HOW TO IMPROVE ACOUSTICS IN A ROOM

The importance of room acoustics 

Room acoustics directly impact the audio quality of your set-up. By effectively managing your room's acoustics, you'll be rewarded with clear sound, balanced frequencies and reduced distortion.

Imagine this: you've invested in quality speakers, an amplifier and premium speaker cables, and you've meticulously set up your audio system in the listening room. However, you don't feel it sounds as good as it should, so you decide to give your new installation time to run in (which you should always do). But after many hours with your new setup, you're still disappointed with the sound but you just accept that's they way it is... but does it have to be?

When it comes to audio, one often overlooked factor is room acoustics. Even the finest Hi-Fi equipment may fall short in a space with poor acoustics.

Optimising your room acoustics is key to unlocking the full potential of your audio setup. It ensures clear sound, balanced frequencies and minimal distortion. Tailoring the acoustics to your room's unique characteristics creates an authentic and immersive listening experience. 

Room dimensions & room modes 

Let's be clear – there are some properties of your listening room that you can't change. No matter the size and shape of your room, some sound frequencies will behave differently than others, ultimately colouring the sound. 

Any room is, to some degree, a resonant space. This is because sound has a wavelength that varies with frequency, and if that wavelength matches the dimensions of a room, the frequency is amplified, or attenuated, more than adjacent frequencies. This is called a room mode and exists in all rooms at several frequencies.

To illustrate this, blow over the mouth of a bottle and hear the "flute" note that emanates at some point. The bottle resonates at a frequency determined by its dimensions once the air pressure has built up enough energy. Now fill the bottle halfway up with water and hear the note change in frequency. It does this because the dimensions of the resonance chamber in the bottle have changed.

Due to the dimensions of typical home listening rooms, room modes occur in the bass region where they can disturb and colour the sound coming out of your speakers. This can be heard as so-called "one-note bass" where some bass notes are considerably louder than others. 

So, what can you do about it? Short of moving your speakers into an open field where there are no room modes, you can try to reduce them with bass absorption. Using various types of absorption materials and products to treat the corners of your room (floor/wall, wall/ceiling, wall/wall) as well as the wall and ceiling surfaces, you can improve things to a degree.

Depending on room size and dimensions, certain frequencies in specific parts of the room will be cancelled out (nodes) or amplified (antinodes). This happens in three dimensions, meaning that peaks and dips at a given frequency can be heard, depending on the listener's location relative to the height, width and depth of a room. 

Unfortunately, many so-called bass traps tend to also dampen mid and high-frequency sounds. For this reason, it's easy to over-treat a room, which will suck the life out of the sound. A more targeted approach is to use narrow-band absorbers, such as so-called Helmholtz resonators – also known as tuned bass traps – which work at specific frequencies. However, you need to know exactly where your room has problematic frequencies, which is normally a job for an expert.

But don't panic, no room is perfect. Remember that you need to feel at home in your room, and a few pieces of soft furniture will start you on the road to a treated room.

Also remember that large speakers playing deep bass at high levels will reveal room modes more readily than smaller speakers playing at moderate levels. There is such a thing as too much bass. 

Room dimensions and room modes are one thing, but surface materials and reflections bring another acoustic factor into play: reverberation time.

Reverberation time 

Imagine listening to Hi-Fi in a giant bathroom with tiled walls or even just having a conversation. You can probably picture what a confusing listening experience that would be, but what exactly is going on in a room like that? 

The muddled sound you would be hearing would be down to the long reverberation time of the sounds being created in the room. 

Reverb is the "tail" of the sound in a room. It's the sound of multiple echoes blending, making them virtually indistinguishable from each other. It's what happens when sound bounces off multiple surfaces at different distances from the listener. Sometimes, however, you'll hear a more clearly defined echo. This often happens between hard, parallel surfaces like bare walls (we'll come back to echoes later). 

Reverberation time is the time it takes the reverb to fade to a level where it's no longer noticeable. In the field of professional acoustics, reverberation time is often measured as RT60.

What is RT60?

Professional acousticians often measure reverberation time as RT60, which is the time it takes a sound to decay by 60 dB. This is a very useful metric when designing professional listening rooms, such as recording studio control rooms and concert halls. However, measuring RT60 in a room correctly requires specialist equipment and skills. Acousticians are highly skilled professionals, which means hiring one can be costly.

Instead of worrying whether your listening room has the right RT60, think of RT60 as a loose guide to making your room sound "good enough". A well-treated room has a relatively short reverberation time, though the ideal RT60 depends on room size and what you listen to.

Small rooms should have a short reverberation time, meaning that RT60 should be somewhere between 0.1 seconds and 0.3 seconds – larger rooms could reach 0.5 seconds. This is because larger rooms don't become saturated with sound energy as quickly as smaller rooms. Put simply, there's room for more sound in a larger room, which is also why large speakers work better in larger rooms. A longer reverberation time can work well for classical music, as it more closely emulates the lively acoustics of a large concert hall.

By the same token, techno music tends to sound best in a club packed with people, so if that's your thing, the reverberation time of your room should be lower. A home cinema will also benefit from a short RT60. Again, this makes sense when you think of the average modern movie theatre, which has an acoustically damped environment.

A poor listening experience can often be caused by an overly long reverberation time, where the sound waves bounce around long enough and loudly enough to make music sound diffuse and smeared. Rhythmic instruments become overpowering, bass sounds become boomy and horns or distorted guitars become unbearable. 

You're not just hearing the sound itself, but also a multitude of echoes of it. If the music you listen to is even slightly busy in terms of rhythm, number of instruments or speed of the notes being played, no single sound will have time to fade away before another comes out of the loudspeaker. Sound is energy, and in a room with a long reverberation time, all that energy barely has time to dissipate – the music just keeps adding more. Similar sounds and notes will reinforce each other, and the room itself will start to resonate. 

This is of course a worst-case scenario but, even if your listening room isn't this bad, there's likely still room for improvement.

Now it's time to use your ears: is it easy to have a conversation in your listening room? Can you easily discern what people are saying, even when several people are talking at once?

If not, this is often a problem in small-to-medium rooms with poor acoustics, as the abundance of early reflections can make speech unintelligible. Read on for more information about early reflections.

Here's an easy way to gauge the reverberation time in your room: Simply clap your hands or speak loudly near every speaker in your system. If you hear a strong reverb or echo in that position, then the sound from your speakers will reflect in the same way, which is a sign that you should optimise your room acoustics. Unless you have a very large room, you'll be hearing quite short echoes, also known as flutter echoes, which make a handclap sound like a ruler vibrating over the edge of a table – a somewhat metallic or robotic effect. Flutter echoes often appear between bare, parallel surfaces, like walls or floors and ceilings. 

It's important to note that the sound coming from your speakers will sound different depending not only where you place them, but also to a large extent on your listening position. As you move yourself or your speakers around, the distance between your ears and any reflecting surfaces in the room will change, as will the sound. That's why setting up a new pair of speakers often involves moving them around to find a spot where they sound good – that's also why your listening position in the room matters.

Early reflections

In any enclosed space, such as a listening room, you'll hear sound coming not just directly from the speakers, but also sound reflected from any hard surface in the room. Generally, the closer you sit to your speakers, the more of the direct speaker sound you'll hear. But you'll still hear indirect sound bouncing off the walls, ceiling and even objects in the room. This indirect sound is known as first or early reflections, which, although is a delayed version of the original sound, is almost as loud.

In most listening rooms, the direct sound from the speakers will inevitably be mixed with the indirect sound bouncing off walls, floor and ceiling. A characteristic of indirect sound is that it tends to take a detour towards your ears, which takes slightly longer to arrive than the direct sound from the speakers. When this happens, you experience a phenomenon known as comb filtering, which can be problematic.

Acoustic phase

When two similar soundwaves are slightly delayed from each other, they're said to be out of phase. This means that as one soundwave is at its peak, the other is at its trough (the lowest point). When this happens, they effectively cancel each other out, creating a dip at certain frequencies. When the peaks of two soundwaves arrive at the same time, they're in phase, resulting in as much as a 6 db rise in amplitude.

Acoustical Treatment 

While a listening room with a high reverberation time is problematic, an acoustically dead (RT60 of 0 s) also isn't desirable, as it will sound unnatural and ruin the soundstage. You should aim for somewhere between the two, where reflections add life to the soundstage without causing acoustic issues elsewhere. 

So, what is acoustical treatment? 

Any sort of material that will either absorb, reflect or diffuse soundwaves can be considered acoustical treatment. This includes everything from fluffy pillows and couches to bookcases, plants and people. To understand how much these everyday objects matter to the sound of a room, you could try removing all of them and hear the difference... or just take our word for it. 

We mentioned that materials either absorb, reflect or diffuse sound. Here's a definition of the three terms:

• Absorption happens when a material is hit by soundwaves, causing them to dissipate some of their energy. This is what happens when you shout into a pillow. Big, heavy, fluffy pieces of furniture often make for excellent absorbents, but you can also place so-called bass traps in corners or hang them on walls, depending on the type and application.

• Reflection, on the other hand, happens when soundwaves bounce off an object in a direction related to the direction they came from, while retaining much of their energy. Reflection should be avoided, or at least controlled, for example by placing a rug on the floor between the listening position and the front speakers.

• Diffusion is another sort of reflection that occurs when soundwaves hit an irregularly shaped object like a bookcase full of books. Here, the soundwaves are scattered in different directions depending on their frequency. Diffusers can improve stereo imaging, especially when placed along sidewalls between the listening position and the front speakers. Purpose-made diffusion panels are best, but anything from a framed painting to plants can help and will usually be better than nothing.

Commercially available acoustic products can address the problems mentioned previously in this article and are available in many shapes, sizes, finishes and at different price levels. With so many options, you should be able to find something that matches your budget and looks good in your listening room – or at least something that doesn't attract the ire of others in your household.

DIY absorbers, reflectors and diffusers 

If you're a do-it-yourselfer or you just feel like a money-saving challenge, why not build your own acoustical absorbers, reflectors and diffusers? While room acoustics is a science (some would say an art form), there's a lot to be said for taking a more relaxed trial-and-error approach. Most of the materials you can use are affordable, for example excellent absorbers can be made from wood, mineral wool and various textiles (even professionally made diffusers are commonly made from wood).

Whether you should go the DIY route depends a lot on the amount of time you can devote to such a project and whether you (and the rest of your household) will be happy to live with the quality of your handiwork.

There are plenty of excellent online resources for learning about DIY acoustical treatment, and while much of it is aimed at recording studios, you can easily adapt it to your home cinema, Hi-Fi listening room or living room project.

For sound absorbers, try searching online for terms like diy bass trap, diy corner bass trap and diy broadband absorber. For diffusers, diy sound diffuser, diy QRD diffuser, diy skyline diffuser and curved diffuser should return some useful results.