Improving the Sound of Your Room with Acoustic Treatment
By Team HC |
Improving the Sound of Your Room with Acoustic Treatment
Great gear is only part of what you need for great sound!
by Terry Hearn
In recent years, the rise of the home studio has democratized the process of creating music through technology. While this offers powerful tools to many people who would otherwise not have access to them, it does not change the fundamentals of a successful studio session. Even when high-quality equipment is readily available, its effect and impact can be severely limited by the environment in which it is used.
Without acoustic treatment sound will echo off walls, the floor, and other surfaces, reducing the clarity of what is being created. This is not just the case for recording studios. Auditoriums, lecture halls, and anywhere that clarity of sound is required in order to communicate, also need to consider the effect. With multiple objects causing reflections, the use of acoustic panels can help to reduce ambiance, making it easier for the listener to hear clearly and comprehend.
Depending on the location, it is also important to consider the frequency of the sounds you are working with. For a theatre or lecture hall, the focus will be on bringing clarity to the human voice, where in a recording studio, the aim is to find a balance between high and low frequencies to ensure the sound recorded accurately reflects what was produced.
How do we control sound?
An important distinction to make is the difference between soundproofing an environment and utilizing acoustic treatment. When soundproofing, the objective is to block out sound entirely by installing dense materials, often built into the walls themselves. While this is fine for purpose-built locations, extensive soundproofing is not always practical or affordable when using rooms that weren’t constructed with sound isolation in mind.
By contrast, acoustic treatment is used to absorb and control the sound inside the room. By identifying areas of the room that naturally cause echo or flutter effects, lightweight panels can be strategically placed to reduce unwanted reflections and improve the overall sound quality of the space.
In large rooms such as churches and halls, it’s common to hear an echo as you walk. This is because the sound waves created by your footsteps are bouncing around the walls and ceiling and being reflected back to you by the room surfaces. In this environment, acoustic treatment using foam, fiberglass or mineral wool panels can help to dampen the echo.
Acoustic foam: the technical elements
Usually made from polyurethane, specialized open-cell acoustic foam is ideal for creating the kind of panels mentioned above, as it uses air resistance and friction to help dissipate unwanted sound waves into heat and control reverberation. The foam is often cut into pyramids or wedge surface patterns to further enhance the results.
Reverberation time (RT60) is measured by the amount of time it takes for a sound to drop in level by 60 decibels. The ideal RT60 for a medium sized live performance venue is between 1.5 and 2.5 seconds. However, recording studios often require a shorter reverberation time than theaters, and just half a second of reverberation time is closer to the ideal for mixing and control rooms.
Other acoustic treatment types, and placement
As different rooms will have so many variables, it can be challenging to determine how much acoustic foam is required and where it needs to be placed to achieve the optimum results. Typically, a recording studio would require a minimum of 20% coverage, but this should always be adjusted to suit the room. The Sabine formula, a calculation developed by the founder of the field of architectural acoustics, Wallace C. Sabine, is a good starting point for making this judgment.
While acoustic foam and other absorptive materials are generally an accessible and affordable option, there are other ways to continue improving the acoustics of a room.
Though acoustic panels are effective for midrange and high frequencies, a good studio should not stop there. Some of the worst problems can come from low-frequency sounds, especially in smaller spaces. For this reason, bass traps are essential and should be placed in the corners of the studio space.
Bass traps come in two types, porous absorbers, and resonant absorbers. A studio could choose to use either, or a combination, to fine-tune their sound. Porous absorbers can be made from acoustic foam, fiberglass, or mineral wool. These materials usually tackle acoustic problems like room modes, standing waves, flutter echo, and speaker boundary interference response-related issues. This versatility is very useful across a wide frequency spectrum, but unless they are spaced far from the wall or are very thick, porous absorbers will not cope with the lowest frequencies. Due to their affordability and effectiveness, especially in small spaces, porous absorbers are the most popular option for non-professional spaces.
Resonant (or pressure) absorbers, while more expensive, are designed to target specific bass frequencies and work best when positioned against a wall, saving space compared to some porous absorbers that require a gap between themselves and the wall to operate most effectively. There are two common types of resonant absorbers - Helmholtz resonators, which use an air-tight cavity with a tuned port or opening to absorb bass frequencies, and diaphragmatic absorbers, that counteract sound waves with a vibrating panel or membrane.
The final type of acoustic treatment is diffusion. By redirecting the sound in multiple directions instead of allowing it to reflect in one primary direction (like a beam of light does when it hits a mirror), diffuser panels spread the sound around the room and diffuse the hard, directional reflections that can make mixing especially challenging. Diffuser panels often look like they are covered in wooden strips or boxes. While these panels are very useful, they can be expensive and are best used in mixing rooms.
Ideal for buildings with high ceilings, ceiling clouds are a form of lightweight acoustic absorption or diffuser panels suspended horizontally from the ceiling. A famous example is the ‘Mushrooms’ at the Royal Albert Hall. 135 fiberglass mushrooms were installed in the 1960s, but this was reduced to 85 following advanced testing in 2001. This adjustment moved panels to the center of the ceiling and directly above the stage to improve the immediacy of performances.
With so much variety it could be daunting for a beginner to try to select the proper acoustical treatment options for their rooms without consulting an expert, but controlling the sound with acoustic treatment is essential at every stage to give you the best possible environment for capturing your recordings, and for optimizing the sound of a live performance venue. - HC-
Written with technical assistance from Technical Foam Services
From an early age, Terry has been passionate about two things, writing, and music, and has tried to combine both ever since. Having played in bands for two decades, his current focus is improving as a songwriter. He has written about music for a number of publications including What Culture and The Metropolist.