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Discussion Starter · #1 ·
Hi Folks,


I'm getting excited as I stake my space out in the 3rd floor attic area for the dedicated HT room. Good news is that I'm going to be able to clear a 14' x 20' space. The not so good news is that because it's an attic, I'm dealing with roof angles on two of the walls.


Facing the screen, the right and rear wall will be vertical for 4' and then angle inward 45 degrees.


Two questions (one that was kicked around a little earlier)


#1. With the right and rear wall having to be 4' tall and then angle, does it make sense to do the same with the left wall even though it could be a straight 8' wall? I'm thinking yes for symmetry but want to get some feedback.


If I did this, I'd have 6' of horizontal ceiling that then slopes downward 45 degrees to 4' vertical walls for a total width of 14'.


#2. With angled walls such as this, does the "standard" accoustical treatment apply or do I need to alter from what's used on "normal" vertical walls?


Much thanks for any feedback.


J
 

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Ethan,


He's sitting at the corner of an attic so there will be 2 adjacent sides that are sloped walls.


That's a side bennie of making the other 'side' wall match the sloping one. You can seal it up square and then put traps, wire, etc in the false angle. You can make most of it 'hard' like the other side but expose pieces of it as traps.
 

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Discussion Starter · #4 ·
Quote:
Originally posted by bpape
Ethan,


He's sitting at the corner of an attic so there will be 2 adjacent sides that are sloped walls.
Thanks bpape,


Yes, you're correct. It's in the corner of a big attic area so two sides deal with roof angles. The way I've got it set up, it's the rear wall and the right side wall (facing the screen)

Quote:
[B}That's a side bennie of making the other 'side' wall match the sloping one. You can seal it up square and then put traps, wire, etc in the false angle. You can make most of it 'hard' like the other side but expose pieces of it as traps. [/b]
So you think matching the wall that could be 8' vertical to slope like the right wall would be the proper thing? Makes sense to me. Since I'll have to build the wall either way, I can make it however I want at this point.


But can you please elaborate on "You can make most of it 'hard' like the other side but expose pieces of it as traps. "?


Much thanks.


J
 

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Hey, your room sounds just like mine.


Check out my web page. I left the back wall and the right hand wall full height. I am glad I did. Now with the black fabric installed, the room looks great. Sound is awsome also. No funny peaks or nulls that are obvious to me and it is definatly not over damped to my ears. I just installed my 110 inch diag screen and it fit perfectly with only 1/4 inch to spare on each side. I will post some new pics soon. Now I only need to install the trim, paint the doors black and mount the pj.


Good luck on your project.

My theater
 

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JoeBryant:


I'm not sure what I'd do with your room.


I don't think it's shaped like PCARACER's room, since you have slopes on the rear and right, whereas PCARACER's slopes are on the left and right.


Symmetry is good.

Volume is good.

Usability is paramount.


From a usability perspective, is there a reason why not to symetrically slope the opposite wall? Walking room? Standing up at a seat?


What would the volume of the room be with and without the slope?


My favourite two easy books on room building acoustics are
Master Handbook of Acoustics and
How to Build A Small Budget Recording Studio From Scratch : With 12 Tested Designs

Which will explain RT60 and some things about what the effects of a room on sound are.


Acoustic treatment is like medical treatment -- there's little point in taking kemo therapy until you're sick. There's little point in putting random absorbtion up because it physically fits, since the frequency curve it targets is more likely to make the room worse than nothing at all. The books may give you some insight into what you can do with your room, and programs like ETF5 will help you diagnose after the room is built.


The rest of this post assumes you go with symmetry.


One possibility for the slope might be slotted absorbers. These would reflect the HF maintaining symetrical imaging, yet absorb the bass (modes). I think that normally slotted absorbers are better at mid frequencies, but if they are deep enough and filled with fluffy fiberglass pink, you might luck out.

But as for whether it would make the room sound better or not, I've got no rules on the topic I can offer you.


This guy's ceiling is symetrical, but the ceiling diffuser was interesting (scroll down a bit).
http://www.toddejones.com/hugebuilding.html


Slotted absorbers can be seen
http://www.saecollege.de/reference_material/ (click on left menu 'absorbers' and tab 'mid frequencies'. Don't use the formulas at this site, but click around for ideas)
http://www.johnlsayers.com/Pages/Bluebear.htm (The wall paneling isn't tight, there's slots that let sound through)


One thing with angled ceilings is that they can focus more reflected sound down to the listeners. You probably don't have the headroom, but some more angles might help create a bit more of a reflection free zone.
http://www.johnlsayers.com/HR/index1.htm
 

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When I said 'make most of it hard', I meant to cover most of it in drywall (a hard reflective surface.)


Bob is correct that you should check out where the issues are in the room before just throwing things up. Reflection points are always a good place from some absorbtion but bass trapping and RT60 (especially in your room) should be measured and then treated accordingly. Bob is also correct in pointing out that usability is of paramount importance. If you have to climb over chairs or do the duck walk to get to a seating position due to ceiling height issues, it really doesn't matter how good it sounds - you won't use it as much.


That said, most rooms can usually benefit from some broadband/ bass absorbtion. Corners are a good place for that due to efficiency. How much, what type, where are determined by what you need. I was simply saying that the 'false angle' provides a nice place for some of that without making it visible or taking up floorspace. Dennis recommends building columns for the same reasons. They offer a place for wiring, acoustic treatments, HVAC, etc. while keeping the look and feel of the room.
 

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Thought you folks would be interested in seeing some of the low order room modes for a cross-section of an attic room. In fact, this is for Joe's room. He asked me to have a look at it.

http://www.tmlaboratories.com/attic.jpg


- Terry
 

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Discussion Starter · #10 ·
Hi Terry,


Thanks so much for taking the time here. That's exactly the shape of my room. That's the shape you'll see sitting down in the seat looking forward and back.


I'm sorry though in that I really don't know what I'm looking at there with the colors. Can someone elaborate / translate?


Thanks a ton.


J
 

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The red and blue are high and low pressure areas. Or vise-versa, since during every cycle of the room mode, they change places. Green is neutral pressure.


If this had been a rectangular room, the modes wouldn't show these interesting radial symmetries.


- Terry
 

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Discussion Starter · #12 ·
Quote:
Originally posted by Terry Montlick
The red and blue are high and low pressure areas. Or vise-versa, since during every cycle of the room mode, they change places. Green is neutral pressure.


If this had been a rectangular room, the modes wouldn't show these interesting radial symmetries.


- Terry
Thanks Terry,


Any ideas on how I should accoustically treat this room differently from a "normal" rectagular room?


Are these radial symmetries a good thing or bad thing or neutral?


Or I guess the more bottom line question, am I heading for trouble with a room of this shape?


Thank you.


J
 

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Quote:
Originally posted by JoeBryant


Are these radial symmetries a good thing or bad thing or neutral?


Or I guess the more bottom line question, am I heading for trouble with a room of this shape?
Neutral -- nothing to worry about. Acousticians like to discuss these things (FEM and BEM models) in the same way doctors like to discuss x-rays. But there's no cause for concern by the patient in this case! :)


- Terry
 
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