Brad Wager

WR-123-05

D. Mount

3 June 2005

Sound and Acoustics: The Building Blocks to a Professional or Home Recording Studio           

            Recording studios are places where the fine details count, with every possible method of increasing the quality of sound for a track considered and used. Besides technical and electronic enhancements like high quality wiring, vintage microphones and preamplifiers, and the techniques used in miking sources, the quality of the source is imperative. The phrase "microphones don't lie" speaks volumes on this topic as it is relative to the acoustical design of the rooms where the recording is taking place. One should note that this phrase is traditionally used to describe the fact that your mistakes stand out greater when recorded than if one is simply listening to a live performance. However, this quality offering the raw truth is very relevant in how a microphone captures the sound of a room versus our ears. Though the person in the room performing truly is the source, the room also plays a major role; as a good room allows the full potential of the performer to be captured to tape, and a bad room limits the possible quality for the performance. Recording spaces that lack attention to acoustical anomalies are likely to produce “recordings (that) seem to sound muddy or cloudy” (Rowlette). This detail can be often overlooked, leading to struggling with equipment and possibly purchasing expensive gear to help alleviate problems in the quality of ones recordings, when the real problem is the room.

            Over the last five years I’ve been involved in audio recording I have learned a great deal about acoustics. My involvement has provided me experience with what works and what doesn’t. This paper is a culmination of my knowledge as a recording engineer of the practical acoustics that can be applied in a recording environment, as well as extensive research of the studied methods and techniques used in the design of professional and project recording studios.

            A focus on the acoustics of a recording studio is vital at maintaining optimal results. To understand acoustics we first must look to the definition of the word: “Acoustics is a branch of physics and is the study of sound, mechanical waves in gases, liquids, and solids” (Wikipedia). To break this down to a bit simpler terms, acoustics is the study of sound. To explore acoustics used in a recording studio, we’ll discuss them in more practical terms rather than ones too deeply scientific.

In order to understand the elements of acoustics as they pertain to the design of a modern recording studio, we will first focus on common problem acoustics that need to be avoided. We will discuss the differences in the human ear versus microphones, as well as common anomalies such as flutter echo and room modes. These topics will help us as we learn about the effects of sound reflections and how sound travels through walls, as well as the devices used to absorb the frequencies occurring in room modes. Once we’ve figured out how to keep the sounds inside our rooms under control, I’ll focus on the methods used to keep that sound in those rooms, in order to provide isolation from outside sounds as well as to keep sounds inside these rooms from leaking out. There is no one way to design a recording studio, and here I’ll present the opinions from professionals in the field and how they may differ from the concepts presented prior and why. I will also discuss the current trend of home recording studios and how to apply the techniques described here in a studio at home.

All of these elements will provide a good understanding of a modern recording studio as well as present some possibilities for variance and potential future developments in recording studio design. The design of a recording studio is an involved process with key elements such as isolation, acoustics, and function. These elements are the topic of debate among top professionals in the field of recording. Understanding potential acoustical challenges can provide insight to the complex recording studio design.

The average person does not consider a room to have either a good or bad sound quality, with the exception of extreme circumstances where reflections are either very noticeable and these room characteristics make it difficult to hear a conversation, or if the room lacks all reflections leaving a dead muted sound that stands out as unique. The sonic character of a room is a vital element in the recording process as the sound of the room will likely affect the sound of the recorded track.

Understanding acoustical problems and solutions requires an understanding of the differences in the way our ears process sound versus how a microphone processes sound. It is important to understand that “our ears compensate for a lot of flaws” as this is the first step in figuring out why rooms can sound good in person and not on tape (Wieczorek). Mats Ulfendahl and Åke Flock studied the active tuning of the ears via the outer hair cells and published a journal article with their findings. This information describes this compensation of frequencies through this active tuning process:

There is now overwhelming experimental evidence that the sharply tuned component originates from the outer hair cells. Due to its biological origin, this component is considered to be an active response that produces a feedback force interacting with the mechanics of the cochlea to enhance or amplify its response (Flock/Ulfendahl).

While our ears may be capable of making active adjustments to offset poor frequency balance in a room a microphone cannot. Microphones, though they do have a frequency response curve of their own, pickup sound in a static manor without continuous variability. Any changes to the frequency response of a microphone must be made via equalizer adjustments either during the recording or mixing phase of the process. However, adjustments often times cannot counteract the poor sound quality of the room, especially without altering the sonic character of the instrument or source being recorded. This is why the acoustic quality of the rooms in a recording studio is vital to an engineer looking to create a good sounding recording with little fuss.

            One common acoustical problem found in many rooms is flutter echo. Flutter echo “happens when sound bounces backwards and forwards between a series of hard surfaces, repeatedly following the same path. Usually the problem is caused by just two hard surfaces, opposite and parallel to each other, although other arrangements can cause this problem” (Woolf). It is common for one to clap their hands when checking a room for flutter echo because a hand clap is a hard percussive sound that is common to setting off rooms susceptible to flutter echo. Methods of curing flutter echo vary based upon situation. “If you’re building from scratch, facing walls can be made out of parallel” (White, Part 3). While this is the best method for solving flutter echo problems in a room if one cannot alter the physical space, the use of “acoustic foam tiles fixed to the side walls on either side of the engineering position will be all that is needed” (White, Part 3). This technique of making walls non-parallel is effective at reducing high frequency flutter echo but is often misunderstood as an ailment for standing wave issues in a room.

            These standing waves can be described in a recording studio setting as room modes. Chips Davis states on room modes that “’The height, length, and width ratio of any space has natural resonances, or modes,’ says Davis. ‘If you’re singing in the shower and you hit a note that fills the whole space without your having to put any energy into singing it, you’ve discovered a natural resonance of that space’” (qtd. in Pederson). The reason people enjoy singing in the shower is the reflective surfaces that provide reverb to their voice, making it sound more enhanced and richer than it actually does. In this example, reverb provides fullness to a voice. Though the following is a bit of an extreme statement, it supports this concept in a very blunt and straight forward way: “Only one thing makes a room sound good. REVERB” (PcMus).

            The issue with room modes is that while they are similar to reverb due to their resonant nature, they are a spike in the resonance of a rooms sound, making the frequency response of the room unbalanced. Just as parallel walls are subject to flutter echo “if a room has dimensions, it has modes” (White, Part 1). Room modes are when bass frequencies bounce around a room without dissipating (Wieczorek). Clearly, room modes and flutter echo are similar in that they are based upon uncontrolled frequencies causing anomalies in the room. However, the way one deals with mid range or high frequency reflections is quite different from how lower frequencies are handled.

Previously, acoustic foam and the method of setting walls out of parallel was sufficient in resolving high frequency problems. It should be understood that “bass frequencies tend to build up in the corners of the room, so an absorptive apparatus called a bass trap can be positioned in these areas to minimize low end woes” (Pederson). With low frequencies, absorption is attained through the use of these bass traps and resonators, designed to counteract the affects of these low frequencies. The design and theory behind these resonators will be discussed at length later.

The potential modes of one’s room can be determined by the dimensions of the room. Room modes are calculated based upon the speed of sound (at 1130 feet per second) and the dimensions of the room. In order to calculate the modes, one divides half of the speed of sound (565) by the distance between the parallel walls or the ceiling and the floor, for example eight feet. This yields the frequency of first mode found in a room with an 8 foot ceiling, which is 70 Hz. The following chart (Figure 1) from Audioholics Online A/V Magazine represents the modes of a room that is sixteen feet wide and twenty-four feet long, with eight foot ceilings.

 

(Figure 1) The room modes found in a room 16’ x 24’ x 8’

This room will have a mode focused around 70 Hz as it appears as a mode between all three of the dimensions. What is happening to create the second and third modes is that the wave is doubling in the room. The first mode is half of a wave, the second one full wave, and the third one and a half. This room would need extreme attenuation at 70 Hz, which can be provided by resonators designed specifically to absorb this frequency (Audioholics).

            Though absorption of these frequencies is possible, resonators and bass traps take up space in the room. When flutter echo was discussed earlier, the scenario of building from scratch allowed us to build walls that weren’t parallel, thus eliminating flutter echo. Just as one would modify the walls to eliminate flutter, it would be in order to check to make sure that a scenario like this with an extreme mode at a given frequency was not the case. One would then modify the dimensions of the room to balance it out as much as possible before building it, and then apply bass traps and resonators to smooth out the low frequency anomalies.

In a control room, the critical listening environment where the music is actually mixed, there is also one final effort that can be made to balance out room issues after resonators have been added. This method is the use of an equalizer in the signal path of the playback speakers. Studio designer Carl Tatz states that one can “’polish’ the system with a high-quality parametric equalizer” as one of the final steps in balancing out the mix position (qtd. in Electronic Musician). This is a great way to catch any final problems in the room, but only applies to the control room because the playback speakers are the source that we are trying to balance out so the mixes done there will be more accurate. In other words, the room in the studio that music is actually recorded in cannot benefit from such an equalizer, and these frequencies will be picked up by the microphones and go to tape. However, the efforts made to balance out the sound of the room through careful choice of dimensions and use of bass traps will dramatically enhance the quality of music recorded in these spaces and benefit both rooms.

            The construction of the studio should provide a room that does not have extensive flutter echo problems or room modes, by ensuring that the walls are not parallel, and have dimensions that don’t lend themselves to potential problem frequencies. Since we know that our ears aren’t “flat” and color and shape sound to make it more pleasing, we understand the need to balance out the sound of a room for optimal recordings.

            With this background of common acoustic problems found in recording spaces, we can now focus on more complex matters which will give way to the creation of a good sounding room for recording. Again, we find that a major enhancement to the sound of a room is the reverberations within the space. Paul White describes reverb as being “created whenever sound energy is fed into a room and the room modes are excited.” White also states that “it occurs in all normal rooms, to the extent that music or speech sounds unnatural without it, but in a studio control room environment, reverb characteristics need to be controlled within fairly close limits if the music produced in the room is to be evaluated with any accuracy.” The reflections and reverberations have an exponential decay rate, this rate is called a T60 or RT60; “the time taken for a sound to die away to one thousandth of its original sound level” (White, Part 3). The T60 common in a control room is about 0.3 seconds, compared to the average living room which yields a T60 of about 0.5 seconds (White, Part 3). For our listening environment, we are looking to hear the sound coming out of the speakers without the reflections from the room altering the playback.

            It is important to understand that “There are three things that can happen when sound hits a wall. It can be reflected, absorbed, or diffused” (Elsea). When sound hits a wall and is absorbed it will then likely pass through the wall and into the adjoining room. This is known as transmission loss, “when sound hits a wall there is a certain proportion of the sound reflected back into the room, some is lost in the absorption of the wall and the rest travels through the wall and is called the transmission loss” (SAE Institute). A room with a lot of transmission loss will have less reflection than a room with little transmission loss. Conversely, a room with little transmission loss or a very isolated room will have a more live sound and thus more reflections within the room (SAE Institute). 

            As we previously discussed, flutter echo is a common problem found in rooms and is a series of reflections following the same path. Relative to flutter echo is comb filtering. When monitoring playback in the control room, the direct sound from the speakers is heard as well as the reflected sound from the surfaces around the mix position. These reflections are a "slightly delayed version" of the original wave and cause a canceling effect that skews the sonic picture of the mix (Storyk). Controlling these reflections is vital at maintaining an accurate listening space.

            There are two common methods for dealing with rooms that have issues with reflections. These two approaches are known as diffusion, and absorption. The diffusion method does not affect the amplitude of the reflections but rather changes their pattern, whereas the use of absorption lowers the amplitude of the reflections without a change in their pattern (Storyk). Similar to room modes and flutter echo, the first step in avoiding comb filtering issues is to ensure that the geometry of the room is right through the use of angled walls and ceilings. A ceiling that slopes down from the front to the back in relation to the mix position or walls that are too close to the sides of the mix position are potential causes for harsh reflections.

            Diffusion is an acoustical method of controlling reflections where a complex surface (Figure 2) is used to scatter "both direction and timing of reflections" (Shirley). These diffusers provide improvement to rooms with standing wave and flutter echo problems in a way that does not create a dull sound that can be found with absorption techniques. According to Dr. John Shirley, diffusion can actually improve the sound of a room by making it sound larger than it really is, though "diffusers are both complex and expensive."

(Figure 2) A diffuser in a home theatre setup to provide control of reflections.

The diffuser is a preferred method of treatment for the ceiling in the studio, and can be positioned above the mix position to provide treatment in this vital area. In a control room with a hardwood floor, diffusion is needed above the mix position because of the live nature of the hardwood. This is due to the need to diffuse these reflections from floor to ceiling without getting rid of the reverberations of the space. The main control room at Falcon Recording Studio in Portland, OR utilizes a live floor around the mix position. This technique of using live materials (like hardwood) only around the mix position coincides with the use of diffusion on the ceiling at this location for similar reasons. Yet, it also is beneficial when using rolling office chairs for seating as it make it easier to make laps back and fourth from the console to the other equipment mounted in the studio.

            One previous example of absorption to control reflections was the use of acoustic foam to the sides of the mix position to control flutter echo. Flutter echo is a high frequency issue and can be controlled by this use of acoustic foam. There are basically three frequency areas we need to focus on in terms of absorption. First we have the high and mid frequencies, which can be fairly easily absorbed by “acoustical tiles, foams and heavy drapes that can effectively soak up frequencies above 300Hz” (White, Part 2). Absorbers for these frequencies are often constructed of a wood frame that houses a two-inch piece of mineral wool with a cloth covering to keep the fibers of the mineral wool from getting into the air. An absorber like this would be spaced roughly two inches from the wall to provide more low frequency absorption. This technique can also be used with acoustic foam or any open-cell foam with the understanding that a one-inch piece of foam is capable of absorption from about 1kHz and up, and a four-inch piece can absorb from around 250Hz providing more low-mid frequency absorption (White, Part 2).

            The absorption of bass frequencies is considerably more complicated. Since the waves found in bass frequencies are very long, the absorption of these frequencies involves the use of a considerable amount of space (Pederson). Acoustician Bob Hodas states that “at 100 Hz you have to deal with a 10-foot wavelength, so you’re going to need two and a half feet of space to absorb it” (qtd. in Pederson). Hodas continues on to explain that “whatever length the bass wave is, it will take a bass trap that is one-quarter the size of the wave to adequately absorb it” (qtd. in Pederson).

            There are two common types of bass traps used, the panel absorber, and the Helmholtz resonator. Both of these traps are resonant traps, meaning that they are built based upon the specific frequencies one is trying to absorb in their environment. The panel absorber is more simple in design and provides a wider frequency attenuation providing a bit of wiggle room in the accuracy of ones design. Similar to our mid and high frequency absorber designs, the panel absorber is a wooden frame that has a thin flexible panel over the top of the frame made of plywood or hard board. The absorber then has insulation such as rigid fiberglass or mineral wool inside placed against the front panel. Figure 3 shows an absorber to be placed upon the rear wall of the studio. This absorber designed by John L. Sayers is made of a MDF box and uses cloth on the front to cover the insulation instead of the thin plywood panel.

(Figure 3) A rear wall absorber made from a airtight MDF box with cloth covering the insulation.

According to Paul White, the more one fills “the cavity with fiberglass or mineral wool tends to lower the resonant frequency by up to 50 percent as well as doubling the effectiveness of the trap.” The use of cloth on the front, as found in John L. Sayers example (Figure 3), provides high frequency absorption as well as the desired low frequency attenuation. If a plywood or similar material is used instead of the cloth, acoustic foam or diffusers can be placed upon this surface if the reflections are a problem (White, Part 2).

            The Helmholtz resonator is more effective than a panel absorber at resolving problem frequencies since it is built with a design specific to absorb these frequencies. Bob Rowlette demonstrates this by stating that “trying to use foam tiles or fiberglass to cure a bad sounding room actually aggravates the problem and results in a very dead sounding room with a loss of the natural clarity and sparkle of voice and instruments.” The Helmholtz resonator, also known as a slot resonator is more frequency specific and leaves less room for error than a panel absorber without affecting the higher frequency characteristics of the room. A common model for the Helmholtz resonator is the pop bottle. When one blows across the top of such a bottle a tone is produced, with variability based upon the volume of the airspace within the bottle (Rowlette). This same design is applied to the slot resonator, where a box is constructed with the front covered by either slats or by a piece of particle board with the perforations used to simulate the pop bottle effect. The resonant frequency is then controlled by the amount of airspace in the depth of the box, and by the size of the openings in the slats or perforations (Rowlette). At this stage, one would take the room modes that had been determined as problems, say 70 Hz from our earlier example (Figure 1), and calculate the resonant frequency of the Helmholtz by using the following equation provided by the Sound and Audio Engineering Institute:

f=2160 x sqrt (r/((d x D)+(r + w)))

Where:

f = resonant frequency in Hertz (Hz)

r = slot width

w = slat width

d = effective depth of slot (1.2 x the actual thickness of the slat)

D = depth of box

If so inclined one could approach this problem algebraically and solve the equation for D, the depth of the box by providing the frequency that needed to be centered upon, and estimating r, w, and d, the slot width, slat width, and effective depth of the slot. Bob Rowlette recommends using a spread sheet “to model various dimensions and tuning for slat-type Helmholtz absorbers.” This technique provides easy representation of the resonators effective frequency allowing one to “easily see how changing any dimension changes the tuning of the absorber” (Rowlette). Lining the interior of the absorber in fiberglass will provide wider band absorption, or frequency attenuation over more frequencies than just the fundamental one (Rowlette). One important aspect to understand of the Helmholtz resonator is that changing the depth of it should not affect the room size as that will alter the modes found in the room, and lessen the effectiveness of the absorber.

            The acoustic concepts presented here provide rooms with the potential to have control over reflections through diffusion or absorption, as well as absorption of bass frequencies through the use of slot resonators like the Helmholtz resonator. These techniques avoid muddy sounds at the mix position by controlling reflections and bass frequency anomalies, contributing to the acoustical quality of the listening space.

            The sound quality inside recording spaces is clearly vital, but another key element to these spaces is isolation from outside sounds. Recording studios are often located near busy streets or neighborhoods where outside sounds like dogs barking, lawn mowers, and even the blast of the horn on a fire truck could ruin a perfect take. Also, sound from the control room leaking into the main tracking room, or sound from an isolation booth or drum booth, must be controlled and isolated to ensure that the different sources being recorded don’t bleed into other microphones and get picked up. In the case of the control room, equipment sounds like computer fans, and tape machines, as well as discussion between the engineer and the producer or client cannot leak into these rooms either. Here the factor at play is the Sound Transmission Class, or STC, which is “the measurement of the amount of sound that is transmitted through the wall” (SAE Institute). Transmission loss, mentioned earlier is very important in isolation because if sound is able to be transmitted through walls or windows, it will leak into other rooms and vice versa.

            The wall construction used is one major factor determining transmission loss. The use of staggered studs (Figure 4) connected only to the same header and footer is one method of providing isolation between rooms through the walls (SAE Institute). A more effective method is to use a metal channel (Figure 5) that the plasterboard is attached to that connects it to the studs isolating the plasterboard (SAE Institute).

 

(Figure 4) Staggered Stud Construction

(Figure 5) Metal Channel Construction

However, when possible the use of double wall construction (Figure 6) with a triple layer is the best possible method of isolation, especially when built on a floating floor (discussed later). A double wall design would have a layer of gypsum sheeting, a timber frame, followed by insulation. This design can be further enhanced with the addition of a particle board layer sandwiched between the first gypsum sheet and another sheet of a different thickness of the first, thus introducing the triple layer. This technique is then used for the wall of the other room with an air gap in between the two walls (SAE Institute).

 

(Figure 6) Double Wall Construction

The double wall design with the triple layer provides great isolation especially when built upon a floating floor. However, the key to a design like this is ensuring that the walls are completely sealed and airtight.

            These construction techniques are methods to guarantee isolation in the studio, but according to Gary Hedden in an article from Electronic Musician “Doors and windows are the weakest link, in terms of construction isolation, because you can’t insulate them like you can a solid wall” (qtd. in Pederson). Hedden suggests the use of solid core doors with either thermal seals, or retracting thresholds that actually lower themselves against the carpet when the door is closed (Pederson). Sliding glass doors are good if dual door designs are used with the doors placed at angles to each other and properly sealed (SAE Institute). The sliding glass doors should be made of the thickest glass possible (within reason) and each door should be made of different thickness to stop the transmission of sound (SAE Institute). The use of sliding glass doors can replace the need for a window into the main tracking room and of course double as a way to get into the studio.

            Windows are necessary for communication purposes in the studio between the performing musicians and the engineer and the musicians. Again, windows don’t have much insulation on their own to stop the transmission of sound, but with a little help they can be both effective in communication and at isolating the rooms. Dual panes of glass are essential in studio windows with different thickness a definite benefit. The thicker pane of glass should be on the control room side, with recommended thickness of 5/16” and 3/8” as minimum useable panes (SAE Institute). Like the sliding glass doors, angles must be in place between the panes of glass. The Sound and Audio Engineering Institute states “the two sheets of glass must be at an angle to each other else the two sheets will react in a resonate sympathy and the sound reduction properties will be reduced.” The construction of the window (Figure 7) uses the same techniques as the double wall design but with a header and footer for the window separated by a air gap to coincide with the air gap between the

walls.

(Figure 7) A detailed view of a dual window pane.

A fiberboard is used at the base and top of the windows gap covered in insulation. Also, the window pane is sealed by resting on a rubber or cork strip and then beaded with silicone (SAE Institute). Construction of a window in this fashion will provide the highest possible amount of isolation and least transmission loss through the glass as long as it is sealed correctly.

            Finally, the technique of floating the floor provides isolation from room to room as well as low rumbles from trucks or booming car stereos outside. SAE Institute describes that “the main advantage of floating rooms is the low frequency isolation it gives.” This will keep these low frequency rumbles out and your low frequency sounds in, to annoy the occupants of surrounding businesses or rooms as little as possible (SAE Institute). Also, a major benefit to the floated floor design is the isolation of noise transmitted through the structure of the building. Peter Elsea describes this problem as being “caused by machinery such as air conditioners and refrigerators which are mounted on floors or walls that can actually shake the structure.” Floating a floor (Figure 8) is an expensive project where 4” x 2” floor joists are built on top of neoprene pads that are positioned the same as the original floor joists. Insulation is then added to the cavity between the old floor and the new floor and the flooring is then laid on top of the new joists (SAE Institute).

(Figure 8) A floated floor cross-section.

This provides isolation through the floor from the potential low end disturbances around the studio.

            Through these isolation techniques the studio has a low transmission loss through the double wall design as well as communication through either dual sliding glass doors on angles or dual paned windows also at angles. Finally, the floating of the floor is in place to provide isolation from any low frequency rumbles getting in or out of the studio.

            There are many viewpoints on how recording studios should be designed as well as what materials and techniques should be used. As we previously learned, reflections provide natural resonance to a space. The use of hardwood floors are commonly understood as benefits to the sound of a room. Ethan Winer states that “A hard floor gives a nice ambience when miking drums, guitar amps, and acoustic instruments.” Earlier we discussed the use of diffusion based upon its capability to produce a sound that actually made the room sound larger than it really was. Some would rather choose the technique of absorption. Specifically, John Shirley PhD who in an article about designing isolation booths states in reference to diffusers that “In fact, they can give the sense that the room is larger than it is. Since that was not the sound I wanted for the room, and diffusers are both complex and expensive, I decided to leave them out of my design.” Clearly there are times to diffuse, and times not to diffuse.

            The use of carpeting can help deaden the sound of a room that is too live, though it will provide attenuation of highs and some mids, without much bass and low mid frequency absorption. The use of carpet for acoustics generally produces a dull boomy room (Winer). This view presents the potential for benefit through the use of carpet, but more importantly points out the potential for carpet to damage the acoustical properties of a room.

            For the purpose of monitoring playback there are a few different viewpoints. It is safe to say that all professional recording studios have two different types of monitors for playback. These are known as mains and near fields. The mains are often mounted in the walls in a technique known as soffit mounting. The main trouble with soffit mounting techniques is that a lot of work is involved since the speakers must be built into a real wall (Winer). The near field monitors found in recording studios are positioned either on stands or on top of the console to use for critical listening. The use of soffit mounting over stands is due to the reflections off the front wall caused by the sound resonating from the back of the speaker cabinet . These reflections then produce clouding of the sonic image through comb filtering.

            The use of Helmholtz resonators was a very common practice in older recording studios and broadcast facilities. The design still holds true today despite the large amount of space that it takes up. However, Paul White states that “panel traps with limp membranes seem more widespread in modern designs.” Along with the Helmholtz resonator White discusses other trends in recording studio control rooms in the past twenty years. One example of a once popular design that has been ruled out is the extensive use of mineral wool providing extremely dead control rooms in all frequencies but the lows. This design lends a unbalanced sound that doesn’t offer the broadband absorption found in more modern designs. Furthermore, there have been designs where the back wall of the studio offered a great deal of reflections and the front wall provided a dead absorbed sound. This was known as the “live end, dead end” approach. Despite all these designs, the latest trend is to provide a combination of broadband absorption and symmetrical designs, with reflections provided by hard floors and diffusers (Pederson).

             In today’s world, the project studio is becoming more and more prevalent, and many professional studios are closing their doors due to a lack of business. In the field there are a handful of reasons that are commonly expressed for this phenomenon. First, the availability and affordability of recording equipment has come down significantly in the last handful of years allowing would be studio customers to run to their nearest Guitar Center and purchase recording equipment instead of studio time. Second, the affordability and power of modern computers has made recording at home accessible to anyone with a computer. Projects are being done at the same place that people are checking their E-mail and playing the latest edition of Warcraft. Most importantly, the quality that the consumer grade equipment is capable of produces recordings that rival commercially produced productions, at least to the average listener.

            Probably the most striking reason for a shift from professional studio to home studio is the shift in how music is listened to and purchased, or “borrowed.” In a discussion with my younger brother the other day he described a new peer to peer program called “Ares“, with iPod in hand of course. He explained to me, though I understand how these systems work, that people post their songs for others to borrow. I found great humor in this as the current method of obtaining music often doesn’t involve any sort of monetary exchange, though listeners do also purchase tracks through online stores like iTunes. This ideology has trickled down, or rather up from the consumers to the musicians. Though often they truly are one in the same providing a do-it-your-self attitude for the least total cost possible; this is very damaging to the audio industry in all facets.

            The aspect that is commonly overlooked is the acoustical properties of the rooms these projects are being recorded in. Often a spare bedroom becomes the “studio” and a desk is pushed into the corner with drums, amplifiers, and vocals are tracked right there in the same room. For years musicians used four track cassette recorders, and four track reel to reel recorders before that, to capture their song ideas or create demos. This equipment was generally not capable of producing high quality recordings, and the quality of acoustics almost didn’t matter since the medium was generally quite poor; no one would know the difference.

            The acoustical principles described here can often be retrofitted to work in a home studio environment. I personally have run my own semi-professional project studio for the past five years with some really great results, but have paid attention to some degree of acoustics all along. Early on I noticed flutter echo problems in my closet that has been converted to an isolation booth and decided to do something about it. I realized that if I hung blankets it would “kill” the room and provide a dead sound, allowing me to add reverberations later. Also, at the advice of musicians along the way I stockpiled egg cartons to place on one wall as a form of diffusion and absorption as the space behind the cartons acted as little tiny bass traps.

            The use of these blankets and egg cartons also provided a more professional appeal, and impressed every customer who walked into my closet, or rather isolation booth. Since it has a dead sound it implies to the average person to be soundproof, though it is definitely far from this. If someone in the house flushes a toilet or runs a bath, it is break time, as the sound of the water through the pipes is quite audible. Worse yet, the dog next door provides a lunch break or possibly even the need to reschedule the current session for the next day, with fingers crossed that the dog won’t be barking. These issues are clearly a hindrance on the operation of a home recording studio and are reasons why professional studios are far superior since the isolation and acoustics are much better.

            Constructing a small isolation booth and setting it up inside of an existing room is one way that the isolation characteristics of the home studio can be enhanced. The booth obviously has to be able to fit into the space allotted but should be large enough to accommodate an acoustic guitarist and microphones. The dimensions can be chosen based upon the concepts of room ratios previous to avoid issues with modes. Also, a hard floor should be used to offer the ambience needed for acoustic instruments since the walls and ceiling will probably be completely covered in foam. If needed, carpets can always be laid down to deaden the floor later. The wall construction should be similar to the designs found earlier. Though space probably won’t allow a double wall design, the triple layer effect where a piece of particle board or MDF is sandwiched between two pieces of gypsum board will help in the isolation effort. Also, material is available that is effective at stopping the transmission of sound called SheetBlokâ. This material comes in rolls and can be placed in between the layers of the isolation booth. SheetBlokâ would probably be best on the outer layer to allow the insulation in between the studs to absorb some sound and provide some transmission loss through the inside wall resulting in less interior reflections. The use of a solid core door is a must, with a window in the door a bonus. The key to an isolation booth like this is to ensure that it is properly sealed around the door.

            If an isolation booth is out of ones budget or space restrictions, the use of a spare room or reasonably large walk in closet will do fine. I am currently in the process of building a hardwood floor section to place in my isolation booth for recording instruments that need the live acoustical properties of a hard floor, and it looks great! The plan is to use hardwood paneling on top of a piece of particle board or plywood, adding trim around the edge to make a nice looking acoustical enhancement to my dead sounding isolation booth.

            Acoustic foam packages are available from pro audio stores with simple foam absorbers and diffusers, in addition to straight sheets of foam to cover large areas. Though the construction of good inexpensive panel absorbers is easy, purchasing these kits is a very common route, and again looks great with little effort. The rear wall absorber design (Figure 3) from John L. Sayers would benefit any control room greatly. Also, his corner absorber design (Figure 9) would provide attenuation of bass frequencies in a control room or medium to large sized tracking room with more effectiveness and less cost than any commercially available foams. Finally, his side wall absorbers (Figure 10) provide a control room with gentle diffusion of high reflections instead of absorption, with the absorption characteristics focused on the lower mid range frequencies leaving a natural sounding room that isn’t completely dead.

(Figure 9) The corner absorber from John L Sayers.

(Figure 10) The side wall absorber from John L Sayers.

These absorbers would be easy to make for the do-it-yourselfer, and would be a great addition to any home recording studio. Diffusers would also help, especially if the studio was carpeted since it would take away from the dead sound of the space. A complex diffuser would be fairly hard to design though one could simply make one by bowing a thin piece of plywood and wedging it in between two pieces of 1” x 2” that were connected to another piece of plywood that was shorter in length than the bowed piece but identical in width. One would probably want to use some sort of foam or insulation on the inside of the arch to avoid resonance, with a wood or cloth covering over the sides to provide a clean look and keep particles in if fiberglass was used. This diffuser could then be suspended above the ceiling above the mix position.

            Clearly the acoustic principles discussed here could be applied to the home studio with a little creativity and patience. In most cases space is at a minimum, and limits the use of large bass traps like the Helmholtz resonator, or the design of large open recording spaces with live sound characteristics. As the technology of both acoustic treatment and recording equipment continue to come down, the home studio will continue to get better and better rivaling the quality of commercial facilities.

            In conclusion, the quality of a recording really starts at the source. If we assume that the equipment is of reasonable quality and the engineer knows how to operate it, the room can take either the credit or the blame for a good or bad sounding recording. The varying opinions on live or dead rooms as well as how to absorb or diffuse sound are good to be aware of, though in the end it is really up to the user. In my studio I currently have a very dead room for recording since my space is very small and it would be hard to get a good live sound in it. The addition of a section of hardwood floor will be a significant benefit for me because it will liven up the room though there will still be little trouble with reflections. In the modern world of home studios, the often overlooked aspect of good acoustics can clearly be damaging to the quality of the recording. After all, microphones don’t lie, but if I could make them lie I’d be a very rich man.

 

 

 

 

 

 

 

 

 

 

 

 

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