Improving the sound quality in a media room, living room, or home recording or music studio has become big business. You can hire a sound specialist or Engineer to tell you what to do and where to place acoustic panels, or you can read this guide! The goal of most acoustic treatments is to reduce reverb, echo, and slap by decreasing soundwave reflection through absorption or diffusion.
Acoustic panels should be centered at the height of the speakers – human or mechanical – and the ear of the listeners. Place the panels on walls where they’ll catch reflections from the speakers. Use a mirror and position panels where the image of the speaker is reflected.
In this guide, we’ll discuss the principles of acoustic room treatment, what an acoustic panel is, and placement guidelines. We’ll also explain how to determine the best placement for your room. Hopefully, our guide will help you place your acoustic panels for optimum sound improvement, and save you money!
Contents (Jump to Topic)
Main Principles of Acoustic Room Treatments
The 5 main principles of soundproofing are increasing mass, decoupling or isolation, absorption, resonance, and conduction. Acoustic treatment in a room needs to address as many of these principles as possible. In most rooms, it is easier to use the first three principles to treat noise problems, which in turn, often help with the last two. Understanding the problem though is the first step to fixing it.
How Does Sound Travel in a Room
Sound travels outward through the air in all directions (360°) from its source. Only some of it travels in a straight line to your ear or microphone. The rest of the sound waves travel onward in all directions until they encounter a surface and either reflect or bounce off in random directions, vibrate through and continue on with less energy, or are absorbed or trapped.
Sound waves that reflect or deflect often do so at random angles depending on the angle of impact. The reflected sound travels on until it strikes another surface and reflects again and again until its energy dissipates. However, some of those reflected sound waves will also travel back to your ears or mic from random directions, but out of sync with those that traveled directly.
The number of times the sound wave changes direction slows it down and often slightly changes the original sound. So, reflected waves picked up by ears and mics sound muddled or dirty. The delayed sound also adds echo, reverberation, or pinging, ringing, or slap noises to what is heard or picked up on a mic.
Why Do Rooms Have Acoustic Issues?
The size and shape of a room, plus the types of reflective surfaces and furnishings affect the movement of sound waves. Our brains use sound waves to tell us where sound is coming from and even what our proximity is to walls and objects. Small rooms and square rooms generate strong standing waves caused by repeated sound wave reflections or bounces. Additionally, small square rooms experience greater bass frequency resonance issues, resulting in more noise problems than rectangular or large rooms. The reverberations not only affect the sound of a room, but also the feel of it.
Boxy rooms, low ceilings, thin walls, vibrating doors and windows, all contribute to a room’s acoustic issues and commonly require more treatment. Small or square rooms often produce a harsh ringing metallic reverberation while larger rectangular rooms with high ceilings generate a more pleasant reverberation. Harsh reverberation requires more absorption to soften and clean up the noise and reduce the standing waves.
The type and amount of furniture, and its placement within a room, also contribute to sound problems. Soft, fluffy furniture absorbs better than wood or metal pieces, which will reflect or deflect sound waves. Furniture for listening placed in relation to sound sources and walls is often restricted in small rooms, which can be an issue in itself too.
Reverberation
Sound energy travels from its source and reflects off the ceiling, floor, doors, walls, windows, furniture, and people. The reflected waves continue to ricocheting back and forth off surfaces until they decay. The combined mix of sound generated is called reverberation and is greater in smaller spaces than larger ones, and almost nonexistent in the outdoors. It is the reverberation that muddies the sounds we hear and makes them difficult to interpret or understand.
Reverberation time is the time it takes for a sound to fade by 60dB once the source stops emitting that sound. However, when listening or recording, sounds are continually being produced which results in a cacophony of sound waves traveling in all directions at once. The length of time for a single wave to decay varies by frequency, room volume, and composition of reflecting surfaces. The longer the reverb time, the more distortion in sound, and thus comprehension of what is heard.
Continually emitted sound waves from fixed sources strike reflected surfaces and ricochet off in repeated patterns. The perfusion of waves often becomes trapped together in one location and forms a standing wave. The energy from some frequencies is canceled out and some transferred or combined with waves having the same frequency and amplitude. The combined waves amplify some sound frequencies and destroy frequency harmony or balance.
Absorption and Diffusion
Reverberations muddy the sound heard or picked up by microphones. Absorption and diffusion are two ways to control sound wave reverberation and clean up the sound in a room. To properly condition the sound in a room, both diffusers and absorbing panels are often used. Absorbers and diffusers are available commercially or as a less expensive DIY project.
Sound absorption panels are made of soft absorbent material that doesn’t reflect the sound waves. The waves enter the material and have to work hard to penetrate through to the reflecting surface behind the panel. The thicker and denser the material, the better.
The sound wave energy changes to heat energy as it vibrates through the material. The energy that does make it through, reflects off the wall and travels back through the absorbent structure, decreasing its energy further, so wave decay is significantly accelerated.
Diffusers use wells and towers, troughs and ridges, or channels to redirect sound waves in different directions than they would if striking a flat reflecting surface. Redirecting the waves in different directions interrupts the wave reflection and reduces or prevents echo. Diffusers help make a small room sound larger and improve the sound quality.
Early Reflections
Direct sound waves travel in a straight line from the source to our ears. Early or first reflections arrive 5 to 100 milliseconds later having reflected once or twice off one or more surfaces. Although our brain uses early reflections to identify our proximity to surfaces and the time delay doesn’t seem enough to be consciously noticeable, it is. Whether off the ceiling, floor, wall, table, or other surfaces, these early reflections can interfere with clarity and comprehension.
Early reflections can also interfere with straight line or direct sound waves. Waves reflecting off side walls, the ceiling, and the floor may cut across direct sound waves between the sound source and the listener or monitor. The reflections can interfere with the direct waves, causing milliseconds of delay, which can distort sound signatures and make them less clear.
Late Reflections
Late reflections are sound waves that take more than two reflections to reach the listener or monitor. They may bounce multiple times from floor to ceiling to floor to wall or other patterns depending on the angle of origin. The smaller the room, the higher the potential for a greater number of reflections in a shorter time period.
The more reflections that accumulate in a room the more persistent some sound signatures become. The noise is often referred to as flutter or echo. The length of time it takes for the echo or sound waves to drop below what is audible is referred to as reverberation or reverb time. Flutter or echo commonly occurs between parallel flat walls or surfaces, and in the upper half of the space above deflective surfaces.
What Is an Acoustic Panel?
Acoustic panels, whether homemade or manufactured, absorb or diffuse sound energy. They are often referred to as sound absorbers, diffusers, traps, and clouds. The name identifies the purpose of the panel and how and where it is commonly used.
Sound absorbing panels can be made from a variety of materials from polyurethane foam, stone wool, fiberglass, cellulose, denim, and even cotton bath toweling. The dense yet soft material absorbs sound energy and converts it to heat, accelerating its decay. They may be fastened to walls and ceiling, freestanding, or even suspended. Wall and ceiling absorbers range from 1” to 4” thick.
Clouds are suspended from the ceiling in strategic locations to absorb waves and are usually12” thick. Traps commonly occupy corners between two walls or walls and ceiling and often are 12” deep at their thickest.
Diffusers frequently have wells and towers or ridges and troughs or channels made of hard material that deflect sound waves in different directions.
They may be made from polyurethane foam, plastic, cork, hardwood, or softwood.
The depth of the well or trough and the length and width within decreasing the sound intensity and redirects and spreads out the sound to produce a fuller sound.
Acoustic Panel Placement Guidelines
No two rooms are exactly alike when it comes to acoustic treatment, nor is the desired outcome necessarily the same either. The guidelines are general and the results depend on the type of treatment, accuracy of placement, and where the sound originates.
Acoustic treatment needs to take into account the type of sound source and its height. Treatment should center at the height of the voice or audio-speaker and where sound will reflect off surfaces. The location of the listener or monitor also needs to be taken into account too.
The three basic guidelines for placing acoustic panels are height, spacing, and symmetry. Consider the volume of the room or space, intended purpose, placement of furniture, location of windows, doors, and HVAC vents, and make your plan. A TV room vs a recording studio has different requirements than an office or living room. Start small and work up until you get the results you want.
Height
The height or level at which the panels are placed depends on room size, the height of the sound source, and the type of sound source. If the sound sources are people talking, the placement of the panels needs to take into consideration the height the voices are being generated at. Sitting heights differ from those when standing.
So, if the majority of the sound is from a sitting position, center the panels 4’ to 5’ above the floor. For standing or those on bar stools, center the treatment between 5’ and 7’.
Audio speakers come in different formats and may be freestanding, shelf, surround, built-in to the device, walls, and ceiling, or a combination of placements. Some audio speakers generate sound in multiple directions simultaneously too. The height, location, and angle of projection of the speakers determine the height and location of the acoustic panels.
A 2’x4’ acoustic panel mounted vertically on an 8’ wall and centered at 4’ or 5’ covers half the wall height. Centering it with the speaker’s reflection increases its effectiveness too.
Spacing
The number of panels you plan to use and what you hope to achieve with them affects the placement. Placing them all in one location won’t have a significant impact unless the sound source is directly across from it, such as a TV. The number and direction of sound sources also need to be considered – surround sound vs the speaker on a TV. A recording studio will require more surface treatment than a TV room, living room, or office too.
Mount panels to cover as much of the wall surface opposite the center of the speaker as the number and size of panels available can cover. The larger the treated surface, the better the results. Placing three 2’x4’ panels tight to form a 6’x 4’ array isn’t as effective as spacing them 6” or more apart on the same wall.
It should be noted that sound travels in multiple directions and reflects off flat walls, so make sure parallel side walls are also treated, or standing waves may be generated. The ceiling is another source of reflection that can be treated with panels or a cloud.
Symmetry
Symmetry and spacing go hand-in-hand. Place panels in symmetrical patterns to balance the reverberation and sound absorption, wall space, and aesthetics. Balancing the space around panels so it is even, and remember, what you do to one parallel side-wall surface should be done to the other. Adjust the pattern if required to accommodate wall and ceiling vents, doors, windows, and other obstructions but try to maintain symmetry.
Where to Place Acoustic Panels for Best Acoustic Treatment?
Most rooms have four walls, a ceiling, and a floor. Sound frequencies of 400 Hz or greater are commonly referred to as directional and tend to bounce or reflect off surfaces and cause noise. The distance surfaces are from the sound sources and the listening or monitoring positions affect the sound quality and speed of reflection. Just hanging acoustic panels helter-skelter won’t solve sound issues and may actually make them worse. You need to first evaluate the room.
1. Evaluate Your Room
The more sound sources in play, the more reflection points or zones there will be. The more you need to minimize and moderate the reflected sound and prevent standing waves, the greater the importance of absorption. Soundwaves travel in straight lines and radiate hemispherically from the sound sources – commonly between 90° and 360°.
The distance the sound has to travel to the listener or monitor affects the sound quality. The straight line from the source to the listener is usually the fastest, however, waves bouncing once or twice off the floor, ceiling, or walls can reach the listening point almost as quickly.
The greater the distance between the source, reflective surface, and the listener the better. Placing acoustic panels where sound will reflect, improves the listening or recording quality.
2. Find the Correct Places for Acoustic Panels
Reflection points or zones are areas where sound first reflects back into a room. Placing acoustic panels where those reflection points occur will significantly address and reduce the reflected noise. Capturing first or primary directional waves before they reflect is one way to reduce reverb and echo.
One of the most effective and easiest ways to locate the reflection points is with a mirror. Although this method is doable by yourself, it is much easier with an assistant.
Side Walls
Sit at the listening or monitoring position, and have your helper move the mirror along the side wall until you can see the sound source. Have them mark the wall where you begin to see the reflected speaker(s) and then where you no longer can. If there is more than one speaker, include them as well.
The area between the start and finish marks is the reflected surface that should be treated. Do both side walls to determine the proper location on each. The whole area doesn’t need to be covered to control the reverb.
Front Wall
Place absorbent panels on the wall behind speakers to remove comb-filtering. If there are speakers behind the listening position, have your assistant move the mirror along the front wall and mark where you see the speaker reflection begin and then end. Absorbers placed between the marks will reduce reverb and clean up the audio.
Rear Wall
Facing the rear wall from the listening or monitoring position, have your helper move the mirror along the wall, marking it where you begin to see the source reflected and where your no longer can. This is the area of rear reflection and where diffusion and absorption panels can be placed.
Place the diffusers in the center with symmetrically placed absorbers around them. If there is more than one sound source, mark the wall for all of the reflections.
Ceiling
Speakers are often either closer to the floor or the ceiling than to the walls, which means the first reflections to reach the listener or monitor bounce off those surfaces. As with the walls, the mirror can be moved along the 8’ or 9’ ceiling between the listener and the source and marks made where the reflection begins and ends. Acoustic panels placed between the marks on the ceiling will delay or diffuse the reflected noise, cleaning up what is heard.
3. Decide on How Many Acoustic Panels Do You Need
Once the reflection zones have been identified, it is easier to determine the surface areas requiring acoustic panels. Measure the distance between the start to finish marks on each surface and multiply by half the surface height or width to get the coverage area.
Use the length and width of the panels selected for acoustic treatment to identify the area one will cover. Divide the area to be treated by the area one panel will cover to identify the number of panels that size required per wall or ceiling.
For example: If the reflected distance on the side wall is 6’ and the wall is 8’ high, the surface area to cover is 6’ x (8’ ÷ 2) = 24ft². If the panels are 2’x4’, or 8 ft², then 24 ft² ÷ 8 ft² = 3 panels. If the panels are 1’x1’, then it will take 24 panels. Spacing the panels out will increase coverage and reduce the number of panels required, but it also affects the efficiency of the layout.
The amount of wall and ceiling surface area covered also determines the surface treatment. Calculate the surface area of the walls and ceiling by multiplying the length by the width or height.
Identify the percentage of area to cover for low (10%), medium (20%), and high (30%+) surface treatment to identify what area the acoustic panels need to cover. Although not effective for placement, this method will assist in determining coverage effectiveness.
General Guidelines for Acoustic Panel Placement
The size, shape, and colors of the panels may help determine the symmetrical pattern for walls and ceilings, however, windows, doors, lights, and vents may alter the placement. Center the panels based on the height of the speaker or sound source and the ear of the listener or monitor. If it isn’t possible to cover all of the direct reflective zones, then space out the acoustic panels for the most effective coverage.
Home Studio
Home recording studios used to record music, podcasts, or audio tracks, don’t welcome reflective noise. Identify the reflective zones around the monitor, mixer, or mic position(s) and cover them fully to ensure recording quality is protected. Alternatively, cover 100% of the surface area if the budget permits.
Home Theater
Identify the reflective point or zone around the listening positions and center acoustic panels at the height of the listener, or about 4’ off the floor. The more surface area treated within the reflective zones, the better the listening experience.
Home Office
Home offices tend to be smaller rooms with one or two listening positions or sound sources. Centering acoustic panels 4’ to 5’ off the floor opposite each listening position and on reflective side wall zones will address echo and reverb.
Large Rooms
Place acoustic panels in a symmetrical pattern so they are centered at the height of the listener and sound source. For sitting positions center at between 4’ and 5’, and for bar stools or standing between 5’ and 7’. It is often necessary to treat walls behind all listening positions and sound sources.
High Ceilings
High flat ceilings allow low volume sound to spread out, dissipate, and decay more before reflecting back into listening or recording areas, thus improving low volume audio. Cathedral or high sloped ceilings do the same but also redirect the sound waves and can further improve low volume sound dynamics.
Louder volumes or surround sound systems, however, may be adversely affected by high ceilings as sound waves have more energy and can reflect off the higher ceilings and distort sound even more. The height can also make it difficult to treat with acoustic panels.
Long and/or Wide Rooms
The greater the distance sound travels the more it spreads out and the less energy it retains. Small rooms have less surface area in the reflective zones, while rooms that are long or wide or both often have larger reflective zones. So, the bottom line is they will require more acoustic panel coverage to sweeten the sound. Spacing panels out may make more sense than full coverage unless the room is a home recording studio.
Conclusion
The placement of acoustic panels depends on room size, height, and shape, the height and positioning of the sound sources and the listener’s ear, and how effective the sound treatment needs to be.
Use a mirror to locate the reflective zones based on the speaker’s and listener’s positions, and determine how much of the zone you can afford to effectively treat based on symmetry and spacing.
Hopefully, you now have a better awareness of the principles of acoustic treatment and where to place acoustic panels for the best sound improvement.