We receive requests every day from musicians, singers and students for advice on how to build their home practice rooms. Everyone wants to know, “What can we put on the walls to keep the sound from bothering the people on the other side of the wall or in the adjacent building?” There is no simple solution, and each case should be evaluated separately.
The first plan of action is just that….make a plan. Remember the 5 P’s: Proper planning prevents poor performance. Take it systematically. First, survey your targeted room and make a list of everywhere that sound passes through. Your best strategy is to listen very carefully and determine where the worst noise leaks are.
Start with the obvious and easy fixes, and proceed through your list, attacking each noise leak separately.
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Take the obvious steps to seal off all cracks, crevices, and paths for sound to escape through. Every little crack will offer sound an escape route. Unless you are thorough in sealing off the entire room, you will not be successful with your sound-proofing project. You need to create an airtight seal, so noise will not pass through. Just as water would pass through a crack, so do sounds! Sometimes this can be difficult to accomplish, depending on the number of vents, electrical plugs, windows, doors, and other breaks in the wall.
Doors and windows are often overlooked. Make sure that doors and windows fit their frames snuggly and that they shut tightly. We offer advice on making “window plugs” as a quick fix for leaky windows. A more permanent solution is to install acoustical windows.
The quality of the finished building depends a great deal on the artisanship and attention to detail of the builder. There must be no loose studs, and the sill plates must really hug the floor. The gypsum must be well fitted, and all potential cracks must be caulked. (Caulk should be flexible, not rigid, and should not crack when the building settles.) Do not put holes in sound walls for outlets or pipes. Use surface-mount electrical fittings and caulk around any wires that pierce the gypsum.
More Sound Theory
Sound is known to travel through any medium. Sound passes through solid materials better than through air. The intensity of sound is reduced in the transition from one material to another. For example, sound intensity is reduced as it travels from the air to a wall and back. The amount of transmission loss or reduction is related to the density of the wall– as long as it does not move in response to the sound.
Unfortunately, walls are flexible. The motion caused by sound hitting one side of the wall will lead to sound radiated by the other side. This is called coupling. And f the sound hits a resonant frequency, the wall should boom like a drum. Most isolation techniques are ways to reduce coupling and prevent resonances.
Airborne Noise and Soundproofing Floors
For airborne noise, we have the perfect answer. Our mass-loaded vinyl sound barrier (also known as American MLV) is an effective, relatively inexpensive treatment for airborne noise. This type of noise is primarily conversations, TV’s, and any sound traveling through the air, and not vibrating through the walls, shaking the windows, etc.
Airborne noise, like any other, must be treated at the source. For multi-level buildings, MLV (mass-loaded vinyl) can be used as an underlayment under the floors. It can be laid directly on the floor or between sheets of plywood or over cement. It makes floors more comfortable while also reducing noise from above and below. It is easily cleaned with water and does not stick or disintegrate. It is ideal for industrial applications as well!
A high-quality sound barrier will not tear or rip, and it will continue to perform over time. Remember that any cracks or holes will allow sound to pass through and are almost impossible to repair once installed. It does not pay to cut corners here since the amount saved does not justify the compromise in quality…
For best results, lay the MLV down on the floor, then add padding and carpet to prevent the sound of footsteps and other airborne noise from being carried through the floor and disturbing the occupants below.
MLV is likened to lead, as it is a very heavy, wear-resistant material that adds mass to the floor, helping to keep the sound from passing through.
When installed in a wall, it more than doubles the STC rating. For instance, a standard hollow sheetrock wall with 1/2″ Gypsum board on metal studs has an STC rating of about 23 (ordinary conversation through it can be understood). Adding the sound barrier (also known as American MLV) mass-loaded vinyl brings the STC rating up to about 49. This is a great improvement!
You can make an impressive contribution to keeping the sound in your room by filling all holes and cracks, no matter how small or indirect. Be sure to caulk the seams of the sound barrier (also known as American MLV) with our acoustical caulk before proceeding to the next step!
Heavy appliances or speakers should be mounted with extreme sound-proofing vibration pads. They are made from elastomeric neoprene and can support 50 lbs per square inch. They come with and without cork – the cork being for heavier loads.
Residential Construction and Insulation
The most effective sound-proofing must be planned and implemented into a home when it is first built. A normal residential wall is made of a frame of 2×4 wood studs covered with 1/2″ or 5/8″ thick gypsum board. Provided that it has no holes, this will provide about 35 dB of isolation. Fiberglass filler, R-7 or better, will increase this by 5 to 8 dB and decrease wall resonance. This is also called “insulation,” but it is designed primarily as “thermal insulation,” such as that manufactured by Owens Corning. Its acoustical properties are limited because it was not designed to provide protection from noise but as a climate control product.
Structural Noise and Preventing It
Doubling the thickness of the gypsum gives another three to six dB of overall isolation. Its most critical effect is lowering the resonant frequency, preferably below the audio range.
Here are some strategies for reducing coupling between the sides of the wall.
One is to make the gypsum to stud connection flexible or springy by hanging a second layer of gypsum on resilient metal channels (i.e., RC-1 or RC-2), perpendicular to the studs, 24″ o.c.
Another variation of this is to use isolation clips and hat track channel (slightly more effective but also more costly) between the two layers of gypsum. The isolation clips have a neoprene grommet and fit onto a hat track channel to decouple the second layer of gypsum from the first.
Still, another way is to use separate studs for each face of the wall, so there is no direct connection between them, in effect, building a double wall. This takes up a lot of space but can produce a transmission loss of over 60 dB. This will produce a better performance than simple cinder block or poured concrete construction!
You can apply the same principles to floors and ceilings. Sound barrier (also known as American MLV), then RC-2 Channel and a second layer of drywall can be installed on a ceiling, provided it is not a low ceiling.
A heavy false ceiling hung on springs should match the performance of a double wall.
More challenging is dealing with sounds transmitted through the frame of the building. The problem is sometimes caused by machinery such as refrigerators and air conditioners, which are mounted on walls or floors and can shake the structure. Similarly, footsteps will cause similar effects to a somewhat lesser extent. Bass frequencies also vibrate through the building structure, rattling windows at the other end of the house if not isolated.
Whenever building a room designed for music, it is imperative that the room first be sound-proofed prior to worrying about any acoustic conditioning for the room. Keeping bass frequencies in can be as challenging as keeping outside noise from mixing with the music being created inside the room. It is particularly challenging in a recording or live performance situation. It is not impossible, however! The staff at Extreme Soundproofing can assist with the most challenging of projects and “help you get the job done right the first time!”
Retrofitting
In a wooden home, sound will be transmitted along the floor joists. Often the best approach is to just relocate offending machines. With concrete and steel buildings, you normally wind up completely “floating” the studio floor, a very complex and expensive operation.
The fewer shared walls with the rest of the house or building, the better. The best room being the basement (if your building has one). Garages tend to have heating and cooling problems and are practically like being outdoors.
Floors will produce the worst sound leaks. If possible, replace your hollow doors with solid ones, and make sure that they are tightly gasketed.
The flat rubber type can be used in a door that does not fit well. Metal and rubber gaskets work on doors that are pretty tight already. The brush material is for sliding surfaces. Do not forget the bottom of the door– the best gaskets are spring-loaded and drop down when the door is shut.
Once the door is sealed, you may still experience leaks around the doorframe. Carefully remove the trim and fill gaps between the gypsum board and frame with caulk. You can also spray polystyrene foam to fill any gap. When you are pulling off trim, check for gaps around any window frames and behind the baseboards.
Many interior doors are hollow. These types of doors do not stop sound effectively, even when tightly gasketed. Replace this type of door with a solid one. Manufacturers will provide data on the amount of transmission loss the door provides. Doors can be reinforced with a layer of thick plywood. You could also hang a second door to open the other way in the frame. If none of this is possible, a really heavy curtain over the door will help some.
A heavy drape will also help block sound from windows and doors. Search online for custom acoustic drapes and learn what features they offer.
Electrical fittings can be another source of leakage. Remove the plates off receptacles and light switches, fill the gaps between the box and the gypsum, and add a sealing gasket when you replace the plate. If receptacles or switches are found back to back on both sides of the wall, the gasket will not be enough to stop the sound—patch over the original hole after you have replaced the electrical box with a surface mount type. If you are not up for rewiring, cover the offending outlets with a weatherproof-hinged cover.
Use closed-cell foam to wrap around electrical plugs that are a source of noise leakage, and water pipes, air ducts, etc. If possible, encase noisy air conditioners and air ducts in an enclosure designed lined with closed-cell foam. Search online to purchase this type of foam.
Even without a direct air route for sound to follow, there may be flanking paths around heavy walls through thin floors or ceilings. The sound will then pass through the crawl space or attic into adjoining areas.
Sound Proofing for Musicians
You can create truly isolated spaces by building a separate room within the room. A room within a room Both the external and the internal rooms have to be tight and heavy. Make sure that there is no solid connection between the two, not even the floor. You can buy prefabricated isolation rooms (at a hefty cost), or you can build one using construction techniques similar to that described above. It is best to work with an architect or a sound-proofing expert.
Floating Floor in a Room within a Room
The inner room should be built on a platform of 2 X 4’s covered with a couple of layers of 3/4 inch plywood. Neoprene pads will support the line up with the floor joists. The cannot be another connection between the room and the home. The ceiling and walls are built on the platform using 2 X4 studs and double gypsum on the inside only. The area between the walls should be no less than one inch (wider if practical) and lined with MLV Sound Barrier. Make sure the air duct is quite long and lined with sound barrier (also known as American MLV) material.
Room Treatment for Sound Proofing
By now, you shouldn’t be surprised to know that the furnishings and shape of a room will have an impact the way things sound. If you recall the sounds of busy restaurants, you know what I mean. These effects can easily happen subtly in your studio, causing inaccuracies in the monitors’ sound. When you mix or record, you adjust the music until it sounds right in your control room. But when you listen to the recording in a neutral environment, the sound is strange and overcompensated.
Even though there are expensive instruments for measuring the sound quality of in a space, the best ones are built-in our heads. The best way to compare rooms by listening to familiar recordings. (You can tell a lot about sound quality from the quality of hiss on a recording.) In a room set up correctly, the bass is balanced and clear, cymbals “shine” without being harsh, and you can easily understand words. A mono signal appears to come from a spot exactly between the speakers, and that spot does not jump around with changes of pitch. Now listen to the quiet– can you hear a refrigerator, a TV, traffic on the street? Clap your hands–you should hear a slight broadening of the sound, but little reverberation and certainly no pitches or echoes.
These simple tests should tell you about any severe problems the room may have. Subtle ones will show up in the music produced in the room, as described above. You may be surprised to find that the control of the sound of a room is not really very complicated and can usually be accomplished with inexpensive materials.
Some More Theory About Sound Proofing
The goal is very simple– we want to get the sound from the speakers to your ears without messing it up. This is really just a matter of what becomes of the sound after it passes your ears.
There are three things that can happen when sound hits a wall. It can be reflected, absorbed, or diffused.
If the wall is flat and hard, the sound will be reflected. A single strong reflection can sometimes be heard as an echo, but in most rooms, a lot of reflections (including reflections of reflections) combine into the reverberation. The aspect of reverberation you hear about the most is reverberation time. This is the amount of time it takes a short, loud sound to die away. “Dying away” can be explained more scientifically as a drop in loudness of 60 dB. Acousticians call this reverberation time RT60.
The amount of reverberation preferred in a room depends on the particular activity. Musicians like fairly long reverberation times, between one and two seconds. This helps them hear themselves play and improves the harmonic effects of the music. (In larger spaces, even more, reverb is desirable. The increase helps fill the space with sound.) For listening to music played or speech through loudspeakers, this degree of reverb will be too much. Values around a second should be more comfortable, and for critical listening to speakers, the RT60 should be close to a half-second.
The volume of the room determines reverberation time. It can be reduced by replacing some of the hard, reflective parts of the walls with soft, absorptive sections. Each material has some absorptive features, which is described by its coefficient of absorption. The coefficient of absorption is a number between 0 and 1. Zero means that the material is totally reflective and one would be wide opened window. As an example, the COE of heavy drapes is around 0.6, whereas for brick is 0.04. The effective absorption of a surface is the area times the COE of the surface in square feet. These numbers are used to compare materials and to predict the results of treatment. The absorption ability of most materials is frequency-dependent, which may cause issues, as you will read later.
Reflections off flat walls can sometimes combine to produce undesirable effects. The worst of these is the standing wave.
Standing Waves
Standing waves are created when you have two parallel-facing walls. There will be a specific set of frequencies that are reinforced by the distance between the walls (the sound makes exactly one round trip on each cycle of the speaker, and the pressure fronts pile up). This is what happens in bathrooms- you likely know one where the deep tones of your voice are supported (Don’t we all sing in the shower?). Most rooms have three pairs of parallel surfaces, and the dimensions are normally ideal for affecting music. An eight-foot ceiling, for instance, reinforces 70 Hz. (This is called a room mode.)
You can prevent this phenomenon by designing the room with nonparallel walls. It can be cured in existing rooms by making one of the walls absorptive or by breaking up the flat surfaces. When sound is reflected off a rounded or complex surface, it is diffused. Diffusion spreads the reverberant sound evenly throughout a room, which not only prevents standing waves but also eliminates “dead spots”– places where components of the sound are missing.
We can break up flat surfaces by hanging large objects called diffusers. The shapes chosen for diffusers are really a matter of taste and cost. Avoid concave curves, which focus on sound instead of dispersing it, but otherwise, pyramids, lattices, or computer-designed random surfaces all work well. The depth of a diffuser determines the lowest frequency that will be affected. A diffuser one foot deep will scatter sound down to 160 Hz.
Reflections can cause a further problem when the principal activity in a room is listening to loudspeakers.
Interference
You may be familiar with phase interference from recording work with multiple microphones. If a sound arrives at a single point via two paths at slightly different times, certain frequencies will be reinforced, and others will be weakened. You can easily hear this by putting your ear close to a wall: the quality of sound will change because the reflections off the wall interfere with the direct sound. The effect is at its worst when the distance the reflected sound travels is only slightly longer than the direct distance.
Phase interference is attacked by careful consideration of the placement of speakers and the listener. In general, avoid locating either so that there are short reflective paths off walls, ceiling, or equipment. The worst problems occur when a speaker winds up in a corner. If this is unavoidable, figure out where the reflections occur and make that part of the wall or ceiling absorptive.
Coloration
As a general rule, high-frequency sound is absorbed more readily than low. That is because as absorption is added to a room, the reverberation becomes more and more bass in tone. Some of this coloration is acceptable, even preferable, but eventually, the room develops a tubby response. If we need a dead room and bass buildup happens, there are instruments called bass traps and Helmholtz resonators that absorb a restricted range of low frequencies. The general idea is, the larger they are, the lower the frequency. Absorption should be used in moderation, and only materials that soak up the full range of sound should be used.
Your acoustic results will quadruple at the low bass end if you bump up from the thickness to the 3″ thickness. Any bass music will require this thicker material. For studio applications, cover 50-70% of your overall wall space. Note also that foam DOES NOT BLOCK sounds from going through a wall. Foam lowers reverb. There is no substitute for “listening” and identifying the trouble spots when a room is almost finished. Acoustic treatment is the last thing to be done in a music room. It is the icing on the cake, so to speak.
Blocking Sound
There are only a few ways of blocking sound.
We can add mass to the walls to keep sounds from traveling through the wall.
To add mass to the walls, we use Mass Loaded Vinyl, commonly known as MLV or Sound Barrier. It is sold by the roll and is very heavy, weighing about 1 lb. per sq. foot. It is very effective because it adds mass (or weight) to your walls. It makes it much more difficult for sound to travel through a heavy wall. This product is easy to install. Simply attach it to the existing drywall and cover it with another layer of drywall. It can also be used to sound-proof fences, floors and ceilings.
When quieting floors, it can be rolled out and used under carpet, tile or any type of flooring product. Be sure to cover the entire surface since any gaps will cause noise leakage and compromise the effort.
Absorption and Closed Cell Foam
For situations involving the need to block sound and absorb reverberation, such as when trying to quiet machinery such as engines, motors, and compressors, you should use a Closed Cell Foam product. This foam can be glued onto the surface with contact adhesive.
This product is a great sound absorber, the thicker the foam, the lower frequencies and the more it will absorb. The most popular thickness is the 1″ thick foam. You can order it by the roll or by the linear foot.
Absorption and Acoustical Draperies
To absorb the excess reverb in a room, we use what we call Acoustical Draperies. These heavy, lined draperies are French Pleated and are not only effective at reducing echo and reverberation in large rooms but are a beautiful decorative addition to the room.
Final Comments on Sound Proofing
There is no substitute for “listening” and identifying the trouble spots when a room is almost finished. Acoustic treatment is the last thing to be done in a music room. It is the icing on the cake, so to speak.
Whether you are muting the high-end hiss of your microphones with pyramid panels or putting up bass traps in the corners of the room to even out the low frequencies, you must first use your keen for those musicians who are building a recording studio. The average home does not have any need for pyramid panels, bass traps, or acoustic treatment of its walls. However, if you are a serious recording artist or music engineer and responsible for producing that perfect sound, you might be inclined to use these products.
This is an information site for those interested in learning about the basics of sound-proofing. The first thing that needs to be done is to draw a distinction between blocking sound and absorbing sound. To be able to control sound effectively, one must examine it and make a plan on how to reduce it.
