A Review By: Alphonso Soosay
Having a noise free atmosphere in a home recording studio is extremely very critical to being able to appreciate natural sounds of a person’s vocal, acoustic musical instruments and a wide dynamic range of sound especially in audio recording and audio mixing. There are many instances where a dynamic musical arrangement brings together a climax of sound level and suddenly stops with dead silence. To hear this expeditious contrast in sound level appreciated to its fullest, your home studio needs to have a realistically very low background noise level. With an acoustically balanced room, anyone can achieve the state-of-the-art sound reproduction in their music room. How? Using proper acoustic control materials in your home music room can improve the acoustics, creating a truly realistic soundstage effectively. So before you spend any more money on upgrading your audio equipment, upgrade that one “Objective” first (room acoustic control) which will give you back your greatest rewards. “Your Natural Sound”.
To building a commercial studio is an expensive proposition.
However, the basic techniques of home studio construction can be carried into a smaller, home space quite effectively. The focus of this review of features will be to outline what happens in a commercial facility and then break it down into some simple, less expensive options for you to use in your own space.
Generally speaking there are five building factors that make up a great audio recording surrounding area.
4) Floating your Studio
5) The Finish
Let’s take a look at the first item “Diffusion”:
The most creative and important thing you can do to a recording and control room space is to break up any parallel surfaces. There are 3 opportunities for parallel surfaces in the studio environment. Two parallel walls, ceiling and floor. When the studio environment is created, the outer wall is considered a starting point and a “building within a building” is designed with acoustic treatments. When the inside shell is designed, it is normally arranged at odd angles to breakup any parallel walls, ceiling or floor. The reason for this is an occurrence called “standing waves”. A standing wave is what happens when a sound wave encounters itself at full, or near full strength when distortion happens. Also looking at the features on phase when two waves encounter each other, there is a possibility for them to be out of-phase or in-phase. When waves encounter each other in-phase it will add up to more energy than the initial wave. When they encounter each others out of phase, they will cancel and subtract energy from the initial wave. Because of the size of low frequency waves, they will tend to “collect” at certain points in the room. These collection points will give you false impressions of the true nature of what’s coming out of the speaker and lead you to false hearing conclusions.
Shocking First Impressions:
Let’s just say that your audio room is poorly constructed and you are making your audio decisions based on a monitoring position that contains some standing waves. You might bring up a Kick-Drum either for mixing or tracking and decide that it sounds Boomy for you. Your reaction would be to hear for the Low Pass Filter or low frequency EQ and remove the offending frequencies. All well and good if you are monitoring speaker position is giving you what’s actually happening in the real world. Next you might bring up the Bass Guitar and react in a similar manner; once again you head for the low frequency cut-off and remove low frequency. Over and over you respond to that standing wave and follow your ears. The problem is when you take the mix out to another listening room area that is properly constructed; you will find that you performed in inaccuracy. Your overall-mix will be lacking in low frequency because you chose to remove it. So what’s going to happen now?
The answer is to make sure that your working space is an accurate one. This can be accomplished by looking for the right studio in Mixing or recording with your own space to break up any parallel surfaces.
Re-Designing Your Space:
Unless an audio recording studio capability is built from the ground up, the audio designers have to deal with the fact that building, both residential and commercial, are built in squares and rectangles. This of course, makes sense as far as utilizing space but it’s not the optimum design for audio recording. A commercial facility must use the “building within a building” approach to make all the internal surfaces non-parallel. This approach is expensive but there are some very practical things you can do to your home audio recording studio to break up the sound waves.
General bits and pieces used as Diffusers:
Sometime ago I have tried setting up a free standing, floor to ceiling bookshelf at the back of my studio space as a diffuser and it seems to works very well. Note, it has to be fully loaded (left to right) with different size books and periodicals.
There are spaces that let some parts of the wave through to the wall and other parts are deflected by the odd shaped books. This does not get rid of all parallel surfaces but diffuses the sound waves considerably. It balances most of the back wall and is a cheap diffuser that’s also good at controlling home audio recording room acoustics.
On a side wall where there is an open space I have tried placing a few free standing CD, Cassette/ organizers on the wall, this is another odd shaped surface, once if it’s weighed down with CD and Dat tapes. What you have to guard against with this is the rattling sounds of CD and Dat tapes this is caused when a loud bass notes or sound wave hits it. It can be controlled by re-arranging it.
Having functional and relatively cheap diffusers is a sturdy asset in a home recording studio. However too much of one size of diffuser can make your space unbalanced. As waves get bigger you need bigger diffused surfaces to help control them. I have built some free standing gobos (partitioning) at “Audio Visual Workshop” in Singapore and “No Sweat Recording Studios” in Perth Australia to help with the low frequency with my room space previously.
Following are the materials I used:
1) 1/2″ Pressboard
2) 1.5 inch Dry Wall Screws
3) Corner brace
4) One Roll of R-11 pink insulation
5) 6′ of 3.25×1/2 inch finished pine
6) Stretchable thick cotton cloth
7) Two door hinges.
The Technique of a show piece:
Out of the pressboard I sectioned 6′ x 6″ and 2′ x 6″ lengths. My goal was to have two frames that were six feet high and two feet wide. I was making two free standing structures 6′ x 2′ and filling it with fibre-glass insulation and covering it with the thick cotton cloth on tie front and the sides. The back would be covered with a pine-wood cover. This would make one side dead and the other side live.
When putting them together I used the corner bracket to make a perfect angle and then screw them together with a drill using the dry wall screws. Once I had the basic structure built, I position in the fibre-glass insulation as far back as I could and tacked it down with an electric tack gun. I then stretched the cloth tightly across the open front and sides of the frame. I tacked it down on the inside of the back of the structure making sure that it looked good at the corners and made sure that I did not get bunched up in spots. Then I positioned the wood cover on the back and screwed it down. After that I positioned the feet on for its stability. Also added is one foot lengths out of the finished pine and screwed them into the bottom of the gobo. I then hinged the two structures together to make a kind of huge book that I could open or close and move around the room. Eventually I made four of these so I could have a vocal booth or a free standing diffuser at any part of the room.
An essential set of laws in studio design is isolation. This is because the real world is a unfavourable environment when it comes to audio recordings. All kinds of environmental noises such as lawn mowing, heavy traffic, air conditioning, computer noise, next door neighbours and air traffic all of these can corrupt your audio tracks. No recording engineer likes to re-take a good recorded performance because of a passing motorcycle or airplane? With home recording studios this can be a problem for two reasons. 1), you do not want what’s outside influencing your audio recording and 2); your neighbours might not want to hear what you are recording while they are having their dinner or watching their TV program. So, to isolate this problem, you must insulate and there are a good number of ways to do that.
The Best Insulator:
The best insulator for cold, heat or sound is a dead air space. It’s the same concept as storm windows and doors. Those of you who use them in winter know how quiet the house gets in the cold months, and also how it helps reduce your heating bills. The isolation property that dead air provides is why a commercial facility will have a building within the existing structure. This gives the designer the opportunity to eliminate parallel surfaces and to trap dead air between the outer and inner shells.
You can use insulation to break up parallel surfaces in the home studio environment. Since building a room within a room is impractical in the home, unless you have a huge family room. Let’s look at some of the things you can do to isolate problem musical instruments.
Easy home recordings:
The home recording studio is great for recordings such as vocals, synthesizer keyboards, acoustic guitars, acoustic piano, wind instruments, percussion instruments, bass (using a DI box) and even horns in small sections with overdubs.
Doors and Windows:
Insulation and isolation is important in home recording studio surroundings. Walls are stationary structures and dead air is easily trapped between the outer shell and your inner walls. However, doors and windows present two special problems, doors have to be opened and have seams where sound can enter and windows must be transparent. The concept of a dead air space applies with doors also. To seal off the passageways between rooms of a studio and the outside world you have to create a sound lock. This involves using double doors with an airspace trapped between when both doors are closed. This of course means using two doors per doorway. Here’s how I did it in the commercial studios in Singapore (Audio Visual Workshop) designed by me in 1980.
Two solid core doors were used to construct each single door. The doorways were going to have to be wide enough to let pass some large pieces of equipment (such as musical instruments and amplifiers), so extra wide doors were constructed by our professional carpenter. A regulation size door was also constructed so we could make a door sandwich that could be flush to both the outside and inside walls but still have no common airway through the seam. The smaller door was then centred on the larger door and bolt holes were drilled so the doors could be sandwiched together. This sandwich would leave a 2 inch wide lip between the doors where mechanical rubber (seal) was laid. The reason for this was that when the door is shut, it would provide some insulation where it laid against the inner wall. For extra build-up, before we put the doors together we put a sheet of lead between. Once we bolted the doors together and put on the hinges (heavy duty to say the least) we had a door that closed like a bank vault.
More about Doors:
A recipe for a door that provided maximum density and isolation in a commercial studio that has been worked on. Of course it would be great to be able to spend $500 on a door that you knew would keep out the majority of noise and sound outside of your control room and studio. But most of home studios are on a budget and need to adapt expensive techniques to our own home space. If you have not noticed, the concept behind this studio doors, then you should take a professional concepts and apply them to your home recording studio. So lets start talking about making doors that will isolate, but for much less than the professional would have to spend. We have already established that dead air is the best insulator around and all you have to do is trap it. Hanging two solid doors with a space between creates what’s called a sound lock. Buying solid core doors can be an expensive matter but sometimes you can find doors that are discarded from previous studios and are just resting at construction Sites or studios that are being remodelled. It will be worth your while to hunt for some bargains at second hand door shops, especially if you have a few entries to address.
Personally, after trying to hang a door myself in 1980, I gave up. I would prefer to get some professional help to come in and hang the doors, construct the doorjambs to make sure it’s done properly (air tight). But that’s your call; if you feel confident with doing things like that, go for it. It’s an experience that you will never forget.
The Sound Lock:
You will not need a large amount of air trapped between the two doors. A little goes a long way. Notice how when the doors are closed there is a dead air space between them. This really helps isolation between rooms outside the studio or the outside world too.
As you have noticed reading along, isolation is the most important goal in the home studio surroundings. That’s to keep out the sounds that would cast a shadow on your treasured audio recordings.
The concept of dead-air as an insulator can be easily carried over to windows. If you had ever noticed the main control room window in a TV or professional audio recording studio you probably would have noticed a few things. 1), that the glass is very thick, 2), it’s angled and 3), there’s more than one piece of glass that separates the control room from the studio. This was how the “Audio Visual Workshop” studio in Singapore and “No Sweat Recording Studios” in Perth Australia was prepared.
Density, Isolation and “Reflection”:
Density is another great way to keep sound from transferring from one place to another. This is because sound waves tend to take a surface and turn it into a resonator. The thicker a material or surface the less it resonates. This is the reason that thick glass is used in audio recording studios all over the world.
If you install the studio window at a 90 degree angle to the floor, it would be perpendicular to the listening position at the console. This would cause problems both with sound and light reflection. So the glass is purposefully angled down both for acoustic and visibility reasons.
The reason for two pains of glass (sometimes three) are used in studio windows is because you can then trap air between the glass panes and as I have explained in past features that dead-air is the best insulator you can get.
Reflections include reverb, echo and standing waves. Each of these affects the sound of your room. Reflections can be detrimental to your recording. The problem is that sound waves bouncing off the walls, ceiling and floor will return to the microphone. This could simply result in the presence of reverb from the room in your recording. Most likely, this reverb will not sound very good. Another problem caused by reflections is phasing, or cancellation. This is caused by the source sound bouncing off the wall and returning to the microphone out of phase with the original sound. Also the sound may be in phase in some frequencies and out of phase at other frequencies. This causes some frequencies to be exaggerated and others to decrease and will prevent you from getting that nice full clear sound that you want to have in your audio recordings. Professional audio recording studios usually use special acoustic materials to remove reflections in the mid and high frequencies. With the home studio, you can obtain good results with much less expensive materials. A common popular material is the moving blankets; this is normally used by the moving companies to protect furniture’s. These materials can be purchased directly from fabric suppliers for less than $10/- a piece. Another material that works well is office dividers used for cubicles. You can often find these at used office furniture stores.
Professional studios have large windows that enhance the visual communication between the control room and studio and also tend to open up the room and make it seem less like the fishbowl that it is. It makes your work easier because you can easily cue a Musician and Singer visually. The bigger and wider is better as far as I am concerned when talking about real professional studio windows.
One possible problem when sandwiching two thick panes of glass together with a hefty air-space between them is that moisture can collect. Than can be remedied by putting up one of the panes of glass, then caulking it with silicon, it can be effectively sealed. Then the other pane of glass is put up and checked for fit and then removed and put aside momentarily. A space on the bottom surface of the airspace must be built down, usually 1 or 2 inches deep and the width of the window. This would resemble a rectangle that would be carried out of the floor of the air space. Then a wood frame with cloth is built so you can cover this area. How it’s usually done is that the cloth covered frame is flushed with the floor of the window airspace. This looks aesthetically pleasing and no one is the wiser as to what’s underneath it. Then you apply silica gel (it’s toxic, so be careful) at the bottom of the space. Silica gel absorbs moisture well and you usually see it in new shoes in a small bag marked (do not eat). However, you would need much more of it for this application. Once you open the can of gel, which resembles rock salt, you must be quick because it stars absorbing immediately. Once the gel is laid out, you apply the cloth covered frame over it and quickly put up the other side of the glass and caulk it. This now seals the area and the gel will absorb all the moisture inside and you will not end up with a problem when the humid summer rolls in.
As mentioned before, offsetting your internal walls will help with standing waves and reflect sound in a beneficial way in the studio environment. When you build these internal walls it will make contact with your existing ceiling and floor. The problem comes when sound waves make their way from the floor to wall or vice versa. This happens when one or the other vibrates and transmits its energy to the next surface.
Therefore floating your floor and walls is essential to proper isolation. How this is achieved is to use mechanical rubber where all surfaces make contact with each other. This is at the bottom side and top of all internal walls in the studio and control room. Before they are anchored to the floor and ceiling, a strip d mechanical rubber is sandwiched between the bottom 2-by-4 timber and the floor and the top 2-by-4 timber and the ceiling. Mechanical rubber comes in long rolls that are two inches wide and is easily positioned out in a straight line. In the case of the floor, the rubber is laid down under the bottom 2-by-4 and then the whole wall is anchored with a Ram-Set. This is a large bolt and washer, which is shot down into the ground using a device that looks much like a gun and uses an explosive charge to do the job. Once you float all the walls at the floor and ceiling your studio becomes a much quieter place and transmitting sounds from the outside becomes much more difficult.
Floating your studio Floor:
After the walls are in place it is necessary to think about the floor. The floor is an excellent place to run cable and therefore it becomes necessary to build up your floor up a bit to allow you to run conduit of sufficient size to run thick snakes of microphone cable. The floor is built up using 2-by-6 lumber placed on edge building a frame that the actual floor surface will sit on. So the actual studio floor where the equipment rests will be six inches above the sub-floor. Before you lay the 2-by-6’s down you use more mechanical rubber between the wood and the concrete floor. This floats your floor and isolates it from the sub-floor.
Finishing the floating Floor and Planning for Wiring:
Before you put the top on the floor you must do some planning for your wiring. To save money on wire you must map out where exactly your equipment will go. The position in the room of your outboard gear, multitrack machines and main audio recording console must be decided at this stage. This is because you will now lay large PVC pipe conduits through your floor frame so that running cables will be easy now and also later if you change your equipment. Once the PVC pipe is position, it’s then time to fill up the resonant cavity that will underlie your floor. If you left the six inches below your floor open it would become like a drum and would be detrimental to having a quiet room, you want the floor beneath to be as solid as possible. So, what you do is to fill all the cavities with clean sand. This of course involves lots of sand, but once you have done it, it’s solid as a rock. The floor being filled is now ready for the top. The top should be a layer of 3/4 inch plywood and then some kind of wood or whatever you like aesthetically on top. I like hard wood surfaces rather than carpet but that depends on the room size and how lively you like it. At the ends of the conduits you must cut a port so that the cable can be pulled. This is usually near walls and corners where the equipment will be set up. It is often hidden from site. One final trick is to never give your blessing to the floor or frame timber to ever touch the walls. You must leave a 2″ air gap space all around the room so that your walls by no means create contact with the floor surface or frame.
Since you have gone through and explored how the audio studio is built from the outside in, now, it’s time to put the finish on our walls, ceilings and floors. Your budget and concerns and preferences about your room will determine a lot of what you do. There are some important things to think about before you cover your walls with the most readily available or affordable finish.
On the strictly budget side of things I have seen young students using egg cartons on a large part of the studio ceiling surface to help break up sound waves. This would work to a certain extent (although it’s unattractive) but if you use too much of one size of a diffused surface in a room it becomes unbalanced. The best studio rooms I have been in have a good variety of surfaces and types of diffusion. A general rule is that the bigger the curve of a surface, the lower the frequency it can handle. For instance, a low frequency wave at a good volume would easily bounce off an egg carton surface and return towards the source almost unaffected. You need a large curved surface to break up large waves. As you start getting into the ready-made available foams Iike Sonex and tube traps you can actually see that acoustic surfaces are designed to work with a certain bandwidth. Manufacturer of each product will tell you exactly what size and frequency of wave that their product will handle. Domestic items such as carpet for instance would kill higher frequencies where as timber or tiles would break up mid to low frequencies. Remember that carpeting can be used on lower walls as well as floors effectively.
For further information on “Room Acoustics” please look up Professional approach to room acoustics by Alphonso Soosay.
The essential goal in designing a room for Audio Recording is to achieve the sound at the listener’s ears that the music producers originally intended. Assuming that we are hearing a flat response from the monitor speakers, this assumes that the room itself does not distort or otherwise alter its overall frequency response, the relative amplitude or the time arrival of any sound events. In order to avoid image shift and distortion problems, you must establish which surfaces could reflect sound off and reach the listeners ears within a very short time after the direct sound. Now is the time to treat these surfaces with sound absorbing materials that are highly efficient at all frequencies above 250Hz. These acoustic materials serve to significantly reduce the energy level of the reflected sound so that it is well below the level of the direct sound. So this means that the amount and location of sound absorbing materials should be very carefully selected at arrive and at a balance between reducing early sound reflections and achieving a target reverberation time goal of around 0.03 to 0.35 seconds at all frequencies between 250 Hz and 4 kHz, and 0.04 to 0.50 seconds at frequencies between 40 Hz and 250 Hz.
Another important reason for using acoustic control is to eliminate the early arriving reflections. Strong reflections can also cause a shifting of an image in the frontal sound stage.
The audio control room atmosphere must not be completely dead or you will find yourself turning up the volume of your speakers to make up for it and you will get fatigue quite easily. There must be some amount of reflection in the room. Pine-wood surfaces do this well, this in conjunction with carpeting or some kind of diffused surface makes for a good combination of dead and live surfaces.
With audio recording studios you can afford to be a bit more live. I find that concrete, wood and some kind of brick or stone and even glass makes for a nice balanced live room. If you have followed the rules of non-parallel surfaces and you finish these walls with the above mentioned items you will find that you have a great room where you can record acoustic drums and or other high SPL instruments and end up with a great sounding product.
If you want to cover both bases in the studio portion of your ability, then there are some other things you can do. I saw this at Paramount studios in LA and I thought it was a remarkable idea. There were huge panels hanging on the wall that were hinged at one side so you could swing them open to either side. One side of the panel was reflective (pinewood) and the other dead (“Sonex” acoustic material). If you wanted a more dead room you just swing a few of the panels open to the other side and you could alter your room acoustics. If the panel was left closed, it was lively and it has to be left swung open and put against the wall. If left the other way completely it becomes controlled (dead) acoustics. It really worked very well and you do not have to commit to anyone style of room acoustics. You can actually control the room acoustics to your liking. Using thick double sided curtains that can be opened or closed also have an extensive effect and can be part of a custom designed room. This would be a cheaper technique for home recording studios.
Audio Recording Engineer Perth