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Hear no Your room can have a huge impact on the sound quality of your finished tunes. Even if you’re on a limited budget, you can dramatically improve your monitoring environment using everyday materials that you may already own...
o r c h t o c t a g i c o n : M a t i o r a u s t r I l l l l u
t’s an unfortunate fact that most project studios are rectangular or square. But admit it, if you had £2,000 to spare, what would you do: consult an architect to modify your room, or spend the money on new gear? You’d spend it on new gear, wouldn’t you? It’s always easy to tell yourself you can ‘get by’ with your room as it is, but somehow there are always excuses to buy new equipment. The fact is that acoustic treatment is vital for professional results and in major studios, extreme measures are taken. The rooms may have strange geometry. The walls and ceilings may be false and constructed out of fabric stretched over wooden frames. Behind these, suspended from the roof, you might find large panels covered in sound-absorbent material. The studio doors may be oversized, filled with sand or lead, and mounted on industrial-strength hinges. The entire room might even be of a floating structure to decouple it from the rest of the building. In a small, home-based project studio room, such measures are impractical – the space left over after treatment would be too small to use – and expensive. But even if you are o n a tight budget, it is possible to dramatically improve the sound quality in your room using everyday materials that you may already have lying around your home. So, now that you’ve cleared out all the junk from that spare room to turn it into a studio, we’re going to, er, tell you to put it all back in again!
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Go untidy your room Perhaps the first question we should consider is why room acoustics can turn out to be such a huge problem. The answer is surprisingly simple: any object can reflect sound, and such reflections interact and can cause problems that spoil one’s ability to hear music properly. Solving these problems isn’t particularly straightforward. While most materials allow low frequencies to pass straight through them, materials that are soft and lightweight tend to absorb high
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evil frequencies, yet hard and heavy materials reflect them back. Ultra low bass frequencies have an remarkable ability to pass through almost anything (just ask your next-door neighbours). We need to use a combination of different materials to solve these problems. Before we do that, though, let’s take a look at the pro blems that unwanted sound reflections can cause. Firstly, if a sound is reflected in phase with itself (ie, both the original sound wave and its reflection are in synchronisation and are perfectly overlapping each other), then that sound becomes reinforced, making it considerably louder. This results in the characteristic boominess of some rooms. This can swamp the room with sound, making it difficult to hear clearly. Secondly, if a room is built in a solid and soundproof manner, bass frequencies build up at the edges of the room, so that the mix sounds radically different depending on where in the room you happen to be standing. Thirdly, if a reflection is out-of-phase (ie, the positioning of the reflected waveform clashes with the original), it causes a comb-filtering effect, making some frequencies leap out more than others. This can mask problems in your mix or exaggerate issues that wouldn’t normally be a problem. As each ear will receive a different reflection pattern, the stereo imaging can also become unclear, and it can be very hard for your brain to identify the different instruments in the mix clearly. If we strive to eliminate every unwanted sound reflection, the resulting sound of the ro om becomes too unnatural and artificial. It doesn’t represent the kind of environment that the mix will typically be played back in. The room feels ‘dead’, claustrophobic and unpleasant to be in. Our brains analyse everyday sound reflections to help orient us (similar to bats in caves), and if we deny ourselves such information, we quickly feel boxed in and extremely uncomfortable. We need an environment where low frequencies don’t accumulate and swamp the sound, and an
environment with a diffuse high-frequency soundfield, creating an uncoloured sense of space in the room we are listening in. You can spend a lot of money treating your room to professional standards, but frankly, this is not money well spent unless you regularly hire out your studio to paying clients. Most of the benefits of effective acoustic treatment can be achieved for little
or no cost if you’re prepared to sacrifice a little room space and be imaginative and creative in the way that you use what is available to you. But before starting, you need to decide whether the approaches we’re about to run through will work for you. Don’t start off unless you are sure that you can get the results you need, and that any bits you need to buy are within your budget. Work out what
How sound travels
We’re so used to seeing the familiar wavy line display – shown in picture 1, above – on computer-based sound editing software that it’s easy to forget that this bears no resemblance to how sound actually moves in the air. When a sound source starts to vibrate, it compresses the air around it. As the air expands again it compresses the air around it, and that, in turn expands. So, the wave action travels outwards like a set of huge wobbly concentric spheres, similar to the cross-section view shown in the lower picture above. So in reality, the actual air around the sound source doesn’t travel to where the sound is picked up. Instead, it is merely the ripple-like action that is transferred to the receiver in a sort of ‘falling domino’ effect.
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items you can recycle from around your house (or from the local rubbish tip), and what things you’ll have to buy. OK, that said, let’s look at the specifics of solving these problems.
Reducing room resonance If two large walls are directly facing each other, some sound will keep bouncing back and forth until it is dissipated as heat or cancels itself out. If the length of the sound wave is exactly the same as the distance between the two walls, it gets reinforced and the room resonates in a boomy way. In fact, if the distance between the walls is any exact multiple of the sound’s wavelength, then some degree of resonance will always result.
The audible effect of resonance depends on the size of the room, but dry drum patterns will show up the defect best. Try comparing different types of snare and bass drum samples, listening first on headphones, and then on speakers. The d rums should be clear-sounding in both cases. A poor, resonant room will add unwanted colouration that isn’t there when listening on headphones. Room resonance happens in three dimensions: between the two side walls, between the front and rear walls, and between the floor and the ceiling. Typically,, the resonance between the floor and ceiling Typically is very much lower, due to floorboards, carpet, and thin ceiling boards reflecting much less sound than hard side walls tend to. We need to break up the pure, rectangular nature of the room to solve this problem.
The solution is simple. Large items of furniture, cupboards, wardrobes, bookcases and display cabinets will break up the room into smaller, less resonant spaces, and will also help absorb sound. But be aware that cheap wardrobes and cabinets can cause problems if their panels are not solidly constructed (especially the large back panel). There is a simple test: bash the panels lightly using the soft palm of your hand. The sound they make should be little more than a ‘slap’ or a ‘thunk’. If any of the panels boom like a bass drum, you know you’re in for trouble. Often, you need only to nail the troublesome panel into place more securely to solve the problem. You don’t want to turn your nice studio into a junk room, but you have to compromise. Those fantastic, minimalist rooms you see in hi-fi adverts are sheer
The proble problems ms speaker
speaker speaker low profile equipment rack
work bench
speaker
speaker low profile equipment rack
work bench
speaker low profile equipment rack
work bench
chair chair
chair
entrance door
Any waveform that fits exactly between parallel walls will cause the room to hoot – or resonate – at that frequency as the sound keeps bouncing between the walls. Most rooms have three such fundamental frequencies: one between the side walls, one between front and back walls, and a third between the floor and the ceiling.
entrance door
entrance door
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Direct and secondary ‘live’ reflections from the walls, ceiling, and any large, flat objects in t he room confuse the stereo imaging and make it difficult to hear exactly what’s happening in terms of instrumentation. 2
But a completely ‘dead’ room that absorbs all the sound lacks essential everyday audio clues that t ell the brain how big a room is, resulting in an unnatural monitoring environment that feels small and cramped and can even induce strange feelings of panic. 3
The solut solutions ions display cabinet speaker
display cabinet
bass trap speaker
work bench
speaker low profile equipment rack
work bench
chair
storage cupboard
bookcase
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speaker low profile equipment rack
bass trap
work bench
bookcase
bass trap
entrance door
The addition of bass traps significantly tightens up the low frequency response of the room, and large curtains soak up live reflections from the upper end of the frequency spectrum downwards. Thicker and heavier curtains absorb frequencies further down the spectrum. 2
storage cupboard
storage cupboard
bookcase
bass trap speaker low profile equipment rack
chair
storage cupboard
entrance door
Bulky items of everyday furniture such as bookcases, cupboards and shelves will break up a room into a non-rectangular shape. The problem is now distributed over so many different areas that it ceases to be significant anymore. 1
display cabinet
bass trap
chair
storage cupboard
bookcase
bass trap speaker
storage cupboard
bookcase
bookcase
entrance door
Finally, the addition of randomly varying hard surfaces such as books and ornaments provides quality diffusion for high frequencies. This restores the feeling of air and space in the room without disturbing the stereo imaging. This can be particularly effective across the back wall of a room. 3
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ACOUSTICS fantasy. In reality, no re ctangular minimalist room with fantasy. bare walls is a good listening environment. You need to make creative use of your furniture to make your room a more complex shape. Be assured, however, that the sonic difference made to a room by such simple additions can be truly astonishing. For a simple example of suitable furniture layout, see the first diagram in The Solutions walkthrough on p62.
Testing your room
3 the length of the room (front to back) and for As a separate set of figures, do the same for
the height (floor to ceiling).
4 SINE mode. While listening to a tone of about
Start the mda TestT estTone one plug-in and switc h it to
1kHz, adjust your speaker volume to a comfortable, moderate listening level.
Taming the bass end Ironically, a very solidly built room tends to have bass Ironically, problems. If your studio is made of flimsy stud walls, excess bass leaks through to adjoining rooms. But in a room made of brick or stone, bass frequencies tend to gather at certain points in the room, and you will notice a dramatic change in the amount of bass depending on where you stand. This can be very worrying. How can you determine how much bass is right for your mix when you might hear little bass in your normal listening position but too much when you listen further back in the room? We need to ‘mop up’ all of that excess bass and make the sound more consistent throughout. Then you’ll be hearing the real amount of bass, instead of bass that’s over-amplified by your room. We achieve this by placing bass traps in the room’s corners. All you need to build them are some large, solid wooden boxes stuffed with non-flammable cotton wool or similar material. Such boxes are available in the form of simple, cheap, display cabinets without doors, or you can knock them up yourself from offcuts of chipboard and a few nails. For stuffing, you can buy very cheap pillows from your local catalogue store. Feather pillows are even better, but are more expensive. Simply place units like this on the floor in the corners of your room. Two are probably enough for most small rooms. They tighten up the bottom end of a room wonderfully. It might take you a while to get used to the new sound! If you want to improve the appearance of these units, cover the entire box with a thin fabric – the material used for covering the front of hi-fi loudspeakers is ideal. You could tell your friends that the entire unit is just an enormous subwoofer speaker used only for dub reggae... You don’t even have to use a dedicated unit as a bass trap. If you are using tall, solidly-built, freestanding bookcases to help break up the shape of the room, you can simply stuff pillows into the bottom two shelves to achieve a similar, bass-damping effect (though this will be less pronounced than units placed in the corners of the room).
Controlling room reflections
5 manually adjust the frequency – very slowly –
Now, starting from a frequency of about 50Hz,
Get your hands on the TestTone plug-in by pointing your browser at www.mda-vst.com
upwards to somewhere just a bove 1kHz. You don’t need to go any higher, because this test becomes much less valid at high frequencies. You need to do this in several steps, using the F1 control on the plug-in to set the frequency range, and F2 to manually sweep through it.
6 carefully as you pass through the resonant
As you sweep up the frequency bands, listen
You can perform a simple test to see if your room suffers from resonance problems. You’ll need to use the mda TestTone TestTone VST plug-in – available as a pack of plug-ins for free download from www.mda-vst.com. This plug-in is just a simple test tone generator which you can use to manually sweep through all of the audio frequencies. Before performing this test, however, you need to observe some precautions, as sine wave testing can damage your speakers if not done with a great deal of care:
• Do not play very high or very low frequencies through domestic-quality loudspeakers • Listen only at a very moderate sound level – quieter than normal music playback • Do not leave the test tone running for extended periods of time • If you cannot hear the test tone, fix the problem before turning the speaker volume up
frequencies you’ve written down. If the volume level of the tone seems to suddenly leap out at you at around this frequency, you know you’ve got a resonance problem that needs addressing. If you pass cleanly through the numbers you’ve written down, you’re in the clear.
7 using this test. Many minor variations in the
It’s important not to get too obsessive when
level of the tone will happen as you sweep; these should be ignored.
8 you sweep through the low frequencies. It
You may notice other significant resonances as
may be the side panels of a wardrobe vibrating in your room, or perhaps a flimsily constructed wall where a cupboard was bui lt into the room. You’ll need to find creative solutions to fix such problems such as these.
9 objects within the room as you sweep
Listen out also for any rattles and buzzes from
The test is performed as follows: Firstly, some maths: the speed of sound is approximately 1,130 feet per second (at room temperature). Divide this number by the width of your room in feet to find the resonant frequency of the side walls. For example, for a room 8.5 feet wide: 1130/8.5=133Hz. Write down your answer.
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2 intervals, write down several multiples of your As the room can also resonate at harmonic
answer (ie, double, triple, four, five, six and seven times your origina l answer. You You don’t normall y need to go any higher than this).
through the low frequencies. There may be several different objects in the room that have been rattling for ages – it’s just that you never noticed them before. The above method, though useful, is still a very crude one that should never be used to fine-tune a room – this technique is far too primitive for that. It is, however, ideal for identifying when either the room, or some object within it, is causing significant and undesirable resonance problems at low-to-mid frequencies.
It’s not just the bass frequencies that need to be tamed, it’s the high frequencies too. But this time, the problem is more complicated. We need to prevent all direct reflections from
Ironically, a very solidly built room tends to have bass problems. If your studio walls are flimsy, excess bass leaks to adjoining rooms 63
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Y M A L A
If you’ve got some spare ceiling tiles lying around, you can improve the absorption of the room by mounting them on the wall
Fire safety It’s lovely to come home to a real fire – unless it happens to be your studio burning down. Avoid damage to equipment, friends and family by following some sensible, basic fire precautions...
• Egg boxes and polystyrene blocks (once popular home-made sound treatments in schools) can pose a major fire risk because of their high flammability. Stay well clear of these dangerous materials unless they have been specially treated for fire safety. • Anything that you attach to your ceiling must be flame retardant. Horrific disco accidents in the 1970s demonstrated that flammable ceiling tiles will rain down dozens of burning droplets of sticky fire into people’s hair and onto their skin and clothes. The consequences are terrifying. • Whatever material you use to create curtains lining your walls, make sure it’s flame retardant. Because curtains are baggy, trap air and hang vertically. They are one of the biggest fire risks in any building. • Wall-wart power supplies jammed into mains distribution boards hidden behind a curtain are a recipe for disaster if left unattended. Use a separate mains outlet for items that absolutely must be left turned on (such as VCRs) and supply everything else from switched outlets so you can turn off everything with just one or two mains switches when your studio is not in use. Wallwarts can get dangerously hot in enclosed spaces overnight, so beware. • Bass traps can double as fire traps because of their box-like construction. Make sure they are
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stuffed with flameproof stuffing only. If in doubt about the choice of stuffing, just use cheap pillows certified to British Standards for Fire Safety in Home Furnishings. • Try to keep the escape route clear of cables. Use longer instrument cables to go around the edge of the room rather than taking a shortcut across the path to the doorway. We’ve all tripped over our own cables at some point; do you want that to happen in the dark, during a night time fire when the power has cut out? • Buy a fire alarm and site it appropriately. They only cost a few pounds and some local councils even give them away for free. They are battery operated and there’s no wiring involved – they simply screw onto the ceiling in just a couple of minutes. Experiment (using sticky tape) to find the best location so that normal activities – like smoking cigarettes (or anything else) – will not set it off accidentally. Otherwise, someone will get annoyed and take the battery out one day and forget to put it back in. • Buy a fire extinguisher suitable for ‘Class E’ (electrical) fires. Keep it accessible and clearly visible. Do not buy a water-based extinguisher; these are too dangerous in a studio that has power supplies and mains boards everywhere. Note that all modern extinguishers are simply coloured red by law (they used to be available in different colours, depending on the contents). The new-style red extinguishers all sport a small rectangular coloured label on the front that states their true contents.
reaching our ears, but if we only do this, we end up with an unresponsive room that feels claustrophobic to work in. We need to create a more diffuse reflection field. But let’s start by removing those troublesome direct reflections. The easiest way to do this is to hang heavy curtains on the walls, but fitting conventional curtains can be a very time consuming business. If, like most of us here at CM , you’d prefer to spend your time making music rather than sweating over a power drill or spending hours threading curtain hooks, then fear not – there is a simple curtain solution that can be fixed up in a few minutes, and is suitable for most small project rooms. The solution is to use a shower rail or similar tube to hang material from. There are cheap, spring-loaded collapsible rails available that are adjustable to fit a range of widths. A pair of these can easily span a small room using either an existing roof beam or a small block of wood between the two. Alternatively, a piece of furniture like a wardrobe or tall bookcase can be used to bridge the gap. For longer spans, any kind of strong, inexpensive tubing, such as wooden dowelling, can be used. You only need simple supports at each end, and perhaps some additional support along its length if it is particularly long. We’d advise against trying to use string or rope to hang your curtains from, as curtain material is very heavy. Using a simple rail for support in this way is quick, easy and doesn’t require expensive ready-made fitted curtains. You can still use pre-made tabbed curtains as shown in the photographs, but any material could easily be hung from the rail. Note that lightly coloured curtains can be hard to keep clean if people smoke, and curtains that are too dark can make a room feel gloomy and sinister. If you’ve got some spare ceiling tiles lying around or have the cash to buy some, you can further improve the absorption of the room by mounting fireproof cork or polystyrene roof tiles directly onto the wall, out of sight behind the curtain. However, this is not absolutely necessary if the curtain material is thick and heavy enough. As shown in diagram 3 in The Solutions walkthrough on p62, you don’t have to hang curtain material around the entire wall; in fact, it’s better if you don’t. By hanging heavy curtain only around the section of room in front of your listening position, you effectively create a sophisticated listening environment known as the ‘Live End – Dead End’ (or LEDE) control room. The concept behind an LEDE room is to make the front half of the room almost completely damped down by heavy materials to keep the sound crisp and dry, but allow the rear half of the room to reflect sound in a relatively lively manner so as to represent a more natural listening environment. The human brain is capable of detecting that the reflected sound is coming from behind you, so you can still concentrate
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ACOUSTICS
Creatin g a bass trap: get stuffed.. stuf fed...
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This simple display can be cannibalised for u se as a bass trap – its size is ideal.
2
We discard the quarter shelves, turn t he unit sideways, and stuff it with four pillows.
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Then we simply leave it in the cor ner of the room. It’s OK to place things on top, such as this CD rack.
Lining a room with curt ains: and coverin covering g chi ldish wall wallpap paper.. er...
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Adjustable, sprung shower rails can be wedged between walls without marking them.
on the uncoloured sound in front of you. That’s the theory, anyway, and in practice this arrangement really does seem to work. It’s used in many top-flight recording studios around the world. Technically speaking, speaking, a true LEDE room would typically include a hard floor covering on at least part of the rear section of the room, but at home, with a parallelfacing floor and ceiling, this might cause more problems than it solves. To further cut costs, you don’t even need to use full-height curtains. An adequate length of curtain hanging at ear-level at your normal listening position may be all that is required, although it is obviously more desirable to have a room where the sound remains consistent regardless of whether you are sitting or standing, and the less curtain you use, the less absorption you will achieve. Finally,, in order to stop the room sounding as dead Finally as an anechoic chamber, we need to create a diffusion or scatter wall to create complex secondary reflections at the back of the room. Custom designed diffusion walls are extremely expensive. However, most homes (and that could include yours) already feature a scatter
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Tabbed curtains or similar material is simply hung from the railings.
wall even though you don’t know it yet – it’s our old friend the bookcase again! Bookshelves and bookcases are a remarkable boon if you want to get a good-sounding room. Firstly, they help break up a square or rectangular room, and – more importantly in this case – they create a pseudorandom hard surface that causes high frequencies to scatter on impact into many directions at once. This is exactly the kind of behaviour we want. You don’t need a floor-to-ceiling covering of books (although there’s no harm in that). All that is needed is a decent wall covering of books at ear level to diffuse the sound. The more random the surface of books, the better, so it’s time to get your books disorganised and mix them up as much as possible so big and small books intermingle in unpredictable ways. The ideal placement for your scatter wall of books is across the back of the ro om, although there is no harm in having them down the sides as well. They should be ideally positioned behind your normal listening position though, so that sound from the monitor speakers bouncing off them hits the back wall before reaching your ears.
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A roof beam can bridge the gap between two curtain rails, or you can use a tall cabinet, as shown here.
Grand designs As we’ve seen, probably the most versatile piece of furniture you can place in your studio room is one or more tall bookcases. The lower shelves can be stuffed with pillows to act as a bass trap, the middle shelves can be stocked with books of random sizes to act as a diffuser wall, and the top shelves can be used, well, as actual shelves to place your bits and pieces on. But remember that before starting the process o f renovating your room, it’s best to design it on paper and make sure you can get ever ything you need within your budget (and within the physical space, too). Test the sound of the room thoroughly by listening to several well-known recordings before even starting to make changes, so you know exactly which of the problems we’ve discussed apply to your room. Keep checking as you go along to find out how well you’re progressing. You’lll be surprised at how dramatically the sound You’l of the room improves as a result of the simple changes we’ve described. And best of all, if you’ve got a well-stocked home, you might be able to do it without spending a single penny.
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