Every recording is made is some sort of space. It might be a room, and studio, a church, a concert hall, or even outside.
The space where the music is performed, and where the microphones pick up the music always influences the sound of the recording.
You might think that close-mic’ing in a dead room eliminates the contribution of the room, but it is still there, for better or worse. The room influences our perception of the performance. Our brain draws conclusions about the space. A listener may form a mental image of the musicians and the room, based on what they hear. Usually, most listeners are unaware of the space, unless it is very obvious. But it does influence their response to your recording.
Learn some of the basics of acoustics that can help you make your studios and control rooms sound better.
email: dwfearn@dwfearn.com
www.youtube.com/c/DWFearn
https://dwfearn.com/
Every recording is made is some sort of space. It might be a room, and studio, a church, a concert hall, or even outside.
The space where the music is performed, and where the microphones pick up the music always influences the sound of the recording.
You might think that close-mic’ing in a dead room eliminates the contribution of the room, but it is still there, for better or worse. The room influences our perception of the performance. Our brain draws conclusions about the space. A listener may form a mental image of the musicians and the room, based on what they hear. Usually, most listeners are unaware of the space, unless it is very obvious. But it does influence their response to your recording.
Learn some of the basics of acoustics that can help you make your studios and control rooms sound better.
email: dwfearn@dwfearn.com
www.youtube.com/c/DWFearn
https://dwfearn.com/
84 Designing Acoustic Spaces
I’m Doug Fearn and this is My Take on Music Recording
Every recording is made is some sort of space. It might be a room, and studio, a church, a concert hall, or even outside.
The space where the music is performed, and where the microphones pick up the music always influences the sound of the recording.
You might think that close-mic’ing in a dead room eliminates the contribution of the room, but it is still there, for better or worse. The room influences our perception of the performance. Our brain draws conclusions about the space. A listener may form a mental image of the musicians and the room, based on what they hear. Usually, most listeners are unaware of the space, unless it is very obvious. But it does influence their response to your recording.
The room also affects the players making the music. Even if they are wearing headphones, they will have a sense of the space where they are playing. That could be good or bad.
If they are playing in a good-sounding room, with acoustics appropriate for the music, they will likely respond positively. They will play better. They can hear their instrument, and any others in the room, better.
A room with inappropriate acoustics, or just plain bad sound, can make the players uncomfortable. They won’t play as well, and they may have trouble hearing themselves and others, even with headphones.
But how much does the sound of the room matter, anyway? Most recordings are made with directional mics placed close to the sound source, so there isn’t much room sound audible. It’s a recording style that might fit your style very well.
But if you want more character in the recording, the room can add that. It’s an important part of many records, even though you might not immediately notice it. In a song with a lot going on, the sound of the room might seem to get lost. But it’s always there, good or bad.
A good room sound enhances what you are recording. That subtle sense of space around the instruments can add a lot to the perception of the performance.
Of course, some music never existed in a real space to begin with. Electronic music, or instruments all recorded direct with a DI will have no room sound. For those sessions, this discussion of room acoustics probably is of little use. But if your music has vocals, the room again becomes important. And if you are recording many instruments at once, or a large ensemble like strings, the room sound will be vital.
It makes sense to optimize the space where we record. But that is easier said than done. There are a lot of misconceptions about how to make a room sound good. And I hope to provide you with some guidance.
I am not an acoustical engineer. But I have studied the topic for over 50 years and I know what sounds good and what sounds not-so-good. We all know what bad acoustics sounds like.
I have designed three different studio complexes for myself, and quite a few for other people. The results have been good, so I feel qualified in giving some general advice. For an expensive build, you probably want to hire a studio designer. But these tips will help you understand the design process and its limitations.
For many of us, we have to be our own acoustical designer.
This is a complex topic, so my coverage will be somewhat simplified. If you want to know more, there are good books out there to help you with the formulas and design guidelines. There are on-line calculators that can be helpful.
But my experience has been that studying the work of academic experts often does not translate well into the needs of real-world recording. I suggest learning as much as you like, but never forget that your ears are the final judge.
First, let’s separate the concepts of sound-proofing vs sound conditioning. They are two entirely different things, and as a general rule, sound conditioning materials do not stop sound from traveling into or out of your studio. And that applies to all the surfaces in the room, including the floor and ceiling.
Stopping sound transmission is fairly simple in concept: You need mass to stop sound. That means heavy walls. Bricks or concrete are good. Drywall and plaster are not. There are ways to make drywall work, but it’s not as simple as typical household or commercial construction.
The second important thing about stopping sound is an air-tight seal. There can be no cracks or gaps in your barrier between your quiet space and the outside world. Even a tiny gap will negate all the money you spent on heavy walls. And those gaps can be hidden within the final finishes, like molding. Your sound isolation will be poor and you can’t figure out why.
When working with contractors, I tell them that the room has to be watertight. I joke that after the job is complete, we will fill the room with water, and if any leaks are found, you won’t get paid. It is stupid, but it does help the contractor understand the unique requirements of studio construction.
You might find a contractor with experience with soundproof construction, but they are rare. Most contractors have misconceptions about sound isolation and nothing you say will convince them otherwise. Better to find someone who is cooperative and wants to learn and do a good job. You will have to watch the construction like a hawk.
That’s all I am going to say about soundproofing in this episode. Maybe I will do one with more depth at some point. Today I want to focus on making the room sound good for music.
As a practical matter, we usually do not have the budget to build the ultimate studio of our dreams. And it’s likely you will have to adapt an existing space for a studio. Many people will be doing a lot of the work themselves, too. You can still do well in this endeavor, if you understand how to do it and have good attention to detail.
First and foremost, in any design, are the proportions of the room. Why is this important? Sound is always reflected off the boundaries of the room. The walls, floor, and ceiling will absorb some of the sound hitting that barrier but most of it will be reflected back.
It’s like light, in a way. A mirror reflects back almost all the light that hits it. A hard, dense, smooth surface reflects sound the same way. In fact, a mirror is a good example of a surface that is highly reflective to both light and sound.
Most materials are less reflective than that. But with common building materials, a distinct echo will be heard. The worst of these are called “slap echoes,” and they sound like an inappropriate digital delay mixed way too loud. A slap echo will bounce back and forth, gradually dying away, like a digital delay with a lot of feedback. Often, the slap echo will be confined to just one section of the room. You might be able to avoid using that part of the studio, but it’s better to not have the echo to begin with.
Sound travels at about 1000 feet per second, as an easy approximation. That’s 1 millisecond per foot. If your walls are 10 feet apart, the sound will take 20 milliseconds to reach the far wall and be reflected back to you.
At 100 feet, it will take 200 milliseconds, or two-tenths of a second.
Short delays, under about 10 milliseconds, are not perceptible as distinct echoes by most people. But it does change the sound in significant ways. Use a digital delay to simulate the delay between the walls in your room and hear what it does. It’s easiest to hear this if the original sound is on one side of a stereo monitor and the reflection is in the other channel. Small rooms mean short delays, which are mostly heard as phase differences, which tend to smear the sound. This is particularly noticeable on percussive sounds, but it exists on every sound.
If we expand this to include all the room surfaces, we now have three different echo paths. Imagine if they were all the same length. The room would be cube. All the echoes would have the same delay. They would reinforce each other and that would sound exceptionally bad.
A cube room is about as bad as it can get. But there’s more to it than just the echoes. I’ll return to that in a minute.
Many rooms are built with standardized building materials, which reduces construction costs. In the U.S., most building materials are multiples of 8 feet. A room might be 16 feet long, 12 feet wide, with an 8-foot ceiling. That’s 4.9 by 3.7 by 2.4 meters for the rest of the world.
Since those are all multiples of each other, the resulting echoes will tend to build up at frequencies spaced at regular intervals. That results in a room which emphasizes some frequencies and diminishes others.
If you were to graph the frequency response of the room, or view it on a spectrum analyzer, you would see peaks and dips spaced at regular intervals. They can be large peaks and nulls, too, easily over 20dB differences. Given enough of these, they tend to even out. But in smaller rooms, like our example, most of the problems will be focused on the mid-range frequencies, and that makes the room sound muddy and indistinct. If you have to add a lot of mid-range cut eq to your tracks, you are probably trying to reduce this room-created muddiness.
If we are designing a space from scratch, we can avoid those dimensions that are multiples of each other. There are formulas that will help spread out the room resonances and prevent them from becoming a problem. You will find ratios of the three dimensions of a room that achieve the same thing. The goal is to avoid a pile-up of resonances at the same frequency.
From this, you can see that the larger the room, the less this becomes a problem. There are more lower frequencies in the room resonances, and by the time you get to the critical mid-range frequencies, there are so many closely-spaced resonances that they tend to blend into each other and essentially disappear. That’s a good thing. It is always easier to get a good sound in a big room.
And by big, I am suggesting that the smallest dimension is at least 14 feet. The ceiling height is almost always the shortest dimension, so any design should start there. Any ceiling under 10 feet is sub-optimal.
How high should the ceiling be? I would say infinite would be good. Humans evolved spending most of our time outside, with an infinite “ceiling” dimension, so our hearing finds that most comfortable and natural.
We can’t have an infinitely high ceiling, so as a practical matter, I would say that anything over 20 feet should sound pretty good.
That’s not practical for most of us, but when searching for a space to build a studio, seek the highest potential ceiling you can find. There is a reason why churches and concert halls sound good, and generous ceiling height is one reason.
After the ceiling is determined, you can use the formulas or on-line calculators to determine the other two dimensions.
For a decent-sounding room, I would suggest that the long dimension should be at least 35 feet. That lowers that room resonance frequency and provides a lot of room to record anything except an orchestra or a big choir.
Use the best ratio for the dimensions and your room is off to a good start.
If you are stuck with existing construction, your options are more limited and the results less likely to be great. An 8-foot ceiling is a serious limitation, but it can be made to sound OK with some additional work.
You may be able to improve the sound of the basic space by expanding into another room. Just be careful knocking down walls without a structural analysis of the building.
If you have a big space, but the dimensions are not close to optimal for sound, you might be able to reduce the size along one axis to create a better-sounding room. You may be able to use that cut-off space for other productive purposes, like an isolation booth, storage closet, equipment room, or bathroom.
In the real world, many of us do not have the luxury of a space large enough to meet these rules. We have to deal with the space we have and make it sound as good as possible.
Let’s define our small studio space as one that has an 8-foot ceiling and is around 20 feet long and 15 feet wide. Those dimensions are not optimum, but are typical of what you might have available.
One approach for small spaces is to make them as acoustically dead as possible. That is the easiest way to eliminate many of the problems of a small room.
The sound in a dead room won’t have much character, and many musicians don’t like the feel of a room like that, but that hasn’t stopped hit records from coming out of small, dead rooms. It’s not optimal, but it isn’t a fatal flaw.
But to make it work, the sound-deadening material has to be carefully chosen and deployed.
When most people picture a dead room, they see walls covered with materials like acoustic tile, foam absorbers, thick drapery, fiberglass insulation, or even moving blankets.
It’s true that all of those materials are good at absorbing sound. The problem is, they absorb high frequencies much more than low and mid frequencies. Rooms treated that way usually have a characteristic sound: dead but with what I call mid-range muddle.
The middle-range frequencies, say from 200Hz to 1kHz, are where the fundamental frequencies of many instruments and voices live. If you were to take a sound that had no room sound at all and equalize it to sound like a small room covered in absorbing material, you find that the extreme lows were attenuated, the mid-range was boosted, and the highs were rolled off above around 3kHz. You would never eq a sound like that unless you were looking for an effect. So our small, dead room is not going to sound very good.
You might be able to salvage it somewhat with some eq that is the reciprocal of the room, but that introduces too many other problems. It will not sound natural. And the characteristics of the room are likely to be different in various places in the room. Sometimes major anomalies in the sound of the room can be just feet apart.
Depending on the type of music you are recording, this could be a major problem, or it might be something that actually enhances the sound you want. Mostly, though, it’s not going to make your recording sound very good. Vocals, especially, suffer in this environment.
What to do? Well, it’s always going to be a challenge if the room is small, but you can improve things by choosing absorptive materials that have a more even response across the audio spectrum.
Achieving any meaningful sound absorption at low frequencies is difficult. Low frequencies have a long wavelength and absorbing them requires a lot of depth.
Think of an anechoic chamber. This is a laboratory space with virtually no sound reflections whatsoever. The walls, floor, and ceiling are treated with sound absorbing materials, usually in a wedge shape, that are many feet deep. You might start with a sizeable room, but the end result is usually just a tiny fraction of the overall size. The floor is usually some sort of metal mesh, so it does not block sound from the absorbers below.
That is definitely not practical for a studio, and sounds awful anyway. But it does illustrate what it takes to get good absorption at low frequencies.
You can use resonant traps designed to capture and eliminate particular low frequency resonances in the room, but those require a lot of depth, too.
We are often saved in typical household or commercial construction by the relatively flimsy materials used for walls, ceilings, or floors.
Picture this: a drummer is playing in your studio space at home. You go into an adjacent room, one separated by typical drywall construction. What do you hear? Mostly kick drum. You hear some of the lower frequencies from the snare and toms. But very little cymbals or rattle of the snares.
Those walls have very little attenuation of low frequencies. Remember the mass rule for stopping sound transmission? You just experienced a real-world demonstration of that.
The sound that passes through the wall does not get reflected back into your studio very much. It is essentially gone. Not eliminated entirely, to be sure, but there is a lot less of it than there would be if you had massive walls.
You have “absorbed” some of the low-frequency energy.
Our example is with walls, but the same applies to floors and ceilings.
In fact, the actual dimensions of the studio, from a low frequency standpoint, can be larger than the actual distance. Here is one case where light construction can be a benefit.
It also means those lows are leaving the confines of your studio, and chances are someone will find that objectionable. Outside noise will be audible in your room as well. It’s a tradeoff between good sound isolation and low-frequency absorption.
If the lows are absorbed by the transmission through the walls, we are left with mid-frequencies that do not have this benefit. They remain in the room, and they sound bad.
Absorbing mid-frequencies is, as you might expect, somewhere in between the difficult challenge of absorbing lows, and the relatively easy challenge of absorbing highs.
For many small studios, this is the limiting factor in the sound of the room. There are ways to reduce these mid-range resonances, but they are complicated, using perforated panels with chambers behind filled with absorptive material. The construction is complex, and the amount of wall space required is a good percentage of the total you have.
But if you can set up an assembly line to build this kind of absorber, and have the skills to build them, they work very well. My favorite reference for this type of absorber is the BBC, which spent years experimenting with the design of these devices and found the optimum, practical way to do it. And it wasn’t all theoretical: they used their designs in hundreds of their studios, ranging from tiny announce booths to large performance spaces.
Not an easy solution, but one that works.
Few of us have the resources, or the free wall space, to utilize that type of absorber. We have to make do with simpler methods.
As a rule of thumb, the thicker the sound absorbing material is, the better it will absorb mid-frequencies. It won’t have the flat response that would be ideal, but it will help. How thick? A lot depends on other factors, but it is going to take a couple of feet of material to have much effect on the lower middle frequencies. And that’s where absorption is needed most. The ceiling may be an option for thick sound-absorbing material, if you have the space.
It’s not practical to get flat reverberation response in a small room, so you may have to live with that mid-range weirdness in the sound of the room.
For high frequencies, almost anything works. High-frequency sound is absorbed by even thin materials, although the thicker it is, the lower the lowest frequency absorbed will be. Even the air absorbs high frequencies.
A common high-frequency absorber design uses a wooden frame around 4 feet square and about 4 inches deep. The frame is filled with rock wool and covered front and back by acoustically-transparent cloth. Fiberglass insulation, without the paper of foil backing, can also be used with somewhat less effectiveness.
You can build these yourself in practically no time, with simple tools. Plans are readily available. Once complete, you can mount them on your walls in various ways. If you space them off the wall by a few inches, they work even better. Highs are always the easiest to control. The absorber panels can be used on the ceiling, too.
So far, we have been talking about absorbing sound. But do we really want to absorb everything? Do we want to maintain some of the sound reflections in our room?
The answer depends on your goals. But I would say that some good room sound is always an enhancement to the sound of your recordings. It has to be good room sound, however, which means something our hearing finds pleasant. Not always easy to define, and even more difficult to achieve. But all of the great studios around the world have, or had, a distinctive sound that enhanced the music and our enjoyment of it.
Think of Abbey Road, Capitol Studios, or the old Columbia Studios in New York, as three examples I know you have heard. Those rooms sounded great. They were each unique.
Of course, they were all big rooms. Not your average personal use studio.
Those big rooms were not dead at all. Most had reverberation times of well over a second. They did not have sound absorbers everywhere. They didn’t need that or want that.
Still, we can get some of the benefit of a great-sounding room in our much smaller space if we use good design.
Part of the great sound of the best studios came from diffusion. That’s the principle of random sound reflection, not just an echo off a solid, flat wall. Imagine a cathedral. It’s made of stone. Almost every bit of sound in that space is stuck inside, echoing around until the sound is fully absorbed by the air and the reverberation dies out, many seconds later. Not the right sound for most recording, but impressive for the music written for that environment.
If you look at the construction of a cathedral you will not find any flat surfaces of any extent, except the floor. The room is punctuated with stone structures, arches, ornaments of significant size and weight, and perhaps adjacent spaces acoustically-coupled to the main hall.
If you built a large boxy room with mirrors covering every square inch, it would be a dazzling space. If you shined your flashlight anywhere, the beam would erupt into confusing mass of light, coming at you from every direction. Impressive, but totally disorienting and uncomfortable.
Change the flashlight to a sound source and the same thing would happen. Confusion. Nothing would make any sense.
But if we aimed every mirror at a different angle, and put some of them at different distances from the outer walls, the result would still be dazzling and confusing but better. The same applies to sound.
This is the principle of diffusion. That’s another important acoustical tool that can be used in a room of any size.
Diffusion breaks up the distinct echoes in the room, with sound-reflective surfaces that scatter the sound in many directions. We don’t have any dominant echoes. The sound is more pleasant to our ears. It is the cathedral principle, only in a much smaller space.
What provides diffusion in a room? Well, anything that reflects sound. That’s part of the reason why an empty room in your house sounds unpleasant until you fill it up with furniture and other stuff. Some of those things provide absorption, while others reflect the sound. The wood of a table is a good sound reflector. The cushions on a sofa or stuffed chair are sound absorbers.
Once we put things in our empty studio, the sound changes. You might have instruments, shelving, chairs, music stands, mic stands. All that stuff is mostly reflective and since a lot of it has surfaces in multiple planes, it reflects the sound randomly around the room. That’s helpful.
People in the room don’t reflect much sound, but they absorb it pretty well. Think of an auditorium with an audience and without. The sound is very different.
No matter how cluttered our studio becomes, it could probably benefit from some additional diffusion.
We can build or buy sound diffusors. Various designs work differently. One common example has random rectangular blocks or wells, a few inches across, with irregular depths. They reflect the sound that hits them and bounce it back at slightly different times, depending on the depth. It’s simple and helpful.
Better, in my experience, are diffusors that have more angles and depth. One classis design uses blocks of wood, typically from 2x4 or 2x3 lumber, cut to different lengths with different angles on the top. These are typically less than a foot deep. They scatter sound nicely, and are visually interesting, too.
You can build those yourself. Be prepared to be appalled at how much lumber it will take!
Another design uses long slats of wood set at different angles. These can be mounted horizontally or vertically, and can be any size. If they are placed in front of a solid wall and left open on the back, they work even better by allowing some sound to pass through and reflect back into the random wood pieces.
An entirely different type of diffusor is a cylinder, or half a cylinder. A common technique in an acoustic echo chamber is to use a section of concrete pipe, a foot or more in diameter, and sitting vertically on the floor. A cap is necessary on top to prevent resonance inside the pipe. Several of these in the highly reflective environment of the echo chamber provide lots of diffusion.
That is not practical in most small studios, due to the valuable floor space it would require. But cylindrical diffusors do not have to made of heavy material. Wood works fine. And you can place them along the walls, if you have enough space.
A half cylinder works almost as well and can be mounted on a wall or ceiling. They are easy to build and look interesting. Placed above the height where someone could walk into them, or above the height of your tallest mic stand, they can add diffusion without taking up usable floor space.
Typical diameter would at least a foot or two.
How do you determine how much absorption and diffusion you need? It is theoretically possible to calculate the number of square feet, the characteristics of the materials, etc. But there are many variables we really can’t account for accurately – like the contribution that thin walls make to low-frequency absorption. Also, there is not much data on the sound absorbing characteristics of things like carpeting and curtains or drapes. Only acoustic materials that are made for professional use have any relevant data for our design purposes.
After doing this for many rooms over many years, I have a pretty good idea of what a particular room might need. But until you get that real-world experience, it is somewhat of an experiment.
That’s not as bad as it might seem, however. You can start out with a moderate amount of absorption and diffusion and listen to how the room sounds on a recording. You should know instantly if you need more treatment.
I’ll give you an example of my current studio, which probably is not unlike a lot of studios you might build at home or in rented space.
My space was once the storage area for the parts used in D.W. Fearn products. It isn’t a huge space, about 40 by 28 feet. It’s not exactly rectangular, either, with some incursions of a few feet here and there. It’s mostly underground, and built with concrete block, so it’s very soundproof. That also means that the walls and floor are solid and nothing gets through them. It all stays in the room.
The ceiling is about twelve feet high, and made of wood on large engineered wood joists and steel I-beams. There are other rooms above, so I get some low-frequency absorption through the ceiling. It is also the perfect space to add sound absorbing materials, and it is filled with about 3 feet of rock wool insulation. There is a drop ceiling below that, made from sound absorbing panels with well-defined characteristics. There is a lot of absorption in the ceiling.
The floor is concrete and covered in commercial carpeting, which is thin enough to roll the grand piano around without a problem. It provides some absorption of high frequencies, and eliminates the “bounce” of sound off the floor. In a bigger room, that floor reflection would be desirable, but my space is too small to make that usable.
Most of the walls are concrete block, but one of the four walls is drywall. On the other side is a large garage. The walls provide some additional low-frequency absorption.
In its raw state, with just the floor and ceiling treated, it sounded about as bad as I expected. There is a lot of mid-range muddiness, and even some slap echo in places. Not usable that way.
The first thing was to add some 5-foot square absorber panels, as I described earlier. All are spaced off the wall by about 4 or 5 inches. They cover about half the wall area. In between the absorber panels are bare, painted, concrete walls, which provide some reflection. The room is far from totally dead.
To that, I added about 100 square feet of diffusion, using the three types of diffusors I mentioned earlier. They made a significant improvement in the sound, and they eliminated the slap echo problem.
Probably some more diffusion would help, but I don’t have much wall area left. I’d like the room to be a bit more live-sounding, but it is acceptable.
The one thing that is still a problem is the lack of meaningful mid-range absorption. My plan is to build some mid-frequency absorber panels. They are much more complex than the absorption panels, so I have not made them yet.
And I carved out about a quarter of the total space for a control room. The control room is too small to really sound good, but it is fine for me most of the time. There is potential for further improvement, but the size will always be the limiting factor.
Control room design is another podcast topic for someday. But if you are interested, there is a video on my YouTube channel that documents the design and construction of the control room. Search YouTube for D.W. Fearn to find it, or click the link in the description.
These are some of the principles of acoustic treatment that can improve the sound of any space. I have talked about studios, but the same applies to control rooms and iso booths. Those may be more challenging still, since the spaces are usually smaller than the performance space.
And remember the floor and ceiling, too. Often, the ceiling is the easiest place to get lots of sound absorption. You can sometimes install rock wool or insulation in the ceiling, more than a foot deep. The deeper the better. Just keep it acoustically-available to the space below with a covering that lets the sound through.
Floors have to be flat, and it is generally not possible to add any significant absorption to a floor. A thick carpet will absorb high frequencies, but may make it difficult to move heavy stuff like big mic stands, pianos, etc. That’s OK. We can get enough absorption in the walls and ceiling. Some reflection off a hard floor can enhance the sound and make it easier for players to hear each other. But that is best for large rooms. Small rooms probably need a relatively thin carpet.
There is often lots of diffusion at the floor level as well, from all the stuff sitting there.
There is much more to the complex topic of acoustics, but these general principles will help you understand what works and what doesn’t. You can make a small space sound a lot better. It will never have the sound of a big studio, but it can work well and help you make good recordings.
You can always reach me at dwfearn@defearn.com with your comments and suggestions for future episodes. Thanks for listening. Please pass along a link to this podcast to anyone you think would be interested. And please subscribe on the podcast platform of your choice. It does make a difference when you subscribe.
This is My Take on Music Recording. I’m Doug Fearn. See you next time.