Musicians, singers, and students need sound advice on how to build their home practice rooms. There is no simple solution to the “sound insulation problem”, and each situation should be assessed individually.
Make A Plan
Making a plan is the first step. Remember the 5 P’s: Proper planning leads to better performance. First, make a thorough inventory of your targeted room and find out where the noise leaks are. A good strategy is to listen very carefully and identify those areas where you can hear the sound coming in and out.
Work through your list, starting with the obvious and easy fixes and then addressing each noise leak individually.
It Is All About Closing Off Escape Routes
All cracks and crevices will offer sound an escape route. Seal all cracks, crevices, and exit paths. Soundproofing a room does not work unless it is thoroughly sealed off, so that sound does not pass through. Like water, sound also goes through cracks. Sealing it all off can be difficult to accomplish sometimes, depending on how many electrical outlets, vents, windows, doors, and other breaks there are in the wall.
Doors And Windows
Be sure that your doors and windows close tightly. The frames of your doors and windows should fit snugly. Making “window plugs” could provide a temporary fix for sound leaky windows.
Installing acoustical windows, such as the ones manufactured by Soundproof Windows, is a more permanent solution. Their website is at www.soundproofwindows.com.
Studs And Sill Plates
It is important that there are no loose studs, and the sill plates go right to the floor. This is determined by the good workmanship of the builder, but if the workmanship is not ideal, you are going to have to rectify it if you want a well-soundproofed room.
Caulk Everything
All cracks should be caulked with flexible caulk that does not crack during the settling process. Make sure outlets and pipes are not run through sound walls, surface mounted electrical fittings are used and caulking put around any wires that pierce the gypsum.
Some General Sound Theory
Sound will travel through any and all available medium. It will pass through a solid more effectively than it will through the air. The intensity of sound will be reduced during the process of transition from one material substance to another material, as what occurs when the sound goes from air to a solid wall and back again.
As long as the wall does not move in response to the sound, the amount of sound reduction increases with density. This is called the transmission loss.
Flexibility Allows Coupling
Unfortunately, all walls are flexible. Any movement caused by a sound striking one side will result in the sound being radiated by the opposite side, a phenomenon known as coupling.
Most isolation methods consist of ways to reduce the coupling effect and also prevent resonances when the sound reaches a resonant frequency with the material.
Soundproofing Floors And Airborne Noise
MVL A Solution For Airborne Noise
A mass-loaded vinyl sound barrier (MLV) is an effective, relatively inexpensive solution for airborne noise. This type of noise consists primarily of conversations and television, as well as any sound that travels through the air, rather than vibrating from the walls or shaking the windows.
The source of airborne noise – like any other – must be treated. MLV can be used beneath the floor of multi-level buildings to absorb it.
It can be spread directly across the floor, between sheets of plywood, and even over concrete. It keeps floors comfortable while at the same time absorbing sound. Its easy to clean with water and does not stick or disintegrate.
In addition, it can be used in industrial applications.
High quality MLV sound barriers will not tear or rip over time.
Don’t Cut Corners When Installing MLV
You should keep in mind that any cracks or holes will allow sound to pass through, and are virtually impossible to repair once installed. Here it doesn’t make sense to cut corners, since the savings aren’t worth the soundproofing compromises that result. You either soundproof or you don’t. Think about it as a bucket with a bunch of holes in it – it is no good for the job intended.
The best method for preventing footsteps and other airborne noise from disrupting the occupants below is to lay the MLV down on the floor and then add padding and carpet on top of it.
By filling cracks and holes, no matter how small or indirect, you can make a huge contribution toward keeping sound in your room. The MLV sound barrier seams should be caulked with acoustical caulk before starting the next step.
Mass Loaded Vinyl And STC Rating
A lot of people compare MLV to lead because it’s a very heavy, wear-resistant material, which adds mass to the floor and absorbs sound.
The STC rating is twofold when MLV is installed inside a wall. One example is a standard hollow sheetrock wall, with a thickness of 1/2″ Gypsum board, attached to metal studs, with a STC rating of approximately 23. With this configuration, ordinary conversation is understandable through it. The STC rating increases to about 49 after adding the MLV sound barrier. This is an amazing improvement!
Use Soundproofing Vibration Pads
Soundproofing vibration pads should be used to mount speakers and heavy appliances. Elastomeric neoprene is used to make the pads, which can support 50 pounds per square inch. It comes with or without cork – the cork being for heavier loads.
Residential Construction and Insulation
It’s best to build a house with the most effective soundproofing from the earliest possible stage. In a residential setting, walls typically consist of frames made as 2×4 wood studs covered with 5/8″ or 1/2″ gypsum board. The isolation will be around 35 dB the case where there are no holes in it. R-7 fiberglass filler will reduce that sound level by 5 up to 8 dB and reduce wall resonance. Acoustic properties of this insulation are limited, and it is designed primarily for its thermal insulation properties . That’s because it wasn’t meant for noise prevention, but rather for climate control.
Structural Noise and Preventing It
Increasing the thickness rating of gypsum can increase the sound isolation by 2 to 4 dB – a relatively minor amount , but its most important action is to lower the resonant frequency to at least below the audible range.
Reducing Coupling
The following are some strategies to reduce coupling between the outside and inside of the wall.
It is possible to make this connection springy or flexible 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 is to use hat track channel and isolation clips (a little more effective but somewhat more costly) between the two layers of gypsum. These isolation clips are made of neoprene, and they have hat track channels that fit on top of the gypsum board to isolate the second layer from the first.
Another solution is to incorporate separated studs for the face of each wall causing there to be no direct connection from one face to the other, thereby creating a double wall. It tends to take up a lot of space, but the transmission loss is over 60 dB – exactly what is needed. This results in an outcome better than using cinder blocks and concrete.
This same principle can be applied to ceilings and floors. A ceiling that (where there is adequate head space) can be installed with a MLV sound barrier, followed by RC-2 Channel and a second layer of drywall.
You can replicate the performance of a double wall using a false ceiling hanging on springs.
It can be more challenging to deal with the transmission of sound through the frame of the building. Problems are sometimes caused by machinery such as air conditioners and refrigerators, which are often mounted on floors and walls and shake the structure. A similar effect can also be caused by footsteps, although less so. Bass frequencies also vibrate through the building structure, rattling windows throughout the house if they aren’t isolated.
Acoustic Conditioning Is Not The Main Issue
Building a music space requires that space be soundproofed first, before considering any acoustic conditioning for the room.
Keeping Bass Frequencies Contained
It can be difficult to keep bass frequencies contained, as much as outside noise from mingling with the music being played inside the room. Getting it right is especially challenging in recording or performing situations. However, it is not impossible! Soundproofing experts can help with your most challenging projects and ensure the job gets done right the first time.
Retrofitting
In a wooden house, sound tends to be transmitted along the floor joists. You may need to ensure that any load noisy machines such as fridges or aircondiioners are moved from connected joists that go into the room you want to isolate.
A studio floor in most existing concrete and steel buildings is usually completely “floated”, a very complex and expensive operation.
Generally, the fewer walls that connect the floor with the rest of the building, the better. The basement is best (if you have one). Garages usually heat and cool unevenly, and it feels like being outdoors – so not the best option.
Doors And Door Frames Are Critical
Generally speaking, the worst source of sound leakage is around doors. It is advisable to replace hollow doors with solid ones, and to make sure they are tightly sealed.
Flat rubber gaskets are used on doors that don’t fit well. Rubber and metal gaskets work well on doors that fit well already. The brush material is a good choice for all sliding surfaces. Don’t forget the bottom of the door – spring-loaded gaskets work the best.
Once the door is sealed, there still may be leaks around the doorframe. After removing the trim carefully, any gaps between the gypsum board adn frame must be caulked or spray filled with polystyrene foam. As long as you are pulling off trim, check for gaps behind the baseboards and around any window frames as well.
Many if not most interior doors are hollow and very light in structure, They do not stop sound well, even when tightly fitted with gaskets. Doors like this need to be replaced with a solid ones. Check manufacturer data on levels of sound transmission loss a given door provides. A think layer of plywood can also be applied to the door to reinforce it, also hanging a second reverse-opening door in the frame opposite it can make the nesseary isolation break. If none of this is practical, a heavy acustic curtain hung over the door will provide some help.
Acustic Drapes May Assist
A drape that consists of heavy material will also help block sound from doors and windows. Check out these options from Amazon.
Manageing Electrical Fittings
Electrical fittings are another source of leakage. Take the plates off light switches and receptacles, fill the gaps between the box and the gypsum, and add a sealing gasket when you put the plate back on. If switches or receptacles are found back to back in both sides of the wall, the gasket will not be enough to stop sound. Replace the electrical box with a surface mount type, and patch over the original hole. If rewiring is not an option, 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. Visit http://www.yahoosoundproofing.com/americamat.html to purchase this type of foam.
Even if there is no direct air route for sound to follow, there can be flanking paths around heavy walls through thin ceilings or floors. The sound will subsequently pass through the crawl space or attic into adjoining areas.
For Musicians
Build a separate room within a room to allow for truly isolated spaces. The external room and the internal room have to be as tight and heavy as possible and the floor must not connect the two. There are prefabricated isolation rooms on the market for a hefty cost, or you can build your own using construction techniques similar to those mentioned above. It would be more appropriate if an architect designed something like this for your specific situation, but here is an example to give you an idea of what it could look like.
Floating Floor in a Room within a Room
There is an inner room built on a platform of 2 X4’s covered in two layers of 3/4 inch plywood. The platform is supported by neoprene pads that line up with the floor joists. It must be self-contained in the house so its walls and ceiling are only constructed inside the walls, containing 2X4 studs and two-inch gypsum. It is advisable to line the space between the walls with MLV Sound Barrier and to leave at least one inch between the walls (a higher number is preferable). The air duct needs to be very long, lined with sound-deadening (also called American MLV) material. Order at this website: http://www.yahoosoundproofing.com/malovi.html
Room Treatment
We know that the shape of a room and its furnishings have an impact on how things sound – we’ve all experienced echoing bathrooms and overcrowded restaurants. A studio can easily be affected in a subtle manner by these effects, causing inaccuracies in the monitors’ sound. During the recording or mixing process, the music is constantly tweaked until it is just right, but once it is played in a neutral arena, the music sounds strange.
A lot of expensive instruments can be used to measure the acoustic quality of a space, but the best ones are those you use on your head. Listening to familiar recordings allows you to compare spaces.
When you are playing in the right room, you hear deep bass, clear cymbals, and understand the words without effort. It appears that the mono signal is coming from a point exactly in the middle of the speakers, and it does not jump around with changes in pitch. Then listen to the silence– can you hear traffic from the street, a television, a refrigerator? Clap your hands, because it should widen the sound, but there should be little resonance and no echoes.
This will tell you whether the room has severe problems, or if there’s a more subtle issue showing up in the music. You might be surprised to learn how easy and inexpensive it is to control the sound level of a room.
Some More Theory
This is really just about how the sound gets from the speakers to the ears without messing it up. This is really just a subject of what happens after it passes your ears.
Essentially, three things that can occur when sound hits a given wall. It can be diffused, reflected, or absorbed.
The sound will be echoed from hard and flat walls. An echo is an example of a single strong reflection, but in general many reflections will interact in multiple ways to create reverberation. The reverberation period is the time it takes for a short loud sound to fade away. The “fading away” can be described scientifically as a drop in loudness of 60 decibels, hence the term RT60.
The amount of reverberation desired in a room depends on the activity taking place within the space. For musicians, the right amount of reverberation time between one and two seconds is preferred. This lets them hear themselves playing and increases the harmonic effects in the music.
The more reverb the better in larger rooms since it fills the hall with sound. Listen to loudspeakers or speakers to hear speech or music. The amount of reverb that would be acceptable for critical listening would be somewhere around .8 to .1 seconds.
A reduction in the reverberation time can be achieved by replacing hard surfaces with more absorptive sections of the walls. The absorption qualities of all materials can be described by their coefficients of absorption, ranging in value from 0 to 1. The lower the number, the more reflective the material. The effective absorption of a surface is simply the COE times the area of the surface in square feet. For instance, the Coefficient of emissivity of brick is 0.04, while that of heavy drapes is around 0.6. Material absorption rates are complex, and for most materials, frequency dependence is significant. If the numbers used to compare materials are used, the predictability of treatment results is greatly enhanced.
The standing wave is the worst effect produced by reflections off flat walls.
Standing Waves
Two parallel walls will create standing waves. Specified frequencies are reinforced by the distance between walls (the sound travels exactly round trips on the speaker’s cycles, thereby causing a pressure front to pile up).
The depth of tone of a voice is helped in bathrooms where several walls are parallel to each other, and the proportions are usually just right for music. In this instance, a ceiling height of 8 feet reinforces the 70 Hz frequency, referred to as a room mode.
A room with parallel walls can be designed to resist this phenomenon, or an existing room can be made to absorb sound by making one wall absorbent or breaking up its planes. Reflecting sound off a rounded surface or a complex surface diffuses it throughout the room. Diffusion works to remove “dead spots” in a room by spreading the reverberating sound evenly throughout the space, preventing standing waves.
The shapes and sizes for diffusers vary depending on taste and cost. Diffusers can be hung over a flat surface to break it up. Usually, pyramid shapes, lattices, or computer-generated random surfaces are best, but refrain from concave-shaped surfaces, which focus the sound rather than disperse it. The lowest frequency that can be affected by a diffuser that is one foot deep is 160 Hz.
Reflections can become more problematic when loudspeakers are the main form of entertainment in a room.
Interference
Phase interference is sometimes encountered when recording with multiple microphones. So if two sound waves arrive at the same point at slightly varying times, something will happen to the frequencies arriving at the same place at slightly different times. By placing your ear close to a wall, you will be able to tell that the direct sound will be interfered with by the reflections off the wall. If the direct distance is only slightly longer than the reflected distance, the effect is at its worst.
In order to combat phase interference, careful consideration must be given to speaker placement and listener placement. Avoid placing either so as to create short reflective paths off equipment, walls, or ceilings. The worst of problems tend to occur when speakers line up with a wall corner. If this cannot be avoided, make sure to design a wall or ceiling surface that will absorb the reflections.
Coloration
The reverberation becomes increasingly bass in tone as absorption increases in a room, so the high-frequency sound becomes more easily absorbed than the low-frequency sound. The room develops a tubby response when the coloring gets too intense. It is possible to block out low-frequency music by using devices known as bass traps and Helmholtz resonators, which absorb certain frequencies. The general rule is that the larger they are, the lower the frequency will be. Absorption should never be used in excessive amounts, and only sound-absorbing materials should be used.
Using thicker material for bass music in the studio requires covering 50-70% of the wall space. Moreover, foam DOES NOT OPPOSE sounds from passing through the walls. Foam lowers reverberation. It is vital to listen and identify trouble spots once a room has been built. The acoustic treatment of a music room is the final step to do it. It’s like the cherry on top, so to speak.
Conclusion
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 to 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. We will be happy to assist you with purchasing the right products for your particular needs, so please call us, and allow us to assist you.