Horse stall becomes a recording booth

Hi everyone. First time poster and I must say this forum is absolutely great! :D Been reading for weeks and have learned so much here. I've ordered Rod's book just to get up-to-date. I have a few other audio and home studio building books dated since 1995 and I'm sure technology has improved a bit since then. I finally have a property where I can build a studio, or part of one. Here in Missouri, we have a 4 acre plot in a housing subdivision and on it sits an Out building we call the 'Barn'. Aerial Google map photo attached. It's nothing like a barn inside though because it's completely finished basically. Concrete floor with outdoor carpeting, lighting, insulated, full HVAC, wood stove, nice furniture etc. It has a second story loft only over part of it which we use for storage. Part of which is the roof to what will be our recording booth. The main room is where the control room/area will be. At this time, since it is a multipurpose room, I can't finish it like a 'real' CR since we use it for full concert rehearsals and recreation area. I am currently underway with converting a corner of the building, previously a dirty 'horse stall/storage room' into a nice recording booth. GOAL Obtain 50+db reduction for this room Barn has a tin roof and 1x12 timbers on both sides of an insulated 7.5 inch space. (2-leaf) Accomplished by 6x6 posts with 2x4s nailed to the outside on which the 1x12 are nailed. 1x12 - 2x4 - 6x6 - 1x12 with insulation between leaves. My goal is to finish the room for high isolation as much as possible from: 1. Rain hitting the tin roof 2. Frequent trains which pass by within 1/10 of mile (65db) at last test outside, which really isn't too bad. 3. The loud Cicada's which occur every fall. The last recording project I had in the Barn, in the main unsoundproofed room, I had to use noise reduction tools to reduce their audibility. ENVIRONMENT/USE Current dB readings on a quiet night: Outside: 41db, inside unfinished room at this point as in pictures, 25db. This booth will be mainly for vocal and acoustic instrument recording. I doubt drums will ever be placed in there although it's possible. More than likely will be loud acoustic instruments such as trumpet, sax, group singers etc that reach beyond 90db. Kind of music is Gospel ranging from quiet to very upbeat but again, any genre can have loud instruments. Once it’s finished I’ll use REW on it to see what I ‘get to use’ or ‘have to live with’. :D :( Nearest homes are 80ft away. My house is 120ft. CONSTRUCTION Using ModeCalc, and the available space I've determined the best dimension for what I have is 117x130x93 in. (w10.8’ x d9.75’ x h7’9”). This will be the finished dimensions of the room. ModeCalc graph is attached. I’ve also attached a result of Knightfly’s RoomTune spreadsheet. I’m not sure how to interpret it but based on comments, I think it means these dimensions are practically ideal! Let me know if that is not the case. I thought the smoother the graph, the better. A surprise since I settled on these dimensions a while back. Waiting for new concrete floor to finish curing this week before we start the inside work. The plan, as in the attach drawings, is a two-leaf system all the way around. Hopefully images are clear. Two Inside barn walls: Dual 5/8 GB (outside) – 2x4 - RSIC channel dual 5/8 with green glue. CR side will have double stud wall plus RSIC and dual 5/8 GB. Outside barn walls: 5/8 Exterior sheathing, ¾ Ultrarock sheetrock to fill the 1.5in space, insulation, RSIC channel dual 5/8 GB with green glue Insulation will be Roxul 3inch ComfortBatt. Window: Angled 1/2 and 3/8 laminated glass. Shown in blue at the top of the diagram of the TOP view. Doors: solid core obviously. Not sure other than that using recommended sealing techniques here. Ceiling: Dual 5/8 GB screwed underneath existing ¾ plywood loft floor joists of second story, followed by Roxul insulation then RSIC channel and dual 5/8 with Green Glue. See diagram. Acoustic caulk all seams of course. Floor: Once concrete floor has sufficiently cured and moisture is at recommended maximum, around 4.5% I read, wood laminate will be put down. Room will be sufficiently ‘bass trapped’ in the corners and plenty of wall and ceiling panels using 703 or premade acoustic panels such as by GIK. Not yet decided. Some diffusion panels desired but primarily absorption. Don’t want the room to be totally dead. For the wood laminate we’ll need to put some self-leveling concrete to make it perfectly flat but can’t put the floor down for at least 3 months from what I read since the pad is 5 inches thick so the pad fully hydrates properly. If anyone has experience with that process and can confirm or say it can be done sooner I would love to finish the room before Feb instead of after. The existing corner barn door, shown in the diagram and photos, will be sealed off using a two-leaf design. The existing door is 1.5 in plywood and I'll add dual 5/8 or maybe single 5/8 to the inside. Insulation will fill to the 2x4 framing on the inside. BUDGET $3-5k QUESTIONS 1. Window construction: With a room-in-room design, you want to prevent any coupling of the walls so the window framing on the bottom which holds up the two panes of glass would normally be two pieces and joined by fiberboard and insulation. My question is since I can’t do a full room-in-room design and my CR-side double wall is already ‘coupled’, is there an acoustic disadvantage to have a single piece of wood for both window panes? See diagram Windows Closeup. 2. Does the double door air lock construction cause the doors to be too close (6-8 inches), even with insulation installed in all the right places? Other option is to create a ‘super door’ as found in the forum or perhaps in Rod’s book which I hope to have in a few days. 3. Should the outer leaf ceiling 5/8 sheets used to beef-up the 3/4 plywood second-story floor joists not be screwed but just held in by Battans and caulked? Seems I've read both ways. Sheetrock for the outer leaf on the walls everywhere else is screwed so don't know why the difference for the ceiling. My inner leaf is decoupled already on RC. The diagram and text on John's 'Recording manual' construction for ceiling shows 2 layers held against the second floor by wood battans with an STC of around 60, but no mention if it is screwed also. My concern is safety. I'm all for best sound isolation though, like everyone else. 4. Any other ‘glaring issues’ anyone might see in the design. Any input is appreciated. Thanks Tim

Got Rod' book in yesterday. Wealth of info. All my questions and more were answered there. 1. Even though I have no room in room design, there are two stud frames separating the windows so I will make sure there is no firm coupling between them during window construction per recommendation. 2. I'll be going with the double door design to try to approach 60+ 3. Beefing up the existing ceiling/loft floor, no GB will be screwed to the 3/4 plywood. I'll be applying 2 GB layers, greenglued together and sealed with Acoustic caulk, using 1x2 or 1x3 battans to secure them against the ceiling per recommendation. Tim

Change in plans. I'm no longer limited to keeping the 2nd story loft floor (existing ceiling), so that is being completely removed. I now have the options to make the ceiling whatever I want as we're rebuilding. Primary reason was joists were unevenly spaced, some constructed incorrectly, and were only 2x6s. We will be putting in 2x10s and doing it right at 16" OC. Since height can be anything I was experimenting with Bob Gold's calculator and Real Traps Mod Calc again. I'd like to raise it above the planned (finished height) of 7'9" to give the room more of a live feel with proper treatment since it's so small. With a much taller ceiling, using some diffusion and absorption up top, perhaps similar to the Bridge Studio live room with corrugated sheets or similar at least in part, absorption on walls and corner bass traps, I was hoping to approach this. I know the ideal dimensions for a room follow a ratio where the height is the smallest component generally however since sound doesn't know "up or down", I found what appears to be a good ratio of mode control with height as the biggest. Attached are results of Bob Golds output and real traps. Any thoughts as to if this is totally not a way to go for some reason? I've seen one picture of a pro studio where the live room definitely had the height as biggest dimension by a large amount. The dimensions I am considering is h11.75 x w9.5 x d10.69. Bob's calculates this as 1:1.12:1.23 and is basically all green. Attached is the output of these two calculators. We're actually starting on the ceiling tomorrow, tearing it down and beginning framing at the new height. This height requires 80 more Sabins to achieve RT60 than the original 7'9". My other option is to just raise no more than a 1 foot or so beyond which creates severe modal issues until you reach the 11+ft height. For the inner leaf and final interior layout I am using Sketchup for planning the rest. Thanks for any input. Tim

Hi Tim, and sorry for the major delay in any response on your thread! :oops: Welcome to the forum! :)

Concrete floor with outdoor carpeting,

The concrete flooring is great, but the carpeting has to go. It will do the exact opposite of what you need, inside your studio.

full HVAC,

Great! You can tap into that for your studio. You'll only need to build silencer boes and some ducting to make that usable for your studio.

Barn has a tin roof and 1x12 timbers on both sides of an insulated 7.5 inch space. (2-leaf) Accomplished by 6x6 posts with 2x4s nailed to the outside on which the 1x12 are nailed. 1x12 - 2x4 - 6x6 - 1x12 with insulation between leaves.

I don't see where the second leaf is in all of that. I see the tin outer leaf, then lots of different size framing and lots of insulation, but no second leaf?

Using ModeCalc, and the available space I've determined the best dimension for what I have is 117x130x93 in. (w10.8’ x d9.75’ x h7’9”). This will be the finished dimensions of the room. ModeCalc graph is attached.

Forget that: ModeCalc only shows you axial modes: it does not show you tangential or oblique modes, which also contribute substantially to overall modal response. Use only Bob Gold's calculator, or AMROC, or something similar that gives you a more complete picture.

Waiting for new concrete floor to finish curing this week

Hang on a sec! I though you just said: " it's completely finished basically. Concrete floor with outdoor carpeting,".... So why does it need another "new concrete floor" if there already was one, and it even had carpet on it already??? :shock:

Window: Angled 1/2 and 3/8 laminated glass.

You don't need to angle them for any acoustic reason, although you might need to for light glare issues. Angling glass REDUCES isolation between rooms, so if you do need it for light glare, then take that into account when you do the calculations for the walls. Ceiling: Dual 5/8 GB screwed underneath existing ¾ plywood loft floor joists of second story, followed by Roxul

insulation then RSIC channel and dual 5/8 with Green Glue. See diagram. Acoustic caulk all seams of course.

:shock: Ummmm.... that would make a THREE-leaf ceiling. That's not what you want! Two leaf, only two-leaf, and nothing but two-leaf.

Change in plans. I'm no longer limited to keeping the 2nd story loft floor (existing ceiling), so that is being completely removed.

Excellent! So you can get a really nice high ceiling now. - Stuart -

Thanks for replying Stuart. No problem in the delay. We're all busy with so many things, especially during the holidays I'm sure and there's so many posters to reply to. For clarification, the horse stall room is the only room getting an acoustic update. The small room in the diagram and in the photos. It didn't have any concrete floor. Just bare ground. Horses like it better that way. :o The main room, CR area, is the one with the concrete floor and outdoor carpeting. Not concerned about that one at this time. I use headphones as primary source of balance and checking mix elsewhere for now. My mix area will have to be treated at some point. Tracking room is main concern for now since we have no isolation anywhere for quiet recordings. The tracking room we're building here will have either stained concrete floor or we may go wood flooring when the concrete cures by Feb or so. Definitely no carpeting. For the leaves description, sorry about the confusion there. I typed the original post late at night so must have had a mental and literal typo or something (1x12 - 2x4 - 6x6 - 1x12 WRONG). The diagrams are basically correct although there have been a few changes. I'll be getting new pics, diagrams and finally a SKP file uploaded. For the two outside walls: 1x12 timber, 22ga steel sheet, thermal bubble wrap, tyvek layer, 5/8 and 3/4 sheet rock layers (leaf 1), 6x6 posts with 2x4 framing filled with Roxul (6" space), RSIC/hat channel, 2 - 5/8 sheetrock and GG (leaf 2). The steel sheeting is the prevent our multitude of squirrels from getting in. They chew right through everything to make the 'barn' a nice home for themselves. Not anymore! For the two inside walls: As in diagram, 2-3 GB layers, insulation, 2GB layers on RSIC with GG. For the ceiling, I am following Rod's book. I understand the concern of two-leaf designs. The tin ceiling is like 10 feet up from the second floor storage area. That floor will have 3/4 ply and 2 layers of 5/8 (the outer leaf). The tin ceiling is way above that. The same design as you wood have in a house when someone is refinishing a basement with an inner ceiling/layer, acoustic separation by RSIC or room-in-room, then outer layer, which is the occupied first floor 'beefed up with GB' as in Rod's book, which then has another ceiling above that, attic and final house roof. By that definition, basement studios end up with 4-6 leafs. I don't see a problem here. I'm primarily concerned with isolation from the loud rain/hail that hits the roof if I don't do this. Am I way off base here? Seems to be the same thing everyone is doing here. We decided we need the extra storage space from that second floor so not sure how high up we'll end up going with the ceiling but current designs put the "inner" ceiling at either 8.75ft or 11.5 ft. There'll be a floating cloud for ceiling treatment and lighting. There's all kinds of stuff put up there on the second floor. You never saw so much 'Diffusion' material. :o I did post the graph from ModeCalc, but yeah, I do rely on Bob's and AMROC more. Window will be 3/4" and 1/2", both laminated. Angled to reduce visible reflection but also from Rod' book and John's Recording manual it was recommended to reduce vibrations between the two panes I understood. I know there is no acoustic benefit in relation to preventing sound reflections into a mic. Thanks for the feedback. Tim

The main room, CR area, is the one with the concrete floor and outdoor carpeting. Not concerned about that one at this time. I use headphones as primary source of balance and checking mix elsewhere for now.

Ahhh, that makes sense. But when the time does come to do the CR right, then that carpet has to go... Despite popular belief (and myth!), carpet is generally not used as treatment in studios. Yes, you do see carpet in many studios, but it is there to HIDE the treatment, behind it. And it is proper acoustic carpet, which is transparent to sound, rather than typical commercial carpet, which isn't.

The tracking room we're building here will have either stained concrete floor or we may go wood flooring when the concrete cures by Feb or so. Definitely no carpeting.

Great! And if you go with wood, then do make sure that there are no cavities under it! That's why laminate flooring is the usual recommendation: it can look really good, and is laid directly on the concrete (with suitable underlay, of course). Other types of wood need air cavities under them, which entails the risk of resonance in the cavity...

For the two outside walls: 1x12 timber, 22ga steel sheet, thermal bubble wrap, tyvek layer, 5/8 and 3/4 sheet rock layers (leaf 1),

In that order? In other words, starting from the outside (facing the wind and the rain), you have your 1x12 siding, which is over the sheet metal, then you have bubble wrap, the Tyvek, then your two layers of drywall, and finally the framing to which all of that is attached? Right? Then on the other side of the framing, you have the clips, hat channel and two layers of drywall for your inner leaf?

The steel sheeting is the prevent our multitude of squirrels from getting in. They chew right through everything to make the 'barn' a nice home for themselves. Not anymore!

:) Makes sense!

For the two inside walls:

Whoaa!!! What "inside walls"? :shock: You already HAVE two leaves! You can't have any more leaves without suffering degradation of low frequency isolation...

As in diagram, 2-3 GB layers, insulation, 2GB layers on RSIC with GG.

That would give you FOUR LEAVES! :shock: Your low frequency isolation will be pretty lousy like that. The rule with studio construction is: two leaves, only two leaves, and nothing but two leaves. A one leaf wall limits you to Mass Law, which is not your friend, and multiply leaves (more than two) introduces the problem of increasingly higher resonant frequencies for the wall assembly as a whole, resulting in increasing poorer performance for low frequencies, and reduced overall isolation. This diagram might help: Going from left to right, the first wall (STC-33) is a typical uninsulated house wall. The second one ("STC-36") is what you have (conceptually): a stud frame with a leaf on each side (in your case, each leaf is built from several layers, which is fine, but the concept is the same). If you build another wall next to that, as you are proposing, also with stud framing and a leaf on each side, then you only get a very small increase in isolation. That's the case shown as "STC-40". Now take a look at the next one over: if you TAKE OFF one leaf inside the wall, your isolation goes UP considerably, from STC-40 to STC-50: That's a major jump: If you then TAKE OFF THE OTHER LEAF inside the wall, you get another INCREASE in isolation. now going to STC-57: And if you then use the stuff you took to add mass to the remaining 2 leaves, you get yet another jump in isolation, all the way up to STC-63. This is not intuitive at first glance, but is the gospel truth about how acoustic isolation works in real life. A 4-leaf wall is a really bad idea. I'd strongly suggest that you re-think your plans for how to build the studio! You DO NOT need the clips and drywall on the existing studs. If you already put them up, then take them down again. In fact, you do not need clips or hat channel at all! If you already bought those, then return them for credit. You are wasting your money there, since that is not what they are meant for. They are superfluous in a proper double-framed wall, which is what you are talking about. They are only needed for single-framed walls, which is not your case. All you really need to do, is to build your second stud frame an inch or so away from the existing frame, and with drywall on only ONE side of it, never on both sides. Since you are going to have several rooms in there, the above applies to each of those rooms: Each room is built as a separate frame with drywall on only one side. That's the way to maximize isolation while minimizing budget: proper fully-decoupled two-leaf MSM walls. Anything else will cost you more and isolate less.

For the ceiling, I am following Rod's book. I understand the concern of two-leaf designs.

Are you sure? :)

The tin ceiling is like 10 feet up from the second floor storage area. That floor will have 3/4 ply and 2 layers of 5/8 (the outer leaf). The tin ceiling is way above that.

Welllll.... strictly speaking, the tin is the outer leaf, since it is what faces the outside world. However, it is ten feet away, so it's not really an issue. So it is OK to consider the floor above you as the outer leaf. But saying that it is "3/4 ply and 2 layers of 5/8" is rather strange: I'm not sure how well drywall stands up to being walked on. I would suggest that you should just put down two or even three layers of plywood for your flooring. Unless you meant that you plan to have ply on top of the joists, and drywall below? But that would bring you back to the same issue of multiple leaves and reduces isolation....

By that definition, basement studios end up with 4-6 leafs. I don't see a problem here. I'm primarily concerned with isolation from the loud rain/hail that hits the roof if I don't do this. Am I way off base here? Seems to be the same thing everyone is doing here.

Here too you are overly complicating things, and spending way more than you need to. As you say, the floor above you will be your outer leaf, but only if it is a SINGLE leaf, with all the layers on only ONE side of the joists.

The same design as you wood have in a house when someone is refinishing a basement with an inner ceiling/layer,

Ummm.... not really: People who turn their basements into studios would take off the ceiling above them and use that drywall to beef up the flooring. They would NOT leave the ceiling in place, if they want good isolation, for the above reasons. Here's another image that shows essentially the same situation as before, but more clearly: Imagine now that you turn it sideways, so it is a floor/ceiling situation, instead of a wall.... The conclusions are obvious... :)

Angled to reduce visible reflection but also from Rod' book and John's Recording manual it was recommended to reduce vibrations between the two panes I understood. I know there is no acoustic benefit in relation to preventing sound reflections into a mic.

Angling glass reduces isolation, not vibration. Here's the issue: any two-leaf wall is a resonant system. It resonates at a fundamental frequency given by only two parameters: the total mass on each leaf, and the distance between them. If you increase the mass, the resonant frequency goes down, so the isolation goes up. If you increase the gap, the resonant frequency goes down, so the isolation goes up. The most basic goal is to get the resonant frequency as low as possible, because at that frequency the wall does not isolate at all: in fact, the exact opposite happens: it resonates, meaning that it not only transfers sound directly from one side to the other, but it also amplifies that sound as it does so! Therefore, the plan is to get the resonant frequency down way below the lowest frequency that you need to isolate. That means you want as much mass as possible on each leaf, and the biggest gap possible between them. Ok, so consider what happens when you angle the glass in a window: You reduce the gap! Along one edge of the glass, the gap between the two panes is much smaller than along the other edge, and much smaller than it would have been of the glass were not angled. So therefore, with a reduced gap, you now have a much higher resonant frequency at that point, and therefore greatly reduced isolation. Here's a couple of diagrams that might help to clarify: So if you need to angle your glass for light glare reasons, then fine, but you'll also need to compensate for the lost isolation by using thicker glass, or increasing the total wall depth so even then thinnest gap is still big enough. Or both. Windows are weak points anyway, for many reasons, so if you have to make them even weaker by angling, then you also have to work harder to compensate for that.

I did post the graph from ModeCalc, but yeah, I do rely on Bob's and AMROC more.

Did you notice on Bob Golds' results that you are failing one of the three BBC critical tests? And also your Bonello chart is not too happy... However, since you'll likely have more room than you had counted on due to the reduced overall thickness of the walls, you can probably adjust the dimensions to fix those rather important issues. By the way: Happy New Year! :) 2014 is just around the corner!!! - Stuart -

Thanks Stuart. Been a long time in replying. After we did some work into November of 2013, we had to stop for a while to plan and execute two, count'em, TWO weddings. My niece and nephew which occurred Jan and Feb 2014. So all studio construction stopped. Other delays postponed this project until later this summer when we finally started back up. :D With that, continued work on the design's room dimensions and interior design and construction continued. I've attached pictures to show progress to date. Almost all framing, wiring nearly complete etc. Quite a bit since first post. From my previous post I think we had a failure to communicate on one point. When I said "Two interior walls", I was referring to the two walls of the room which face the interior of the building (South and East) as opposed to the walls facing the building's exterior (North and West). The original post's diagram didn't really identify interior/exterior. You'd have to infer from pictures. This is a corner room in the building. Sorry if that came across as 4-leaf construction, a definite no-no. I have a definite 2-leaf construction here. 1x12 timber, steel, 2 GB layers, Roxul in 7inch gap, 2 - 5/8 GB and GG on Clips/Hat channel on the two exterior walls (North and West). The Sound/East walls have 2-leafs but different layers. Two GB+GG, Roxul, two GB+GG. I'll post more pictures but the HVAC is done and tested. Silencer boxes work well. No sound on the supply register at all. A Fantec FG6 runs the return vent and has a speed control for me to adjust the amount I wish on return flow. The whole barn runs on a 3.5 ton Carrier system supplying Heat and cooling. The main barn area and live room are not zone controlled. We decide to put a thermostat in the room which controls a remote 6 inch damper hooked to the main plenum so when the furnace continues running for the rest of the barn and the live room has reached temp, the damper closes or opens as needed. Works well and much less expensive than modifying the existing system to be zone controlled. The diagram shows the layout as before but there have been a number of adjustments from the original design. The final room dimensions are 10.64ft W x 9.66ft L x 8.19ft H. Using Bob Golds, all dimensions pass. The bonello could be better though. Note, this is a LIVE room and will be mainly used for vocals. As diagrammed, will put in bass traps in the corners but wall treatment will be decided more after an REW pass. There will be two ceiling clouds in the room, covering most of the area. See new diagram. Only 16 inches around the perimeter will have the ceiling exposed and track lighting and the two AC silencer box registers are in that area. The two boxes in corners showing the yellow insulation are the silencer extensions lined with John Mansville ductliner. In the diagram the ceiling clouds are the two gray boxes with 3 can lights down the middle of them. These will have roxul or 2in 703 and the top of the clouds was going to be open. QUESTION: I know this is considered room treatment and not room dimensions, but acoustically, if I put a hard back on the clouds, say 3/4 ply, will that have any affect on the modes at all, to some degree at least the same as having a lower ceiling since nearly the entire ceiling is covered? If I lower the clouds several inches more than planned, with the hardback of the clouds being at 7.85 inches, effectively lowering the ceiling height, the bonello charts smooths out quite a bit on the high end. Final ceiling height is 8.19ft (8' 2"). Pictures attached showing the difference between actual ceiling at 8.19 and 7.85ft. Will this happen? The hardback will have an affect but need your opinion on whether it will be worth it or not to do this. Thanks for any input. Tim

More pictures. The silencer boxes are constructed with 2 layers of 3/4 ply and green glued. 6 inch ducts feed into 6x14 registers over two 1/2 inch layers of duct liner.

It may be a little confusing from the diagram and pictures why the interior leaf east wall framing containing the window and door has no clips or hat channel while the other sides do. That wall is already isolated, screwed to clips/hat channel across the top attached to the 2x10 ceiling joists and secured to the outer leaf frame using 4 pac-intl DC04 isolators. Two layers of 5/8 GB and GG will be screwed directly to that frame, so no hat channel is necessary.

HVAC is hooked up to the silencer boxes and tested. Attached is a wide angle view of the area above the studio roof showing both boxes hooked up and the fantech FG6 used for the return vent. The silencer box extenders shown in a previous post go through both leaves but touch only the outer leaf framing. Backer rod and caulk will make sure the extender does not touch the inner leaf sheetrock once everything is in place.

I know this is considered room treatment and not room dimensions, but acoustically, if I put a hard back on the clouds, say 3/4 ply, will that have any affect on the modes at all,

That's sort of an in between question: part treatment, part dimensions! The answer is yes, it does have a useful effect. A hard-backed cloud placed at an angle can indeed break up the modal response to a certain extent. It's not as effective as an actual angled ceiling, of course, but it is still a useful tool. And as mentioned above, instead of just leaving the cloud flat, it is better to angle it, so that one edge is closer to the ceiling and the opposite edge is further away. The bigger the angle you can get, the more useful it is.

The hardback will have an affect but need your opinion on whether it will be worth it or not to do this.

Definitely worthwhile, if the cloud is large enough, and the hard back is dense enough. Your plan should work well. But by the same token, don't go nuts trying to adjust the Bonello chart! It's just a graphical representation of the mathematical spread of the room modes, on a musical scale. There's a point at which modes suddenly flip from being counted in one segment of the graph, to being counted in the next segment up or down, so the graph can actually jump from "good" to "bad" by just nudging the room dimensions by small fractions of an inch, when in reality that would make practically no difference at all to a real room. Your graph looks fine, either way, so I wouldn't sweat it too much. The angled hard-backed cloud will have good effects anyway, in other areas, even if the Bonello chart doesn't change much. - Stuart -