Hi-Fi DIY: Changing Rooms – Part Two

Last month, we identified the various acoustic issues commonly found in domestic listening environments. Now it’s time to consider what we can do to alleviate those problems. Huw Price seeks treatment…

acoustic issues

There was a time when hi-fi enthusiasts seeking help with acoustic treatments would’ve needed to track down some arcane tome on studio design at the local library. Probably written by BBC-trained engineers, said book would’ve been packed with impenetrable maths formulae, complex diagrams and instructions for building outlandish acoustic-treatment devices.

While the contents remain as relevant as they ever were, now it’s much easier to access information online, and you don’t need to be a trained acoustician to make use of it. Furthermore, the explosion in home recording has created a widespread awareness of acoustic-treatment methods, along with an industry producing off-the-shelf solutions at every price point.
Inevitably, this has filtered through to the spheres of hi-fi and home cinema, with many listeners coming to understand the potentially enormous benefits of acoustic treatment. So long as you’re able to understand some basic rules, it’s completely possible to tune your room to enjoy improved clarity and imaging, tighter grooves and coherent bass. So let’s check out some treatment methods.

Absorbing information

Last month, we described how rooms with hard surfaces tend to make hi-fi systems sound bright and image poorly. One of the most popular methods for tightening and softening the sound is absorption.

It’s best to think of the process as energy conversion, so in this case, we’re turning acoustic energy into heat. Some of the items in your listening room may already be absorbing sound energy – for instance, a fabric sofa, curtains or fabric wall hangings. If your room sounds too bright or reverberant, you can start by putting a large rug on wood or tiled floors in front of the speakers and drawing the curtains to catch soundwaves bouncing off your windows.

“So long as you are able to understand some basic rules, it’s completely possible to tune your room to enjoy improved clarity and imaging”

Regarding curtains, if the material is porous, the sound waves can pass into the fabric, causing the fibres to rub together and generate heat. Velvet is an ideal material and if the drapes are pleated, the surface area is increased and absorption efficiency is improved.
Drapes also make more efficient absorbers when they are hung at a distance from the reflective surface, because soundwaves that make it through on the first pass can be caught when they bounce back. If there’s a wall behind your listening position, consider a wall hanging such as an oriental rug or a tapestry. Some acoustic-solutions companies actually market acoustic drapes.
Rockwool provides efficient acoustic absorption and has long been used in the studio industry. It can be bought in slabs designed specifically for acoustic treatment, but it must be covered and contained to prevent fibres from shedding.

It’s relatively easy to make your own acoustic panels, and you can find instructions and YouTube tutorials online. Alternatively, you can buy pre-fabricated Rockwool absorbers with a variety of attractive fabric coverings.
In recent years, foam panels have become very popular – because they’re cheap, easy to handle and readily available. But we’re talking about acoustic foam, rather than the stuff you might pick up on the industrial estate. Foam’s efficiency for absorbing sound depends on its permeability, and ordinary foam has a closed surface that prevents sound waves from penetrating.
Acoustic foam is ‘fire polished’ or dipped in caustic chemicals to open up the pores. This allows the sound waves to enter the foam more easily where friction occurs between the fibres, dissipating the sound as heat.

Spreading diffusion

The downsides of absorption methods are that they work best at upper-midrange and treble frequencies, and that rooms with excessive absorption can sound dull, lifeless and bass-heavy. You’ll also have to drive your speakers harder in order to achieve the same degree of loudness, and this can induce distortion in your amp and speakers, and damage your ears.

Slightly reverberant rooms make more enjoyable listening environments, so rather than absorb all the sound waves to eliminate strong reflections, standing waves and flutter echoes, diffusers can be used to break up the waves and scatter them around in all possible directions. They can be used in conjunction with absorbers and actually improve their efficiency – so you’ll need fewer absorption panels and they’ll take up less wall space.
Diffusers are basically irregular geometric shapes, so if you have bookshelves, mix up the books so the depths all vary, rather than lining up exactly. You can also buy relatively small diffusers that can be hung from ceilings and mounted on walls. Many look sculptural and decorative, and thanks to some clever mathematics, they’re highly effective.

On Reflection

As well as using strategically placed rugs, curtains, fabrics, wall hangings and wall-mounted panels to treat acoustic issues in your room, you can also buy all kinds of absorbers, bass traps and diffusers – made from a variety of materials, including Rockwool, foam and fibreglass.

Bass traps

This is the tricky one, because so often, speakers are blamed for poor bass performance when room acoustics are the real issue. Although foam absorbers can be used to control bass, they must be quite deep and placed away from a wall to be effective. Few of us would want metre-deep foam slabs protruding from living-room walls…

Fibreglass is a more efficient absorption material, so you can achieve better performance with the same depth of material, but in small rooms it’s impossible to achieve total control over bass frequencies without encroaching significantly on space.
Rather than try to control all bass frequencies where space is restricted, tuned bass traps can target frequencies that are problematic within any acoustic space. Examples include Helmholtz and diaphragmatic resonators, which can be tuned to notch out specific frequencies or narrow bands of frequencies around a given point. So if your room has a build-up at, say, 125Hz, this type of resonator can be used like a graphic equaliser.

Hitting targets

You can go online and check out how commercially available absorbers, bass traps and diffusers look and decide what might look acceptable in your home. Companies such as GIK Acoustics, Auralex and Advanced Acoustics offer a wide range of products and installation guides.

Some products combine absorption and diffusion or bass trapping and diffusion duties. You may be surprised to find that many products, sold individually and as complete room kits, cost less than you might consider spending on a turntable or speaker upgrade.

“Diffusers are irregular geometric shapes, so if you have bookshelves, try mixing up the books so that the depths all vary, rather than lining up exactly”

Where wall space is at a premium, hanging panels from the ceiling can be a very effective measure and, if the colour of the panels matches your decor, fairly unobtrusive.
High ceilings allow you to leave space between the panel and the ceiling, so leave a gap if you can. Ideally, the first position to try would be exactly halfway between your speakers and your listening position.
If there are side walls close to your speakers, try placing panels on each wall. While sitting in your usual listening spot, have an assistant move along the wall with a mirror. When you can see the speaker in the mirror, you have identified the first reflection point – and that’s the best spot for an absorption panel. Do the same on the other side and you should notice that the imaging sharpens considerably.

Bass tends to build up in corners and the junctions between walls and ceilings. Since this is usually unused space, it means that placing absorbers and bass traps in those spots is both convenient and effective. Try hanging panels across the corners, preferably leaving some air gaps behind. Placement of bass traps is slightly less critical, so long as you can get some in somewhere. However, the corners and ceiling junction areas behind the speakers would be our preferred place to start.
If there’s a wall close behind your listening spot, your hi-fi will sound bassier than it should. One remedy for this would be to consider placing drapes or bass traps against the wall.
Diffusers will work in various positions, and if there’s more space behind the listening spot, they can work well on the rear wall of the room. You may also use diffusion on the wall behind the speakers or at various spots on the walls or ceiling. If possible, try placing your treatment products temporarily to hear how they affect the sound, before making any of your installations permanent.

Put in place

Hopefully, the last three articles on speaker placement and room acoustics will have inspired you to try out some of our recommendations. If you’re content with a hi-fi system that merely provides background sound, that’s fair enough.

But stop to consider how much craft went into the recording and mixing of your favourite records. Leaving aside the acoustic design that went into creating the studio spaces and the incredible engineering behind the microphones, mixing desks and tape machines, what about the sound engineers, producers, mixers, mastering engineers and, most importantly, the musicians themselves?
You can be sure that the technicians trained for years and worked hours that might put junior doctors to shame, and the musicians committed time and money to acquiring the best equipment and honing their musical skills. Every detail, from the moment when a song went from the germ of an idea to the cutting of the acetate, would have been agonised over.
Put it this way – neglecting the setup of your speakers and disregarding room acoustics is tantamount to walking around an art museum wearing sunglasses, or buying the finest high-resolution TV you can afford only to use it to watch VHS videos.
By doing so, you can never fully experience the artistry encompassed within those records. However, setting up your speakers and listening room with care allows you to listen to your records in a way your musical heroes intended for them to be heard. That’s the best tribute you can give, and it’s no less than they deserve.