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Chapter V: The IsoDamp System™ Wall System - The construction of our listening room provided me with amazing learning opportunities. During the process I needed to overcome past misconceptions. One of my largest mistaken beliefs involved the nature of wall construction. Being unconcerned with soundproofing, I'd thought that rigid construction would be better. We all know that loose flabby things vibrate so conversely, my thought was to simply stiffen up the walls with 2 x 6 and double sheet rock. Presto, problem solved. Not. This would do little more than tighten the skin on a drum. It’s still going to vibrate. Since a vibrating wall in effect becomes a poor speaker, we have to solve the problem at the source. We have to deal with the energy of the sound wave when it hits the wall.

Fortunately, ASC has a solution. The first step in the complete ASC treatment plan is the IsoDamp System™, an integrated wall damping system that stops the transmission of noise, limits  sympathetic wall vibrations and controls low-end bass resonances.  To understand the IsoDamp™  effect, we have to first look at the three possibilities when sound strikes a surface such as a wall. 
  • The wall can absorb the energy.
  • It can pass or transmit the energy through the wall (to the outside or an adjacent room or closet).
  • It can reflect the energy (sound) back into the room. 
Unless your walls are made from solid granite or a totally absorbent material such as fiberglass, the real-world result is actually a combination of all three possibilities. Their interaction becomes rather more complex due to the nature of how a typical wall stores and reflects the sound energy back into the room. As you will see, the characteristics of the sound that hit the wall are not the same as that of the sound reflected back into the room.

The ASC IsoDamp System™ uses multiple techniques including a viscoelastic dampening material (WallDamp™) which reduces vibration amplitude at resonant frequencies. The WallDamp™ material converts the energy of the vibrating surface into heat, thus damping the energy of the resonance. 

The room with the IsoDamp™ construction:
In my room, four of the six walls are bounded by concrete or wood over concrete. All walls are 2" x 6" construction twelve inches on center. Clearly, the room was solidly built. But as I already stated, rigidity is not the solution. Also, modern drywall very effectively reflects the sound back into the room. ASC describes the problem: "The wood stud acts like a spring and the sheet rock acts like a weight connected to the spring. The result is a wall/stud resonance, a sympathetic resonance of the walls at about 70Hz."

It gets worse. The energy stored in the walls releases relatively slowly. When a magnificent 40Hz organ note hits your drywall, that drywall broadcasts a delayed muddy 70Hz sound back into the room, distorting and interfering with the original sound. The original signal is now overlaid and degraded, utterly destroying any semblance of quality sound. Add-on room treatments, even Tube Traps can’t solve structure-borne vibrations. They have to be solved at the source.

The IsoDamp System™ is comprised of several elements. Its inherent design decouples the drywall from the struts and then damps the wall vibration energy by converting it to heat. Modern sheetrock is designed to be inexpensive and quickly installed but it was never designed to maximize the acoustics of high-end sound rooms nor deal with the sonic stresses of a home theater.

"When a subwoofer produces powerful low-frequency acoustic energy, that wave front travels through the room and then collides with the wall and ceiling surfaces. Upon collision, much of that kinetic energy of the wave front is converted into mechanical (vibrational) energy, which sets the thin flexible wall surface into motion. This vibration is easily conducted through solid surfaces it is in contact with, such as the studs, joists and flooring. The vibration travels up and through the framing of the house, vibrating the walls, floors and ceilings as it passes them. What you get is a quaking house full of noise. This is what is known as structure-borne sound transmission. The fact of the matter is, conventional wall and ceiling construction methods easily conduct low-frequency sounds and are poor at blocking them out." The ASC ISO Damp system treats these problems by:
  1. Blocking the sound by increasing the mass (thickness & density) of the walls through a double layer of wallboard, thereby doubling the mass of the wall and minimizing resonant coupling by the use of different density sheetrock.
  2. Minimizing the transmission paths for vibrations and sound to travel through. The walls and ceiling float off the studs.
  3. Damping  the vibrational energy with WallDamp™ material on the hat channel surface and between drywall layers.

One of the keys to the system is the WallDamp™ material but what is this stuff? Well, it’s a proprietary viscoelastic. It looks like a thin sheet of black foam with glue on both sides. It might at first appear to be a rubber-type product but it’s not. WallDamp™ combines two very different types of material. First is a viscous material which deforms as it absorbs energy. When its shape is changed, it maintains that new shape. Flattening a ball of clay requires energy. When done, the clay maintains the flattened shape.

The second ingredient is an elastic product. Deforming an elastic such as a bounce ball also requires work but the ball stores the energy like a spring and returns to its original shape.

The viscoelastic composite material requires energy to deform and return to its original state but since it does not store energy, a viscoelastic ball will not bounce back. It extracts energy from motion and converts it to heat instead of bouncing it back into the room.

According to ASC, WallDamp material is "…made to extract energy from microscopic movements. That's good because very small movements are involved in the making of sound, especially when it comes to surfaces as big as walls, floors and ceilings … WallDamp is relatively hard but that is because the deformation it has to process is measured in thousandths of an inch or less. The hardness corresponds to the force and the deformation involved. WallDamp is made for structural damping."

In his writings, Art Noxon explains its function far better than I could. "When sound or vibration tries to pass through the walls, floor or ceiling of a room, is causes those surfaces and the structure behind each of them to move. When a wall, floor or ceiling vibrates, it changes shape. If WallDamp is located at the joints between each of the parts that make up the wall, floor or ceiling, then any movement at all by the wall, floor or ceiling causes a distortion of the WallDamp. This distortion then absorbs energy and any vibration is quieted right down.

"To improve the ability of WallDamp to extract energy out of the micro movement of a structure, the viscoelastic sheet is coated with a strong adhesive on both sides. This means that even the slightest movement at the joint between members of a structure produces distortion of the WallDamp material. What is fantastic about WallDamp construction is that it not only keeps sound and vibration from passing through the surfaces of the room but that it actually absorbs it. By comparison, a concrete room is well known for keeping sound from getting out but it's bad for the person left in the room, the listener. If sound can't get out of a room it has to stay in the room and reverberate. Carpet, draperies and furnishings may provide some acoustic friction inside the room to attenuate sounds in the treble range but they supply little to no absorption for sounds in the bass range. That is why concrete rooms are very boomy. Only WallDamp provides for both a soundproof and an energy-absorbing wall."

In my IsoDamp room a damped double-layer gypsum board wall "rides on standard resilient channels, flexible metal strips which are attached to the sides of the studs or for the ceiling, to the bottom sides of the joists. The pressure fluctuations from low frequency sound can still move the walls ever so slightly but now when the walls move, they no longer directly push the studs or joists. Since movement of the wall doesn't push the studs, it cannot transfer sonic pressure pulses into the structure of the house … With standard isolation construction methods, once the walls begin shaking under sound, they continue shaking even after the sound stops. This isn't much different than the concrete room except that this time the reverberant vibration is not in the air but in the shuddering walls…"

I’m going into some detail about wall construction because unlike fixed room dimensions, most drywall rooms can be converted to the IsoDamp System™. If you are handy with drywall installation, it could even be a DIY project. Or it could be broken up into two steps. You could install the IsoDamp System™ up to the drywall, then have a professional contractor tape and finish it. So let’s step through the installation of an IsoDamp System™. This is not meant to be a complete guide, just an overview.

• The IsoDamp System™ is applied over bare studs. The studs are measured and marked off according to a planning grid similar to Figure A.
• The stud cavity is filled with insulation.
• The RSIC-1 Sound Isolation Clip is a clip that isolates and decouples. When the clip is attached to a stud, the rubber center maintains the contact with the stud, isolating the clip from it. It breaks the transfer of the both structural and airborne vibrations.

• This clip, in turn, supports the hat or furring channel. The hat channels are cut and mounted on RSIC-1 clips (the channels and clips decouple the mass of the wall from the spring of the studs). The combination of these stops the transfer of sound, whether structural (vibrating studs) or airborne (the drum-like effect of drywall). This part of the system is an industry standard and used for noise reduction between rooms in apartment buildings for example. Just for these elements alone you can end up with a 20-point increase in the SCT rating, which is an industry measuring scale of mid-frequency noise reduction.
• A perimeter gasket is glued around the edges of the wall.
• The 1 ½" x 48" WallDamp strips are applied to the outer face of the hat channel.
• The first layer of drywall is screwed to the hat channel making sure that the screws do not penetrate the studs.
• The WallDamp squares are placed in a pattern 12" on center to cover the first layer of drywall.
• The second layer of drywall is screwed through the first and into the hat channel, again not penetrating the stud.
• The top drywall surface is taped and finished traditionally with joint compound.
• The edges of the walls are caulked with an acoustical sealant.

The entire process is shown in this cutaway picture from ASC. With the room shell finally complete, the next chapter will take a brief look at the installation of the Wilson Alexandrias.
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