If you've been following along, I dropped a healthy dose of theory on which acoustic problems your room is likely to have and how to cost-effectively solve them. Then I began to do the very same for myself.
Treating my sidewall first reflection points was very valuable, and the sound I was hearing was much improved. But still, that's only the beginning. If one aims to significantly clean up the bass, there's more work to be done.
In this post, I'll describe the second stage in my room treatment project, directly aimed at addressing the low-frequency issues in my room.
What I Built
If you're not familiar with "super-chunk bass traps", it may be worth skipping over to Google Images for a moment to see what I'm referring to. The physics involved dictate that low-frequency energy builds up in the corners, and the only thing required to prove this is to stick your head in the corner of your room while your subwoofer is exercising. The strategy behind super-chunk traps is to put as much absorptive material in the corners as possible.
The theory is that in doing so, kick drums will start and stop more percussively, according to the source material; bass notes will sound with greater tunefulness, according to the notes played in the recording; room dimension-shaped bass buildups at specific frequencies will be reduced; and room dimension-shaped bass nulls at other specific frequencies will also be reduced. Resulting in hearing a flatter low frequency response that's more accurate to the sound coming out of the speakers.
I don't put much faith in the dainty corner traps many companies like to sell. How much low energy is absorbed is directly related to how thick the absorption is that's placed in the corners. Towards this end, most super-chunk builders aim for fiberglass or mineral wool triangles of about 24" by 24" by 33". These triangles are stacked floor-to-ceiling in the corner of the room, ideally in as many corners as are available and can be treated within the budget.
To avoid insulation sag, to save my apartment walls, and to keep my super-chunk traps portable in expectation of my next move, I opted to build four triangular frames for the two corners I treated. I blazed my own trail in this regard, making my own measurements and my own plan, since most available plans are designed for more permanent installs.
Home Depot cut the lengths of 1x4 common board for me, but they don't cut diagonally, so I had to branch out to cut the 2' by 2' plywood sheets used to make the top and bottom triangles of each frame. If you have a woodworking shop, this likely won't be a problem for you. If you don't, you'll likely have to hire a woodworker like I did to make the cuts. Fortunately, it was a fast job that took no more than ten minutes of an expert's time.
Cutting the insulation was the arduous part. Owens Corning sells 703 fiberglass most affordably in 2' by 4' sheets that are each 2" thick. It was my job to cut each sheet three times: once in half to make 2' by 2' squares, and twice more to cut each of those squares diagonally. I'm not particularly concerned about handling fiberglass with bare hands, but the dust and airborne particles from cutting fiberglass are cause for concern. I made the cuts outside on my apartment's concrete patio wearing a breathing mask. I used a long insulation knife to make a series of increasingly deep scores in the direction needed for each cut, with a sheet of cardboard beneath the cuts to protect the concrete and my knife.
My ceilings are just a hair under 9' high. Leaving room for the frames, I was able to fit 53 triangles 2" tall in each of the two corners I treated. This required 26.5 sheets of fiberglass, and the 80 cuts took me most of a day.
As before, I bought silky textured fabric from Jo-Ann Fabric and Crafts for the frames. I built simple wooden frames out of 1x4 common board and stapled the fabric to the frames with a staple gun.
Where I Placed Them
I only had the budget for two super-chunk bass traps. Fortunately, the two corners in the front of the room were available, and that's where I stacked the frames. I had the best luck filling each frame about halfway before putting it in place, then filling the remaining space with fiberglass triangles by hand. This created an avoidable fiberglass mess on the studio floor, but I discovered the hard way that the frames were just too heavy to handle alone once completely filled.
How It Sounds
In the last three rooms I've had my studio in, I've had a devil of a time getting the bass to sound right. Partly, I was confounded by a defective or broken measurement mic that was leading me to EQ out my bass at a slope of about 6 dB per octave, but that's another story. The other part was that things just weren't congealing in the middle. Two rooms ago, I had loads of deep bass 20' behind the listening position in the kitchen of my apartment, but not in the listening seat. And in my last room, I could hear deep bass while standing in the doorway, but not inside the room. I tried more than a dozen sub arrangements in that room, and more than a dozen in the room I'm in now. But the best I could do was to have somewhat of a bass suck-out around 50-60 Hz that left bass guitar and bass synths sounding mostly okay, but kick drums just weren't rewarding until I stood up and took a couple of steps towards the door.
Well, problem no more. With the super-chunks installed, the kick drum finally has slam in the listening seat. Fantastic! Also, bass guitars and bass synths sound more tuneful, in that I'm able to more clearly discern which pitches they are playing even when there aren't high frequency cues to give it away. I'm hearing the interaction between the kick and bass more clearly, and both the kick and bass are more discernible from each other than they were before. This is all excellent, and as expected.
Another aspect to note is that I'm now able to hear the reverb and decay on the kick drum, on songs the engineers decided needed reverb on the kick drum. It gives a more prolonged, cinematic thud than I'm accustomed to hearing. And now that I can hear the difference between percussive kicks and spacious kicks, I have yet another tool to add to my production arsenal to control the emotion and feel of my own music.
There are two aspects that confound me, however. First, and I have no idea how, the flutter echo in my room is significantly worse with the super-chunks installed. Not subtly, but dramatically. This doesn't make sense to me at all, considering I just added a massive amount of absorption. All things considered, I'm not recording percussive sounds in my space, and flutter echo from clapping in my listening seat doesn't affect a speaker's job to produce full-spectrum sound from the speaker stand. With this in mind, I'm not exceedingly concerned, but I still find it a little odd.
Second, and this also surprises me, the bass now actually sounds louder. By absorbing bass energy from the room, by more quickly killing the low-frequency decay in my room, bass now sounds louder?? I expected it to be the opposite: that much of the low-frequency sound I was hearing was due to low-frequency energy bouncing around the room, being reflected back into the room at each wall. Before, my subs were turned a little low so as not to bother my neighbors more than necessary. But now, I'm tempted to turn my subs down a little.
I have a guess as to why: every room has peaks and nulls in the low frequency according to the dimensions of the room. And by soaking up the low-frequency energy before it has time to peak and null, I'm hearing the bass more directly from the subs to my ears without it being masked and cancelled by bass reflections. And maybe reducing my room's ability to null is what results in the louder-sounding bass.
Conclusion
I'm only two steps into my room treatment journey, but already I'm hooked. I'm motivated to keep working on the project, and I'm not sure I could ever go without my new beloved bass traps. And though my monitoring system is somewhat humble, I'm already afraid that I won't care for most all of the exotic stereos I'll hear at Rocky Mountain Audio Fest this year, after growing accustomed to how a more modest playback system can sound in a room with effective treatment. I'm reminded more than ever that room acoustics equal speakers in the importance of how a stereo sounds. Comparatively, the quality of amplifiers seems of little importance relative to how much acoustic treatment can improve sound.
I'll keep you posted on the next steps in my journey.