Building a room...need some wall treatment ideas - Page 4 - AVS Forum
Forum Jump: 
 
Thread Tools
post #91 of 275 Old 02-02-2004, 04:12 PM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,747
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 131
Bob,

> I also believe (without evidence) that you end up with a less absorbed notch in the middle <

Yes, and I have measured that. There's only so far you can take the notion of using thinner and thinner material spaced farther and farther from the wall!

--Ethan

RealTraps - The acoustic treatment experts
Ethan's Audio Expert book

Ethan Winer is offline  
Sponsored Links
Advertisement
 
post #92 of 275 Old 02-02-2004, 04:16 PM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,747
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 131
Chris and Terry,

> Does that mean there isn't a relationship between material density and absorption? Or, just that Mechel's results don't demonstrate such a relationship? <

I have to stress that one important factor which is not accounted for in OC's data or Michel's paper is the way denser materials behave when spaced away from the boundary. I do not have a conclusive answer for this either, but I'm still thinking that a denser panel behaves as a membrane all by itself.

--Ethan

RealTraps - The acoustic treatment experts
Ethan's Audio Expert book

Ethan Winer is offline  
post #93 of 275 Old 02-02-2004, 04:27 PM
AVS Special Member
 
Terry Montlick's Avatar
 
Join Date: Jul 2003
Location: State of Rhode Island and Providence Plantations
Posts: 3,261
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
Quote:
Originally posted by Ethan Winer

I have to stress that one important factor which is not accounted for in OC's data or Michel's paper is the way denser materials behave when spaced away from the boundary. I do not have a conclusive answer for this either, but I'm still thinking that a denser panel behaves as a membrane all by itself.

--Ethan
Actually, Mechel's paper DOES address this. See Section V, "Formulas for Multilayer Absorbers" and Section VI, "Examples of Layered Absorbers." See Figures 13 through 19, which are design charts for porous absorbers with varying air gaps behind them.

Regards,
Terry

Terry Montlick Laboratories
Home Theater Acoustics
Critical Listening Rooms
Design, Evaluation, Alpha Certification®
www.tmlaboratories.com
Terry Montlick is offline  
post #94 of 275 Old 02-02-2004, 04:57 PM
AVS Special Member
 
dave7's Avatar
 
Join Date: Oct 2002
Location: Outside Philly
Posts: 1,159
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
If anyone is interested in alternatives to the 700 series materials, and you want to go on specific published data, then Owens Corning also produces something called "Sound Attenuation Fire Batts" that appear to be very absorptive. I found that 32 square feet costs $27 (4 - 2x4 sheets).

Does anyone have opinions on this stuff?

Page down the below pdf link until you see it:

http://www.owenscorning.com/comminsu...ta%20Guide.pdf

Dave
dave7 is offline  
post #95 of 275 Old 02-02-2004, 05:43 PM
AVS Club Gold
 
Dennis Erskine's Avatar
 
Join Date: Jul 1999
Location: Near an airport
Posts: 9,136
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 45
Air gaps behind porous materials significantly increase low frequency absorption capabilities as Ethan has pointed out. There is a limit to this which generally falls in the range of 3" to 4".

Ethan, it is possible a 'denser' material would function as both a porous absorber and a diaphragmatic absorber. Typically, the rough calculation for a diaphragmatic absorber utilizes surface density. It is likewise reasonable that as the interstices are smaller and smaller and resistance to air flow through the material increases, the object itself could resonate as well as the individual fibers thus creating your porous diaphramatic absorber. The surface density of fiberglass board products is such that it's effectiveness could be measured but not audible. On the other hand certain composite materials can produce some interesting results. The common method in the texts using surface density fails to address other significant material properties, elasticity among them.

If you'd like to go digging into a rat hole, consider that in a porous absorber, the acoustic air flow moves an individual fiber, which mechanically resists the movement and shows it's anger by dissipation of heat. (The principal is the same, the process is different in a non-fiberous porous material like concrete block.) Now consider the diaphragmatic absorber ... it's really nothing more than that fiber but on a larger scale.

Dennis Erskine CFI, CFII, MEI
Architectural Acoustics
Subject Matter Expert
Certified Home Theater Designer
CEDIA Board of Directors
www.erskine-group.com
www.CinemaForte.net
Dennis Erskine is offline  
post #96 of 275 Old 02-03-2004, 09:07 AM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,747
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 131
Dennis,

> it is possible a 'denser' material would function as both a porous absorber and a diaphragmatic absorber. <

Yes, that's what I'm thinking. I've done some testing of different thicknesses and densities of rigid fiberglass, but not exhaustive enough to arrive at a real conclusion on this specific issue. I figure to really learn what I need will require 24 separate tests! I'd want to test 701, 703, and 705, in both normal and FRK types, each at 1, 2, 3, and 4 inches thick, and all across a corner.

One of these days...

Thanks.

--Ethan

RealTraps - The acoustic treatment experts
Ethan's Audio Expert book

Ethan Winer is offline  
post #97 of 275 Old 02-06-2004, 11:40 AM - Thread Starter
Senior Member
 
psuie23's Avatar
 
Join Date: Jan 2004
Location: Sturbridge, MA
Posts: 324
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
hello all..i need to bring up my ceiling problem again. I may be adding additional ducts to my basement. If so, I am going to have to put in drop ceilings, and the entire ceiling will have to be around 6'5" off the ground. Is there any issue with haveing the ceiling so low accoustically?

jay
psuie23 is offline  
post #98 of 275 Old 02-06-2004, 11:56 AM
AVS Special Member
 
dave7's Avatar
 
Join Date: Oct 2002
Location: Outside Philly
Posts: 1,159
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
BTW - That Owens Corning product (solserene) is said to be $8-$12/square foot installed.

I am not qualified to answer your height question, but if you have no choice, what else can you do? 6'5" is pretty low.

Go to this link and page down really far. There are some fiberglass based drop-in tiles that I am looking at that have an NRC of .85 to 1.00. They run $3.5/square foot (I think) and some have a sound block material added to the backside.

http://www.armstrong.com/commceiling...fire=&x=26&y=6

Hope this helps.

Let us know what you come up with. It might help others.

Dave
dave7 is offline  
post #99 of 275 Old 02-06-2004, 11:57 AM
AVS Special Member
 
dave7's Avatar
 
Join Date: Oct 2002
Location: Outside Philly
Posts: 1,159
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
How wide of an area of drop ceiling are you looking at?

Dave
dave7 is offline  
post #100 of 275 Old 02-06-2004, 02:14 PM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,747
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 131
Jay,

> the entire ceiling will have to be around 6'5" off the ground. Is there any issue with haveing the ceiling so low accoustically? <

Not if the ceiling is a hung ceiling with acoustic tiles. In fact, the space between the tiles and the "hard" ceiling above helps acoustically.

--Ethan

RealTraps - The acoustic treatment experts
Ethan's Audio Expert book

Ethan Winer is offline  
post #101 of 275 Old 02-06-2004, 02:33 PM - Thread Starter
Senior Member
 
psuie23's Avatar
 
Join Date: Jan 2004
Location: Sturbridge, MA
Posts: 324
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
the area would be the full room ~12.75' x 18 '


Where would i find accoustic tiles? When i went to lowes or home depot (can't remember which one it was), they had ordinary tiles (around $22 for 10 2'x4' tiles) and then really fancy ones that were a lot more expensive. Do you know where "acoustic tiles" can be found and about how much they are?

thanks
jay
psuie23 is offline  
post #102 of 275 Old 02-06-2004, 03:11 PM
AVS Special Member
 
dave7's Avatar
 
Join Date: Oct 2002
Location: Outside Philly
Posts: 1,159
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Lowes and Home Depot only ever carry entry level cheap items. I think I just called the Armstrong 800 number and they told me someone local. The place I called had the stuff on display in different finishes (nice beveled edged 24 x 24 fiberglass based drop-in tile with an NRC of about 1.00). I have been sidetracked lately and have not been over there to see for myself. I was asking about Armstrong item #3253 (Optima Open 24x24x1.5) and item #3200 (painted nubby Open 24x24x1).

The place I called was definitely under $4/square foot. As mentioned earlier it was about $3.50 plus like $.03/square foot extra for the sound blocking back.

Dave
dave7 is offline  
post #103 of 275 Old 02-06-2004, 05:34 PM - Thread Starter
Senior Member
 
psuie23's Avatar
 
Join Date: Jan 2004
Location: Sturbridge, MA
Posts: 324
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
4 / sq ft?? That's over $900 just in ceiling tiles...a bit more than i had planned on spending. Is there anything more in between?
psuie23 is offline  
post #104 of 275 Old 02-06-2004, 07:14 PM
AVS Special Member
 
dave7's Avatar
 
Join Date: Oct 2002
Location: Outside Philly
Posts: 1,159
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
You're right, it does add up too quickly.

I went back to read your first few posts.

Why not simply drywall the ceiling (with a layer of acoustibloc - or whatever it's called - available at Home Depot for 6-$7 per 4x8 sheet), then if needed make a thin absorber panel or "cloud" panel on the ceiling at the first reflection point, if it is even needed. For this piece get some 1" 703 from Ethan.

If you can, install as much "fluffy" insulation as you can in the joists to keep whatever sound that does pass into the joist cavities under a little more control.

This will keep your ceiling height high, and it would look more normal.

Do you even need to keep the sound from migrating outside the room? It seems to be tough to do without total commitment.

There are others in the forum who have more experience than I, even I'd like to hear from them.

Dave
dave7 is offline  
post #105 of 275 Old 02-06-2004, 09:21 PM - Thread Starter
Senior Member
 
psuie23's Avatar
 
Join Date: Jan 2004
Location: Sturbridge, MA
Posts: 324
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I have considered drywall...and i still will. I just like the flexibility of the drop ceiling. I think I can get it almost right on those vents, and it will allow me to still be able to access everything above it. Aesthetically, I would prefer the drywall...just makes me nervous..especially if I might be adding an lcd projector later...and will have to run more lines at that time.

If I go with the tiles that they have at home depot, how different will it be from drywall, acoustically...
psuie23 is offline  
post #106 of 275 Old 02-06-2004, 10:16 PM
AVS Special Member
 
dave7's Avatar
 
Join Date: Oct 2002
Location: Outside Philly
Posts: 1,159
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
My guess (I am no expert!!) is that in the room the Home Depot tiles would be very slightly absorptive (like an NRC of .65 for whatever that worth). I have a partial drop ceiling (about 250 square feet). The tiles I am using are considered "acoustic" with an NRC of .65. I must say that I believe a lot of sound transmits through this area to the floor above. I have no way of proving it until I take some measures to prevent this sound leakage. (damn...i am too used to Word's automatic "I" capitalization)

I believe drywall blocks more noise, especially if there is that acoustibloc stuff behind it. You must be sure to seal every seam though...even around recessed lights, and the lights should not allow much sound transmission. That means more $ on the recessed fixtures themselves so that insulation can be packed right up the the fixture without a fire hazard.

If you use a drop ceiling, I would (and I will be doing this) pack fiberglass batting in every crevice possible. I have some noise blocking vinyl that I intend to put up. It is real expensive, and super heavy (6lbs/square foot). It is not be easy to work with. In addition, I am not convinced that it was a particularly wise purchase, but I don't have the nuts to return some 300 lbs of vinyl.

What is your time frame?

I am taking my time with my project and would be happy to keep you posted with successes and failures.

My room is very large compared to yours. It is not rectangular, but it's length is roughly 33 feet long and 18 feet at the narrowest part. Your room might benefit from Ethan's Realtraps for bass control. The mini traps also do a fine job with higher frequencies.

Regardless, if you go to Realtraps.com there is a lot of useful information and Ethan is very easy to get along with.

One thing to remember with the projector...it only does video. You could consider running a component cable and a DVI cable now so you won't have to do it later. I suspect everything will be DVI soon...at least for DLP and LCD provided your DVD player, or whatever, has the appropriate output. There will e a whole lot of source components coming out this year with DVI/HDMI outputs and scaling built-in.

Check out the Ceiling max link below - it might help with your headroom issue:

http://www.ceilingmax.com/

I have not used this.

It is getting too late for me...I think I am loosing it.

Good luck

Dave
dave7 is offline  
post #107 of 275 Old 02-06-2004, 10:27 PM
AVS Special Member
 
dave7's Avatar
 
Join Date: Oct 2002
Location: Outside Philly
Posts: 1,159
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
dave7 is offline  
post #108 of 275 Old 02-07-2004, 06:02 AM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,747
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 131
Jay,

> That's over $900 just in ceiling tiles <

What are you trying to accomplish, and how good results would you like? This is really the key to knowing what's worth buying.

If you don't need isolation to the upstairs, install a hung ceiling with tiles. Sheetrock will improve isolation, but it will also make the low frequency response inside the basement room much worse. If you don't care about the acoustics inside your room you can use cheap office tiles. If you do care then thick tiles made of rigid fiberglass will absorb much better, and even serve as bass trapping.

--Ethan

RealTraps - The acoustic treatment experts
Ethan's Audio Expert book

Ethan Winer is offline  
post #109 of 275 Old 02-07-2004, 06:51 AM
AVS Special Member
 
Terry Montlick's Avatar
 
Join Date: Jul 2003
Location: State of Rhode Island and Providence Plantations
Posts: 3,261
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
Quote:
Originally posted by dave7

... The tiles I am using are considered "acoustic" with an NRC of .65. I must say that I believe a lot of sound transmits through this area to the floor above.
It's very important to understand what "NRC" means. It stands for "Noise Reduction Coefficient." This is a measure of how much sound is absorbed by a material inside a room. This number tells you how much quieter the room will be from sounds generated within the room.

This is completely different from the measurement called "STC", which is the "Sound Transmission Class." This number measures the ability of a material to block sound either leaving or entering a room.

Both of these are weighted averages across several octave bands in the audio spectrum. But the two measures are not related. Knowing one doesn't give you any information about the other.

Regards,
Terry

Terry Montlick Laboratories
Home Theater Acoustics
Critical Listening Rooms
Design, Evaluation, Alpha Certification®
www.tmlaboratories.com
Terry Montlick is offline  
post #110 of 275 Old 02-07-2004, 07:11 AM
AVS Special Member
 
dave7's Avatar
 
Join Date: Oct 2002
Location: Outside Philly
Posts: 1,159
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
This was what I was trying to say (what Ethan and Terry said). To limit the sound traveling outside that room, use Drywall with perhaps some sound blocking backing installed before the drywall is hung.

If you don't care about the sound traveling upstairs then the suspended ceiling is a good option.

If you want a suspended ceiling for access reasons, AND sound isolation as well, then you must do some extra work to keep that sound from going upstairs.

The NRC of .65 is very MILDLY absorptive, and if you read Ethan's papers you will learn that that number does not give a complete picture of what is getting absorbed.

As I mentioned, my tiles have an NRC of .65 and the sound goes right through this area...I believe anyway.

The drywall is VERY reflective, especially in higher frequencies. Walk into an empty room and you'll hear it with a simple hand clap.

Nuff said...Terry and Ethan live this stuff, they have been very helpful to many of us.

Dave
dave7 is offline  
post #111 of 275 Old 02-07-2004, 08:01 AM - Thread Starter
Senior Member
 
psuie23's Avatar
 
Join Date: Jan 2004
Location: Sturbridge, MA
Posts: 324
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I don't care too much about sound getting upstairs, so I don;t need the drywall really. And having a really reflective surface that close to the sitting position, may not be the best idea anyways. So.. (still thinking outloud) the suspended is probably the best option.

In terms of how much do i want to pay vs how great do I want it to sound? .... I want a good sounding room. I'm a bit anal on my setup, but i don't have the BEST ear in the world. As long as the room sounds good, I am ok with it. I imagine even with the cheap tiles it will sound a lot better than my current setup.

The tiles i looked at were around 27 cents a square ft (more or less). I would definitely be willing to pay 2 x that...perhaps even 3x or 4x (if it would make a big difference). But my budget for making this room is around $2500. having the ceilings tiles alone be 1/3 of that, won't really work for me....
psuie23 is offline  
post #112 of 275 Old 02-07-2004, 08:35 AM
AVS Special Member
 
BasementBob's Avatar
 
Join Date: Jan 2004
Location: Oakville, Ontario, Canada
Posts: 4,620
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked: 68
Ethan wrote:
Quote:
If you don't need isolation to the upstairs, install a hung ceiling with tiles. Sheetrock will improve isolation, but it will also make the low frequency response inside the basement room much worse. If you don't care about the acoustics inside your room you can use cheap office tiles. If you do care then thick tiles made of rigid fiberglass will absorb much better, and even serve as bass trapping.
Most of that sounds bang on. But I have a question
Quote:
Sheetrock ... will also make the low frequency response inside the basement room much worse
Sounded a little bit odd to me. Could you explain that one a bit please?


BTW dave7: I believe, generally speaking, that one layer of:
Acoustic Ceiling Tiles have a high NRC (.5 to 1.0) and a low STC (0 to 1)
Sheetrock/Drywall/Gypsum has a high STC (28) and a low NRC (0.01).
My use of 'high' and 'low' are simply relative adjectives. For example there are STC 70 wall configurations that block a lot more than a single sheet of sheetrock.
This I think matches what you posted.

For psuie23's room with the drop ceilings for the additional ducts, a way to get both STC and NRC, if such a thing were desired by psuie23, would be to
a) if there are open joists then fiberglass insulate them
b) put sheetrock on the ceiling at the 7'3" level. Perhaps 1" of it.
c) put in the new ducts
d) put in a drop ceiling at 6'5", with fiberglass on top of it.

The fiberglass in (d) should extend the NRC of the ceiling into lower frequencies. Particularly if it is rigid fiberglass or rigid rockwool.

Regards
Bob

An amateur built the Ark. Titanic was built by professionals. Of course Noah took a little advice.
BasementBob is online now  
post #113 of 275 Old 02-07-2004, 09:03 AM
AVS Special Member
 
dave7's Avatar
 
Join Date: Oct 2002
Location: Outside Philly
Posts: 1,159
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Bob,

Yes, that is what I am saying.

I believe what Ethan is saying (correct me if I am wrong here) is that a sheet of drywall is very rigid, so it is less likely to be compliant by any frequency sound wave that hits it. Therefore, most frequencies - even very low frequencies - simply reflect off it.

Since a suspended ceiling allows a lot of sound penetration, then, if there is thick batting behind it, there is an opportunity for more sound absorption, including low frequencies due to the depth of the batting (8" or more). Could the tiles themselves could act as sort of membranes for low frequency absorption? I am not sure about that because they would not have an air tight seal.

Ethan/Terry - I would really like to hear a comment on the above two paragraphs. I know much of it sounds like fact, but it is really all a question.

Anyway Jay, it sounds like a drop ceiling is the way to go. It keeps you flexible. Check out the CeilingMax system I linked to earlier. I think a lot of people in the forum have used it because I have seen it mentioned before. Perhaps starting another thread asking about it could get some valuable feedback on how it installs and looks afterward.

Dave
dave7 is offline  
post #114 of 275 Old 02-07-2004, 09:08 AM
AVS Special Member
 
dave7's Avatar
 
Join Date: Oct 2002
Location: Outside Philly
Posts: 1,159
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
You know, the more I think about it, the more I wonder if that $3.50/square foot ceiling tile is even worth it if you have the ability to stuff the area above it with loose fiberglass batting.

Simply buy the tiles that look the nicest to you (budget limited I am sure), and treat the area above the tile as best you can.

I wonder if that would give you the same effect as an expensive purpose designed tile.

Ethan/Terry?

Dave
dave7 is offline  
post #115 of 275 Old 02-07-2004, 09:10 AM
AVS Special Member
 
dave7's Avatar
 
Join Date: Oct 2002
Location: Outside Philly
Posts: 1,159
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
See this for info on STC values using different construction methods:

http://www.thermafiber.com/PDFs/TF885.pdf

You'll have to scroll down a few pages.

Dave
dave7 is offline  
post #116 of 275 Old 02-07-2004, 10:01 AM
AVS Special Member
 
BasementBob's Avatar
 
Join Date: Jan 2004
Location: Oakville, Ontario, Canada
Posts: 4,620
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked: 68
psuie23 has a 13'x18' ceiling, and a limit of $1 per square foot, or $234.

2'x4'x2" Rigid Rockwool from Roxul are $5.25 CDN each. 30 of them would cover that ceiling (to get a number more accurate than '30' you'd have to think more than I'm doing right now). So that's $160.

You have to cover them in something to keep the fibers from falling out.

Certainly Polyester Quilt Batting would do the job. 108"x90" is about $12. Each of those will cover 4 panels so you'd need 8 of them or $96. Perhaps WalMart is cheaper. But lets assume you can skip the batting completely.

Instead of that how about we simply glue some fabric that you can breath through onto the panels (wrapped like a christmas present, glued at the overlap with 3M super 77 spray adhesive). 3'x150' of natural burlap is $52, and the spray is another $10.

You need to support the cloth, and the tiles. I don't know how to do that, but I assume that some wire and screws into the ceiling and a bolt and a washer at the panel will do. With 30 panels, that's 120 corners, so we'd need 120' of wire and 120 screws and 120 1/4" bolts and 120 washers. Eye Bolts 3/16 inch X 2 1/2 inch are $6 for 20, so that's $36. The screws and washers and wire probably won't come to more than $30.
BTW, you might want to put the bolts on before you cover the panels, that way the shiny silver corners won't be visible from below.

Alternatively you could save money on the eye bolts and just poke the wire through and tie it to small sticks of wood.

So let's add it up. $160 + $52 + $10 + $30 = $252.
That's over budget, but at least it's in the ballpark.

That'll cover the ceiling, give lots of absorbtion (2" of stuff + 1' airspace).
Seems a lot of work though.

The question is, is it too much absorbtion for the room?
Is it even enough absorbtion for the room?

Oh, understand that I'm just stream of thoughting here.
Untreated burlap may be a fire hazard.
I have no idea if this sort of construction is still safe to breath.

An amateur built the Ark. Titanic was built by professionals. Of course Noah took a little advice.
BasementBob is online now  
post #117 of 275 Old 02-07-2004, 10:11 AM
AVS Special Member
 
Terry Montlick's Avatar
 
Join Date: Jul 2003
Location: State of Rhode Island and Providence Plantations
Posts: 3,261
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
Quote:
Originally posted by dave7

Since a suspended ceiling allows a lot of sound penetration, then, if there is thick batting behind it, there is an opportunity for more sound absorption, including low frequencies due to the depth of the batting (8" or more). Could the tiles themselves could act as sort of membranes for low frequency absorption? I am not sure about that because they would not have an air tight seal.
I've measured batting + acoustical tile ceilings which had extremely good wide-band absorption.

Membrane absorbers are typically relatively air-tight. This allows the mass of air behind the membrane to act as a cushion, and create resonance in combination with the mass of the vibrating membrane. There is then an easy formula to compute the resonant frequency of the absorber, based solely on the mass and air space depth.

Adding a porous absorber to this air space does a couple of things. It absorbs resonant sound energy, reducing the "Q" and therefore broadening the absorption curve. It also effectively adds greater volume to the airspace, further lowering the resonant frequency. This has to do with adiabatic gas compression (and so forth). Speaker builders use the phenomenon all the time in the design of enclosures.

On the other hand, without an air-tight membrane, porous absorbers act in a different fashion. They absorb different sound frequencies depending on their thickness, depth, specific acoustical resistance (and so forth), as well as their distance to other non-porous surfaces.

Building some combination of the above absorbers is certainly possible. Knowing its properties is another matter. There are two ways:

1. Build it, and test it under laboratory conditions.

2. Simulate it, using one or more computer methods (transfer matrix method, finite element method, and so forth).

1 has the advantage that you don't have to know anything about the properties of the materials. The disadvantages are that you need access to a testing lab, and also the results with your specific materials may not be generalizable to other materials and geometries.

2 has the advantage that you can play with parameters for the simple cost of a computer run. On the other hand, you need to develop and program the model, and the results depend upon the verisimilitude of this model and a knowledge of the relevant material physical properties.

This is of course just a complicated was of saying that we don't know the general answer to your question. ;)

Regards,
Terry

Terry Montlick Laboratories
Home Theater Acoustics
Critical Listening Rooms
Design, Evaluation, Alpha Certification®
www.tmlaboratories.com
Terry Montlick is offline  
post #118 of 275 Old 02-07-2004, 11:18 AM
AVS Club Gold
 
Dennis Erskine's Avatar
 
Join Date: Jul 1999
Location: Near an airport
Posts: 9,136
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 45
Quote:
I don't care too much about sound getting upstairs
That's fair. If you don't, you don't. On the other hand, you do care about the sound from outside the room entering the room.

Dennis Erskine CFI, CFII, MEI
Architectural Acoustics
Subject Matter Expert
Certified Home Theater Designer
CEDIA Board of Directors
www.erskine-group.com
www.CinemaForte.net
Dennis Erskine is offline  
post #119 of 275 Old 02-08-2004, 10:12 AM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,747
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 131
Dave and Bob,

> I believe what Ethan is saying (correct me if I am wrong here) is that a sheet of drywall is very rigid, so it is less likely to be compliant by any frequency sound wave that hits it. Therefore, most frequencies - even very low frequencies - simply reflect off it. <

Exactly. And Dave's comment to pack the space between the joists with fluffy fiberglass is also right on. I'm embarrased I didn't mention that! If you have 12 inches, then fill the entire cavity with 12-inch thick fluffy fiberglass. Then even if you use cheap ceiling tiles you'll still have a substantial amount of bass trapping because low frequencies go right through the cheap ceiling tiles into the fiberglass. If Jay does this he'll also have the option to replace selected tiles with thin plywood panels, or maybe painted Masonite, so the entire ceiling isn't dead at mid and high frequencies.

Also, Dennis made an excellent point: Even if you don't care about sound getting out, you still don't want to be disturbed by footsteps as people above walk around. However, 12 inches of fiberglass between the joists will reduce that problem quite a bit.

--Ethan

RealTraps - The acoustic treatment experts
Ethan's Audio Expert book

Ethan Winer is offline  
post #120 of 275 Old 02-08-2004, 10:18 AM
AVS Special Member
 
BasementBob's Avatar
 
Join Date: Jan 2004
Location: Oakville, Ontario, Canada
Posts: 4,620
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked: 68
Ethan:

I know that all frequencies bounce off sheetrock, although at the same time walls are bass absorbers. But you wrote
Quote:
make the low frequency response inside the basement room much worse
How does adding a sheetrock ceiling make the LOW frequencies MUCH worse?

I can see making a room smaller affecting the room modes. But that could be a good or bad thing. (putting a piece of sheetrock under 2x12's would make the room 12" smaller)

Since a large room requires a large subwoofer, presumably the opposite is true, that when a room is made smaller one should turn the subwoofer volume down.

Regards
Bob

An amateur built the Ark. Titanic was built by professionals. Of course Noah took a little advice.
BasementBob is online now  
Closed Thread Dedicated Theater Design & Construction

User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off