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.

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 soundproofing 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, such as those manufactured by Soundproof Windows, one of our associates.Their website is at www.soundproofwindows.com.

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 can travel through any medium-- in fact it passes through solids better than through air. Sound intensity is reduced in the transition from one material to another, as from the air to a wall and back. The amount of reduction (called the transmission loss) is related to the density of the wall-- as long as it does not move in response to the sound.

Unfortunately, all walls are somewhat flexible. Any motion caused by sound striking one side of the wall will result in sound radiated by the other side, an effect called coupling. If the sound hits a resonant frequency, the wall will boom like a drum. Most isolation techniques are really 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 cleansed with water and does not stick or disintegrate.

It is ideal for industrial applications as well!

Our sound barrier (also known as American MLV) is of high quality, will not tear or rip, and 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 though the floor and disturbing the occupants below.

MLV is likened to lead, as it is very heavy, wear resistant material which 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 a 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 amazing contribution to keeping the sound in your room by filling all cracks and holes, 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!

If you have any doubt as to its effectiveness, please let me know and we will ship you a roll to cover 100 sq. ft, which weighs 100 lbs! If you are shopping for a deal, however, we can offer you a great discount on bigger rolls that weigh over 200 lbs! (Special equipment is required on the jobsite to handle this).

Heavy appliances or speakers should be mounted with our Extreme Soundproofing 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 soundproofing must be planned and implemented into a house when it is first built. A typical residential wall is made of a frame of 2x4 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. Fiberglas filler, R-7 or better, will increase this by 5 to 8 dB and decrease wall resonance. This is also called "insulation" but it 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 gypsum gives another 3 to 6 dB of overall isolation, but its most important effect is lowering the resonant frequency, hopefully below the audio range.

Here are some strategies for reducing coupling between the two 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 give a transmission loss of over 60 dB. This is actually better performance than simple cinder block or poured concrete construction!

These same principles can be applied 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 can 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 air conditioners and refrigerators which are mounted on floors or walls and can actually shake the structure. Footsteps can 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 soundproofed, 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 house, sound tends to be transmitted along the floor joists, so some problems can be solved by simply moving the offending machines. With concrete and steel buildings, you usually wind up completely "floating" the studio floor, a very complex and expensive operation.

The fewer walls in common with the rest of the 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.

The worst sound leaks will be around doors. If possible, replace your hollow doors with solid ones, and make sure that they are tightly gasketed.

The flat rubber type is used in a door that does not fit well, rubber and metal 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 closed.

Once the door is sealed, there still may be leaks around the doorframe. Carefully remove the trim and fill any gap between the frame and gypsum board with caulk or spray polystyrene foam. As long as you are pulling off trim, check for gaps behind the baseboards and around any window frames.

Incidentally, many interior doors are hollow and light and do not really stop sound well even when tightly gasketed. Such a door should be replaced with a solid one. Manufacturers will supply data on the amount of transmission loss a door can provide. Alternatively, the door can be reinforced with a layer of thick plywood, or you may want to hang a second door that opens the other way in the frame. If none of this is practical, a really heavy curtain over the door will help some.

A heavy drape will also help block sound from windows and doors. Check out this site for custom acoustic drapes to see what we they offer. http://coasttocoastdraperies.com.

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 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. 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 then pass through the attic or crawl space into adjoining areas.

FOR MUSICIANS*

Truly isolated spaces are created by building a separate room within the room. Both the external room and the internal room have to be tight and heavy and there must be 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. Something like this should really be designed by an architect to fit your situation, but here is a typical plan to give you the idea.

Floating Floor in a Room within a Room

The inner room is built on a platform of 2 X4's covered with two layers of 3/4 inch plywood. The platform is supported by neoprene pads that line up with the floor joists. There must be no other connection between the room and the house. The walls and ceiling are built on the platform using 2 X4 studs and double gypsum on the inside only. The space between the walls should be at least one inch (wider if practical) and lined with MLV Sound Barrier. The air duct should be very long and lined with sound barrier (also known as American MLV) material.  Order at this website: http://www.yahoosoundproofing.com/malovi.html

Room Treatment

You will not be surprised to hear that the shape and furnishings of a room can affect the way things sound-- we have all experienced extreme cases such as large echoey bathrooms and overstuffed restaurants. These effects can easily happen in a subtle way in your studio, causing inaccuracies in the sound from the monitors. When you record or mix, you adjust the music until it is right in your control room, but when you play the tape in a neutral environment the sound is overcompensated and strange.

There are expensive instruments available to measure the quality of sound in a space, but the best ones are on the sides of your head. You can compare rooms by listening to familiar recordings. (It does not have to be on CD-- you can tell a lot from the quality of hiss on a tape.) In a good room, the bass is balanced and clear, cymbals "shine" without being harsh, and you can understand words without effort. 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

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 loud short sound to die away. "Dying away" can be defined more scientifically as a drop in loudness of 60 dB, so acousticians call reverberation time RT60.

The amount of reverberation desired in a room depends on the activity going on. Musicians like fairly long reverberation times; between one and two seconds. This allows them to hear themselves play and enhances the harmonic effects of the music. (In larger rooms, even more reverb is desirable because it helps fill the hall with sound.) For listening to speech or music played through loudspeakers this amount of reverb is too much-- values around a second are more comfortable, and for critical listening to speakers the RT60 should be close to a half second.

Reverberation time is determined by the volume of the room. It can be reduced by replacing some of the hard, reflective parts of the walls with soft, absorptive sections. Every material has some absorptive qualities. This is described by its coefficient of absorption, a number between 0 and 1, with 0 being totally reflective and 1 being an open window. For instance, the COE of brick is 0.04, whereas that for heavy drapes is around 0.6. The effective absorption of a surface is simply the COE times the area of the surface in square feet. These numbers can be used to compare materials and to predict the results of treatment. The absorption ability of most materials is frequency dependent, which can cause problems as described 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 particular 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 probably know one where the deep tones of your voice are tremendously supported (doesn't everybody sing in the shower?). Most rooms have three pairs of parallel surfaces, and the dimensions are usually just right to affect music. An eight-foot ceiling, for instance, reinforces 70 Hz. (This is called a room mode.)

This phenomenon can be prevented 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 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, so 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 very dead room and bass buildup occurs there are devices called bass traps and Helmholtz resonators that absorb a restricted range of very low frequencies. The general principle is, the larger they are, the lower the frequency. Absorption should be used only 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 to a music room. It is the icing on the cake, so to speak.

Final Comments

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.

We do not have a large staff, so please leave a message, and even call us back if you need assistance.