Acoustic FAQ2020-11-23T13:04:26-08:00
We are replacing carpeting, what alternatives are available and what is their acoustic impact?2020-11-23T13:11:19-08:00

This is a classic question asked time and time again. Let’s examine the impact of carpeting in the sanctuary. Carpets kill sibilance – the “tssss” “shhhh” sounds. This takes the life out of the sonic aire. Carpets have no effect on the vowel sounds – a, e, i, o, u. The issue with acoustics is, to a significant degree, the frequency response of the material. Carpet kills treble and does nothing to the bass.

Generally, carpeted floors are not good for congregational singing. They leave the singing space too dull and boomy. On the other hand, if you like the sound of your sanctuary with the current carpet, then you should replace the carpet with a like carpet. If it feels too dead, particularly for congregational singing, consider removing, rather than replacing, the carpet. As an alternative, you might consider Berber which has a very tight weave and does almost nothing to the sound, but it is rather expensive.

The point is that hard surfaces support congregational singing and, generally speaking, churches like to have bright and lively sounding congregational areas. Many churches have carpeted walkways and wood or concrete flooring under the pews. This way there is a quiet entry and exit path with a lively singing space.

Another carpet problem to consider is that when a piano is played over carpet it dulls the sound. Try adding an office chair plastic carpet protector under the piano and you’ll hear how it brightens up and starts to actually sound like a real wood instrument. Choirs are plagued by the same problem. Putting a choir on a carpeted floor is like pulling out vocal chords.

In contrast to this, putting carpet on the floors under the chairs in Sunday school and in office spaces is an excellent idea. The rooms tend to be smaller and there is a lot of “creature noises”, such as shifting chairs, bodies, and papers. Carpet is great at quieting these noises.

Be sure you know the reasons why you want to change carpet before doing so. This will help you select the best solution for your situation. Remember, any change in the acoustics load will appear in the voice of the room. Carpet has lots of fibers which present acoustic friction. Removing carpet changes the amount of acoustic friction in the room, which changes the reverberation of the room.

Our sound technician keeps complaining about echoes and feedback and always tries to fix them by buying new speakers and microphones and moving everything around, but the problem is never completely fixed. Is he doing something wrong?2020-11-23T13:11:49-08:00

This is exactly what people always try first. They generally exhaust themselves dealing with this very issue. They buy more and more electronic equipment without ever getting the improvement they need until they’re finally ready to give up on the allure of electronics, sit down, and listen and learn about the world of acoustics.

Acoustics is a whole world, invisible to the eye, but very audible to the ear. Once the sound is launched in the air, only acoustics can help guide it to where it is supposed to go. That’s what we do at ASC. We take over where the electronics leave off. Here is how we work: we get photos, floor plans, elevations, descriptions of the problem, and often times audio recordings from you. Then we estimate the probable cost for the “fix” for your particular situation. Now you have a budget to talk about. Once you decide that your ready to start working to fix the problem, we analyze the problem in detail, design and build the solution and you install it. You get to skip the middle man by purchasing the proper solution direct from the factory.

We can also work with your audio technician, train them to do the testing we need to analyze the room, provide appropriate photos, and conduct interviews. We do our homework before we invest any time in working up a design. We have to know what the rules are within the church so we can work within those guidelines.

To answer some of your specific concerns, you should know that it is the echoes that create feedback. Sound technicians are always fighting “gain before feedback”. Improving the on-stage acoustics is one way to improve this. Eliminating echoes also helps to improve the mic problems. Of course, it is always a good idea to first check to make sure the sound system is set up properly and not aimed directly at the microphones. Beyond this, it is the acoustics that can make the necessary improvements.

My church is undergoing an interior restoration/rennovation project. There are many things we are considering in our endeavor, but the one major object involves the placement of our church organ and choir. I have heard that the best acoustical position for the organ is on the main axis of the church. Can you confirm this or shed some light on this theory?2020-11-23T13:17:16-08:00

What would be the best acoustical positions for the choir and organ? First, it’s important to note that the physical location of the organ keyboard is one thing and the locations of the pipes or speakers is another. The type of organ or keyboard can make a difference as to where to best place it. An organ is typically played in a reverberant space. Organ music is written so that the reverberation left over from the prior note mixes with the sound of the next note to form a chord. It is important to protect the reverberant part of the sanctuary for the sake of the organ. The organ is usually located in a position that easily and loudly stimulates the reverberation of the hall in which it is located. If you move the organ, you change the relationship between the sound generated by the organ and the reverberation of the hall. The ceiling often has impact on how the sound is stored and diffused throughout the space. If you move the organ, it will change how the sound is fed to the ceiling, changing the way it sounds in the hall. Organs are often located along the centerline of a church so that they can stimulate as much reverberation in the room as possible.

It’s a good idea to contact the organ manufacturer or installer before moving the organ. They usually have a lot of experience matching the organ to the hall.

Everything pertaining to the organ also applies to the choir. Except that the choir must also be able to hear themselves. Placing the choir in a gallery allows some of the sound to be held within the gallery. The choir sound heard by the congregation is “pre-blended” by the walls, ceiling, and floor of the gallery. This makes their sound sweeter, more full, and almost larger than life. The people in the choir can hear themselves and each other because they are essentially singing in a room that happens to have a large door (the opening to the rest of the church). Choir members who can hear themselves and each other better stay in tune and on tempo better.

If you move the choir too far out into the open they struggle against the thinness of their sound. However, there are some churches who tire of the old world sounds of worship. The reverberant organ and choir may no longer be a valued part of their service. Perhaps the organ is being moved forward to join a contemporary praise band. Likewise, the choir may be being turned into the backup vocalists for the lead voices in the band. In this case, gut the old gallery, turn it into a spotlight deck and get on with the show. But, be aware that now their is a whole new issue of acoustics to deal with: the interaction of amplified sound within your reverberant hall.

We are building a new sanctuary and we’re trying to decide between flat or vaulted ceiling. Which would be better for the acoustics?2020-11-23T13:14:56-08:00

A shallow vaulted ceiling is better than a flat ceiling. Most churches build their vaults running front to back so that there is a high wall section at the front. However, a shallow vaulted ceiling actually sounds better if the vault runs side to side. This is because the sound is stored in the high volume part of the space, which is located under the peak of the vault. So, the sound is stored side to side in the area where the people sit.

Furthermore, people’s ears are separated sideways so we are more sensitive to side to side sounds. People tend to like the spacious effect of side to side sound storage. A slightly sloped ceiling at the front of the church moves sound away from the front towards the congregation, keeping the launched sound clear and unmuddled. A slightly sloped ceiling towards the back of the seating area compresses the sound coming from the front making it louder for people sitting further away, which is good, too.

A slightly sloped ceiling still keeps the sound of congregational singing within the congregation, where it belongs, just like a flat ceiling does, which is good. Flat ceilings are not good, though. All sounds that hit the flat ceiling are reflected back down to the floor at the same time. The timing for floor-ceiling reflections is the same everywhere in the church. This creates a horrible droning tone problem.

Remember that, no matter whether you build your church with flat ceiling or sloped ceiling, or which direction you aim your vault, you will still need to address the acoustics of the space. This means you will typically need ASC acoustical treatment on the back wall and on the side walls.

The front of the church is usually built with a raised stage that is carpeted. You’ll want to make sure the stage is quieted from drumming and thudding sounds by building it with ASC WallDamp between the joints and filling the cavity under the stage with ASC SonicSnow. The front of most churches can be left fairly reflective.

Choir areas need proper design. Don’t put them out in the open, they need reflections returned to them so they can hear themselves and stay in tune. Don’t use carpet under the piano or choir. Carpet the speaking area and, if there is a praise band, you’ll need additional ASC acoustics to get the loudness under control and to get the mics working right.

Use one high central speaker cluster for speech and two side main speakers for music. Only the soloist should sing through the central cluster.

Things always work best if you design the church from the beginning around the acoustics. After all, if people can’t hear what’s being said, they stop coming.

If we have a sealed box subwoofer in a very small room, 8’x8’x8’, playing 40Hz wavelength 28’ or even lower, will a TubeTrap that absorbs 40 Hz or lower be useful?2020-09-29T10:40:35-07:00

If we have a sealed box subwoofer in a very small room, 8’x8’x8’, playing 40Hz wavelength 28’ or even lower, will a TubeTrap that absorbs 40 Hz or lower be useful?

Essentially, if a standing wave cannot be created, will TubeTraps do anything

Short answer is yes. If there are pressure fluctuations near the TubeTrap within its frequency range of operation it will absorb acoustic energy.

Longer answer includes the answer to another question: Is it useful to use a TubeTrap in such a situation?

Let’s go over the situation in slow motion. When the listening room is less than say 1/5th wavelength the concept of distributed acoustics tends to fade, transitioning in the “pressure pot” or “breathing mode” realm of acoustics. Envision a large hollow dumb bell, two spheres connected together with a large tube. One sphere might be 8’ in diameter and the other might be 4’ in diameter. The 8’ sphere is a model for a small room and the 4’ diameter is a model for a sealed box subwoofer cabinet. The tube between them is essentially the 15” woofer.

As the woofer shuttles air back and forth between the two sphere volumes. Here is the “standing wave” effect. At one instant we have the speaker cone pushing far forward, creating a positive pressure in the big sphere and pulling a vacuum in the smaller sphere.

At this moment we have no speaker movement, it’s fully extended, and we have no kinetic energy in the system but lots of potential, pressure energy. A quarter cycle later the piston if flying past the neutral point of the driver and the pressure in both spheres has been returned to Po, ambient pressure. When the pressures are zero, atmospheric, we have no PE and lots of moving air, which is KE, kinetic energy.

Another quarter cycle later the speaker has continued on, pulling further back until it reaches its maximum extension in reverse position, where the pressures in the two spheres are also reversed from before. Clearly, we have a resonance which alternates between potential and kinetic energy. The fraction energy absorption or leakage each cycle compared to the total energy of the system is the Q or damping factor of the resonant system. We know from experience that a Q of 10 seems to be reasonable enough in the realm of room acoustics.

There is a formula that relates room Q to Room RT60. I presented many room Q relationships in my second AES paper in 1986, Listening Room and Low frequency Acoustics. All my AES papers are available on the ASC web site. I didn’t cover this breathing mode of the room in the paper, however the formula doesn’t change.
Q = f xT60 / 2.2. At 30 Hz and with a room Q = 10 the RT60 = 2.2 Q/f = 2.2 x 10 / 30 = 2/3rds second. Pretty fast RT for 30 Hz.

So, without any energy absorbing system at work the speaker will simply oscillate between its inertial condition and the collective stiffness of the air spring of the two air cavities. And finally, we have the answer as to why adding a bass trap to this air vibration mode is useful, which is because it helps to dampen the spring in the spring-mass system.

This discussion has excluded any consideration of the walls, floor and ceiling as if the room was a solid concrete sealed room. Most room surfaces are not solid but vented through doorways and have flexible surfaces, like sheetrock and stud walls or windows. In general, TubeTrap or other bass traps do not significantly load with friction or dampen flexing wall, floor, and ceiling movement. This is why ASC developed the WallDamp system, which extracts energy through shear stress damping from each movement of constructed wall and ceiling assemblies, back in1987 and continues to provide WallDamp through this day.

How many TubeTraps will it take to get a Q of 10 or 15 in a small volume space?

Basically, it’s about the volume ratio between the volume of the TubeTraps and the volume of the room. Let’s say we are going for Q of 10. This means 1/10th or 10% of the energy must be removed each cycle. There are two pressure changes each cycle, one positive pressure and the other is negative pressure. The TubeTrap extracts energy out of each pressure change. That means the same TubeTrap absorbs energy out of the room twice per cycle. That means we only need 1/20th or 5% of the energy in the room volume to be removed each half cycle.

If the volume of the room is 500 cubic feet we need 1/20th of that volume performing 100% energy absorption each half cycle, which is 25 cubic feet of air volume. A 16×4 IsoThermal TubeTrap has 5 cubic feet of volume. It also should produce 50% efficiency at 30 Hz and so we need 50 cubic feet of this size trap in the room or ten of these units. We put two in each vertical corner and we are up to 8 traps already. That is a difference between Q = 10 and Q = 12.5, which is close enough.

A seasoned acoustic person might be thinking about the pressure boost, increased sound-absorbing power due to TubeTraps in corners. In the breathing mode, all pressure is same everywhere in the room, and so there is no pressure buildup in the corner.

Thanks for asking…..Art Noxon

What is Sound Absorption?2020-11-23T13:20:14-08:00

Sound Absorption is the conversion of sonic energy into thermal energy.

When air becomes energized by sound waves passing through it and we could watch the air through a slow-motion microscope we would see air moving back and forth along the direction of the sound wave. As the air moves we would also notice small pressure changes; the air moving forward is slightly compressed (higher pressure) and the air moving backwards is slightly expanded (lower pressure).

Other absorber technologies exist, such as an Impedance-Matched Capacitor-Resistor Circuit, which allows lower frequencies to be absorbed than thickness would normally permit. Additionally, resonant absorbers can dissipate sound energy by means of a sympathetic membrane which also converts bass energy to heat. Common sound absorbers include: flat wall panels, corner loaded bass traps, curtains/draperies, foam, soft furniture, and a clothed human body.

As the wave passes by our ear, it is these pressure changes that push and pull on our ear drum and become what we call sound, hence “sound wave”. Sound absorption, on the other hand, takes place where the silent movements of the air rub against a surface.

We are familiar with the most common form of a sound absorber; a panel of open cell foam or compressed fiberglass that is open enough to allow sound waves to penetrate into the volume of the absorber where the motion part of the sound wave can rub over the multitude of microscopic surfaces in the sound panel and cause enough friction to dissipate energy from the sound wave.

This type of sound absorber directly involves the sound wave itself and how much it absorbs depends on the fraction of the wavelength it is in contact with. A 2” deep sound panel absorbs high frequency sound down to about middle C of the piano, 260 Hz. The wavelength of 260 Hz is 4.33 feet and the ¼ wavelength is about 13”. The depth of the sound absorbing panel is about 1/6th of the ¼ wavelength dimension. This is a wavelength type sound absorber in that it reacts to the distributed acoustic nature of sound, the wavelength.

There is another kind of sound absorber, particularly useful in low-frequency absorbers, bass traps. Instead of interacting with the wavelength of sound, they interact with the frequency of the sound. The frequency type of sound absorber is designed similar to an electronic circuit, except they use acoustic resistors, acoustic capacitors and acoustic coils to create an acoustic circuit device. This is referred to “lumped parameter” acoustic design which is very different from the “distributed parameter” version of wavelength acoustics.

Initially ASC was a factory that was dedicated to building the lumped parameter type bass trap, the TubeTrap. Over time we realized our clients also wanted their sound panels to both look and sound like the TubeTrap style, where each product is voiced to have a blend of lower frequency absorption overlaid with a % of higher frequency diffusion. And so we build a full bandwidth product line: Lumped parameter bass traps + distributed parameter treble sound panels.

Not all absorption is good. Too much absorption over deadens the room. Our built-in diffusers help to compensate for the absorption being added into the room by backscattering 25 to 50% of the incident upper frequency energy back into the room. We use both the reflective and diffractive diffusion techniques to smoothly distribute room ambience as quickly as possible.

We use a second technique for developing acoustic control in the room. The amount of sound power absorbed depends on the surface area and efficiency of the absorber, but also how loud the sound is in front of the absorber. We place our absorption in locations where the sound is the loudest so we remove acoustic energy from the room before it has been reflected multiple times within the room. By this we lower the level of the reverberation in the room while at the same time speed up the decay rate of the reverberation in the room.

Room Modes: Reverberation is sonic energy stored in a chaotic form in a room. Room modes is sonic energy stored in a very organized form in a room, where sound is reflected over and over again between the two same parallel walls. This is the first order type of modes, second and 3rd order modes also exist in rooms but they die out relatively quickly.

When a sound wave impacts a wall at an angle (2nd and 3rd order modes) some of the wave has motion parallel to the surface, where friction occurs and sound is absorbed. When the wave impacts the wall squarely (1st order mode) there is no air motion along the surface of the wall and therefore no friction, hence no absorption. Adding wavelength type sound panels do not work because there is no air movement on the reflecting walls. The only type of sound absorber that works on 1st order modes is the frequency type bass trap, like TubeTraps.

Other absorber technologies exist, such as an Impedance-Matched Capacitor-Resistor Circuit, which allow lower frequencies to be absorbed than thickness would normally permit. Additionally, resonant absorbers can dissipate sound energy by means of a sympathetic membrane which also converts bass energy to heat. Common sound absorbers include: flat wall panels, corner loaded bass traps, curtains/draperies, foam, soft furniture, and a clothed human body.

Why do I need acoustics?2020-11-23T13:21:00-08:00

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?2020-11-23T13:24:44-08:00

This will depend on your particular application.

If you are an audiophile looking to improve your Hifi system playback, look at our Hifi page

If you are working in a Recording or Mixing Studio, if you are looking for a completely portable system, the AttackWall and Quick Sound Field is the answer.

Check our our Specialty products which have been designed and manufactured to meet specific needs

Otherwise, every room is different and we recommend consulting with us to find the best solution to your particular situation.

How do I build the perfect studio?2020-11-23T13:51:50-08:00

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?2020-11-23T13:26:02-08:00

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.

What is the Quick Sound Field, and how is it used?2020-11-23T13:52:14-08:00

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.

Learn more on our Product Page for the Quick Sound Field.

What is the ATTACK Wall?2020-11-23T13:51:42-08:00

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.

Check out our AttackWall page

What is the MixStation?2020-11-23T13:51:33-08:00

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.

See our MixStation page

Where should I place my monitors?2020-11-23T13:51:27-08:00

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 minimized. Mounting the speakers on solid stands makes quite a difference.

See our MonitorStands page

Acoustic Basics For the Control Room and Mix Environment2020-12-08T16:15:45-08:00

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.

“Room” acoustics takes on a whole new meaning with ASC’s 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.

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.

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.

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.

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.

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.

Acoustic 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.

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.



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