The first step is always defining the problem, but at a higher level of detail than "I'm looking to treat my home theater." There are two general approaches you can use:
- measure your room acoustics, identify specific acoustic issues, address them, measure the change to assess effectiveness, repeat until happy
- apply some of the common "rule of thumb" approaches and listen for major residual issues, then address the major issues.
Clearly, the former starts with mic, mixer, PC with sound card, software, etc. Not everyone wants to start here; the inital cost isn't prohibitive, but the learning curve is intimidating.
The latter will be incomplete to the extent that some acoustic issues may not be audible to you, but it's where you'll get the most bang for your effort, and I can make some suggestions. If you don't have Toole's book, buy it. Most of this comes from his conclusions regarding what's generally applicable. I also have a link for Everest's Master Handbook of Acoustics which complements Toole by providing construction details.
Be aware that acoustic issues (and their remedies) are of two very different types, depending on frequency above or below the "transition frequency."
- Below the transition frequency range, room modes are isolated and audible so we apply wave interference analysis methods and use acoustic devices that are effective at low frequency.
- above the transition frequency range, room modes are very dense and so merge to become inaudible. We use ray tracing methods to analyze the room, and a wide range of acoustic devices as these frequencies are more easily absorbed.
Lookinig at the photos, I assume:
- above grade construction
- stick construction walls
- a basement below and more rooms above
I also observe:
- wall-wall carpeting, hopefully with a thick pad beneath,
- non-porous (acoustically reflective) furniture
- thin, sparsely-pleated curtains on the windows
My assumptions are major drivers of bass issues, my observations major drivers at higher frequencies. All affect the acoustics.
Generically, Toole recommends:
- absorption on the front wall
- absorption on the rear wall.
- diffusion on the side walls
- no treatment at first reflection points when the goal is enjoymnet (you're not looking for a recording studio...)
The former are the panels you've likely seen, 2'x4' based on commercial fiberglass or mineral wool panel insulation. These are most effective at higher frequencies, gaining low-end effect by becoming larger, and being spaced farther from walls than your room supports. You could also increase the density of the curtains, and should consider a matching set for the doorways (symmetry is beneficial). Diffusers are designed to reflect sound in various directions, masking the direction of the initial sound. Both are working above the transition frequency, so they're only one half of the equation.
Bass modes will be determined by room dimensions - any frequency that has a wavelength that matches the room size will resonate like a pipe organ. This is one you'll hear as a variation in bass response with seating position, and with subwoofer location in the room. Just as room furnishings absorb higher frequencies, room constuction may do the same for the bass. Stick walls are more transparent to bass than cinderblocks, and windows have a degree of bass absorption as well. The quesiton becomes whether underdamped resonances still exist that intererfere with your enjoyment, as the most effective bass traps are both large and complex, compared with acoustic panels.
So... what size is the room, how's it built, and how handy are you? I tend to DIY rather than buy, but that's by choice.
PS Ethan's a bit of a salesman, but so are most entrepreneurs. If you aren't DIY-ish, I'd take him up on his offer. Lots of experience in this area...