[Roc]

Let me start by saying i have a rather large (14x23x8) dedicated listening room, with lots of acoustic treatments available. My issue was that with a conventional system setup (speakers in corners, listener in ctr. of room) the system was very clear, but had terrible bass response, and OK imaging. 
I tried the speakers on every wall with many combo's of seating and acoustic treatment placements, but i never got all 3: great image, great clarity, acceptable bass response.
Then one day (2 yrs ago) i read about the "back against the wall" (BAW) setup and decided to give it a go.  Heads Up: With this setup the listening position and speaker positions are CRITICAL, and the back wall allows new early reflection paths that muddy the sound. This was a huge problem to overcome, but for the most part I think I've got it.
After much tweaking, and i tweak more than anyone i know, i ended up with the setup shown below. The rear wall reflections were tamed by installing 8" wedge foam.  In fact initially i used the 8" on the walls beside me too.  So i was sitting in the (very) dead end of the room.

How does it sound. WOW!  Bass response is excellent, clarity is good, but what really jumps out at you is the image.  I never realized this before, but the musicians tend to be located at the front wall.  So with the conventional room setup they were 12 ft. in front of me, not too realistic.  Now they are still at the front wall, but are 21 ft. from me. It's like being in the concert hall, everyone is in their place, and about the same distance from me as if I were there, sitting up front.  Just incredible!

After a while I got tired of the stuffy, non-linear room response caused by super thick acoustic foam so i built 4 QRD's to replace the foam on the side walls.  Very nice improvement in linearity, but there was a lot of energy on my side of the room, which i did not enjoy.  I really liked the deadness on my side of the room.  Adding mid-room acoustic foam panels, flanking the listener, solved that issue, without hurting the linearity much.

I invite anyone who has experimented with the BAW setup to share their experiences too.

Dave

[max190]

Dave, excellent detail on your layout but you forgot to add the light switches
Where did you get the idea to use the roofing panels? Did you add absorption behind these panels?

[Hipper]

I have VMPS RM30Ms and you can see my set up in the gallery. My seat is on the back wall and speakers on the front wall but I don't have the space you have. It is a conventional 'live end - dead end' set up.

Originally I liked the idea of a nearfield listening arrangement, cutting out all reflections and just hearing direct sound. Now however I find some reflection off the side walls makes for a better musical experience.

My chair has a head rest and that cuts out reflections off the rear wall. I would have thought that any reflections off the rear wall in your situation would not muddy the sounds as the difference in the time of arrival at your ear of the sound direct from your speakers and the reflections from the rear wall would not be large enough (there needs to be a gap of greater then 30 milliseconds for our brain to distinguish echoes from direct sound, and it is thought that for a gap of 20ms - the equivalant of 22 feet - or less, the sounds would only add volume).

Looking at your plan it seems to me that some of the panels and foam are not nescessary. What, for example, do the scatter panels behind the speakers do? The acoustic foam where the CD panels are and the QRDs on the side walls seems to be duplication although I appreciate they may help with controlling  some frequencies.

I should add of course that it is your listening room and you know best. I'm just going from my impressions from the drawing.

And I agree with Max - the location of the light switches is crucial to the sound.

[Roc]

Dave, excellent detail on your layout but you forgot to add the light switches
Where did you get the idea to use the roofing panels? Did you add absorption behind these panels?

I'll add the switches ASAP.  Hey i'm an engineer, what can i say.  Nope no absorption behind the roofing panels.  I saw them a lowes and tried a couple of them to see if they work, and yes they do, just give em some bow, not flat against the wall.

[Roc]

I would have thought that any reflections off the rear wall in your situation would not muddy the sounds as the difference in the time of arrival at your ear of the sound direct from your speakers and the reflections from the rear wall would not be large enough (there needs to be a gap of greater then 30 milliseconds for our brain to distinguish echoes from direct sound, and it is thought that for a gap of 20ms - the equivalant of 22 feet - or less, the sounds would only add volume).

Hipper:  something doesn't sound right about your numbers.  early reflections off of the side wall add a bunch of mud to the sound, and that path is only a few feet longer than the direct sound.

Once i made the listener side very dead it became apparent that the reflections off of the far walls, front & sides, were clearly audible and needed attention.  I used foam initially, which worked great, but back to the dull room.  So that's when i started looking for cheap ways to diffuse/scatter those paths.  Hence the roofing panels, which work fine, once you get the correct bow established.

Regarding redundant panels, I'm actually going the opposite way, building more QRD's to replace the roofing panels, and adding more to the listener side wall.

Dave

[Roc]

I would have thought that any reflections off the rear wall in your situation would not muddy the sounds as the difference in the time of arrival at your ear of the sound direct from your speakers and the reflections from the rear wall would not be large enough (there needs to be a gap of greater then 30 milliseconds for our brain to distinguish echoes from direct sound, and it is thought that for a gap of 20ms - the equivalant of 22 feet - or less, the sounds would only add volume).

Looking at your plan it seems to me that some of the panels and foam are not nescessary. What, for example, do the scatter panels behind the speakers do? The acoustic foam where the CD panels are and the QRDs on the side walls seems to be duplication although I appreciate they may help with controlling  some frequencies.

Hipper:  I had to rush out of the door this morning and didn't do your questions justice. 

First let me say i love your speakers!  got a chance to demo the RM30's at Brian Cheney's house a few years back, but went with the RM40's.  I'm using the Ampzilla's too.  Great combo with the VMPS's.

I think you've got the timing issue backward.  less than 20 -30 ms difference in arrival time causes confusion/mud, while later arrivals are ignored by the brain as echos.  Or is that what you were saying all along ?

You are not the first person to suggest that the mid room absorption panels might be an overkill.  When i first installed the QRD's i didn't include these panels.  The QRD's eliminated the early reflections and greatly improved linearity in the room, which was what i wanted, but there was a bunch of energy in the listener end of the room that didn't sound right at all.   Back when i had the 8" wedge foam surrounding the listener all of the music/sound/energy seemed to eminate from the live/far end of the room.  It was fantastic.  Now all of a sudden there was energy where it never was before.  So I added the mid room absorbers and it got back to normal.  Super realistic, and now more linear.

I would encourage everyone to experiment with mid room absorption panels flanking the listener.  I built a set for my sisters listening room, which worked so well we eliminated the need for foam on the side walls.   And when done listening she moves them out of the way, improving the WAF factor.

Back to the scatter panels: I found that as i improved the room acoustics I began to hear things I never heard before.  Not just in the music, but in the room itself.  When i made the dead end real dead I started hearing those (longer) early reflections on the furthest walls..  These reflections were screwing with the soundstage as much as the clarity. Adding the scatter panels made a big impovement.  But since these are all just experiments even the scatter panels will be removed this summer, when I build QRD's to replace them.

If you are ever in the Pitsburgh area come by and we'll do some listening.

[Mmaxed]

Very interesting set up.  Any chance we could get a picture of the scatter panels and more info on the material used for them?

[Hipper]

I meant that a reflected sound arriving 20 milliseconds or less after the direct sound are not noticed as echos - our brain combines it with the first sound heard. Above 20 milliseconds and our brains split the sounds up - it becomes an echo.

20 milleseconds equates roughly to 22 feet, using the speed of sound in feet per seconds.

Anyway, that's what I meant. Am I right? Now I'm not sure! I think I was referring to the Haas effect (or Precedence Effect) but that seems to describe the difference in timing of arrival of sounds between the two ears and our determination of the sound's location.

http://www.rane.com/par-h.html

The figure of 20 ms is not exact either it seems. I picked up on this idea from reading books like Floyd Toole's 'Sound Reproduction' but maybe it's much more complicated then that.

Perhaps it does not apply to sound recieved in only one ear? I don't know but if your back wall - and side walls - were muddying your sound then it doesn't  seem to apply.

I should repeat though that I have some side wall reflections now and it doesn't muddy the sound - just enhances spaciousness a bit.

What I do know is that you are going about this the right way. Start with what the experts say but then tinker with things until it sounds good for you.

My understanding is that the panel drivers on our speakers have a spread of 30 degrees, but I would guess that means there are still weaker sounds beyond that otherwise there would be no first side wall reflections in mine or your walls.

I'm impressed that you get a soundstage 21 feet away. I wonder how that comes about?

[mcgsxr]

Interesting layout, experimentation can be fun!

How tall are the cd racks?  That seems visually odd to have something between you and the speakers like that, but if it sounds good... it usually is!

[Roc]

Very interesting set up.  Any chance we could get a picture of the scatter panels and more info on the material used for them?

The panels are asphalt roofing panels made by Ondura, available at Home Depot for about $20 each.  They actually look pretty good in the room. Get ones that have some permanent sag in them.  They work best when given a "bow", making them convex in two planes.  No foam or other damping was required behind the scatter panels since they are extremely dead without help.

I personally would not use these panels in the speaker/listener area. I'd use acoustic foam there instead. I use them on my front/side walls since they are so far away, with the BAW set up.

When using them on the side walls the amount of bow becomes important, requiring some bend-n-try.  When used on the front wall the amount of bow is less important. 

The bottom picture shows the room before building/installing the QRDs.  The brown wood panels placed on the floor are an experiment to eliminate (deflect) floor reflections.

[Roc]

What I do know is that you are going about this the right way. Start with what the experts say but then tinker with things until it sounds good for you.

My understanding is that the panel drivers on our speakers have a spread of 30 degrees, but I would guess that means there are still weaker sounds beyond that otherwise there would be no first side wall reflections in mine or your walls.

I'm impressed that you get a soundstage 21 feet away. I wonder how that comes about?

The soundstage starts just behind the speakers and extends out to the front wall.  This results in the deepest (most 3D) sound stage i've ever heard.  That alone was enough for me to spend 2 years optimizing the setup.

I'm guessing the engineers actually want the musicians to sound about 20 ft. from the listener.  If my room were 100 ft. long odds are they would still sound about 20 ft. away.

[Roc]

Interesting layout, experimentation can be fun!

How tall are the cd racks?  That seems visually odd to have something between you and the speakers like that, but if it sounds good... it usually is!

The CD racks are off to the side actually.  About 3 ft. tall.

CHECK OUT MY GALLERY SHOWING SOME OF MY OTHER EXPERIMENTS.

[rbbert]

Do you use old or new style CDWG's, or none at all?

[Roc]

Do you use old or new style CDWG's, or none at all?

RM40's came with the older solid piece CDWG which i discontinued using within a month or so.
Last year i got a set of the Gen 2 guides.  Have had them on and off many times.  They improve clarity a bit, and focus is much improved, but they sound stuffy, reduced/rounded leading edge attack, and  less realistic overall, so i have discontinued using them, in search of a better way to get the same improvements.  The experiments continue.

[audiotom]

I don't understand wedging the listening chair between the foam stands
I think I get the concept
it may take too much ambience out (go to any live performance)

also have you considered placing your speakers on the long wall

you seem to be using half your room
when you could utilize the width to effectively remove a lot of the sidewall effect
and have more access to your laundry room

[Roc]

I don't understand wedging the listening chair between the foam stands
I think I get the concept
it may take too much ambience out (go to any live performance)

also have you considered placing your speakers on the long wall

you seem to be using half your room
when you could utilize the width to effectively remove a lot of the sidewall effect
and have more access to your laundry room

Audio Tom: I've had the speakers on all of the walls, at least twice each.  The system sounds better (in my case) with the speakers on one of the short walls, and better now in the middle of the room, using the BAW approach.

When i removed the wedge foam from the side walls and installed the QRD's the room got too lively.  The energy created by the QRD's was annoying. Adding back the mid-room absorption made the room just right. Making the room just right takes some cut-n-try.

While it sounds wrong, even to me initially, that large space/area between the speakers and the front wall is where all the magic takes place.

I've added a layout sketch in my Gallery showing what we did at my sisters house.  We totally eliminated the fixed foam on the side walls using mid-room absorption panels.  And these panels can be moved when done listening.  In the sketch I show the importance of the panel positions and angles for blocking/absorbing early reflections.

[audiotom]

interesting quest Roc

the fact that you have tried everything and came up with converging adjustments is great

having a dedicated room is always nice


I have a 15 by 27 room where I'm along the long wall
I really like the sound with realtraps absorption and diffusion
the layout of the room doesn't work any other way

thanks for the explanation Roc

[Roc]

I have a 15 by 27 room where I'm along the long wall
I really like the sound with realtraps absorption and diffusion
the layout of the room doesn't work any other way

thanks for the explanation Roc

You have a bigger room than me ! Nice acoustic treatments too, must sound sweet !
I wish i could have used the long wall, as you are.  But the 1st and 2nd order room modes predict what I already know, my room is bass challenged everywhere i try to sit.

That's one reason i started this thread, cause i'm willing to bet some other audiophiles have Low-B and don't want to buy a couple more subwoofers to see if they fix the problem.  The BAW setup may be a solution for some of them ???

[andyr]

Let me start by saying i have a rather large (14x23x8) dedicated listening room
Dave

IMO, Dave, 23' x 14' is not "large" ... although I guess it depends whereabouts in the world you reside.  In England, I could imagine it might be considered "large".  In Oz, my 27' x 17' is "medium" ... but my mate's 40' x 30' room truly is "large"!

Then one day (2 yrs ago) i read about the "back against the wall" (BAW) setup and decided to give it a go.  Heads Up: With this setup the listening position and speaker positions are CRITICAL, and the back wall allows new early reflection paths that muddy the sound.

I can see from your diagram what "BAW" means.  But why did you decide to position your speakers so far off the front wall?

AIUI, 1/3rd into the room is the optimum for bass response (if you have the space) but you seem to be more than half way into the room? 

Regards,

Andy

[Roc]

IMO, Dave, 23' x 14' is not "large" ... although I guess it depends whereabouts in the world you reside.  In England, I could imagine it might be considered "large".  In Oz, my 27' x 17' is "medium" ... but my mate's 40' x 30' room truly is "large"!

I can see from your diagram what "BAW" means.  But why did you decide to position your speakers so far off the front wall?

AIUI, 1/3rd into the room is the optimum for bass response (if you have the space) but you seem to be more than half way into the room? 

Hi Andy

Yep, large is relative, but 30x40 is a ballroom!   I used the word "large" to convey that it was by choice i moved the listener to the rear wall, not because the room was too small.  And indeed it was for heightened bass response, which i did indeed get with the BAW scheme.
I can't remember if i ever had the speakers 1/3 into the room, using a conventional system set-up, but i probably did. 
Once i moved the listener to the rear wall i had to start over again with speaker placement.  Placement was found to be critical and the position shown was where they wanted to be.  Any closer or further from the listener resulted in boomy bass, and/or bass echo's.  Side wall position is the same as with a conventional set-up.

Dave