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Acoustical Treatments Master Thread - Page 223

post #6661 of 10217
12 inches by 12 inches by what?
post #6662 of 10217
12x12 bass traps might help a little if they're at least 4 inches thick, but it's not a real solution unless you have like 20 of them.

--Ethan
post #6663 of 10217
Quote:
Originally Posted by nathan_h View Post

12 inches by 12 inches by what?

By a 3rd row bar!
post #6664 of 10217
I need advice. I moved and am setting up an new HT.

Room is 17'3" front to back, 19'2" wide, 9'10" tall. Drywall, perfect rectangle. Only openings are 6' wide glass doors on each side wall, centered on the L and 1' forward of center on R. I plan on treating these with 4" of 703 for 1st reflections and bass trapping. Also treating the ceiling 1st reflection with 2" of 703. Best seats have heads 6' from rear wall, 11' from front.

Equipment: Lexicon DC2, Atlantic Tech 450 LCR, side and rear surrounds. 2 M+K 350 THX subs that I will place where advised, but an favoring the midpoints on the front and rear walls with time delay correction.

The screen is 10' wide and flanked by velvet curtains so none of the front wall will show at all and I can do any treatments so they will be invisible.

Years ago I built 3 DIY "tube traps" 18" diam. 8' tall. fiberglass insulation sandwiched tightly between wire cylinders, hollow center. I dont know if these are still considered good or if the 4" thick flat panels of 703 are better. I would still use them somewhere, as it seems the advice here is "more is better."

Corners - is the superchunk method worth it or are flat panels with air gaps (or with loose fill behind) better. I read all I could, and Ethan says at one point that the air gap is better because there's no energy to absorb at the wall, but in another place he seems to say better performance could be gained by filling the area behind a corner base trap. I think these statements may have been years apart.

Superchunks - if the best DIY bang for the buck, is it better to have the 24" wide go floor to ceiling or the 34" wide just do the 8 corners, with a gap in the middle. This is a cost question, as both cost the same but the 34" size would put more mass in the 8 corners.

Wild idea - carpet the entire front wall. I found an infinite supply of used carpet, and could put it 2-3 layers thick on the entire front wall, either on the wall, or hanging 3-4" off with an air gap. I could also use rolled pieces up to 12" rolls all along the floor at the front walls. None of this would be seen, so color or style wouldn't matter, and I could add later as needed. I thought about how much sound the carpet absorbed when walking in the store between the aisles. Would this work? Its free, and I could never afford 703 in those areas.

Finally, need advise on where to place the side and rear surrounds. Is it a obvious as 2 on the side walls as far back as head level and 2 on the rear walls? Any advice there?
post #6665 of 10217
Filling a corner solid is better than a flat panel straddling the corner, but only a little better. If the cost of materials is not a concern, go ahead and fill the corner. Otherwise don't bother, and instead use the same amount of material to have more bass traps straddling additional corners.

--Ethan
post #6666 of 10217
So, is it better to do the entire corner (where walls meet - about 10' tall) floor to ceiling with the flat trap, or just the 8 corners (where floor or ceiling and 2 walls meet) with triangles? From reading your (and other) site, I would guess do the corners heavier.

For the same money, I could do the top and bottom 2' with 34" wide 703 or the top and bottom 4' with 24" wide 703 in triangle chunks. Which would be better bang for the buck?

If needed, another $70-80 would get me 34" wide triangles covering the top and bottom 30"...again, where's the happy medium?

I would do all 8 corners the same. I can afford the 34" in all 8 corners, but is 24" tall enough or does it need to be taller? For another $70-80 I could make all 8 corners 34" wide and 36" tall.

I'll try to get your opinion on this part first before asking about other ideas...I realize I asked a lot at once.
post #6667 of 10217
Quote:
Originally Posted by nathan_h View Post

12 inches by 12 inches by what?


So are you saying I didn't give enough info??? LOL...

Room is irregular as you can see. 50' long by 18' in most areas and 22' in the widest. I am doing BTs in the front corners...1" on the false wall and along the sides from floor to soffits as drawn... I am going to add a 12x12 bt in the corner of the bar area.... 4" on the back wall...

My problems is the floor is tiled, and along one side I have a large sliding glass window and then at the end of the room 3 large bay windows that will have stones around them...light is not a problem....

So I need all the help I can get. I am also going to punch a bunch of holes in the riser that is build in chambers the largest is half of the riser and then the next 3 each half of each other...I know this can be tricky.... I may also if I need the extra help knock some 8"x8" holes all around the soffits that are filled all the way up with insulation and then put some type of decorative cloth over them...

My question was for under the 3rd row bar which is about 11'L... because I will have some pictures on the back wall I wanted something under there to catch any rebounds so to speak.....

Thoughts?
LL
post #6668 of 10217
oh...and the darker lines on the sides of the theater are where the 1" is and I am also going to go with 2" under bar.
post #6669 of 10217
I would say make the stuff on front and side walls thicker, but -- especially on the side walls -- don't cover "everything". Use the mirror trick on the side walls. You'll still end up with a lot of coverage but less than you are planning. Making the panels thicker will do a better job of consistently treating the sound over a broader range of frequencies, instead of just killing the high end and air. And covering less wall will leave some liveliness in the room.

On the back, if you can leave that open to the other area (which I think is your plan) I would not worry too much about panels. That much space is even better than panels, IMO.
post #6670 of 10217
Anyone ever think of hanging mult layers of old carpet on the front wall? I have found an infinite supply of free used carpet, and my front wall is completely hidden by screen and velvet curtains, so nothing shows. I would put 3-4 layers thick, nail gun the top to a 2x4 from the side wall to the screen, and hang the 2x4 from the wall or ceiling joists. Simple and easy to adjust the air gap behind from 0-X inches. I could cover floor to ceiling...go stand in a carpet store and listen as you move near rolls stacked up, impressive quietness. This could be a free DIY addition.

The other thing that's cheap for a front wall I thought of (using Bob Golds absorbtion coefficients) was unfaced R38, 12" thick fiberglass batts on the whole wall. Covered with a cheap sheet to keep fibers from flying free, still behing the velvet curtains. The absorbtion coefficients for this is far more than any of the fiberboards (Rockboard 60, 703, etc, even at 4") and its cheaper by far also (although not free like the carpet).
post #6671 of 10217
Quote:
Originally Posted by Jeff Smith View Post

So, is it better to do the entire corner (where walls meet - about 10' tall) floor to ceiling with the flat trap, or just the 8 corners (where floor or ceiling and 2 walls meet) with triangles?

What matters is the total amount of corner surface that is covered. Also, a rectangle room has 12 corners, not just 4. The more total corner surface you cover the better. When you treat an entire corner, such as where two walls meet from floor to ceiling, you are also including the tri-corners. So that's the way to think about this.

--Ethan
post #6672 of 10217
So I'm still not clear. I know it has 12 corners, and 8 trangle corners (never thought 4m of either).

Given a budget which can purchase a fixed amount of 703 or rockboard, better to concentrate heavier on the tricorners, or lighter and extend down thw walls from the tricorners. ceiling/wallfloor corners are out-WAF, and the front floor is hidden, that's ok.

How about carpet?
post #6673 of 10217
This is impossible to answer without 1) knowing the total amount of corner surface, 2) the total amount of 703 you can afford, and 3) being there to try different 703 placements while measuring the results. Again, if you can cover the entire length of all junctions with 703 at least four inches thick, that's what you should aim for. If you can't afford that much 703 now, do only some corners completely and plan to do more in the future.

--Ethan
post #6674 of 10217
Quote:
Originally Posted by Jeff Smith View Post

I just reread Bob Golds absorbsion coefficients. It looks like a single 12" deep batt of "fluffy pink" OC R38, mounted on wall with no gap, absorbs better at allmost all frequencies than 703. Why not just use this? Cheaper, and I could cover all the front 4 corners and the soffet over the screen, and, in reality, the entire front wall that isnt taken up by the screen for much less than 703. None of this would show, and I would still run 4" 2' wide, floor to ceiling rear corners like you suggest-as they would show.

Other than more pleasing esthetics, why not go this route. Its far cheaper, and (if you believe his numbers) a better absorber. I know it's less dense but the thickness seems to make up for it. Again, this would all be hidden.

A 6" thick OC 703 on wall absorbs more than the 12" of "fluffy pink" on wall.

EDIT: How did my post get ahead of yours??? I must have read your mind!
post #6675 of 10217
I just reread Bob Golds absorbsion coefficients. It looks like a single 12" deep batt of "fluffy pink" OC R38, mounted on wall with no gap, absorbs better at allmost all frequencies than 703. Why not just use this? Cheaper, and I could cover all the front 4 corners and the soffet over the screen, and, in reality, the entire front wall that isnt taken up by the screen for much less than 703. None of this would show, and I would still run 4" 2' wide, floor to ceiling rear corners like you suggest-as they would show.

Other than more pleasing esthetics, why not go this route. Its far cheaper, and (if you believe his numbers) a better absorber. I know it's less dense but the thickness seems to make up for it. Again, this would all be hidden.
post #6676 of 10217
Quote:


How did my post get ahead of yours??? I must have read your mind!

It's that international date line thingy between the two of you.

His today is your tomorrow, so you saw the post before he posted it .. that time warp will get you everytime. I have that same issue with my clients in OZ. They send me comments on my design ideas before I do them. Great time saver.
post #6677 of 10217
Quote:
Originally Posted by Jeff Smith View Post

I just reread Bob Golds absorbsion coefficients. It looks like a single 12" deep batt of "fluffy pink" OC R38, mounted on wall with no gap, absorbs better at allmost all frequencies than 703. Why not just use this? Cheaper, and I could cover all the front 4 corners and the soffet over the screen, and, in reality, the entire front wall that isnt taken up by the screen for much less than 703. None of this would show, and I would still run 4" 2' wide, floor to ceiling rear corners like you suggest-as they would show.

Other than more pleasing esthetics, why not go this route. Its far cheaper, and (if you believe his numbers) a better absorber. I know it's less dense but the thickness seems to make up for it. Again, this would all be hidden.

You are right , it's the rigidity and relatively less bulky nature of the 703 which make it the more popular choice, not the superiority of 703's acoustic properties. If you have space and a way to contain it without solid covering for a foot thick / deep of fluffy pink that's not a bad choice.
post #6678 of 10217
Quote:
Originally Posted by dennis erskine View Post

it's that international date line thingy between the two of you. :d

his today is your tomorrow, so you saw the post before he posted it .. That time warp will get you everytime. I have that same issue with my clients in oz. They send me comments on my design ideas before i do them. Great time saver.

lol :d
post #6679 of 10217
Just like you leave from Tokyo on evening and land in LA at 1100 AM same day, earlier than you started.
post #6680 of 10217
Quote:
Originally Posted by nathan_h View Post

I would say make the stuff on front and side walls thicker, but -- especially on the side walls -- don't cover "everything". Use the mirror trick on the side walls. You'll still end up with a lot of coverage but less than you are planning. Making the panels thicker will do a better job of consistently treating the sound over a broader range of frequencies, instead of just killing the high end and air. And covering less wall will leave some liveliness in the room.

On the back, if you can leave that open to the other area (which I think is your plan) I would not worry too much about panels. That much space is even better than panels, IMO.

I'l LOVE to not have to order that much 703 but I worry with the tile and the soffit adding more corners...add in all the glass, stone work around the windows and irregular shape...I'm worried what you are suggesting isn't enough! Also I didn't put in the plans but I have 2 columns that stick out about 6" on the sides and they would about half way in the path of the "mirror" trick....

any thoughts out there to this?
post #6681 of 10217
Quote:
Originally Posted by FuzzyZipperbaum View Post

I'l LOVE to not have to order that much 703 but I worry with the tile and the soffit adding more corners...add in all the glass, stone work around the windows and irregular shape...I'm worried what you are suggesting isn't enough! Also I didn't put in the plans but I have 2 columns that stick out about 6" on the sides and they would about half way in the path of the "mirror" trick....

any thoughts out there to this?

Those columns blocking the "mirror" trick would similarly block the sound reflection. The "mirror" trick will show you how much.
post #6682 of 10217
Quote:
Originally Posted by erkq View Post

Those columns blocking the "mirror" trick would similarly block the sound reflection. The "mirror" trick will show you how much.

If you consider the column just a part of the wall and not an obstacle, it will work just fine. There have been several designs where the column is right in the "middle" of the primary side wall reflections, and that's ok as long as it's keep in mind that the column will have to be treated as well. This can be done easily without making it look like it was treated. It all depends on how the columns are designed. Best wishes!
post #6683 of 10217
The plan has always been to cover the columns for that reason...I guess the question I am wrestling with is do I go with 703 2"thick 54" up and leave an untreated wall to the soffit or just stick to my original plan and do 1" all the way up.
post #6684 of 10217
Quote:
Just like you leave from Tokyo on evening and land in LA at 1100 AM same day, earlier than you started.

I had the opportunity years ago to fly the Concorde from London to Washington, D.C. I really like that arriving before I left thing.
post #6685 of 10217
Quote:
Originally Posted by FuzzyZipperbaum View Post

The plan has always been to cover the columns for that reason...I guess the question I am wrestling with is do I go with 703 2"thick 54" up and leave an untreated wall to the soffit or just stick to my original plan and do 1" all the way up.

Hi Fuzzy,

You can actually design it so that the fuzzy stuff is flush with the column edges inside the column face. If you do that, you could do whatever you wish, but I would likely go most of the way up. Thickness is dependent on what you are trying to target, but I generally use 2". My suggestion though on using strictly broadband absorption is that it will likely not produce the sound you may be after. I would suggest something along the abfusor idea. Best wishes!
post #6686 of 10217
Below find a cross section of the equipment rack for my planned theater.

The rack is built into the wall of the theater. The backend of the rack lives in an adjacent alcove. The backend of the equipment rack will be enclosed by a cabinet.



I'm trying to accomplish two objectives simultaneously. Cool the equipment in the rack and get some air changes in the theater.

On the very left you can see the back/side of a maple facia for the equipment rack. Then the rails to which standard trays will be bolted. The rack cavity where the equipment will live. Towards the top there is a serpentine air path winding its way through 3 layers of 1 inch 703 like fiberglass. Although not shown, the walls of the cabinet will also be lined with 703.

At the top is a Panasonic bathroom fan/air mover. The air mover vents out the top of the cabinet in the alcove.

The thin black line attempts to show the basic airflow.

The theater is ~2700 ft^3. The larger Panasonic fans claim 130 cfm even with significant backpressure. 2700/130 = 20 minutes/air change, or three per hour. Given this type of airflow, I'm not worried about equipment overheating.

The alcove into which I'm going to dump warm, humid theater noise laden air is rarely occupied. Its more of a service area than a living area. It is also quiet. I'm not so worried about impacting this area, or about noise from this area impacting the theater.

Fan noise raising the noise floor of the theater may be an issue. The Panasonic fans are alleged to be quiet, but this is as applied to a bathroom, not a home theater. I'm expecting (hoping) the circuitous, fiberglass lined air path will aborb most of the fan noise.

Any comments about my contraption?

Will I achieve my objectives?

Any ideas how to make it better?

Thanks.

llj
post #6687 of 10217
I can offer some info on the fan as we have the 240cfm in our bathroom. It is recommended to install the fan 8' downstream (using insulated duct), so I would imagine that is where they get the db rating from. I would try to find out the actual dbs at the mouth of the fan. Or maybe you can mount the fan further away from the cabinet? I would also anticipate a little rattling at a later date, just in case........
post #6688 of 10217
I see a number of issues with your plan and here are some of the reasons why I would not recommend this route:
- Why put the "muffler" inside the equipment rack instead of building it on top to conserve precious rack space?
- The idea of lining the inside of the cabinet with 703 as compared with the outside is also not ideal since you will constantly have small glass fibers & dust raining on your equipment. I would use two layers of substrate - even green glue on the outside of the cabinet to reduce the impact of noise to your other area
- The Panasonic fans are very quiet, but I would be hesitant to use this as a source of ventilation for your theater in addition to your rack. Without a lengthy HVAC conversation on pressure balancing, it is generally a bad idea to try to vent to another closed zone - the air has to go somewhere and be relatively "free"
- Another reason to not oversize the cooling fan is you will be sucking a HUGE amount of dust in through the front of your rack. Give it even just a day to build up and you would probably regret such a ventilation system, not to mention the potential for "whistling" through the rack if you used custom rack shelves
- How do you plan to wire / access the wires to this system? I could not discern from your diagram and descriptions. You may only need to connect something every once in a while, but with only front access it would be a major PITA
- And how is this fan controlled? By a simple wall switch? There is always high potential for those not experienced with your system to not know to turn the fan on and off. Even if your system is "off" your equipment will still generate heat that you may wish to evacuate through automated control / thermostat.

My recommendation would be to get an appropriately sized (rack height) Middle Atlantic AXS rack with a quiet fan panel which is thermostatically controlled. First, build a completely sealed box in your alcove with two layers of 1/2" ply with green glue in-between that will fit the rough dimensions of your AXS rack. Run a dedicated power outlet using a surface mount box on the upper part of the rack. Then, get yourself a Middle Atlantic AXS rack to fit your new sealed alcove. Use a 3-space quiet fan panel with thermostatic control at the top three spaces of the rack.

As for the warm theater - just deal with that separately through additional HVAC supply or have a professional balance your system with dampers for increased supply in your theater area. Your rack will be a few degrees within the theater's ambient temperature and then you can adjust your house system to make your theater more comfortable.

I hope this helps and good luck!
post #6689 of 10217
I just received a Panasonic FV-08VK1. This is a DC motor powered, 80 CFM, 4" duct unit.

I have another application (non theater) for this, but part of the reason I bought it was to do a little hands on experimentation.

Sitting on the bench, it is indeed quiet. I think my contraption would probably render the bench measured noise level inaudible inside the theater.

However... if you restrict the inlet, or the outlet, thereby increasing backpressure, fan speed and noise increase. Not dramatically, but noticeably.

The key to achieving low fan noise is achieving unrestricted airflow. The outlet vent pipe has a single elbow and short run. There's not much I can do about it. On the inlet side I can manipulate the rack design, giving priority to airflow.

There's one more mystery... the speed controller in the Panasonic fan. Pressure sensors wouldn't work. They must be generating some sort tach speed versus current load line and then intersecting some airflow line. Don't know enough about DC motors to know for sure. Its a good trick. Probably something on the Internet if I wanted to look for it.

llj
post #6690 of 10217
Thanks for such a thoughtful reply.

As far as HVAC goes... the theater is unusual because it has no HVAC vents. This
might seem strange, but its not. The concrete floor has radiant heat. The room
is more or less in a basement and nominally doesn't need air conditioning.

So, there is no HVAC system to balance.

I recognized from the beginning that a dozen bodies in a closed room, plus equipment, etc is probably going to get stuffy. I've installed the wiring and tubing for a mini-split air conditioner. But this is my backup plan. I really don't want an air conditioner and am attempting to get the air changes high enough to avoid it. Perhaps the air conditioning would only be necessary for a packed house.

There is a spot for a fresh air inlet to the theater. This is also required for the planned projector doghouse. I'm planning a similar setup to suck theater air through the doghouse and eject it outside the theater. I pick up some more air changes with this, but they won't be across the occupied section of the theater so they're not so effective.

As far as the double wall green glue etc.... well, I'm rack width constrained. Although maybe I could sandwich a couple layers of 1'4" MDF and green glue? The drawback of this is I lose the absorbtion on the inside of the rack.

As for the fiberglass particles... isn't this stuff supposed to used inside HVAC ducts? or is that Linacoustic? Would Linacoustic work?

As for the dust... In my living room, I've got a somewhat similar system. Much more ad hoc and after the fact than this. Its been there for seven years without problems. In fact I expected more dust than I've seen. I don't think its ever been cleaned.

Controlling fan operation is an issue because the room may be used for purposes other than theater. In which case a thermostat in the rack won't work. One way to cover most usage models is to implement an "OR" function of occupancy and theater active. Developing the theater active signal is easy. The occupancy signal is more difficult. May have to compromise with "lights on".

LV wiring and power comes down inside the wall and into the rack. Some details to work out here. Worst case is I'll have to give up a rack slot for the wires.

The rear of the rack box is accessible when the cabinet door on the alcove side is opened. The rear of the rack box will be removeable or maybe hinged. I probably don't have room for a slideout rack.

llj
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