. Noises are disturbing sounds that can become annoying to the point of causing mild to major irritation or discomfort.
Acoustic Treatment in Conjunction With Soundproofing
Acoustics is the science behind the production, control, transmission, reception, and perception of sound. In the context of sounds around the house, solving noise problems means getting a complete picture of the propagation of sound along with the quality of a room to reflect sound waves with a low reverberation time, appropriate sound levels, minimal echoes, and low background noises. Noise from outside sources getting in through walls, floors, and ceilings, will also affect the quality of a room’s acoustics.
This is where soundproofing becomes an integral part of the acoustic treatment of a room. It doesn’t involve manipulating sound waves within a room but is rather about keeping noises from getting in, to begin with. Soundproofing is normally accomplished by adding sound-absorbing layers from heavy dense materials inside the walls preventing any sounds from getting through, one way or another, thus minimizing the level of sound that passes through the wall.
The management of the acoustics inside that same room is part of the treatment intended to control the sound reflections within that room, for example, for a recording studio or a movie theatre room. But before tackling the acoustics of a room, a careful study of the soundproofing properties of the walls, floor, and ceiling should be performed with special considerations given to the possibilities available to accomplish the modifications. Then only, should you look at the acoustic treatments that will need to be added to the room.
Noises You Might Want to Blot Out
A great deal of money and renovations can be spent on soundproofing a room, considering the amount and the types of absorbing materials you’ll decide to add inside your walls, floor, and ceiling. It is therefore important before you begin your renovations to pay attention to and consider the environment you live in and what types of noises, how much there is, and how loud they can get around the area and the building where you live.
As examples of disturbing noises, you have trucks such as garbage trucks or dump trucks working in the street, backup beeping signals from construction vehicles, jack-hammering down the street, low-flying airplanes, loud playing music, baby screaming, alarms, beeping appliances, and the list goes on indefinitely. Studies show that when people hear sounds that are particularly annoying to them, it triggers a heightened emotional response in the brain that alters their perception of it.
As a constant part of our everyday lives, noises come in all sorts of intensities, levels, and resonance—and we simply cannot escape the noise. But we can try to understand different categories of noises, and how they transfer from one media type to another.
Continuous Noise vs. Intermittent Noise
Continuous noises generated continuously by machinery, for example, that runs without stopping such as ventilation and heating systems, engines running, factory equipment where you work, nearby highway traffic, etc. Intermittent noises are the type of noise that runs for a while only then stops at the end of their cycle such as for some factory equipment running in cycles for instance, but some of those noises are also generated by transport trucks driving by on the highway, aircraft passing over your house, train going by, etc.
Impulse noises
These are sharp impulse-like sounds often but not exclusively associated with the construction industry, caused by explosions, pile driving equipment, etc., but also by gunshots, engine backfiring, etc. Such unwanted and impulse-like noises also exist in acoustics as a result of electromagnetic interference, scratched disk, synchronization problems issued in digital audio, etc.
Low Frequencies
Low-frequency noises happen to be the most difficult to control at their source and at the same time are the ones likely to spread for miles around. You’re constantly exposed to those noises as they’re generated from the roaring of large diesel engines, and hum from power stations, wind turbines, compressors, lawn tractors, earth-moving equipment, etc.
Soundproofing or Noise Abatement
Soundproofing is just one method of controlling the sound environment by creating a barrier to keep foreign sounds from penetrating the room as opposed to acoustics which lets you control the sounds already present inside the room by using special panels and products made of soft absorbing materials that soak up some of the sounds while bouncing the abated difference back into the room at reduced levels to consequently prevents echoing, reverberation, and all different sorts of sound quality issues.
Soundproofing materials are mostly solid and heavy since it has to be dense enough to reflect back sounds and keep them in the same space where they originated. Some of the circumstances where soundproofing is the most suitable solution method of controlling sound are for theatres, cinemas, radio, and TV studios—where unwanted sounds cannot be allowed to enter the room or where generated sounds cannot be allowed to escape into adjacent rooms.
Understanding Wall and Ceiling Decoupling
If you look at how walls and ceilings are built, you have first the wood or metal framing which is one layer making up your structure. With a normal structure, this 1st layer is then covered over with a 2nd layer on the side of the wall where you’re standing inside the room. This 2nd layer is made up of furring strips applied directly over the framing studs or the joists 12 inches apart and solidly secured with nails or screws. The sheeting applied over the furring strips is yet another layer (a 3rd layer in this case) and is very commonly composed of Sheetrock or drywall.
Since both sides of the walls are built in the same manner, you end up with at least 5 different layers all fastened together in one solid block. If you submit sound waves on one side of the finished wall structure so that sound waves energy vibrates the wall surface, the vibrations will be transmitted from one layer to the next until it reaches the opposite side of the wall and radiates into the air on that side reproducing the same noise.
In order to soundproof such a structure, you have to go through a decoupling process of the walls and ceiling in order to minimize the amount of vibrations that will pass through to the other side. Decoupling a wall or a ceiling is simply the means of mechanically separating different layers of a wall or ceiling so that vibrations submitted to one layer will not be transmitted to the next.
Resilient Channels
Decoupling can be achieved with the use of special metal strips, usually made of aluminum or steel. They are available in different shapes and in offset depth (from the flange to the crown) of 7/8 inch to 1-1/2 inches (22 to 38 mm) creating an airspace to effectively improve the sound control effectiveness. The strips referred to as resilient channels are perforated metal strips bent in such a way that the cross-sectional view for some looks something like a skimmer hat, while others look more like “Z-shaped” metal strips but without the acute angle in the bend.
Either installed on their own or with resilient clips, they’re normally mounted perpendicular to the framing of the structure onto which they are fastened to form a grid-like network on the wall or ceiling. In a perfect world, resilient channels could be installed directly onto the studs and joists on their own without any additional hardware. But in reality, however, such a construction will always leave the possibility of someone driving a screw into the wall for hanging a painting for instance, and short-circuit the decoupling.
This is where the “Hat-Channel” complemented with the “resilient clip” makes the best available option when it comes to decoupling techniques. The resilient Hat Channel and the clips should therefore be purchased together and chosen for compatibility. The installation will require more expertise on your part, but done properly, it will leave you with a reliable and trouble-free soundproof room.
Acoustical Short-Circuit
But soundproofing is not necessarily a foolproof solution to altering a wall or a ceiling surface and a poor installation can lead to an acoustical short circuit. An installation using only resilient channels with the flange directly fastened to the framing on one side while the other side is used to attach or secure the decoupled layer creates the risk of a screw coming in touch with the stud or the joist and consequently defeating the purpose and benefits of decoupling.
This could likely happen after the installation when you inadvertently hang a painting or something on the wall. It could easily happen also when longer screws are unintentionally threaded through the drywall into the stud or the joist. The “short-circuit” thus created by the screw provides a path for the noise to travel through the no-longer-isolated wallboard to the underlying construction it is attached to. Besides limiting the acoustical benefits of the assembly, short circuits are extremely difficult to identify or pinpoint accurately.
Using Resilient Clips
Resilient clips or sound isolation clips with a rubber cushion effectively provide a good sound insulation solution for a proper decoupling of the wallboard. The small clips ensure that both the wallboard and the screws are properly isolated from the framing beneath. Although available in various designs depending on the manufacturer, resilient clips pretty much all work the same. The use of resilient clips ensures that your wallboard is well-secured while preventing short circuits. Good decoupling work will prevent expensive remedial repairs in the future.
Understanding Acoustics
Acoustic treatments are solutions that help to absorb or diffuse sound to improve the acoustic quality of a space. Now that your room is soundproofed and keeping most unwanted sounds outside, it is time to manage the sounds that are meaningful, and generated inside the room itself. That means that the following aspects of sound will have to be addressed with specific acoustic treatments.
Reflection
Reflection is a common problem when sound waves run into surfaces such as walls or furniture and bounces off in a different direction. Reflection can lead to reverberation.
Reverberation
Reverberation is what causes some rooms to sound echoey. This would be more noticeable inside a room with no one else around while multiple sound waves would bounce around converging together continuously between hard surfaces. Reverberation deteriorates the sound quality inside the room. It can also make it difficult to carry on a conversation over the loud echoey sounds traveling throughout the room.
Resonance
Resonance comes from the concept that every objects and materials vibrate at a natural frequency. So when a sound wave encounters an object that vibrates at the same natural frequency, it causes the object to vibrate more powerfully thus amplifying the sound. This results in the sounds becoming loud and distorted—referred to as “boomy” in the sound engineering trade—thus causing feedback in sound systems.
While acoustically treating a room won’t reduce sound transmission in and out of that room like soundproofing, it can reduce the acoustic energy in the room by absorbing sound that would otherwise bounce around the space. This can make it easier to communicate, concentrate, and work or study. It can dramatically improve the experience of listening to music and movies. Even with the best speaker system, the frequency response you actually realize in an untreated room is likely to show variations of over 30dB between peaks and dips.
Choosing the Right Acoustic Treatment
Acoustic issues such as reflection, reverberation, and resonance, can be addressed with very specific solutions. Let’s begin with the low-frequency sound waves which are the most difficult to regulate. These sounds usually collect in corners making the bass sound too loud in a room. This is where the bass traps, designed to absorb low-frequency bass sounds, can be strategically placed in the corners of a room to better regulate those sounds. Depending on the material they’re made from, those traps can also be effective to absorb mid and high frequencies.
Acoustic panels are also sound traps designed to absorb sound waves, but being especially thin compared to bass traps, they’re not nearly as effective at trapping lower frequencies. Except for bass sounds or frequencies, acoustic panels will provide a significant improvement in your sound quality by absorbing rather than allowing the sound waves to bounce back in spaces where reverberation and echoing are an issue.
The high ceilings in some buildings can also cause excessive sound reverberation. Special lightweight acoustic panels known as ceiling clouds are made from various materials and are available in different styles to be suspended horizontally from the ceiling and counteract the reverberation effects of the sound waves. Ceiling clouds can also be made to blend inconspicuously with the decor.
While bass traps and acoustic panels absorb sound, the effect can dampen the sound to the point of sounding too quiet. In some instances, you might want to eliminate the echo without fully absorbing too much of the sound. This would require adding diffuser panels into the acoustic treatment. With sections protruding at different angles, the three-dimensional concept leaves the sound waves to disperse in all different directions keeping the space sounding live.
Diffuser panels can be used on their own but they can also be used to complement the sound-absorbing treatment of the bass traps, the acoustic panels, and the acoustic clouds.
While not as aesthetically appealing as acoustic panels, acoustic foam usually comes as tiles with the outside surface embossed with either pyramids, cones, wedges or uneven cuboid shapes. The irregularly shaped material is made from polyurethane or melamine foam and is more commonly used in places such as recording studios for more practical and heavy-duty acoustic treatment.
Aside from its soundproofing qualities, fiberglass insulation can also work to absorb sound and reduce reverberation and other acoustic problems. Thinner panels of insulation installed with a gap left between the wall and the insulation panel can help to absorb lower frequencies although thicker fiberglass panels are better suited to absorb bass sounds and as such, they could be installed in corners to achieve a bass trap effect.
When all else fails to resolve an ongoing resonance issue, it might be worth your while to use a Helmholtz resonator. The sphere-like apparatus with a small opening protruding at the top is designed to absorb sounds of similar frequencies to its own natural frequency. They come in different sizes and shapes to absorb different frequencies and although not especially popular in acoustic treatment, they can help neutralize specific frequency issues.
There are a lot more to be learned and tips to follow when soundproofing a room or fixing a TV room or a home studio for proper acoustic results. A lot more is available from DIYers on this web site, such as “How to Restore an Acoustic Ceiling”, “Acoustic Walls Insulation Tips”, or “Structural Soundproofing for Better Acoustics”. Just click on the links to find out more.