Acoustic Insulation

From traffic sounds and neighborhood clamor to excess internal echos in crowded rooms, unwanted noise acts as a major annoyance in almost any setting. To combat noise and increase the serenity of your space, consider adding acoustic insulation to walls and ceilings in your home. Different types of acoustic insulation are designed to deflect, absorb and dissipate noise to keep sound levels at a more manageable level.

Mid-floor / ceiling

On average, noise coming through a mid-floor is the worst soundproofing problem you’re likely to encounter. The reason is two-fold. First, the hard flooring choices of today don’t help the noise control problem at all. Carpet and underlay is used to reduce a lot of the noise. However, Hardwood, linoleum and tile are not the friends of the neighbor below. Second, a footfall (direct impact) introduces a great deal of energy into a very small cross section of floor. This can overwhelm many common soundproofing efforts. Here’s what you’re up against.

Imagine your neighbor walking on the floor above. These footprints create large amounts of vibration which travel through the flooring into the framing and then out the plaster board. The framing is very conductive, so vibration passes through easily. Your ceiling plaster board is solidly fixed to this framing, so the sound travels straight through. Another problem with vibration entering the ceiling framing is that your walls downstairs are holding up the mid-floor framing. So the sound is also entering your room through your walls. This is known as flanking noise. Not as much sound will come through the walls, perhaps 5% to 25% of the noise. Other areas where sound can travel between the floor are through holes in your ceiling for lights, ventilation, fans and pipes. These are also possible flanking paths that need to be dealt with.

Do I treat the noise from above or below the mid-floor?

When designing any soundproofing solution, you should always treat the noise at its source. This allows us to control and reduce the (sound) vibration before it enters the building’s framing. If we can treat the floor above to immediately destroy the vibration before it gets into your ceiling framing, things would be a lot easier. With a hard finished floor above, however, this is generally not possible, very costly and your neighbor who doesn’t have the problem is unlikely to want to spend money to help. So really all you can do is treat the ceiling on your side.
So you have decided to reduce the noise in your mid-floor.

The cheapest and easiest option is to have insultech insulation blow a dry mineral wool product into the cavity, by doing this the vibrations in the floor framing will be partly reduced and by filling the cavity between the floors the insulation absorbs a large part of the indirect or airborne noise from reverberating within the cavity.

Suspended ceiling. This is costly (approx. three times as much as just insulating the cavity) but will give you the best results. Because this requires a full renovation to the floor /ceiling space, you should look at getting other work done at the same time. The basic suspended acoustic ceiling / floor is done by removing the linings on the underside of the floor and putting up a Rondo ceiling system with acoustic mounts, acoustic insulation and two layers of acoustic plasterboard with Green Glue between them.

Rondo

Acoustic walls

Acoustic walls are almost the same as a mid-floor or ceiling only turned sideways. There is one major difference here though and that is flanking noise (see below) .
Flanking noise is where the sound instead of traveling through the wall now goes over or around the wall. To fix this problem it is sometimes required to acoustically insulate the floor below and the ceiling above from the wall. Most people find the wall alone makes enough difference for them but it is worth considering if you want the job done right.

How is sound transferred

Sound is transmitted through most walls and floors by setting the structure into vibration. This vibration generates new sound waves of reduced intensity on the other side. The passage of sound into one room of a building from a source located in another room or outside the building is termed ”sound transmission”.

Transmission loss or Sound Transmission Class (STC), is a measure of the effectiveness of a wall, floor, door or other barrier in restricting the passage of sound. The transmission loss varies with frequency and the loss is usually greater at higher frequencies. The unit of measure of sound transmission loss is the decibel (dB). The higher the transmission loss of a wall, the better it functions as a barrier to the passage of unwanted noise.

There are two types of sound in buildings: airborne (Indirect) and impact (Direct).
– Indirect or airborne sound is created by TVs, people talking, cars driving by, basically anything that makes a noise without directly touching the surface of an object.
– Direct or impact sound is created by people walking on the floor above or tapping on a wall or table. Ie anything that is touched directly to produce a sound. This type of sound is a lot harder to reduce.

Sound Isolation Techniques

Typical interior walls in homes are made of (1 sheet of 10 mm) plaster wallboard (drywall) on either side of a 90 mm wood frame. When asked to rate their acoustical performance, people often describe these walls as “paper thin,” as they offer little in the way of privacy.

Standard wall

Sound Absorption
Adding absorptive materials to the interior surfaces of rooms (e.g. fabric-faced fiberglass panels, thick curtains) will result in a decrease of airborne sound energy within the room. However, absorptive interior surface treatments do not significantly improve the sound isolation from one room to another through partitions over the typical frequency range measured. Installing absorptive insulation (e.g., fiberglass batts, blown-in mineral wool ie CosyWall) into the wall or ceiling cavities effects the sound isolation of the partition to varying degrees, depending on the framing configuration and joist or stud depth. For example, the presence of fibreglass or mineral wool insulation in single standard 90mm wood stud framing can reduce the transmitted airborne noise dramatically through the wall.

WoodWall

Mass
This one is pretty straightforward. More density = more sound absorption. However it needs to be REALLY dense to make a big difference ie concrete, so simply adding a layer of drywall to an existing wall will only give you a slight decrease in sound transmission.

Doubling the mass of a partition does not double the STC, as the STC is calculated from a non-linear decibel sound transmission loss measurement. So, whereas installing an additional layer of plaster wallboard to a light-gauge (25-ga. or lighter) steel stud partition will result in about a 5 STC-point increase, doing the same on wood stud will result in only 2 to 3 additional STC points. Adding a second additional layer (to the already 3-layer system) does not result in as drastic an STC change as the first additional layer.

Decoupling
Structurally decoupling the plaster wallboard panels from the partition framing can result in a large increase in sound isolation when installed correctly. Examples of structural decoupling in building construction include resilient channels, sound isolation clips and hat channels, ie Rondo, and staggered or double-stud framing. The STC results of decoupling in wall and ceiling assemblies varies significantly depending on the framing type, air cavity volume, and decoupling material type. Great care must be taken in each type of decoupled partition construction, as any fastener that becomes mechanically (rigidly) coupled to the framing can short-circuit the decoupling and result in drastically lower sound isolation results.

Double Stud with batts

Sound Flanking
Sound isolation metrics, such as the STC, are measured in specially-isolated and designed laboratory test chambers. It is important to note that there are nearly infinite field conditions that will affect sound isolation in situ when designing or remodeling building partitions and enclosures. Partitions that are inadequately or inappropriately sealed—that contain back-to-back electrical boxes, untreated recessed lighting, and unsealed pipes to name just a few—provide flanking paths for sound. Sound flanking paths include any sound transmission path other than the wall or ceiling partition itself

soung-flanking