Acoustic Basics & FAQ's

ASC brings to your project the experience, acoustic products, and soundproofing materials you need to build a listening room or home theater that doesn’t shake itself apart or keep the neighbors up at night and sounds even better than it looks. Don't know where to start? Below is some general information in regards to Acoustic Basics and Frequently Asked Questions.

Acoustic Basics

For the Control Room and Mix Environment

Although the acoustic treatment required to optimize the sound is different for every room, every setup, and each unique application, there are still some basic acoustic concepts that are applied universally in a properly treated room. In this section of our web site we will present 5 of the more fundamental acoustic topics addressed in a properly treated control room or other mixing environment.

  1. Room Resonance Control: Bass Traps
  2. Comb Filtering for speakers and microphones
  3. Flutter Echo
  4. Reflection Control
  5. Reverberation Time

"Room" acoustics takes on a whole new meaning with ASC's trademarked AttackWall™ and Quick Sound Field™ portable, modular acoustic sub-spaces. With these systems, you get to define the acoustic signature of your recording or mixing space.


1. Room Resonance Control: Bass Traps

Sound is conveyed through waves in the air. Waves that exist between a pair of surfaces can create standing wave resonances whenever the distance between the surfaces is any even multiple of one-half of the wavelength. At resonant frequencies (tones), the sound is louder and decays much more slowly than at non-resonant frequencies, causing uneven tonal quality and interference with clarity. Resonant frequencies occur mainly in the bass range, due to the relationship between the wavelengths of low-frequency sounds and the typical sizes of people's rooms.

 

This wave is in a standing wave resonance 
since it's wavelength equals the distance 
between the pair of surfaces.

Every room has its associated resonant frequencies. Rooms built using preferred dimensions ratios have potentially more even distributions of these resonant frequencies. Room built with angles walls or ceilings have more complicated resonant modes than typical rectangular rooms and the resonances can be potentially less severe. But, no matter what the size or shape of the room, resonant frequencies can be controlled through the use of bass traps.

"Bass" frequencies occupy all the notes on the left half of the keyboard (Everything below middle C). Since this is such a large portion of the musical spectrum, and because every room has potential resonant frequency problems in this bass range, it is imperative that the low frequencies be the first issue to address in improving any room's acoustics. Of course, each specific room's geometry, setup, and application dictate how to best optimize the bass performance. However, there are some general enhancements that can be made using ASC Tube Traps that are sure to offer improvement in any room.


2. Comb Filtering/ Phase Interference

Sound and music propagate through waves and, therefore, must abide by the laws of wave physics. This means that when 2 waves "collide", they do not bounce off one another as is the case with physical objects. Instead, at that location in space and moment in time, they either add their combined amplitudes to some degree or cancel their combined amplitudes to some degree.

Waves exactly in phase add to make a wave with twice the amplitude.          
Waves exactly out of phase add to make a wave of zero amplitude.
  Waves out of phase to a small degree add to make a wave with slightly higher amplitude than either wave individually.

The wavelength of the 2 sound waves and the difference in the distances they have traveled determine whether they add to or subtract from the combined resulting amplitude. This means that there are a series of adds and cancels at various frequencies of sound for any given room setup.


 
 

There are many potential reflection points that can cause a sound launched from a source to return to that source and interfere with itself. There are also many potential ways for sounds to travel from one source to another and cause interference. Likewise, there are many ways for sounds launched from single or multiple sources to arrive at the mix position or mic position at different times and interfere with one another there. All of these interfering waves cause the resulting amplitude of the sound to either increase or decrease to some degree depending upon the frequency (tone) of the wave. The resulting adjustment to the amplitudes at each frequency is called a comb filter.

Comb filtering effects are reduced by placing acoustically absorptive materials at the reflection points responsible for the interfering waves. The materials must be of a size and type to properly address the frequencies of each specific problem. Rearranging the speaker or mic setup will simply shift the locations of reflections and alter the problem frequencies, but does not remove the problem.ASC Sound Panels, Sound Planks, and Fractional Tube Traps are often used to control comb filter reflections, with the appropriate device chosen based upon the frequency of the problem. Although locating the precise positions of problem reflections can be a complex task, there are a few locations where controlling the reflected wave is sure to make an improvement to the sound.

 

3. Flutter Echo

There are certain paths for sound that produce a repeating loop. Every time the wavefront passes the engineer or artist, it is heard as the sound is intended, but with a twist. Just as when you "click" the individual prongs on a comb in quick succession, the quickly repeating sound of the wavefront continuously passing the listener produces a distinctive "zinging" tone. This is known as flutter echo and is due to our brain's desire to interpret air pressure fluctuations at some frequency as a particular tone. For this is exactly what is occurring as the wavefront continuously passes your ear at some rapid rate.

The flutter paths are most commonly located along lines between parallel surfaces. Speakers or recorded sound sources located between parallel surfaces are constantly sending sonic wavefronts into the repeating loops of these flutter paths.

 

 
Speaker Flutter in the Mix Environment
   
 
Flutter in the Tracking Room (top view)

 

Placing ASC Tube Traps, Sound Planks, or Sound Panels at the reflection points for these flutter paths breaks up the flutter. This removes the tonal discoloration caused by the "zinging" sounds our brain interprets from the repeating wavefronts it encounters.


4. Reflection Control

As seen in sections 2 and 3, controlling room reflections is fundamental to creating accurate sound reproduction in any room. In addition to utilizing precisely selected panels addressing comb filter and flutter problems, it is also generally desired to include the proper combination of absorption and diffusion to control sounds reflected throughout the room. The desired balance of absorption and diffusion is obtained through selection of appropriate absorptive material and proper placement to create diffractive diffusion and/or multiple time-delayed specular diffusion.

  Edge-effect diffractive diffusion
     
  Multiple time-delayed specular diffusion

The proper placement and selection of panels to attain the desired reflection control is determined on a case-by-case basis due to the large number of variables involved.


5. Reverberation Time

Sound produced within any enclosed space will continue to exist in that space for some amount of time after it is created, decaying away until it is inaudible. If this decay time, known as the room's reverberation time, is too long, sounds will linger within the space and begin to overlap with new sounds being made, creating an unintelligible cacophony.

  Long reverberation time = Poor Intelligibility
     
  Short reverberation time = Good Intelligibility

A sufficient amount of acoustic absorption is required at all audible frequencies of sound in order to keep the reverberation time in a room short enough to have good intelligibility. The measurement of the reverberation time in a room is often referred to as RT60. The desired RT60 at an frequency varies from room to room. All ASC acoustic treatments alter the RT60 of a room to some degree. Acoustic treatment is developed with desired RT60 levels in mind.


Frequently Asked Questions

The Room
Recording Techniques

The Room


Why do I need acoustics?

Even the greatest engineer working with the best equipment can't overcome a poor sounding room. If you want to take your project or professional recording studio to the next level, it is critical to address the acoustic treatment of the room with proven recording studio gear such as bass traps, tube traps, studio traps, soundproofing, sound panels, a quick sound field or attack wall.


What is the best acoustic treatment I can get?

This will depend on your particular application. In general, if you are looking for a completely portable system, the AttackWalland Quick Sound Field is the answer.

Otherwise, every room is different and we recommend consulting with us to find the best solution to your particular situation. You can call us direct to speak with one of our experts at 1-800 ASC-TUBE.


How do I build the perfect studio?

A great studio relies on a combination of soundproofing, sound conditioning (making the structural portion of the room acoustically controlled) and acoustic absorption-diffusion. If you in the enviable position of building a studio from the ground up, start with proven soundproofing construction methods and materials from ASC.


How do I soundproof my walls? Floor? Ceiling?

If you are concerned with sound isolation, either from within the studio, or from outside, the ASC Iso-Wall System is the answer. This unique construction system has been developed over 15 years in the design and building of professional recording studios. It is the only isolation system that we know of that is specifically engineered for audio.

The ASC Iso-Wall out-performs all forms of standard construction by combining the necessary elements required for superb playback performance. The room's interior becomes peaceful and quiet--free from disturbing exterior noises. At the same time, sound within the room is contained, and 'noise leakage' to the rest of the structure is minimized.

Beyond its sound isolating characteristics, an ASC-built wall has the added ability to condition the room's acoustic signature in the low-end bass frequency spectrum. By utilizing our proprietary WallDamp material (a visco-elastic polymer) throughout the system, low frequency energy is absorbed into the wall. This reduces bass feedback and shuddering walls, which results in a clean, rich sound and well-balanced frequency response.

The ASC IsoDeck is a great way to isolate your floor and prevent unwanted room coloration due to resonance and rattle. Unlike rubber "boots" that can transmit sound, IsoDeck uses wool felt for a truly floating floor. Great for drum kit platforms or the entire studio floor.

ASC's Cable Pass Through product makes it easy to run cables up to 3/4" thick through walls, while maintaining a tight soundproof seal.


Recording Techniques


What is the Quick Sound Field, and how is it used?

The Quick Sound Field is an incredibly versatile, adjustable and portable recording environment. The QSF allows the engineer to create an acoustically perfect sub-space within any recording environment. A virtual studio within a studio. Quick Sound Field is a recording technique that uses 8 or more StudioTraps.

ASC's Quick Sound Field has revolutionized the recording industry by enabling the engineer to simply bypass the problems due to poor room acoustics and easily set up a controlled acoustic subspace system that delivers depth and clarity to your tracks, time and time again.

In a normal room, the sound is reflected off wall, ceiling and floor surfaces to produce a room signature signal that leaks back into the mic. Typical wall treatments, including acoustic foams and fiberglass panels, will dramatically reduce sound reflections, but the end result is that typical dead studio sound with no presence or ambiance that is followed by some sort of loud level room honk. Our QSF system can offer you a controlled acoustic environment, and save you time, hassles and money. No more wishing you could fix it at the mix!

The Quick Sound Field is created out of an array of ASC's patented StudioTraps, the most versatile acoustic tool for today's modern recording studio. The front half of the StudioTrap is treble range reflective and the back side is treble range absorptive. The entire surface of the Trap is bass range absorptive. This remarkable blend of acoustic properties provides a means to the balanced, broadband control of sound.

StudioTraps are adjustable in height and are usually set up midway between the floor and ceiling, but they can be raised or lowered for different mic positions or line of sight requirements. By setting up the StudioTraps around the talent, iso-booth techniques can be developed to more easily control the sound. In the treble range, the QSF eliminates undesirable room reflections while creating a time-delayed diffusive backfill, injecting a sense of acoustic presence into the track.

The QSF satisfies all the requirements necessary for a professional iso-booth. Engineers and talent love the level of detail they can get with the QSF. They get the sound that couldn't be heard before, even in some of the world's most advanced studios.


What is the ATTACK Wall?

The AttackWall is the mixing complement to the Quick Sound Field. Enclosing your monitors, console and mix position with an AttackWall converts any space into a world class control room. Legendary engineer Bruce Swedien says, "No matter where I go, I take these wonderful devices with me." Studios may come and go, and the AttackWall goes where ever you go.


What is the MixStation?

ASC's MixStation is a modular recording environment. The Mix Station is a prefabricated wall mounted system of specialized sound absorptive and diffusive panels that is easy to set up in almost any room. Perfect for home studios that want to get that "big studio" acoustic.

"Mix Station is awesome!" -Loren Alldrin, Pro Audio Review. Read her full review.


Where should I place my monitors?

The speakers will need to be positioned so that they sit symmetrically between the walls of the room, otherwise the stereo image will be distorted. Putting speakers too close to corners tends to emphasize the bass in an unpredictable way, so try to place your speakers away from the room boundaries and make sure the setup is symmetrical, with the tweeters pointing at your head in your normal monitoring position.

Relatively small changes in speaker position can affect the sound quite significantly, so experiment with moving your speakers forward or backwards while some known commercial material is playing and aim for a smooth response, especially at the low end. If some bass notes seem louder than others, move the speakers around until the problem is minimised. Mounting the speakers on solid stands makes quite a difference.