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The JohnBomb build

16K views 104 replies 23 participants last post by  Elill 
#1 ·
Well, after a year of construction, I figure it's about time to show some results. We started a remodel in October of 2009 and finished this summer: the kids got a new playroom, and dad inherited the whole basement! Yes!


Of course, like everyone else here, I decided a little demolition was in order. I wish I had taken more pictures as I went along, but I was too busy chopping up 2x4s and MDF to stop and smell the sawdust. So, without further ado, here are some pics:


#1: Sorry, no predemo photo! (got lost)


#2-4: We now join our regularly scheduled program, already in progress! I have partitioned the long part of the "L" with the rear subwoofer closet (the back part of a double bass array- see here: http://www.avsforum.com/avs-vb/showthread.php?t=837744 )


5) A wideangle view of the back of the room, including curved soffits.


That's a pretty good overview for now. I'll go into much more detail with the design, goals, and problems soon.


Stay tuned!


John




 
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#2 ·
I remember that soffit.



I spy an SKB rack too!


Looks interesting - more please.
 
#3 ·
Thank you for bringing up that information on the DBA sub array. I definitely want to learn more about this as you progress and hopefully see the measured results when you cross the finish line!


Those soffits are unique. Can't wait to see the design concept come together.
 
#4 ·
Thanks guys! Whew... where do I begin... The problem with starting a thread a year into the build is how to organize the thing. While I ponder that, I'll show you what I've been working on for the past few weeks.


First, some background. My house was originally built in the late '20s or early '30s, and, needless to say, construction techniques were somewhat different than they are today.


The previous owner had taken the basement, initially unfinished, and turned it into a wonderful finished basement, with 8 foot ceilings, new concrete slab floor, and double wall construction. Since I pulled the drywall off in order to access the guts and make way for my acoustical treatments (I'll eventually get to that), I decided to "tighten up" everything as much as possible.


Pics#1-4 show the inside of the right sided theater wall after drywall and rockwool removal. Notice the diagonal siding. Outside, on top of that, resides the exterior siding. Not surprisingly, it acts like a sieve for my HVAC dollars.


Pic #5 shows the tightened result: OSB backed w/ liquid nails, secured w/ lots of screws, and finally sealed w/ foam and caulk. I then added new R13 and stapled down the Kraft paper. I didn't realize how much of a difference the staples made!


So what did I learn? The 3 forms of heat loss are convection, conduction, and radiation. Convection, that is the transfer of heat from hot to cold via air movement (for residential purposes), is the most efficient and therefore the most costly. These "infiltrations" absolutely kill your R value and have to be dealt with harshly. You can run your hand along the wall slowly and feel for any leaks. Kill those, and you're saving money.




 
#5 ·
John, I posted a comment about your cool soffits in another thread, but now I see you are using the DBA concept I have some questions.


The DBA concept has fascinated me since I read about it a few years back. As I understand it, you need a consistent rectangular room and mirrored placement of subs (both front and rear and with the mirrored drivers on the side walls) to set up a planar wave.


The question is that with such a set up I would assume that any bass treatment would actually be detrimental to the effect. Those beautiful soffits look like they could function as bass traps that would both absorb bass energy and make the room less than a perfect rectangle?


Another question regards EQing the result. Obviously the critical parameter is the delay to the rear subs. But does this setup preclude the use of something like Audyssey which through its use of IIR filters would mess with phase?


Anyway I'm subscribed and looking forward to watching your progress.


Cheers!
 
#6 ·
Hey John!


I guess I need to read about DBAs, before I can say something intelligent.


Right now, all I can say is that we have the same vacuum.



Subscribed!
 
#7 ·
Thanks guys! And now, on to design...


Once I knew that I had control of the basement, I felt like a kid in a candy store. I didn't do any extensive preplanning: no CAD, no sketchup, not even napkin chicken scratch. I just visualized as best I could some design ideas. That'll almost certainly bite me in the ass later one way or another, but hey, that's how I do it.


First, I had to settle upon room dimensions. Since the sidewalls and ceiling were already built at about 12 x 8 feet respectively, all I needed to chose was the room length. After reading a fair amount of info on ideal ratios for listening rooms (there are many good ratios) I decided that 19 feet would work well. It turns out that 8 x 12 x 19 feet is a pretty good ratio for the distribution of modal energy:

http://www.bobgolds.com/Mode/RoomModes.htm


ideal room ratio discussion:

http://forum.studiotips.com/viewtopic.php?p=5570


This would place the back wall just inside a window on the side wall. Because I don't plan on having more than 4 people in the room at any one time (my wife, me, and my 2 kids), this size didn't feel too small... not yet anyway.


With the thought experiment out of the way, it was time to start the rear wall, aka the front side of the rear subwoofer closet. I knew a while back that I had to take a shot at building a double bass array (DBA). But not just any DBA: I also wanted to incorporate large and low tuned designing (LLT) into the build. See this link for DBA discussion:

http://www.hometheatershack.com/foru...explained.html


The DBA will consist of two subwoofer closets, one in the front of the theater and one in the back, housing four 15" drivers and two 5x16 inch ports apiece. Each closet will be powered by a QSC 3602 amp, capable of up to 3600 watts total at 2 Ohms. If I design and build this thing properly, I'll be able to play reference levels (115db) flat to 10 Hz, with significantly attenuated room modes up to 70-80 Hz or so.


Of course, that all depends on how well I can tune it. Moggie, you're almost certainly right about the DBA and the effects of the soffits on bass attenuation. Those soffits are stuffed with lots of fiberglass and also alter the room geometry quite a bit. I'm going to have to play with EQ and probably phase and delay to get an optimized response. This whole build is one big science experiment for me, but as they say, no guts, no glory. At the very least, I think the soffits look cool, and that is a primary goal of mine for this build. Also, hopefully we'll all learn something about DBAs and what it takes to make them work.


More to come,

John
 
#8 ·
Why the curved soffits? Why not, I say. I had a 12" trunk line in the upper left corner of the theater, and I had to do something about it. It's wrapped in insulation, and probably measured about 15-16" in diameter total. A rectangle or square soffit would have been huge, and besides, I've always enjoyed looking at curves... after all, very few straight lines exist naturally.


So, going with the curve idea, I thought that I could kill 2, 3, maybe even 4 birds with one stone:


1) I like curves.


2) I could incorporate diffusion into the design (see below).


3) By stuffing the soffit with fiberglass, I could cut way down on the air noise in the duct.


4) By building a mirror image on the right, I could create a deadvent air return: see here: http://www.avsforum.com/avs-vb/showt...1256990&page=4 post #104. I used 12" concrete former tubes from Home Depot to form the scaffolding in which I ran 10" flex duct. I had to strip the insulation off of the flex duct to fit it into the tubes, but it worked out well. Very quiet!


5) Maybe good, maybe bad: lots of fiberglass inside the soffits makes for some bass trapping. However, I don't know what frequencies are attenuated yet- I'll measure later.


Here's how I built them. I had two 1x10" oak rails on legs that I had left over from a previous project. I joined them together at their ends to form a long, narrow rectangle, whose ends I made coplanar using 2 levels as "winding sticks." That served as my jig for framing up the soffits. See next post, image #1 for a partial view of the jig.


I decided to build the soffits as three separate frames per side and to stagger them about 5 inches apart. I figured that one long, curved soffit would look a little blah, and, more importantly, would be harder to build
.


For the first curve, I freehanded a 3 inch wide ellipse "rib" on some MDF, using a technique like this: http://www.mathopenref.com/constellipse1.html I then cut that out with a band saw and sanded down the rough spots. This was my template for the ribs that I made out of OSB: I attached this template to jigsawed roughcut OSB via three screws, and the ran it over a table router with a flush cut bit, such as this: http://www.woodcraft.com/Product/200...-CL-14-SH.aspx


After making about 9-10 of these ribs, I laid them out on the jig so that their convex sides pointed up. I joined them with roughly 2x1s that I cut down from 2x4s using deckmate screws. Once the frame was done, it looked sort of like an inverted boat hull.


Next, I covered the frame in plastic and placed upon it 1/4" drywall which I had soaked on one side with water, wet side down. The trick to bending drywall is to take your time! I came up with a pretty good, controlled way to do it: place levels on either edge, and slowly clamp them down until the drywall is flush with the frame. I let that sit overnight and then took it off to dry.


Then, I picked up the frame and hoisted it into position, tacking it down with clamps. Once I liked where it was, I thoroughly screwed it into place. I used a plum bob that I bought at home depot to check reference points on the floor, something like this: http://www.amazon.com/Stanley-47-969.../dp/B00009OYGP


The tough part about placing the frames on the wall was knowing what to use as a reference. If the room had been perfectly square, the it would have been easy, but since it wasn't, I had to go a bit by eye.


For the second frame rib template, I flexed a dowel to form a curve and then traced that onto MDF. For the third, I combined elements of both curves. The idea was to create three different diffusing surfaces, none of which was based on semicircles- I read somewhere that semicircles don't work as well for diffusion.




 
#9 ·
After I had the frames on the wall, I stuffed them with lots of fluffy fiberglass: some pink, some white (the white stuff is JohnsManville formaldehyde free). I wore a chemical spill suit and used a respirator. No itch, no coughing up blood! Finally, I lifted the drywall onto the frames and screwed them down. I taped and mudded the first to see how it would look and to see if I had the skill to sand curved drywall smooth. Answer: yes, I got it done (still some touch up left). Drywall is pretty forgiving: if you botch it, just remud and resand. The trick to sanding drywall: pay very close attention to each stroke once you get a high spot almost flush. Each stroke needs to have a purpose!


John


 
#11 ·
Love the curved soffits, very cool!
 
#12 ·

Quote:
Originally Posted by johnbomb /forum/post/19640654


This whole build is one big science experiment for me, but as they say, no guts, no glory. At the very least, I think the soffits look cool, and that is a primary goal of mine for this build. Also, hopefully we'll all learn something about DBAs and what it takes to make them work.

Cool, I love science experiments! Seriously I hope you can use a tool like REW and demonstrate how the DBAs work out before adding too much treatment and decor (like seats).
 
#13 ·
Thanks everyone for the very kind words! I've got about 10 days off coming up, so I hope to make a really big dent in my front speaker box construction. I've decided to go with an external "sheathing" wall to keep the box temps as close to the HT temps as possible. See this thread I started for more:

http://www.avsforum.com/avs-vb/showthread.php?t=1297500


My rationale is as follows: I'll assume an HT ambient temperature of 70 degrees at 50% humidity. According this dewpoint calculator below, I'll need to keep the temperature of the box greater than about 50 degrees to prevent internal condensation. With circulating air between within the channel created by the sheath wall and the box external wall, I think (hope!) this will work.

http://www.decatur.de/javascript/dew/index.html


Because concrete gets really cold in winter, I furthered the idea by adding an MDF floor to the box elevated about 1/2" above the concrete slab with 1x2s and cork underlayment to allow for a floor air channel. See image for cutaway view of floor proposal.


The more I think about it, maybe I should adhere the cork underlayment to the concrete with mastic instead of to the undersurface of the MDF. With the cork on concrete, it seems that the dewpoint temp would then occur somewhere within either the cork or the mastic, as opposed to between cork and MDF, if I build it as drawn. I'm all ears if someone has a thought on this one.


@Moggie: Oh yeah, I'll be going crazy w/ Room EQ Wizard before I build any more wall or ceiling. I'm currently reading up on SBIR and how to diagnose and then attack reflections through the use of the impulse response and ETC features of REW. If interested, start searching Gearslutz.com for lots of indepth discussion. Some brilliant folks like to post over there. When I finally get to that stage, I'll post lots of graphs and pics of what I do.


Thanks,

John
 
#14 ·
Made a bit of progress since 12/15/10...


Crappy image of the originally planned storage closet in the carport. This will become the speaker box for the front part of the DBA. At this point, it's a catchall for whatever we didn't want in the house...
 
#15 ·
I had to tear out part of the wall of this closet and bring it up to snuff. I took down the OSB and cement board and will hopefully reuse the cement board later. Man, this stuff just eats up time...




 
#16 ·
Fuse boxes exposed...

 
#17 ·
Got the fuse boxes covered. Check out the rubble... and the baby monitor!




 
#18 ·
Got the wall nice and tight, and I finagled the air return line into the half bath: air will pass from the HT, between the speaker box and its jacket wall, into the half bath- this will become clear later.

 
#19 ·
and now, some speaker box progress!




 
#20 ·
So, that room...is a speaker box?


And, I feel your baby monitor pain.
 
#21 ·

Quote:
Originally Posted by Neurorad /forum/post/19788804


So, that room...is a speaker box?


And, I feel your baby monitor pain.

Yeah, it's the biggest subwoofer box I've ever seen. It's so big, in fact, that it has its own low frequency room modes! I'll go into design/results detail once I have the whole thing up and (hopefully) running.


Gotta love the baby monitor... the good news is that my son learned to sleep during our remodel, so loud noise usually doesn't wake him up from his nap.


John
 
#22 ·
Been pretty busy w/ the subs. Here's a teaser of the description to come...


Hint: SBA, 4 different listening positions, no EQ



John
 
#23 ·
That peak at 12 Hz might loosen the Tapcons.



I hope to get over there soon to check it out in person.
 
#24 ·
Here are some pics of the speaker box construction. These first 4 show the actual woofer box construction: cutting the wall to make way for the port (5x16x29"!).


John



 
#25 ·
These next 2 pics show where I am as of 3/21/11: 1 panel to go- almost done!


John

 
#26 ·
These last 4 show close ups of the ductwork for the speaker box. The 1st shows the inline fan, and the last 3 show the room intake elbow encased w/ foam (Dow GreatStuff). I'm also building an egress door beneath the elbow (framing shown in pic #3).


John



 
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