Why This $200k
Room Did Not Work
Acoustic Redesign by Acoustic Fields
What went wrong?
Our client spent 200,000.00 in this room. He spent two weeks listening to the room when it was built and treated. He walked out and never went back. He locked the door and now uses it for storage space. What went wrong? How can the design miss so many requirements for good sound quality that is consistent and predictable? How can it be fixed?. Let’s examine the design technologies used and see if we can discover what went wrong and more importantly, how can we fix it keeping in mind 200K was already spent.
Use The TAP Method
You must use the TAP ( Type, Amount, Position) method. You must select the type of treatment to deal with your issues after identified at that room location for frequency and amplitude. The treatment selected must treat the wall surface area-specific frequency and amplitudes You must select the amount of treatment required. It’s all about meeting the square footage requirements. You must know the rate and level of absorption of the treatment type you are using. You must know the frequency response of the quadratic diffusers you are using and the distance from the diffuser to the listener’s ears. You must know what position on each room boundary surface to place the specified treatment type and amount. You must know these three variables before you have any chance of creating a sound system strategy. Not a room with misapplied tactics that have no relevance to the total room acoustic strategy.
Treating Low-Frequency Issues First
You have all heard me say many times that achieving quality sound within a room is all about doing a lot of small things correctly but just as important doing them in the proper order. You have all heard me say that we must go after and treat the low-frequency issues in any critical listening environment first and foremost since low-frequency issues produce middle and high-frequency issues. You have all heard me say that surface area treatments for low, middle, and high-frequency absorption/diffusion must cover the entire surface area that is producing the frequency and amplitude issues. Low-frequency energy issues are produced by a minimum of two walls in parallel. Tangential modes are between four surface areas. Oblique modes are between six surface areas. Forget about that corner treatment nonsense.
No Internal Fill Material
In this project, we see that the TAP principles were not followed in some areas and followed too much in others. For this project, they did line the rear of the walls with a diaphragmatic absorber. However, upon closer inspection, the cavities were not the proper depths to deal with the frequency issues let alone absorb any sufficient amount of that frequency and above for each wall surface area. Most cavities were 5″ – 7″ in depth which acting as a diaphragmatic absorber, you get a resonant frequency of 50 Hz. No wall surface area within this room exhibited 50 Hz. start point. The short walls started at 30 Hz. and the sidewalls at 40 Hz. Following our TAP principle, we had the correct type of low-frequency management. However, they did not match the frequency treatment to the wall location. Secondly, the interior fill material used inside the diaphragmatic absorber which controls the rate of absorption was nonexistent. There was no internal fill material.
Managing Primary, Secondary & Tertiary Reflections
Sidewall reflections are another concern for image centering, soundstage width, and definition. We have primary, secondary, and tertiary reflections to manage from sidewall to sidewall. We have the primary reflection which is the first reflection from the sidewall boundary surface. That primary reflection then travels across the room and strikes the opposite sidewall. It is now a secondary reflection with a completely different time signature than the primary reflection. This secondary reflection then travels across the room and returns home to its original wall. The tertiary reflection has a different time signature than the secondary and primary reflections. With all of this energy movement at different time signatures going back and forth between the sidewalls, we need a predictable and consistent rate and level of absorption. What we have here is a series of hemispheric shapes that are sound redirection devices. They are not diffusers. They redirect sound energy out in the opposite direction from which they strike the surface area. They not only redirect sound, but they also have hollow recesses around the hemispheres. Nothing is predictable or consistent when that is what we must have with the primary, secondary, and tertiary reflections.
Helmholtz Resonators On The Ceiling
The ceiling is a series of Helmholtz resonators. Using out TAP (type, amount, position) process, we look at the type of treatment selected. A Helmholz resonator is a low frequency absorbing technology. The floor to ceiling dimension is the smallest of the three, so it will exhibit the largest low-frequency issues below 80 Hz. Treating them with Helmholtz resonators that are 6″ – 8″ deep will not go low enough to work with the frequency and amplitudes exhibited by an 8′ ceiling height in a two-channel listening room. This is the wrong technology misapplied across the total ceiling surface area. The irregular design of the Helmholtz with its tube face is not a good surface for sound energy to strike. The ceiling and floor reflections are the first to strike your ears. We must control the time signature of the ceiling surface area reflections at the listening position. You can not do that with hollow tubes and resonating chambers. You must choose diffusion or absorption that has the proper rates and levels of absorption along with the correct frequency response determined by the 8′ ceiling height.
Wrong Diffusion Sequences
Let’s take a look at the front and rear wall diffusion sequences. They are one dimensional quadratic with a prime number sequence that is custom designed. Whatever sequence that was used, it failed to address the frequency ranges required for the usage and the width of the room. In a two-channel listening room, the front and rear wall diffusion are always welcome. However, the front and rear wall diffusion sequences must do two things correctly. First, it must satisfy the room width frequency range requirements and secondly, both front and rear wall diffusion sequences must complement each other must work together as opposing surface areas to create a true diffused sound field. We have found that opposing wall surface areas with diffusion work best if basic prime number sequences are used. There is immediate compatibility between the prime number with no phase issues. Using custom-designed sequences is too complicated and not necessary for two-channel listening rooms.
Redesign by Acoustic Fields
Stay tuned for Part Two in this series. We have gutted the room and removed all but the rear wall diffusers. We have redesigned all the treatment types, amounts, and positions using our TAP approach. Listen to the client comment on what he did not like in this room and what he likes about our technology. We have turned the room into a proper two-channel listening position with diaphragmatic absorption for the low-frequencies, middle and high-frequency diffusion, and absorption. Listen to the changes. All stored items have been removed and only a single chair remains.
Ceiling Diffuser Module
Wood unit is positioned both “vertically” and “horizontally” throughout the ceiling surface area with particular emphasize paid to the distance from listening position to speakers. Numerous wood choices are available.
QD-23 Quadratic Diffuser
The QD-23 is used for those that have large space requirements. With its 17″ depth, it is designed for large spaces. It can be arranged in both a vertical and horizontal array to accomplish two dimensions of diffusion.
ACDA-12 Carbon Absorber
With the ACDA-12, you’re going to feel the power of every single bass note in a way that few ever get to hear. It’s that connection to the music which makes all the difference to your enjoyment of it. It’s the dynamics and separation of instruments with crystal clear clarity definition, which creates the spine tingling, hairs on the back of the neck sensation that you desire so much from your mixing efforts and music collection.
I invented our acoustic panels because I was unhappy with the performance of current open celled acoustic foams. Why? Because current foam technologies do well at absorbing frequencies above 500 Hz. but do little to absorb much energy below that level.