Small Rooms Defined

Small rooms that have a volume of less than 100 cu.ft. are rooms in transition. They have all the acoustical issues of larger rooms, with a greater emphasize on low and middle frequencies. In these sized rooms, people become part of the room acoustic. Each human has the absorption coefficient of around 10 sq. ft. of carpeting. That amount has an impact on small room sound.

Make a Big Deal Out Of Everything

Everything is exaggerated within a small room. Even the surface material of the room boundary surfaces can have an impact. One must make sure all the individuals that will be involved in the recording process within the room must be calculated in during the sound check phase prior to recording anything. A single person’s room position change in a small room can be noticed in the recording.

Variable Acoustics/Low Frequencies

The only way to achieve some sonic sense to a small room is to have moveable panels. Small rooms have no space for low frequencies to go. They must be made smaller to sound larger. Low frequency management must be attempted to be dealt with. Only a diaphragmatic absorber can provide the necessary rate and level of absorption for a small room. It must also be mobile, so it can adapt to different sound recording requirements. Resonances will move around more easily within a smaller room depending on the pressure created by the source instrument.

Variable Acoustics/Reflections

Movable panels or variable acoustics help change the direct to reflected energy stream or direction. If our small room has close in proximity room boundary surfaces then we need to be able to redirect the reflections along different energy pathways. Close, parallel surfaces, give rise to flutter echo which is never wanted in any size room. Anything that has the word echo in its name can not be good.

Mids and Highs

Middle and high frequencies can be managed using absorption and maybe diffusion depending on the room’s use. Diffusion requires certain distances in order for the diffused waveform to expand fully, so a small room may lack the space requirements for diffusion. Sound absorption technologies can be readily employed. Care must be taken not to over absorb at all frequencies.

Reflections

Reflections within our small room takes on a new meaning. How do we separate the direct sound from the reflected sound within our small room. We need to hear the direct sound first, but with close room boundaries we are always competing to find the direct sound. Trying to find that balance between direct and reflected energy at the microphone position is critical in a small room. The musicians must also be able to hear each other or all is lost.

Room Sound

Small room coloration can be used to one’s benefit especially with today’s modern music. Everyone is always looking for a different sound to record with this instrument or that vocal. A small room can add numerous effects if you will to your sound. Care must be taken not to be to taken with new and seemingly unique sounds for they can tire quickly if overused.

Their Own Sound

All small rooms have a characteristic sound to them. In fact, if one goes in enough of them, one can tell which sound absorbent technology is being employed. One can even tell who the manufacturer is. Small rooms receive large amounts of absorbent technologies because reflections are competing with direct sound from sources.

Time Domain, Not Frequency

This unique sound we hear in small rooms is attributed to time not frequency response. The frequency response does fill the room with sound, but it is the push and pull of the pressure areas of room modes and the abundant reflections from the close in proximity room boundary surfaces. EQ can not even compensate for these deficiencies.

Source Correctness

Care must always be taken from the very beginning of the recording process. It must be monitored closely and the purest waveform recorded. It can not be fixed later in the mix. All of this is hypercritical when it comes to small rooms because the reflections and room modes will leak into everything and do it quickly. Do not assume mic position # 1 will work with all instrument and vocal amplitudes.

Restrict Uses

Small rooms should have small uses. By that we mean that one should find the two uses for the room that sound the best and stay with those uses. Small rooms can not and should not do everything. They can do some things well, things that have less energy associated with them. Small rooms are energy sensitive at all room locations.

Special Needs

Small rooms have special acoustical needs. Their use needs to be limited to the uses that produce the best sound. Resonances and reflections abound, so care must be taken to try and address these issues along with finding the proper microphone position for optimal sound recording. Variable acoustics will help us but there is still no substitute for cubic volume.

Reverberant Fields

When we look at the sound in a room and in particular the reverberation times and reverberation fields in a room, we seek to find true reverberation. true reverberation exists only in a diffuse sound field. All reverberation must be spread everywhere equally for true reverberation to take place. It must be equal energy and equal volume. It must also be 100 % diffuse. This is not an easy scenario to find.

Many Issues To Consider

There are many issues that prevent us from having a true reverberate field in our rooms. Room modal resonances can impact our reverberation uniformity requirement. Resonances are pockets of energy that lie in particular room locations. These positions are determined by the room dimensions and associated volumes.

Resonances

Resonances radiate energy in certain directions and at certain frequencies which interfere with reflections which must develop into a true reverberate sound field. as resonance energy radiates from its center point it can add large pressure gains at their respective room locations. A microphone placed into a room mode, may “hear” some frequencies, but may miss others.

Furniture

The furniture within our room minimizes our efforts to achieve a true diffuse reverberant filed. A console or back wall couch can add impediments towards our reflections equally spread out. The absorption coefficient of the piece of furniture coupled with its size, all add negative variables to our equation. Reflections from the furniture surface materials can also add to the positioning of reflections in areas not necessary towards our true reverberant field goal.

Direct vs. Reflected

Our room is a combination of direct and reflected sound. Direct sound is the sound energy that travels in a straight line from the source, say a loudspeaker, to your ears. Reflected sound is everything else you hear. Reflected sound comes from the room boundaries to your ears. The direct sound emits from the source or loudspeaker and travels directly in a straight line to your ears.

Power Loss

We know from basic physics that sound energy loses power as it travels farther from its source. Physics tells us that our direct energy will reduce by a factor of 6dB for every doubling of the traveled distance from its source. The reverberate field created by all room boundary surface reflections will still be spread out and evenly distributed within the room.

Low Frequencies

Low frequencies within our room are a different animal. Low frequencies radiate 360 degrees from any source producing low frequencies. We mean frequencies below 100 cycles. No matter what the low frequency producing source this radiation pattern exists. With this 360 degree radiation pattern, we have the low frequency waves striking multiple wall or boundary surfaces. All of this energy will impact itself upon our reverberate sound field.

Critical Distance

Critical distance is finding that balance between the direct sound from our sources and the reflections from our room boundary surfaces. Where a person sits or stands within the room can make a large difference. There are paces within the room where the room sound or reverberate field would be 20dB or greater above the threshold of the direct sound. The area within the room where the two sound fields are equal is termed the critical distance.

Formula For Everything

To find this number we turn to physics and the associated mathematics. We look at two variables that impact themselves on our formula room constant number. They are the room constant or absorption coefficient and the directivity of the loudspeaker. We can even find the distance for our critical distance with both low and high frequencies.

Critical Distance Meaning

What does this critical distance mean in our listening or monitoring rooms. If we run the numbers and we get back say six feet for high frequencies and maybe 3 feet for low frequencies, we need to seriously address both low frequency control and reflection management from our room boundary surfaces.

Rule Of Thirds

Another good start, would be to divide the room into thirds. The middle of the room would be the middle third. The remaining thirds would be the front and rear portions of our room. start with your listening distance in the rear third of the room and move towards room center. You will immediately begin to hear the differences. You will also see the need for proper room boundary reflection management either through absorption or diffusion technologies.

Different Uses

We do not want the room sound to predominate at ant position within the room. We also do not want the direct sound to dominate. We do not want direct sound to dominate in our listening rooms. We do not want room sound to dominate at our monitoring or mix position. There needs to be a balance of direct and reflected energy for both room type applications.

We Have The Technology

One can treat the room with acoustic treatments to bring our critical distance more in focus with our acoustical needs. Low frequency management can be installed at room boundary intersections. Middle and high frequency absorption and diffusion technologies can be implemented upon individual room boundary surfaces. Today, we have the technology to maximize the critical distance formula and make it usable for the intended acoustic purpose.

Piano Woman

I just left a customer, well at least I thought possible customer. Isn’t this the basis for our business appointments. Customer x has an acoustic issue and company y is there to design a solution for the issue. That is the basis for our meeting and spending time together. In fact, if it wasn’t for that reason, we may never have met at all.

Acoustic Issue

The acoustic issue is usually described as “It sounds bad” or “The sound in the room drives people out of the room when I play piano”. There are others such as its too loud in this part of the room and you can not hear anything at all in this part of the room like you can the other part. After all of these comments, I am not so sure I want to go into the room.

Referral

I was referred to this customer by a dealer. She had a grand piano in her room and it was a larger room actually a good size for just a piano. Unfortunately, the room had to be a living room, a dining room, and a music room for the piano. One of the comments above was from this customer. It does not matter which one.

Need Surface Area

When I spoke with the customer on the telephone, I informed that her acoustic issues would take wall surface area to fix and would she be willing to install absorption technology over those wall surface areas. She said she understood and had no issue with that. She did not have an issue with that. I never thought to ask about the husband. It never even occurred to me. I figured if the wife was fine with wall surface treatment the husband was good, too.

Room From Hell

When I walked into the room, my worst fears were realized. The room was good size with 25′ ceilings but the piano was in the corner. To make matters worse, one of the corner walls was glass. I should have ran as fast as I could at that point, but I remembered my conversation with the woman customer on the telephone about willing to treat offending surfaces.

Issues Described

After about 15 minutes of explaining the issue and the treatment, I settled on a room tuning approach. The customer had no idea on what type of sound she wanted, but she definitely did not like the sound that she had. I decided to let her tell me what she liked after I brought in some acoustic foam to assist her in her tuning efforts. This is 2″ open celled acoustic foam.

Starting Point

I estimated she would need about 10, 3′x 5′ pieces strategically placed to produce a noticeable difference in the rooms decay times. It would not bring the reverberation times down far enough into the acoustically acceptable range, but there would be a distinct audible difference to the lay person. This was my hope, since the woman was a musician.

Plan In Place

We all decided on an approach. I would bring the 10 pieces over and place them in her room around the piano. She could then practice or play the piano and listen to the result. She could add or remove units at will and try to find a sound that was more to her liking. It is difficult to try and figure out what people consider good sound. There are too many human and subjective variables to consider.

A Four Unit Start

I did not have 10 with me but I did have 4 in my vehicle. I positioned the foam pieces around the panel in the room corner covering the one glass “wall”. I instructed her to take her time with the foam and I would be calling her next week to deliver and set up the remaining pieces for her to complete her room tuning process with. They both agreed and on my way I went.

Call Back

About two miles down the road, I received a telephone call. It was the client and she said that her husband was upset because he found the 4 panels too visibly obtrusive. I said that I would return since I was still in the area and we could discuss this issue. I headed back to the appointment.

Role Reversal

After I arrived, I listened to the husband tell me that numerous foam panels on the wall would destroy the balance of the room. He stated that panels on those two walls would be overwhelming and bring a lop sided balance to the room when one was looking out the window. Everything the husband said was what I would have expected from the wife. I thought I was in a parallel universe.

I explained that 4 units would just be a beginning and that we all agreed to try 10 total. If you find 4 obtrusive, what will you think about 6 more. I picked up my foam and left, mumbling to myself, “Please, try harder to understand acoustics”. Well, something along that line.

Full Range Instrument

When we have a piano in the room, we have an instrument that is capable of producing all frequencies that the human ear can assimilate. We can go down to 20 Hz. and upwards past 10,000 cycles which gives us a representation of all of our hearing critical bands. It is a powerful source and must be granted the utmost acoustic consideration ans respect.

Stay Away From Walls

Since it is a physically large instrument, it must not be placed next to a wall. This is just an absolute no when it comes to acoustics. There are many nos but this one is high upon the list. The first energy boundary reflection point can not be a wall that is one foot away. Don’t do that to the room and please do not do that to the piano. Put the piano in the center of the room.

Piano Against Wall

Room Center Placement

By placing the piano in room center, we fit the piano into the room acoustically. Since our sound energy from the piano is radiating at many 360 degree radius, we allow that direct sound source energy to radiate from the piano into the room. If all room surface ares are away from our piano source, we are staying acoustically true to the instrument itself. The room will add its own stink to our sound but by placing the piano in room center at least we have a chance of minimizing or maximizing that room sound.

Elevate Don’t Deviate

Our next surface issue is the floor. The floor is the closest surface next to our piano unless we shove the piano against the wall which we have agreed never to do. We must raise the piano off of the floor. It must be elevated from the floor as much as our room height will allow for. If we have 30′ ceilings, raise it 5′ in the air. If we have 12′ ceilings raise it 2′. This will improve instrument and room response.

Vibrations

Vibrational energy from the piano to the elevated platform, needs to be managed. Vibrational isolators must be chosen to compliment the vibrational energy ranges exhibited by the piano to surface area. These isolation devices can also be used to produce different piano sounds especially when it comes to attack and decay rates.

Absorption And Diffusion

Room treatment in our room, should be a combination of absorption and diffusion for all room boundary surfaces except the floor. Diffusion can add to the spaciousness of the already spacious piano sound especially at the microphone position. Reflections can be minimized through diffusion and can be spread out away from the direct sound of the piano. Absorption can be distributed to absorb any excess energy that would contribute to unwanted room decay times.

Variable Acoustics

If possible, a variable acoustic room treatment program would be desirable. The ability to alternate between different acoustic technologies at will and on all surfaces would be a valuable tool. In a rectangular room it would be desirable to have the flexibility of changing the acoustical treatment on the short side or rear walls versus the others. Having a variable acoustic ceiling in a piano room would be highly welcome especially by the microphones themselves.

Platform Acoustics

Since our piano is elevated on a platform, we now have space for acoustic treatment. We must now address the lower frequencies that can get trapped between the platform and the piano. We raised the piano off of the existing floor to improve room frequency response, now we must deal with resonances that will exist between the piano and its new platform.

Comb Filtering

These are resonances that occur from two physical objects in close proximity to one another, one of which is a sound producing instrument. We will have mostly mid frequency and low frequency resonances to content with. They will be over a limited frequency range, but they are there. We need to absorb them because they can blur or smear those instruments that generate sound within those frequencies.

Reduce Carefully

We also need to absorb these resonances at an even rate no matter what level of frequency absorption we design for. Our absorption goal will be to reduce all troubling frequencies at just enough in level to reduce their sonic impact. We do not want to take a 100 % of everything. We want to reduce the amplitude of the existing resonance so that it does not interfere with the piano player or the recording engineer.

Broadband Absorber

A broadband, low frequency absorber is necessary that extends from 30 Hz. – 200 Hz. would be a good start. If we can reduce overall amplitudes or resonances of these resonances that fall within this range, by a factor of 20 – 30%, we will have gone a long way to minimizing all associated sonic issues. No foam technology need apply for this job. A more powerful absorber technology is needed.

Diaphragmatic Absorption

Diaphragmatic absorption can provide the necessary rates and levels of absorption to handle this issue. It is also a dense technology that will lend itself well to installation in our piano platform. It can be designed and inserted into the platform directly below the piano bed. It will be close to the area of maximum pressure created by the piano, so it will perform at its best.

Microphone Positions First

All that is left to do is find your mic positions for recording both the direct sound from the piano and the room sound. This will take some practice. Don’t forget about the variable acoustics on each surface area. Get as close as you can to the sound you want by moving the microphones and then fine tune it by moving the acoustics around.

Pressure Zones

The pressure zone of a room is defined as that pressure area that exists below the frequency of the lowest room mode. This pressure zone is dependent upon the room’s dimensions. The room’s dimensions will tell us what our lowest resonant frequency is going to be. Anything below that frequency we are entering the pressure zone.

Pressure Zone Pressure

The move into the pressure zone is a gradual slope within the frequency response of the room. The rate of this transition depends on the strength of the resonance. Inside our room’s pressure zones, waves of energy do not exist. They energy in the room is raised or lowered through the diaphragmatic action of the speaker driver. There are points of pressure maximum and pressure minimums within these pressure zones.

Look Below 100 Cycles

If the room is considered acoustically a small room, then we need to look at 100 cycles as the frequency where our pressure zones can be considered acoustically useful. The longest dimension in our control rooms should be at a half wavelength of the designed for lowest frequency we need to hear clearly without room resonance distortion. If we use 20 cycles as our designed for lowest frequency, then half a wavelength would be 28′. With this dimension, we would have no speaker response within the pressure zone.

Room Mode Sketch

Room Modal Response

Modal room responses are the track that the room’s frequency response “rides” upon. Under every trough in our frequency response curve lies a room mode. Each room mode has an amplitude and width, starting at one frequency and ending at another. This is the domain of the mode with the modal response frequency at the center point in the mode.

Q Value

Modes can have a high Q value which would be a squashed bell shaped curve and a low Q value which will result in a more peaked and narrow bell shaped curve. It is desirable to have each of these modes underlying the room’s frequency response to be at least 10 Hz. apart in order to not increase our pressure issues in different room locations.

Locate Room Modes

Looking at the frequency response of the room we now need to place that energy picture with all the underlining modes within the physical room. Lets go room mode hunting. Lets first start in the room’s corners. Next, all floor and wall boundary intersections. Third, the walls and ceiling join points and the floor to ceiling area. The strongest axial mode will between the two farthest apart room surfaces.

High And Low Pressure Areas

Between each room modal pressure area, there are areas of high and low pressure. Depending on the frequency of resonance, there will be areas of high pressure at the mode frequency and then radiating out from that high pressure area in a series of lower pressure rings as we get away from the modal frequency. This radiating effect is similar to throwing a stone in calm water. Higher pressure waves begin at the stone/water entry point and radiate out from this center point losing intensity as it moves away from the source.

Anti-Node

A loudspeaker placed into a pressure anti-mode would fill that anti-mode with pressure as sound waves generated from the loudspeaker. If we place a listener in this anti-node position, they would also hear an amplified sound. This frequency of resonance would produce no sound for a listener in an anti-node. Having all these modes in certain room positions, makes finding the correct location for both listener and loudspeaker spatially dependent.

Reflections

Reflections from room boundary surfaces can also factor to our response graph effect frequency response. If we look at the floor bounce, we see a dip in the frequency response curve of a typical room. This usually occurs around 200 cycles. The ceiling adds another bounce at 200 – 300 Hz. Increasing the same frequencies that the ceiling bounce caused. The back wall increases the hatching of our frequency response curve. Adding in the side walls, we have an all boundary response curve with many more jagged edges especially above 100 cycles.

No Cube Shaped Room

It goes without saying that we do not want two identical dimensions within our room. If we take a cube room, we have all axial modes at full strength. They will superimpose themselves upon each other and this will produce strong resonances. There will be greater spaces between modal frequencies because there will be less frequency distribution than would be the case if the height,width, and depth would be different dimensions.

Non – Parallel Walls

Non parallel wall surfaces will reduce reflections and smooth out our room frequency response. This approach will not make the number of room resonances smaller. Only room dimensions can have that impact. One can reduce some impact of resonance modes to a certain degree with non parallel surfaces. However, no standard formula exists to determine what impact and where non parallel walls will have that impact. Only the experience of the room designer can help here.

Listening Experience

Most individuals that want to build a room to record sound energy within have not done done much listening in actual rooms. They have spent time sitting near field in front of their monitors but they really do not know how a room sounds. Their listening framework consists of all of their experience through the tears, sorry years, of listening to many different speakers within many different rooms. Familiarity breeds comfort, even if some comfort is missing.

No Pain, No Gain

Engineers who receive recognition and fame may have earned that recognition and fame for a single hit or song. Their overall knowledge level about good room sound may not equal their recording skill set. Marketing creates hype with flash and sizzle that no engineer can keep up with in order to try and make a living in the business. If it is not good sound, they may not know and do not want to say. Unrealistic expectations combined with this marketing hype creates a need to go along with the status quo and not upset the apple cart, even if the majority of the apples are spoiled.

Many Variables

There are so many variables that must be considered, it is difficult to get a good consensus on what a good sounding room is. Room size, equipment, and the quality levels of musicians are critical. What materials do we use within the room to create the sounds at the microphone position we need for that particular instrument? Where do we locate the microphone, once we have designed the rooms for minimum resonances at the microphone position.

Peer Pressure

Marketing programs by large corporations create a following that then turns into peer pressure. This peer pressure turns into expectations and maybe these expectations are realized but mostly they are not. We all have heard how foam can stop excessive low frequency energy within our small rooms. Nothing could be further from the truth, but they say it anyway. Unfortunately, people literally buy into it.

Real Room Acoustics

A room designer must wade through all the noise to find the truth. He must deal with all of these human perceptions and myths and construct a room that has some basic consistencies to it. There must be some givens in the room design equation that must be met and there is no compromise on these variables. We must start with room size.

Size Does Matter

There is a minimum room size we must have to start. It is a room size and volume that can deal with room resonances and not make things worse for recording or monitoring. There is a ratio of room sizes that lend themselves to good acoustics. One of the most important dimensions is room length. We must have at least 30′ in room length to have a room that will have a chance of measuring down into the 20 cycle range. There is no exception to this requirement.

Room Height

Room height is another no compromise situation. The parallel surfaces between the floor and the ceiling are big contributors to low frequency build up and a whole host of middle and high frequency issues. There must be adequate height in our golden ratio of height,width, and length, to be conducive to minimizing those issues. We must have a minimum height of 12′ to accomplish at a minimum these acoustical objectives. There is no exception to this requirement.

Wall Construction Techniques

The wall construction methodology must use block or brick. Wood frame is not acceptable to producing real quality sound. Frame does not produce any isolation nor does it produce any real quality sound. Frame construction moves too much. Sound pressure energy can cause frame construction to move or vibrate just like a speaker does. The wall goes diaphragmatic and begins producing sound of its own. The vibrational plates of frame construction adds to the vibrational levels within the room and will contribute to the room’s sonic signature. Walk into a wood framed room. Now, walk into a brick room.It is not difficult to hear the difference. Lower structural vibrations are always conducive to a better sounding room.

Low Frequency Absorption

Low frequency absorption must have the necessary rates and levels of absorption to insure all low frequency resonances are under control. Proper low frequency management techniques must be employed at the proper room position to absorb the necessary magnitude of the resonance. Foam will not work and do not believe the marketing slogans. Foam is only applicable above 100 Hz. no matter what the manufacture claims its low frequency absorption capacities are.

Middle and High Frequency Absorption

Middle and high frequency absorption technologies must also have the necessary rates and levels of absorption in order to maintain the musical integrity of the reflection we are controlling. We do not want to over absorb the reflection. We just want to minimize its strength to reduce its impact at the monitoring or listening position.

More Not Better

Most middle and high frequency technologies in the marketplace today over absorb energy to reach high absorption coefficients in order to sell more product. More is not necessarily better when dealing with reflections. We do not need to destroy energy through too much absorption in order to manage it.

No Compromise

Everything in life is a compromise. However, when one is concerned about and places a high value on sound quality within a room, there are areas that can not be compromised. Designers must stick to their beliefs and tell a client to choose another room if compromises for the chosen room look longer on a list than does the equipment. Sometimes, one must just say no.

Different Sounds

As I go into many project and full studios, it is always amazing to me how different each control room sounds. Each engineer has selected what he or she thinks will produce the desired sound when it comes to equipment and especially the speakers. Engineers will keep using the same monitor that they have been using even though a newer monitor may bring different variables to the monitored sounds and perform better.

All Sizes And Shapes

I see many shapes and sizes in different control rooms. In full time studios, we see both large and small monitors. In project studios, we mostly see smaller monitors. There is also, mostly in full time studios, a smaller speaker that is designed to sound like speakers found in computers, radios, and other common listening devices. The thinking is that this quality level and speaker size is what a large segment of the marketplace listen to music on.

All Speaker Sizes Found

Classical Recordings

The classical recording process is different. The classical recording process uses very small speakers, namely headphones. Headphones are used because they provide the detail necessary to monitor the sounds. They also provide isolation from outside noise. If monitors are employed, they are larger ones that represent a higher quality sound level. The classical recording artists and engineers focus on the producing a classical sound in the recordings, so electronic signal manipulation is frowned upon.

Acoustical Pallet

Each speaker or monitor produces a different color if you will upon our acoustic palette. The engineer will choose this or that monitor that will create the sound the engineer wants to produce and would be considered by the engineer to be good sound. The engineer must create sounds with a big picture in mind. He or she must fit the electronic pieces together to form a larger picture.

Mid Range Music

The music is always found in the mid ranges. It is that middle frequency range where our vocals lie. It is the area where layers and layers of sound are stacked upon each other and all must be able to be heard. A speaker must be able to produce this middle range energy and do it in a manner that will create an emotional connection between the music and the listener. It is even welcome to select a monitor that has more of a forward sounding mid range.

No Standardization

All of this subjectivity and impression creating, lends itself to a lack of standardization in the recording, especially monitoring process. Most engineers do not care about how a monitor works but rather really only care about that monitor working for them and helping them to create their sound. In a playback mode, they want to not hear all the little sounds that took to make the recording but rather the sum of all of these parts to produce a musically sounding piece of work.

Hi- Fi Everything

The hi-fi person wants to hear everything. Hi-fi people want a speaker to be revealing and produce resolution and detail. Hi-fi people want to hear all of the parts. The recording engineer just wants to hear the music, not all the parts. Each uses a speaker to accomplish what each one considers to be good sound. It is all about what each person wants to hear and that want is based on many different variables.

Manufacturers Part Of Problem

All of this subjectivity, enters into decisions manufacturers make. Manufacturers do not assist in the sound quality producing process. They will design a loudspeaker to fit into a particular price point or even appearance point. Sound quality may be a sixth or seventh priority in the total loudspeaker design considerations. Marketing and saleability overrides sound quality.

Room Sound / Speaker Sound

How the speaker sounds in the room is another variable. Near field monitoring will only do so much to eliminate the room sound. The room is always in the mix and must be adjusted for. Fighting a bad room can only add more noise and confusion to our mixes, especially in the low end. Rooms and speakers need to be sized matched in order to avoid room distortions. Large drivers in small rooms goes against both common and acoustical sense.

Recording Standards

There needs to be a better definition of what a good recorded sound is. When I play back any recorded music within my listening room, I am always grabbing for a knob on my EQ at the listening position. Every recording has some acoustic abnormality that needs to be addressed. The issues are usually focused on the low end of the recorded source. There is usually a need to reduce through EQ some part of the low end frequency response , so that the low frequency energy produced by the speakers from the recording will fit into the room.

THX Equipment Requirements

THX uses this standardization process to apply to the speakers and amplifiers that they want to produce their source data. They require that amplifiers have a particular or minimum power handling capacity to be able to cover large transient ranges from gun shots to explosions. Speakers reproducing the THX format must have a full range frequency response handling capacity and match the amplifier power ratings. This certification process specifies the necessary performance minimums of the equipment but does not really do anything about what the room sounds like.

Standardization Need

We need some type of acoustic standardization for our sound engineers to follow. We need to raise the minimum performance levels and standards of our recording engineers, so that we are all at least starting from a similar page. I am thankful that there are always engineers who have read farther into the acoustic book. Their recordings really do sound good.

Noise is everywhere, but we can not let it in our studios. We must reflect or absorb it away. In order to do this, we must build a protective barrier between us and the noise. Here is how to begin.

Quiet, Please.

One must make their rooms as quiet as possible. The act of quieter is a component in your system much more powerful than your monitors or board. The room is an extension of the instrument or vocal that is vibrating within it. The room must not speak and if it does, we want to bring it down to the level of a whisper. No whispers or sound from the outside either.

Need Different Technologies

We achieve this quiet through the use of different technologies. Our outside room shell is a barrier between our music room and the outside world of noise. The inside of our room must deal with low frequency resonance control and reflections from all room boundary surfaces. It is this balance between barriers and inside room treatment that must be dealt with.

Barrier Technology

Barrier technology does two things. It reflects outside sourced sound energy that strikes it, back to the outside. It also takes the energy that is generated from within the room by instruments and vocals and bounces it back into the room. It sends the sound energy that leaves the room back to its source direction by striking the inside of our shell barrier. We must use special care in addressing this relationship between the room and our shell.

Air And Noise

Noise is transmitted through the air. It strikes our shell barrier and parts of that energy is sent back using the reflection process. When it strikes our shell or barrier it is now vibrational energy and our structural goal is to minimize the transmissions of that vibrational energy through our barrier. We measure the amount of vibrational transmission that is lost within our structure design.

Design Goals

Our goal in our professional studio is 25 – 30 dBA. Any noise above that range will begin to appear in our microphones when recording. This noise level can degrade the clarity and definition of our recordings. There will will low level tone and timbre that may be masked by any noise levels higher than 25 – 30 dBA. I see studios with 50dBA of computer and fan noise and monitoring limits of 90 dB SPL. This mixture produces a signal to noise ratio of only 40 dB. We must work and balance both inside and outside noise levels.

Balance Needed

This balancing act must occur prior to building the structure and before choosing a location. It is highly advisable to call in an acoustical engineer prior to selecting the site and definitely before building the structure. It is much easier to change a line on a drawing than to knock down a resonance producing wall dimension.

Modern Day Construction Techniques

Most current building types are lightweight in construction and situated in near proximity to a noisy source. This lightweight construction found in new buildings does not follow the three requirements of any good studio construction. In all studio construction and location techniques, we need mass, rigidity, and space. The lightweight construction is cheaper to build and that is the main reason people buy them. It is not the reason to use that room for music playback and recording.

Space,The Final Frontier

All good sounding recording studios have one thing in common, plenty of space. This space is the result of a high ceiling. The parallel surfaces from floor to ceiling must be separated with space. The floors are reflective at lower frequencies, so there is a strong need for proper studio design to avoid vertical room modal issues.

Lots Of Space

Space is also required for microphone placement. Moving instruments and microphones around a room requires space. Instruments find their own acoustic home and microphones must follow them. Microphones must have the necessary space for positioning correctly and not be next to any room boundary surface. In the studios we have been working with, it appears those that have at least a 20′ height allow for adequate microphone positioning above the instruments and away from room boundary surfaces.

Floor Concerns

Floors are another concern. All barrier technologies require mass and mass has weight. There are no general guidelines to illustrate this principle but one can break the weight factor down into a square foot calculation for discussion purposes. If we take a room 30′ long, 18′ high, and 12′ wide, we can look at over 40 tons of mass required for both ceiling and floor isolation. This would equate to around 140 pounds per square foot. Barriers need mass to work.

Mass Support

The mass requirements in room acoustics need strong structural support. The newer, cheaper, build construction of today’s buildings will not support the additional weight that is acoustically required. Every dB of isolation costs money and if we have to reinforce the existing structure so it can support the barrier technology mass, we are increasing our costs and time frames exponentially.

Start Fresh And At Beginning

All of these variables must be addressed at the project beginning. We must decide on our space requirements inside and then the structural isolation components for the outside barrier technologies. We must look at site locations that are away from noise producing sources. It is always a balancing act with all parts working together. It is for this balance that one hires a professional to achieve in the correct proportions.

Art And Science

Acoustics is both a blend of art and science. Sometimes there is more art when there needs to be science. Here are some examples of art replacing science.

Small And Large Rooms

As I work back and forth between large room reverberation times and small room resonances, one gets the opportunity to speak with many individuals associated with the audio and video equipment within those large and small rooms. There is a understanding and general agreement about their current acoustic issues but a lot of misunderstanding on how to solve the issues and with what materials to use.

Egg Carton

One popular misconception is about room treatments. We all remember the egg carton. It was the cure all from sound isolation to bass absorption. It was a natural diffusor. It does look like some type of exotic, two dimensional diffusor, but its ability to provide any diffusion is negligible, if any at all. It has absolutely nothing to contribute to sound isolation other than how can I remove this from the job site. It has no mass for sound isolation and did not absorb or diffuse any amounts of sound energy.

Carpeting

Carpeting is another standard room item that has taken on all kinds of mythical proportions. Remember, when you saw it on walls in studios. Right idea, wrong material. Although those shag carpets of the 70′s might have had higher than normal carpet absorption coefficients, carpet was given more acoustic credit than it deserved. It is nice to have carpet on the floor in a control room. It would not be wanted in a live room where cellists and acoustic bass ground their instruments to the floor. Carpet in this case can damp the resonance of the acoustical instrument. Once again, as with the egg cartons, no mass for sound isolation and really not a consistent and predictable wall treatment for reflection control.

Furniture

Furniture is not acoustic room treatment. A couch is not a “bass trap”. A couch can have an impact on middle low frequencies, but will do nothing for a 40 Hz. wave and all of its fundamental cousins. It can because of its size have an impact on reflections, but that impact depends on its covering type. If it is fabric we are probably fine, leather surface treatment may even add to our reflection issues.

Bass Traps

Treating the low frequency resonances in small room acoustics takes up a lot of space. This is partly true when one look at the small room project studio. A 12″ deep “bass trap” does take up a lot of space if your room is only 10′ wide. If your room is 20′ long, it is not that much space for the benefit received. Contrary to common marketing practices and claims, foam will not stop low frequency energy. Here’s a good tip: If you can pick up the low frequency absorbing unit by yourself and move it easily around, It is not a very powerful absorber at lower frequencies. There simply is no better way reflected in the current technology to absorb bass wave energy without using mass.

Room Shape

Room shape is critical. A rectangular room offers predictable and consistent reflections that one can then apply consistent and predictable treatment to. Room resonances are highly predictable in a rectangular room and are readily determined by the dimensions of the room. One can apply low frequency resonance control to a rectangular room at the corners and at all room boundary intersections.

Size Does Matter

Room size does matter in the recording process. One can not avoid the laws of physics and squeeze a smooth frequency response out of smaller rooms. It is just not possible. Well, it can be done but one may have to make the room smaller by applying low frequency treatment in the ceiling area. No one wants to hear that. Sometimes, we must talk our clients out of using that small room for anything but storage for a future room build that has the necessary dimensions to minimize room resonance issues.

Speaker Positioning Does Matter

Speaker or monitor positions do matter. A speaker is a device that produces acoustic energy and then interjects into a box or room. The acoustic energy produced travels at the speed of sound which is a constant. In order to achieve stereo imaging, we must have both distances from all room surfaces in some balanced dimensional pattern. Speaker to speaker distances must be balanced and first side wall surface reflections must be equal on both speaker sides. Not only do we want the direct sound to travel straight to our listening or monitoring position, but we also want the side wall reflection arrival times to be the same at the listening or monitoring position to create the proper stereo image.

EQ Given Too Much Credit

Equalization will not solve all your issues. One needs to get it right in the room. Choose the right microphone and place it in the correct room location and contribute these processes to achieving the best sound you can without adding any electronics to it. If you have a purer original signal then less electronic manipulation is needed with the board. Less is always more in this process.

Band Articulation

Bobby Owsinski talks about 3 quick things a band can do as a group to improve quickly. He talks about dynamics, attack and releases, and turnarounds. All three of these have application for bands but they are also applicable for room acoustics.

Band Dynamics

Dynamics is the difference between the loud and soft passages in your music. If you play softly and then loudly, that difference is your dynamic range, if you will, as a band. Variable loudness playing can allow your vocals to be heard more when you are playing softly and then can allow for more emphasize when you need to convey more emotion by raising your vocal loudness level. If you start soft, you have more “headroom” with dynamic range. If you start loud then you must get louder for dynamic impact or stay at the same volume. Neither is welcome for good quality sound recording.

Room Dynamics

Dynamics in room acoustics works in a similar way. Your room should allow for dynamics to be represented completely. Quiet passages must be heard. Over absorption can smother quiet passages. Too much diffusion can produce a separation in vocals and instruments that can be confusing. Comb filtering can blur and smear any difference in volume between quiet and louder passages. Our room must be able to hear both quiet and loud passages with the same clarity.

Sound Isolation

Proper sound isolation techniques employed in your room, will make lower noise levels within the room, so that quiet passages and lower volumes can be heard. Barrier technology is not cheap, but quiet rooms are a great joy. There is no substitute for the quiet in a room that is measuring between 35 – 40 SPL. I was in a room once that was at 28 SPL continually. There were 4 SPL meters that had LED displays that one could read easily. They would move back and forth with 28 SPL as a low. I can still “hear” that room. I will never forget it.

Quiet, Please

Can you imagine playing a soft passage in this room and then a louder one. With a start point in SPL of 28, a loud passage would appear at say, 38 SPL. This would be real room dynamics with a range more conducive to human hearing. Start your car and let the motor idle. Do not move the car. Listen to music with the engine running. Turn the engine off. Listen to the same music. Now you hear what I mean. If we lower the noise floor, we allow for more headroom.

Low Frequency Control

Low frequency control is another part of dynamics that must be dealt with. There is a lot of important sound energy from 30 – 60 cycles. Your room must provide the necessary acoustic “room” for acoustic and electric bass notes. Both of these instruments represent dynamic ranges from soft to loud. Within those two domains are layers of energy that your room low frequency absorption must be able to differentiate. Your room must allow for the dynamics of each low frequency layer of frequencies to be heard in its entirety. High sound pressure areas in the room must be treated with low frequency absorption that addresses not only the pressure’s level but it must also absorb this excess low frequency energy at a high rate.

Attack And Release

Attack and release are another live sound area that can be related to a band and a room. Bobby tells us that a bands ability to begin a phrase and end it is critical to producing a good sounding recording. Vocals must begin and end with the proper phrasing. Instruments must begin and release correctly and on time in a regular and predictable time. Bobby cites the Eagle’s Hotel California as a good example of attack and release, especially with the guitars.

Attack And Decay

Attack and release in room acoustics translates to attack and decay with musical sound energy within our room. Attack must be defined. We must have low SPL levels within our room using barrier technology in order to hear every attack note at its certain pressure level. We must also have a room that has the correct balance of rigidity in room wall construction and surface materials on these walls. Sound energy takes on the characteristics of the surface it strikes. Strike glass, receive glass in your room sound. With these two conditions in place, it is possible to hear the attack of a note and the following decay without it getting smothered by another attack and decay sequence.

Balance Needed

The room must have the necessary rate and level of absorption at all frequencies to maintain a balance between attack and decay energy requirements. Sound absorption technology used within the room must be smooth in absorption rate so that there is no over absorption occurring at any frequency. Middle and high frequencies must have proper spectral balance between reflections and direct sound. Low frequency absorption rates and levels must be in place to provide enough absorption levels and rates for attacks to occur and then decay on their own volition.

Band Turnarounds

Turnarounds are that few bars between each part of the song you are playing. Bobby cites the area between the “verse and chorus, chorus and verse, verse and outro, and chorus and bridge.” it is a critical part because it is played differently from the rest of the song. A drummer can begin a roll and end segueing into the next section. Other band players may continue to play over the roll. If everyone has their start place and end place, all can be heard in the song.

Places, Please

In room acoustics, all sound absorbing and diffusing technology must be placed in the proper place or surface area within our room, so that the room’s turnaround is predictable, tight, and consistent. Location of different technologies in different room positions will produce different “sounds” within the room. One can produce a wide and deep sound stage by using sound diffusion technology on the front and rear walls of a listening room. In a control room, diffusion on the rear wall can negate the delay in our signal from the rear wall to our monitoring position.

Diffusion Friendly

Diffusion both horizontal and vertical can add sound stage depth and height in a playback environment. Small room playback environments need to create an acoustical space within a small amount of square footage and room volume. Diffusion, and in particular quadratic diffusion, can give us the sensation of a larger room by front and rear wall placement. Side wall absorption, provided it is done at the correct rates and levels, can contribute to vocal and instrument separtion along with increased definition.

Dynamics – Attack – Release

Dynamics, attack and release, and turnarounds are three things Bobby Owsinski tells us will help a band show immediate improvement if followed. These three variables can also be applied to the science of room acoustics. In room acoustics, attack and release becomes attack and decay. Turnarounds become the predictable and consistent room acoustic behavior.