Diffusors vs. absorbers room treatment

I agree with the above post as far as placement of absorbers. I've got wall treatments on the sides, rear wall and on the ceiling of my listening room. Many experts will say that diffusors should be placed in the rear of the room and are used to expand your room as they spread out the sound. You really have to experiment to see what suits your room the best. I am using Argent Room Lens clones and CD racks at the rear corners of my room to act as diffusors. Moving the room lenses as little as a couple of inches makes a difference in your soundstage. I've placed the room lenses at the mirror image points to the sides of my speakers and behind each left and right speaker. Both absorbers and lenses are DIY following John Risch's on-line instuctions. You can see pics of my room if you look at my "system".

I like the link Psychicanimal posted. I loved the comment--"with all the complexities of room acoustics it's no wonder I spent my money on a power cord" (or something like that). It is so true! I read this original posting earlier and wanted to point out the complexities--but the problem with that is that it just makes people avoid the room issue altogether, which is the worst thing you can do. We offer services that engineer the entire room without having to go the trial and error route. We also do not sell acoustical treatment--thus there is no incentive for us to tell people to buy something they don't need--in fact most of our designs are more like the John Rische pages (being true designs that can be built), but sometimes people want things that can be simply bought. That being said, we also understand that not everyone can or is willing to pay for a service. Let's face it--you don't get a fancy item in a fancy box--it's all designs. But still our goal is the room. We firmly believe that the room is so often ignored in favor of power cords and other things that have such a small effect on the sound relative to a well designed room or acoustical treatment of room.

Now I'll get off my biased soap box and say for the DIY people--don't be afraid to work on it and try things. How many cables have you tried? How many components? Think of how many things you've done to your system that didn't work out? Guess what--when you get into room acoustics--the same thing will happen. You will try some things and they won't work--but you'll try some other things and they will. Keep in mind--like system synergy the same is true for room acoustics. If you change one thing--it affects others and so sometimes the path to the best sound isn't that clear. For some people they want to get to the end point quickly and relatively painlessly--or they are willing to invest substantially in construction costs in building a dedicated listening rooms. In either of these cases it's crazy to try the trial and error process--you will be frustrated, confused, and possibly out a lot of money without too much to show for it. However, if you are the audiophile that likes to tinker, tweak, try things and see for yourself what the results are--by all means--do it! Some of these links above are great. There are also some books by Alton Everest (Master Handbook of Acoustics and Studio on a budget) that are very good. Most acoustical treatments can be built yourself for little money if you are reasonably handy. The real trick is knowing what to use, where and how much, so that everything works together. For example, every material has a particular bandwidth for both absorption and diffusion. You need to know these to calculate how the room will react with a certain amount of certain material. Some of these calculations are complex--some are very basic. But there are some basic principles that almost always work. Have some absorption on the first reflection points (owens corning 703 wrapped fiber board works well and has a better bandwidth than most foam products), have diffusion behind the listener. If everyone just started there it would be a huge improvement over doing nothing. Then over time, read more, learn more, and listen more. You can hear the difference of every type of absorber and diffusor and just by moving these throughout the room you will learn their effects. This is not a short process--but can be a fun one--if you like doing things like this.

Obviously, we would love to design the listening room, but if we can't we want to encourage and hopefully provide some useful tips on how the DIYer might improve their room. We do have a small tutorial (although the books are much more in depth and highly recommended) at the listening room at http://www.rivesaudio.com. Hope it is helpful.

Try CARA software:
rhintek

Rives, I like what you're doing for home audio/video. It's really commendable. Way out of my budget, though. I am working on the acoustics of the new townhome I moved to. The Carlo Foam Factory (www.foambymail.com)is about 1 1/2 hr from me and I've been invited to visit their showroom. Lak and I are planning on going pretty soon...

Yesterday I received a DOD 31 band/ch Eq I plan to use with a pair of Bose 901 IV's in my living room (2 ch HT/ background music). As I expected, room boom @ 80 Hz and what Tom (Nightdoggy) had diagnosed: screeching resonances in the x-over range of my Swans (3 - 5 KHz). Nothing that couldn't be solved with proper room treatment alone.

The Eq is for me to be able to get a flat response out of the 901's (they will be firing in direct mode). Tom had told me the Bose weren't as bad as people thought--that their Eq was responsible for a lot of the sound degradation, not the speakers. I wonder if the DOD will be able to substitute the Bose Eq. My 901's were a given by a friend and the foam surrounds need replacement. I think it will be a good project and will be better than those cheapo HT packages. Also, my entire living room, dining room and kitchen will be filled w/ music...

An easy rule of thumb for people people who don't know their way around acoustics well, is that "smaller rooms"(home audio applications) will likely do better with more diffusion, while larger rooms will require a bit more absorbtion to balance out the reverberation equation. Smaller rooms(for HT/music purposes...but don't forget HT systems can get away with more absorbtion in mid/treble) of standard drywall/stud construction will absorb less bass, while larager rooms absorb much more bass thoughout the spectrum. If you don't absorb a little more of the midrange/upper frequencies in a large room(and say, have mostly hard floors and flat walls), the spectral tilt and reverb of the room will seem "too bright" and "top heavy"! It's the converse in a smaller room. You have a shorter reverb time in a smaller room in the mid/treble. So coupled with the fact that there's "excess" bass reverb and less bass absorbtion in smaller rooms, you need to keep the reverb time higher in the mid/uppers.
That will all balance out in terms of how(and with what materials) you treat your reflection points in the room as well.
Case in point: In a smaller, say 12x14x8 foot carpeted floor room, where you are doing a balance of HT/music, you should consider perhaps doing reflection/diffusion treatments on the side and back walls(covering first reflection points), with maybe diffusion up front as well, but possibly treating the first reflection pionts on the front wall(front speakers) with absorbtion...still maintaining some diffusion upfront. I think you'll find this will still have "life" enough in the sound for music, but be more than acceptable to handle HT as well.
For a larger room(domestic house rooms of course), say 19x24x9, you might consider doing more absorbtion around the front and front/sidewalls for acoustic treatment in various places, but maintaining diffusive/reflective treatment(or elements) along the back/sides and back of the room...treating front reflection spots with more absorbtion than in a small room. Of course, you'll need to consider the overall reverb and balance of the room, and you're ear will be the final determining factor. Considering a "medium sized room", you'll have to balance somewhere "in the middle" of the above two scenarios.
Still, ofcourse, there's a lot more to it. But I think if you experiment, you'll find what I mentioned about right for most peoples taste.
F.Alton Everest's "master handbook of Acoustics" states(along with a bunch of other acoustic publishings) that "many professional acoustic engineers will even dissagree as to what exactly is the best overall reverberation times, and approaches to treating listening rooms", and that "tastes differ!"....it's like anything else really. But, experiement around with the stuff if you will, and you'll get an idea yourself.
One more word to consider here, and that's that different speaker systems do diffent in differnt acoustical environment perceptually! For instance, Horn speakers, some THX designs, bipols/dipols and say planar or electrostatic speakers will possbily require different room acoustic treatment approaches! where there's more "dirrect" radiated sound patterns you'll "less of the room reflections early" But where there's more "back wave" sound distibution, you might find you need more "reflection and diffusion" around the room to give a proper sound from that kind of speaker system. So there's no "one best" room acoustic treatment approach in all pertinent aspects...YOU GOTTA EXPERIMENT IN YOUR ROOM WITH YOUR GEAR!...and for your own tastes.(hint, no two recording studio's are alike either!) For that matter no two audio systems are usually alike, and there's an infinite varriety of domestic house rooms out there as well.
You can check out some helful acoustic websites(which you'll have to dig up yourself...but they're there) to figure out room modes, reverberation RT60 times, even plot potential room acoustics treatment approaches.
Still, there's no replacment for the "professional" when it comes to "doing this acoustics stuff right!" If you need it done right the first time, you can always call the professionals! Rivesaudio.com is one to consult if you need someone to contact online for acoustics help.
Otherwise, have fun and good luck with your endevore
Hope this helps