Rebuilding My Music Room, Part 2

Build Bass Trapping Into Walls and Floors; Owens Corning Fiberglass Insulation. One of the things I did was to reinforce the floor of the listening room (described in Part 1). This required opening the floor, and that turned out to be one of the great unanticipated opportunities of the project. I realized that if I could create an opening in the floor that didn’t look out of place and was not in the way, I could place acoustic materials under the opening and use the cavity in the floor to create a very significant bass trap that could virtually eliminate floor-to-ceiling bass buildup in the front of the room. Below are some pictures that show the acoustic materials being installed under the open floor and the location of the floor opening covered by metal HVAC grates. The grates are very sturdy and can support very heavy weight. Note that the opening is located below the acoustic soffit, and the effect of the two traps is to eliminate the huge bass buildup I always experienced along the front wall of the room. (In the second picture you can also see the supporting concrete strips that were poured under the floor.)

This is a good time to talk about the acoustic materials used in creating the built-in bass traps. Three different materials were used: Owens Corning 703 and FRK 703 and Knauf EcoBatt Quiet. The Owens Corning materials were used for bass trapping, while the Knauf was used for in-wall sound insulation between the listening room and the adjoining dining room. The OC 703 was employed when we used an external scatter plate (described below) to reflect mid and treble frequencies and the OC FRK 703 was used when we needed an alternative reflective surface to reflect those frequencies. The bass trap installed under the floor used FRK on top (up against the floor grate) and regular 703 for the lower layers. We used five layers of 3-inch thick 703 in the floor. This is not the place for a full discussion of how to build a bass trap, but it’s important to note that not only is a bass trap more effective the more insulation you use, but the amount of open air behind the insulation materials makes a big difference. In the case of the bass trapping in the floor, we have a huge amount of air under 80% of the floor since the OC 703 is concentrated under the 20% of the floor that is located at the front center of the room.

In addition to the bass trapping in the floor, we created some bass traps in the walls. As I mentioned in Part 1, in the rear left of the room I have a protrusion in the ceiling because of a stairway on the other side of the wall. I felt this created an imbalance I could rectify by building out an identical protrusion on the opposite side of the room. I also realized that this built out section could easily be turned into a bass trap. We used OC 703 and the opening was covered with a scatter plate that was identical to those used on the triangular corner bass traps (see below). Here is a picture so you can see what was done. To make it all consistent, we also cut out a portion of the existing protrusion and installed an identical scatter plate there.

Finally, there is a utility closet built in to the rear side of the room, which is very deep and can accommodate a lot of storage. We determined we could take part of the interior space to make another bass trap. We similarly covered the opening with a scatter plate that is identical to the scatter plates used in the protrusions and in the triangular corner bass traps. See pictures below.

Triangular Corner Bass Traps: GIK Acoustics Corner CT Alpha Bass Traps. I spent a lot of time researching options for my front corner bass traps. Not only would they be acoustically very important, but they would dominate the visual theme/design of the room. I settled on GIK Acoustics’ Corner CT Alpha Bass Traps. I loved the fact that they used a scientifically-calculated but attractively-designed scatter plate that could be stained the same stain color as all the other treatments in the room. Even though they don’t usually do this, they also graciously allowed me to separately purchase additional scatter plates that were used on the built-in traps at the rear of the room (see above). I plan to write a separate article on these excellent products.

The pictures below illustrate the final result of using the GIK bass traps. Two traps were stacked on each other, and my carpenter built a custom wood stand that fit under the two stacked pieces and caused the traps to be visually flush with both the floor and ceiling.

Select Acoustic Fabric and Wood Stain Colors. There are many sources for a huge variety of acoustical fabrics. I didn’t spend too much time on researching the specific materials, and simply focused on the class of fabrics designed to cover speaker transducers, which are designed to be acoustically transparent but visually opaque so that the transducers aren’t visible. The wood stain was selected primarily to ensure that the scatter plates would match the custom Jatoba wood shelves my carpenter was making for me (see below).

Carpeting and Acoustics. The floor-to-ceiling acoustic interactions in a room are most easily tamed by use of carpeting. However, you ideally want carpeting that employs high thread count (but not too tightly packed), does not have an impervious backing, and which is installed on plush hotel-grade felt pad. There are NRC ratings for carpeting, and that will tell you a lot about the carpet’s absorptive properties.

To give you a clearer picture of what kind of carpeting works best, envision a high grade Persian rug sitting on an inch thick felt pad. I decided to look for carpeting that was as close as possible to the characteristics of such a Persian rug. Once I specified the characteristics, it turns out that there are not very many carpets that match the specifications. Most have drawbacks: either (a) a high fiber count, but with extreme density (think Berber carpets) that makes them more reflective than absorptive; or (b) a sealed back with relatively few threads, which also make the carpet quite reflective. My final choice came from a limited pool that met the specifications, but luckily that pool consisted of very excellent carpets with beautiful patterns. Not so luckily, the carpeting was very expensive (you don’t even want to know)!

The net effect of the room treatments was a revelation, and you can walk into the room and immediately note how much quieter it is than the adjacent rooms, but without killing the sound. Below I will discuss how use of tweaks and electronic room correction took the solid foundation provided by the acoustic treatments and turned the room into a top notch listening environment that stands out even when using average equipment.

After Your Room Acoustics, the Most Important Thing Is Your Power. I probably learned as much or more about this topic as I did about room treatments. I’d been messing with room treatments a long time, but for many years power tweaking was limited to trying different power cords and outlets. Only in recent years did I consider separate high power circuits for amps, and only in this last remodel did I look at my whole electrical system. Despite all the research, I still had a few unexpected results that I wish I had known about in advance.