Home Cinema Anatomy: Soundproofing
What is Soundproofing?
Soundproofing is the process of reducing or eliminating the transmission of sound between spaces. Sound is transmitted through the air, and through solid materials by way of vibrations. Soundproofing involves using various materials and techniques to create a barrier that prevents sound from escaping or entering adjacent spaces. The key areas we focus on during construction are:
Wall, ceiling, floor, and door(s) construction.
HVAC systems and their pathways.
Small flanking pathways such as conduits and penetrations for electrical and low voltage cabling.
Soundproofing, also known as 'Acoustic Isolation', is often confused with 'Acoustic Treatment'. Some examples of acoustic treatment are acoustic foam, acoustic panels, and even soft furnishings such as rugs. These internal acoustic treatments help to improve the quality of the sound inside the room, but do not soundproof or isolate the room in a noticeable way.
Why is Soundproofing Important in a Home Cinema?
1. Immersion: A home cinema is a place where you can escape reality and immerse yourself in a different world. To fully enjoy this experience, it is crucial to have a space that is free from external noise distractions. Soundproofing ensures that you can focus entirely on the audio and visual aspects of your entertainment without any unnecessary distractions. Some passages in movies are also mastered at levels lower than average household sounds, so in order to experience the soundscape exactly how the director and sound engineers intended, it is crucial to reduce as much background noise as possible.
2. Dynamics: Lowering the background noise (noise floor) in your home cinema allows for a more appropriate range between quiet and loud sounds (dynamic range). An example of poor dynamic range due to a high noise floor is experienced frequently when watching TV. It's not uncommon to struggle to hear dialogue when watching TV; but when the action starts it is too loud and the small TV speakers struggle to produce good quality sound. This is caused by too much background noise, combined with speakers that can't reach the required performance level to compensate. High performance speaker systems can meet the performance requirements to overcome background noise; however, listening to any system with unnecessary background noise is like running a race with a backpack on, you're going to need to work harder than you otherwise should. Put simply, you won't be maximising the capability of your home cinema system's dynamic range without appropriate soundproofing.
3. Privacy: Home cinemas often have powerful speaker systems, with an ever growing number of surround sound channels to facilitate new and improved object based surround sound formats. These systems can produce extremely high volume levels. Without proper soundproofing, the noise from your home cinema can easily disrupt adjacent areas of your home or disturb your neighbours. Soundproofing helps to contain the sound within the designated space, allowing you to enjoy your movies or music without disturbing others. Appropriate sound isolation should allow use of the space any time of the day or night.
How Do We Measure Noise Reduction?
The most common method is Sound Transmission Class (STC) ratings. STC provides a noise reduction measurement in decibels (dB) and is centred around 500Hz, which the human ear is quite sensitive to. Generally speaking, the higher the STC rating, the better the material is at reducing sound.
Another measurement is Impact Insulation Class (IIC), which measures a material's ability to reduce impact noise, such as footsteps or bass energy from subwoofers vibrating through a surface.
The final, and one of the most relevant, is Sound Reduction Index (SRI). SRI is a global standard and typically provides more useable acoustic data across the measurement range than STC, but unfortunately is not currently used as often by product manufacturers.
It is important to note that any rating system providing a single number for noise reduction does so for the purposes of simplicity. Sound absorption fluctuates across the frequency range depending on the products used and their application, the numbers provided are just an average. The frequencies generated inside a home cinema room are also inconsistent, with bass frequencies, which present some of the greatest challenges, typically being produced at peaks 10dB higher than that of other sounds. As such it is critical to have a professional review the acoustic isolation design for your home cinema in order to achieve the desired results both in and outside of your room.