Amelior Insulation

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Acoustic Sound Insulation

A woman sits on her couch and hold her ears. She needs to get acoustic insulation installed in her walls.

Acoustic insulation (also known as sound insulation or soundproofing insulation) is a material or a combination of materials designed to reduce the transmission of sound between spaces or to absorb sound within a space. Soundproofing insulation is typically dense and thick, and is most commonly installed in walls.

Difference Between Thermal and Acoustic Insulation

Thermal insulation helps control indoor temperatures and save energy, while acoustic insulation reduces noise for more peace and privacy. The main difference is that acoustic insulation has a higher density, making it much more effective at absorbing sound.

Most batt insulation, like glasswool, will do both jobs well. For example, if you get a standard R2.5 thermal glasswool batt, the thickness of it will help to dampen some sound, even though it’s not an acoustic batt. Similarly, an acoustic insulation batt will offer great thermal insulation properties, giving you the best of both worlds.

How Sound Transmission Works

Sound transmission occurs when sound waves (created by vibrations) travel through a medium such as air, water or solids and reach a receiver.

These vibrations travel outward in all directions, and when these waves reach the receiver (e.g. the ear or a microphone), they cause it to vibrate, which is then converted into electrical signals for interpretation by the brain or electronic device.

Here’s a more detailed explanation:

1. Source of sound

First, there needs to be a sound. This could be anything that creates vibrations, such as a person speaking, a musical instrument playing or a car horn honking

2. Vibrations

The source emits vibrations, which are rapid back-and-forth movements of molecules in the air (or other medium) around it. These vibrations create compressions and rarefactions in the air molecules, essentially forming sound waves.

3. Propagation

The sound waves travel outward in all directions from the source. This propagation occurs through the transfer of energy from one molecule to the next in the medium (air, water or solid).

4. Medium

The medium through which sound travels plays a significant role in its transmission. Sound travels faster in denser mediums because molecules are closer together, allowing for quicker transfer of energy. For example, sound travels faster in water than in air, and even faster in solids like metal.

5. Reception

When the sound waves reach the ear or a listening device, they cause the eardrum (or microphone diaphragm) to vibrate at the same frequency as the sound waves. These vibrations are then converted into electrical signals by the ear (or microphone) and transmitted to the brain (or electronic device) for interpretation.

6. Interpretation

Finally, the brain processes these electrical signals and interprets them as sound, allowing us to perceive and understand the original source of the sound.

Soundwaves entering a human ear.
Sound transmission occurs when sound waves travel through a medium such as air, water or solids and reach a receiver.

How Did People Acoustically Insulate Their Homes in the Past?

When modern-day insulation didn’t exist or wasn’t legally required, people acoustically insulated their homes in various ways. They often relied on natural materials and/or strategic home design to minimise sound transmission. Some common techniques included:

  • Thick walls. Buildings with thick walls made from materials like stone, brick or adobe naturally provided some level of sound insulation due to the mass of the material absorbing sound vibrations.
  • Heavy curtains and drapes. Thick curtains and drapes were hung over windows and doorways to absorb sound waves and reduce their transmission into or out of a room.
  • Soft furnishings. Carpets, rugs, tapestries and upholstered furniture were used extensively to dampen sound reflections within rooms and reduce overall noise levels.
  • Strategic placement of rooms. Architects and builders often designed homes with considerations for sound transmission in mind, placing noisy rooms such as kitchens away from bedrooms and living spaces to minimise disruption.

All of the above methods of soundproofing still work, however proper insulation is the most simple and effective, and lasts longer than e.g. curtains.

How is Acoustic Insulation Density Expressed?

When we discuss density of an acoustic insulation product, we use kg/m³. The higher the number, the denser the product. A denser insulation material is better at absorbing sound.

Where Should I Install Acoustic Insulation in My Home?

When installing acoustic insulation in a new home, you can pick exactly where you want to put it. The main rooms homeowners choose to install acoustic insulation are:

  • Bedrooms. Installing acoustic insulation in bedroom walls can help reduce noise from neighbouring rooms or outside traffic.
  • Home office. If you work from home or have a designated office space, soundproofing the walls can minimise distractions from household activities or external noises, allowing you to focus better on your work.
  • Home theatre or entertainment room. To create a high-quality audio experience without disturbing other household members or neighbours, adding acoustic insulation to the walls of your entertainment room can help contain sound within the space.
  • Music room or studio. If you play musical instruments or enjoy recording music at home, soundproofing the walls of your music room can prevent sound leakage and improve the overall acoustics of the space.
  • Bathrooms. While bathrooms typically don’t require as much acoustic insulation as other rooms, adding some insulation to the walls can improve privacy and reduce echoing.
  • Laundry. Installing acoustic insulation in the walls of the laundry room can help minimise the noise generated by washing machines and dryers.
  • Playroom. If you have a designated play area for your children, soundproofing the walls allows kids to have fun without disturbing other household members, especially during early morning hours.

Internal vs. External Walls

Internal walls are those on the inside of the house, while external walls are those that are on the outside

The primary purpose of internal walls is to divide the building into smaller spaces/rooms. The external walls are typically made of brick, concrete or timber and are thicker and stronger than internal walls, which are usually made from plasterboard.

Generally, you’ll want a high R-value, thermal insulation in your external walls, and a mix of thermal insulation and dense sound insulation in your internal walls. The sound insulation can go wherever privacy is needed most. However, if you live on a busy or loud street, installing some acoustic insulation in your external walls will create a noticeably quieter home.

A woman sits comfortably in her quiet, acoustically insulated living room, holding a cup of tea.
Installing acoustic insulation around your house will create a more peaceful home environment.

Types of Acoustic Insulation

Acoustic insulation is necessary to control sound transmission in many environments, from residential homes to industrial spaces. There are many materials you can use to soundproof your walls, but the most popular is glasswool/fibreglass insulation:

Fibreglass insulation

Fibreglass is one of the most common materials used for acoustic insulation. It’s made from fine glass fibres and is available in batts, rolls or loose-fill forms. Fiberglass insulation effectively absorbs sound waves and reduces noise transmission.

Mineral wool insulation

Mineral wool, also known as rock wool or stone wool, is made from natural minerals like basalt or diabase. It is similar to fibreglass insulation but has denser fibres, providing excellent sound absorption and thermal insulation properties.

Cellulose insulation

Cellulose insulation is made from recycled paper fibres treated with fire retardants. It is eco-friendly and offers good sound absorption capabilities. Cellulose insulation can be blown or sprayed into wall cavities, attics or floors.

Mass-loaded vinyl (MLV)

Mass-loaded vinyl is a dense, flexible material containing barium salts and plasticisers. It is highly effective at blocking sound transmission due to its mass and flexibility. MLV is often used as a barrier in walls, floors and ceilings to reduce noise from adjacent rooms or the outdoors.

Spray foam insulation

Spray foam insulation expands upon application, filling gaps and cracks to create an airtight seal. Open-cell spray foam provides good sound insulation and is commonly used in walls, ceilings and floors for both thermal and acoustic purposes.

Soundproofing membranes

Soundproofing membranes are thin materials installed under flooring or within walls to reduce impact noise, such as footsteps or vibrations. These membranes often consist of rubber or cork and help isolate sound transmission between floors or rooms.

Each type of acoustic insulation has advantages and disadvantages. Remember that all bulk insulation (such as Bradford Gold and Knauf Earthwool) have some acoustic properties, even if they’re not labelled ‘acoustic’ or ‘soundproofing’. If it is thick, it can dampen some sound.

Reach out to an insulation specialist if you need advice or assistance.

In Which Parts of the Building Can Acoustic Insulation Be Installed?

The most common place for acoustic insulation to be installed is inside the walls of a building. This is because walls are the primary pathway for sound transmission between rooms and between the interior and exterior of a building. With insulation installed in the walls, external sounds, such as lawnmowers, loud neighbours and busy traffic, will be dampened significantly. The sound of children yelling in the playroom, a movie playing in the lounge room or the vacuum being used around the house will also be quieter with acoustic wall insulation installed.

Acoustic wall insulation is installed when the house is being built or when the house is being renovated. Selecting the right material and insulation R-value before installation is vital. Replacing or topping the wall insulation up in the future will require tearing open the plaster, which is expensive and troublesome. It’s best to get it right the first time.

Soundproofing insulation can also be installed in the:

  • underfloor
  • midfloor
  • ceiling
  • roof.

It’s quite uncommon that acoustic insulation is installed under floors. There’s not much noise that needs to be dampened from that direction, so regular, thermal insulation will suffice. If a building has several stories, it’s very valuable having midfloor insulation installed between the floors for privacy and general noise reduction.

If rain falls very loudly onto your roof or you live near an airport or airfield, acoustic roof insulation is highly recommended. However, if you already have acoustic insulation installed in the ceiling, you generally won’t need it installed in the roof, unless you live in an extremely noisy area, want your home to be as soundproof as possible and have the budget for it. 

Soundproofing a ceiling is very popular in cafes, auditoriums and other locations where excessive echo can be an issue.

A male insulation installer installs acoustic insulation in a roof.
Installing acoustic insulation in both the ceiling and roof is generally not necessary.

Important Considerations When Installing Acoustic Insulation

There are three main points to be aware of when getting acoustic insulation installed:

  1. Do not compress the insulation. Whether you’re installing yourself or hiring acoustic insulation installers, it’s important that the insulation isn’t squashed into the cavity. It’s better to leave an air gap between the insulation and the boards than compress it.

  2. Doubling the thickness of insulation won’t double the soundproofing effectiveness. Although thickness can help reduce sound transfer, density will have the biggest impact.

  3. There should be no gaps in coverage. Having gaps in your insulation allows air and sound to leak through, diminishing its effectiveness.

If you are looking for acoustic insulation installers in Sydney or Canberra, feel free to contact Amelior Insulation. We specialise in ceilings and underfloors and will install your acoustic insulation professionally to ensure optimal soundproofing.

Is Acoustic Insulation Worth It?

Whether acoustic insulation is worth it really depends on your specific needs. If you’re bothered by noise and value privacy and comfort, it’s likely a good investment. However, if noise isn’t a concern for you, then it may not be necessary and thermal insulation should do.

Best Acoustic Insulation in Australia

Insulation batts and boards/panels are generally going to be your best bet when soundproofing a house. The higher density of these products make them excellent at quietening sound. There are a couple of products that are favoured among homeowners and acoustic insulation installers. These are:

  • Knauf Earthwool Sound Shield
  • Bradford SoundScreen
  • Bradford Polymax Acousitc Insulation
  • Pink Soundbreak
  • Polyester acoustic batts

To select the right acoustic batts for your project:

  1. Check the batts size requirements by measuring the cavity depth and stud width. The cavities are the individual, rectangle slots you are going to be insulating. In a wall, the stud width is generally 450mm or 600mm and depth is around 90mm.
  2. Choose an insulation material (e.g. glasswool).
  3. Opt for the highest density batt that fits your cavity and budget. Consider densities like 14kg/m3, 25kg/m3, 35kg/m3 and 45kg/m3. Remember – higher density means better soundproofing.