Skip to main content
Featured ArticlesRoom Acoustics Training

Recording Studios Bass Control Project

By May 22, 2012No Comments

I had the privilege and pleasure to spend most of the afternoon and the evening in recording studios in Phoenix. My first studio visit was to assist the owner in tightening up the bass in his rooms. He has three rooms and two were dimensionally wonderful when it comes to modal resonances. There was at least a 6 Hz. spread between all axial, tangential, and oblique modes. All modes were spread apart by at least 6 Hz. which makes resonance issues easier to deal with. Two of the larger rooms had room volumes over 6,000 cu. ft., so our low pressure energy from the monitors and subs had some room to distribute itself without “clumping up” in some room part. We need room volume for the 4 freestanding sub woofers and the low frequency drivers of the Westlake monitors.

Good Beginning Science

The science behind the room build and design was well thought out. Proper room dimensions were chosen from the beginning and all wall surfaces were angled and splayed as mush as 30 degrees. The room design and shape was patterned after Chip Davis’s live end / dead end room concept and great care was taken in the room’s construction. Block construction with sand filled block and numerous layers of material on the inside of each room provided some more sound isolation and sound absorption properties. Once you have the science in place and build to the science, one can then voice the room.

Room Voicing

Voicing the room is like piano tuning. You take the space you are given or have built and place the electronics in the room you wish to use. You then live with this arrangement and play music through the electronics, always with an ear to the room. Over time, you will hear certain sonic issues or concerns make their appearance on a consistent basis after you play numerous source material. The bass is the first thing most people want to room tune for. This is our task.

Reduce Pressure Levels

Low frequency “control” is all about sound pressure reduction. If you reduce the pressure levels in the room generated by 4 sub woofers and the bass drivers in the monitors, you can effectively manage low frequency attack and decay issues. One must focus on the attack and decay of bass notes within the room because that is where all the information lies in bass notes. There is a lot of information from 20 Hz. – 50 Hz. Reducing the pressure levels in this frequency range will allow for the attack of a 40 Hz. electric bass note and the corresponding decay to be heard or probably better felt. It is this introduction and dance that we want. If you can’t feel it correctly, you will never hear it.

How do we reduce pressure levels in a room that is designed to keep that same pressure in the room. We need real estate. We calculate how much energy we need to absorb and place the correct type and amount of absorbers in the room to achieve this. This is our start. We start with the numbers science tells us and go from that point. The numbers assist us by telling us the number of units to build and their size and frequency range to be absorbed. Once we have this data, we can find places to install them.

Diaphragmatic Absorption A Must

Diaphragmatic absorption is the only current low frequency absorption technology that has the horse power to handle low frequency energy absorption. It must be designed to perform at high rates and levels of absorption to deal with the excess energy of 4 sub woofer cabinets and also the low frequency drivers of our monitors. Diaphragmatic absorption works best when placed close to the sound generating source. Diaphragmatic absorbers respond to the pressure from our speakers. With our 4 sub woofers, we will raise them off the floor, so we can place a diaphragmatic absorber under each sub woofer cabinet. How much closer to the source can we get than under each sub woofer cabinet itself. Raising the subs off of the floor will also improve the low end frequency response of the room.

Room In Wall Cavities

Next, we looked at in wall openings behind the current monitors. Originally, the room had in wall, Dyne Audio, monitors. Once replaced with the new freestanding monitors, the replaced monitors left an opening in the wall that was large enough to produce resonances of their own and we had one behind each new monitor. This space can be filled with a diaphragmatic absorber and this will accomplish two purposes. First, we will tame any unwanted resonances from the in wall, old monitor cavities and by taming these resonances we also provide in room bass absorption in the region of highest pressure which exists behind the monitors.

When dealing with low frequency issues, it is best to apply it to the front and rear walls to start. With the front wall, sub woofers on absorbers, our in wall, old monitor cavities filled with absorbers, we have made a impact on the front wall and front of the room pressure areas. Lets move to the rear wall where we have an area directly behind the couch where clients sit and listen. We have room for both vertically positioned absorbers behind the couch and horizontal absorbers that people can sit on next to the couch. Lets add up what we have done to reduce the low frequency pressure levels in our room.

Must Use Mass

We have added absorbers under each of the 4 sub woofer cabinets. Each absorber weighs 100 pounds. We have filled the old monitor, in wall cavities with absorbers that weigh 150 pounds each. Rear wall absorbers covering an area 6′ x 7′ area behind the couch weigh in at 1,000 pounds total. Our absorber seats on each couch side weigh in at 175 pounds each for a total of 350 pounds for the “seats”. Adding it up, we have 700 pounds on and in the front wall and 1,350 pounds on the rear wall and floor seating area for a total of 2,350 pounds or a little over one ton of absorbers for a single room. Let the battle begin. More on this project after installation and hours of listening.


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+

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.