Noise-Busters Acoustical Products Co.

7320 State Road, Parma, Ohio 44134-4958

Tel: (440) 885-5974, Fax: (440) 885-5975, Email: Sales@Noise-Busters.com

The "Original" Noise-Busters Soundproofing Page

The overwhelming majority of recent web inquiries have dealt with "Sound Proofing" in private residences including stereo listening rooms, instrument practice rooms, home theaters and home recording studios.  Although it is not practical or affordable to completely soundproof a room, we will offer you some suggestions on how to inexpensively reduce the sound escaping from these rooms to more acceptable levels.  Any additional comments or suggestions from those of you who have successfully soundproofed one or more rooms would be greatly appreciated.   We're sure there are other solutions not mentioned here that would benefit our readers.

Please Note: In the following text the words "sound" and "noise" are interchangeable.

Basic Soundproofing: (Noise 101)

1.    Sound (noise), as you all know, is energy (the movement/modulation of air).  If you are able to successfully interrupt the path of the sound, by absorption, reflection or altering the modulation, it is possible to reduce or eliminate the sound received at the recipient's ears.  There are many ways to interrupt sound.  Here are just a few examples:

Passive Absorption: When sound passes through an acoustically absorptive material like fiber insulation or acoustic foam (absorber), the sound waves are forced to change directions many times and travel great distances before the sound passes completely through the absorptive material.  Each time a sound waves change direction, a portion of the energy is absorbed (converted to heat).  When there is a reflective surface behind the absorber, the sound which successfully passes through the absorber will be reflected back and through the absorber once again (effectively doubling the absorption).  Absorbers work best when there is some sort of a reflective surface.  All absorbers react differently as they are moved away from the reflective surface.  There is a significant benefit to having an air gap behind the absorber at the mid and low frequencies.  Acoustics manufacturers design and tune their products to take advantage of this reflective surface and air gap. (More on this subject later.)

Barriers:   A noise barrier can be constructed from almost any non porous material.  Since sound is energy, an effective barrier must have enough mass (weight and density) and a low resonant frequency to stop (or reflect) this energy.  As sound pressure levels increase so does the sound power (energy). Many of you have purchased multi channel high power amplifiers to produce realistic (live) music reproduction.  These high sound power levels will excite any surface they encounter causing the surface to resonate (vibrate) at complementary frequencies (that's why your walls shake folks).  Low frequency sound contains more energy, because you are modulating a large volume of air to produce the long frequency waves associated with bass and sub bass frequencies.  These low frequency sounds easily excite most common building materials like wood and 1/2" thick plasterboard.  For a barrier to perform properly, it must have enough weight (mass) and a low resonant frequency to prevent the incident sound waves from exciting the surface.  An excellent barrier is lead sheet, it is a dense yet limp material with a very low resonant frequency meaning it is not easily excited. Since dense limp materials like lead and loaded vinyl composites are expensive and not well suited for actually constructing walls, they are generally used as a composite in acoustical curtains or septum's inside studio walls and industrial barriers to increase the sound transmission coefficient.  An effective barrier must have sufficient density, weight and a low resonant frequency to stop noise.  (More on this subject later.) Quality barriers usually incorporate some form of absorption both inside and outside, since a non absorptive barrier will only reflect incident sound.  Barriers such as walls and ceilings are best constructed with a little knowledge of basic acoustical design and that's what we'll try to give you here.

Active Noise Cancellation:   Since we have no field experience with active noise cancellation technology, we will only present a little information about this form of noise reduction.  In a nutshell, when two sound waves arrive together 180°out of phase, noise cancellation takes place.  If you would like to see how this works, wire up one of your stereo speakers out of phase (reverse the + and - wires), face your two speakers towards each other at a distance of about 3 feet.  Switch your amplifier to "Mono" (mono works better than stereo) and put on a music selection.   Slowly decrease the distance between the speakers and listen to the results.   Don't forget to re-wire your out of phase speaker correctly after the demo, since out of phase information not only reduces the sound levels it also destroys the stereo imaging.  There are companies marketing sophisticated active electronic noise cancellation products, many of which are targeted toward industrial and commercial uses.  A good example of noise cancellation for audiophiles are the noise cancellation headphones which are presently on the market.  Although we have not experienced music on a set of these headphones, we have heard from people who gave them good reviews.  We know of no working applications involving active noise cancellation in the home.  There are many sites to be found on the Internet where Active Noise Cancellation is discussed in great detail.

Passive Resonators:   Resonators (Helmholtz type) take advantage of passive noise cancellation.   Simply stated a Helmholtz resonator is another form of passive absorber comprised of a series of tuned cavities which are sized for a specific frequency or range of frequencies.  The cavities serve to cancel (by phase reversal) any incident sound waves which enter.  Many successful resonator designs also incorporate some form of absorption like fibrous insulation or acoustical foam.  Designing and building effective resonators requires a working knowledge of acoustics and acoustical mathematics and is best left to acoustical engineers.  Many products like tuned traps have some form of an internal resonator incorporated into the design.

Sound Control in the Home:

For those of you who want to soundproof one or more rooms in your home, here's some suggestions that will get you started:

1.    Most commercial noise control products are expensive, although they are very effective when used properly.  We recommend homeowners first consider using commercially available building products which will produce similar results at a greatly reduced cost.

2.    Since we already discussed barrier basics above.  Here's a way to increase the sound transmission loss through existing walls and ceilings. (We'll discuss new wall construction later.)  Most homes in the USA are built with lumber and plasterboard (gypsum drywall).  Interior walls are usually 2 x 4 wood stud construction with one layer of 1/2 inch drywall applied to each side of the studs with no insulation between the studs.  This construction is adequate for speech privacy and is widely accepted as the de-facto building standard for single family homes.  Once you go beyond speech privacy this construction is inadequate.

2.a.    Drywall is an inexpensive, dense material well suited for use as a noise barrier.  When used and applied properly you can build high STC walls at minimal cost.  With existing walls and ceilings, you can beef up the construction by adding additional layers of 5/8" thick drywall to both sides of walls and additional layer(s) to the ceiling.  This will greatly improve the STC (sound transmission coefficient).  One additional layer works for most applications, but some home theater rooms and home recording studio's may require more layers.  To increase the efficiency of the added layer(s) of drywall, resilient furring strips should be used to de-couple the new layer(s) from the existing layer.   This partially isolates the new layer(s) from the structure minimizing the amount of noise which will travel through the structure to the other side of the wall.  If it is possible to blow-in insulation, do so before adding additional layers of drywall.   Blown-in insulation will help dampen vibrations and absorb some of the sound which enters the wall cavity.  Although the insulation is not absolutely necessary, it is highly recommended.  Be sure to completely cover the existing walls and tape all the joints (even between layers).  In most cases, you may skip the outside walls if you are not concerned about disturbing your neighbor(s).

2.b.    You will most likely have a problem with the existing door(s) to the room.  Most if not all residential doors are hollow core construction (two layers of 1/4" veneer plywood with a honeycomb core).  These doors are almost transparent to sound since they are rigid and have no weight or mass.  Replace the existing door and frame with a good quality 1-3/4" thick solid core commercial door.  You will have to special order the frame or install jamb extensions, since a standard 4-1/2" frame will not fit properly with the additional layers of drywall.  We also recommend you seriously consider using good quality weather-stripping around the door to seal in the sound.   Rubber seals work best and they are almost air tight.  A door bottom seal is also recommended, install a sweeper type or an automatic drop down seal.  A complete set of quality seals will cost around $125.00 depending on the source.  There are manufacturers like "National Guard Products" who sell a variety of acoustical door seals, they cost a little more and they work better.

3.    Once you have the walls, ceiling and door(s) beefed up you could add some absorption and possibly diffusion into the room.  In addition to the benefit of reducing room reverberation times, the perceived sound quality of your system components will be greatly improved.  There is a balance between too little and too much absorption for any size room.  Too little absorption or the wrong type of absorption may not noticeably improve the room acoustics.   Too much absorption can make the room dead and you will loose the live sound.  With the correct selection and positioning of absorbers and diffusers it is possible to minimize or eliminate standing waves, harmonic distortion, phase shifting, bass buildup and other noise phenomenon common to rooms with hard reflective surfaces.

New Sound Wall Construction:

Sound walls are easily constructed from common building materials provided you adhere to the recommendations and instructions below.

An effective noise barrier (wall) starts with two (2) parallel rows of wood or metal stud framing. The studs should be installed on 16" or 24" centers and the studs of each parallel row must be staggered so that they cannot be in contact with any studs in the other row.  You should have two (2) separate walls that are not attached to each other anywhere if possible.  Install insulation between the studs and attach one, two or three layers of 5/8" thick drywall to both sides of the wall.  You may use 1/2" thick drywall, but a minimum of two (2) layers should be applied to each side of the wall.   Stagger the layers of drywall so that no two seams occur over each other on the same stud.  Caulk or tape the joints of the first layer(s) before applying a second or third layer.  Caulk any gaps that exist at the floor or ceiling lines.  A good sound wall must be airtight.  Any electrical boxes (outlets) installed in the wall should be staggered so that there are no two outlets back to back on the wall.   Some variations of this design are as follows:

a.    Wood Construction:  Build the framing with 2 x 6 top and bottom plates and 2 x 4 studs.  Attach (nail or screw) the first row of studs flush with one edge of the 2 x 6 plates and attach the second row flush with the other edge of the plates.  If the studs are on 16" centers you would have 8" between studs and if the studs are placed on 24" centers you will have 12" between studs.

b.    Wood Construction (alternate):  Build the wall from 2 x 4 lumber, cut a minimum 1/8" wide slot (1/4" recommended) completely through the middle of each stud leaving about 4 to 6 inches uncut at each end before nailing to the top and bottom plates.   This will give you two separate 1-11/16" studs attached to each other at both ends.  This method is not recommended, but if you are on a budget it saves on materials.  Be careful not to nail or screw through one side into the other when attaching the drywall, thereby joining the two sides together at the fastener.

c.    Metal Stud Construction:  Build the framing with 6" metal floor and ceiling (top) track and attach (screw) a row of 3-5/8" metal studs to one side of the 6" track and attach the second row to the other side of the track.  If the studs are on 16" centers you would have 8" between studs and if the studs are placed on 24" centers you will have 12" between studs.

d.    Metal Stud Construction:  You can also build the framing with 3-5/8" metal floor and ceiling (top) track and attach (screw) a row of 2-1/2" metal studs to one side of the 3-5/8" track and attach the second row to the other side of the track.  If the studs are on 16" centers you would have 8" between studs and if the studs are placed on 24" centers you will have 12" between studs.

Things to avoid when constructing or modifying walls and ceilings:

1.    Styrofoam and other forms of Rigid Foams & Insulation "are not", we repeat "are not" interchangeable with fiberglass or mineral fiber bats when constructing sound walls.  Rigid foam, although an excellent thermal insulator, is a poor choice for insulation in a wall designed to stop noise.  Styrofoam being rigid and lightweight is an excellent conductor of noise (maybe one of the best conductors of noise you can buy).  Rigid foam type products will actually degrade the noise reducing performance of a wall.  You must avoid using these products in sound walls.

2.    Acoustical Ceiling Tiles, their name seems to indicate they are acoustical when in fact they are poor acoustical products when used incorrectly.  For example:  Many commercial offices are constructed with metal stud and gypsum drywall partitions which go up to and end at the bottom of the ceiling grid.  Two layers of drywall on 3-5/8" stud has a Sound Transmission Coefficient (STC) of around 38.  Most ceiling tiles have an STC much less than 38 because they are made from a dense, lightweight, fiberous material and are generally not thicker than 5/8" of an inch.  These tiles are designed to absorb a portion of the room noise and to stop a portion of the noise from traveling through the tile.  They were never designed to replace a drywall ceiling, wall or partition.  If you have an acoustical ceiling as the only barrier between your conference room or office and the adjoining room or office, you will have a noise problem.   Demising walls (constructed from top of floor to bottom of floor above) are always the best choice when noise is a concern.  To increase the performance of a suspended ceiling, we suggest the addition of a layer of drywall cut to the ceiling tile sizes.   The drywall can be laid on top of the ceiling tiles in the grid to stop noise.   You must check the grid suspension system design to insure that it will hold the added weight of drywall.  Inspect existing grids thoroughly before making any modifications.  Many older grids use thin hanger wires, have insufficient anchor points, etc..  All design and construction deficiencies should be corrected.

More to follow in our next update.

Happy Building!

Please stay tuned.  This page and links will be updated frequently.

"Always Under Construction"