“Your design [Carry-On Vocal Booth] is lighter, easier to use, sounds better, and, in my opinion, far more functional than any other portable VO booth I’ve seen. Harlan’s booth uses Auralex pyramid foam, which does a good job of diffusing the sound, but does only a fair job of absorption . . .I like yours much better!”
VocalBoothToGo was borne literally by the audio producer's demand for efficient and price conscious products. As technology developed, artists were able to create music and record audio in their home. But even though technology allowed easy recording and editing of the files, the laws of physics did not change and the room acoustics had to be handled properly.
The Hanging Vocal Booth Made My Day!
“This is really going to help me progress in this great buisness. I live on the gulf coast, and there isn’t access to many studios so I was trying to make my own in my home.The hanging booth will instantly improve on the quality of my recordings. Once again, great product ……. “
Vocal Booth– An “A” and Delivers Exactly What It Says!
“The Vocal Booth on Tracks in an Option for Space Challenged Voice Talents . . . and Yahoo! I now have my own recording room and, even better, I can whisk its walls aside whenever I need to.”
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How to Control Sound Reflections in a Voice Over Recording Studio
What are sound reflections and reverberations and why do you need to care?
When we talk about sound reflections think echo.
If you are in mountains, a cave, large hall or an empty room, say something or just clap your hands – that sound gets back to you as an echo ( reflections) and repeats itself over and over ( reverberations) until it loses its energy and dies (reverberant decay). This is because the sound reflects from one hard surface goes to the other and reflects over and over again until it loses its energy.
The same exact process happens in your studio, except that you might not hear it as loud as in a cave, but sensitive microphone will pick it up and your recording will be “inadequate”.
HOW THE SOUND BEHAVES IN A VOICE OVER STUDIO
Sound energy can be reflected by the surfaces in the room and bounce around or it can be partially absorbed, lose some of that energy and bounce around a bit less, or it can hit an odd shaped object, break apart and go in different directions with diminished energy (diffused).
These behaviors can be problematic in a recording studio – sound waves bouncing inside the room can interfere with each other, cancel or reinforce the energy at certain points, which makes a recording in the room difficult.
How your recording affected by the way sound waves behave in a room depends on a number of factors – the frequency of the sound wave; the shape and dimensions of the room; the materials that the walls and ceiling and floor are made of and covered with; how many doors and windows are there, and where they are placed, location of the microphone and voice other actor in relation to the nearest walls , etc., and the contents of the room ( furniture, tapestry, equipment etc.)
One of the biggest factors that determine what happens with sound in a room is the frequency of the sound wave. As we discussed in the previous article, lower frequencies wavelengths are long, and sound waves are more powerful. Low-frequency sound wave cannot be reflected by a small obstacle, so it bends around objects in the room and passes through lighter materials
At mid and high frequencies, say 100Hz or so and above – sound waves are more straightforward and easier to control.
Their behavior in the room can be compared to that of a tennis ball: they bounce from hard surfaces and being slowed down (absorbed) by soft surfaces.
First reflection:
Then it will bounce from a corner:
Then from the other wall:
And so on until it loses its energy. The harder and flatter the surface – the stronger the reflected sound and the longer it will be bouncing around before it dies.
(This is just a simplified example, in reality, a surface has to have a dimension equal to a wavelength to reflect sound in this manner. So our 100Hz wave will bounce off a roughly 12 ft wide wall. But will diffract (bend around) around objects that have dimensions smaller than 12 ft wide. Also, sound waves are omnidirectional, meaning that they go in all directions at once, so when they reflect they also interact and affect each other).
However, throw a ball against a pillow and it will stop because the direct energy will be absorbed by the pillow.
That’s the basic idea.
WHY REFLECTIONS ARE BAD FOR YOUR RECORDING
In reality, the voice over actor is positioned right in front of a microphone, so the microphone will pick up the sound coming directly from you, the speaker, but it will also record the sound waves reflected off by nearby walls and other surfaces.
The problem is that the microphone will record the sound from the voice over actor a very short time before the sound reflected off the walls gets to it too. How long the delay depends on how far away the nearest reflective surface is.
This delay between the two sound waves ( direct and reflected) can result in phase differences in the waves.
As the direct sound waves of your voice and the reflected sound combine, the time/phase delay can cause cancellations and/or reinforcements in the sound waves, changing the tonality of what you are recording.
This effect is known as “comb filtering”. And if the tonality is changed, you are not recording what you are really saying, or rather not the way you say it.
ARE THERE BAD AND GOOD REFLECTIONS?
Well, ideally you do not want any reflections in your recording. You want only direct sound to be recorded. But some reflections are indeed worse than others.
First reflections.
The worst and most powerful are the so-called first reflections. These are the sound waves that bounced the first time, less than 20 milliseconds or so after the direct sound. Sound travels at a rate of about one foot per millisecond, so that means that any reflective surface within about 10 feet or so of the recording position will cause problems.
There are also Secondary (second bounce) and tertiary (third bounce) reflections.
Flutter echo
Flutter echo happens when the sound waves are reflected directly between two parallel surfaces – say opposing walls in a small room – back and forth. Try it in a smallish room with hard parallel bare walls: clap your hands and you’ll hear a rattling sound – that is flatter echo.
Most of apartment and house rooms have parallel walls, so flutter echo can be a real problem when you are recording with a microphone.
Reverberant decay
Reverberation is the sound left ringing in the room after the direct sound from the sound source stops. It is those secondary and tertiary reflections, it is that remaining reflected sound that tends to wash together.
For most recording too much reverberation that lasts too long is a problem – recording clarity will be compromised, and there may be phase problems.
Equally important is making sure that the reverberant decay across the frequency range is even. If the reverberant decay for high frequencies is different than for low frequencies, the room will have a characteristic sound that probably won’t be desirable – a bright ring, boomy low end, or uneven midrange. However, if the reverberant decay is too short, the room will have a dry, dead feeling and sound that will be uncomfortable.
HOW TO MANAGE REFLECTIONS AND REVERBERATIONS.
If you are thinking of setting up your voice over recording studio you might be choosing a spot in a bedroom a walk-in closet or may be in a spare room.
If you start with an empty room with hard surfaces on the walls, ceiling, and floors what do you do to manage reflections and reverberant decay? There are two different methods: absorption and diffusion, each of which is effective for solving certain problems. But in small rooms such as home recording studio diffusion is not as effective as absorption. We will stop on Diffusion briefly because they are not exclusive and a combination of the two methods can be used successfully.
DIFFUSION
“Diffusion” is breaking a single sound wave into smaller reflections and dispersing them in different directions. Because there are no big reflections going back to the microphone, first reflection problems are reduced, and because diffusive materials are irregular in shape, flatter echo is eliminated. Although reverberation won’t be eliminated, scattering and breaking up the reflections tends to result in a smoother reverberation at a lower level.
While any irregular surface can break down reflections at some frequencies to a degree, to figure out exactly how to make a diffuser that evenly scatters a broad frequency range of sound waves requires specialized diffusion materials. Such specialized diffusers are hard to build and they can be expensive.
ABSORPTION
Remember the example of echo in the mountains? Now, why is it so quiet when the snow is falling? That is because the snowflakes absorb the sound and speed up the reverberant decay.
For voice over recording studios, absorption is the main method for managing first reflections in mid- and high-frequency range, flutter echo and reverberant decay.
The idea is to use sound absorption materials placed at the main reflection points to reduce – absorb – sound energy so that the level of the reflected sound waves is significantly quieter than the direct sound.
Absorption works best with high- and midrange frequencies. Lower frequencies require large quantities of absorptive material for effective energy reduction.
Very high frequencies have a very little energy compared to low frequencies, so thin, soft materials can be used to absorb them. As the frequency gets lower, thicker and heavier absorptive materials are required. Those thicker sound absorption materials are even more effective at controlling high frequencies.
There is an array or sound absorption materials that can be used and we will talk in details about it later. Most fall into the category of porous absorbers. These materials consist mineral wool, acoustic blankets, clothing, curtains, carpets and acoustic foam
The sound-absorbing effect comes from the fact that the sound energy can penetrate the material on hitting the surface. Here, the sound energy is converted into heat energy, so that only a small part is reflected in the form of sound energy. In other words, the material has absorbed some of the sounds.
The sound absorption in acoustic foam and acoustic sound absorption blankets works differently.
Acoustic foam is a popular material for lining up the recording studios. They are often shaped in a conical or egg crate shape. The make of acoustic foam is different from the make of the packing foam even though they might look the same and even YouTubers may claim they can stuff the packing foam in the box and it works great. Packing foam made out of CLOSED channel foam, so the air trapped in the channels provides more cushioning. But for the sound to be absorbed, it has to have a way to enter the material. This is why acoustic foam is made with OPEN channels. So-called “Open Cell Foam” The sound gets in and then travels through the twisted channels bouncing off the internal walls and losing its energy. The reason for the egg crate surface of the foam is to increase the absorption area and allow more opportunity for the sound to get in. The thicker the foam the more sound it absorbs. This is why unechoic chamber lined up with acoustic foam with two feet deep wedges.
The other difference is that acoustic foam is generally rated as fire retardant – an important factor because some types of foam are extremely flammable and therefore not safe for residences and businesses
Acoustic blankets, on the other hand, work differently. Unlike moving blankets filled with low quality mixed with recycled polyester and cotton fibers, specialized acoustic Blankets known as “Producer’s choice”, filled with highly absorptive cotton. As the sound gets in it agitates the cotton fibers and by making them vibrate it loses its own energy.
The thicker the blanket, the more filler it has, the better its sound absorption efficiency and broader its frequency range. Using blankets in pleated fashion increases the absorption surface and increases the total quantity of absorption material in the room.
Fiberglass Insulation. Glass fiber is another common absorptive material. The rigid variety such as Owens Corning 700 fiberglass series provides decent absorption in high and mid frequency range. Rock wool Safe and Sound is used to fill the space between drywall during construction for better soundproofing. It is also can be used in the corners as a bass trap. RockWool and Glass fiber, of course, can be a major irritant, so make sure to cover it and do not disturb, to prevent strands from getting into the air.
Regular household materials such as soft furniture with fabric upholstery, pillows, curtains and drapes, blankets, carpet and so on, all absorb sound to one degree or another at mid and high frequencies.
HOW MUCH ABSORPTION SHOULD YOU USE?
So you have to get rid of reflections do you just line up the walls, floor and ceiling of your studio with sound absorbing the material and start recording?
But it’s not quite that simple. Many types of absorptive materials only work well on higher frequencies, leaving midrange sound bouncing around without much control.
This can result in an odd, dark –sounding room with no high end. If you have too much absorption in the upper frequencies, the mid- and high-frequency reflections will be reduced, but the bass frequencies will be bouncing around, resulting in a boomy, bassy room that sounds muddy. Too much of the overall absorption and the room will sound too dead and it will be uncomfortable to work in.
The idea is to use just enough to control first reflections and to tame reverberation decay. Keep in mind that you can always add more absorption if the room still seems too live.
The right balance is the key to finding the right amount of absorption in the proper location so they will be as effective as possible – enough to control the mid and high range, and enough bass traps to end up with a balanced room response and an even reverberant decay across the frequency range.
HOW DOES IT RELATE TO VOICE OVER RECORDING?
The purest and cleanest of all is the direct sound energy. This is the sound that travels in a direct (straight) line from the voice actor to the microphone
Sound energy reflected from objects in a room confuse the direct sound of our voice and make recording “mudded”.
You want to have everything in the recording, emotions and different intonations and do not want to hear any sonic additions from your recording room.
Unfortunately, you must record in a “box” or room that has walls, ceiling, and a floor. When you speak into a microphone the sound radiates in many directions. The sound of your voice goes through the room until it hits an object or wall, then it reflects back and gets recorded by your microphone over what you are saying at the moment.
Unlike the reflections in a control room where the sound comes from a speaker and reaches the engineer at some distance, in voice over recording you position yourself right in front of the microphone. So your first reflections would be the reflections from the nearest reflective surface: laptop screen, walls to the right or left of you and a wall in front or behind you if you are sitting close to a wall. Wherever the closest reflective surface is – that will be your first reflection point to treat acoustically.
Do not forget the ceiling and the Floor. They are also reflective.
Reflections arrive at your microphone delayed in time and add sonic distortions to your voice narration. To minimize the sound of the room sound absorption works best for small recording studios such as home voice over studio.
For voice over actor who does individual work (one person commercial or book narration), having a small acoustic booth might be an easier and more effective and practical way to create the great sound recording environment, rather than acoustically treating the whole room.
Portable or small acoustic vocal booths are easy to set up and also easy to take with you if you have to move.
Untreated reflective surface reflecting the sound back at the microphone.
Reflective surface was treated with an acoustic blanket. Reflected sound comes back with considerably reduced energy.
Signature:
VocalBoothToGo.com ( VocalBoothToGo.co.uk) specializes in providing effective and inexpensive acoustic room treatment products, such as Producers choice acoustic blankets for sound reflection control, Noise control products, mobile sound booth, portable vocal booths and Vocal booth Rentals.
support@vocalboothtogo.com
Meet the Voices Behind Cortana and Siri
Ever wondered how Cortana or Siri came to be? We have to admit, it is extremely convenient (and loads of fun) to converse with these voice assistants. The voices have to have come from somebody, but who?
Meet Jen Taylor, the voice actor behind Microsoft’s voice assistant Cortana. Cortana was made available to Microsoft mobile in 2014 when Microsoft launched their Windows Phone 8.1.
If the name Cortana sounds familiar it’s because Cortana is also the artificial intelligence companion for one of the best-selling military science fiction video game Halo of Bungie, a subsidiary of Microsoft Studios. Unlike Siri, whose identity was unknown for a while, people almost immediately recognized the voice behind Cortana, as Microsoft didn’t look further into finding the voice for their phone’s personal assistant; they tapped the talents of Jen Taylor.
Jen is active in their local theater but has also been a voice actress since the late 1990’s, mostly voicing for video game roles like Left for Dead as Zoey and in various Mario games as Princess Peach, Toad, and Toadette. Jen shares, “Voice acting is just like regular acting, but without the lights.” She started playing the role of Cortana in 2001 and has since been part of the game franchise.
You can watch an interview of Jen Taylor below:
The voice actor for Siri, however, was a secret for a long time. Kept unknown for many years, Susan Bennett finally revealed in an interview with CNN in 2013 about her identity.
Susan and Apple’s relationship all started with a text-to-speech project of Apple’s ScanSoft in 2005, recording various sentences, 4 hours a day for a whole month. Later on, these recordings were linked together to form various sentences and phrases to what we now know as Siri’s voice. Unlike Microsoft, Apple has not made it official that Susan is the voice of Siri, however, with CNN sponsored audio-forensic tests, it is confirmed that Susan Bennett is indeed 100% Siri.
This was not the first time Susan’s voice was used for a “machine.” Her first big break was with First National Bank of Atlanta as the voice Tillie the All-Time Teller, the first automated teller machine (ATM). She went on to voice the public address system of Delta Air Lines, various GPS navigation software and telephone system.
This seasoned voice actress of more than 40 years experience found it “creepy” the first time hearing her voice in something interactive, but she is now used to it and declares that she and Siri are friends.
You can watch her CNN interview below:
Why You Need to Pay Attention to Your Room Acoustics and Basics About Sound
With the availability of more compact and less expensive recording gear, available and easy to use software, it becomes very easy to record your gigs at home.
But despite the fact this gear has definitely become much better, there is a limitation on home voice over recordings. Most professional magazines talk about latest and most sensitive microphones or software that allows to “filter” the noise and “make you sound better”, yet it still does not sound as good as a recording made in a “professional” recording studio.
The reason is acoustics. If your room does not sound good – it will be very difficult to produce great sounding results. This, of course, translates to your ability to get repeat business and eventually make a good living doing what you love.
Acoustics can get intimidatingly complex, but treating tour room acoustically does not have to be difficult, or require hours in front of a calculator. Understanding how sound works in the room and how to apply that to creating your home recording space can get you a long way to sounding your best without major construction work or spending too much money.
Whether you are converting your garage, bedroom or a closet into your voice over recording studio, knowing the basic principles of how the sound works will help you to improve the sound in the room you are making the recording.
Acoustics is defined as
- the science that deals with the production, control, transmission, reception, and effects of sound and
- the qualities or characteristics of a room, auditorium, stadium, etc., that determine the audibility or fidelity of sounds in it.
In most cases improving the acoustics in your room will result in the biggest improvement in the way your recording sounds.
So while the expensive microphones allow you to capture your best sound, it is the room acoustics is what allows you to sound your best.
This is why commercial studios spend tens of thousands of dollars to design and build acoustically optimized spaces. But you do not have to spend thousands to make your room sound good. For very little money you can make even the worst space sound good. So how?
First, we need to define two major aspects of your room treatment:
Acoustics and Sound Isolation
When we talk about the “acoustic room treatment” we are not talking about stopping construction noise from the street getting into your mic. And we are not talking about your own voice annoying your neighbors. These are examples of “soundproofing” or rather “sound isolation” – stopping the transmission of sound from one point to another. We can talk about this in a different article.
Room acoustics, or the way the sound generated inside the room behaves within the room itself, has very little to do with the ability of the sound to go through the barriers and spread out ( or into) your recording space. The approach is different, the materials are different as well.
People often get this confused, but materials used to “soundproof” your room will do nothing for helping your room acoustically and actually in some cases can make it even worse.
So what is Sound?
“Sound” in most people experience is what we can hear. In physics, “sound” is a vibration that propagates as a typically audible mechanical wave of pressure and displacement, through a transmission medium such as air or water.
So basically sound is the energy of vibration, and that energy requires some sort of medium to spread around. It spreads by agitating/vibrating adjacent molecules in the medium, so it can go through the air, water, steel etc. The denser the medium the faster it travels. In the absence of a medium, such as in vacuum it ( sound energy) cannot spread so there is no sound in Space.
Since it is the energy of vibration, sound travels in waves. Called “soundwaves”. Like if you wave your hand in a bathtub water you will create waves. In this example your “vibrating” hand simulates a sound source and the waves in the water will be like “sound waves” spreading all around the tub.
Now you can wave your hand faster or more slowly and with more force, the resulting waves in the tub will also change the pattern. That wave pattern is important in understanding of basic characteristics of sound: Frequency, Wave length, Amplitude and Phase.
Try to vibrate your hand fast and easy – the resulting waves will be shallow, frequent and low in height. It will require very little effort on your part to make them.
Now try to wave your hand wider and more forcefully , this will be much harder to do and the waves will be deeper/higher and then will come not as often, and most probably will splash out of the bathtub because they are so high and strong.
You will also notice that the waves are bouncing back from the walls of the bathtub. You can stop and watch what happens to the waves after you stopped generating more of them.
What you just did you created a model of how the sound waves work. A model that you can actually see.
Have that image in mind this might make it easier to understand how the sound works.
Sound waves and Frequency
Sound travels in waves. Unlike your bathtub water waves, sound creates area of Dense (wave peak) and Rare (wave valley) pressure, because the sound spreads in all directions at the same time (omnidirectionally). The frequency of the waves or how fast and how often the waves come, determine the pitch of the sound. Frequency is measured in Hz (“Hertz”, after Heinrich Hertz, who had described this first). The higher the frequency, the higher the note.
Human ear generally can hear between 20 to 20 000 Hz. Sound above 20 000 inaudible to the human ear is called ultrasound. Ultrasound is used by some animals for echolocation.
Sounds below 20 Hz called Infrasound. Infrasounds used for communication by some animals and also by people for monitoring earthquakes (seismic activity).
But for acoustic purposes we are mostly concerned with the audible range of frequencies. And the related aspect here is “frequency response” .
Frequency response refers to the way a microphone responds to different frequencies. It is a characteristic of all microphones that some frequencies are exaggerated and others are attenuated (reduced). For example, a frequency response which favours high frequencies means that the resulting audio output will sound more trebly than the original sound.
Ideally response should be the same for all frequencies or “flat response” . This is virtually impossible to do, so the goal here is to “smooth things out”.
Amplitude of Sound
This is the Volume of sound, that measured in dB. A decibel is defined as the smallest volume that can be perceived by human ear in isolation. ( note “in isolation” means without reference to another sound. In reference to another sound trained ear can perceive sound volume changes as low as 1/10th of a decibel).
A very quiet professional recording studio may have 30 to 40 dB of background noise, while Jet airplane engine can produce 140 dB of noise. This is not that the Jet engine noise is only 4-5 times louder than a professional recording studio, but dB level is measured on a logarithmic scale. In approximation, every 10 dB difference is about a 100 times change in sound energy level.
Wavelength
Wavelength is the length of a sound wave. (did I have to explain that?) It is related to the frequency of the sound waves. The higher the frequency – the shorter then waves. The lower the frequency the longer the waves. Think of the bathtub example or the ocean. On a nice calm day, you can see multiple small shallow waves coming onshore in brief succession. Or you can see huge long waves crashing against the rocks during a storm.
The wavelength is important in combination with “phase” when dealing with room acoustics.
Phase
As the ocean waves have the Peaks and valleys, the sound waves also have the peak and trough. The term “phase” describes the relationship of two waves in time. If two identical waves that are at the different points of their cycle are combined, they may cause problems.
Phase is important in the acoustics and recording because the waves that are out of phase can cancel each other or vice versa reinforce each other resulting in tonal changes.
Phase problems occur when the sound bounces around the room. Sound reflection is not a characteristic of sound per se, but it plays a major role in the room acoustics. The reflective waves interfere with each other destructively, causing all sorts of problems. Sound intensity near the hard surfaces because reflected wave adds to the original sound wave.
So Reflection control will be our next topic.
Signature:
VocalBoothToGo.com ( VocalBoothToGo.co.uk) specializes in providing effective and inexpensive acoustic room treatment products, such as Producer’s Choice acoustic blankets for sound reflection control, Noise control products, mobile sound booth, portable vocal booths and Vocal booth Rentals.
If you have any questions, contact us!
Sound Absorbing Ceiling Baffles
Vocal Booth To Go is happy to offer a new product to help get your home studio acoustics under control.
Most acoustical solutions are either mounted on a wall like acoustic foam or sound absorbing panels, or standing on the floor, like free-standing sound absorption gobo. These surfaces are lending themselves for easy support. But what about the ceiling?
Ceilings are a major reflective surface and often remains untreated.
VocalBoothToGo has been offering the ceiling tiles, that have grommets all around the perimeter and can be suspended on hooks off the ceiling. These tiles work well in small enclosures to cover the ceiling in your booth.
For larger studios, installation is a bit less convenient since there is a need to use several hooks to hang the blanket. This requires you to do more work and make more holes in the ceiling.
Now we offer a new product – The Ceiling Baffle.
This “new” product is actually a forgotten yet very effective old sound absorption ceiling baffle.
It has several advantages:
First of all, the baffle can be suspended from the ceiling using only two hooks or strings. So installing several baffles in a larger studio is much easier and requires less drilling and less hardware.
Secondly, the baffle not only cancels the sound reflected directly off the ceiling, but also the sound going across the room. And because you would normally install several baffles in a ceiling, they may absorb more low-frequency noise than an acoustic blanket that is installed flat on the ceiling.
Thirdly, it can be shaped in a semicircle or to go around obstacles, such as air ducts or pipes. It can also be used to hang in front of the air ducts to cover the ugly pipes and have a great acoustic treatment at the same time. We provide 8 grommets per baffle in order to be able to hang the blankets in a shape the best helps to fix your room’s acoustic problems
This Ceiling Baffle allows you to control the noise and reverberation reflected off of the ceilings and add dimension and acoustical control right where you need it the most.
This product is made out of our Producer’s Choice sound absorption material, NRC 0.8 ( 80% noise reduction). The length is 78 inches and the width is 19 inches. Its design allows you to hang the baffle in any shape to fit your needs.
This product is a great addition to noise reduction panels and sound absorption blankets.
If you have any questions about our Ceiling Baffle, give us a call at (877) 428-6225 or fill out our contact form.
SOUND AND SOUNDPROOFING
Many people who are starting to set up their home recording studio often get confused on what is soundproofing, and what is acoustic treatment.The materials and techniques used in soundproofing are very different from what needs to be used foracoustic room treatment. And, when you are preparing to set up your home recording studio, you need to understand the differences before shopping for soundproofing products. Understanding of basic principles of soundproofing will help you make right decisions, save you time and money, and a lot of headache down the road.
Many people who are starting to set up their home recording studio often get confused on what is soundproofing, and what is acoustic treatment.
The materials and techniques used in soundproofing are very different from what needs to be used foracoustic room treatment. And, when you are preparing to set up your home recording studio, you need to understand the differences before shopping for soundproofing products. Understanding of basic principles of soundproofing will help you make right decisions, save you time and money, and a lot of headache down the road.
Definition of Soundproofing
In a nut shell, soundproofing means that the sound has to be stopped from leaking in or out of an enclosure. Soundproofing, in essence, is reducing the sound pressure between the source of sound that is generating the actual sound pressure and the receiver of the sound – such as a microphone or human ear.
For example: If a lawn mower or airplane passes by your home, it generates a pressure wave of a certain frequency. That wave travels to your house and will be heard and possibly physically felt, depending on the frequency generated. To keep those sounds out, a recording studio needs to be isolated from the outside world. Sound isolation works the same — both ways — so there’s no difference in the approach of keeping sound in or out.
However, don’t be misled. It is very hard to achieve a 100% sound isolation on a small budget. But, knowing the physics of sound and understanding how sound transmits can help to achieve the best sound isolation possible.
The Science Behind “Sound”
The science of sound might have sounded boring when you had to learn it in school, but now, when you are building your own recording studio, it has a very practical application.
So, what exactly is “sound” ?
Sound is a type of energy made by vibrations. Vibrating objects create a mechanical disturbance in the medium in which it is directly adjacent to. Usually, the medium is air. So sound is actually a pressure wave.
When an object vibrates, it causes movement in the surrounding particles. These particles bump into the particles close to them, which also make them vibrate — causing them to bump into more air particles. The energy of their interaction creates ripples of more dense (higher pressure) to less dense (lower pressure) air molecules, with pressures above and below the normal atmospheric pressure. When the molecules are pushed closer together, it is called compression; when they are pulled apart, it is called rarefaction.
The back and forth oscillation of pressure produces sound waves. The frequency of the waves depends on the frequency of the vibrations. This movement keeps going until it runs out of energy.
The other thing to consider is that a sound wave is a form of a traveling wave, in that the air molecules disturbed by the sound source are unlikely to be the ones hitting your eardrum, but transfer their energy to other neighboring molecules. These mechanical vibrations are able to travel through all forms of matter: gases, liquids, solids. Sound cannot travel through vacuum because there are no particles to transfer the sound energy.
In summary:
- For sound to be generated and transmitted something must be vibrating;
- Sound waves travel by passing energy form a particle to a particle;
- Sound dies out eventually when it loses its energy. (It happens due to friction in the air itself or in trying to move (vibrate) the barriers it encounters. Sound energy does not just disappear, but have to be spent on doing some work and while doing the work it is converted to heat. )
- Sound can be transmitted through anything that has particles air, wood, concrete etc. (not vacuum).
How to use that knowledge to soundproof a room, a door, sound booth or any type of soundproofing?
1 Since sound is transmitted by air you need to make an air tight enclosure, that does not let the sound waves in or out;
2 Because Sound energy can make particles in your enclosure vibrate and get through this way, you need to make it (a barrier) as heavy as possible. (Construct the barriers (walls) using materials that are hard to move, have a lot of mass and it take a lot of energy to get vibrating);
3 Because the sound waves can be transmitted through existing structural elements of the building ( like wall, floors, ceilings) you need to separate the vocal booth enclosure from other structural elements of the building it adjacent to, which may transmit the sound energy from the outside world.
Is soundproofing that simple?
This sounds pretty simple, isn’t it? In theory. But in practice you have to deal with materials that can achieve the level of isolation you require and the costs of those materials.
Theoretically one may suggest surrounding the room with a layer of vacuum, but that is probably for a Sci-Fi.
In real life you have to use what is available and it gets complicated.
This is where the secret is: What and How of soundproofing. What materials to use? How to install them?
Using mass for soundproofing
Although sound can’t escape directly from an airtight environment, its vibration energy causes the walls of the room to vibrate, and they in turn launch new sound waves. That is why it is important to make walls that would not move. And the heavier the walls, the more energy it requires to get them vibrating. So naturally, the simplest thing that can be done is to add mass to the walls.
But different materials have different sound transmission properties (see What is STC – Sound Transmission Class).
Brick is better than plywood, and then there are loss of materials like sand.
(For example, a given thickness of glass may transmit (let through) more sound energy than the same thickness and mass of sand, because the sand particles tend to lose more energy through friction between the individual particles.)
NOTE: As a rule of thumb, if the mass of a wall doubled (by doubling its thickness, for instance) amount of sound leakage will be reduced by 6 dB.
Using decoupling for soundproofing.
Separating the sound enclosure from structural elements of the building it’s adjacent to, (decoupling) helps to block structure-borne sound. Sound energy travels very efficiently, as mechanical vibrations, through wooden joists or steel girders. Special attention needs to be paid to floor supports as most unwanted energy gets injected into the floor.
NOTE: If sonic vibrations are injected into these components, they’ll bypass all soundproofing.
Sound frequencies and soundproofing.
Another issue that makes soundproofing complicated is that the sound waves have a range of frequencies and the isolation provided by a structure reduces with lower frequency. While high frequencies are easy to keep in or out, low frequencies are far more difficult to contain.
Since different frequencies have different wave length for every frequency above a certain, critical value, there’ll be an angle of incidence for which the wavelength within the material is equal to the wavelength of the sound incident upon the material, and when this occurs the attenuation drops significantly. This is why using layers of materials with different acoustic properties can help to improve soundproofing characteristics of a wall.
NOTE: The rule of thumb here is that for every octave drop in pitch the amount of sound isolation is halved.
Using air gap for cost effective soundproofing.
But, things are even more complex than this. Sheer increase in mass and thickness of the wall is not always feasible or cost effective. The best sound proofing method, which is used by most professional studios, is to build double walls with an air gap between them. The cushion of air between the walls separates energy from one wall to the other, and the wider the air gap, the better the isolation (most noticeable at low frequencies again).
NOTE: Unless the walls are separated by a considerable distance, the cushion of air between the walls couples energy from one wall to the other, reducing the isolation. But double wall structure will invariably perform significantly better than a single-layer barrier of similar mass, even if the air gap is only a few inches wide.
When soundproofing your voice over studio or recording room, combinations of factors must be considered. Doing your homework and understanding the science behind the sound will greatly help you to create a more successful home recording studio.
BUILDING YOUR OWN VOCAL BOOTH
The vocal booth is an integral part of audio recording business. If you are planning to build a sound booth for yourself, consider first what is the desirable outcome: If you have to work with a low budget, think what you can live with. If you want a studio quality booth, this might take some dough.
The primary purpose of building a vocal booth is to create an acoustically engineered enclosure where the unwanted sounds either external or internal can be controlled.
Part 1. Considering building your own vocal studio.
The vocal booth is an integral part of audio recording business. If you are planning to build a sound booth for yourself, consider first what is the desirable outcome: If you have to work with a low budget, think what you can live with. If you want a studio quality booth, this might take some dough.
The primary purpose of building a vocal booth is to create an acoustically engineered enclosure where the unwanted sounds either external or internal can be controlled.
And external interference as well as internal echoing is eliminated. This can make crucial difference in your recording.
Vocal booths also need to isolate the recording artist and contain the sound rather than risk getting contained by angry neighbors and doing so on a budget can be a real challenge.
Where to Build the Vocal Booth?
Now we are talking home, apartment, backyard, not a warehouse or professional studio space.
What to consider on a planning stage:
1) Will it disturb the neighbors? This actually should be the number one question to consider. If you build your vocal booth adjacent to your neighbors wall, and it is leaking sound the whole affair can turn very ugly very fast and police will be knocking at your door pretty often and pretty soon.
Conclusion try to stay away from the partition walls. Try not to unnerve the neighbors.
Solution select Outer wall, below ground Basement, garage. If you have no other options, then soundproof the wall properly. It will be a shame to have to redo everything and it will get more expensive.
2) How large of a vocal booth do you need? Besides the obvious capacity, or what can you fit in that booth, there is a consideration of acoustics. Sound behaves differently in small rooms and large rooms.
3) What is the shape of the room. Again , it is easier to build the square room, but this will create some problems down the line, like reverberation, standing waves etc.
4) — How permanent of a structure do you need? Is it going to be the forever room or just a makeshift for a limited term. (like if you are renting for example).
Once you figure this out you are ready to think of building materials.
The second question is Volume. How large you want it to be? So the next issue will be:
How to Build the Vocal Booth?
What materials to use etc.
Two components of building acoustically designed rooms or sound booths is Soundproofing and Acoustic performance, which are not exactly the same.
To make your vocal booth sound proof, Ideally your sound booth should be a totally isolated sound enclosure, lifted off the floor, separated from the walls and ceilings. That is because sound waves/vibrations are transmitted through structural elements, concrete walls, etc. therefore you need to separate it.
This will not help you with acoustic quality of the room, but will have everything to do with soundproofing.
The size, shape of your structure and acoustic treatment of the room (once the structure has been built) will have everything to do with the sound quality you can record.