[GregN]

From what I've read about positioning absorption panels mounted behind the speakers, it's best for the panels to be mounted a little bit towards the inner edges of each speaker. In other words, instead of positioning dead center where the panel would evenly "frame" the speaker in front of it, it's better to have it located off-center to the inside position (i.e., a bit to the left for a right channel speaker, a bit to the right for the left channel speaker) with maybe half of the panel overlapping with the speaker placed in front of it.

First of all, is this true? And secondly, how does speaker toe-in placement change this rule of thumb, if at all?


As a sort of PART II to all the above, would the answers to those questions primarily relate to dedicated 2 channel rooms, where there will be a single primary listening location and as such, every treatment decision is made for optimizing that one listening position?

If, on the other hand, you have a multi-purpose audio/video room, with a few different seating positions throughout the room, how would you proceed with respect to the front wall? Extend or widen the span of absorption treatments to cover more wall space given that you want to correct for multiple positions within the room? If so, extend by how much? at least a foot all around each speaker ? a few feet all around?

I'm mainly interested in getting answers to the PART II questions, as that is how I will be using my room, multi-purpose, etc.

thanks!   

[bpape]

I don't think you can have a rule of thumb like that.  Rooms are too different, desired GOAL for those panels can change, speakers vary wildly, etc.

For multichannel use, usually the entire front wall is dead.  For 2 channel, it varies depending on the above. 

SBIR is the effect of the spherically radiated bass coming off the wall behind the speaker and coming back at you in varying phase with regard to the direct signal depending on frequency and accompanying wavelength.   That is going to happen on both sides of the speaker so in that case, it's almost better to have them directly behind.  Now, if you need to absorb some on the front wall between the speakers to help with imaging, then what you proposed might help, a little. 

Bryan

[GregN]

For multichannel use, usually the entire front wall is dead.   

Bryan, are you saying that with multi channel systems (for example, a pair of bookshelves, a center channel and sub situated along that front wall), it's often recommended that the entire front wall, or at least a significant amount, be treated?   

SBIR is the effect of the spherically radiated bass coming off the wall behind the speaker and coming back at you in varying phase with regard to the direct signal depending on frequency and accompanying wavelength.   That is going to happen on both sides of the speaker so in that case, it's almost better to have them directly behind. 

"almost better to have them directly behind"... and so, about how far would this coverage extend out in each direction of the speaker; left, right, above, below? Can I tease out of you at least a minimum likely amount of surrounding coverage for each of the main speakers? These latter questions may be rendered moot if you answer the prior question about multi-channel. Please just throw me a solid and meaty bone here, Bryan.


I realize experimenting with mounting location is the ideal way of finding optimal placement, amount of coverage, etc., but I'm still hoping for even just a little bit of "rule-of-thumb" here, not necessarily a guaranteed and precise recommendation, which I understand cannot be provided. As I'm still in the 'just figuring out what size and quantity of pieces' phase of the project for my front wall, I'd like to be able to hone in at least a little bit more in terms of minimum/maximum parameters of that wall coverage. Maybe that's asking too much.

As it stands, I've got at least a half dozen notions as to sizing and quantities of panels for that front wall. It would be nice to be able to narrow that down to only a couple sizing/quantity scenarios, especially because some of these scenarios are with custom sizes making the stakes somewhat higher given the higher costs involved.

If I order wrong sizes or too many, I know that I have side and back wall issues for which I can use them for, but I would much prefer to be able to consider those areas separately using sizes ideal for those locations. (yes, I make everything in my life this complicated!  )

THANKS again.

[jazzcourier]

 Having just moved my two channel system to a much larger room i was not sure what the sound was going to be like.Coming from a smaller room with great side wall absorption{floor to ceiling records on both sides} i knew there was going to be a surprise.Welcome to the boom boom room! Any prep,pre system move went out the window fast.First i set the speakers in position,of course after much moving and re-positioning they finally clicked in focus.I have purchased 8 real traps-this is where it gets interesting-i needed to toy with the traps in various positions before i mounted them-i put one each in the corners behind the speakers on chairs and one each behind the rear ported Cremona's and zap! two more on each side first reflection points and two in the rear corners.It was those two directly behind the speakers that made the big difference.They are almost next to the corner traps as well.The first effect was a huge soundstage and minimum boom.I will still fuss with the positions and have to deal with the ceiling but it has greatly improved.This room is 22 feet long 14 feet wide and ceiling a little over 8 foot high.Speakers are 36 inch from wall,speakers about 6 1/2 feet apart and 2 1/2 feet each from side wall.Listening spot is some 8 feet or so from speakers another 3 feet to back wall.As i add various absorption items to the room the dynamics will change and adjustments will have to be made,but i feel i have won the first battle of the boom.Good luck!

[bpape]

IF the multi-channel is purely LCR with no surrounds, then treating the whole front wall is not necessary as there are no rear channels to reflect off the front wall and mix with the front surround stage.  If there are side and/or rear channels, then yes, the entire surface should be treated.  The trick is to get what you need in these terms without adversely effecting the bass response of the speaker.   Sometimes you use the SBIR abberations to your advantage.

Let's say we have restricted seating placement with regard to the room length and this causes a peak in response at the listening position at frequency X.  If we can get good imaging and find a place with regard to the wall behind and beside the speakers that will introduce a dip in response at frequency X without causing too many other abberations, that's a benefit overall.  However, if we then treat the wall behind/beside it to damp the reflections that are causing that dip, we're out of luck. If we treat those walls in such a way as to treat only above that frequency and leave that alone, we're good.

Sometimes in smaller spaces (again, one of the dependencies), there aren't a ton of response problems below say 50hz.  It's nice and smooth and then gets ragged above that.  Again, I don't necessarily WANT to kill anything below 50Hz (on the front wall anyway) which could introduce issues.  So I stay with a thinner material that will work above there but do little to nothing from there down.

IMO (and some will disagree), as long as it's not a dipole, I'd like to have absorbtion from 1' OUTSIDE the left and right speaker all the way across.  I personally prefer a dead(er) front wall for the upper bass up.  Normally, 2" is fine.  I find that it tightens up image specificity and focus.    At a minimum, I'd want 1 panel directly behind the speaker and probably 2 (assuming panels are 2' wide).

My very strong recommendation is to play with seating and speaker (and sub if applicable) locations to find what works best with no treatment.  Don't settle.  Deliberately move things around to see what frequencies change when you move the seat front to back, side to side - move the speakers closer and farther from the front and side walls.  Then you'll know what's helping and hurting where.  Then you can make informed decisions as to how best to attack the treatment.  

When in doubt, start with less - you can always buy more.  That said, there is a minimum amount that'll be required in terms of bass decay time control and minimal things that need to be addressed such as early reflections.  Also, when looking at bass abberations, don't forget the middle of the back wall for a place to treat.  Many times, some of the worst nulls are a function of the distance from your ears to the wall behind you.  Killing that wave coming off of it will minimize cancellations and smooth response.

Bryan

[GregN]

Bryan,

Thanks again for the detailed reply here. I've read and re-read it a few times, just to be sure I am grasping the nuances. It's reminded me again of the fact that when it comes to treating a room, unless you are working with a common or predictable room dimension, treatment decisions must be approached tentatively and with flexibility.

Given all the variables to treatment issues, not to mention the fluidity of my housing situation, it looks like I need to reign in some of my tendency to want to predetermine the ideal sizes and types or styles of treatments (from an aesthetic standpoint), even before experimentation or practical experience with any treatments takes place. Along with it, I'll probably need to keep in check my accompanying desire for an ideal in which those same pieces can form a core or baseline of treatments that I can utilize to positive effect both now and somewhere else in the future.

Part of the problem is that I can envision how I want certain treatments to look or compliment one another location and appearance-wise, before having a firm enough grasp on whether it would make the best sense acoustically. For example, going in to this thread, I had a fairly clear idealization of how I wanted my front wall treatments to look and how they are to be arranged in relation to furniture. Cart before the horse, etc.

Plus, my personality or natural inclination is such that I want to completely analyze everything in my head, come to a decision that way and be done with it, as opposed to experimenting and playing around with different treatments. Again here, probably not the best way to approach these types of questions. Reality check time, I guess. boo hiss.

[bpape]

Sorry.  Odd rooms do tend to complicate things.  Add in the transient nature of the situation only makes it harder.  My suggestion is to get a few basic pieces that can be used in a variety of places and see what works best for you.  You'll need:

- Corner broadband absorbtion - start with 2-4

- Some 4" thick panels that could be used either centered on the rear wall or directly behind the speakers - start with 2

- Some 2" panels for side wall reflections and also to experiment with the difference between 4" and 2" behind the speakers if selected SBIR control is desired.  Start with 2-4

Unless your next room is a closet, all of those elements are usable in a new room for similar things and are somewhat interchangable given the situation.  Starting small also allows you to experiment with things and learn for yourself what your room is doing, what each pieces of treatment does for you, etc.  And, it lets you do so at a reasonable cost and without 'wasting' anything in the new later environment.

Bryan