Studio Acoustics Explained – This is what you need to know!


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Studio Acoustics

How and why does sound move around your studio?  Howard Turner from Studio Wizard explains some theories about sound, and looks at the basic techniques that can be used in any studio to create a great sounding room.

Most of us in the music business have a pretty good grasp of how sound behaves and what that means to us as musicians and recording engineers. We can manipulate sound in a PC or via a desk, but what about when it comes to physically manipulating the sound in a room?  Or perhaps trying to stop the sound travelling from one area to another?  That’s a whole new ball game.

Lets clear something up.  These two issues are not one and the same thing.

Trying to make a studio sound good and easy to mix in:  that’s best described as  ‘room acoustics

Ensuring you don’t keep the neighbours awake whilst tracking / mixing:  that’s ‘isolation’.  They may be related, but they are entirely separate matters physically.  Once you’ve ‘isolated’ and trapped all the sound inside a room; it’s going to rattle around in there and sound awful unless you do something about the ‘room acoustics’.


For anyone with a studio, isolation is probably the first of these to occur to them, as the studio gets busier – and louder (or indeed if your neighbour suddenly decides to join in with some DIY hammering and drilling when you’re in the middle of some important vocal parts!).  So what’s to be done?

The tools available to you are just the same whether you are a multi-million pound pro facility, or a bedroom studio.

Firstly we need to stop sound travelling in or out through the air – so we need to make the room airtight.  Lets seal up all the air holes, put good seals on the doors and windows.  This is very important – knock a one-inch air hole in a 60dB isolation wall and you’ll discover that it has suddenly become a 20dB wall!  It really does make that much difference, so hunt out every crack and get busy with the filler.

Secondly we need to make sure that the walls/floor/ceiling/doors/windows are stiff enough that they don’t vibrate and transmit sound through them.  Now it starts to get a bit trickier:  we’re into double glazing windows, fitting double ‘soundlock’ entry doors and increasing mass by adding extra layers of plasterboard to walls etc.

These two are easy enough to achieve, and will get rid of most mid and high frequency leakage but the third tool at our disposal is the real key to successful wide band isolation, and the hardest to achieve:  Decouple the noisy room from the rest of the building.  This entails building an entirely separate ‘floating room’ – incorporating elements of the first two criteria – which is not fixed to the existing structure whatsoever, and sits upon some bouncy material (such as Rockwool) to keep it isolated even from the floor.

If we’ve done the best we can with the existing structure in terms of air-tightness and rigidity, and then we drop a floating room inside it, we can achieve startling levels of isolation, even at low frequencies.  Just remember that it’s going to be air tight, and probably the best insulated room you’ve ever seen.  So if something isn’t done about ventilation and cooling, it’s a gamble to see whether you suffocate before you cook!

Carry that weight.

Before you try this at home, do note that even a small bedroom-sized floating room will weigh the best part of a metric tonne, so make sure that a structural engineer has checked the floor it’s to stand on to make sure your upstairs studio doesn’t suddenly arrive downstairs…

Shape & Design.

Ok, so the floating room is in – and it sounds awful!  What went wrong?

Well nothing – if you stop all the sound getting out, then it’s just going to rattle around in the room, meaning that we now have to do some serious manipulation of the room’s internal acoustics to get us back to a ‘normal’ sounding room.

Before we start to add acoustic treatments to the room, there are three factors we can take into account in the design of the room shape that will help.

Firstly we can make sure that none of the surfaces are parallel – including floor-to-ceiling.  There are three frequencies that a room will resonate at, which correspond to the length, width and height.  These are the ‘axial modes’.  Now if a pair of surfaces is absolutely parallel, they will ring at exactly one frequency.  Should the surfaces be offset by around 5 degrees or more, rather than producing a distinct note, they will just produce a ‘lump’ in the bass response; and you can knock that out with a ‘bass trap’.

Secondly we can look at the infamous ‘Bolt Graph’ and see if we can make the dimensions of our floating room fall within the Bolt Area.

The Bolt Area.  This graph illustrates room ratios of length to width when height = 1.

Rooms whose ratios fall within the shaded area will exhibit a favourably uniform distribution of modal frequencies ie: the bottom end will be less lumpy…

Bolt assumes our room will be rectangular, but rest assured, applying a 5-degree offset to a Bolt room will further help improve diffusion and axial mode problems.  Sadly, very few real rooms will fit into the Bolt area; so don’t fret if you can’t squeeze into that shaded blob.  Just make sure you aren’t going the other way and building a perfect cube, where all the axial modes will club together to create the mother of all bass resonances at just one centre frequency!

Thirdly, we can look at the layout of the room internally; at this point we are largely interested in the symmetry of the room from the monitors to the engineers ears, and mating this symmetry with an ergonomically useable layout.  I will deal with the symmetry issue in the next section, but this further illustrates how the design of a control room needs to constantly balance the competing needs of isolation, acoustics and ergonomics; after all there’s no point in having a quiet, great sounding room, if you can’t reach the gear to work in it!

Room Acoustics.

Our aim is simply to create a room whose characteristic sound we understand almost instinctively.  Hardly surprisingly, it appears that the sort of room we understand is one whose sound characteristics closely ape those of an idealised domestic sitting room.  In brief this will entail a shortish reverb (or RT60) time (typically in the RT60 range of 0.15 to 0.35 sec)  in the midrange.  It is considered acceptable for high frequency RT60 to be reduced by up to 50 percent from this figure, and also for Bass RT60 to climb to 120 percent of this figure at 125hz and even up to 180 percent at 63Hz.

Just how a nomad who grew up in a tent (Reverb: non-existent) will relate to such a room design I don’t know, but it does generally seem to work for the rest of us.  When I build a control room the best compliment I can get is someone saying ‘Well it sounds just like any other control room’; then I know I got it right!

Now back to the floating room.  You’re about to chuck a load of gear and furniture – almost all of which is comprised of hard surfaces – into a room where the reverb time is already too long by virtue of having stopped all the sound getting out.  Consequently in order to mimic the ‘sound’ of a domestic room, we are going to have to introduce a serious amount of ‘soft stuff’ (generally some grade of Rockwool tm covered by hessian) to absorb higher frequencies and mimic the effect of carpet, sofas and curtains, along with some tuned resonant bass traps to level out any bumps in the LF response and others to generally absorb the bass in the same way as the windows, doors and ceiling etc were before we stopped them.

Good reflections (and bad ones).

We also want to provide a symmetrical acoustic environment from the speakers to the engineers ears.  Why?  Well for example if there’s a window one side, then to the engineer the speaker that side will seem to be ‘brighter’ by virtue of the extra reflected sound coming off the window.  Hence all the mixes done in that room will sound ‘toppy’ on the other side, as the engineer unconsciously compensates for the room imbalance.   A large void to one side will produce the reverse effect.

The reason reflections are bad news off the side walls is due to the Haas effect.  Sound from a speaker bouncing off a wall to get to you has a longer path to travel than the direct sound from the speaker.  However, Hass discovered that unless this early reflection path is long enough to introduce a delay of over 50msec (which it never is) then the listener’s brain will not identify it as a reflection, but as part of the original sound.  Hence the perceived increase in top in the example above.  Also in stereo placement Haas has implications, as the tweeter now appears to be a wide smear of sound stretching from the tweeter to the point the sound reflected off the wall – in other words, you’ll be lucky to merely identify if sound sources are left, right, or centre in such a room, accurate stereo placement would be impossible.

Typical Small Studio Layout showing offset walls, & a symmetrical monitoring environment.

So, the front end of the room will be pretty much all soft trapped for highs and mids.  In the past the tendency was to let the rear of the room ‘liven up’ a bit so as not to end up with too short a RT60, but the advent of 5.1 monitoring requires that the rear speakers also are free from early reflections, so control rooms are consequently tending to sound a little deader at the back than they used to.

Bass Traps.

These come in two flavours: tuned and general.  The tuned ones are designed to knock out any specific ‘lumps’ in the low frequency response the room exhibits.  The general ones are there to absorb bass over a wide range of frequencies and help the low end reverb time of the room return to a suitable low figure.

There are many complex and elegant trap designs in existence, but lets look at two simple ones.

Absorbent Traps.  Basically just a lot of Rockwool or foam.  And when I say a lot I mean it!  If you want to make an effective bass trap centred at 50Hz, then you will be building a trap of solid Rockwool 22 feet deep!  Now that’s not feasible in the real world.  You might also like to ponder on the efficacy of some of the foam ‘bass traps’ currently on the market that are generally about 2 feet deep, ie with a centre frequency of only 550Hz!  Better build your own!

A Limp Membrane Tuned Bass Trap.  A series of these will typically cover the majority of the rear wall of a studio.

Tuned ‘Limp Membrane’ Traps.  Works a bit like a drum.  A flexible membrane (usually plywood) at the front of a solid heavy box resonates centred on a frequency determined by the mass/sq metre of the ply and the depth of the box.  100mm or so of Rockwool at the back of the trap does the absorbing for us.  A 50Hz trap to this design would be around 450mm deep – that’s more like it!

A General Bass Trap.  A pair of these will usually be positioned in the corners facing the main monitors.

Add more Rockwool, and the trap sucks harder, but at less of a specific frequency (a bit like turning the ‘q’ down on a parametric eq).  So if we build the trap in a corner (where the depth varies) and fill it full of Rockwool, then it is now a ‘General’ bass trap, absorbing all low frequencies.

Building Regulations.

As of this July an important new set of building regulations has come into force.  Called Building Bulletin 93, this regulation has to do with acoustics in schools, but in the process it lays down specific strict criteria for the acoustic performance and isolation of recording studios in schools.  This set of specs can be a useful benchmark to aim at if you are building a studio yourself.  Note that currently the vast majority of educational studios do not meet these specifications, a situation which many schools and colleges are unaware of – so don’t be tempted to copy their designs!  Theoretically such studios could be subject to enforcement if found to fail to meet the criteria.  Expect the quality of educational studios to start to improve over the next few years!

And in summary.

So, there you have it.  How to build a studio?  Of course not!  In an article such as this I can only scratch the surface of such a complex subject, but hopefully I have given you some insight, and unravelled a few myths along the way.

If you are about to embark on a studio build yourself, make sure you are fully aware of your construction methods and also fully understand why you are following those specific techniques.  Sadly without the right build methods, it is possible to use all the right materials and get no effective result whatsoever.  Call a specialist studio consultant if you are in any doubt.  Also if there are any heavy construction elements in your studio design, make sure you have enlisted the help of a competent architect and/or structural engineer.



More Information.


Master Handbook of Acoustics, F. Alton Everest, McGraw Hill. ISBN 0-07-136097-2

Building Bulletin 93, HMSO, 2003.

Sound Engineers Pocket Book, M. Talbot-Smith, Focal Press. ISBN 0-240-51612-5

Acoustics and Psychoacoustics, D. Howard & J. Angus, Focal Press ISBN 0-240-51428-9

The Author.

Howard Turner has over 30 years experience in the studio business, and for the last two decades his Studio Wizard Organisation has allowed him to stop shouting at musicians and going to sleep on the mixing desk all of the time, instead he gets to design studios and shout at builders for a change…  Further information:  +447803 666789 web:

Tech Terms.

RT60:  The time taken for the level of reverberation to fall to 60 decibels below it’s peak level.

Axial Mode:  The resonant note created by two parallel surfaces.

dBa:  A decibel measurement scale commonly used in the building industry.  This scale is heavily weighted towards the frequencies of human speech.  Consequently manufacturers acoustic specs on building materials are usually only good for this limited midrange bandwidth.  As a result, the published figure for a standard wall construction might look good on paper, but when you fire a kick drum at it it’ll probably go through it like it wasn’t there.

dBc  The scale we wish everyone used!  This is unweighted; ie it measures accurately at all audible frequencies.

The myth of the eggboxes.

Materials that absorb sound actually allow the vibrating air into their structure, where the molecules collide with the absorbent material, converting the sound energy into heat energy.  Hence stiff, hairy Rockwool and dense open cell foam (the sort you can blow through) both fit the bill as suitable absorbing materials.

What matters is the thickness of the soft stuff.  If we are generous and say that the lowest frequency a material is absorbing effectively at is one with a wavelength 8 times the materials thickness (1/8th wave) then we can see that 50mm of Rockwool will be effective down to around 850Hz  (divide speed of sound in air: 340m/s by thickness in metres x8:  ie 340/0.4=850); not bad.

On the other hand carpet (thickness 6mm) runs out of steam at 7kHz, and egg boxes (thickness 3mm) are useless below 14kHz!  Forget about them as treatment materials!

NC Curves.

Studio gear is getting noisier.  Fans and hard-drives make it harder than ever to achieve the sort of quiet we need to be able to monitor effectively, or self-op a vocal or acoustic instrument in the control room.  The accepted way of defining noise is by NC curves (illustrated above).  The NC measurement of a room is the curve which the background noise never exceeds.  We should expect to find NC20-25 in a control room, NC15-20 in a live room and as little as NC5-10 in a voice over booth.  With a noisy PC and a fan cooled desk, you’ll be struggling to make NC45-50!  So; you monitor loud to hear the detail over the background noise, your ears get tired, you get deaf and your neighbours get tetchy.  Time to build some silenced cabinets! (but that’s another story)…

Yes chaps – It’s official – It’s Snake Oil.


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So, do commercially available soft bass traps work?

Today I visited a client who had purchased £500 worth of soft material bass traps from a ‘reputable’ company.  Each was around 600mm x 1200mm – 3 traps in total.


These traps were advertised to have function in the range of 40-600Hz, but as we can see, they have no significant function below 500Hz.  Bearing in mind that a room will generally need to see corrections of greater than 3dB (otherwise, why would the operator even notice it was wrong?), then the fact that these alleged ‘wide range’ traps are only capable of occasional 3dB changes over very narrow bands in the top of the LF range shows that effectively these traps DO NOTHING to the sound of the room.

Before we tested we removed an old double mattress from the back of the room – I’d put money on the fact that that old mattress was absorbing more bass than these flimsy little traps!

So there you have it – the King is wearing no clothes, and the Studio Wizard told you first.

I’ll be loving the comments on here when they come!  ht

About the Author:

Howard Turner has over 30 years experience in the studio business, and for the last 2 decades, his Studio Wizard Organisation have been at the forefront of the development of effective & affordable designs and solutions for studios.  We design and troubleshoot studios worldwide.  Further information:  +44(0)7803666789 web:


Monitors and Mixing – Are you hearing the truth? Lend me your ears…


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Your monitors want to tell you something – but are you listening – and more to the point – is it the truth?  Howard hacks through the monitoring myths to help you hear what’s really happening.

Your monitor speakers are the most important investment you can make in your studio.  Really.  Bar none.  They are what let you judge your material; they are your quality control.

I’ve heard stunning recordings done on a cassette 4 track – with decent monitors attached.  And I’ve heard the results of hundreds of thousands of pounds of gear and time ruined by reliance upon rough, or badly installed, monitoring.

It can be ProTools or an Edisonwax cylinder, Nuendo or Logic, but if you can’t hear what’s going on, then you’re up, as the German’s call it, ‘Scheissen Strasse’…

Studio Monitor or HiFi Speaker?

First of all, lets get one thing straight.  Studio Monitors and HiFi speakers have very little in common other than being made of (mostly) wood and having wobbly plastic bits on the front.  A HiFi speaker is usually built to the following brief; it must be:

  • Flattering to the programme material – hide shortcomings.
  • Sound rich and full (so it uses harmonic ‘tricks’ to make things sound good and to extend the apparent bass response).
  • Be cheap to produce.

It also is never expected to have to playback anything other than nice, mixed, compressed finished material – no solo’d kick drums here!

As a result your average 100w RMS HiFi box has a tweeter rated at (if you’re lucky) 3 or 4 watts.  This is going to burn out the first time a decent lump of feedback or high square-wavy synth is chucked at it!  Also it was never designed to be run at anything like rated power for more than a few minutes at a time.

Your studio monitor is a different beast altogether, it’s design brief is to:

  • Tell the truth, even when it’s painful.
  • Show up every bit of programme distortion.
  • Deliver accurate bass within the constraints of the cabinet size.
  • Be able to survive feedback and high transient impulse noise.
  • Be capable of running at rated full power for extended periods.

It’s also likely to have a minimum of a 50 watt tweeter in a 100 watt speaker.

By making everything sound ‘nice’ the HiFi speaker is making mixing almost impossible.  And it’s going to blow up.

Now that those Japanese hifi wonders are safely in the dustbin, what sort of studio monitors are going to be best for you?

Nowadays, there are almost as many new manufacturers making monitors as there are  producing microphones, and inevitably, some are great, some are not so great, and a few are little more than horrid HiFi speakers in disguise;  beware!  Buy with your ears…

Get active.

Monitor speakers can be divided up in two different ways, firstly there are either 2 driver and 3 driver (or more) systems, secondly, but possibly even more importantly, there are either active or passive speaker systems.

Unless a speaker is tiny (and therefore very quiet) it is impossible to manufacture a single speaker capable of producing the raw energy required for bass reproduction (the cone needs to move a long way) and the fast changes of direction required for treble (transient) reproduction.  Consequently speakers come with different drivers each coping with a small part of the frequency range, a great idea until we try to cope with managing how just the right part of the frequency spectrum goes to each driver.

Passive systems take a speaker level feed from a separate power amplifier.  The signal is then split by a passive (unpowered) crossover to (hopefully) feed the right bits of the signal to each driver.  As the whole splitting thing in a passive speaker is done with high(ish) voltage, high(ish) current speaker level signals, then the technology is of necessity crude and almost Victorian – all coils, fat capacitors and big wire resistors – impressive, but none too subtle when it comes to fine tuning the speaker to the room…

A ‘proper’ active system splits the signal at line (mixer) levels, with a great degree of finesse – the split signal is then sent to several dedicated amps each working with, designed for, and damping, it’s own driver.  Accurate crossover control is therefore available with small line level signals easily being manipulated much like the signals in a mixer, and a good match to the room is easily achievable.  Sadly a lot of passive speaker manufacturers have jumped on the active bandwagon by bolting an amp on the back of a passively crossed over speaker and calling it active – beware!  If it hasn’t got an amp per driver – it’s not active – it’s a passive design in drag!

All those Drivers

The driver issue is one that also has great influence on the output of our studios.  We are all used to the sound of domestic 2 driver speakers, which, as they crossover the sound between the woofer and tweeter at around 2 kHz, are consequently distorting the sound at this point, causing a blip in the frequency response curve right at the critical point where lies the bite of the snare, the rasp of the vocal, and the snarl of the guitar etc.  As a result it is easy to overcook these things on a 2-driver system, resulting in mixes that are painful to listen to on car hifi, pa systems and the like.  A 3-driver system with a midrange driver dedicated to these critical frequencies creates two crossover points one above and one below the critical 1-2kHz region, giving a more faithful reproduction of the important speech frequencies.  This may well sound over-middly at first (to our ‘2 driver’ ears).   We need to ‘unlearn’ the conditioning of listening to 2 drivers and start to listen to these 3 driver systems as though we are in the room with the musicians.  Once you have acquired this ability – the difference in perception is astounding!


A natural extension of a multi driver system is to dedicate a speaker and amp to the frequencies that are too low for the main cabinets to handle – this is a Subwoofer, and (owing to the fact that we have a hard time telling where bass noise is coming from) this should be capable of being situated anywhere in the room.  Realistically, the Sub still produces frequencies that yield some positional information, so sticking it anywhere is an old wives tale – you’ll need to place it centrally and at the front.  With the advent of 5.1 surround monitoring systems, the sub has been pressed into use carrying the ‘FX’ or ‘earthquake’ information too, placing additional constraints on sub placement.   5.1 is a topic in itself, so discussion of surround monitoring will be the subject of another post in the future.

Amps & Cabling

If your speaker system is passive, or a big enough active system, then the amps (and in the case of the active system the crossovers too) will probably be mounted remotely in a rack somewhere.  This helps get rid of fan noise from big amps, but it also raises two more issues; amp power and speaker cabling.


If you buy amp(s) separately from a speaker system, make sure they are big enough.  In contradiction to the strange HiFi rule where the speakers should have twice the power rating of the amp, in studios we accept that the amp should have double the rating of the speakers!  This is because if the amp goes into distortion, the majority of the distorted signal will route to the tweeter – probably frying it in the process.  My old Phase Linear 400 pro amp from the early 70’s is 200watts RMS/channel, but when the meters read 0vu it’s pumping out just 45watts – the rest is headroom…



When the signal from an amp forces a bass driver forwards, it doesn’t want to stop when it gets to the other end of its travel.  The cone over-run generates a small electrical signal, which gets back to the amp, which in turn generates feedback to suppress this over-run.  If flimsy wires are used between amp and speaker, the resistance of the wires will hinder this damping, and the consequent cone overrun will make the bass sound muddy, so speaker cabling needs to be massive & low resistance.  I’m going to be shouted at for the next suggestion, but having done many technical and subjective tests over the years, I can confidently assure you that in most situations the best and most cost effective cable to use between an amp and a speaker is 2.5mmsq T&E solid ring main cable.  It ain’t sexy, but it’s cheap and it works brilliantly – in some cases noticeably better than some ‘audiophile’ products costing hugely more.

Stands & Soffits

When amps were weak, and speakers couldn’t handle the power, then the only way to get high volume at low frequencies was to ‘soffit’ mount the speakers actually in the monitor wall, which has the effect of lifting the bass end by some 6-9dB.  Individual monitor walls tended to colour the speaker such that consistent results were rare.  Nowadays this practice is only required in the largest and loudest pro studio installations.  Elsewhere speaker and amp designs are now more than capable of producing the bass we need without help.

What we do need, however, is to support the speaker rigidly.  If the room is well designed, then the speaker can be happily coupled to the room by a simple rigid, heavy stand; hollow timber filled with sand, a brick column or the like.  If the room is resonant or leaky, then spikes must be employed to cut down structure-born transmission of bass.


Old fashioned speakers with horn loaded tweeters were designed to focus all the HF information into a ‘sweet spot’ where you HAD to sit to make any sense of the sound, and to get a stereo image.  Engineers and producers used to have to fight to occupy that precious football-sized spot during a mix or a cut!  Luckily modern dome tweeter speakers are designed for a wide, even dispersion of sound, allowing everyone in the room to hear something (tonally) close to what’s happening in the sweet spot, even if they don’t get the stereo, and also creating a much larger sweet-spot to boot.

For stereo, there are some simple rules regarding placement that will ensure you make the most of your speakers:

1)  The speakers and listener should be at the 3 corners of an equilateral triangle.  If the speakers are too far apart you will have a ‘hole’ in the centre of the stereo image.  In fact with modern dome tweeters you can stretch this rule a bit.  In the diagram below you can see that domes produce a decent sized elliptical sweet spot, so by careful placement you can put the engineer at the front of the spot and make room for others to squeeze in behind for critical listening.

2) The ‘virtual source’ of the sound should be at ear height.  Yeah, but when you are standing or sitting?  If you only ever sit to mix, then around 1300mm is a reasonable height (measure the floor to your ears if you’re not sure).  If you mix a lot standing, then raise them up to an in-between compromise height (between 1500-1600mm for instance).

3) Keep the drivers vertically oriented to get the best stereo image.  I know you like the look of them when they’re on their sides, but you’ll get much better stereo if they’re upright – trust me!


Virtual Source.  A typical 2-driver monitor speaker in vertical orientation, showing the position of the virtual source (i.e. the position the sound appears to emanate from).  (Image courtesy of Genelec).


Stereo Monitor Placement.  Showing the equilateral triangle of placement and the elliptical ‘sweet-spot’.

Lend me your ears…

Finally, don’t forget that you never listen to your speakers alone.  You always listen to them in a room.  Consequently the design & layout of your control room can make, or ruin, the sound of your monitors.  If you get a chance to listen to some professionally designed rooms, you will see just what I mean!

About the Author:

Howard Turner has over 30 years experience in the studio business, and for the last 2 decades, his Studio Wizard Organisation have been at the forefront of the development of effective & affordable designs and solutions for studios.  We design and troubleshoot studios worldwide.  Further information:  +44(0)7803666789 web:

The drum sound you’ve always wanted! (Or how to get your drum mics in phase):


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Drum mic phasing is one of the lost arts of sound recording.  If all those mics on the kit are feeding ambient spill off the kit randomly out of phase, the consequent cancellation effects give rise to that characteristic ’sucked out’ demo drum sound.

Here’s how to avoid that and create vastly improved drum sounds:


1)   Pull up one overhead mic (doesn’t matter which) – this is the reference.  Get it levelled with the drummer playing round the kit and mute it.

2)   Pull up another mic (any) – get the drummer to play floor tom.  Set the level so that the floor tom volume is the same as the OH in 1).

3)   Unmute the OH and mono the mix. Keep the drummer playing floor tom.  You are now listening to the OH mic and the new mic with similar levels of floor tom in a mono mix.

4)   Switch the phase on the ‘new’ mic (not the OH) one way round there will be loads more bass content in the signal.  This is ‘in phase’ and correct.  Leave the new mic this way.

5)   Move on to the next mic comparing to the same overhead.

6)   Carry on like this til you get to the floor tom mic, when you will need to get the drummer to hit the kick drum instead.

7)   Having got the phasing right – return to the start and get the levels and eq right for all the mics.

8)   You are ready to roll tape!

The Author

Howard Turner has over 30 years experience in the studio business, and for the last 2 decades, his Studio Wizard Organisation have been at the forefront of the development of effective & affordable designs and solutions for studios.  Further information:  07092 123666 web:

The Mixing Desk – what you need to know to fly one…


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Mixers – Knob city or simple switches?  Howard Turner from Studio Wizard gets on the Busses…

Once upon a time everything was recorded in mono.  With one mic.  How simple was that?  A mic, a mic amp, a recorder.  Then someone in the 30’s decided that it sounded better if he also laid some close mics on the soloists to bring the solos up in the recording.  That meant some signals had to be mixed together, and the mixer as we know it was born.

History Repeating.

The earliest mixers had just two purposes;  1) They allowed you to introduce more than one input, and send them out to more than one destination.  So they had to ‘route’ signals.  2) They also allowed the relative levels of these multiple signals to be adjusted with ‘faders’ so that the output wasn’t too loud or quiet.

Oh, then someone decided that adjusting the frequency response of the signal might be a good idea and equalisation or ‘EQ’ was invented – although even in the days of the Beatles the EQ was a switch marked ‘pop’ or ‘classical’ – in classical mode the signal went straight through, in pop mode all frequencies above 5k were cut…

3 track Multitrack tape came along in the early 60’s and brought with it the concept of recording some signals whilst listening back to others, and the mixer started to look slightly like the ones we still see today, with sections dedicated to the functions it has to perform; inputs, groups and monitoring, each with identical controls for all the different in’s and out’s

The path is clear.

So there are two sound sources in a studio: the current live performance, and the stuff playing back from the recorder that has already been done.  There are also two destinations: the recorder to record the current performance as a ‘overdub’ on another track, and the main mix output, where engineer and performer get to listen to a rough approximation of the final result (the ‘monitor’ mix).

So the mixer is divided up thus:

The Input Section, where the inputs come in.

The Monitor section, where the pre-recorded parts are listened to.

The (sub)Group section, where signals are adjusted for level before they go off to the recorder.

The Master section, where the final mix output controls are lumped together with all the other bits of the mixer that haven’t got a home, like Control Room volume, Aux outputs etc…

Lets look at a simple desk layout –this desk has 3 inputs, 2 sends to tape, 2 tape monitors and a single mono output.

new diag 1

Diag 1.  A basic mixer. A format that carries on to this day and is still extensively modelled in software and digital products.

The long wires that the inputs and outputs feed their signal onto, or take their signal off of, are the ‘Busses’.  A name whose origins date back to the heavy metal ‘buss bars’ that went up and down the length of old industrial revolution factories.

The earliest desks had these sections split up in their layout, generally thus:

new diag 2

Diag 2. The ‘Split’ format mixer.  Easy to understand, but quite wasteful of space.


And here’s one we made earlier.  A rare example of a compact split format console the Allen & Heath Mix wizard 20-8-2 – clearly showing the separate sections for inputs, outputs, tape monitors etc, although the group faders have been omitted to save space. (photo courtesy


Big enough to sleep on!  Split consoles are so space-hungry that this type of design was generally used in large studio consoles, like the MTA980 here, although even here the in-line design is now king. (Photo courtesy

Not Fade Away.

We admitted earlier that performers may need to listen to a mix so different from that which the engineer has that a separate set of mix faders needs to be provided.  These produce a mix totally separate from that made by the engineer, the source of these signals is before the engineers’ faders and unaffected by their movement – this ‘Auxilliary’ mix is therefore before or ‘Pre’ Fader.

new diag 3

Diag 3. Pre-Fade.  The same mixer input channel with a pre-fader Auxiliary (usually on a knob, not a fader) for creating headphone monitor mixes. 

Great Aux

Another use for an auxiliary send would be to feed signals to a reverb or other time delay effect.  Now when we vary the level of the unaffected ‘dry’ signal with a fader, we expect the reverb for that signal to vary in proportion, so we need to pick up a feed for this sort of auxiliary send after (‘post’) the fader.

new diag 4

Diag 4. Post-Fade.  It’s that mixer again, with a post-fader Auxiliary option for feeding a fader-related signal to reverb and other associated effects.  On most desks today, some Aux’s are pre, some are post, and some can be switched either way…

Esoteric Insertions

Now auxiliaries are fine for ‘effects’ (i.e. things that take the original signal, mess with it and then are added to the mix via another mixer channel).  But what about signal processing that affects the whole signal?  Like a gate, or a compressor, or an external EQ?  Now here we need a mechanism by which we can effectively ‘insert’ an external processing box into the signal chain, by way of, unsurprisingly, an ‘insert point’.

new diag 5

Diag 5. Insert point.  Now we have a way to drop an external processor into the signal path, replacing the original signal with the processed version.  The insert is provided by either a pair of, or single, stereo, jack – specially wired to break the path when something is plugged in.  With nothing plugged, the signal passes uninterrupted.  Some big mixers offer insert points both pre and post EQ.  We have shown the most common position in an analogue desk – post.  It must be noted that in all digital desks, the analogue insert is before the A-D converters, and thus is pre-EQ.

The Levellers.

Lets pay a bit more attention to the input stage now.  As most of you probably know, the first choice facing you when plugging a signal into a mixer is: ‘mic’ or ‘line’?  The mixer will only work it’s best with a signal lying between quite distinct level (voltage) limits (see ‘Tech Terms’), so it’s the job of the input stage to boost or cut the input signal to match what the desk likes.  Most ‘line’ level signals (synths, outboard, recorders etc) have outputs pretty close to line, and only need a modicum of adjustment to meet with the mixers approval – these use the ‘line’ input setting to provide a small amount of trim.  Microphones on the other hand, have signal outputs a couple of powers of ten below line, and so need these tiny signals boosting heavily, and a separate specialist amp section is employed to achieve this high gain result.  At this stage you will probably also encounter a ‘Pad’ which will shift the gain window of either of these two input stages down by 20 dB (to avoid distortion with louder signals), and a phase reverse switch (more of which another time I’m sure!) which (briefly) makes sure that in multi-mic set-ups the mic signal waveforms are rising and falling in unison and not cancelling each other out.  Last but not least is the switch for microphone 48volt phantom power for condenser mics.

input stage

A typical mic input stage.  Showing all the controls mentioned above.

The Great God Pan

In all these illustrations we’ve been looking at mono signals for simplicity.  All you need to do to create a stereo mix buss is to have 2 busses; L & R and a pan pot to fade the signal between them.  A pan pot (that’s a potentiometer to you)  is basically 2 rotary faders ganged together, except one works backwards so that as one gets turned down, the other gets turned up.  In the middle they feed equal amounts to both L & R.

Do the Splits?

Thus far we’ve also just been looking at split format mixers – but they have a big disadvantage – size.  What if we incorporated input channel 1, group out 1, & monitor 1 all onto the same strip of metal?  This is called an ‘in-line’ mixer, and virtually all recording mixers now follow this format.  This makes the mixer around half the width and thus cheaper – and easier to work with too, once you have got your head round the fact that all the controls on each channel strip actually aren’t affecting the same signal path!  It also allows, for example, auxes and eq’s to be physically switched between the channel strips input and monitor signal paths, thus making the mixer more flexible and reducing the number of actual knobs on the desk.


An’ In-Line desk’  The MTA 924 inline console featuring 24 fully specified channels and monitors –  all in an amazingly compact frame.  (Photo courtesy

 sol module

An In-Line channel-strip  The Soundtracs Solitaire in-line input channel in detail, showing all the different sections we have talked about combined in an in-line channel – note that a group output trim control is missing – a common omission in in-line designs. (Picture courtesy



























The Telephone Exchange

As a mixer is essentially an overgrown set of switches, it is not surprising that in order to give the routing of signals maximum flexibility it incorporates a patch bay.  This large array of identical jacks is effectively the sockets on the back of every single item of gear in the studio brought up into one place where experimentation with routing can be achieved without any crawling around the back of things.  It also creates a stable grounding environment regardless of how the gear is actually plugged up.  Without it, experimentation is awkward and the consequent unstable earthing of the studio is just inviting interference and noise.


A patchbay beside a TL Audio VTC at Bath Spa University.

Digital Mixers

Whilst we have been talking about analogue mixers so far, pretty much all of what has been said applies to digital consoles too.  Why?  Well because so far all digital consoles have been designed to model the internal architecture of the analogue desks that preceded them.  This made good sense, as engineers didn’t have to learn a new architecture.  Indeed once you have got your head round analogue console architecture, the inner workings of your 02r or whatever seem an awful lot less complicated, and the way that you can program changes to the internal architecture of digital desks reveals their true power.

Of course, digital desks ape analogue ones ‘so far’.  Because it can only be a matter of time before someone with no previous analogue desk knowledge gets to design a digital desk whose architecture is driven only by the designers’ own creative experience.  The first of this breed may be poorly received, if only because our previous experience of traditional desks is no longer applicable and indeed hinders our ability to work on such consoles, but to some, these new desks may well be the key to unlocking their creativity.  We await developments…


Every desk will have it’s own quirks in the nature of it’s function, so this article is not intended to be a short-form manual for your desk.  What it is, however, is an introduction to the underlying signal structure that exists in any mixer design, be it analogue, digital, or even virtual in your PC!  Once you can sit there with your eyes closed and visualise every wire and connection, then the gear will never get in the way of your creativity ever again.

Some light reading:

Sound Recording Practice – Fourth Edition, J Borwick Ed., APRS/Oxford University Press 1994. ISBN 0-19-816381-9

Modern Recording Techniques, D M Huber & R E Runstein, Focal Press ISBN0-240-80308-6

Sound Engineers Pocket Book, M. Talbot-Smith, Focal Press. ISBN 0-240-51612-5


Tech Terms

Line Level – When the meters on a desk read 0 (or as we call it 0Vu – that’s ‘volume units’ by the way) then you can be pretty sure that the voltage on the line will be at one of two standard voltages.

+4dBm: The old pro standard that most gear with jacks and xlr’s uses is what we call +4dBm; there’s a long winded historical reason why we ended up with this standard that we won’t go into here – suffice to say that on this scale 0Vu = approx 1.25volts RMS (ie 4dB more than 0dBm which is .775vRMS)

-10dBv:  A semi pro standard you find generally in things that have phono (RCA) plugs on them like hi-fi etc.  This is based on dBv standard where 0dBv=1vRMS, but in this case when the meters on the gear read 0vu, the actual signal level is tiny; 0Vu= approx 0.3vRMS, (ie 10dB less than 0dBv)

The –10 standard has been designed to allow cheap low voltage power supplies and even 9v battery power to be used in the equipment (if you think about it, it’s obvious that the signal peak-to-peak voltage has to be less than the power supply voltage, so low psu voltages can only sustain low voltage signals without distortion).  The payoff in this case is that the signal level is some 12dB lower than in +4 pro gear (so they have difficulty communicating with each other without generating either noise or distortion) the noise floor on –10 stuff  is 12dB poorer in theory (and probably even worse in practice) than the pro stuff.  Try not to mix the two in your studio – it’ll always cause trouble somewhere ‘down the line’…

Effects – Reverb, Echo, Delay, Harmoniser etc – generally all ‘time delay’ derived effects.  These take the signal, mess with it and then you add a little of this into the mix to augment the original ‘dry’ signal.  These will be fed from a post fader Auxiliary and returned down a separate channel input or effects return (which is just a crude input with less options than the main ones).

Processors – Compressors, Gates, Eq’s etc.  These affect the whole signal i.e. the processed signal replaces the original.  These are put into the signal chain via an Insert point.

About the author

Howard Turner has over 30 years experience in the studio business, and for the last two decades his Studio Wizard Organisation has allowed him to stop shouting at musicians and going to sleep on the mixing desk all of the time, instead he gets to design studios and shout at builders for a change…  Further information:  07092 123666 web:

Criteria for the design of isolated studio rooms. A layman’s guide.


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The studio rooms should be sufficiently acoustically isolated from each other and the surrounding non-studio spaces that use of one space is not compromised by noise emitting from another.  In the building of suitable rooms, isolation is on a sliding scale dependent on the techniques employed, however there is a sizeable jump in the level of isolation available (especially at lower frequencies) when room-in-room construction techniques are used which drastically cut structure-borne noise transmission.  As a result the method of creating such isolation structures is not one that lends itself to cost-cutting.

OA aerial


Having trapped all sound within each of the recording rooms, such sound (which in normal rooms escapes from windows, doors, ceilings etc.), rattles around the room, producing a cacophony of reverberation, rendering the room useless for any acoustic purpose.  As a result, acoustic trapping must be applied to bring the internal ‘sound’ of the room back to ‘normal’ i.e. the reverb times across the frequency spectrum must be adjusted to a figure generally considered acceptable for the purpose for which the room is to be used.

The internal acoustics of control rooms will further be refined to produce an exceptional stereo imaging from the monitor speakers, allowing the engineer to hear the results of his/her endeavours as free as possible from room artefacts.  This is taken a stage further in 5.1 ‘surround’ rooms, where surround sound imaging must be stable from all directions, not just the front of the room, and where there has to be an allowance for the presence of (at various times) unused surround speakers acting as unwanted tuned absorbers.

Typically, Control rooms will have a ‘flat’ frequency response, with a reverb time consistent across the frequency range that is slightly shorter than the typical domestic environment.  In contrast, recording spaces will vary depending on the purpose for which they are to be used.  Indeed the recording engineer uses the ‘sound’ of spaces as part of the palette of sound ‘colours’ with which he/she ‘paints’ a recording.  The net result of this is that a good studio usually contains a range of different sounding acoustic spaces from which the engineer can choose.  These will range from near anechoic (vocals, acoustic guitar), to heavily reverberant (drums, choirs, and again – acoustic guitar!).


The isolation shells will reduce the internal size of the rooms, so special attention has to be paid to the ergonomics of the rooms and the utilisation of space so as to maximise the working area.  This is best served by careful design of the space allied with furniture designed to fit the room rather than off-the-shelf free-standing furniture.


The listening environment must be essentially quiet so that monitor speaker levels do not have to be turned up high in order to listen ‘over’ the background noise (Such practices result in listener fatigue and shorter critical attention spans when mixing).

In a recording room, where microphones are used, the problem is even more critical.

As a result, unwanted noise sources within the room (e.g. Computers, a/c etc) must either be removed or neutralised (acoustic cabinets etc.).


An isolated room is by it’s very nature totally airtight, fresh air ventilation is a must as the oxygen / CO2 balance in the rooms will otherwise soon change, leading to headaches, reduced attention span and worse…..

Also, isolated rooms are heavily heat-insulated, as the Rockwool used for sound trapping is similar to that used to heat-insulate houses.  This – combined with the not insignificant amount of heat generated by the audio equipment means that air-conditioning is an essential.  Indeed, even in cold climates such as the UK, most studio a/c systems are cooling (rather than heating) their spaces even in mid winter.

The background noise criteria mentioned above, mean that un-silenced ventilation, normal ducted, or on-the-wall ‘cassette’ a/c systems, are completely unsuitable for studio use.  The correct way to ventilate and condition is to use an inherently quiet ducted split a/c unit, which introduces a percentage of fresh air in each cycle.  This must then be passed through critically mounted custom silencers (commercial silencers are not up to the job).  These silencers stop ingress and egress of external and a/c noise, and also allow more than one room to be fed by the unit without excessively compromising the isolation.


Whilst there are no specific regulations for commercial audio facilities, the new BB93 for acoustics in schools came into force in July 2003, and, whilst (as far as I am aware) this is only applicable if studios have regular use teaching children of school age, the criteria contained therein form a suitable base specification to which all studio projects should aspire as a bare minimum specification for a workable facility.

Many of the educational facilities for which we design studios are not, in fact, schools as defined in the Building Regulations.  Universities, Colleges of Further Education and some sixth-form colleges do not have to comply with BB93.   But by publishing, for the first time, definitive standards for studios in schools, the DfES has set a standard, which even those institutions should consider.  Anyone designing a studio for a College or University to a lesser standard than that required for a school should, at the very least, be able to give a good reason for this.  Ignorance of the criteria in BB93 will probably not be considered a valid excuse if at a later date it is found that the studios fall within the remit of the regulations.

The Author

Howard Turner has over 30 years experience in the studio business, and for the last 2 decades, his Studio Wizard Organisation have been at the forefront of the development of effective & affordable designs and solutions for studios.  Further information:  +44 7803 666789 web:

Regulation of Sound – Studios in Schools


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When is a recording studio not a recording studio?  When it’s a bog-standard classroom with some gear in!  Howard Turner from Studio Wizard looks at what it takes to make a proper educational audio facility, and how recent regulations should have spelt the end for shoddy school studios.

If your PE teacher was given a swimming pool full of mud, and told that this was the ‘new purpose built facility for gymnastics’, you’d probably forgive that colleague for getting more than a little upset!  However at the commencement of each term, we get calls from schools and colleges where equally inappropriate spaces have been foisted on Music Departments claiming to be ‘Recording Studios’.  We know it’s wrong, you know it’s wrong, and now the government have given us the means to do something about it!

Since July 2003, new approved Document E of Building Regulations came into force.  Since then, all new school facilities must meet strict standards for noise levels, sound insulation and room acoustics.  These standards are set out in DfES Building Bulletin 93 “Acoustic Design of Schools” and cover all areas of schools, including music & drama facilities, and in great detail, recording studios & control rooms.  If your school is planning a recording facility, you need to know about this, as a non-compliant facility could be forced to close!

Adrian James, one of the handful of specialist acousticians who contributed to the contents of BB93 describes it thus:  “BB93 is a unique document which has to fulfil the roles both of a regulatory document and of a design guide.”  “It contains a wealth of data, advice and examples covering all aspects of acoustics in schools” he adds, but stresses that the regulations are far from a textbook on studio design and that “specialised facilities such as studios really require input from an experienced consultant.”

A typical commercial ‘home studio’ facility.

Colours of Sound

So, what is so important about studio acoustics?  Well, every sound we hear is coloured by the environment in which we hear it.  We all know that for an art space to work (be it painters’ studio or gallery) the lighting has to be balanced and neutral so that the eye can perceive the subject and/or picture.

By the same token, the sonic qualities of a studio control room must be understandable and neutral.  Our aim is simply to create a room whose characteristic sound we understand almost instinctively.  Hardly surprisingly, it appears that the sort of room we understand is one whose sound characteristics closely ape those of an idealised domestic sitting room.  Add to this a need to exclude distracting background noises and stop our endeavours affecting the occupants of adjacent rooms and we have described the basic criteria; Room Acoustics and Isolation.  These two issues are not one and the same.  In fact one makes the other worse.  Once you’ve ‘Isolated’ and trapped all the sound inside a room; it’s going to rattle around in there and sound awful unless you do something about the ‘Room Acoustics’.  After all, if we cannot understand what is coming out of those speakers, how can we hope to balance the instruments and vocals in a mix, with the room forcing some to the fore, and masking others?  Similarly, how can we demonstrate manipulation of sound when each listener in the room is hearing something different?

So, control rooms have to have a standardised acoustic in terms of reverberation & background noise (from outside and from ventilation), and out of respect for our neighbours we have to keep our sonic excesses in.  Live recording spaces might by contrast benefit from a variety of acoustics ‘colours’, however the issue of control of noise ingress and egress is even more to the fore.

A virtual overview of an educational facility.  One room stereo, the other 5.1 surround.

A Bluffers Guide to Studio Building.

So, your institution has a grand plan to provide a studio facility – the pictures will look great on the prospectus. But how can you be sure that they have recruited the right team to design and build it?

Well almost without exception, if the design/build team chosen are a local architect and conventional builder, they will not have the skills to create a workable facility – large parts of their training teach them ‘unbreakable golden rules’ which must be broken in order to create a studio.  If they have not got a studio acoustic consultant on board supervising (not any old noise consultant, but a bona fide studio specialist) then certainly the project is doomed.

If you are offered a pre-fab for your studio complex, it will be incapable of providing compliant studio isolation and noise control unless conventional studio techniques are used inside, with the pre-fab just keeping the rain out.

Tender Trap

Building tender processes, common on school projects, are based around setting up an adversarial relationship between designer and builder, whereas in the studio world, each designer has pet ‘teams’; who understand his/her designs and will build them appropriately, cooperating closely with the designer at all stages.  Competently defined tender documentation is essential if the process is not to end in tears!

Warning Signs

Common misconceptions abound in the architecture & building world, ranging from the; ‘oh you’ll need a lot of egg boxes then’ (no we won’t!), to the horrifyingly common belief that there are magic forms of plasterboard or soft foam that stop all sound passing when you stick them to the walls.  Sadly, these mythical treatment items are quite commonly brought into conversation by otherwise sane and competent professionals.  Part of the problem is that a lot of common building materials have published noise reduction figures that seem quite high, but beware – these published figures are measured only at the frequencies of human speech.  Shout at a bit of plasterboard and hardly anything will get through it, fire a big bass drum at it and it’ll go through like the board isn’t there…

A surround sound teaching control room NSAD Norwich.

How to Spot a Lemon:

The architect has done some impressive pictures, but is that a super studio or sad shambles on the table before you?  Some questions to answer:

Are there drawings of isolated ‘rooms within room’ designs?

Are the walls, floors & ceilings at an angle to each other, i.e. non-parallel?

Has the designer drawn in the orientation of the equipment (especially the monitor speakers)?

Is the end of the room with the speakers in it symmetrically laid out?

Are there only soft surfaces on the walls beside the speakers?

Are there indications of acoustic treatments on all surfaces, including ‘bass traps’?

Are there reverb times specified across different frequency bands (there may be 6+ separate figures) in the finished room?

Are there background noise figures specified for the finished studio rooms and the adjacent non-studio spaces?

Is there evidence that the air conditioning system (there must be one to be legal) has silencers to control ventilation noise and also leakage between studio spaces?

Are there double sound lock doors into the studios (i.e. where you enter one door & close it before opening the second)?

If the answer is ‘no’ to any of these questions then you need to proceed with extreme caution!  Don’t be afraid to ask an independent consultant to vet the designs and offer comments.   And if the building is already under construction, don’t rely on council Building Control to test the rooms for you – they may be unaware of the requirement, and reluctant to hire in the necessary skills.

In the recent years we in the studio build industry have seen tens of millions of pounds of public money wasted on ill-thought-through school studio projects, when just the same amount of money could have delivered excellent facilities.  These cases range from a normally built classroom with a plaque saying ‘Studio’ on the door, to purpose built multi-million pound new structures where every acoustic rule has been broken, and where remedial work is all but impossible owing to fundamental design errors.

Typical Small Studio Layout showing offset walls, & a symmetrical monitoring environment.

And In Summary.

As long ago as 1975 the need for appropriate acoustics in schools was recognised in law.  BB93 takes that further by defining minimum standards, and stating that:

Each room and other space in a school building shall be designed and constructed in such a way that they have the acoustic conditions and the insulation against disturbance by noise appropriate to its normal use”.

“BB93 sets minimum criteria for compliance with Building Regulations so it is not surprising that these are not particularly demanding requirements by the standards of professional studio design.” says Adrian James, adding that although BB93 “is a bit short on detailed guidance on studio design.  There are a few rather old-fashioned examples in the chapter on design of music rooms, and a useful case study in the appendices.”

The most important advice is there in BB93 too: use a specialist, and get them involved as early as possible.

A final word fromAdrian:  “No designer has yet been taken to court for failing to meet these standards.”  But as spend on school studio facilities rises, it can only be a matter of time….

More Information


Master Handbook of Acoustics, F. Alton Everest, McGraw Hill. ISBN 0-07-136097-2

BB93 is available on paper as ISBN 0 11 271105 7 from the Stationery Office (

Or can be downloaded free of charge from the DfES website


Adrian James Acoustics Ltd.

The Studio Wizard Organisation.

The Author

Howard Turner has over 30 years experience in the studio business, and for the last 2 decades, his Studio Wizard Organisation have been at the forefront of the development of effective & affordable designs and solutions for studios.  Further information:  07092 123666 web: