studio construction and acoustic treatment
TRANSCRIPT
Studio Construction and Acoustic Treatment
Acoustic Treatment and Design for Recording Studios and Listening Rooms INTRODUCTION It is very pleased to see the current growing interest in acoustic treatment. Even as recently as five years ago, it was rare to read a magazine article or newsgroup posting about acoustic, bass traps, diffusers, room modes, and so forth. Today such discussions are common. And well they should be – the acoustics of a recording or listening room are arguably more important than almost anything else! These days, all gear is acceptably flat over the most important parts of the audio range. Distortion, aside from loudspeakers and microphones, is low enough to be inconsequential. And noise – a big problem with analog tape records – is now pretty much irrelevant with modem digital recording. Indeed, given the current high quality of even semi‐pro audio gear, the real issue these days is your skill as a recording engineer and the quality of the rooms in which you record and make mixing decisions. What’s the point in buying a microphone preamp that is ruler flat from DC to microwaves when the acoustic in your control room create peaks and dips as large as 20 dB throughout the entire bass range? How, important really are jitter artifacts 110 dB below the music when standing waves in your studio cause a huge hole at 80 Hz exactly where you placed a mike for the acoustic bass? Clearly , frequency response errors of this magnitude are an enormous problem, yet most studios and control rooms suffer from this defect. Worse, many studio owners have no idea their rooms have such a skewed response! Without knowing what your music really sounds like, it is difficult to produce a quality product, and even more difficult to create mixes that sound the same outside your control room. This article explains the basic principles of acoustic treatment magazine. However the vast majority is new content that does not appears anywhere else. I have consolidated this information here to provide a single comprehensive source that is free of commercial references. My goal is to offer advice that is complete and accurate, yet easy to understand using common sense explanations instead of math and formulas. Although many books about recording studio and listening room acoustics are available, most of the better ones are too technical for the average audio enthusiast to understand without effort. And you’d need to purchase and read many books to learn a few relevant items from each. Please understand that I am not a degreed acoustician or studio architect. However, I am very experienced in acoustic treatment, and particularly in bass traps. The recommendation
described here are the result of my own personal experience and should not be taken as the final word. Although this article is intended mainly for audio engineers and home recordists, all of the information applies equally to home theaters. Small churches and auditoriums, and other rooms where high quality reproduction of audio and music is required. PART 1: ACOUSTIC TREATMENT There are four primary goals of acoustic treatment: 1) To prevent standing waves and acoustic interface from affecting the frequency response of recording studios and listening rooms: 2) to reduce modal ringing in small rooms and lower the reverb time in larger studios, churches, and auditoriums, : 3) to absorb or diffuse sound in the room to avoid ringing and flutter echoes, and improve stereo imaging; and 4) to keep sound from leaking into or out of a room. That is, to prevent your music from disturbing the neighbors, and to keep the sound of passing trucks from getting into your microphones. Please understand that acoustic treatment as described here is designed to control the sound quality within a room. It is not intended to prevent sound propagation between rooms. Sound transmission and leakage are reduced via construction – using thick massive walls, and isolating the building structures – generally by floating the walls and floors, and hanging the ceilings with shock mounts. Proper acoustic treatment can transform a muddy sounding room, having poor midrange definition and erratic bass response, into one that sounds clear and tight, and is a pleasure to work and listen in. Without effective acoustic treatment, it is difficult to hear what you’re doing, making you work much harder to create a good mix. In a home theater, poor acoustics can make the sound less clear, harder to localize, and with an uneven frequency response. Even if you spent many thousands of Rupees on the most accurate loudspeakers and other equipment available, the frequency response you actually realize in an untreated room is likely to vary by 30 dB or even more. There are two basic types of acoustic treatment – absorbers and diffusers. There are also two types of absorbers. One type controls midrange and high frequency reflections; the other, a bass trap, is mainly for low frequencies. All three types of treatment are usually required before a room is suitable for making mixing decisions and for serious listening. Many studio owners and audiophiles install acoustic foam all over their walls, mistakenly believing that is sufficient. After all, if you clap your hands in a room treated with foam (of fiberglass, blankets, or egg crates ) , you won’t hear any reverb or echoes. But thin treatments do nothing to control low frequency reverb or reflections, and hand claps won’t reveal that. Basement studio and living rooms having walls made of brick or concrete are especially prone to this problem – the more rigid the walls, the more reflective they are at low frequencies. Indeed, simply building a new sheet rock wall a frequencies because a sheet rock wall that flexes also absorbs a little.
You may ask why you need acoustic treatment at all, since few people listening to your music will be in a room that is acoustically treated. The reason is simple: All rooms sound differently, both in their amount of levelness and their frequency response. If you create a mix that sounds good in your room, which has its own particular frequency response, it is likely to sound very different in other rooms. For example, if your room has a sever lack of deep bass, your mixes will probably contain too much bass as you incorrectly compensate based on what you are hearing. And if someone else plays your music in a room that has too much deep bass, the error will be exaggerated, and they will hear way too much deep bass. Therefore, the only practical solution is to make your room as accurate as possible so any variation others experience is due solely to the response of their room. DIFFUSORS AND ABSORBERS Diffusers are used to reduce or eliminate repetitive echoes that in rooms having parallel walls and a flat ceiling. Although there are different philosophies about how much natural reverberation recording studios and listening rooms should have, all professional studio designers agree that periodic reflections caused by parallel walls are best avoided. Therefore, diffusion is often used in addition to absorption to tame these reflections. Such treatment is universally accepted as better that making the room completely dead by covering all of the walls with absorptive material. For me, the ideal listening room has a mix of reflective and absorptive surfaces, with no one large area all live or all dead sounding. Understand that “live” and “dead” as described here concern only the mid and upper frequencies. Low frequency treatment is another matter entirely, and will be described separately. The simplest type of diffuser is one or more sheets of plywood attached to a wall at a slight angle, to prevent sound from bouncing repeatedly between the same two walls. alternatively, the plywood can be bent into a curved shape, though that is more difficult to install. In truth, this is really a deflector, not a diffuser, as described in more detail below. However, a deflector is sufficient to avoid flutter echoes between parallel surfaces. The photo below shows a curved deflector a friend and I built for the control room in his home recording studio. It is placed opposite the control room window and is exactly the same size as the window (six by three feet) to maintain symmetry in the room. If you build a deflector like this, be sure to pack fluffy fiberglass in the air space behind the wood to keep the cavity from resonating. Ideally, the amount of curve should be greater than shown here, with the center of the panel farther from the wall. My friend already had some 3/8 – inch plywood so we used that, but it was very difficult to bend. Had we used 1/4 – inch plywood it would have bent more easily, letting us increase the amount of curving.
An Introduction to Recording Studio Design
• What is a recording Studios?
• Multitrack Recording and Stereo
• Studio Types o Home studio
Semi‐pro Pro
o Professional Studios Sound to picture Radio, speech, and drama Cutting Pre‐production Sampling Mix – down
• Commercial Considerations o Costings o Locations
How big should it be? Noise Parking facilities Planning or development permissions
o What do you record on? Table 1. Some possible Recording Formats
• Technical Considerations o External noise Bus/ Horn o Building construction
Internal noise AC/ Tube light/ food step Floor loadings External Noise Control
o The Electric Connection metal coneute Ndú;d l, hq;=hs
Electrical Noise Audio / Eletrical wave tlg fhÿ úg
Electrical safety 90 A 10ma RCCB Grounding (Earthing) Electrical load
Audio 20 A
AC 20 A
Plug 20 A
What is a recording Studio? Before we can talk about the design process, it might be useful (especially for those of you who don’t know anything about this) to have a more exact idea of what I mean by a ‘Recording Studio’. What is a Recording Studio? Here’s ponderous definition: A recoding studio is an assemblage of equipment, spaces and persons such that a performance in sound may be created and recorded onto a medium for later reproduction. I told you it was ponderous! Try this one: A recording studio is where most music is recorded. Is that any better? It’s less accurate, though. The word studio has two distinct uses in this field, as in some others: first there’s the approximate sense of somewhere where work and study is done, hence recording ‘studio’ and secondly, there’s the exact sense of ‘the studio room’, which (traditionally) was where ‘control room’, where the controls are operated. Nothing is as clear‐cut as this any more, so I’ll describe some of the varying types of facilities and what they are used for. First, though, we’d better quickly describe ‘multitrack recording’. Studio Types Various Sound Studio types exist. The traditional down‐maker ‘demo’ studio, which was used for low cost recording of demonstration material, is either very rapidly disappearing or already gone. The cost of low‐end professional‐quality equipment has dropped, so the output‐quality distinctions between studios are less clear‐cut nowadays. However, some fairly arbitrary classification into types can be made. The descriptive labels I use (other commentators may well differ) are us follows: Home studio A studio built in someone’s home! This is not in any way a pejorative description. A lot of high – performance but economical equipment is available now to enable the creation of release‐quality material in home studios. We can make a distinction, based on the general quality of output thus: Semi‐pro A semi‐pro studio will have the facilities to make demonstration material and experiment with production ideas without incurring the high cost of using a professional studio.
Pro A ‘pro’ home studio is essentially a private professional recording studio, with all the same design criteria applying. Material can be recorded to release standard. Professional Studios Sound to picture These studios primarily deal with the addition of soundtrack material to the finished edited visuals for movies and commercials. They will often have facilities for recording large‐scale orchestral performances whilst simultaneously projecting the film that is being worked on. Equipment will include that necessary for synchronization of audio to film, and processing films for Dolby or multi‐channel formats. Radio, speech and drama Radio studios have to deals with a broad range of material. Small studios are used for voice material such as interviews and drama; slightly larger ones can also deal with small‐scale music recording. Speech and drama studio are optimized in terms of acoustics and equipment for speech recording. There are very few studios of this type outside radio. Cutting Cutting studios specifically deal with transfer of material form tape source to master discs, with appropriate ‘final tuning’ for best results. In the original (1990) version of this article, I predicted that ‘the number in this category will drop as more direct digital materials is released on CD’, but I was wrong in that prediction. The expertise of the mastering engineers in getting the best possible result in the final processing is just as relevant to making a CD, so now they cut CD pressing masters instead! Pre‐production There were once two main categories of pre‐production studio – MIDI based and ‘track‐laying’ studios, though they now are merging into an indistinguishable whole. A MIDI (Musical Instrument Digital Interface) studio is primarily computer based, with usually a software‐based sequencer (there’s still some dedicated ones available) controlling various sound sources, keyboards, drum units and effects units. The advent of low‐cost fully digital mixers has meant that a high level of automation can be applied, though (speaking from personal experience!) this can take more time to set up than it saves. The whole lot will be locked to a timing mechanism either recorded on one track of an analog multitrack recorder or generated by a digital one, which is then used for synchronized vocals, guitar and other ‘real’ sound sources that are at present not equipped with digital I/O. A track‐laying studio concentrates more on providing excellent quality acoustic recording (usually offering only limited mix‐down facilities), so that the built of recording hours can be done at relatively low cost. The output will normally be taken to another (expensive) studio for final polishing and mix‐down.
Sampling Sampling‐oriented studio are now commonplace, in fact almost all chart‐oriented work includes some sampling. What you’ve got is a MIDI studio, but instead of the sequencer playing back ‘raw’ instruments from the MIDI sources, whole sections of music are played back from a ‘sample’ which is just a digital sound recorder specialized for manipulating short sections (from tenths of seconds up to a few minutes) of digital recordings. In this way it is possible to take the ‘feel’ from a track that you like and thus not have to learn to play it properly yourself. You may gather from this remark that I started out not being over‐keen on the sampling approach, which proves I suppose that I’m getting to be an old****. “You lot don’t know when you’re well off; back in my day, you’d have to live for a week on the price of a cup of coffee now, andn a musician was a mus…” yeah all right I’ll shut up. a few years ago there was a great deal of fuss about sampling, but it all seems to have settled down now, and the music business seems to continue to make a profit, somehow (poor things). Of course, as is always the case, some artistic have taken the sampling technology and come up with something really special that cannot be regarded as derivative of anyone or anything. In sampling you are sometimes working with complete tracks of (say) bass, drums, percussion, rhythm instruments. For this reason, it’s not always necessary to have a huge number of recording tracks on the main recorder (whatever you’re using). We could paraphrase a remark here: ‘It’s never possible to be too rich, too young or have too many recording tracks’ (thank you, Mrs. Simpson) but in a sampling environment you can get away with less tracks than in some other circumstance and still produce professional results. Mix‐down The old type of Mix‐down or Remix studio specifically dealt with the reduction of multirack material to finished masters, usually stereo. A remix studio will concentrate more on making new versions from existing multitrack masters. They will have heavy investment in sound processors and modifiers, and whole racks of samplers. They’ll often have the ability to synchronize several multi‐track recorders to allow new material to be added to the original but on a separate tape, to maintain the original recording. All of these studios can be constructed on a small or large scale, depending on the intended market and budget. It is common for a particular studio to be able to cover more than one of these applications, and large complexes may offer all of these facilities in house. Costings What’s the difference between budget and cost? The budget is the amount you are willing to pay to get the studio going. The cost is the amount you end up paying. You’ll perhaps not
be surprised to hear that the two rarely coincide, and I bet you can guess which one usually is the larger. Building Construction Internal noise The likely noise sources within the finished studio need to be evaluated and provision made to isolate them acoustically. A condenser microphone can pick up the noise from a ‘soil pipe’ from quite remarkable distances! In one place I worked this gave an entirely new complexion to the phrase ‘flushed with success’, which did not in any way speed up the recording process:) . Floor loadings Studio floors have to take a considerable weight. A lot depends, as usual, on the exact use of the studio, but think ‘grand piano, two tons of musicians, drums, gear and hangers on, plus the multitrack machines (if any), mixer, large studio monitor speakers…’ and on (and on…) to get the idea. With an existing building, allowance has to be made for sound treatment being laid on top of the existing floor, as well as loading to go on top of that. Often the answer is a new floor, ‘floating’ on top of the existing floor or independently supported from the walls. External Noise Control There is a very simple way of reducing noise transmission, and that is to use ‘non‐resonant mass’, lots of it, in the way of the noise source. Really there isn’t any other way to do it, and no innovations on the horizon (to my knowledge). The problem is that massive construction is heavy, putting stress on existing structures. It is costly and takes up space, so the absolute minimum of mass will be used commensurate with the required noise reduction. As long as a wall is non‐resonant (it doesn’t ‘ring’), it will block incident sound to a precise degree, which is known as its Sound Reduction Index – (SRI). This is directly proportional to its mass, and directly proportional to the frequency of the impinging energy. The theoretical SRI will increase by 6 dB (this is sound‐speak for ‘doubles’) at a fixed frequency for the doubling of mass, and for a fixed mass by 6 dB (same) per octave increase in frequency. In this diagram the ‘mass law’ is shown as the solid line. The amount of external noise will have been established from the site survey, and the required internal levels will normally be established by reference to Noise Rating (NR) curves general, levels between NR 0 and NR 35 will be needed, depending on the application. To give you some idea of what this means, the levels in typically living rooms are also shown for comparison. To attain and maintain these levels requires some effort (!).
The addition of massive structures is fairly straightforward, but keeping them non‐resonant is much harder. Getting light and air to the workspace is important, which also means removing the stale air, usually by ducting. Any gap at all in the massive structure will completely negate the purpose of the exercise, to keep the noise out, so doors must have a very good seal. There are usually two doors in a sound‐lock ( a bit like an air‐lock‐ normally only one door open at any time), sol that noise does not get into the studio area as people enter and leave. There are specialist suppliers of doors, and having tried building custom ones, I would go for the specialist item every time! Windows are another difficult issue. People (even musicians!) quite naturally prefer to work with daylight. Many studios have given up at this point; just imagine the window construction needed to give the same sound loss as two double brick thickness plastered walls. Well you don’t have to imagine it, take look at which is roughly equivalent to a single brick wall and –a bit in sound loss, so you might need two of them together…. The Electric Connection Electrical Noise It is usual to provide a ‘clean feed’ of electricity to power all the control room equipment, and this supply will often be taken from a different phase from that used to supply power and lighting for general use within the building. The studio itself also requires a clean feed and caution must be exercised here, as it is not unknown for musicians to mix phases when playing their guitar in the control room with the amp in the studio. Embarrassing results can transpire (the musicians, of course, can expire‐ not good for return bookings). So it is better to keep control room and studio on the same electrical phase. The cable runs have to be carefully planned, usually with dirty power and lighting runs placed up high, and clean power down low. Audio cable often is run in the middle of the wall at a convenient height for connection boxes. It gets complex when there are two or three studio all needing separate isolated clan feeds. Standard triac (volume‐knob) dimmers are generally doubtful assets in a studio, as they can broadcast radio and line noise if not very carefully suppressed. You can still get variac transformers, though, which make no electrical noise and little heat. Electrical Safety In a studio there are a lot of people handling a lot of mains powered equipment, so RCBs (Residual Current contact Breakers – sometimes called ELCB or ECB) are a necessity. Some countries have them as standard fitting to installations to deal with the vagaries (or vague‐aries) of the local electricians. But the standard type has a relatively high break current of 30 mA or so That’s not much unless you’re guitarist holding onto it with your two b. are ( and rather sweaty) hands, so I’d recommend the 10 mA‐break types for this job (if you can get hold of them).
Grounding (Earthing) Earthing (grounding) problems can be a nightmare, with ground (earth!) loops often being set up at the interface of professional and semi‐professional equipment. Double insulation of much musician add‐on gear and gizmos (so there’s no ground / earth connection needed) has helped somewhat with this. But the proper, safe, and certain solution is the isolating transformer. These are now unfashionable due to the alleged effect on the sound fidelity. I’d point out that most of the best‐selling records of all time were made with equipment that was stuffed full of transformers – and many other things to give a hi‐fi geek (me?) the horrors, all of them being then (as now!) the cheapest available parts that would do the job! Personally, I still use transformers. If, however, they are to be avoided, then lots of time will be required to get the system quiet, and much care needed to keep it so. Why not just fit transformers to all inputs that a muso is liable to plug in to, and just lie about it if anyone asks?:) Electrical load Studio recording equipment doesn’t itself use a great deal of power, but the associated lighting, heating and air conditioning have to be considered within a large complex, and so there can overall be a pretty heavy consumption. This in itself is unlikely to be a problem, but the voltage droop on the main feeder from the fused supply box when 50 kW of air conditioning cuts in and out every five minutes or so can be. It may be necessary to arrange special feeds from the nearest substation transformer, or fit a local transformer. Larger (or subterranean) studios will need at the very least back‐up lighting to conform with safety regulations, and almost all large (or country) studios will have a backup generator capable of supplying the full base load of the complex. the necessity of this is obvious; if not, then you can consider the scenario of a studio full of orchestral musicians (say one hundred or so), all quite rightly on Musician’s Union rates, waiting for eight hours for power (not!) to be re‐established. It’s happened… It is just as bad at the lower end having even two people just sitting around waiting for power for the whole day, because you can’t really bill them for you doing nothing!
BUILDING YOUR HOEM RECORDING STUDIO A system of production where workers make or work on products (such as clothes), usually at home, for a merchant or distribution company who pays them for their work. HOME Recording Industry: A system of recording a music production where much of the recording is done in a well‐equipped home studio and a larger, better‐equipped studio is only used for recording or mixing functions that are beyond the capabilities of the home studio. The HOME recording studio began appearing in the 1970’s where major record producers and recording artists began to install home studios to “try‐out” or “start” a production without the cost or pressure of a professional recording studio. Originally this was a “rich‐man’s activity” with “cheep” 24 track recorders costing Rs 300000 and decent recording consoles costing Rs 500000, Today, however, 8 track 20 bit master recorder can be had for less than Rs 200000 and a full‐function all‐digital console can be purchased for as little as Rs 400000. Thus the “Home Recording Industry” is booming. The cottage recording studio is the premium home recording studio. For anyone interested in home recording, it is ultimate. We understand that you may not want to make your home recording studio as good as the plans laid out in this article. You will, however, find ideas about studio design that you can apply to any budget. The Problem: Many people have put “home recording studios” in their basement. The basement home recording studio is fun, but has inherent difficulties when trying to use it as a cottage studio, as follows: 1. The ceilings are usually to low to provide the best sound and isolation form the living area of the house. 2. It is difficult to isolate the family activities of (for example) using the kitchen or laundry area, from interfering with the studio operation. 3. It is difficult to isolate traffic from the living area of the house. Many spouse will object to “clients” wandering through the house. The Solution: Many houses have an associated building called a “Garage.” The garage usually houses the car, the lawn mower, and a bunch of junk. The lawn mower and garden tools/equipment can go into an inexpensive shed next to the garage. The car can be parked in the driveway and the junk can go in the basement. The cottage studio can go in the garage.
With its higher ceilings (usually 8 feet) and large area (usually 24 feet by 20 feet), its peaked roof, and its isolation from the house, it is a much more suitable area for a studio than the basement. Famous professional studios have started in the garage. This plan is a guide that the author feels will provide acceptable results. Before actually starting construction, one must check with local authorities to make sure the construction will meet local building and zoning codes. Permits and licenses may be necessary to legally start construction or use the facility once it is built. Local, legally‐binding, codes vary a great deal from one area to another. Urban areas tend to be more restrictive than rural areas. Because of this, it is also suggested that you get some legal advice from a local attorney. A clerk in a city office may want to put you through more red tape than you legally have to endure. an attorney may help you fill out applications with the least hassle from authorities. Assumptions & Basic Floor Plan: We are assuming that you have a stand‐alone or attached garage that measures 20’X22’ with a peaked rood and on a concrete slab. Sizes of garages vary from 20’X20’ to 22’X24’ which means the basic floor plan may have to be modified slightly to fit your garage size. Surveying a national building supply chain, we found the 20’X22’ to be the most common size. Room 1: The Studio area that measure approximately 16’X10’ that would be used for the drums and musicians for recording. Room 2: The Control Room area, measuring 11’4”X7’. Room 3: A main isolation booth of approximately 5’6”X4” that can be used for guitar or vocals during the session. Room 4: A 3’X4’ closet area for storage of studio equipment and that can be used as a second guitar booth. Room 5: A 8’6”X8’ “Entrance area” that can be used as an office or divided up into storage lockers for tapes and control room supplies. This area can also be an “emergency” isolation room. This plan assumes you want to be able to record bands with live drums. If you expect your studio to specialize is MIDI work with synthesizers and drum machines, the larger room could be the control room and Room 2 could function as a small studio/large isolation room.
You could still do drums in a pinch, but musician eye contact would be harder to achieve. Keeping Room 1 as the Studio will yield a better drum sound. Room Dimensions: The first two rooms (Studio and Control Room) are carefully modified from the ancient Golden Section dimensions. A Golden Section is an area that has a specific ratio of height to width to depth. The ratio is approximately 1 (high) by 1.6 (deep) by 2.6 (wide). When a room conforms to these dimensions, it will evenly reflect all frequencies so that any area sounds substantially the same. The ambience in the room will reinforce the tone of the instruments rather that sounding “muddy” or “thin”. In smaller studios, it becomes impossible to strictly maintain the Golden Section dimensions. Often the ceiling would be too low to be practical. If you take one of the surfaces of the room and increase the dimensions (like ceiling height) and you can maintain much of the Golden Section acoustics if you make the surface evenly reflect the frequencies and the 6th surface will not reflect sound. If you need to modify the room dimensions to fit your specific garage, keep the room 1.6 times wider that the depth to maintain the Golden Section acoustics. General Construction Techniques: We will get as specific as room allows for this article. Unfortunately, we don’t have the room to get to every specific detail. Shell Preparation The garage will need some modifications to prevent as much sound leakage into the neighborhood as possible. The side door of the garage may have to be moved into the right area, although it should be approximately correct without moving it. You will probably want to replace the door with a well fitting, solid‐core door with proper weather stripping to make an air‐tight seal. Often the door is only 30 inches wide, and you may want to modify the opening to accept a 36” wide door. Garage often have small windows. Any window should be removed and the open area framed in and covered to match the normal garage wall. The garage door should be fastened shut and get an air‐tight seal around the entire opening. The opening for the should be framed in so that the area has studs, just like the other walls.
In the area where the roof meets the walls, there is usually an air gap of 1/2 to 1”. This allows the garage to “breathe”. These areas should be well‐stuffed with high‐quality fiberglass isolation. The entire wall and roof surface should be closely inspected and sealed with caulk so that there is an air‐tight seal to the outside world in all areas expect where the roof meets the walls. Pay particular attention to how the wall meets the slab and where there are seams in the siding. Finally, all of the shell surface area gets 6” layer high‐quality fiberglass insulation. This includes the wall areas and the entire inside of the roof area. Cracks and gaps between the studs and the door jam of the outside door get stuffed with fiberglass. Dry Walling the Shell Walls: Before the dry wall is installed, any electrical boxes needed for switches and outlets are installed. These backs and sides of these boxes should be wrapped in fiberglass insulation to prevent sound leakage. Duct tape can be used to keep the fiberglass in place. The fiberglass should lap‐out a half‐inch in front of the box so that the installation of the dry‐wall compacts the fiberglass, making a good sound seal. The openings in the dry‐wall for the electrical boxes should be closely and accurate cut. All of the shell walls will be try walled. All dry walling will be applied in two layers of 8’X4’ half inch dry wall sheets. The first layer will have the seams running vertically. This layer needs to be sealed with tape and joint compound, to get a good seal between sheets and between the sheets and slab. The second layer is applied with the seams running horizontally. The final layer is sealed with tape and joint compound. Main Isolation Wall: Next, we install the main wall that isolates the Studio from the Control Room. This wall is a double‐stud wall with an inner and outer set of studs placed two inches apart. As per the figure, the studs are arranged in a staggered manner so that the vertical studs of the outer wall are placed between the vertical studs of the inner wall. Any opening for electrical boxes (etc.) in the inner wall should be 4 feet away from any opening put into the outer wall. This main isolation wall goes from the floor to the roof. The inner and outer set of studs each get 6” fiberglass insulation. Dry‐walling is done to the inner‐surface of the inner wall and the outer surface of the outer wall. Each surface will be two‐layers of half‐inch dry wall installed in the same way as the drywall sheets were installed for the shell walls. The isolation wall is well‐sealed to both the roof, and the slab floor.
Control Room Windows: The window between the Control Room and the Studio is actually two separate windows that do not physically touch. Each window is installed in its own frame and set in a felt or cork filled channel. A felt runner can be placed between the windows to dress up the gap between the panes. For proper isolation, it is important that the windows are each thick and of different thickness. We recommend (as a minimum) that one pane be 3/8” thick and the other pane be 1/4 inch thick. The different thickness means that the two windows tend to vibrate at different frequencies. The window on the studio side should slant down so that the bottom of the window is 3 to 4 inches into the opening compares to the top. This slant helps with sound isolation and helps control reflections of instruments’ sound off of the studio side of the window. Inner Walls: A double inner stud wall is placed whenever a Control Room, Studio or Isolation Room wall is an outside wall of the shell garage. These walls are places two inches from the outer wall, have 6 inches of fiberglass and are covered with two layers of sheet drywall. Single stud walls will separate the Control from the Entrance Room and the Isolation Rooms from the Studio and each other. The single stud walls are packed with fiberglass and covered with two drywall layers on both sides. All of these walls use similar construction techniques to the other walls making sure that each layer of drywall is well‐sealed. These walls are 8’high. Doors should be solid core with weather stripping for an air‐tight seal. Gaps and cracks between the studs and door jams should be fiberglass stuffed. Ceilings: All of the ceilings are suspended ceiling construction with porous (absorbent) acoustic tiles. It is suggested that 2” fiberglass sheeting be placed above the suspended acoustic panels. Any lighting fixtures that extend into the ceiling should be wrapped with fiberglass. Any access holes for fixtures and cables cut into the ceiling tiles should have cracks/gaps stuffed with fiberglass. Electrical: You will want to provide a 90 amp (minimum) service panel for your cottage studio. Off o f this service, you will want to run a minimum of four 20 amp circuits. Circuits should be run in metal conduit. Non metallic electrical cabling often doesn’t meet electrical codes and,
more importantly, radiates a strong magnetic field that can be picked by audio equipment and wiring. As easy to use flexible conduit can be purchased that already has wires installed in the conduit; The grater expense of this type of cablings is well worth it. Circuits 1 & 2 : These circuits are used for lighting and for any “office’ plugs in the Entrance Room that are used for office equipment. It is especially important that a copier be on a circuit that doesn’t have any studio/control room equipment plugs. Keeping the audio equipment electrically separate from the lighting & office equipment will allow dimmers to be used with the lighting. Lighting is probably best accomplished with track lighting. Alternatively, in‐ceiling fixtures may be used. In any case, the lighting should be incandescent, not florescent. Circuits 3: This circuit is for your cooling and heating. You can easily verify that one circuit is sufficient if the heating is a gas forced‐air furnace. If electrical heat is installed, more heating circuits and a larger central service panel will be required. Circuit 4: This circuit is for your audio equipment. Studio plugs that will be used for synthesizers and guitar amplifiers are hooked into this circuit. It is important that the ground wire of every plug be separately run back to the service panel and there is a separate ground wire in each run. Do not count on the conduit properly grounding the plug. You can get away with as little as 2 to 3 plugs, using heavy duty extension cords and power strips to branch the power out where it is needed. Cooling: Cooling is probably best accomplished by a small forced central air installed in the Entrance room. Because of the large amount of insulation, a relatively small capacity until can be used. To determine the exact size, consult with a cooling contractor or building material supplier. Lined ducts should branch out close to the unit and be separately run to each room that has a set of registers. Using lined ducts and separately running them, greatly reduces sound transmission through the duct work. Generally, try to use a duct size somewhat larger that a contactor would recommend; the air flow out of large ducts is slower and therefore quieter. Any openings in walls or ceilings for ducts and registers must be packaged with fiberglass to help maintain a sound barrier. This article has reached its size limit. As stated, you should be able to obtain a professional, usable studio converted from your under‐used garage area. The result may not be good enough to record metal bands at midnight in a crowded urban area, but you should be able to mix at a reasonable monitor volumes late into the night.
I am experienced enough to know that people will want to use shortcuts to save money. If you are tempted to do this, try to get the installation as close as possible to the plain. This is a relatively inexpensive proposition, especially if you are doing the labor yourself. If you have to save money, try cutting down on cooling and lighting that don’t effect sound quality. Remember that it is more expensive to try and bring a poor job up to snuff than it is to do it right the first time.
R oom 1 (S tudio)16 ' x 10 '
R oom 2 (C ontro l R oom )11 '4" x 7 '
R oom 5 (Entrance / O ffice)
8 '6" x 8 '
R oom 4 (C loset)3 ' x 4 '
R oom 3 (Iso la tion R oom )
5 '6" x 4 '
How to Construct a Soundproof Home Recording Studio Building Instructions The best method for creating a practice studio which will let you do live rehearsals and recordings is to follow the instructions in the free brochure. Acoustics 101 which you can download from www.auralex.com. You’ll learn that maximum soundproofing for your music studio requires construction of a “room within a room.” The ideas in this brochure can be used, however, for any sort of room soundproofing project, because the concept it describes takes advantage of the sealed air space which you’ll created between the new walls of you music studio and the old walls of the original room. If space allows, you can dampen the noise you’ll be making even further by constructing a separate ceiling for your room within a room, but that’s not always practical. What will be practical is for you to frame the walls for your new room flat on the floor and then lift them into position. Adding Soundproofing Material If you must keep the original ceiling, soundproof it either with mass loaded vinyl (MLV) or a blend of MLV and closed cell foam. When you’ve finished framing the walls, and measured for dead air space, you can begin soundproofing the new room. I recommend lining the pockets between the new and old walls with American Mat or a similar foam of closed cell vinyl nitrile, which is usually 1/4” thick and will be glued to the studs, joists, and interior cavity walls with contact cement. You won’t be filling the cavities with the American Mat: you’ll only be lining them. Adding Insulation and Decoupling If your room within a room is being constructed in an unheated garage or basement, you might decide that thermal insulation is a good idea. If so, I suggest you use Roxul, a terrific batt insulation of thermal rock wool which also has great Soundproofing properties. If most of the noise your band makes is low frequency noise coming from either acoustic drums or a bass amplifier, you should now decouple the walls. We’ll discuss decoupling methods in further articles, but if you are using high‐powered amplifiers (4X12 cabinets with fifty‐watt amps, for example) along with an Ampeg bass system and miked acoustic drums, then you can get by without decoupling.
Finishing Your Home Recording Studio If you won’t be decoupling, then get some more high quality and staple it directly either to the joists or the studs on your assembled walls. Overlap the seams and seal them with OSL acoustical caulk, and then tape them with either heavy PVC or lead tape. When you’ve finished sealing, put in a final layer of 5/8” drywall, buttering its edges with more of the acoustical caulk. Then tape, mud, and paint it, and you’re finished! You have your own in home soundproof recording studio! Recording Studio Design
Small sound reproduction rooms pose particular problems in acoustic design. Go into a small untreated bare room and clap your hands, and you usually get a distorted sound. The sound direct from your hands is quickly followed by reflections from the walls, ceiling and floor. Figure 1 shows a plan view of a small rectangular room, highlighting a first order reflection from the right side wall in red. In small rooms, first order reflections tend to be loud and quick to arrive. These reflections can cause the sound to be coloured, or to put it another way, the timbre of the sound will change. In extreme cases it can also cause the sound image to appear to come from the wrong directions. Consequently, to avoid colouration and imaging problems, the acoustic design of post‐production studio needs to first concentrate on the treatment of the first arriving reflections. There are two basic forms of acoustic treatment to deal with early reflections, namely absorption and diffusion. Figure 2 shows a rear view of a room with considerable acoustic treatment. One solution to the early reflections is to apply absorption to the wall, which will remove reflections as shown on the left wall in Figure 1. This absorption can be a specialist product such as ones made of mineral wool, open cell foam, or a recycled material, but it can also be a more commonplace object such as curtains, a sofa or carpet. If there is too much absorption, however, the room will sound ‘dead’. It would be like listening outdoors, where only the direct sound from the sound source is heard. While a few people favour
such acoustic non‐environments for mixing, for most people these are rather oppressive spaces too far removed from normal listening conditions. Diffusers are used to spatially disperse reflections, and are shown dealing with the first order rear wall reflection in Figure 1. Some dispersion can be caused by appropriately placing book cases and other furniture, but specialist diffusing surfaces should be favoured where possible, as they achieve greater dispersion in a more controlled manner. By using diffusers, first order reflections are dispersed to be heard latter by the listener, after reflection off other surfaces. Indeed, by removing and delaying early reflections, diffusion and absorption can make a small post‐production studio like a larger room. Consequently, design is about locating the reflection points for first order reflections, and applying appropriate treatment there. While it is possible to treat surfaces separately with diffusers and absorbers, it can be more efficient and cost effective to use a hybrid surface. a Binary amplitude Diffuser is such a surface. It offers partial absorption while dispersing and diffusing any reflections. It was developed by Jamie Angus who is now Professor of Audio Technology at Salford University. A curved version of this panel is used extensively in Figure 2, although they are hidden behind cloth wrapping. The BAD panel is a piece of absorbent covered by a perforated sheet. The locations of the perforations form a distinctive pattern as shown in Figure 3.The arrangement of the patches is determined by special number sequence. Indeed, it is a strange coincidence that this diffuser exploits number sequences similar to those used in digital audio error coding systems. While flat BAD panels produce good budget performance, much more dispersion can be achieved if the surface is also corrugated. Most forms of corrugation will create the dispersion, but the best possible performance is usually achieved if a numerical optimisation is used in the design process. In a numerical optimisation, a computer is tasked to search for the best diffuser shape. The computer keeps altering the diffuser’s shape and testing the performance of the dispersion produced. This is an iterative process and continues until the best shape is found. This is all done virtually in the computers memory; even so, it can be a rather slow and tedious process. Figure 2 showed a post‐production studio using a curved optimised diffuser on the ceiling; this ceiling was designed by myself. Read more about diffuser design. So far, the treatment discussed have concerned mid and treble sounds. The bass sounds in small rooms are often also problematical. Any room has resonances. Resonances are frequencies or note pitches at which the room creates a loud sound. Go up or down in pitch from that note, and the sound will go quieter. If you were to play a perfect glissando on a bass instrument in a small untreated room, you would hear the note go louder and quieter due to room resonances. Resonance is the phenomena that caused the millennium bridge in
London to wobble. To cure the millennium bridge they added damping, similarly room resonances must be treated with damping. This means adding specially tuned resonant acoustic absorbers, often referred to as bass bins or traps. If you blow over the top of a beer bottle you get a resonant note because the bottle is acting as a Helmholtz resonator. If a cloth is placed in the neck of the bottle, a Helmholtz absorber is formed which removes sound at the pitch of the resonant note. This is the principle of a Helmholtz absorber, which is one of the most effective bass trap designs. Another solution to bass resonances is to correctly proportion the room and to find the best places for the recording engineer and the loudspeakers. By setting the room in the correct proportions, for example by not having the length, width and height all the same, the audible effect of resonances can be reduced. There are various methods for determining the correct ratio between the room dimensions. Read more about this here. For instance, Salford University and RPG Diffuser Systems Inc. pioneered the use of a computer based optimisation, where a computer is tasked to search for the best dimensions. It is also possible to use a computer to find the best positions for the loudspeakers and listeners as well. Alternatively, good position can be found using listening tests and trial and error. It is vital to go through this process, as poor positioning can have a serious detrimental effect on sound quality. Recording studio A recording studio is a facility for sound recording. Ideally, the space is specially designed by an acoustician to achieve the desired acoustic properties (sound diffusion, low level of reflections, adequate reverberation time for the size of the ambient, etc.). Different types of studios record bands and artists, voiceovers and music for television shows, movies, cartoons, and commercials, and/or even record a full orchestra. The typical recording studio consists of a room called the “studio”, where instrumentalists and vocalists perform; and the “control room”, which houses the equipment for recording, routing and manipulating the sound. Often, there will be smaller rooms called “isolation booths” present to accommodate loud instruments such as drums or electric guitar, to keep these sounds from being audible to the microphones that are capturing the sounds from other instruments or vocalists.
A vocalist inside the “studio”, or “live room” area of a recording studio.
Watching a trumpet player from the control room, during a recording. Design and equipment Recording studios generally consist of three rooms: the studio itself, where the sound for the recording is created (often referred to as the “live room”) , the control room, where the sound from the studio is recorded and manipulated, and the machine room, where noisier equipment that may interfere with the recording process is kept. Recording studios are carefully designed around the principles of room acoustics to create a set of spaces with acoustical properties required for recording sound with precision and accuracy. This will consist of both room treatment (through the use of absorption and diffusion materials on the surfaces of the room and also consideration of the physical dimensions of the room itself in order to make the room respond to sound in a desired way) and soundproofing (to provide sonic isolation between the rooms). A recording studio may also include additional rooms, such as a vocal booth – a small room designed for voice recording, as well as one or more extra control rooms. Equipment found in a recording studio commonly includes:
• Mixing console
• Multitack recorder
• Microphones
• Reference monitors, which are loudspeakers with a flat frequency response Equipment may also include: There are variation of the same concept, including a portable standalone isolation booth, a compact guitar speaker isolation cabinet, or a larger guitar speaker cabinet isolation box. A gobo panel achieves the same idea to a much more moderate extent; for example, a drum kit that is too loud in the live room or on stage can have acrylic glass see‐through gobo
panels placed around it to deflect the sound and keep it from bleeding in to the other microphones, allowing more independent control of each instrument channel at the mixing board. All rooms in a recording studio may have a reconfigurable combination of reflective and non‐reflective surfaces, to control the amount of reverberation.’ History 1940s to 1970s In the era of acoustical recordings (prior to the introduction of microphones, electrical recording and amplification), the earliest recording studio were very basic facilities, being essentially soundproof rooms that isolated the performers from outside noise. During this era it was not uncommon for recordings to be made in any available location, such as a local ballroom, using portable acoustic recording equipment. In this period, master recordings were made using a direct – to – disc cutting process. Performers were typically grouped around a large acoustic horn (an enlarged version of the familiar photograph horn). The acoustic energy from the voices and/or instruments was channeled through the horn’s diaphragm to a mechanical cutting lath located in the next room, which inscribed the signal as a modulated groove directly on to the surface of the master cylinder or disc. Following the invention and commercial introduction of the microphone, the electronic amplifier, the mixing desk and the loudspeaker, the recording industry gradually converted to electric recording, and by 1925 this technology had replaced mechanical acoustic recording methods for such major labels as RCA Victor and Columbia, and by 1933 acoustic recording was completely disused. Siemens Sound Studio 1956 Electrical recording was common by the early 1930s, and mastering lathes were now electrically powered, but master recording still had to be cut direct – to – disc. In line with the prevailing musical trends, studios in this period were primarily designed for the live recording of symphony orchestras and other large instrumental ensembles. Engineers soon found that large, reverberant spaces like concert halls created a vibrant acoustic signature that greatly enhanced the sound of the recording, and in this period large, acoustically “live” halls were favored, rather than the acoustically “dead” booths and studio rooms that became common after the 1960s.