WallDamp and Soundproofing

Basic Soundproofing

Sound spends most of it's time "flying" through the air but sound in a room keeps on running into the surfaces of the room. Each time sound impacts a wall, floor or ceiling of a room most of the energy reflects off the wall. But all of it doesn't reflect, some of the energy is transmitted directly into the wallboard. The wallboard is teeming with sound which can easily be heard by using a mechanic's stethoscope. Part of this sound, trapped in the wallboard leaks out of the wallboard and excites the air inside the wall cavity. Another part of the sound is conducted into the wood stud to which the wallboard is nailed or screwed. In either case, the wallboard on the far side of the wall becomes energized and fills with sound as well. This excited wallboard then stimulates the air near the wall on the other side of the wall. Sound "leaks" through the wall two ways, by air borne conduction and by structure borne conduction.

Most builders know to add fiberglass insulation between the studs, in the wall cavity in order to add soundproofing to a standard interior wall. The insulation reduces the build up of sound within the air cavity of the walls. The less noise there is in the air cavity, the less noise is transmitted through the wall into the next room. Adding fiberglass to the wall cavity is usually done during construction. Batt insulation, R-11 is 3 1/2" thick and costs about $0.25/sq ft. Blown insulation is a good way to retrofit a wall with insulation and this costs about $1.00/sq ft.

Once the air cavity inside the wall is quieted down, adding more insulation does not help make things more quiet. This is because the sound you now hear is being conducted mainly from the wallboard of one room through the stud and into the wallboard of the next room. Adding WallDamp to the face of the framing, between the wallboard and the framing creates a sound attenuating gap in the sound conducting path. What fiberglass does for the air in the wall cavity, WallDamp does for the wood or metal in wall framing.

Not So Basic Soundproofing

When WallDamp is placed between the stud face and the wallboard, the sound conducting path between the two sides of the wall is disconnected, interrupted by a thin layer of sound deadening material. Like adding fiberglass to the wall cavity, adding WallDamp to the framing faces improves soundproofing a wall in the higher frequency ranges of sound, the treble range. But there is more to the conveying of sound through a wall than the air and structure borne sound paths. Walls vibrate. Whenever a wall vibrates as a whole or in parts, sound energy rides the vibration right through the wall. WallDamp also controls the free vibration of the wall and puts a damper on sounds free ride through the vibrating wall.

A wall is basically a sheet of thin wallboard tacked to studs. The studs are typically 16" apart. If the wallboard is tapped with the finger or rapped with the knuckle somewhere between the studs, it twangs. The free vibration of that one section transfers across the stud to the next section and soon it is vibrating. Then the next section of wall between the studs picks up the motion and soon, the entire wall is quivering with the vibration. And the vibration is conducted through the stud and the air cavity to the wallboard on the other side which also vibrates freely at this same frequency. One good rap and the entire wall becomes engulfed in a twanging condition. Certain tones are easily conducted from one side of the wall to the other side by this mechanism. Adding WallDamp to the wallboard facing sides of the framing members calms down the wall twang, the plate vibration effect and improves the soundproof quality of the wall.

The wall as a whole is attached to the upper and lower plates which are rigidly affixed to the other and more heavy framing members. The mid section of the assembled wall however is free to vibrate out and in. A solid thump with the tight heel of the fist will send most any wall into it's fundamental structural mode of vibration. The entire wall shudders and the sound of the shudder is as loud in one room as the other. Adding WallDamp to the wallboard facing sides of the framing members causes damping of this major mode wall vibration and improves it's soundproof quality.

Although it may be interesting that the soundproof quality of a wall, it's resistance to being knocked on or thumped is improved with the addition of WallDamp, such is not the usual reason for adding WallDamp. It isn't someone's hand that is usually exciting the wall into a vibration, it is sound itself that does it. Sound generated by the powerful loudspeakers found in today's home theater, media and audio rooms. The subwoofer provides ample thumping energy and the 5 regular speakers setup right next to the walls in today's home theater systems provide plenty of knuckle tapping energy.

WallDamp is Broadband Soundproofing

The addition of fiberglass to the wall cavity is only improves it's soundproofing performance in the upper frequency range (tweeter range). Fiberglass has no effect on midrange or low frequency soundproofing. Despite it's reputation in the construction trades for soundproofing, fiberglass in the wall cavity provides but a fraction of the improvement available from WallDamp. However, fiberglass in the wall cavity with WallDamp on the framing faces is one-two combination punch that is almost too simple to do, almost too easy to work with and so very hard to beat.

WallDamp blocks the high frequency sound that is conducted through the wallboard and framing. WallDamp calms down the midrange plate vibrations of the wallboard twanging between the studs. And WallDamp controls the large displacement structural vibration of the mid section of the entire wall, the low frequency wall shudder. WallDamp is a broadband soundproofing construction material.

How do we hear or notice sound proofing improvements made to a wall? One way is to just listen to conversations or a radio playing in the adjoining room. With speech there are three basic frequency ranges. The bass sound is the drone tone of the voice. The middle range adds coloration to the drone tone to make different sounds as in the vowels, a e i o u. Then there is the tsss type sounds, and they are in the high frequency range. The sound that comes through a regular frame and gypboard wall will be muffled in all three frequency ranges of speech.

When fiberglass is added to soundproof a wall, what does it sound like? Fiberglass improves the soundproof quality of a wall in the high frequency range. This means that the hiss type sounds we make will seem more muted but the vowels and the bass range drone tone of our voice will remain just as loud through the wall.

But what is the difference between a wall that has been treated with fiberglass insulation for soundproofing and a wall that has both fiberglass and WallDamp as treatment? The WallDamp improves the soundproof quality of the wall in all frequency ranges. Not only will the hiss sounds we make when speaking will seem quieter but also vowels and the bass drone tones we make will be more quiet and muffled. WallDamp greatly improves the full bandwidth soundproof quality of any wall, ceiling or floor.