I’ve taken only a couple photographs so far and I wish now that I’d been taking shots while I was working, but fear not! There will be in depth illustrations in the book I’m working on. 

 

John: Sure. Favorite albums, you know, are going to vary a lot. And when I’m thinking of favorite albums relative to a listening environment I’m thinking in terms of acoustics, playability, or transferability of studio B to C to D. We call that translation; does the studio translate well? I tend to go after particular producers and their certain bodies of work or a particular production team as opposed to just an artist. And the only artist that I would say I would do that with would be someone like a Pink Floyd because their artistry and music is embedded in their production style and they’re very, very picky about it. I wouldn’t put that with any other band; they’re kind of in their own world. One, because they don’t release very much, and two, when they do release, they’re nit-picky about every [darn] detail, even when they play live. And even when they were [together], once every five years was probably quick for them because of the detail they put into their productions. So for a band, I wouldn’t have a favorite for the purposes of translation, but for a producer, people like Quincy Jones would come to mind and [otherwise] it would be a producer [and it] wouldn’t matter which genre of production [he or she] did. You know his productions are all going to be pretty good because his standards of arrangement and production and the quality of his engineering staff are all quite high. So those Quincy Jones productions by and large, would be good to check out. As far as trying to find out “how did your room do,” Pink Floyd albums would be good to check that out. A lot of artists’ albums I would not try to check anything [with] because one might sound really good but actually might be kind of lousy because they [use] different production teams a lot of the time. So that being said, you know, I’d rather not get into the genres of this band or that band. I don’t think of it that way when I pick people to play. Only in an environment where I want to check out the sounds [would I] pick [these things], you know.

Jake: And how would you define the field you’re working in?

John: As far as my own studio and the kind of places that I work in (whether its a commercial studio where I record somebody and track somebody, [or] whether its my room where I’m mixing people and doing the posting of their work) I work pretty much most of the time in the music business […]. So its music CDs, music sound… I do live sound too. I don’t do a lot of it; I used to do a lot of it. Now I [do] just occasionally when there’s a huge concert where they’re looking back and finding teams that they’ve used in the past for large concerts. [Then] I’ll go out and do one, but other than that its mostly in the post production and production of music albums. Other than that, I have done film soundtracks, I have done sound design for film soundtracks… but I don’t do that regularly. There’s only been four or five in a period of 25-30 years as opposed to albums, [where] I’ve been doing those at a rate of about usually four to nine albums a year.

Jake: So broadly, you’re an audio engineer, in the audio engineering field.

John: Yeah. I’ve also designed systems for people. I’ve designed sound reinforcement systems for theaters. I’ve designed sound reinforcements for churches. I’ve designed sound reinforcements for schools; I’ve designed many studios and control rooms for a lot of local studios. They just pay me to consult. I go in there and its a lot cheaper than them going in and hiring an acoustician to do it. And no I’m not in the same league as [acousticians] are; you can’t tell me “I need a reverb time on my room of X” and expect me to tell you exactly how to build the room and what types of things to put on the walls. I can’t do that; I’ve never been in that category, nor do I want to be. That’s a very specialized field. I wish I could afford to hire those guys to work on one of the studios that I work in. I’ve worked in some of the studios they’ve built for other people and some of them I liked and some of them I didn’t; you know, which I also find kind of interesting.

The studio I found that changed what I look for (and how I think about what I look for) was actually designed by a friend. Actually, it was a type of system for [the] acoustics of a control room, which was starting to get fairly famous or infamous at that time. If you owned a studio previously, he was infamous, because nobody liked to hear it. If you didn’t have a studio yet but you were thinking about building one, now he was kind of famous and you wanted to know what he had to say since he was a famous acoustics kind of person. And for me, he had designed a room (which was one of the first of its kind in California) which was a live-end –dead-end room. It happened that some of my friends worked in and owned that first studio he did. So I was there for opening night and saw both the friend that designed it as well as the people who owned it and they went through the whole deal about what to listen for (did you bring something that we could play? and all this stuff) and the room was really a beautiful sounding room that I really liked. So I rented some time to do an album I was working on. Soon after that (a couple of weeks maybe), I was in there and it only took me one session to realize how, not only did it sound good, but that everything went faster in that room. It was as if I was doing everything more quickly than I normally do and I wasn’t rushing; I wasn’t going any faster than I normally do, but I was saving time. And the more I thought about it (after a couple of days working in there), the more I asked myself, “wow, what the heck’s going on?” I was estimating five hours but I did it in four, I estimated seven and I did it in five. Its like, “What the heck is happening?” It turned out… when you start EQing something or when you start panning stuff and you’re doing everything with reverbs and delays and stuff, typically you’ll do it and then you’ll have an idea and you’ll start fine tuning it. What I was realizing was those things happened effortlessly and very quickly in that room. All the EQing, it was either white or black, and usually when you’re EQing its kind of like “well that’s better but maybe a little more” but in that room it was kind of like “oh no there it is, oh went a little too far, no there it is!” and then you just move on to the next thing and after a little while its like “this is cool!” You almost felt like when you panned things, when you move them in the space, it was almost so clear that it seemed like you could reach out and touch where that sound was. And I had never experienced that in any kind of control room I’d ever been in. I’d never noticed that anywhere else.

So I did more work there and I didn’t want to go anywhere else. Then about a year and a half later they were having a little bit of a problem just keeping the space rented all the time and they were looking at possibly selling or leasing it. Narada Michael Walden, another producer, eventually bought it. At that point, I couldn’t get in and Narada is a good friend, too, but I had to beg and barter to get in there for a few hours to work. So it was kind of like “oh gosh, now I need to find another one of these dead rooms” because I really liked working in that room and everywhere else I worked I had trouble… not trouble, I just had what everybody else had, and things weren’t as clearly defined as in that space. And that led me, little by little, to keep talking to Chips Davis (the guy who designed the idea of the live-end – dead-end room and the physics of it) and I picked his brain whenever I could, to build my own, which I finally did, and that was then resolved.

The only problem now is I don’t have a tracking room. Most of the other rooms around here say, “I have a live-end –dead-end,” well, most of them have the idea of it but are not all the way live-end – dead-end. And it takes quite a bit to be that. So anyway, that’s kind of where I’m coming from. And that changed from that point on how I deal with “how did I pick a studio.”

Jake: So I have a small space (approximately 2000^3 ft.) for an average studio apartment to use for something. For example mixing, single-track recording, mastering… and I can afford maybe a thousand dollars to get it to the next level up from just a studio. What should I do?

John: Well, the first thing would be to determine where you are going to place you’re speakers. You don’t want doors opening and closing between the listening position and the speakers. You don’t want glass anywhere in between you at the listening position and your speakers – if there is any glass, which, you know, can mess with a lot of stuff – you have a problem. There’s very little you can do.

Jake: You mean on the walls?

John: On the walls, on the ceiling, on the floor. Anything, yeah. Live-end – dead-end rooms, from the back end of the speakers, on the ceiling, on the floor, on the sidewalls, including the back wall which the speakers are at, facing back at you. They must be 100% dead. Now that gets to be a little difficult if your control room glass, where you can see the artists, is there. We don’t want to block the control room glass because we want to see the artists and vise versa. Bad news is, if we block that, sonically that room is better; practically, that room is not better, Okay? I’ve even been in rooms where they tried to do this and they were using video cameras and the artists felt terrible. Because they don’t see anybody and there’s the booth with, you know, video cameras looking at them! And its like “this is bad enough,” it’s almost like the fish in the fish bowl kind of thing, where everyone is looking at them. So there’s a lot to be said for trying to design a control room studio where its livable to see, it has good visual contact with artists and the artists have visual contacts with the production team and yet, we can still have a dead environment between the speakers and the listener. That is hard in a lot of cases. Which is one of the reasons why when I built mine I did not try to do that. Instead I’m only making the control room. Period. I do not want the studio. I don’t want it because of all the hassle of having artists there, plus I didn’t have enough space to have a high enough space and a large enough volume of room to do drums justice. Mine is 19×21 ft. And that’s a nice size for a control room. It’s much bigger than this control room. But I can put the walls where I want. I don’t have to have any windows if I don’t want to. I can put the doors in the back or the front as long as I know “where do I put the speakers; is anything going to move up in that area,” you know.

Now what I’m going to do to deaden it: You don’t want doors, you don’t want somebody coming in and out of the door which would then change your acoustic space between the speaker and the listening environment because, essentially, from the listening environment, when you’re at the console, that spot from there to the speakers has to be dead. Straight up, all the way to the front, to the speakers, behind the speakers, to the sides of the speakers, on the floor, [and] all the way up to you. And that raises some problems; you’re going to have a board there for sure, [and] it’s going to be a big flat surface that the sound is going to bounce off of. However, if sound bounces off it and goes straight up and your ceiling is dead, at least it’s going to bounce once and deaden out again. So you have to control for all of those things. A lot of people who did live-end– dead-end found out that the back end of the board which the speakers are hitting as its traveling towards you, was a bummer because it usually projected it back up and a lot of control rooms have some sort of other things that it could bounce off of once it came back. So they would be putting deadening material on the back end of the board, all over the plugs to keep them from vibrating and all kinds of things like that. So there are a lot of little things. But generally, its “what area do you want the speakers in,” then it’s “pad it all down” (there’s a lot of ways to pad it down, you can buy normal insulation, you could cover it with fabric, you could put foam on the walls, but its got to be full band).

Jake: Like 703?

John: Yeah, or it can’t be some kind of thin acoustic tile. It’s going to have to be something fairly heavy.

Jake: So lets say that we accomplished deadening with the thousand dollars and we’ve already got the speakers in place…

John: I would say for a thousand dollars, it’d probably only cost you…

Jake: It’d probably cost you twice that much for the measurement equipment.

John: Yeah, but if you just had to buy the absorption stuff… $500, $600. As long as you didn’t buy the custom foam stuff… that’s very expensive, I would not go there.

Jake: So after you spent that $600, lets say you’ve got another thousand. What would you do next?

John: A live-end—dead-end room means that from you to the mixer to the speakers is dead. However, when I went to Tres Virgos, which was the name of that studio before Narada got it, who then switched it to Tarpan… They were under the assumption that the live section could be anything, it could be hardwood floors, a hardwood floor back wall, it doesn’t matter. And it may not matter all the time; however, if you have a flat back wall it’s going to bounce all the sound in one direction. I’ve been in rooms that did that. In my room I tried that and then tried to diffuse it, to see if that was any better. Then I tried different materials on the walls, not just wood, some wood, maybe some glass, but also some wood with some glass. Also some materials to absorb in certain spots. And I found that I liked controlling it with some deadening material. Not way dead, in other words, not what we’d put in the dead side of the room. What I’m meaning about dead is the difference between a hardwood wall and one layer of fabric over the hardwood wall. Or a little bit of sound absorption that was only maybe a quarter inch thick. It would take down some of the upper mid range. And then experiment, shoot the room again, see where we are. Do we need a little bit more in the corners? Because corners are where the bass will start building up on you. So if your bass was a little loose, what I’ve found was when I left the back wall fairly live, like “was it shot when I first went in there?” I didn’t like the bass as much. It was a little too bouncy for me. And as I experimented with “I’ll put a little bass trap here and there; lets not do the whole wall, lets just do the corners” and little by little, just getting it a little bit more dead, the bass way up in the front of the room was changing radically. Because you didn’t hear it bounce off that back wall, the back wall disappeared, [it] sounded like you were outside. [It] felt like you were outside, acoustically. That’s what it sounded like. But you heard it and it changed the tightness of the bass popping. If you had a really tight bass, like a kick drum or a bass where it was played very percussively, you know, that’s like slammin’ the fingers. It’d be a little messy with it all live in the back. As you put a little bit of absorption here and there, you could get it to where it was really tight; it didn’t slop over time. And so it was a matter of just kind of getting it in to tune to do that. So for me that’s what it took, rather than just leaving it all.

Jake: Probably based on something based on the room you were working in previously.

John: Yes, absolutely, and we were using sheetrock on some of those walls and the sound of any audio stuff hitting sheetrock is not always pleasant. It’s very dank sounding. It almost sounds like you’re in a dank cement type room; it does bounce off of it but the bounce that comes off is kind of upper mid oriented. Like 1k, 2k. And you don’t here the extreme his at all. So what I found was it’s nice to put a very thin fabric layer or some wood on the sidewalls, for instance. So my sidewalls are cedar. It could be redwood, could be oak; something that gives you a little bit of reflection, makes everything that’s coming from [the front and going] to the back hit sidewalls then bounce behind the listening position. And then it hits the back wall and comes back to give you a little bit of natural reflection. But then you’re controlling the amount of natural reflection in the back because you’re not letting the whole thing be completely live. You’re deadening parts and parts are going to be fairly live and that’s what I’ve found to be rule of thumb. Lets make it sound very, very natural and that’s taken a bit of doing.

Jake: So as a side note, when you’re shooting the room, what do you use for the microphone, for the hardware, do you use any software?

John: I have; I’ve used white analyzers, I’ve used IVIE, … one of the best systems is the TEFF system and that’s beautiful but its very expensive and I had somebody come in and look at it through there too. Its able to see reflections and tell you exactly how long it took to get back to a spot or how many times it bounced and where it bounced; its really cool, but they’re ten thousand dollar things, so I don’t own one. But what I’ve found was that as you put in these systems and you check the lows, the mids, the highs, and then you start shooting the room, once the room got fairly close I usually stopped analyzing the rooms. I didn’t keep tuning them to the analyzers; I started that way just to get them at least in the ball park and at least close, what I did after that was put them through kind of what you asked me before; what kinds of products would you put on the system to find out well “you’ve heard the Quincy Jones production on this system and you’ve heard it in thirty five systems, what does it sound like in this system?” and then what would it sound like if you left all the EQs out of the circuit and you just brought up a little bit more of the subs? Because it’s a four way active system, and what would’ve happened if you just brought up the low-mids compared to the subs? Just [brought them up] a tiny bit. Would it get more boomy? Would it keep things tight? What would it do? And what did it do to the flatness of the whole room? So what I found was that a lot of tuning had to go into the timing and the placement of the drivers in the room. Boy that’s…

Jake: That’s about half of it right there.

John: That’s a lot more critical than I ever thought. Yeah, you know, I mean people tell you, “hey if you really want a good mono than [one speaker] better not be a couple thousandths closer than the other [to the listening position], its like “wow, [isn’t] that true” plus if you have a system like this, where you got a four-way and [each driver is] dealing with different frequencies […], they’re all traveling different speeds, so even thought they’re kind of lined up visually, to you, [it] does not mean [they’ll be accurate]. Because one’s got low-mids compared to the other one, [which has] got lows; the lows are traveling slower and the low-mids faster and how do you deal with that? I deal with it with time delays in my crossovers. Very short delays you can tune. [… The] placement of the speakers is critical in getting a really tight signal. [That way] your mono is really mono. And that’s when you really start to reach out and grab the stuff, its right there. If you don’t do that, you’ll never experience that kind of a space. But [these things] had a lot more to do with it than I expected. The other thing that I found out was kind of a detriment: […] as I was doing that, I was going “wow, this is getting tighter and tighter. Wow, the image is getting better and better. If I move things… like, I got the board kind of in the middle but its far enough forward so as not to block the speakers [from] hitting me. For a while I had other equipment — outboard gear — off to the right or to the left of that board and for a while I had stacked up, […] not high, but [high enough so that] if I was sitting down at the board it might have been not at my eye level but below almost shoulder level or a little below shoulder level. That messed things up, big time. The whole image was screwed up. And as I was pulling the box out [I was] going “wait a minute, wait a minute, something’s moving; something’s changing. What’s happening?” And it was me, piling up FX boxes on the side. So then I took all the FX boxes out and tried it again. Everything cleaned up. So now I don’t have anything on my sides as the speakers are coming in my ears […] above 28 inches or so. Low! Very low! Because like we were saying, are the speaker’s sounds going to hit the back end of that board? Yeah! And it does get in.

Jake: So that’s all I have.

John: Ok hopefully that helped.

Jake: Anything else you’d like to add?

John: No, I think it’s a good project to do, […] in fact, its probably (I think) worse now than it used to be in that people now are given the ease of having a computer and having things in a work station. They think that because they can manipulate the digital parts of it that some how the acoustics don’t seem to matter as much. […] The acoustics matter a whole lot because you’re still basing all of your trust about “do I need it brighter, do I need it bass-ier, do I need it (whatever I need); do I need more ambiance, less, wetter, drier;” all of those things you’re basing on how you heard it coming out of the speakers and the speakers are extremely affected by the room and the acoustics of the room. […] You look at pictures of control rooms in magazines; and you go “look at that room, there’s crap everywhere in that room, how in the world could they ever work in there?” They can work in there, [but] they can’t work in there very accurately, and obviously a lot of people don’t understand that.

Jake: Doesn’t translate well.

John: Doesn’t translate well; might sound great in the control room; sounds great then you get it home and you go “what the hell am I listening too,” that kind of stuff happens. Its interesting, the publisher of mix magazine in the last issue was talking about exactly what we’re talking about right now saying […] “the audio guys got those computers and everyone seems to […] not even think about that stuff.” But just because you bought a fairly decent set of speakers doesn’t mean they’re going to be accurate. It just means you got one of the pieces that needed to be accurate but where you put them, how you put them in, what amp did you talk to [which are talking] to those speakers, and where did you put them in the room, and what did the acoustics in the room do to them… It’s a huge thing. It’s just as important as “what happened as the sound left the instruments before the microphones pick[ed] them up?” Both of those are extremely important and we’re getting to the point now where most people are more concerned with manipulating them in the digital domain because they have so much […] power to do stuff that that’s all there is and its like no, if you have bad sounds going in, all you’re going to do is band-aid them up even worse. So it’s a good thing to put things like this out there so that people are aware of the problem and then can kind of address it.

Jake: All right, thank you.

John: You’re welcome.

Abstract

Literature review of acoustical properties of various materials for use in treatment of a home studio. Focus is on inexpensive products and designs to correct the most common and problematic studio flaws with simple, do-it-yourself projects. Minimal discussion of physical mathematics.

Acoustical Treatment of Home Studios

The independent label or artist no longer struggles to find professional quality recording equipment at an affordable price; however, home studios still go acoustically untreated. Given that the recording industry been shifting toward smaller and less expensive organizations that are producing, recording, and mixing music, controlled and predictive acoustical designs for home studios with are now in great demand. Those who want better room acoustics are not necessarily the same people who want to learn all about sound physics. Musicians, it would seem, make the bulk of the growing population of home studio enthusiasts.

This research is therefore aimed at the home studio owner whose field is not engineering but art, a field which can require frugality when working alone or in small groups. It covers necessities to begin the process of treatment for any box-shaped room in a normal home or office setting. Limited discussion of math up through algebra is used to convey principles and define terms. When treating a room for the use of others who are paying well to use it, more should be taken into consideration than what is presented in this research.

This research begins with a discussion of sound physics used in room treatment such as absorption coefficients, cut-off frequencies, wave scattering, and modes. Following is a simple method for isolating the most common outside noises from penetrating the studio. Next, a set of materials commonly used to treat a room is laid out followed by a quick explanation of how best to use each material with minimal construction and cost. The set of materials includes fiberglass boards, block-type and perforated Helmholtz resonators, corner absorbers, and ceiling diffusers.

Basic Sound Physics Sound physics is traditionally studied with calculus and linear algebra to accurately predict the propagation of sound waves and their tendencies against various surfaces at various angles. However, for the average artist and home studio operator, simple definitions will do in

order to keep the intended effects of any treatments in mind. All calculations are estimates but are close enough to get the job done.

To start, a brief definition of wavelength and frequency are in order. A wavelength (ë) is the measure of length of a wave; in the case of this research it is in feet. It is inversely related to its corresponding frequency ( f ) and is given by the equation ë = (c / f ), where c is the speed of sound. A frequency is given by the equation ƒ = (c / ë) and is measured in Hz, which are cycles per second. That is, a wave with a frequency of 10 Hz will travel the distance of 10 of its own wavelength in 1 second. The term frequency is used in acoustics more frequently than wavelength. The term frequency response, used later on, refers to a range of frequencies at which something will respond such as the frequency response of a Shure SM57 microphone being more prominent at 1000 Hz.

When treating a room, the objective is the keep a fairly even frequency response throughout the room’s full volume so a microphone and instrument can be placed at any point and produce similar results to being placed anywhere else. In other words, the room becomes predictable. A metaphor by Philip Newell is that rooms are instruments that, in order to be played correctly, must be destroyed and rebuilt for predictability (1998, p. 30).

For the purposes of this research total destruction and rebuild are generally assumed to be out of reach, so instead absorption and diffusion of sound are needed in order to achieve the desired predictability. Absorption of sound, a less costly and time consuming objective, is described as the conversion of wave energy into heat in the air and in the walls (Morse, 1948, p. 385). After a wave is created by any means, be it a note on a trombone or an anvil falling to the ground, the energy of the wave will be absorbed until the wave no longer exists. In a perfectly open space with no walls and nothing but air and a sound wave propagating through it, the wave will continue until the friction between the air molecules dissolves it, which will take a very long time. Similarly, in a perfectly reverberant room (that is, one in which the wave looses no energy when it bounces from wall to wall), a wave will continue until that same friction in air stops it.

The difference is in the number of times this wave can be heard by an observer. In the open space, the wave only comes to a given point exactly one time and the sound of the wave is heard that one time for exactly what it is. In the room, the sound is heard possibly thousands of times, each time overlapping the last, making a (you guessed it) reverberation sound until it becomes inaudible.

Luckily, no room can be considered perfectly reverberant, and in most cases a room’s walls do absorb a great deal of wave energy. The variable describing just how absorptive a material is is called the absorption coefficient (a) which varies from 0 (perfectly reverberant) to 1 (perfectly absorptive). Morse (1948, p. 385) defines the absorption coefficient as the percent of energy absorbed by an object. For the purposes of this research, a will refer to the coefficient of audible and sub-audible frequencies absorbed. The difference may seem negligible but ‘energy’ can refer to any kind wave in any spectrum, whereas a will only include energy that our ears (and at very low frequencies, our hair follicles and skin) can detect.

The dimensions of a room determine its cutoff frequency and the modes at which frequencies can pile up (Shea & Everest, 2002, p. 3-4). The cutoff frequency is the frequency above which no modes will be transmitted (Morse, 1948, p. 308). Most home studios are six sided, having 4 walls, a ceiling, and a floor, each at 90 degree angles from one another. Such rooms, while not ideal for a professional recording studio, make the cutoff frequency and mode calculations much easier because there already exist a wealth of handy equations and web-based calculators for the do-it-yourselfer. There are even some free programs that can give a graphical representation of a room’s modes and where to dampen them.

Shea & Everest (2002) give the formula for cutoff frequency by Cf = 20,000 v(T/V) where Cf is the room’s cutoff frequency, T is the reverberation time in seconds, and V is the volume of the room (Length x Width x Height) in cubic feet (p. 263). But this doesn’t help when accurately calculating the reverberation time and can be extremely tedious for anyone but the architect who designed the room in the first place. An alternative calculator for the reverberation time can be found at http://www.mhsoft.nl/Rt60/Rt60.asp that, while making some assumptions about the building materials, does not require the user to know exactly what the room is made of and what lies beneath and above it.

Shea & Everest discuss that a room’s modes, determined by the ratio of length to width to height, are given by a series of calculations that lead to frequencies at which the walls will vibrate and generate reverberations. These reverberations occur as a wave bounces from one wall to another and back. Each reverberation works not only on its specific frequency (such as 141.2 Hz) but on all its multiples on upward (282.4 Hz - 2x, 423.6 Hz - 3x, etc.) and contribute to an unwanted coloration of the sound through 300 Hz. Such coloration occurs as each of the three axial modes (the three that interact between parallel walls and the floor and ceiling) generate similar or identical frequency modes (2002, p. 3-4), ergo a room with a ratio of 12:14:8 ft, which reduces to 1:1.167:0.667, has a pile-up of all three axial mode frequencies at 282.5 Hz (Wieczorek, 2004). Such calculations were made by an online calculator (see address under Wieczorek, M. in the references section).

Waves bouncing from wall to wall aren’t the only physics which dictate a room’s character. Wave scattering can either help the predictability of a room’s acoustics by averaging the reverberations around the entire room as has been more recently discovered (Peterson, 2001) or, as Morse puts it, it can hurt by distorting and interfering with the sound source. A wave is scattered when part of it bounces from an obstacle in a new direction and the rest continues on its original path (1948, p. 346).

Materials

A large part of making a room desirable for recording is keeping outside noise out. This is commonly referred to as isolation. The largest problems in isolation facing home studios are windows and doors, which can make up the bulk of openings and the uninsulated layers of a room. Double pane windows are known to insulate both thermally and acoustically and are easy to install. Standard home doors are too thin to absorb anything but the slightest of noises and will let neighbors now about each and every take that is made, but 1¾” solid core doors have a 33 dB transmission loss in the mid range (approx. 500 Hz) and weatherstripping can be added to complete the room’s isolation (Shea & Everest, 2002, p. 17). Both take less effort than most other parts of acoustical treatments for a home studios and professional studios alike. In a traditional studio, however, sound locks are common practice. Sound locks are hallways that have solid doors and airtight seals for three of more openings. They open up into the the control room(s), the studio(s), and the rooms outside such as a parlor so that sound doesn’t travel between each room during the recording process.

Once a room has been isolated to a satisfying degree, the objective is then to dampen trouble frequencies caused by modal pile-up below the cutoff frequency and to create a fairly predictable acoustical environment throughout the audible spectrum wherever a microphone might be placed. The smaller the room, the less treatment material might be necessary, the larger the room, the fewer frequencies will be a problem for modal compensation (Shea & Everest, 2002).

In order to catch a specific modal frequency, a Helmholtz resonator is built and tuned to that frequency (Shea & Everest, 2002, p 245; Sapoval, Haeberle’, & Russ, 1997, p. 2014). By the German name, it might sound complicated and expensive to design and build a working resonator but there are plenty of ready-made designs using materials costing less than $50. There is no great

difference between perforated and slit-type resonators, but the method of finding each one’s peak absorption frequency and tuning it to the correct peak is different (Shea & Everest, 2002, p. 246).

If the modal frequencies to be controlled are floor-axis based or for any other reason should be structurally capable of withstanding physical force, a block-type resonator will be better equipped to handle the conditions. Block-type resonators are constructed by making a box with a port hole which is of a diameter that resonates at the desired peak frequency (Shea & Everest, 2002, p. 245). When building a block-type resonator, using a neck shape resembling that of a funnel over the port hole will control high frequency absorption and still allow for low end absorption (Sakamoto, 2000, p. 14-15). Type R proprietary Soundblox use a block and funnel design which absorb well at 125-250 Hz and don’t absorb much past 500 Hz (Shea & Everest, 2002, p. 252).

If the modes include more than one wall-axis, a perforated panel with an absorbent material such as fiberglass will act as a Helmholtz resonator. For the home studio owner, a preferred perforation equation is f = 200 v(p/(d)(t)) where f is the absorbed frequency, p is the percent area of the panel covered in perforations, t is the panel thickness + (0.8)(hole diameter), and d is the air space depth behind the panel in inches. This will suffice when building a tried and true perforated resonator; however, new absorbers called microperforated panels (MPPs) are seen as attractive alternatives for the latest sound insulation systems (Sakagami, Morimoto, & Yairi, 2005, p. 204). Sakagami, et al. continue that by using acrylic glass panels of significant mass, such as 2 kg/m2, and by placing holes at distances of 3.5 mm from one another, absorption can be controlled via hole diameter as in standard perforation techniques. The difference is a 0.2 mm diameter will cover a broad spectrum from 125 Hz to 2 kHz (a = 0.35) while a 0.7 mm diameter will focus absorption at 500 Hz (a = 0.95). The absorption spectrum and a vary respectively between the two diameters (2005, p. 205).

Now that the modal frequencies are dealt with, any further treatment for predictability will be relatively simple. With newly abundant commercial products for sound absorption, it could be confusing to the home studio owner as to which products are necessarily expensive and which products can be fabricated by hand with less expensive materials. Numerous foams are now available that require very little effort and do a good job at absorption with a generous frequency range for a premium cost of about $3.90 per square foot (Auralex 2″ SonoFlat Studiofoam). The same foams can reach a necessary depth of 125 Hz at a respectable á when doubled up upon each other for a total cost of about $7.80 per square foot. For reference, this would be over $1300 of foam for the walls of the previous example room’s dimensions (12 x 14 ft).

On the other hand, Shea and Everest (2002) explain that porous foams are more expensive and only slightly more absorbent than their fiberglass counterparts (p. 31). So the same $1300 job can be done with fiberglass type 703 (which is just a part number by one company that produces 3 lb/ft2 fiberglass (Shea & Everest, 2002, p. 31)) panels for under $300. The only difference is the preparation needed for the fiberglass (Shea & Everest, 2002, p. 255). Fiberglass can be flaky and the fibers are irritative to the skin and harmful to the eyes so care must be taken when handling and light weight, loose cloth such as burlap should be used to cover each panel (p. 255).

For placement of the paneling, several factors can affect the sound absorption characteristics and should be taken into account when deciding upon a strategy for the absorption at various frequencies. The best practice in such strategies is to absorb on all frequencies evenly when all is said and done and then to allow for adjustment to different situations. Situations that might come up are vocals that need to sound “sweeter” in the mid range or bass drums that are acting on a mode that was not tuned for (Greg Demascio, personal communication, June 28, 2005). For the paneling described above, keep in mind that for panels put directly on a wall, an unsupported panel cannot reach the lower frequencies; a supported panel’s frequency absorptionis directly related to the stiffness of its support (fiberglass mounted on a drape will only absorb the frequencies the drape will); and a porous material, when thicker than a given wavelength, will completely absorb the wave’s energy (Morse, 1948, p. 362-364). For general practice, remember that walls are perpendicular to the most coloring of sound waves so to put something directly on a wall will maintain that perpendicularity. The absorption coefficient of a material with an uneven surface or a material on an incline is greater than that of a material with an even surface on a material perpendicular to the sound wave (Skibata & Yasuro, 2003, p. 155). This is especially useful when damping corners.

Corner absorbers, due to the acoustic nature of modes, effectively absorb on all modes in a room (Shea & Everest, 2002, p. 31). A design put into practice at Paul Stubblebine Mastering of San Francisco is to place tall sheets of fiberglass, covered with a loose finishing cloth in the corners of their mastering rooms at an angle so that the sheets are not perpendicular to any wall, nor are they strait up and down.

For ceiling treatment, Shea & Everest (2002) suggest anything that will absorb well what the floor is not absorbing should be used on the ceiling (p. 144). This sounds simpler than it usually is. Carpet absorbs increasingly with frequency, leaving the low end almost completely to reflect off whatever is beneath it (p. 251) so if carpet is on top of anything but a good low-end absorber, the ceiling should pick up the slack. So far, materials discussed that can do such absorption and that aren’t too bulky to hang or attach to a ceiling are 2-ply 2” 3lb/ft2 fiberglass panels and perforated resonators. Shea & Everest (2002, p. 144) don’t suggest this in most cases only because its significantly harder than putting absorbing materials on the walls.

Going beyond absorption for the ceiling, diffusion scatters waves evenly about the room, making them more equally present at every point and therefor more predictable. There are dozens of prefabricated products to handle this and it might be one place where the do-it-yourselfer callsthe professionals. Peterson says reflection phase grating type diffusers create the most predictable levels which have been described to make walls seem nonexistent. The key is in the many depths of the various panels that make up the ceiling (Peterson, 2001). In these types of diffusers, a cross section looks a lot like a bar graph where each bar is of a different length than its neighbor but a repeating pattern can be seen across the whole. That pattern is called a quadratic residue sequence (Shea & Everest, 2002, p. 239; Peterson, 2001). The standard now in quadratic residue sequences is as follows: 1, 4, 9, 16, 8, 2, 15, 13, 13, 15, 2, 8, 16, 9, 4, 1; where each number in the sequence is multiplied by the longest wavelength to be diffused, giving the depth of each piece of the diffuser (Shea & Everest, 2002, p. 239; Peterson, 2001). If something more simple and within reach to the home studio owner is desired, small plastic diffusers that fit into the square partitions in office ceilings are commercially available at around $50 and using one such diffuser every so often in a pattern will help considerably, especially if the studio happens to be in some kind of office space where sound below the high frequencies will penetrate the thin ceiling tiles.

Quick and Dirty For the very budget conscious and time deprived home studio owner, a cheap and effective way to get a studio isolated with barely adequately treatment is certainly possible. A suggestion is to buy rolls of fiberglass wool of 3lb/ft2 and attach them to the walls and ceiling with staples and consider the solid core doors and double paned windows further down the line.

For the rest, a great many books, articles, calculators, and helpful engineers are available and the quantity and quality of all are increasing with time. For further reading, see Shea & Everest in the References section.

References

Morse, P. M. (1948). Vibration and sound (2nd ed.). New York: McGraw-Hill.

Newell, P. R. (1998). Recording Spaces. Woburn, MA: Focal Press.

Peterson, I. (2001). Acoustic Residues. Science News 160(1). Retrieved June 30, 2005, from http://www.sciencenews.org/articles/20010707/mathtrek.asp Sakagami, K., Morimoto, M., & Yairi, M. (2005). A note on the effect of vibration of a microperforated panel on its sound absorption characteristics. Acoustical Science and Technology, 26(2), 204-207.

Sakamoto, S., Mukai, H., & Tachibana, H. (2000). Numerical study on sound absorption characteristics of resonance-type brick/block walls. Journal of Acoustical Society of Japan, 21(1), 9-15.

Sapoval, B., Haeberle’, O., & Russ, S. (1997). Acoustical properties of irregular and fractal cavities. Journal of the Acoustical Society of America, 102(4), 2014.

Shea, M. & Everest, F. A. (2002). How to build a small budget recording studio from scratch (3rd ed.). New York: McGraw-Hill.

Shibata, K., & Yasuro, H. (2003). Numerical analysis of sound absorption characteristics of the sound absorbing wedge. Acoustical Science and Technology, 24(3), 155-156.

Wieczorek, M. (2004). Room mode / standing wave calculator. Retrieved June 25, 2005, from http://www.marktaw.com/recording/Acoustics/RoomModeStandingWaveCalcu.html

Paul: Sure I know lots of favorite songs and albums.

Jake: Anything in particular?

Paul: Alright, the most played album in my collection is Kenny Burrell and Jimmy Smith – Blue Bash. I’ve worn out one copy on vinyl and I’m in the enjoyable process of wearing out my second. I have it on CD also but it doesn’t sound nearly as good as the vinyl. Recorded by Van Gelder. Recorded in his home, his personal studio… actually his parents home.

Jake: How would you define the field you’re working in?

Paul: The field I’m working in, I help musicians get their music out so that it can be heard at its best.

Jake: I understand you have more than a working knowledge of acoustics because of your interest in sound production. More broadly though, how does acoustical knowledge help you do what you do?

Paul: The biggest way is it allowed me to design a room for careful listening, which is what we’re sitting in right now and its a very important tool in what I do. So over the years having worked in a few studios and having built several I’d learned enough that when I built these two new rooms I had a lot better idea what I was doing than previously and so I was able to build very workable tools, that’s the main thing that counts. Additionally, when I have to listen in other rooms, I have a better idea of what I’m listening around. And I do listen in other rooms, I check my work in a variety of other rooms including cars, and so that’s helpful. That’s the main thing.

Jake: So if I have a small studio apartment, approximately 2000 cubic feet, and I’d like to use if, for example: for mixing, single track recording and mastering; and I can afford maybe $1000 to improve the acoustics, what should I do?

Paul: Well it depends whether you can spend all that money on the listening acoustics or if you have to spend some of that money isolating things. Isolating is expensive, generally speaking. So if you have that issue, then you’re going to decide how much you have to spend there and how much is left over to improve your listening acoustics. If you’re asking what you can get for a thousand dollars to improve the listening acoustics (lets say you’re lucky and you don’t have to worry about isolation), then not knowing what your layout is, I’d say what I would look for first is a place that you can create a situation where you have symmetry, left to right symmetry in your monitoring and in the acoustics of the monitoring. That’s a huge thing. If you can achieve it, it gives you a huge advantage in mixing and mastering. So first I would look at what’s available. And see what where you can put together something where the side walls are not too close yet not too far and that there would be… that you’d be able to achieve symmetry. Symmetry, meaning that the speakers are equal distances for their respective side walls and that the treatment that you wind up with is equivalent on left side and the right side. It may be that you only have to treat one, maybe one side already has big windows but they have big curtains and the other side has a blank wall; then you treat the blank wall and then you have symmetry because you’ve got absorption on both sides.

Then the next thing I would do once discovering where that is and making a plan to put the monitoring there, is determine how smooth you can get the bass response before treatment and that means that you try driving the room from different locations, moving the woofer around, and either by measuring if you’re lucky or by listening if you’re not find the spot that gives the smoothest response, and again, you want symmetry so if your left channel you can find one spot that gives you a smooth response but the symmetrical position on the other side does not give you a smooth response, then you haven’t finished yet, you haven’t found it. So keep moving it around until you can find locations that give you a smooth low end response in the room at the listening position, or as smooth as you can, and still are symmetrical.

So you haven’t really spent any money yet, you’ve just started identifying stuff And that’ll tell you what you have to spend money on. As I said, you may have to… once you’ve found that much, then you want to pay attention to you’re early reflections. You want to identify what surfaces will give you one bounce reflections you’re only concerned with one bounce at the moment. Which, you know, you can use the mirror technique¹ to find that. So you’re going to spend a little money dampening those. So that you don’t have any one bounce reflections from your monitors to your ear. Then I would say the next thing is, once you’ve taken care of that, is how smooth did you get the low end response, and if you still have big problems, then you’re going to want to start building bass treatments to try and deal with them.

Jake: You mentioned measurement if you’re lucky enough, what things would you be measuring for?

Paul: Well I was talking about the first stage where you’re trying to find a location that’ll give you the smoothest low end response so you’re just measuring low end response, and looking for resonances, particularly that are poking out (they’re actually more of a problem then the holes in the response (although they’re both bad)) so you’re trying to find the smoothest and once you get to the third stage, after you’ve got your symmetry your smoothest low end response and your first reflections dealt with, then you’re looking for overall power response in the room. We hear, from loud speakers, a combination of power response in the entire room and the direct sounds coming to our ears. And in the low end its all power response. Our ear do not discriminate between the direct sound coming off the front of the speaker right to our ear and the sound that went out to the side walls and reached our ear later. At the very low frequencies, there is no difference because it doesn’t behave like ray tracing at low frequencies, but even through the low-mids, the way it adds up, the overall power response is what we hear. As you get higher and higher in frequency, the ear discriminates more and more and you’re hearing more of the frequency response of the direct signal but the power in the room still has an effect. So that’s the other place you start to get benefit from measurement is when you start to figure out how to smooth our the power response.

Jake: Ok, now some time has passed, I’ve earned some money mixing my friends’ demos, so I can afford another thousand to improve the same space; what should I do?
Paul: Well, after that, the question is how good are your speakers and amps; I think they’re about equally important If you’ve got the first three, four things we talked about acoustically pretty much under control, then the quality is determined pretty much by how good the speakers are… speakers and amps.

Jake: Alright, that’s all I’ve got, is there anything we haven’t covered you’d like to add?

Paul: Well lets see, if we are talking about listening quality, acoustics for listening quality, I would mention we talked a lot about absorption, I should mention there is such a thing as too much absorption. So we definitely want to control those early reflections, but its good if the rest of those surfaces in the room are a little live, particularly if you can get them diffusing, any way you can get them diffusing. So that you have some liveness in the room, its just late enough its not in the real early arrival window so its not confusing the sound its just giving it some acoustic support.

Jake: Thank you very much, that’s all.

What to get and why to get it.

A. Decide what you want to do.

1. For general purpose isolators in studios, 4’ high absorbers block out most lateral bleed from drums and amps at the frequencies that really matter.

2. To absorb anything effectively, a barrier that surrounds the subject to be isolated needs to be made so that no gaps (small enough to fit a paper through) are open between the four corners. To achieve this, I suggest making the sides of the isolators fit together with soft, durable materials, then lock with something like a well placed gate latch. Its time consuming but without such locking, it might not work half as well.

3. If the barrier isn’t going to be permanently in one location, weight and mobility will be an issue, so wheels should be designed into the end product. Wheels open a new can of worms with the issue of ground clearance leaving space for sound leakage between the floor and the bottom of the barrier. This is easily solved by cutting sheets of fiberglass and/or plywood that fit into this space after the barriers are moved into place.

4. 4 separate isolators will be needed to make an adequate barrier in a square shape around the subject unless the subject is put in a corner (then you’d only need two). Each one should be exactly the same and should be wide enough to encapsulate a drummer and all his drums, since that will likely be the largest space you’ll need to isolate during a normal session.

B. Get materials.

1. 703 or equivalent density (about 3 lbs/square foot) fiberglass panels

a. Height should be 4’ or greater, Width should be 4 to 8’.

b. To absorb down to 125 Hz, 4” depth is needed but you can pile sheets together to get depth. 2 sets of 4” depth will be needed to sandwich the isolating materials with absorption. This means that for every isolator, 8” x 4’ x 4 to 8’ of fiberglass 703 will be necessary. If your absorbers only need to go down to 250 Hz, the thickness of 703 needed is halved to 2” depth per side.

c. 703 by spec is yellow but Western MacArthur Co. has carried black and they sell 703 in quantities large enough for this project.

d. One standard sheet of fiberglass is 4’ x 8’ so just get as close to 4” depth as possible. If you want shorter, standard cuts are usually 4’ or 6’ long (which is an easier length to ship, as well).

e. All-Rite carries fiberglass that might fit the bill and isn’t filing for bankruptcy (like Western MacArthur)! Contact info:

All-Rite California

1500 Shelton Drive

Hollister, CA 95023

(800) 642-9988

Western MacArthur Co.’s contact info (if they’re still around):

2855 Mandela Pkwy, Oakland, CA

(800) 992-7374, (510)251-2102

2. Sheetrock panels to match height and width of 703

a. Sheetrock (also called drywall) is used in most modern houses and is just as good an isolator of sound as lead when used in the same surface density.

b. For our purposes, the standard thickness of about ½” is fine.

c. Available at Home Depot, OSH, ACE, etc.

3. Plywood panels to match 703 and Sheetrock

a. Plywood makes an excellent complement to Sheetrock for isolation since it’s more durable and doesn’t give off a tinny sound, and it isn’t as heavy as another slab of rock.

b. ½” total thickness along with the rock is enough to isolate against most trouble frequencies and is practically impenetrable to high frequencies.

4. Frame materials

a. The frame will need to encompass 9 inches of materials. Many things can be used to frame the material sandwich we’re about to create. A nice smooth, durable wood (around ½” thick) will be an easy solution. As I’m writing this, I see on the Home Depot website that “Millstead 1 In. x 10 In. x 10 Ft. Whitewood Board (Model 914916)” is less than $12.00 per board. When all is said and done, three boards of length 8′ 3” or greater for each isolator will be necessary.

5. Casters for mobility

a. Casters are small self contained wheels which need only to be bolted to the underside of a surface. They’re typically more expensive in the sizes needed for a project of this weight but its still well worth it when it comes to setting up the barriers before a session in a hurry.

b. Since all things touching the ground together will resonate together, better insulation is achieved through thick rubber casters which vibrate less than plastic-rubber alternatives.

c. “Shepherd® Hardware Swivel Plate Caster (9277)” - a 3” swivel caster with a locking mechanism (Very Useful!) sells for about $18.00 a piece. Four will be needed per isolator (or just one with a lock, three without). I found this one on ACE’s website.

6. Glue and fasteners to hold it together

a. The kits for many casters come with screws and this is fine but bolts will hold far into the future and aren’t expensive. They just take an extra few minutes of measuring, drilling, and wrenching to put on correctly. The size of the bolt should closely match the size of the holes in the casters and washers should always be used over the holes through the bolts. Nuts of course will be needed to fit to every bolt on the other side of the hole.

b. Drywall screws come by the 100 and are perfect for fitting the plywood to the sheetrock after the two are glued together. Always remember when using drywall screws laterally in materials like plywood, where the wood has been pressed together, to drill a pilot hole first! A pilot hole is a small hole drilled with a drill bit before the screw is drilled into the same place. Pilot holes help maintain the integrity of the wood and without them, the wood may split, ruining both expensive wood and a partially finished project.

c. Construction glue of any variety will be used to plaster the Sheet Rock to the Plywood before attaching the 703 or the frame. These glues come in caulk tubes to be used in caulking guns - so you’ll need a caulking gun too. Most real men have a good long caulk tube and a gun.

d. There are special glues for fitting sound absorption materials together but from what I’ve heard, they’re only marginally more useful than standard construction caulk.

Building an isolator: To be continued…