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Mix Magazine Tech Talk – Kevin Becka

MikeSorensen May 6, 2012 No Comments
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I recently read Kevin Becka’s article in April’s issue of Mix Magazine Tech Talk entitled,”I need Treatment”. Kevin walked us through his approach to acoustically treating his new monitoring room. He chose an initial balance of diffusion and absorption technology to begin the process. He also warned us about thinking our current equipment set up before treatment will necessarily be the same positions after room treatment. There will be a completely different room dynamic before and after absorption technologies are applied. Room modes can surface more quickly after certain rates and levels of middle and high frequency absorption is interjected into the room. We are in essence reducing pressure levels and lowering the acoustic noise floor in the room with absorption technology. Many gremlins can appear as we reduce room pressure levels.

Side Wall Reflections

Kevin addresses the side wall reflection issues at the monitoring position. Side wall reflections become laced with the direct sound from our monitors at the monitoring position. Side wall reflections add too much room sound to our mixes. We want to hear the direct or shortest distance between our ears and our monitors, without the room sound. We must reduce side wall reflections completely in monitoring rooms through the use of absorptive or diffusive technologies. Sometimes it can be beneficial to do both.

Glass Sound

Kevin also discusses the perils of “glass sound”. Reflections off of any surface in our control rooms must be addressed. Spurious reflections of of any surface, let alone a glass surface, will place too many acoustical variables into our decision making process. Like the table top surface that was discovered by Keith Morris from Rational Acoustics and all the comb filtering issues. Comb filtered sound is not real sound. It has evil mixed in with it to produce distortion. There is no decision to be made when it comes to glass. It must be covered with some type of absorption technology. The glass window should also be secured to minimize any chance of vibration to occur at higher operating pressure levels.

Absorbers Please

Low frequency, broadband absorbers were also place along the areas of greatest pressure in the room; the joint between two wall or wall/ceiling surface. In his photo, Kevin shows the absorbers placed along the floor/wall “corner” and the ceiling/wall intersection. These are good ares to start with, since they are higher pressure ares in the room and that is where we need to begin our initial focus.

Room Voicing

Kevin also interjects that room tuning is a process. It is a process that you begin here and end up there. It takes time and numerous music and vocal sources played into the room with the same monitors only, please. Each different monitor pair will produce a different acoustic into the room and probably require a changed acoustical treatment. One must hear the same song or sound over and over again in order to fine tune the room. Kevin stated that experimentation is the key. He is correct. It is experimentation over time. As listening time periods increase, acoustical treatment repositioning will also decrease. When you do not move anything for at least three months, you probably have got it the way you want it. Room voicing is an art and science project with science providing the acoustical foundation to begin with and art taking over from there.

Don’t Forget Real Low frequencies

One thing not addressed in Kevin’s room was the need to manage frequencies that go lower than the broadband absorbers he used at the room wall intersections both towards the ceiling and the floor. Those absorbers work well within their design parameters, but Kevin’s room needs more low end control. I do not believe Kevin mentioned the dimensions of his new room, but looking at the photo, it is no match for low frequency, bass energy. We need a room at least 30′ in length to have a flat 20 Hz. room response. We do not have this. We need to manage low frequency bass energy.

There is Hope

We can not absorb all the excess bass energy within Kevin’s room, due to its size. What we can do is manage the bass energy by absorbing very high rates and levels from 30 Hz.-50 Hz. We need as big as sponge as possible with high rates and levels at these frequencies. There is room for these in each of Kevin’s room corners. This is a problematic frequency range present in over 90% of rooms.

We also also need a broadband absorber that goes from 30Hz.- 100Hz to assist us with axial mode issues when we have narrow rooms. A blend of frequency specific and broadband low frequency absorbers will manage the low end levels in Kevin’s room so that there is a definition to his bass in his mixes and that each bass note has the proper rate and decay at playback so every bass not is heard within their respective layers. All low frequency absorbers must have the higher rates and levels of absorption required to deal with these large low frequency pressure waves.

Don”t forget about the frequencies below 60Hz. in your smaller rooms. It is even more necessary. Even though most absorbers on the market are not designed to go that low, one must address these bass note issues. It is not a lost cause. The technology is available. Do your homework like Kevin did.

MikeSorensen

I am a structural engineer as well as a master furniture maker. I design cabinets for low frequency, activated carbon absorbers. Connect with me on Google+

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