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.

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.

Does your listening room have poor acoustics? 

There are several ways to find out if your room needs improving. The quickest way is, paradoxically, to use your eyes rather than your ears. For instance, which materials do you have on the walls, floor and ceiling? Different materials respond differently to sound. Smooth concrete or ceramic tiles, for example, absorb absolutely no sound and reflect everything.

Hint: if your room is built like a bathroom, it probably sounds like one.

Is your room filled with furniture, books and rugs, or have you taken a minimalist approach to your living space? Any object will reflect and/or absorb sound, and that goes for everything from plush couches to plants and bookshelves (preferably filled with books).

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.

Here are three simple ways to improve your listening room acoustics...

Lay a rug

Reduce floor reflections by placing a heavy rug on the floor between the speakers and your listening position. It will absorb early reflections of high and midrange frequencies, which can muddy the stereo image.

Add a bookshelf

Diffuse reflections of high and midrange frequencies by placing a filled bookshelf along the side walls or the rear wall of your room. This will scatter unwanted reflections in all directions, reducing the sound waves arriving simultaneously at the listening position.