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Rebuilding My Music Room, Part 2

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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.

7 Responses to Rebuilding My Music Room, Part 2

  1. Demerara says:

    The thought and detail that went into consideration of all the elements is impressive. I may have missed your comment about it if you addressed it, but do you find the bank of windows without any apparent treatment creates any issues with the sound?

    • Ed Momkus says:

      Hi Demerara – I’m so sorry that I didn’t respond months ago to your inquiry. I failed to check the comments after posting this article. Yin short, the window bank in its configuration has very minimal effect of the room’s sound. It is well above the main listening zone of the room, and in addition, I have tuning dots on the fixed glass panes, and they have always worked for me to control glass reflections. However, I would never want a listening room to have regular windows or tall windows without having acoustic curtains in place. — Ed Momkus

  2. Ostap Nakoneczny says:

    I am also in the process of building a dedicated A/V room in my basement. I also have been thinking of the installing built- in bass traps. Can the traps be initially tuned to a particular frequency by first varying the size of the cavity along with the size of the opening in the wall? Would the damping material then be used to fine tune the trap? I’m starting with a decoupled room.

    • Ed Momkus says:

      Hi Ostap – I’m sorry about the delay in responding to your inquiry from when you first posted your question. I’m probably too late, but here goes. I’m not an acoustics expert by any means, but I have learned some basic principles. First, the thicker the absorptive material the more effective it will be. In my opinion, a 4 inch thickness is the MINIMUM, and 8 inches is much better. Second, the bigger the rear cavity the better – at least 12 inches in my opinion. This is already unacceptable in many rooms. There is a mathematical formula you can look up that calculates the ideal cavity size, and the size is huge – you would in effect have to build a room-within-a-room and lose four or more feet on every wall, and that doesn’t address floor-to-ceiling issues. Note that, conceptually, the sound waves pass through the absorptive material once, dissipate further as they traverse the cavity, hit the rear of the cavity and bounce back, then pass through the absorptive material a second time before returning into the open room. The lowest notes need more thickness/cavity size, so in this sense you can “tune” the bass tap, but really you’re just making it more effective in absorbing the entire bass frequency range. Remember that most of the available absorptive materials absorb full-spectrum (including everything above the bass range), so you also need some reflective material on the front to reflect minds and highs. Otherwise your room will be too “dead”. (Of course, this material must allow the bass to pass through.)– Ed

  3. Paul says:

    Really informative article. I have a question about the Legacy Wavelet and its ADC. Since I listen equally to digital and analog (VPI Classic 3, TriPlanar Mk VII Ultimate arm, Dynavector XV-1s cartridge, and Pass XP-15 phono), it’s important that the ADC is up to the task. Will the Wavelet be equally good for both formats?

    I’m also intrigued by your custom Jatoba rack. Where did you source the Jatoba shelves?

    • Ed Momkus says:

      Hi Paul,

      I have to first apologize for the delay in responding. I just submitted my review of the Wavelet, and it should be published soon. In a nutshell it is highly recommended.

      I need some clarification on your question about the “ADC”. I’m not aware of any Analog-to-Digital conversion done by the Wavelet. It has its own DAC, but a digital outboard device that has its own built-in DAC can be plugged into the analog inputs, and analog sources just get plugged in the analog inputs the same way.

      If your question is how the Wavelet sounds when using the analog inputs, it’s very good. I did not specifically do a critical-listening comparison of vinyl sources, but I did listen to digital devices that had their own DACs, and the sound of their analog output into the Wavelet’s analog inputs was quite good – IMO equally to very high quality analog preamps.

      As for the custom Jatoba racks, I had a carpenter select and make the shelves. He sourced the Jatoba slabs from a well-known local commercial lumber distributor – Oak Hardwood Lumber in Lombard IL.

  4. Michael says:

    Ed, great article. I have the Esoteric Grandioso C1 and M1 amps as well. I also ran multiple dedicated 8 gauge circuits of the same exact length. My question is if I run a JPS Labs in-wall power cable for a separate circuit just for my front end, will I get a ground loop problem if the length is different than my 8 gauge circuits? Thanks.

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