# Bass Trapping in the Proscenium?



## YW84U (Apr 29, 2007)

I'm in the throes of finishing off my stage/proscenium, and have been anguishing over the following idea:

First, here is a photo of what I am working with:










There is a Paradigm PW1000 sub in the bottom left corner (only place it could go...), with two Monitor 7's about 42" up in the columns. CC270 sits up top, angled down towards the listening positions. 3 can lights generating a modest amount of heat. The depth of the columns et al is approximately 24" for the shadowbox, and extends a bit further due to the 30 degree angle on the column faces. Room dimensions are 12.5w x 19 d x 90 in h. There is also a 28" wide door just to the side of the right column as well.

After tons of reading, I have convinced myself that treating these areas is a must-do! What I was thinking, is by using whatever amount of the structure that is now open, and placing Roxul Mineral Wool (no OC703 around here) to fill most if not all of the cavities. This would be in an attempt to 1) create bass trapping and 2) deaden the front wall to improve imaging 3) treat beside/behind the mains to help combat SBIR, as things are in there fairly 'snug' :whistling:


The question: On the bottom right, would I be better to stack triangles there, or would it serve better to just fill the entire cavity with "rectangular' pieces stacked? The majority of the traps I've seen are the triangle style chunks. Same token, is there a benefit to filling all of the cavities before my fabric panels go up?

I took a test drive with REW/BFD the other night, and made my very-firstest (yup, I've got kids!) graph. Not too telling, as I'm not 100% convinced that I did it right yet! (I ran it through the BFD instead of via the AVR....my bad...)










I'm still getting used to the BFD and will be setting filters as I progress. I'm also planning to treat the first reflection points with the mineral wool also, encased in panels I have yet to build...

Just FYI, the rear of the space looks like this:










so the option of trapping there is not so good. Mind you, I have storage behind the louvered bifolds on the right, and can easily place absorption there and/or in the equipment closet.

Any guidance/suggestions/opinions are greatly welcomed and appreciated!

Thanks in Advance,


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## bpape (Sep 14, 2006)

Down low in the front is a good place for broadband bass control. 

Also, if you can go up high along the ceiling for the full space depth wise behind the screen wall that will help too.

Bryan


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## YW84U (Apr 29, 2007)

Thanks Bryan!

So complete filling of the cavities will be on my list this weekend (save and except for just around the screen can lights for heat dissipation).

I was also thinking, when addressing the first reflection points, of constructing a pair of 'clouds' to hang for the centre channel along the ceiling between the overhead lights. What I'm kicking around is building two trapezoidal-shaped panels deep enough to hold the Roxul, and 'overlap' them - sort of like tipped over dominoes - angling down towards the stage by a few degrees but not so much that they block the projection. They would be about 5 feet long, 2 feet wide, and overlap about 60% of each other. Am I correct in the belief that not only will this address the reflections, but due to the overlapping and subsequent increase in depth of absorption, that this will also add to the control of the bass frequencies? Will this be overkill and adversely affect the centre?

As well, for the other reflections, place two small 2x2ish panels L/R on the ceiling for the mains, plus the 'usual' panels along the side walls.....

Am I going down the right path?


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## bpape (Sep 14, 2006)

I must be dense today - I'm not at all understanding what you're thinking of. 

I'd just do the lower section and up by the ceiling. The rest of the wall should be maybe 2" thick 3lb-4.5lb mineral wool if you can't get 703.

You can also do the side walls behind the false area in some 4"

Bryan


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## YW84U (Apr 29, 2007)

Sorry Bryan, my bad.......sometimes what looks okay in my head loses cohesion while articulating it 

This better represents what I was contemplating:



















The two gray funky looking panels are what I was thinking of building with about ~3 inches of Roxul each. Those would then be flanked by regular flush-mounted panels 2ft x 2ft to treat the first refections from the mains.

And just so I'm certain of your direction, I would stuff these areas complete with the mineral wool(pardon my photshop skills!!):










And then go on to place 2" thick wool against the only the two wall faces behind and beside the mains as so:










Hope this helps to better visualize where I'm at , and I very much appreciate your assistance!!!


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## YW84U (Apr 29, 2007)

Oh, as well, I apologize for breaking some of the rules....



> - Don't put a sub in a corner if you can help it. Almost never is this even close to the best place for a sub. While it will yield the most sheer output, it will also yield the least smooth frequency response curve.
> 
> - Don't force too big a screen into a room. This causes you to compromise on seating and speaker positioning. Set the seating right FIRST, then look at the appropriate screen size for that viewing distance that still allows good speaker placement.


I embarked on this project before I read enough!! :reading:


I wear the Cloak Of Shame :nono:


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## YW84U (Apr 29, 2007)

The latest edition:




























I hope I'm on the right track.....I'll have to pick up some more Roxul to finish off the upper areas as well as the left main. I'll try and post a graph for if anyone is curious as to the impact of this experiment


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## bpape (Sep 14, 2006)

Yup - you're on the right track. You can hang the cloak back in the closet 

BTW, whatever part of the white wall you're not going to project on should also have absorbtion on it.

Bryan


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## YW84U (Apr 29, 2007)

[Cloak]

The white wall comprises the entire projected image, save and except for a ~3 inch border.....

[/Cloak]

:R

An AT screen and reconfig may be in my future, but that will be quite a ways down the road (the Mrs agreed to do this project **ahead** of the kitchen remodel, so I don't want to burn any bridges!!)

Tx Bryan!


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## tonyvdb (Sep 5, 2007)

Hi Tom,

Bass trapping is not my specialty but just wanted to say that is quite the room you have. What size screen is that? I'm impressed.
I have to convince my wife to let me raise my rear seating like you have done.:unbelievable:


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## YW84U (Apr 29, 2007)

Tx Tony! It's been one year + 2 months of DIY building so far......I'm so very glad the Mrs is supportive of my hobbies! 

The screen is 16x9 at 138" - comprised of drywall, primer, and some topcoats of what could be considered Behr 'silverscreen' flat paint. First row seating sits at 12 feet, second at 17, and is on ~13" of riser. From my experience, the back row seems to be the most popular (even though the best audio is geared towards the front). I would encourage you to consider incorporating a riser if you can - it certainly adds to the cinematic 'feel' overall.


If you're curious about the birth of this project, I've got a build thread over here:

http://www.avsforum.com/avs-vb/showthread.php?p=8715622#post8715622

I plan to post the same info over here in the construction forums once I get a chance.

Back to topic, tonight I finished off the rest of the Roxul into all of the cavities. After a couple of test movies/songs, I've come to the following conclusions:

#1 - My God, that sounds better. Waaaay better! Deadening the front wall is a must for anyone. Imaging is vastly improved.

#2 - I have surrounds in the rear!! I'll have to recalibrate them, as they seem like they are now at +15 over the mains.

I haven't measured the response difference with the trapping yet, but subjectively, I didn't realize just how such a minor change could reveal huge results.

Now onto the panels for the first reflection points.....this just keeps getting better and better!

Again, thanks everyone for their advice and input!

Cheers,


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## bpape (Sep 14, 2006)

Bravo. Another convert to the dark side. 

Yes - getting the room under control makes a big difference. 

Bryan


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## Guest (Sep 24, 2007)

Lovely room Sir, I may have to steal some of your ideas if I may!
regards


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