More Than One Third Octave Needed

In an attempt to standardize all control rooms, so we can determine what good sound is we must look at room designer Tom Hidley. Tom Hidley came from the school of thought that looked at one-third octave room response and if balanced we were good to go. We now know today that this approach does not take into consideration phase and without phase considerations, we can not have a proper transient response within the room. We need to look at wall surfaces and composition.

Stevie Wonder

During this time period rooms were viewed as over trapped. This term came about because individuals felt that the bass did not have the same balance as the middle and high frequencies. Individuals were not able to figure this issue out because the analyzers were all measuring flat. The room in question was booked for Stevie Wonder. During the session, Stevie Wonder kept referencing and pointing to the loudspeakers. However, The locations he was pointing to were not where the speakers were located. Localization of the speakers was difficult because there were too many reflections.

Japan Journey

His next journey took him to Japan where he was to build two rooms which were similar in design to rooms he had made in the past. The terms and conditions of this task were rather unique. He consented to building the rooms but he had certain requirements. He would build one room the way the client wanted it and the other room he would build the way he wanted it. Whatever room was the best liked by musicians and engineers, would be the room to stay built. The other room would have to be demolished and the favored room would be built into its place. The winning room was termed the Non-Environment design.

Non Environment Room

The new Non-Environmental design was different. It had low decay times, hard front walls, and of course flush mounted, front wall monitors. This was a radical departure from current “live end dead end” acoustical studio approaches that were currently being built in the USA. Chip Davis pioneered this technology which had the front of the room treated with absorption and the rear of the room left more lively through no treatment or the application of diffusion technologies. Vertically aligned monitors were introduced at this time into the Non Environment Room.

Vertically Aligned Monitors

With this new control room design, it was a relatively easy to fire the vertically aligned monitors into a highly absorbent rear wall. That issue was resolved. However, now Tom had to address the omni-directional low frequency energy within the room. Different sized rooms produce resonances at different frequencies because of the given room dimensions. He needed a universal type of low frequency absorber that could be applied to any room size, if we are going to standardize a room for the sound quality.

Membrane / Diaphragmatic Absorption

The solution to the low frequency absorption standardization technique came about with membrane absorbers in front of a panel or diaphragmatic absorption as we know it in North America. The membrane absorbers were good down to 100 cycles and then the panel or diaphragmatic absorbers would handle below 100 Hz. One could lower the resonant frequency of the diaphragmatic absorber by making the panel depth larger and also by lowering the Q value of the cabinet.

Modeling Not Easy

To make life easier, Tom tried to model this new room and come up with a standard that could be applied universally. He was designing rooms that had 10 Hz. cycles to design for, so a low frequency component that could be placed inside the rooms was paramount. He used a one tenth modeling of all absorptive systems, but this model did not seem to translate to real sound properties. Modeling of complex systems within a room is difficult.

Hard Front Walls

There was a general balancing of materials and construction methods that did appear on a consistent basis. The first was hard front walls. This was very different to what anyone was doing at the time. Absorptive front control room walls were the norm. Monitors built into the front wall were also new. This approach allows for the omni-directional energy that radiates from the speaker to be manged and it also allows for vibrational control of cabinet vibrations at higher sound pressure levels.

Hard Floors Everywhere

Hard floors were prescribed throughout the whole control room. The rear wall was to be highly absorbent along with the sides and ceiling. There was some degree of variability at these surfaces. If more absorption was deemed necessary by the end user on the rear wall then so be it. Ceiling and side wall reflections could also be managed in a similar fashion.

Non Environment Rooms / Playback

With the new Non Environment Rooms, one did not have to have a separate playback room to make sure our mix translated well. With the Non Environment Room, we had all the sounds present and accounted for in a nice and real balance. All low ends were tight and their place along with the middle and high frequency riding firmly on the bass notes. All images were focused and in place on the sound stage.

Balanced Standard

Tom Hadley’s Non Environment Rooms were unique for their time and are still used today. The goal was to minimize all the contributing components of room sound so that the combined room sound variables all together did not add up to an issue. Reducing the room sound error rate with the room acoustical components down to their minimum influence levels, would produce a room with less errors and less room sound. Standardizing the room surface treatments for proper reflection control and a throughout the room low frequency control approach, provided the proper standardization for all of this room sound minimization to occur.

Control Room Goals

The primary goal of control room design is to achieve a flat or smooth frequency response that would translate into a similar response time in domestic and consumer rooms. This room response was also to have a decay rate that was equally representative of end user listening rooms. Our acoustic goals for our control room on the professional side was a compatibility between control rooms so a mix in one control room would translate into another control room. Secondly, our control rooms must be designed to provide a comfortable working environment for the engineers who must spend hours working in the control room.

Standardization

In order to make sure that mixes that are made in one control room will translate into another control room we need a standard set of conditions present in one control room translates into another control room. The European Broadcasting Union tried this standardization many years ago but could not get anyone to agree. Control rooms are all different and dissimilar.

Monitor Location

The first and most important factor in any control room standardization process is the location of the monitors or loudspeakers. The location of the monitors is directly responsible for the frequency response in the control room. The position of the monitors is directly responsible for the cumulative response and blending of the direct and reflected sound which is critical to any uniformity or standardization of sound. Flush mounting of the monitor speakers in the front wall will go along way to achieving some sound standardization and cross studio translation. A control rooms goal is to add nothing to the mix sound.

Near Field Monitoring

Near field monitoring is a best effort to minimize room response issues. With near field monitoring, engineers can hear the sound of the monitors with minimum room sound entering in to the equation. With near field monitoring we are sitting within the critical distance. The critical distance is the area where the direct sound or straight line sound from the monitors predominates. With monitors positioned within the critical distance, the reflections from room boundary surfaces are minimized. Lets push the critical distance to be “outside” the boundaries of our control room. lets design rooms that have all reflected energy under control.

Near Field Pros and Cons

Near field listening has its benefits and disadvantages. If everyone near field listened, we would have a large number of engineers who at least knew of the sound of a group of monitors. This would be a benefit for all concerned. Work performed on near field monitors could be judged and compared with other control rooms. However, near field monitors lack good transient accuracy and can not reproduce the lower critical bands of energy that provide the foundation of low frequency energy in our mixes.

Dynamic Range Limitations

Dynamic range of near field monitors is also limited. Without the ability to have dynamic range response in our monitors, we can not assess the critical low level detail. This low level detail can only be realized if our loudspeaker has the necessary dynamic range to permit the distance between low and high energy passages to be heard. What we need to do is to extend the benefits of near field listening, namely staying within the critical distance parameters to the rest of the room.

Low Energy Management

We also need our rooms to provide the proper rates and levels of low frequency control and management, so that our critical distance is available throughout the room and low frequency pressure build ups will be evenly distributed within the room. We need low frequency absorption that can handle the lowest frequency issues our room dimensions dictate and also provide the proper amount of absorption to provide the necessary attack and decay so necessary with lower frequencies.

Golden Ratios

Proper room dimensions are critical if we are to have a running start to manage low frequency energy. It is always better to choose the correct room dimensions to minimize the impact of room dimensional resonances. Certain room heights, widths, and lengths are more favorable to producing less room resonances. We need to find those “golden ratios” and utilize them in our room size choice. We may even have to make the room smaller to allow for reduced modal resonances.

Reflection Control

Near field monitoring minimizes the impact of room boundary reflections. If we are to extend this concept to the whole room, we must use current absorption and diffusion technologies to bring the rate and level of these reflections down below the direct sound from our control room monitors. We must address the rear wall reflections that produce a time delayed signal of its own at the listening position. A balance of current absorption and diffusion technologies can accomplish this for us.

Ceiling And Side Walls

Ceiling and side wall reflections must be addressed in a similar fashion as our rear wall. We must use a balance of absorption and diffusion technologies to reduce the time signature on these surface reflections, so that it does not interfere with the direct sound from our monitors. Near Field monitoring is a direct response from engineers to minimize these surface reflections by sitting closely to the speakers. We need to extend this concept by treating the whole room so it does not produce the reflections that engineers are running away from by sitting near field.

Standardization Components

If we place our monitors in a surface mount position in the front wall and treat all room boundary surfaces with the proper amount of diffusion and absorption technologies, we can go along way to achieving some type of standardization in the monitor or control rooms of our studios. Front wall flush mounting will standardize the frequency response in our rooms and the treatment of all room boundary surfaces will minimize the impact of these time delayed energy on our mixes. Proper room dimensions and boundary surface reflection control are a must if we are to begin to achieve the direct versus reflected energy ratio we must have for any control room standardization to occur.

Diaphragmatic Absorbers

Diaphragmatic absorbers are powerful, low frequency, absorbing technologies. One must build a solid, sealed box that has a front wall that can “move” in reaction to sound pressure waves. This front wall movement slows the wave down, so that it can enter the inside of our sealed cabinet. Yes, the cabinet is sealed without any air holes. Low frequency waves that are 40 and 50 feet long do not care about some 1/4″ air holes in any type of absorber. With low frequencies we are dealing with waves of energy not rays.

Cabinet Construction

The cabinet that supports the front wall must be as inert as possible and not move. It must be rigid, so that only the front wall is moving in response to the sound pressure exerted upon it and not the sides or cabinet rear wall. Rear wall construction must be thicker than the side walls in order to obtain the proper rigidity ratios between the sides,the rear wall, and front wall. Since the side walls are shorter in length, they possess more rigidity and thus we need to add mass to the rear wall to keep our rigidity ratios between the surfaces correct and balanced. Viseo-elastic damping compounds between the cabinet’s layers of materials is a good way to minimize cabinet sides and rear wall vibrations and maximize cabinet rigidity.

Resonant Frequency

To achieve the proper resonate frequency of our diaphragmatic absorber, we must calculate cabinet material density and the depth of the cabinet itself. We are designing a cabinet that has a certain density in the materials we are using and has a certain depth inside the cabinet. If we do our calculations correctly, we build a cabinet that has a certain resonant frequency. This resonant frequency number is our sound absorption baseline. Any frequency above our diaphragmatic absorbers’ resonant frequency will be absorbed and any frequency or wavelength striking our cabinet that is below our resonant frequency will not be absorbed.

Inside The Cabinet

Inside the sealed cabinet is an air space. Conventional thought usually declares that one should fill this cavity with a fiberglass, insulating material, or some other foam based product. I have even seen spray foam used inside the cabinet. None of these materials address the issues necessary to achieve a low frequency absorber that absorbs greater than the physical dimensions of the cabinet tell us. They are cabinet fillers which are supposed to minimize the cabinets internal resonances. Minimizing the internal cabinet resonances is short sighted and does not take into account the power that a diaphragmatic absorber is capable of. We need to lower the internal cabinet’s Q value to a level that will radically increase the unit’s absorption capabilities.

Charcoal Filter Insert For Diaphragmatic Absorber

Q Value

A cabinet’s Q value is a ratio of how well the given space we are discussing performs in relation to the size of the space. A cabinets Q value is the bandwidth of our resonating system or diaphragmatic absorber internal space. With traditional cabinet fill materials such as foam and fiberglass, all we are doing is minimizing the cabinets internal resonances. Granted this minimizing does increase the cabinets bandwidth and thus performance but not to the degree necessary for frequencies below 80 Hz. If we are going to achieve the high rates and low levels of absorption necessary in our diaphragmatic absorber in the smallest cabinet size possible, we need to increase the cabinets Q value through a process termed acoustical compliance enhancement or ACE.

Acoustical Compliance Enhancement

Acoustical Compliance Enhancement is a process where we make something perform better than its physical size and contents tell us it should perform at. If you take a car with an engine that uses fuel and air through a carburetor into the engine, that engine will produce a certain amount of horsepower for the size of that engine. If we take that number and use that number as a benchmark, we can increase the horsepower of that engine by adding fuel injection and replacing the carburetor. We have not changed the size of the engine, but simply the method in which the engine receives its fuel and air for combustion. We have made our engine more efficient without increasing its size.

Activated Carbon Granules

Activated Carbon

Acoustical Compliance Enhancement or ACE is the same process one can use to increase the cabinet’s internal Q value or bandwidth of our diaphragmatic absorber. Instead of replacing a carburetor with fuel injectors, we use a substance called activated carbon inside the diaphragmatic absorber. Activated carbon or charcoal has a high degree of porosity and is a powerful absorbing material. It is used to filter water and air. Activated carbon granules look like miniature meteors. Each granule of charcoal has numerous holes or pores in it. Each pore is a perfect place for sound to enter into and be absorbed. Each activated carbon granule has many pores and these pores translate into a large amount of surface area. If we could unfold one gram of activated charcoal it would equal anywhere from 500 to 1500 m2. One teaspoon of activated charcoal powder (about 3.3 gm.) has about the same surface area as a football field. This surface area translates into a tremendous potential to “absorb” large amounts of sound energy.

Diaphragmatic absorption is a sound absorbing technology that has been around for years and is used extensively in professional studio and home theater construction. A diaphragmatic absorber is a sealed box that has a surface that vibrates in sympathy to sound pressure waves. Inside that sealed box is placed building insulation type materials and even construction foam which assists in minimizing internal cabinet resonance but does nothing to actually make the absorber more powerful. One can increase the performance of a diaphragmatic absorber by using a different fill material called activated carbon.

Acoustical Science

In the science of room acoustics, we have many variables that we can measure. We can measure resonances, reverberation, and frequency response not to mention a host of others. Each variable has an associated acoustic sound in our room. We measure these variables using science to assist us with certain starting points. That is all science can do for us is give us a starting point and for that we are thankful. The real “science” occurs when we take our personal perception of what good sound actually is to us and use this perception to voice the room.

Science and Art

Voicing a room is a blend of science and art. The science comes from measurements and numbers. The art comes from taking those numbers and fitting them or parts of them into our sonic perception of how much,for example, reverberation should we have? We know the numbers, but where on each side of those numbers does it lie for us. Which ones and how many of the resonances should we tame to allow us to be comfortable with the low end of our room? Is the attack and decay rate what we want? How much absorption do we use to minimize reflections? We must balance science and art.

Easy Science

It is easy to “get the numbers” to any variable. We can measure for it or look it up in a book. We can do this using very little time or energy. However, we must ask,”How does it sound to me”? Do I like it? Can I and do I become emotionally involved with the music. Does the room help me with my emotional connection with the music? What little things can I do to make it sound the way I want it to. This is the voicing part of the equation. This part takes much longer and is way more fun. It is a journey that must be taken slowly and done over longer periods of time.

Low Frequency Resonances

There are three parts to voicing a room. The first part is getting all resonances or most of them managed. Low frequency issues are present in almost any room. Room resonances at lower frequencies, especially those below 100 cycles, can ruin any quality sonic presentation. Low frequency resonances are like bulls in a china shop. They charge into everything and bump into everything else. They trample over our middle frequencies and can even have an impact on higher frequencies.

Attack And Decay

Low frequency resonances can impact attack and decay times with individual bass notes or chords. Excess resonant energy at lower frequencies can exaggerate some bass notes and completely eliminate others if our listening or monitoring position falls within a room mode. If we can’t hear where one bass note begins and ends in its entirety, we are missing too much music. There is a lot of music below 60 cycles. Don’t let the room get in the way of the music. Proper low frequency resonance control is a must have. There is no art needed on this one.

Middle Frequencies

Middle frequency ranges are plagued by reflections from our room boundary surfaces. All of these reflections add up to a certain reverberation time in our room. If we are listening to music and not recording instruments or vocals, we want a certain amount of reverberation in our room. Reverberation assists us in feeling the music all around us. It is different with a microphone. The microphone normally does not like reflections and will tell you so in the mix.

Vocals Are Emotion

Our vocals lie in this range of frequencies. Vocals are our primary source and link to the emotional content of the music. We must have a balance of the direct sound from our speakers and the reflected energy from our room. In a professional monitoring studio room, we want no reflections, so the engineer does not have to contend with room sound in the mix. In our listening or home theater rooms, we want the music to be part of the room and we want the room sound in our musical presentation for more emotional involvement and realism. We want to hear room sound and mix sound.

Time After Time

Achieving this balance between science and emotion takes time. It takes time because no one set of measurements will ever produce emotion or feelings. It is the sum of many variables with the personality and sonic preferences of the listener and room user thrown in. This emotional drive can be taken every time in a room where one has spent a great deal of time listening to music from many different genres.

Thunder And Lightening

We want the thunder from a bass kettle drum in our classical music. We want the attack and decay of every note to be heard and felt in our room. Only numerous playing and listening sessions will reveal the true color of the room. Once we have found out over time and patience what we like about the room and what we don’t, we can try and voice for the likes and try to eliminate or manage the dislikes.

Resonant Hunting

With low frequency resonances, we must find their locations within the room and place large low frequency sponges in those locations. Please, no foam. Low frequency resonances must be identified and the proper low frequency absorption technology applied. Please, once again, no foam. If you are serious and you must be when dealing with low frequency resonances, you must employ diaphragmatic absorption or a Helmholtz resonator that is frequency tuned. Resonances don’t play around. There only mission is destruction.

Check The Corners

Start in the corners first, going floor to ceiling. Next, look at all room boundary intersections. Treat the ceiling to wall intersection and the floor to side wall intersection. These are the areas of greatest pressure within our rooms. Do not forget the area behind the speakers; the area between the front wall and speaker back. This is a high pressure area where resonances like to get together and party. Please, no foam.

No Foam

Alright, I will stop saying, no foam. We have to get away from the myth that foam can absorb low frequency energy. It can not. I do not know how this myth officially got started but I have a good idea. For years, acoustic products companies have been distorting the term low frequency absorber. Some companies even call them “bass traps”. Most “bass traps” do nothing to absorb any energy below 100 cycles. They definitely do not “trap” any bass.

Definition Alert

Acoustic products companies have been raising the sound absorption bar when it comes to promoting their “low frequency” absorbers. If you examine some companies definition of bass absorber, you will see that it will not be low enough in frequency to absorb below 100 cycles. One company claims that 400 Hz. is even a low frequency. Lets stop this nonsense. Make sure you obtain the performance numbers on any bass absorber first and foremost from a manufacturer prior to purchase, if you can find them.

Reflection Control

One can control reflections through absorption. Once we have our primary and secondary side wall reflections managed correctly, so our sound stage has width, depth, and height, we are free to add or subtract absorption technology over time and many different listening sessions. We can add or subtract materials from different places in the room to find that correct balance between direct and reflected or room sound that brings us closer to the music. It takes time and many efforts, but the destination is worth the journey.

Voicing our rooms is an art form that we personally get to exert upon our room. We get to add or subtract different acoustical technologies over time to help us better emotionally connect to the music by emotionally connecting to our rooms. We develop this working relationship with our rooms by first knowing how the room sounds with all types of music and then listening to the changes our voicing makes in the existing room sound. This knowing our room and what we need to do to help it help us emotionally better connect to our music is what voicing is all about. I am connected to my room but my connection to my room transcends even feelings.

This Room Sounds Too Bright

What is a bright room? We have all heard the expression, this room is too bright. What constitutes a bright room? To determine what causes a “bright room”, we have to look at the surface material of the room. What materials comprise the walls and in particular the walls that surround us on a horizontal plane at our listening position. We also need to examine reflections from these same surfaces.

Parallel Walls

Parallel, flat, room surfaces create numerous acoustical issues that must be dealt with in a bright room. The parallel surfaces create flutter echo which is a baby echo. It has all the makings of what we would consider to be a full echo but not in the required amount and duration because of the room boundary dimensions. These are termed specular reflections and add to the final sum when it comes to room brightness. We want to produce fewer specular reflections to minimize brightness in our flat surface rooms.

Different Surfaces

We must create surfaces that when the sound energy strikes it, it is not returned in a patterned and somewhat predictable way. We want the surface to reflect or better yet diffuse the incoming energy into it out into the room in a somewhat unpredictable fashion. The irregular shape of our room surfaces can have a large impact on the redistribution of unwanted reflections.

Small Rooms

If one compares two rooms that are the same in surface material, the smaller room will have the lower reverberation time because there will be more sound energy to surface contacts occurring in the room with the smaller size. These surface contacts will also be increased when one measures a particular time interval which will show a higher density of reflections within that particular time span.

What Is Good Sound?

I am in and out of full time and project studios almost every week. All the engineers who I speak with thinks that their sound is good sound. How can this be? They all sound so different to me. They all have different rooms, monitors, microphones, you name it. Does all of it qualify as good sound? The answer is that there is no such thing as “good sound”.

Many Different Monitors

Each recording is played back on different monitors. Monitors are as different in sound from each other as are microphones. Obviously, small monitors sound different than larger ones, but controlling for size, we still have many different sounds from many different manufactures no matter what the size. Some monitors are active some are passive. One can even hear the difference between a two way and a three way. The monitors add their own sonic signature to everything.

Separate Speakers

A lot of times engineers use separate speakers for playback and recording. I have seen them using separate speakers for recording, mixing, and listening. I see large full range monitors used for monitoring recordings and then see the recording played back on a much lower quality sound loudspeaker for mixing. If you go to the engineer’s home, you will see an audiophile playback system. Is this good sound?

Different Rooms

The rooms in every studio in which the recordings were made are vastly different. Full time studios have dedicated rooms. There are separate rooms for drums and separate rooms for vocals. The nice thing about the dedicated room is that you can tune it over time to achieve the sound you are after. One can learn the room sound after recording in it over time and thus find the correct microphone positions within the room. Only trial and error over an extended time will find these locations.

Too Many Choices

Smaller project studios which are limited on space must make do with one room performing many functions. One room must record vocals and instruments. This is never welcome. Vocals and instruments require different approaches to room acoustical treatment. I have even seen one room that was the control room, vocal booth, and drum room all in one room. Is this good sound?

Good Speakers / Good Sound

Are today’s speakers up to the task of producing good sound? If good sound is so different because of so many variables, maybe we need to look towards the speaker’s performance as our good sound indicator. If we examine the frequency response curves of each different speaker manufacturers, we see different response curves. Some have attenuation in their curves to compensate for room boundary effects. Some mid ranges are more forward than others. Is this good sound?

Headphones Only

Why do engineers who record classical music use mostly headphones? I have never seen one use monitors during the process. I have seen them using monitors when they do a final or close to the end playback. They are always using headphones. Does this process make for a good recording? Since classical engineers use headphones, should they be our new good sound reference. There are many who think this way.

Playback / Recording

Should we have separate playback rooms within our recording studios? Should that help us with producing good sounding recordings. Is there a playback standard sound quality we should strive to record for that will have a great sound in a playback system, hi-fi or otherwise? Do we need to produce a recording that takes into account the environment that the recording is to be played in. Would this approach give us a good sound standard to go by. Who is John Galt?

Room Sound

Every room I am in has different levels of room sound in it. Most professionals have a basic understanding of acoustical treatment but most do not completely understand the impact of room acoustics in their mixes. They continually live with and work around this resonance or back wall delay issue without dealing with it from an acoustical perspective. Ask any engineer what issues he or she is having with the room and they will tell you in great detail. Ask them what they have done to resolve those issues and you get a blank stare or an explanation that will not come close to a remedy for the sonic issue.

Low End Issues

The low end of most rooms blurs and smears the mids at certain frequencies and at those frequency harmonics. Most engineers work around this elephant in the control room. Is this part of the process of achieving a good sounding recording? Are we supposed to work around something to achieve something else. Maybe in other parts of life but in recording and playing music, we have the technology to deal with these issues. We have the capacity to solve these resonances. The recording should be about the music and not the room.

Middle And High Frequencies

Middle and high frequency reflections from all room boundary surfaces are present in almost every studio I have been in. These reflections have to add their own stink to the mix. We have reflections from side walls, a rear wall, and don’t forget about the ceiling. We have reflections from the console and equipment that we must use to perform our craft. These reflections must be delayed in time and strength to minimize their impact at the monitoring or mix position. Every studio uses a different approach to this treatment. Is this good sound?

Opinions Vary

The term good sounding recording is a little like an opinion. Everyone has one but most are different from each other. The opinion is based on that individuals experience and frame of reference. It is highly subjective. We need a “good sound” standard to be established and then adapted by all to raise the sonic bar to a certain level and then we can exceed that benchmark by producing a new term with no standard: “great sound”.

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.