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Discussion Starter #1
Hello all you dedicated theater specialist!!!



I am in the middle of construction myself and actually should start a build thread but I feel I am too slow for that. Things were coming along until I decided to take on a new DIY build. I am planning on building some thinner mains.


Anyways, I wanted to get some quick advice on treating the first reflections in the my room. I have all over the forums trying to learn as much as I can in the limited amount of time that I have. I have a couple of ideas that I wanted to throw out there to see if I am on the right track.


Here's some pics

My room is approx. 12'X21'X8'



Close up of the right side. As you can see, I definitely need to address that window.



Kind of difficult to see but the side wall is framed with drywall installed on the outside



Picture of the rear portion of the room. The couches are just temporary until I decide on theater seating.



Big props to Brad Horstkotte and his thread for giving me good inspiration for my theater (Columns, and Furring strip fabric panels of the side walls). He has an unbelievable looking room.


As mentioned above, I plan on using furring strips on the side walls with fabric panels. This will allow me to put 1" linacoustics or Owens Corning along the side walls in any manner I please.


Where it gets a little quirky is the window that is right at the first reflection point. I thought of a way to where I might be able to use this to my advantage. This is my proposal:


Line the wall with furring strips as stated, frame and plug the window but in a manner to where I can use 3" OC in that frame area. That way I can get a little more absorption at the first reflection. then just continue my fabric paneling design as if the window was not there at all.


The beauty of this idea is that I could possibly compliment this on the other side of the room because I have virtually the same amount of depth at the first reflection point with the framed wall that is not drywalled. I could theoretically place strips of 3" OC in between the 16" spacings and then continue with the fabric panel method over that (no drywall needed).


Does this sound like a viable option???


I have read of buying Owens Corning that has a face on it and installing one face down and one face up and so on to prevent the room from being totally dead while still getting effective sound absorption. I figure at the first reflections I would want full absorption though. Mostly on the back wall would I probably play around with this idea.


Please don't be shy.......to reply
. thanks in advance


Please help BIGmouthinDC!!!!
 

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Your ideas are sound! I like the layout, it looks well thought out. And the stage,the rear riser very nice. I once had a theater with your rooms dimensions, i did enjoy that theater. It had one window at the front wall, what i did was to get some foam batting and plugged the window,covered it with black fabric. After that i covered the entire front wall with bass traps. Nice job!
 

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Discussion Starter #3

Quote:
Originally Posted by dragonleepenn /forum/post/20937712


Your ideas are sound! I like the layout, it looks well thought out. And the stage,the rear riser very nice. I once had a theater with your rooms dimensions, i did enjoy that theater. It had one window at the front wall, what i did was to get some foam batting and plugged the window,covered it with black fabric. After that i covered the entire front wall with bass traps. Nice job!

Dragonlee,


Thanks for the reply. I was thinking blackout cloth lining the furthest outside layer of the window and then using the 3" OC within a wooden frame. I would possibly staple the blackout cloth to a frame, fit it in there along with some felt to seal the light gaps.


From what I've read and heard, the window exposure is not bad for low frequencys because they have very little reflection off of windows. The bass just leaves the room.


This is why I didn't want to fully plug the window. The OC will handle the mid and higher frequency reflections and the low frequencies will penetrate that and (for lack of a better word) leave!!!



Unfortunately, I am unable to do bass traps on the front wall at all because I have two DTS-10s that fill virtually that whole nook space you see. I am cursed by the width (or lack of width) of my room.
 

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Quote:
Originally Posted by orcarola25 /forum/post/20938932


From what I've read and heard, the window exposure is not bad for low frequencys because they have very little reflection off of windows. The bass just leaves the room.


This is why I didn't want to fully plug the window. The OC will handle the mid and higher frequency reflections and the low frequencies will penetrate that and (for lack of a better word) leave!!!



Unfortunately, I am unable to do bass traps on the front wall

for the most part, yes...but understand that with regards to treating the 'first reflection point' you are attacking specular energy that can be modeled like light (hence, finding the geometric reflection point). in a small acoustical space (dependent upon dimensions), this will likely yield you down to 500hz where sonic energy behaves and can be modeled this way. while one does not break up a specular reflection in terms of frequency, the broadband absorber must be effective enough to fully attenuate the entire reflection (in gain) to the user's requirements (eg, -X dB). ~500hz (lower end of specular region) will still likely be reflective off of the window and your absorber should be sufficient and effective enough to attenuate.


below this region is the modal region, where LF (bass) will behave with wave properties. so, LF does not follow a 'reflection point' path like specular energy does - and thus, your window will not likely have a drastic effect on modal issues.


this is why there are two entirely different approaches to addressing LF modal issues (function as waves) and specular reflection issues (function/modeled like 'light').


just fyi -
 

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Discussion Starter #5

Quote:
Originally Posted by localhost127 /forum/post/20939220


for the most part, yes...but understand that with regards to treating the 'first reflection point' you are attacking specular energy that can be modeled like light (hence, finding the geometric reflection point). in a small acoustical space (dependent upon dimensions), this will likely yield you down to 500hz where sonic energy behaves and can be modeled this way. while one does not break up a specular reflection in terms of frequency, the broadband absorber must be effective enough to fully attenuate the entire reflection (in gain) to the user's requirements (eg, -X dB). ~500hz (lower end of specular region) will still likely be reflective off of the window and your absorber should be sufficient and effective enough to attenuate.


below this region is the modal region, where LF (bass) will behave with wave properties. so, LF does not follow a 'reflection point' path like specular energy does - and thus, your window will not likely have a drastic effect on modal issues.


this is why there are two entirely different approaches to addressing LF modal issues (function as waves) and specular reflection issues (function/modeled like 'light').


just fyi -

Thank you for the informative reply. What your saying is that my absorbers need to be sufficient enough to attenuate specular reflections down to around 500hz. Past that, no other treatment is needed at that point as the window itself will aid in the modal region. Did I get that right?


I guess the next question for you is whether or not my approach should be modified in any way. I would think leaving the window exposed (while controlling specular reflections) is somewhat of a dual purpose treatment.
 

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Quote:
Originally Posted by orcarola25 /forum/post/20939421


What your saying is that my absorbers need to be sufficient enough to attenuate specular reflections down to around 500hz. Past that, no other treatment is needed at that point as the window itself will aid in the modal region. Did I get that right?

what i was referring to was that below that 500hz mark (not exact but keeping it simple for sake of conversation) -- where LF starts to have wave properties, you won't be modeling the LF the same was as you do the higher frequencies with regards to 'reflection points'. so you won't have a 30hz wave acting as a specular reflection which would have a direct flight path from the speaker through the window. bass will not behave like the higher freq content that you model like light and as such, find geometric reflection points. if using porous material for LF absorption, you will need to attack in the corners.


it's more about the understanding of how the energy behaves within your room. specular energy behaves like light so you can model it and find geometric reflection points where energy will reflect off of a boundary (wall) and arrive at the listening position (like pool balls on a pool/billiards table; angle of incidence = angle of reflection). this is why one can use the 'mirror-trick' to get an approximation of where the absorber should be placed. but LF bass does not behave this way.

Quote:
Originally Posted by orcarola25 /forum/post/20939421


I guess the next question for you is whether or not my approach should be modified in any way. I would think leaving the window exposed (while controlling specular reflections) is somewhat of a dual purpose treatment.

every user has their own design constraints. if you want to build a broadband absorber for specular reflections that functions as a 'plug' into the window sill/frame that you can quickly install when listening (and easily remove when not), then that sounds like a good plan.
 

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Discussion Starter #7

Quote:
Originally Posted by localhost127 /forum/post/20939490


what i was referring to was that below that 500hz mark (not exact but keeping it simple for sake of conversation) -- where LF starts to have wave properties, you won't be modeling the LF the same was as you do the higher frequencies with regards to 'reflection points'. so you won't have a 30hz wave acting as a specular reflection which would have a direct flight path from the speaker through the window. bass will not behave like the higher freq content that you model like light and as such, find geometric reflection points. if using porous material for LF absorption, you will need to attack in the corners.


it's more about the understanding of how the energy behaves within your room. specular energy behaves like light so you can model it and find geometric reflection points where energy will reflect off of a boundary (wall) and arrive at the listening position (like pool balls on a pool/billiards table; angle of incidence = angle of reflection). this is why one can use the 'mirror-trick' to get an approximation of where the absorber should be placed. but LF bass does not behave this way.




every user has their own design constraints. if you want to build a broadband absorber for specular reflections that functions as a 'plug' into the window sill/frame that you can quickly install when listening (and easily remove when not), then that sounds like a good plan.

Ok. I understand now!!!
. Your were referring to two regions (model and specular) having totally different characteristics when interacting with the room. This requires two separate demands with regards to treatments.


I will probably be able to treat the back corners but I do not have a way to treat the front at all aside from 1" linacoustic. Not sure that would do much unless I was using dipole designed mains.
 

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I defer to the Acoustic gurus on the forum but the first thing that popped into my head when looking at the pictures is why not stuff that soffit with cotton and turn it into a bass trap. Instead of covering the soffit with a hard surface use fabric.


As for the window and going a little deeper for more absorption I don't have a clue how doing one side and not the other and having one side backed by glass is going to effect the balance of the sound-field in the room.


You may want to contact BPape and get his input, of course you should buy your cotton from him as well.
 

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Discussion Starter #9

Quote:
Originally Posted by BIGmouthinDC /forum/post/20944636


I defer to the Acoustic gurus on the forum but the first thing that popped into my head when looking at the pictures is why not stuff that soffit with cotton and turn it into a bass trap. Instead of covering the soffit with a hard surface use fabric.


As for the window and going a little deeper for more absorption I don't have a clue how doing one side and not the other and having one side backed by glass is going to effect the balance of the sound-field in the room.


You may want to contact BPape and get his input, of course you should buy your cotton from him as well.

I did think of that as an option. Before I pursue the soffit idea I want to wait on my measurement equipment to see how the low frequency is interacting with my room.


I want to push forward with the side wall reflections because I know for a fact they need to be addressed. I will try and get in touch with Bpape and see what he can help me with.


Thanks BIG!!!
 

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Discussion Starter #11

Quote:
Originally Posted by Dennis Erskine /forum/post/20945626


Don't know what you mean by "drastic"; but, the window is a low pass filter.

Dennis,


I am assuming you mean the window is limiting the possibilities of "bad" room gain consistent of a room (with no windows or concrete walls) with peaks and nulls caused by modal dispersion.


Now, determining the effect of the window within the frequency response or at the low pass is probably going to take some measuring.


Is that what you meant by low pass filter?
 

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Quote:
Originally Posted by Dennis Erskine /forum/post/20945626


Don't know what you mean by "drastic"; but, the window is a low pass filter.

i concur - but he will still likely have modal issues in the other two planes of the room, which would still require attention (if he is so inclined to address).


i would not insist that the window will solve the bulk of his LF modal issues in that small space ('drastic'), but if it does --- then all the more better for the OP !
 

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Quote:
Originally Posted by localhost127 /forum/post/20947882


i concur - but he will still likely have modal issues in the other two planes of the room, which would still require attention (if he is so inclined to address).


i would not insist that the window will solve the bulk of his LF modal issues in that small space ('drastic'), but if it does --- then all the more better for the OP !

Not sure what you mean by inclined to address these issues but please shoot. Which two planes do you speak of?


I am willing to address any issues. All a part of learning



Thanks for your input!!!
 

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What about using the riser as a bass trap.? Unfortunately that puts you a little further behind in the schedule for building but might free up more room versus having corner bass traps. It's something that I cannot do for my current room, but would like to do

with my next one.


Darren A.
 

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Orcarola,


If you do decide to start a theater build thread, I'd subscribe.
My room is similar to yours (a couple feet wider). I also have JTR speakers. Mine are the Triple12HTs, is that what you have? I also have a couple of Captivator subs. I haven't started work on my room yet, so I'd be interested on how things come together for you. Are you going to put your center speaker behind an acoustically transparent screen?


Will
 

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Discussion Starter #18

Quote:
Originally Posted by optoguy /forum/post/20950407


What about using the riser as a bass trap.? Unfortunately that puts you a little further behind in the schedule for building but might free up more room versus having corner bass traps. It's something that I cannot do for my current room, but would like to do

with my next one.


Darren A.

Do you mean fill the riser with something like OC 705 or Rockwool? My initial thoughts are what kind of performance gains I would be getting for the added expense (as opposed to corner traps). I was always under the assumption that "generally" trouble spots for modal waves occur in the corners of the rooms.


I am not sure if making the riser a bass trap would aid in addressing the main issues on the low end.
 

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Discussion Starter #19

Quote:
Originally Posted by localhost127 /forum/post/20949307


measuring and experimenting within your room is the best way to learn. take a look at Room EQ Wizard (free download):

http://www.hometheatershack.com/roomeq/

I have the program. I am just waiting on my mic to come in to get familiar with it.


I just figured I could pull some opinions of the room from helpful members who know a lot more on the topic then me. Just to ensure I am not completely off base in the determinations I have made according to the research I have done. You can only do so much reading in a day. A lot of people can't really afford trial and error.
 

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Quote:
Originally Posted by willscam /forum/post/20950428


Orcarola,


If you do decide to start a theater build thread, I'd subscribe.
My room is similar to yours (a couple feet wider). I also have JTR speakers. Mine are the Triple12HTs, is that what you have? I also have a couple of Captivator subs. I haven't started work on my room yet, so I'd be interested on how things come together for you. Are you going to put your center speaker behind an acoustically transparent screen?


Will

Hi Will,


I most likely will start a build. The project is evolving as I am going along. Those are the T12HTs in the picture. I am determined to do an AT screen because I personally prefer the sound of the entire front stage in the same configuration. Unfortunately, I have two DTS-10s that are going behind the screen as well that do not allow for this so I need to either have Jeff build some thinner cabinets (which will cost me money in the end) or possibly build a better set of mains with the money from selling the T12s.


This, along with a few other things on my plate makes my progress slower then usual. Thats why I haven't started a build thread yet.
 
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