acoustic absorbers vs diffusers

Koven,
I was in your shoes a while back so I know how daunting and confusing the topic of acoustical treatments can be.

Best thing is to educate yourself first before spending money foolishly or buying the wrong stuff. I recommend you buy Dr Floyd Toole's latest book to bring you up the learning curve.

Within it you will learn that the frequency spectrum is essentially split into two zones - the mid-to-high frequencies above the room's transition zone or Schroeder frequency which for your room size is likely around 500Hz and the bass frequencies below 500Hz. Each zone should be treated differently. The bass zone can't be diffused due it's long wavelengths so absorption and parametric eq are the ways to deal with cutting bass node peaks. Bass traps come in a variety of kinds with the most popular being stuffed with fibreglass which is called a "resistive" bass trap. Resistive bass traps should be a minimum of 4" thick with the thicker the better and must be pulled out from the wall equal to one-quarter the wavelength of the transition zone frequency. So, 500Hz with a wavelength of 2.26 feet has a one-quarter wavelength of 6.6", so start by pulling your bass traps away 6.6" from the wall and extend them into the room by double / triple stacking them as far as you can so the absorption extends down to deeper frequencies. If the footprint of the bass traps is too large for your room then consider a "diaphragmatic" trap from RPG which works best when sound partical pressure (not motion like with resistive bass traps) is at its maximum which is right against the wall, so diaphragmatic traps hang right on your walls with much smaller footprints. Bass traps should be placed in all four room corners from floor to ceiling as a starter. Additional bass traps can be placed in the middle of the front or rear walls for the floor-lower wall corner and/or along mid-side walls. RealTraps and GIK and likely other resistive trap makers will tell you to "stradle the corners" with the traps but they aren't telling you the entire story which is to use them properly is to pull them away from the wall corners as explained above. Perhaps they can sell more traps by not telling you how to max the effectiveness of your purchase . . .

Take care of the bass zone first as it'll payback higher sonic dividends quickly. With the bass out of the way turn to the mid-to-high frequency zone where you can use (i)reflection, and (ii)absorption, and (iii)diffusion as your tools of choice. If you are using your room to master CDs or mixing your own music or for comparing listening components, then put absorption (4" minimum to be effective across a wide freq band to keep the sonic spectrum in balance) on your side wall 1st reflection points which will make the musicians appear as small and specific locations within space and narrows the perceived soundstage width. Otherwise use bare wall reflections or diffusion on the side walls to widen the apparent sound width and soundstage making the musicians appear more life-like in size.

Diffusion for the rear wall behind the listening chair is also important provided you can sit a minimum of 3 wavelengths of its lowest frequency that it works to away from it. For smallish rooms I'd suggest Skyline diffusers which diffuse in two dimensions - horizontaly and vertically. You can make your own (email me and I'll send you instructions) or buy them from Auralex or RPG. Get the ones with the deepest well depths so they extend down closer to the room's transitional zone frequency (i.e. 500Hz)

The front wall is the least important and diffusion or absorption can be used here depending on if your like your roome "alive" or "dead" sounding.

The ceiling's first reflection points could usually use diffusion it it's a short ceiling; the diffusion will help to raise the apparent ceiling height a little.

Hope this helps. Take lots of time and some $$ too but it's likely the best "component" investment you'll make.

Kevin

absorbers go in the corners where the excess bass energy is. diffusers along the front and side walls.

thanks, i plan to put diffusers behind the speakers and absorbers on the side walls

Diffusive elements along the front wall, behind the speakers and along the side walls as I described. Absorptive elements along the side walls.

Go to Acoustic Sciences Corp (ASC) web site for some good info. You can also Rives Audio for excellent information as well.

thanks for the info, it's all new to me and is a lot to take in, but im trying

let's say i have an equal amount of diffusers and absorbers... which goes on the front wall and which goes on the side walls/ceiling/rear etc

thanks

thanks for the info, it's all new to me and is a lot to take in, but im trying

let's say i have an equal amount of diffusers and absorbers... which goes on the front wall and which goes on the side walls/ceiling/rear etc

Room corners and placing speakers close to room boundaries; floors, walls, cause / result in the reinforcement of low frequencies that can smear detail in the midrange and low treble. It is necessary to remove this excess energy or absorb it through the use of bass traps.These are large (due to the long wavelengths of the frequencies involved) in order to be effective at low frequencies.

The sound you hear at the listening seat is a combination of direct energy from the speakers and reflected energy from the room boundaries. As frequencies increase, they become more directional and behave more and more like light, i.e. they reflect off flat, hard surfaces. If the reflected sound arrives at your ears within too short a period than the direct sound from the speakers, it will confuse your brain and result in loss of imaging and soundstaging. This is because the reflected sound must arrive at your ears later than approximately 7ms after the direct sound from your speakers so that your brain can distinguish direct from reflected sound. This is primarily a problem from sound reflected from what is called the first reflection point. That is the point along the ceiling or wall at which the direct speaker radiation first strikes and reflects off at an angle that will hit the listening position. The way to prevent this and to improve ambience in the room is to diffuse the sound striking off the floor. This is done with curved devices or irregularly shaped panels. These are best characterized by half round columns from companies such as ASC or square panels with irregular, skyline shaped surfaces from RPG. Their placement is determined by having someone sit at the listening position while an assistance moves a mirror down a wall adjacent to each speaker. The point along the wall at which the listener sees the speaker adjacent to it reflected in the mirror is the point at which the diffusing element is placed. The same can be done along the ceiling.

There's much more to this, but this should be a start.

I dealt with Ready Acoustics. Found them to be knowledgeable, honest and reasonable. If you send them a photo of your room they will make suggestions. My room is far better after installing their panels, which are very easy to install and quite attractive. Even my wife thinks so. Not connected to them except as a customer. They recently got a good review in either Stereophile or AS, forget which.