Above is a ceiling to wall assembly illustrating how a ceiling and the wall drywall layers should intersect to provide a good seal. Note that we want solid drywall to drywall contact. Don’t try and leave a gap. The illustration shows a gap that is 1/32 of an inch. Most drywall installers do not hang drywall to this tolerance, but the point is you are not trying to leave a gap on purpose. After drywall is hung, seal the seam tight with Acoustical Sealant.

Summary:

Applying Acoustical Sealant reduces the risk of seal failure as the gap is small and easy to maintain over time. We are also maintaining mass in the gap area but sealing it tight like a fish tank. Nice and tight, be have now removed the possibility of a sound leak.

Wall Assembly: Addition of Sound Isolation Clips and Drywall Furring Channels

Funny Name, Serious Noise Barrier

When Recording’s editor asked me about the new substance called Green Glue, and asked if I could share real life stories of jobs involving sound control, I ran down a list in my mind, from clients with loudly snoring family members to a studio with a neighbor’s barking dogs (a job where I did a spectral analysis and devised a system of construction materials that kept the bark’s frequency range outside … ).

The problem area

Shaggy dog stories aside: In general, the most difficult and costly frequencies to address have always been those in the area of 125 Hz and below, which coincidentally happens to be, in our musical world, the power behind most of our music and special effects. Cut off everything below 125 Hz in your mix and see what you have left.

Unfortunately, 125 Hz is where the all-powerful, yet imperfect and archaic STC (sound transmission class) rating stops. How convenient for the manufacturers! Don’t get me started on this subject. See www.stcratings.com and for more on STC Information read www.greengluecompany.com

Realistic expectations

When clients call and mention “soundproofing” I quickly suggest we’d better talk in terms of sound control, noise control, or noise abatement-all valid terms that don’t come with the baggage of unrealistic expectations that “soundproofing” carries with it. Sure, that word is being used by makers and sellers of many such products, but don’t you feel better knowing that we are discussing a goal that is achievable?

Materials old and new

The best ally the studio builder has had for low frequencies of 250 Hz and below, short of inner-wall and massive thick space-consuming construction, has been 5/8″ layers of drywall in conjunction with layers of loaded vinyl or lead sheeting products. Loaded vinyl and lead sheeting products are very expensive for the project studio builder on a budget.

Now there is help and hope in the form of a product called Green Glue. Yes, it really is called Green Glue. It comes in caulking tubes for a gun, and in bulk, in 5-gallon buckets if you are a contractor doing some volume work. This viscoelastic material (meaning it doesn’t harden or dry out) has some amazing low frequency damping properties, as well as being able to affect the rest of the frequency range. When applied correctly, and let me say that again, correctly, between layers of drywall, it can give you a huge reduction in low frequency transmission. And if you have the budget and can also throw in a layer of loaded vinyl, you are really getting considerable reduction without building three foot thick walls that would reduce the size of most project studios by twenty percent!

Less pricey, better in some ways

By the time you factor in labor and materials, a wall which consists of two layers of 5/8″ drywall with Green Glue in between is no more than half the price of a loaded vinyl wall of the same composition, and better in some parts of the frequency spectrum. It is also much faster, cheaper and easier to install if you are trying to do the work yourself. Green Glue at roughly $15.00/tube, with 2 tubes per 4 x 8 sheet of drywall, works out to be about $0.94/square foot. Loaded vinyl can be $3.00/square foot.

I was introduced to Green Glue by my Drywall Contractor and friend Robert Ishida whose company specializes in sound-reduction product installation in Los Angeles. I always involve Robert in all my studio construction situations where this kind of knowledge and craftsmanship is needed. When I asked Robert to contribute information regarding how Green Glue helped in his field of expertise, this is how he responded.

The main result we get from using Green Glue is the effective damping of low-frequency sounds through the dispersal within mass barriers (i.e., double layers of 5/8 drywall” or 5/8″ drywall + Mass Loaded Vinyl). On its own, Green Glue provides a 10 STC lower than double drywall by itself. Mass Loaded Vinyl with Green Glue gives us 26 lower STC. When taking into consideration the cost of Mass Loaded Vinyl or #2 lead sheeting you get a lot of bang for your buck by using Green Glue (maybe I should say “you get a lot LESS bang for your buck”).

The cool thing about using the product has been to show the clients its effect as we are installing it. For example, we had a commercial studio in which we were providing sound control to two mixing rooms. I decided to show the effects of Green Glue to our client by using Green Glue in between layers on one wall, and just double layer on another wall. With someone talking on one side of the treated wall a person directly on the other side of the wall had trouble making out the words at about 4′ from the wall. The non-treated wall allowed the person to hear up to 11′ away. It was a simple test, but needless to say, the client was convinced, making my job a lot smoother and more profitable.

It has become very beneficial to me to buy the 5-gallon buckets of Green Glue and using the custom applicators to save a lot of time, about 40%, and money. The guns are durable and clean-up is easy.

Ultimately the best endorsement I give is that since we started using Green Glue in various applications we have not had to field any complaints or return to studios needing upgrades or modifications. We are achieving the desired result on the first try!

On doing it right–the first time

I can’t stress enough the importance of proper procedure when installing any kind of sound reduction system or product. Overlooking one detail can negate everything you are trying to accomplish. So in closing, if you are trying to do this for yourself: Read the darn directions, for once, and use Green Glue! ~

About Brian Gadson:

Brian Gadson (gadson@recordingmag .com) is a studio designer and studio owner, recording musician, engineer, and producer, with a general contractor background, available for consultation on studio design and sound issues. Find out more at his company website at www.earsneyes.com.
Brian would like to thank Robert Ishida of Ishida Drywall Corporation for his contribution to this article.

About Robert E. Ishida; C.O.O Ishida Drywall Corp:

Since Ishida Drywall Corp. was founded in 1989 in Los Angeles Ca., soundproofing and acoustical treatments have been a large and exciting focus of our company, from no-expenses spared recording studios for the biggest companies in various industries to residential garage improvements for the aspiring musician.  Ishida Drywall has had the privilege of working with numerous and varied people who have allowed us to establish our name as a leader in acoustical treatment applications in Southern California.

As the research and technology in this industry evolves, it is imperative that we, as a company, keep pace with advancements being made weekly.  Since we were introduced to the Soundproofing Company over 3 years ago, our ability to keep up with technology and the new methods of efficiency has been made as easy as picking up the phone or sending an email, one example being our incorporation of the use of Green Glue to our treatments and getting the necessary results for our very specific clientele.  Soundproofing Company has not only provided us with Green Glue itself, but the instructions and diagrams as well as the technical consulting necessary when we encounter sound isolation issues we haven’t seen before.  All we do is send pictures from the jobsite and they design a solution.

Although it can be daunting and expensive when dealing with sound isolation, we try to keep it simple and effective.  Since there are many different ways to go about sound isolation issues, including very exotic and very expensive systems, SPC has shown us that these are not the only ways to go.  The relationship with SPC has given Ishida Drywall Corp. an important tool in our ability to expand our business and ultimately provide satisfaction to our clients.

• Sound is a wave, a longitudinal wave
• Sound needs a medium to travel
• Waves have amplitude (volume) frequency (pitch), wavelength (speed), etc.

In air 331 meter per second (mps) creates something of a “chain reaction,” If you watch this closely, you’ll notice that the wave forms because an individual air molecule gets a push, which causes it to push on the air molecule right next to it. As each air molecule recovers from its push, the wave passes.

It turns out that air is able to support not just one wave, but many different waves simultaneously. This means various pure tones can be mixed, and sent through the air at the same time. This is where music, speech, and other “noise” come from.

When we draw a sound wave, the wave peaks and valleys are close together or far apart. Sound waves vibrate at different rates or “frequencies” as they move through the air. Frequency is measured in cycles per second, or Hertz, after the German physicist who experimented with sound in the 19th century. The faster an object vibrates, i.e. the higher the frequency, then the higher the pitch of the sound. For example, a tuning fork for A above middle C will vibrate 440 times per second and has a frequency of 440 Hertz.

When a wave is created, the distance between one compression and the next compression is called the wavelength. The faster the sound waves pass a given point, the shorter the wavelength and the higher the frequency. Sounds of all frequencies travel at the same rate in the same medium. (Sound in dry air at 0 C travels at the rate of 1200 kilometres per hour, or 331.6 mps; in a solid medium the sound waves travel faster.)

The vibrations can also “squeeze” the air molecules together very hard or very gently. This squeezing is called “amplitude” and is represented on the top half of the diagram below. The bottom half of the diagram is a representation of the pressure of the air during a sound wave. The horizontal line represents normal air pressure.

The more we push an object to make it vibrate, the larger the vibrations and the louder the sound, or the greater the amplitude. Sound waves with the same frequency can have different amplitudes.

The amplitude is half the height of the sound wave

Since sound is a form of energy, it can be changed from one form to another. Other forms of energy can be transformed into sound. Sound energy can be changed into electrical energy. Sound waves that are changed into electricity can be seen on an oscilloscope.

Sound travels quickly in air at nearly 340 meters per second but can travel through steel at about 5,200 meters per second. 770 MPH, is the speed of sound, or Mach 1.

When you go to a rock concert, you may have to cover your ears because the sound is so loud. This loudness is called intensity. Intensity is measured in units called decibels or dB. The threshold of sound is 0dB. A rock concert has an intensity of 120 decibels. Sounds of 120 decibels or greater can cause people pain and ear damage.

Sound travels as sound waves. The bigger the vibration, the greater the amplitude of the waves and the louder the sound.

Pitch

A sound can range from a high to a low pitch. The pitch of a sound depends upon the frequency of the vibrations that cause it. The frequency of a sound is the number of complete waves or vibrations that go past a particular place each second.

• If there are lots of vibrations per second, the frequency is high and the sound has a high pitch.
• If there are few vibrations per second, the frequency is low and the sound has a low pitch.

Frequency is measured in hertz (pronounced “hurts”), with the symbol Hz. For example, a sound with a frequency of 880 Hz is an octave higher than one with a frequency of 440 Hz.

For humans, hearing is limited to frequencies between about 20 Hz and 20000 Hz, with the upper limit generally decreasing with age.

In short, STC gives you a rough idea how much sound a wall, for example, might stop. STC, Sound Transmission Class, is the most common sound reduction measurement in use. As common as this measurement is, it is quite limited and should not be totally relied upon for real world soundproofing expectations.

Lets first cover a few concepts.

Decibels: Written as dB in literature, dB is simply a measurement of how loud a noise is. 50dB is quiet, while 140 dB is so loud that is can immediately injure your ears. Think of dB as the volume knob on your receiver.

Transmission Loss is a measurement of the dB (volume) difference on either side of a wall. Let’s say we have a 100dB tone on one side of a wall. Pretty loud. We measure this same tone on the other side of the wall and find we have 75 dB. So we would say that at this tone or pitch, we have 25 dB Transmission Loss. 25 dB less sound energy made it through the wall to the other side.

Interestingly, a test tone with a different pitch sent through that same wall might only see a 4 dB Transmission loss. The performance of a wall will vary a great deal depending on the tone (frequency) of the sound.

Frequency: Written as Hertz or Hz., this is the measurement of the tone or musical note of the sound. Is it a really high pitch like a Flute might make (2000 Hz) or a low pitch from a Tuba (as low as 29 Hz)? Most humans are born with the ability to hear frequencies from about 20 Hz (low) up to 20,000 Hz (high) but that range shrinks as we get older.

What is STC?

Now that we have an understanding of a few basic terms we can describe what STC is. Way back in 1961, STC was introduced as the method for comparing various wall, ceiling, floor, door, and window assemblies. STC is calculated by taking the Transmission Loss (TL) values tested at 16 standard frequencies over the range of 125 Hz to 4000 Hz and plotted on a graph. Your curve (what you actually measured) is compared to standard STC reference curves (see appendix). If your wall graph is closest to a standard STC 35 curve, your wall is said to have an STC of 35.

The MAGENTA line in that graph is the standard reference STC contour. The BLUE line is the performance of the wall. To calculate TL and STC, the performance data should be obtained from a certified laboratory.

Higher STC is generally better, though not always, as we will see below.

Caution: The largest problem with relying on an STC number alone is that STC only considers frequencies down to 125 Hz. This can be very misleading due to the fact that most sound isolation complaints are from noise sources that are below 125 Hz.

Here are a few examples of noise sources that are below 125 Hz

• Most of the sound energy generated by the average home theater
• Traffic noise from airplanes, trucks and heavy equipment operation
• Guitar, bass, drums
• Industrial Equipment, especially pump systems.

The example above demonstrates the problem with not considering data below 125 Hz. Frankly, neither of these walls stop much sound. Both are mediocre, with a low frequency problem near 125 Hz. However one wall is STC 32, the other is STC 42!

This is because with the blue wall, the big problem occurs at 125 Hz, and is therefore measured by STC. The black wall has essentially the same problem; however it occurs just below 125 Hz, and is therefore not calculated.

Here’s another example of how relying on STC alone is a bad idea when low frequency noise sources are present.

We see two walls, one has a STC 47, the other a STC 48. Note that in the low frequency range – important for music, theaters, traffic, aircraft, and most other real-world noise sources – the lower STC wall is literally 30 decibels better, yet lower STC

The actual 1961 standard which explains how to calculate STC (ASTM E413) describes the limitations of its use: “These single-number (STC) ratings correlate in a general way with subjective impressions of sound transmission for speech, radio, television, and similar sources of noise in offices and buildings. This classification method is not appropriate for sound sources with spectra significantly different from those sources listed above. Such sources include machinery, industrial processes, bowling allies, power transformers, musical instruments, many music systems and transportation noises such as motor vehicles, aircraft and trains. For these sources, accurate assessment of sound transmission requires a detailed analysis in frequency bands.”

Caution: STC is not a measure of how many decibels of sound a wall can stop. If you have an STC 45 wall, this does not mean the wall stops 45 dB of sound.

Caution: You cannot add STC ratings. They are logarithmic values and cannot simply be added. If you have an STC 33 wall and decide to add another sheet of drywall with an STC of 20 you do not get a finished wall with an STC of 53. You might get something around STC 35.

STC Examples

STC Examples

STC ratings courtesy of the NRC and Green Glue Company, reprinted with permission.

Changes in STC/Changes in Apparent Loudness

Appendix – calculating STC.

Noise is generated in one room and the sound pressure levels in decibels (dB) are measured in both rooms at 16 distinct frequencies between 125 Hz and 4,000 Hz. The difference in levels is corrected to account for the acoustical properties of the receiving room.

We are looking for the Transmission Loss at these 16 frequencies (see table below). This is ASTM E90 Standard Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions. The Sound Transmission Class (STC) is determined in accordance with ASTM E413, Classification for Rating Sound Insulation.

An excellent description for the STC calculation process is provided by Brian Ravnaas at Green Glue Company.

Calculating STC involves adding something called “deficiencies” and utilizing the STC contour In the table you supply the Transmission Loss data. Then you add the STC contour adjustment to attain the adjusted transmission loss. Then you basically play with numbers in the “STC you wish to test column” until one of the 2 limiting conditions listed below are met. The highest number that satisfies both of those conditions is the STC.

The two STC Conditions:

1. No single frequency band may have more than 8 deficiencies
2. The total deficiencies may not exceed 32

In the case above, the highest # of deficiencies in any frequency band is 4, and the total deficiencies are 21. So both condition 1 and condition 2 are passed. The appropriate thing to do in this situation would then be to raise the STC you are testing to 56. In this case, the wall would pass again at 56, as shown in this table here:

Now the total deficiencies are 30, and it is clear that if we raised the number we wish to test to 57 that the number of deficiencies would exceed 32, and thus the wall could not pass at 57.

Therefore, the STC of this wall is 56.

Lastly, it is important to note that to accommodate the fact that the human hearing system is more sensitive to some frequencies than others, an equal-loudness contour is applied to the frequencies tested. This accommodation is known as A-weighting. In general, low frequency and high frequency sounds appear to be less loud than mid-frequency sounds, and the effect is more pronounced at low levels, with a flattening of response at high levels. A-weighted frequencies are measured in units called phons.

MASS-AIR-MASS-SYSTEM:

Solid mass is not effective, practical or economical. So what can we do? We can increase our sound isolation if we introduce an air cavity and another leaf. The resulting Mass-Air-Mass system is common and well known.

When we design a sound isolation system, we generally incorporate a large air cavity.

GO BIG OR GO HOME:

Not all air cavities are created equal. This is one case where size matters. A large air cavity can be a great isolator, especially in decoupled systems. A small air cavity, on the other hand, can make things a lot worse.

Larger air cavities perform better. Compare the performance of these two glass panels when we increase the air cavity.

We see that one large air cavity a real benefit for soundproofing.
Interestingly, if we add a second air cavity that is small, our performance plummets.

Sound Isolation Performance: Each system has approximately the same mass:

When we introduce a small air cavity, things improve, but not nearly as well as if we had a single larger cavity. We’ve doubled the drywall, added a resilient channel, added insulation however this small cavity example does not add much, especially considering the time and expense to install it.

However let’s compare if we were to install the same materials using the proper methodology and avoid the triple leaf altogether:

Here you can again see that the introduction of a larger air cavity next to the first improves things, however performance would be significantly better if we unified those two air cavities while decoupling the ceiling drywall.

It’s very clear that the small air cavity was very counterproductive.
Why does the size of the air cavity matter? The answer is resonance.

THE RESONATING AIR CAVITY:

We’ve all blown across the top of a soda pop bottle and listened to a seashell up to our ear. These are two examples of resonating air cavities. Resonance can really make things loud.

Resonance is a frequency-dependant phenomenon. The soda pop bottle will always have the same frequency or musical “note,” no matter how hard you blow. Want to change the frequency? Add some water. The now smaller air cavity will have a higher resonance frequency and therefore “play” a higher note. The size of the air cavity therefore has a corresponding resonance frequency.

How does resonance affect the soundproofing ability of a wall or ceiling? Let’s say we have a single air cavity. Let’s also say because of its size, the air cavity also has a natural resonance of 300 Hz.

An imaginary wall with a natural 300Hz resonance point

Notice that performance drops when the 300Hz wall gets hit with close to a 300Hz sound wave. At resonance the air cavity amplifies that frequency and helps pass it through the wall or ceiling. So things are bad when we have resonance.

WHAT CAN WE DO WITH THIS RESONANCE INFORMATION?

We know that an any cavity will resonate at some frequency, and poor sound isolation results. We can’t prevent resonance, but maybe we can MOVE the resonance point. Move it to a frequency that we don’t encounter very often. Such a frequency would be low, since low frequencies are less frequently encountered.

IS THE DEPTH OF THE AIR CAVITY THE
ONLY FACTOR THAT DEFINES THE RESONANCE POINT?

No. If we assume the walls are decoupled, then absorption and mass will also affect the frequency. Adding absorption (insulation) will lower that resonance point.

What are the other advantages of having a low frequency wall?

A wall that has a lower resonance point will stop low frequencies better.

WHAT IS THE TRIPLE LEAF EFFECT?

If you research soundproofing topics online, you’re bound to come across the Triple Leaf Effect. So what the heck is it? A “leaf” is a layer of mass. Like a layer of drywall on a framed wall. A typical wall has one air cavity and two “leaves” of drywall.

A triple leaf simply has three leaves, and therefore two air cavities. You may hear that a triple leaf is to be avoided at all costs. This is partly true. The real problem is that a triple leaf often has a small air cavity. A triple leaf wall that has two giant air cavities is not such a bad thing, but as we saw earlier in this article, a small air cavity can make things much worse. It is much better in most instances to remove the leaf in the middle to join the two smaller air cavities into one large one.

You can see that no matter how you slice it, it’s always better to have one bigger air cavity.

CONCRETE + DRYWALL FURRING CHANNELS

Single concrete structures present an interesting acoustical phenomenon. It is a very common practice to want to drywall a concrete wall or ceiling to increase the sound isolation or aesthetics. Such a practice will introduce a small air cavity on one or both sides of the concrete. What happens when we introduce this air cavity?

Here we see a concrete wall assembly and the corresponding STC Transmission Loss graph. The higher the line, the greater the sound isolation.

Now let’s attach a sheet of drywall directly to the block wall. Note that there is an unavoidable tiny air cavity between the drywall and the block. We can see that the performance is very slightly increased from 400 to 2500Hz, but performance is slightly reduced below 400Hz.

Next, we’ll attach wood furring strip to the block, and then add the drywall on one side. The air cavity is larger now and we see improvement across a broader frequency range, now from 180Hz to 2500Hz. Also we note that the curve is higher now, representing more sound being blocked at those frequencies. However, we also see a reduced performance below 180Hz. Worse performance than the smaller air cavity we just looked at.

Next, we’ll attach wood furring strip and drywall to both sides. This will give us the largest air cavity yet. We see the same improvement range of 180Hz to 2500Hz, but the curve is much higher, so higher frequencies are better isolated. However, our low frequency performance is also the worst of all walls looked at so far.

Lastly, let’s add insulation to the furring channel and drywall on one side. For thermodynamic reasons, insulation essentially mimics a somewhat larger air cavity. When we compare the test data, as anticipated we see the performance fall somewhere between the small air cavity and large air cavity tests (walls III and IV).

Bottom Line: For single concrete walls and ceilings, bigger air cavities are better at higher frequencies, but much worse at lower frequencies. This is because the system is coupled. All rigidly connected.

The system will only significantly improve by decoupling a new stud wall from the block wall and then adding drywall and insulation. As long as the system is coupled, performance will be seriously compromised in the low frequencies.

A typical room will need a 6″ supply and comparable return. These ducts are a large cross section for sound to freely escape, regardless of the direction of airflow.

Tying in the room to the main HVAC system, whether in a home or commercial building, introduces the opportunity to pour noise directly into the ductwork. A flanking nightmare. Consider building a Dead Vent to muffle the sound as it exits with the air. Ideally you would have one Dead Vent for each supply, and one for each air return. You can use a Dead Vent as a buffer between the sound room and the main HVAC system.

“Subject to local code and HVAC contractor recommendations” Hot air is pulled through soffit to Dead Vent. The biggest issue with super tight rooms is cooling them. If built below grade (basements, lower levels, etc) consider simply exchanging the theater room air with the rest of the lower level. This avoids tying the sound controlled into the main HVAC.

There are some basic fundamental principles at work in the Dead Vent:

First is a containment structure that is massive and damped. The entire vent is encased in double 5/8″ drywall for mass, and Green Glue for damping. This will not only contain sound, but damp it as well.

You can install a flared duct piece here. The significant increase in surface area slows the air speed, but maintains the volume, so less chance for a large grill cover to whistle. The flare can be 16″ wide and 16″ tall.

Second is a great deal of absorption within the containment structure. The structure is filled with fiberglass, mineral wool or a low density fill of cellulose. This insulation will help absorb mid and upper frequency sound.

Third is a large change in cross sectional area and volume. This is a fundamental principle behind a silencer for a gun. The large and dramatic increase in the air volume of the silencer relative to the gun barrel is a large part of the function. The 6″ diameter supply has a cross sectional area of about 28 square inches. Compare that to the internal cross sectional area of the Dead Vent containment structure of 175 square inches (13.5″ x 13.5″). Note that for low frequencies, the flex duct is acoustically transparent, so the entire volume inside the Vent is used for absorption.

Fourth is forced interaction of the airborne sound with the absorptive material. A very straight duct run doesn’t promote much interaction of sound waves and absorptive material. Having the duct make a few curves or bends forces the sound wave to bump up against absorptive material as the sound wave and air travel through the vent.

A few comments

• For many rooms including basement home theaters and recording studios, you may only need to consider cooling the air in the room by exchanging this air with the remainder of the basement air. Basements are obviously naturally cool all the time.
• Consider installing a variable speed control. Speed controllers for ceiling fans generally work, but check the spec first. Keeping the fan(s) on a low setting all the time will keep the air in the room from becoming musty and stale.
• Consider a dehumidifier outside the dedicated room if you are simply exchanging the air with the balance of the basement air.
• Follow local building codes for construction and ventilation.

1. Removed the first layer of drywall from the wall to expose the stud framing. Setup a table saw to rip the 2×4 stud material down.

2. The red boards are 2×1 furring strips we cut down to run around the perimeter of the wall.

3. Cut 2×4 into 2×1 furring strips.

4. Apply Acoustical Sealant to the 2×1 furring strips. You want to make a good seal between the original wall and the newly added 2×1.

5. Position the furring strip into place.

6. Firmly press the furring strip against the bottom plate.You will continue these steps around the perimeter of the wall.

7. Closeup of the the newly added 2×1 furring strip.

8. Secure the furring strip with nails every 8-16 inches. Always follow local building codes.

9. Remove the existing wall insulation. If you are lucky you can keep this and reinstall it after the new set of studs are installed.

10. Install the new wall studs 16″ o.c. The new studs will fall in between the current wall studs (so the completed assembly will be 8″ o.c.).

11. Continue installing studs. Since this is a rebuild we are toe-nailing them in place. A nailing gun is always helpful if you have one available.

12. Cut insulation down to fit in between the studs. You want to make sure it fits into place. In this case I cut the insulation into 6.5″ strips.

13. Gently place insulation into the wall cavity. You may wish to use paper faced insulation so you can staple into place.

14. Continue installing the insulation.

15. Top view of the wall framing. The top plate has been removed to show the staggered studs.

16. Diagram illustrates the staggered stud effect.

This construction is seen most commonly when there is a great deal of noise to be contained within the room, or contained outside the room.

Common Room Examples:

• Heavy Industrial Equipment Isolation
• Commercial or Residential Home Theaters
• Recording Studios
• Rooms of solitude where you won’t be bothered by any outside noise.

For this high level of isolation you will want a room within a room. All 4 Elements of Soundproofing should be deployed.

This is a basic description of the room construction. Links are provided throughout if you want greater detail and understanding.

Framing

Let’s start with the wall framing. We would prefer to have a double wall system for maximum isolation. Other options would be a staggered stud wall, or a single stud wall equipped with resilient clips and channel. All three of these walls are decoupled.

Keep in mind that if the room is in a basement, the foundation counts as one of the two walls needed for a double wall. Simply build a standard (wood or steel) 2×4 stud wall a few inches away from the foundation.

How deep a wall do you want? The deeper the better. Deeper walls have a greater air volume and will isolate low frequencies better. If you plan to have several subwoofers, you should try and have the deepest walls possible. This does not mean build with 2×6 or 2×8 wall studs. Rather, space the two 2×4 walls as far apart as you can.

How about that ceiling framing? This is the tough spot in most residential applications. It is the largest single surface, and it is generally in direct contact with living space above. While we can easily construct double walls, double ceilings are more difficult to accommodate. We would like to have some element of decoupling if possible however. Our last choice would be to install drywall directly to the ceiling joists. So what are our options?

1. You can install a floating ceiling. This is the best and most complete level of decoupling. Essentially you weave new ceiling joists in between the original joists.

The biggest limitation of this system is that it doesn’t fit if you have a great deal of mechanicals like ductwork and plumbing up in those cavities.

2. Use resilient clips and hat channel. This system is easy to install on any joist system, and generally you can count on losing only 1 3/8″ of ceiling height, not counting the drywall.

Insulating

Insulation on its own provides minimal sound attenuation. In conjunction with other techniques however, insulation becomes a great asset. Don’t worry about filling the cavity completely. Don’t over compress, and don’t bother with more than a total of 6″ of material (typically two layers of R13). Standard fiberglass batts are as good as it gets.

Drywall

Mass is one of the big contributors to sound isolation. Drywall is a great source for mass (darned heavy). In a decoupled system, mass is particularly effective. Really, no wall or ceiling should have less than two sheets of drywall. You would prefer to use 5/8″ drywall since it’s heavier (more mass). For the ceiling, consider the use of three sheets of drywall. Sounds odd, but ceilings are problematic and you want to throw everything you have at it.

You can consider using a base layer of plywood or OSB, then adding a layer of drywall to finish. Many people like the ability to insert a screw anywhere in the wall, and a plywood layer accommodates this.

Different thicknesses of drywall are often recommended. Read this next section that describes damping, but if you do not damp the drywall, then consider mixing 1/2″ and 5/8″ drywall. Each will resonate at a different point. If you are planning to damp the drywall, then forget mixing the thicknesses. Just go with the thickest and heaviest drywall you can deal with.

Damping

This is the last component of room construction. A damped drywall layer will remove a great deal of the sound vibration before it enters the wall or ceiling framing. This makes it highly recommended. There are commercially available “soundproof drywall” panels, but if you compare, you will find that while many (not all) of them work well, they are rather expensive and don’t perform well in the problematic low frequencies. Better and less expensive results are found by using standard drywall and damping compounds such as Green Glue. Green Glue Testing

That’s really about it. Rooms like this will contain a great deal of sound. The only issue that will compromise such a room construction is sound “flanking.” This is a large enough issue that we have dedicated an article to discussing flanking, and what you can do. Understanding Flanking