Room acoustics can be the difference between achieving muddy, incoherent audio for your podcast or the clear, accurate sound your audience will want to listen to.
In fact, audio quality is almost more important than the content when it comes to podcasting – an audience won’t stick around to listen to muffled voices, no matter how interesting.
Likewise, room acoustics can’t be avoided with any amount of expensive gear.
In this article, we’re going to dive into this fascinating topic and give you the information you need to take your podcast to the next level should you wish to go down the route of acoustically treating the room in which you record your show.
Table of Contents
What are Room Acoustics?
Room acoustics starts with sound waves, these are longitudinal waves i.e. pressure waves caused by the vibration of particles. Sound waves are produced by a source – your speakers when mixing or your voice whilst recording and they travel outwards spherically and in all directions.
A small amount of the sound will travel in a straight line from your speakers to your ears (or your mouth to the microphone), this is direct sound; the direct sound is untouched by the room making it accurate.
This means the rest of the sound is not direct – its indirect, and it’s a problem.
When sound reaches a surface, it can be absorbed or reflected back into the room. Indirect sound will run wild in your studio, bouncing off of surfaces and eventually making its way back to your ears or microphone causing undesirable artifacts – these are known as reflections.
Reflections contain your original sound but now also hold all the information of the room. You will have heard these reflections as reverberation. Reverb is the decay of sound once the source has stopped.
Excessive reverb can be detrimental to the intelligibility of your podcast audio. A podcast should be effortless to listen to whilst low intelligibility will have your audience straining to understand what’s being said.
What Can Impact Room Acoustics?
Parallel walls are an acoustician’s worst nightmare and, chances are, your studio has them. They allow reflections to interfere with the initial sound causing low frequencies to resonate at certain points of your room – known as a standing wave.
Standing waves cause room modes, these are dips and peaks in the frequency response at specific points within a room. Online calculators like this one can help you quickly find and treat room modes.
Ceiling height is another factor that can affect how you’ll hear sound in a room. Higher ceilings will create bigger reverberation as the sound will have further to travel before being reflected. You’ll also be left with a lot of ‘dead space’ where sound will resonate above your head.
Any surface can interact with sound, not only the walls, ceiling, and floor but any furniture in the room will absorb or reflect sound based on the material qualities.
Often a sofa or bed in a room not only creates a multi-purpose room but helps deaden a room with its absorptive qualities.
What Is Acoustic Treatment?
It’s important to note, acoustic treatment isn’t the same as soundproofing. Acoustic treatment will help improve the reproduction of sound within your room whilst soundproofing stops sound entering or leaving the room.
Both need to be addressed separately for an optimal studio experience.
There are 3 main types of acoustic treatment:
- Bass Traps
- Absorption Tiles
- Diffusion Tiles
And you can prioritize them in that order!
Absorption panels are made of porous materials allowing sound waves to permeate through. Some of the sound energy is transferred into heat whilst the rest continues through the panel – the energy is mostly unable to enter back into the room (dependant on the quality of the absorber) and the reflections are diminished.
Most commonly, the material used in absorber tiles is acoustic foam, differing from regular foam in its higher density and textured surface. Other materials can be used too, especially if you’re on a budget. The way to know how much absorption will take place using a specific material is by looking up or testing its absorption coefficient
The sound absorption coefficient is the ratio of absorbed sound energy to the incident energy – the closer this number is to 1, the better the absorber. Generally, Google can provide you with the coefficient of most materials however, for added accuracy, you can use the calculation below.
Not all acoustic treatment provides the same absorption coefficient; absorption panels made from polyurethane foam provides an absorption coefficient of around 0.3 whilst cellulose fibers or semi-rigid fiberglass will give a much higher 0.75 coefficient.
Polyurethane foam is often a cheaper solution, whilst it may seem to have low absorptive properties, a painted wall will only provide a coefficient between 0.025-0.05 so 0.3 will still provide a large, audible difference.
By keeping an eye on the absorption coefficients you’re putting into a room, you’ll gain control over how live or dead you make it.
Many articles suggest carpeting a room to help with the absorption however carpet and wood often provide similar levels of absorption. Wood and carpet are however much more absorptive than linoleum or tile.
The ultimate flooring for a room you want to remove reflections in would be carpet over foam rubber providing around 0.55 absorption coefficient.
There are some DIY possibilities for a cheap solution to absorption panels – egg boxes are not one!
Simply putting an absorptive material over a wooden frame with air gaps inside will suffice as good acoustic treatment
Another way to increase this coefficient in any material is by allowing an air gap between the panel and wall
Allowing low frequencies to resonate freely in your studio will quickly muddy up your recordings or change how you’ll hear your mix.
The length of a sound wave is dependent on its frequency – higher frequencies produce a shorter wavelength whilst lower frequencies are defined by their long wavelengths making them harder to attenuate.
Low frequencies are often unaffected by absorbers.
Bass traps are absorbers, in that, they attenuate sound by absorbing initial reflections however they’re much thicker and denser than regular absorbers allowing the attenuation of low frequencies, as well as mids and highs.
Whilst bass traps are ultimately better absorbers, they’re often more expensive and take up more space which could reduce the space you have too much and leave you with a muffled sound.
Bass traps should be made a priority to ensure muddy, low-frequency reflections are absorbed however using them alongside absorbers, especially in smaller rooms, is a good idea.
Diffusers don’t remove sound energy from the room but instead scatter it, lowering the sound’s intensity and ensuring no one frequency builds up to create standing waves.
The surface of a diffuser is made up of different depths to spread out the waves hitting it.
Diffusers are usually lower down on the priority list and in smaller rooms you might be better off skipping them entirely. As they still allow sound energy back into the room, artifacts are sometimes introduced into the mix – whilst inaudible in larger rooms, these can make all the difference if you’re sat close to one.
One issue with buying a diffuser is that many companies sell foam diffusion panels. Foam is an absorptive material, whilst this will still treat your room, you won’t get the diffusion properties you’ve probably paid extra for.
Diffusers are most effectively made from wood or other hard, reflective materials. This ensures the sound is still being dispersed back into the room rather than absorbed and removed.
A DIY method you might have seen are bookcases filled with different sized books. Bookcases are worth experimenting with as you may find a cheap solution to a nice sounding room however it’s important to note the bookcase will be more absorptive and will likely have very little diffusive properties.
Do you Need Acoustic Treatment?
The short answer is yes!
… But it doesn’t have to be the most expensive acoustic gear or even the most accurate.
You’ll find that any acoustic treatment you use in your room will audibly help out with quality and make the difference to your recordings – even DIY solutions.
You can also help to minimize how much treatment you’ll need by finding the room’s ‘sweet spot’. Sitting in the rooms acoustic sweet spot will give you the best quality of sound whilst mixing and it’s easily achievable!
You should start the process by placing your speakers. They should sit at least 3m away from any surrounding walls if possible and ideally be on stands rather than the desk to avoid resonance from the desk.
Most importantly, your speakers should be symmetrical in the room – this can be achieved in any sized space and will mean you hear the same reflections from the left and right.
With the speakers on a 60° angle pointing inwards, you should be sat at the center point – equidistant from both speakers – in an equilateral triangle formation.
Testing your Room
Testing a room can be as simple as using your ears to get an idea of the amount of echo and reverb present or using software such as FuzzMeasure or 3D modeling software for a more precise evaluation.
Auralex is free software I often use which calculates the amount of absorption coverage needed depending on your room size and purpose.
On a budget, your ears will be the best tool for assessing the room. By clapping in an untreated room, you’ll hear any echo and reverberation that require treatment.
If you’re unsure, clap in multiple rooms – take note of each room’s qualities; the size, height, and any materials inside. Leaving some nice reverb, found in larger rooms, can be useful to keep a room characterful (especially whilst recording) however you should work to eliminate any unpleasant metallic ringing, slap, or flutter echo.
Continuously using the clap method throughout installing any acoustic treatment can help to monitor any progress and quickly find any issues caused by wrong placement.
Another test to help with the placement of acoustic panels is the mirror test. The mirror test indicates the first reflection points – these are the cause of the first and most noticeable reflections.
Move a mirror along the surrounding walls, when you can see your listening position in the mirror, you should mark the spot for initial treatment.
How to Approach Setting Up Acoustic Treatment
The aim of acoustic treatment will change depending on whether you’re creating a recording room or mixing studio. In a recording room, using too much treatment will deaden the room whilst in a mixing room an almost dead room is preferable to mix accurately.
If you’re using the same room for both, you should aim to create a natural-sounding environment to suit both purposes.
Sound waves tend to build up corners so this should be your starting point.
Your room will have dihedral corners, where 2 surfaces meet, and trihedral corners, where 3 surfaces meet. Trihedral corners can be found in the corners of your ceiling and floor – they are, unfortunately, the best at collecting bass and creating obnoxious resonance. Bass traps are the solution – remembering to leave an air gap – the bass will be entirely absorbed.
As a 2nd priority, bass traps can be put in the dihedral corners too to eliminate the formation of standing waves here.
Absorption will also be required on the flat walls of your room to avoid standing waves – particularly parallel walls. Absorption can be used to eliminate any parallel surfaces by placing the panels opposite to each other in a checked pattern on each wall.
It’s also important to not cover your entire room in absorption panels to ensure the room retains character. If you’ve ever visited an anechoic chamber, you’ll know it can be uncomfortable to work in a super absorptive space and difficult for our brains to comprehend and ignore.
Diffusion needs to be kept away from people. As the reflections are scattered back into the room, barely audible artifacts are created that wouldn’t be heard when a little distance is put between them and the listener.
In a smaller room, it can be helpful to experiment putting diffusion high up on the back wall or on the ceiling to allow for some diffusion in the room.
Ultimately though, your room should be fine without diffusion so don’t invest tons in it without some testing first.
Many companies offer acoustic kits to help get started, some of my favorites include;
Auralex Acoustics D36-DST Roominator Acoustic Absorption Treatment Room Kit (Amazon)
Kit Includes 18 DST-112 Panels and 18 DST-114 Panels
– Includes two types of absorber panel but no diffusers or bass traps
Primacoustic London 12 (Sweetwater)
– 2 48″ Broadband Panels
– 8 Control 48″ Columns
– 12 Scatter 12″ Blocks
– 28 Surface Impalers
– 8 Corner impalers
+ High quality, fiberglass panels
+ Complete set, no-fuss solution
These packs are perfect if you have the money to spare and want a quick and easy setup however might not provide as accurate results as you would gain from testing and choosing your own acoustic gear – they’ll definitely achieve the next best thing.
For recording it might be useful to invest in some reflection filters – these are absorptive shields that cover your microphone to eliminate some of the background noise and stop spill into separate mics. For more information on reflection filters and our thoughts on the effectiveness of them, see our article Are Reflection Filters Worth it? We put it to the Test.
Matching your Gear to the Acoustics of the Room
Nearfield monitors revolutionized music production, setting off the home studio trend in the 80s. They allow for close proximity listening, useful for small spaces whilst ensuring you hear mainly direct sound with fewer reflections. Monitors, appose to hi-fi speakers, are designed to reproduce sound as accurately as possible – uncolored by any of the speaker’s characteristics.
Equally as important as a flat frequency response, you should look out for a neutral tonal response as this represents how the speakers will behave within your room including the direct sound and its reflections.
Choosing the right microphone can make all the difference in a recording studio. If your room is struggling acoustically, a cardioid polar pattern will help eliminate echo by focusing more closely on the direct sound.
On the other hand, in a nice sounding space, you might want to experiment with hyper-cardioid polar patterns to capture the characteristics of the room. Including the room in your recording can help create a more natural sound and give the recording ambiance – this means less editing and fewer mistakes attempting to create a natural sound, unnaturally.
This is a good solution if your podcast works on a microphone per person basis however when using one mic between two, a bidirectional polar pattern would be more suited.
Treating your room can seem like a complicated process at first and it won’t be perfect first time. Keep experimenting with your room and testing throughout and you’ll see the hard work pay off.