[youngho]

Interestingly, on Ethan Winer's website at http://www.realtraps.com/art_room-setup.htm, he discusses the 38% rule as "the best listening position is 38 percent into the length of the room, when measured from either the front or rear wall. This offers the best compromise of peaks versus nulls for any given room size" (I apologize, Ethan, if cutting and pasting violates any rules of fair use), so I'm surprised that you've heard such bad things about 41%. In fact, according to your own argument that the next rigid barrier beyond the ceiling must be considered, then 40" is almost exactly 38%!

In an earlier post, you argued that a 70 Hz peak is noticeable in the seated position in a 8' tall room. In a subsequent post, you acknowledge the existence of a node at 48". Because the antinodes for the height dimension are located at the floor and ceiling, and because the node is located at the midpoint, the peak of the first-order mode noticed by the listener will diminish as he or she approaches the midpoint until a critical point is reached, beyond which he or she will notice a relative null or suckout, which is maximal at the midpoint. Where is this critical point? That depends on the room and will be best found through measurement. If it's >38-41%, which is relatively unlikely, then the listener will experience that peak, but if it's <38-41%, then that is not the case. Listeners don't perceive nulls nearly as well as peaks, of course. It's possible that modal ringing will actually increase their perception of this modal frequency, which might offset the relative null, although that would depend on the Q of the curve. Anyway, this is why I think that the vertical placement of the subwoofer is not nearly as critical as the other two dimensions.

If you place the subwoofer in the corner, then it will maximally excite all modes. The room dimensions will determine the distribution of these modes. The listener's position will determine the perception of these modes. Reviewing Toole's paper, you'll see that even rooms with non-"ideal" measurements can have reasonably smooth bass if the subwoofer and listener are positioned well, and Toole illustrates clearly that corner placement of the subwoofer can work well in a certain room. If you look really closely at this white paper on multiple subwoofers at the section where they took out equalization, you'll see that with a single subwoofer in that particular theoretical room, putting the subwoofer in the corner was better than putting it in the middle of the front wall, yet you argue that the ideal height for the subwoofer would be at 50% of the height of the room. Also interesting was the fact that the corner placement of the single subwoofer beat a number of the two subwoofer placements in this particular test.

It's funny that you criticize Everest's Handbook and Toole's white paper on bass but reference the paper on multiple subs because it is also dependent on perfectly rectangular rooms in order to take advantage of mode cancellation and placing the subwoofers in the nodes for odd-order modes. Toole specifically discusses room walls and the problems associated with stiff, massive walls, so he does NOT "relate in terms of purely rigid rooms". Both he and Everest do NOT "deal with purely axial theory" since tangential and oblique modes are specifically discussed. By the way, Toole recommends EQ because he also discusses modes as minimum phase phenomena, although Ethan and others would dispute this. The white paper on multiple subs used equalization for most of the testing.

Anyway, for the original poster, I reiterate that Toole's paper is a good place to start learning. Unlike what you may have heard, it does not deal in purely axial theory. It does not relate in terms of purely rigid rooms. It does discuss real world cases. It does advocate measurement. It avoids blanket recommendations like "Get the sub up off the floor." I think I'm done, unless I've written anything incorrect above.

Young-Ho

[satfrat]

I would also like to add that I live in an old rented house with a boulder cellar foundation and a sagging wood floor.with a sub on the floor,the whole room became an extension of the sub and it just muddied up the bass. Getting the sub off the floor and isolating it cleaned this up considerably. It may not be an ideal answer but it was my answer that works. Just thought I'd share, FWIW. 


Cheers,
Robin

[youngho]

I wonder if isolating it made more of a difference than raising it, although this would depend on how tall you are and how tall your ceilings are. I also wonder if putting it so close to your right speaker may have significantly improved integration with the mains.

Whatever happened to the RealTrap Soffit?

Young-Ho

[TomS]

I would also like to add that I live in an old rented house with a boulder cellar foundation and a sagging wood floor.with a sub on the floor,the whole room became an extension of the sub and it just muddied up the bass. Getting the sub off the floor and isolating it cleaned this up considerably. It may not be an ideal answer but it was my answer that works. Just thought I'd share, FWIW. 


Cheers,
Robin

Robin,

Thanks for sharing what you came up with to isolate the sub - fascinating solution.  I've learned a lot of new things about sub placements from this thread already.  I am wondering though, how did you come up such a complex concoction for the isolation platform?  Is it based on ASC or some other design that's out there or just trial and error?

Inquiring minds want to know 

Tom

[satfrat]

I wonder if isolating it made more of a difference than raising it, although this would depend on how tall you are and how tall your ceilings are. I also wonder if putting it so close to your right speaker may have significantly improved integration with the mains.

Whatever happened to the RealTrap Soffit?

Young-Ho

You'd have to ask Ethen about that. I for 1 loved them and if I had higher than 7' ceilings(and my own house), I would have rather installed these Soffits around the ceiling/walls instead of using 8th Nerve Adapt Rectangles. Hell all they were was corigated cardboard boxes filled with fiberglass. But I thought they work damn well at tighening up bass. The fact that my downfiring sub openings are just below the Lorelei's midrange driver is exactly the reason when there's such good integration. I just have 1 flimsy house and putting a sub (even with cones) on the floor would constantly rattle the walls. I don't get that rattling all that much anymore and the bass from my Force XL is fast n' tight.

Hey, I hope you can take a joke cuz I mean no offense but the first time I saw your name, the first thing that pooped into my mind was "I wonder if Young-Ho is a woman?"   Not likely but hey, it could happen!  

[bpape]

I'm not at all criticizing Everest's book.  It's an excellent resource and has a lot of good information.  Not sure where you got that idea.  What I said was that there is a recommendation to start with the sub in the corner to maximize output and then conflicting studies that show that this is not among the optimal locations.

38% and 62% inside the room are in fact very good starting points.  Between 33 and 38% is acceptable and normally where the smoothest response will occur.  Going the other way toward 50% gets you into many deep nulls and peaks.  I always tell people that if they have to err, err toward 33% or 66% rather than 40 or 60%.  Ask Ethan personally.  He'll agree with me that around 40% is a terrible place to sit in any dimension.

The cavity below does in fact make the modes shift a bit but not completely eliminating the modes that occur in the inner shell itself.  It is more of an additive thing - sorry if I wasn't clear about that.  I meant to finish the thought but didn't.

You're only looking at part of that paper.  Look at the part where they use a single sub in the middle of the room to minimize the DEEP primary null of a specific dimension.  We can live with a bit more bumpiness in order to minimize the really obnoxious ones (especially nulls) that cannot be EQ'd away.  

As for the 70Hz peak, what I said was that in an 8' room with speakers and seating in 'normal' positions, you'll experience that peak.  

Yes - we can get pretty good response in a less than optimal room via proper placement of speakers, sub(s) and seating.  Again, I never said any different.  In fact, raising the sub off the floor is part of that process.  I'm just advocating dealing with all 3 dimensions instead of just the length and width.

Sorry, but all of the formulas you'll find do in fact assume perfectly rigid and perfectly rectangular rooms.  In the paper, they even mention it as a reason WHY they have to do real world measurements because the predictions aren't completely accurate due to things like doors reducing the rigidity of walls, etc.

Not trying to be argumentative but just accurate.  So again, why is it that it is widely accepted to keep speakers away from boundaries (and a lot of the reason for this is to minimize bass response issues - not just imaging) yet it is not acceptable to you to suggest that he try raising the sub off of the 3rd boundary of the room?  Sorry but main speaker or sub, bass still radiates spherically, it still interacts with boudaries and is still sensitive to positioning.

I'm not and never did say that it is optimal in all rooms.  I merely said that people forget about it and it's something that should be considered.  To consider one of the 3 dimensions as any less important than any of the others is IMO not looking at the whole picture.  The height is no different than the length or width - other than the fact that it is difficult to change the height of the listening position unlike the length and width.  I'll just say that few people have actually tried it.  Of those who have (as you're seeing posted here in this thread) most find that it can in fact help.

Bryan

[Ethan Winer]

I apologize, Ethan, if cutting and pasting violates any rules of fair use

Heck no! I wrote it so others can benefit. Paste (and link) away.

As for 38 percent versus 40 percent, I can't see why it really matters all that much. In most rooms that's a few inches or maybe one foot, and most people lean forward and back that much as they watch TV or listen to music. My own setup is not even close to 38 percent, because that's just not practical in my living room. I'm a little behind the halfway point. But with all my bass traps - even with a huge sub smack in the front corner - the response is perfectly wonderful.

About SoffitTraps, we discontinued them last year because they didn't sell as well as we hoped. Everyone loved the idea! But not many bought them. Also, I often found myself trying to talk people out of buying them because all rooms need broadband absorption, not just bass trapping. So when it was time for us to buy more of the casing material we decided to drop them instead.

--Ethan

[BobM]

Instead of raising the sub you could also just turn it upside down, like I did with my Rel Strata III. I put a board on top of the now up facing feet with something heavy on that (I used my old rarely used reel to reel). This definitely tightened things up and got rid of any boom that may have been there.

Enjoy,
Bob

[satfrat]

I would also like to add that I live in an old rented house with a boulder cellar foundation and a sagging wood floor.with a sub on the floor,the whole room became an extension of the sub and it just muddied up the bass. Getting the sub off the floor and isolating it cleaned this up considerably. It may not be an ideal answer but it was my answer that works. Just thought I'd share, FWIW. 


Cheers,
Robin

Robin,

Thanks for sharing what you came up with to isolate the sub - fascinating solution.  I've learned a lot of new things about sub placements from this thread already.  I am wondering though, how did you come up such a complex concoction for the isolation platform?  Is it based on ASC or some other design that's out there or just trial and error?

Inquiring minds want to know 

Tom

Just used some Vermont jury rigging,,,, we're pretty good at using what you can get our hands on.   Actually Ethen had a picture of a Soffit being used as a plant stand so I made 1 up and it worked pretty good at tightening up the bass but the walls/floors were still singing tenor. I had been looking at the ASC sub stand and saw that they used fiberglass but I thought the build was cheap looking,,, plus I have an oak fetish. So I had Ethan cut me up a 20" section and Chris of Timberlands(who made my center channel oak stand of Sound Anchor design) make me up two 2" oak platforms 15" x 18.5" and four 2" x 20"h leg corners that have a 1" cutout so they fit over the corners of the Soffit for added support. I sprayed the Soffit with a spray can of black granite Stone Creations and then sprayed a clear coat polyerathane to the particles wouldn't rub off. The Soffits came with cardboard caps on each end that had a 1.5" gap. I had read that open cell foam was the best foam to get for soaking up vibration so I thought if I got the stiffest open cell memory foam that was twice as thick as the gap, then when it was compressed to 1/2 it's width, it would make an ideal barrier for vibration obsorption. So I did this for both ends and then glued the whole damn thing using weights to hold down the platforms and bungie cords to hold the corner legs. I still get wall interaction during some movies but it's pretty much nil for music and that's what it's all about for me.  

Hope that'll satisfy your inquirying mind.  aa

Cheers,
Robin

[TomS]

Thanks - I have a real visual now of you wrestling that whole deal into a sandwich, Vermont style    Glad it works well for your situation, which is what matters.  Tom

[bpape]

Turning a downfiring sub over can certainly provide a quick and easy way to see if it makes a difference in your room and with your setup.

Ethan,

You surprise me.  As many times as I've seen you post about how just a few inches can completely change the curve you hear... 

If you look at the distribution of the nulls and peaks:

At approx 38%, you're going to hit 1 of the first 4 harmonic nulls - and it's the 4th IIRC.  At 40% and more, you're getting deeper into the primary and 3rd pretty heavily which are obviously lower and harder to deal with. 

Anyway, we're pretty far off topic here.  I'll just reiterate that it's something to try and 33-38% is a good starting point for seating positioning.

Bryan

[youngho]

Ethan, thanks for your generous attitude regarding the sharing of information. I also thought the SoffitTrap was an interesting product, and I had noticed that it disappeared from your website. I hadn't realized until recently that ASC makes something similar.

Bryan, neither white paper shows a real-world investigation or case where the subwoofer is placed in the center of the room. If you can reference which paper you're talking about and specify the slide number, I would appreciate. There are illustrations showing how putting the subwoofer in midpoint between two boundaries avoids exciting odd-order modes related to the length and width of a room, but it will still excite the even-order ones. Surely this can't be what you're talking about.

I specifically referenced one book (Everest) and one paper (Toole's white paper on bass) in my third post, and you wrote in follow-up "Yes, I've read those papers and the books - some of them many times.  Many of them deal with purely axial theory and relate in terms of purely rigid rooms (none are) and perfectly rectangular spaces (few are)." Since I only specifically referenced one book and one paper, I got confused about what you meant. Clearly, you meant that you read those papers and books I wasn't talking about. I probably haven't read them.

You wrote earlier that "People completely forget about the height of the sub. It's just as critical as the other two." Again for the reasons noted above, I think it's much less critical because of the average seated listener in an average room. The ASC SubTrap retails for $398. Why recommend spending hundreds of dollars on a problem that's likely not to be significant for most listeners? I don't know how much your product will cost, so perhaps it will be so ridiculously cheap what is a relatively minor issue for most folks, which could typically be easily fixed by slouching a little in the chair, which some people do as they relax, anyway.

Acecdotal evidence is great but of limited value. Many people have tried expensive cables, wood resonators, sticky dots, cable lifts, and quantum modifiers and found them to make a significant difference in their listening experience. People tried the Cathedral Sound Room Dampening Panels that are discussed on Ethan's website; this product was even "highly recommended" in Positive Feedback!

Satfrat, I learned long ago to take a joke about my name, which is Korean. Fortunately, I'm not a girl. My friends like to call me "The Ho," nonetheless.

Young-Ho

p.s. I'm modifying the post to apologize for the somewhat snide tone of the third paragraph. Also, in the fifth paragraph, I don't mean any disrespect to people's subjective experiences, but some of these tweaks have not had measurable effects, and some seem to lose their effect in blinded testing. Lastly, Bryan, I think you're one of the good guys, but on this particular point, I think you're wrong. We can agree to disagree. Anyone who hasn't taken the time to read Toole's white paper on bass would be well served to do so before spending money.

[satfrat]

Thanks for not getting upset Young-Ho.  I took my fair share of harassment when i was a boy named Robin, If i had a nickel everytime someone would say, where's Batman? 

Cheers,
Robin

[ctviggen]

You wrote earlier that "People completely forget about the height of the sub. It's just as critical as the other two." Again for the reasons noted above, I think it's much less critical because of the average seated listener in an average room. The ASC SubTrap retails for $398. Why recommend spending hundreds of dollars on a problem that's likely not to be significant for most listeners? I don't know how much your product will cost, so perhaps it will be so ridiculously cheap what is a relatively minor issue for most folks, which could typically be easily fixed by slouching a little in the chair, which some people do as they relax, anyway.

So, you're slamming him for not providing evidence, yet you're not providing evidence for this, are you?  Why do you think it's not significant?  I can tell you that I ordered two subtraps from ASC and I do believe the differences were well worth the money.  Now, you could also just raise the height of the sub using wood or whatever and that would also help.  You don't have to buy a subtrap.   Plus, who the heck wants to slouch in a chair?  If I ever get my act together, I could also get real data for use of the subtrap based on ETF.  I can perform this test sometime toward August of next year.

[bpape]

Bryan, neither white paper shows a real-world investigation or case where the subwoofer is placed in the center of the room. If you can reference which paper you're talking about and specify the slide number, I would appreciate. There are illustrations showing how putting the subwoofer in midpoint between two boundaries avoids exciting odd-order modes related to the length and width of a room, but it will still excite the even-order ones. Surely this can't be what you're talking about.

I specifically referenced one book (Everest) and one paper (Toole's white paper on bass) in my third post, and you wrote in follow-up "Yes, I've read those papers and the books - some of them many times.  Many of them deal with purely axial theory and relate in terms of purely rigid rooms (none are) and perfectly rectangular spaces (few are)." Since I only specifically referenced one book and one paper, I got confused about what you meant. Clearly, you meant that you read those papers and books I wasn't talking about. I probably haven't read them.

You wrote earlier that "People completely forget about the height of the sub. It's just as critical as the other two." Again for the reasons noted above, I think it's much less critical because of the average seated listener in an average room. The ASC SubTrap retails for $398. Why recommend spending hundreds of dollars on a problem that's likely not to be significant for most listeners? I don't know how much your product will cost, so perhaps it will be so ridiculously cheap what is a relatively minor issue for most folks, which could typically be easily fixed by slouching a little in the chair, which some people do as they relax, anyway.

Acecdotal evidence is great but of limited value. Many people have tried expensive cables, wood resonators, sticky dots, cable lifts, and quantum modifiers and found them to make a significant difference in their listening experience. People tried the Cathedral Sound Room Dampening Panels that are discussed on Ethan's website; this product was even "highly recommended" in Positive Feedback!

Young-Ho

That was exactly the section I was referring to.  There is no magic bullet that will deal with all modal issues.  But, in theory, if we can help with half of them, isn't that better than none of them?

Believe what you will about the basis for the formulas.  I'll just say again that all the formulas you see to calculate room modes assume perfectly rigid boundaries and perfectly rectangular spaces.

As for spending $400, did you see me recommend buying anything before trying it?  No.  Someone else brought up the ASC product.  Heck, try sitting the sub on an old milk crate.  That's free and will tell you quickly if it will help in your situation.  Turning a down firing sub upside down is another way to try it that's free.

Do you know how many speaker designers spend a ton of time getting the distance of their woofer just right off the floor in their cabinets?  Paul Hilgeman of Nomad told me once that getting the woofer position right in relation to the floor and the other drivers took him much longer than the rest of the design.  Why?  Because he was trying to find the best blend to the upper section and still get good coupling (but not too much) with the floor.  When using a sub with mains, you're trying to get that same integration and at the same time, get it somewhere that gives you good output but not at the expense of the integration or smooth response.

Overall, you'll believe what you want.  You'll likely never try this because you don't believe it can work.  That's your choice.  That's your loss potentially - potentially not.  Doesn't mean others shouldn't try - especially when it's something you can do for free.  There isn't much in the audio world that's free.

As for anecdotal evidence, I'd much rather listen to real world users like the folks here on AC than a magazine who's potentially in the pocket of the product manufacturer.  Robin has nothing to gain from this.  He's not selling anything.  He's not even using a commercial product - yet he finds benefit.  Others have experienced the same thing.  

The whole point of this thread was about the relationship between sub location and room treatments.  I simply offered an additional piece of advice for the OP to try.  Your opinion is that you don't think it will work so he shouldn't even try it?

Bryan

[youngho]

Ctviggen: I'm unclear on how exactly I "slammed" Bryan. Did I call him names? Was my criticism overly harsh? Please let me know. I thought I was reasonably civil during this exchange. Please show me specific examples how I can improve my manners.

The reasons why I don't think the vertical position of the subwoofer is likely to have a hugely significant effect for most people is laid out in the previous posts. I could copy and paste these parts if you wish. As for your own experiences, I know nothing about your specifics, like your height, the height of your ceilings, the nature of your listening room construction. I don't know the isolation benefits of the SubTrap. However, if it does help you, and if you have 8' tall ceilings, and if you listen while in a seated position, I don't think it's likely to be a result of a change in the activation in the first-order height mode unless you have integration problems in the crossover region. It may help for other reasons, but probably not because of that.

Lots of people sit in a comfortable chair during listening sessions or when watching movies. Often, rather than sitting perfectly upright, they'll scoot their butt forward and lean back. Sometimes, they lace their fingers across their belly, perhaps even holding a beer there. This is what I mean by slouching. You can see this at any movie theater, minus the beer. That's who the heck would want to slouch in their chair. As you can imagine, this would move their ears down a few inches in the vertical plane. What is your experience with this? Do you listen while sitting straight up?

Bryan: You wrote about "the part where they use a single sub in the middle of the room." I interpreted this to mean literally that there was a subwoofer in actual use in the middle of a room, which is similar to an approach suggested by Dr Hsu of the subwoofer company. In retrospect, it's now clear that you meant "the part where they show a picture of a subwoofer placed in the midpoint between two boundaries." I'm sorry I had difficulty comprehending that.

In terms of formulas, the usual 1130/2f for a first-order mode does not assume both "perfectly rigid boundaries and perfectly rectangular spaces," but rather two parallel rigid surfaces. Obviously, the nature of those surfaces will shift the frequency downward, but the basic physics of standing waves still applies, or so it would seem.

I thought Robin and I were getting along just fine, and if I'm not mistaken, he's using a SoffitTrap, which was a commercial product that he then modified. At no point did I suggest that he's selling a product or that he had anything to gain. I readily acknowledge that he sees a benefit in his room, but I explicitly wondered whether some of the benefit that he perceived was related to isolation, rather than the change in the the vertical dimension, which he acknowledged might be a possibility. Who knows? Maybe he thinks I "slammed" him, too.

With respect to speaker designers, I don't know any personally. Full-range speakers and subwoofer/satellite systems can follow different rules because of the possibility of setting delay. Although I do know of a commercial product which is no longer on the market but which had the driver firing upwards from a height of approximately 50', the vast majority of subwoofers on the market locate the driver near the floor for a very good reason.

At this point, this thread has really trailed off into trivial and unimportant details, as well as straw man arguments that are too tedious to address. Perhaps we can all agree to call it a day by saying simply that my opinion is that the vertical placement of a subwoofer is not as critical as placement in the other two dimensions, which is what Bryan originally asserted, for reasons that I discussed above and supported with specific references to a widely recognized handbook and a widely recognized acoustic guru. Ultimately, as everyone sees, the answer to the question asked in the original post about where good and bad locations to put the subwoofer is, as I wrote in my first post in this thread, "complicated."

Young-Ho

[bpape]

"In terms of formulas, the usual 1130/2f for a first-order mode does not assume both "perfectly rigid boundaries and perfectly rectangular spaces," but rather two parallel rigid surfaces. Obviously, the nature of those surfaces will shift the frequency downward, but the basic physics of standing waves still applies, or so it would seem."

Correct - but you're only talking about axial modes here.  I'm talking about the decay time, intensity and longevity of standing and travelling waves, etc. - which exist in a closed 3 dimensional space - like a listening room.  If you only had the 2 walls, there would be no tangential or oblique modes, an almost instantaneous drop to zero decay time, etc.  Add to that the absorbtion of the wall structure and what frequency it absorbs best at based on wall thickness, construction, damping, mass of the covering, etc. and it's not quite so simple to pinpoint things - hence the reason the paper I cited made expressed that caveat and did real world testing as opposed to just using the formulas. 


I didn't mean to imply that you were slamming Robin at all.  Sorry if it came across that way.  I guess my point was that you had implied (perhaps unintentionally) that I was merely trying to drum up business for a product and/or recommending the purchase of the ASC product - or - that I was trying to float a solution to a problem that didn't really exist.  I was simply responding that Robin had no 'dog in the fight' and had come to this conclusion of benefit on his own using what I'll agree was a commercial product - but hardly one designed for this purpose.  Part of the benefit he's hearing could absolutely be from isolation - and part of it could be from not exciting the vertical room modes in the same way as having it on the floor.  Most likely, it's a combination of both.

At this point I'll agree that there is simply a difference of opinion as to the efficacy of considering placement in the height dimension just as important as placement in the length and width dimension.  If things ever settle down a bit, I'll take some measurements and post the results so everyone can form their own opinion based on actual measured data rather than on speculation and theory.

Bryan

[Ethan Winer]

Ethan, You surprise me.  As many times as I've seen you post about how just a few inches can completely change the curve you hear... If you look at the distribution of the nulls and peaks:

Yes, we all know that the response changes significantly over small distances. But I have a lot of bass traps, and that greatly reduces the change. More so than adding mid/high frequency absorption reduces the changes at mid/high frequencies. Even with all my bass traps (43 now, plus two bass trap / diffusors), the bass response still changes a little around the room. We all know this is inevitable too. My point is that even though my own setup is fairly far from the ideal - whether one prefers 38 percent or 33 percent - the bottom line is the bass response and overall sound quality in my room are fabulous. So I'm satisfied, and I'm done tweaking.

Also, the 38 percent "rule" is purely theoretical. As we know now after my illuminating posts a few years ago at Recording.org, modes as measured can vary a lot from what's predicted due to wall construction and other reasons. So a rule like this applies only in a cement bunker. Anywhere else I'd say it's more of a starting point.

--Ethan

[jpv]

This is a great post so far. I have aquestion regarding the placement of a sub in the height dimension.
My room is 13.5 wide x 18.5 long and 10 feet height. My system is set up along the sort wall.
My question is my ceiling slopes up from 5 feet from the side walls to 10 feet in the center. Do I need to worry about modes in that direction. If so what effect does a sloped ceiling have on the sound. The rest of my room I have 3 corner bass traps and 4 bass panel traps, Broadband absortpion at the first reflection points.
John

[bpape]

Ethan, You surprise me.  As many times as I've seen you post about how just a few inches can completely change the curve you hear... If you look at the distribution of the nulls and peaks:

Yes, we all know that the response changes significantly over small distances. But I have a lot of bass traps, and that greatly reduces the change. More so than adding mid/high frequency absorption reduces the changes at mid/high frequencies. Even with all my bass traps (43 now, plus two bass trap / diffusors), the bass response still changes a little around the room. We all know this is inevitable too. My point is that even though my own setup is fairly far from the ideal - whether one prefers 38 percent or 33 percent - the bottom line is the bass response and overall sound quality in my room are fabulous. So I'm satisfied, and I'm done tweaking.

Also, the 38 percent "rule" is purely theoretical. As we know now after my illuminating posts a few years ago at Recording.org, modes as measured can vary a lot from what's predicted due to wall construction and other reasons. So a rule like this applies only in a cement bunker. Anywhere else I'd say it's more of a starting point.

--Ethan

I couldn't agree more Ethan.  Unfortunately, not everyone can have 40+ bass absorbers in their room    I also agree that the 38% is a starting point since room construction does in fact change the modal centers and how they interact.  I guess all I was trying to say is that if you look at the distribution of the modes and which harmonics we're dealing with, I've found that if you have to move away from the 38%, moving toward 33% is far preferable than moving toward 50%.

John.

With a peaked ceiling like that, it would be to your benefit to hang some absorbers up high covering that corners with their faces parallel to the floor.  It's still a corner and one that is right over your head acting like a horn.  It's not so much a modal thing as it is a focusing of sound in your case.

Bryan