Low-frequency pressure is everywhere in our small rooms. It is all along the side walls. It is all through the area from the floor to the ceiling. It is between the front and rear walls traveling back and forth through our listening or monitoring positions. We have three sound fields within our rooms and unwanted low-frequency pressure is in all of them. What does it look like? What does it do to our sound? How can we avoid or if we can’t avoid, how do we treat it? Does it require special treatment types and amounts of treatments?
The T.A.P. Principle
T.A.P. : TYPE – AMOUNT – POSITION: USE THIS TO IMPROVE YOUR ROOM ACOUSTIC
At Acoustic Fields, we have a database of over 130 built and measured rooms. The smallest room size/volume is 10′ x 8′ x 10′ . The largest is 40′ x 20′ x 40′ . There are many numerous size and volume combinations between those two extremes. We have even measured the vibration signatures of the walls, floors, and ceilings. We know which treatment construction techniques work best with what barrier technology. It is always a balance between rigidity and flexibility when it comes to both barrier and treatment. Let’s focus on the treatment side of this equation for our low, middle, and high frequencies.
Laws of Physics & Treatment Technologies
When it comes to all audio rooms regardless of the usage, you must match the size and volume of the room to what you are trying to do in the room. Certain room sizes and volumes work best for certain usages. This is not opinion. It is a fact. The energy produced by certain usages define the size of the container that they fit within and produce fewer issues to treat. There are minimum sizes and volumes that work best for certain usages.
The laws of physics and the power of the treatment technologies those same laws allow us to create must be balanced with the energy produced by the usage. Drums won’t physically fit into a closet, neither will the low-frequency energy produced by the kick drum.
It is always a balancing act between energy produced within the room and the treatment requirements to manage that energy. You always focus first on the low frequency waves that wont fit into the room. If they will not fit, everything else will suffer. Low-frequency energy management takes up a lot of space. It always takes up more space than the corners regardless of what you have been told. Large issues require large amounts of surface area treatments. You must have a room large enough that the most difficult waves will fit and then have enough space to treat those that will not behave. We need a good size and volume for your usage but just as important, the space to treat the energy that won’t fit.
Room Zones Explained
The red group are rooms that produce so many low, middle, and high frequency energy issues, that large amounts of absorption treatments are required. There is not enough space for diffusion in terms of surface area or distance for wave lengths to fully form. It is the room sizes that are below 2,000 cu. ft. in total volume. The large amounts of treatment surface area, especially in the lower frequencies, will take up so much space that you might not be able to work in it.
The yellow group of room sizes is from 2,000 – 4,000 cu. ft. This group has the necessary space to allow for enough low, middle, and high frequency absorption along with enough space for diffusion. You have the space to place the appropriate low frequency absorption technologies and enough distance for diffusion to work. You will still have issues, especially in the low end but they can be predicted and managed.
The third group (green) of room sizes and volumes is greater than 4,000 cu. ft. It is an ideal grouping of width, height, and length to allow for almost any usage wanted. These rooms have enough distance to allow for appropriate management of all reflection time signatures, unwanted modal pressures, along with enough distances to allow for diffusion to do its job correctly and allow for all diffused sound wave forms to fully form.
Working With The Most Powerful Of All Low-Frequency Technologies
The red/yellow/green graphic gives us sizes and volumes for a starting point that balances usage with available treatment space. The red zone is too small for everything except voice and you should consider finding another room size and volume or change the usage of the room. The yellow zone gives us enough space to treat 70 % of the low-frequency issues. The green zone gives us space for enough treatment that we can use EQ to polish up the response curve without audible artifacts. Middle and high frequencies in the yellow and green zones do not present any time signature issues with reflections. We have the required space and distance for proper middle and high-frequency management.
T.A.P. stands for type, amount, and position of all treatment technologies. In treating low-frequency issues, we use diaphragmatic absorption. It is the most powerful of all the low-frequency technologies. We must have power since we have minimum treatment space in today’s small room. The graphics illustrate the amount required for an absolute solution for the given usage and space requirements. Middle and high-frequency absorption requires less space but just as much surface area. Diffusion requires distance so that the lowest octave has time and distance to travel to listening or monitoring position. Any audio room treatment is a balancing act between usage and treatment.