Turning a Suspended Ceiling into a Bass Trap?

[craig john]

I currently have a suspended "acoustical" ceiling in my basement HT. It's mostly white 1/2" x 2' x 2' tiles. I say "mostly white" because I have painted the first two rows of tiles black to reduce light reflections off my FP screen. I realize this affects the acoustic properties of the tiles, but I have been willing to live with this due to the benefit of the light absorption. I am now thinking I want the entire ceiling black. Therefore, I'm thinking about replacing the whole thing with black ceiling tiles and black gridwork. While investigating the various options, I came across these tiles from Acoustical Solutions:

Acoustical Solutions 2" Ceiling Tiles.

Note that these tiles have a noise reduction coefficient of .22 @125 Hz. My ceiling is dropped 4" below the overhead joists. Above that, the 9.5" intra-joist spaces are filled with standard thermal insulation bats. However, I have some leftover pieces of 2" OC SelectSound Acoustic Boards, which have a NRC value of .25 @ 125 Hz. I have enough that I could install 2" of SelectSound into the intra-joist spaces around the perimeter of the room out to about 24" from the wall. I am wondering if the combination of 2" of ceiling tile with 2" of OC SelectSound and the intervening airspaces would then become an effective bass trap, similar to some of the soffit type bass traps other have built.

What I know about bass traps is that they need to be thick, (at least 4"), dense, (both products seem dense enough), and have an airspace, (I would have two, the one between the ceiling tile and the SelectSound, (2") and the one between the SelectSound and the overhead floor, (~7.5") with the second being filled with thermal fiberglass.) The overall dimension of 13.5" plus the two dead air spaces leads me to believe this would be an effective bass trap.

However, before I spend $1.2K on this, I would like some of the experts opinions. I can replace my existing ceiling with 1/2" black tiles with no bass absorption for about 1/3 the cost of these tiles. Is the extra $$$ well spent for the bass absorption? BTW, my room has two major bass problems; a huge resonance from 45 to 55 Hz, and a huge null at ~125 Hz. If I can improve the null at 125, I can deal with the resonance at 50 with EQ.

Thoughts?

Craig

[bpape]

Personally, I think you'd be just as well off if not better to do the less expensive tiles and filling the cavity above with some R-30. That would give you more, deeper, broader, etc.

You have the thickness and the spacing - density can be compromised if you have enough of the other 2.

Bryan

[Scott R. Foster]

Those 2" tiles look nice, but I got to agree with Bryan - the easy way to go is a standard high NRC tile with standard batts as thick as will fit - keep you money in your pocket.

You can paint the tiles black and not cause a significant decrease in absorptive quality - the trick is apparently thin layers of paint [spray gun - not driveway roller]. Check out the second post on this page of the thread - by Eric on test of the effects of paint on acoustic tiles.

http://forum.studiotips.com/viewtopi...tile&start=160

[craig john]

Thanks Bryan,

I didn't mention the *other* reason I'm considering this. I'm hearing some rattles, squeaks and groans from the ceiling, especially in the corners during deep bass passages. I can't tell if the tiles are rattling in the gridwork or if the gridwork itself is rattling. Nonetheless, I think the higher mass ceiling tiles will be less likely to vibrate and will keep the gridwork from rattling also.

Anyway, do you think this combo of ceiling tiles and SelectSound will make a serviceable bass trap? I'm probably going to do the ceiling tiles anyway, but if you think I'm wasting my time with the SelectSound between the joists, I won't bother with it.

Craig

[craig john]

Thanks for the reply Scott. I actually tried spray painting the tiles initially and I couldn't get them to look even. I tried about 5 or 6 thin coats, but they still looked uneven. I eventually painted them with a roller and they looked much better. Obviously I compromised on the sound absorption, but what I was after at the time was light absorption. This time around, I want to optimize both characteristics, if possible, and at the same time reduce the unwanted sounds eminating from the ceiling.

the easy way to go is a standard high NRC tile with standard batts as thick as will fit

Assuming I'm go with the higher mass ceiling tiles, should I stuff the space between the joists with the standard batts *and* the deadspace between the ceiling and the joists? Should I abandon the SelectSound altogether?

Craig

[Ethan Winer]

Craig,

> I'm thinking about replacing the whole thing with black ceiling tiles and black gridwork. <

Even better is to just pull out the grid, which will give you more height, and pack the cavities between joists entirely with fluffy fiberglass. Then you can staple fabric to the joist bottoms, and add thin wood trim strips to cover the staples. This will be much more absorbent at high frequencies than any ceiling tile, and all that fiberglass will give a nice amount of bass trapping. It will also cost less than replacing one grid with another, and is probably less work too.

--Ethan

[craig john]

Interesting idea Ethan. Unfortunately, my wife custom made some red velvet drapes for the front and side walls. They are made to fit floor to ceiling. If I lose the ceiling tiles and gridwork, they'll be 4" too short. I doubt she would be willing to re-make them for me as she spent a significant amount of time making them in the first place.

If I stuff the cavities between the joists with fibergalss and hang the ceiling below it, (forgetting about the SelectSound), will I still get the same bass trapping? The ceiling tiles should let the bass pass through to be trapped by the fiberglass, correct?

Thanks.

Craig

[Scott R. Foster]

Originally Posted by craig john

Assuming I'm go with the higher mass ceiling tiles, should I stuff the space between the joists with the standard batts *and* the deadspace between the ceiling and the joists? Should I abandon the SelectSound altogether?

If you want effectiveness at 50 Hz I would plan getting a nice thick layer of mineral fiber in the cavity. SelectSound is a reasonable option... but i would shop locally for best price - it might be rock wool in your locale.

Density is not a defining attribute of the benefit any given material type will provide... assuming that it is will just lead you to buy a more expensive material. In large part the cost per unit volume of treatment will go up in linear to the density of the material you choose.. the absorption performance will not.

Originally Posted by craig john

The ceiling tiles should let the bass pass through to be trapped by the fiberglass, correct?

Yep... well sort of... the tile and the mineral fiber in the cavity are essentially the same material doing the same job. The tile part of the installation is merely providing the aesthetic finish.

The technique Ethan describes of thick batts between joists and a fabric ceiling finish has been used effectively - and can yield a nice look if done right. But I am a skeptical about the idea that demolition of the the grid in place only to rebuild a ceiling finish of a different sort will be cheaper / easier than simply beefing up the contents in and above the grid you have.. but you will know best what is practical in your room.

FWIW I have seen standard [not expensive] ceiling tiles in black. Perhaps you can order those without opting for a specialty product. Then fill the cavity with the least expensive mineral fiber product per unit volume in your local market.

Also, do you have bass traps in the room corners? That would be my next step after getting the ceiling squared away.

[bpape]

If you just need some additional mass to keep the tiles pressed down, just try cutting up some leftover drywall and laying it on top of the tiles. Obviously you don't want to cover the whole thing but even an inch thick piece - maybe 6"x6" in the center of each tile should let you know if that's going to solve the problem or not.

Try it just in an area that you can identify as 'rattling' and see if it resolves the problem.

Bryan

[Scott R. Foster]

You may have some loose hanger wire on your grid, or something like a signal wire or HVAC component causing that rattle... stick your head up there and look around, you may be able to fix that problem with a little strapping or wire tightening.

[JamesE]

Here is my solution. Assuming that you that you have room height to lose, make up your own RPG Skyline panels. http://rpginc.com/products/skylinelp/index.htm


These panels may be any depth that you choose. If you have the room height to spare, make the longest blocks in the panel 6 inches. The overall panel cannot be over 23 ¾ x 23 ¾ inches so they slide up into the ceiling. You could make them with a lip but I don’t think your going to have the room to get them up into the grid. Without a lip your have to have a system for hanging the panels from the grid. I would take the finished panel and make a ¼ inch deep saw cut in them ½ from the top of the panel and insert something like popsicle sticks in the side of the panel (into the saw cut) after you have pushed the panel up through the grid.

The panels will be composed of approximately 2 inch by 2 inch blocks of varying depths. So there is a 12 block by 12 block pattern.

To calculate the depth of the blocks divide the longest block by 12. Example: longest block is 6 inches. Your blocks are .5, 1 1.5, 2 etc.

Now make one pattern panel. Just arrange the block so they are random visually pleasing. Test the panel in your ceiling to make sure that it slides up into the grid easily. If the grid was installed out of square, then the panels will have to be made smaller.

Next find someone that does Dryvit. http://www.thermalfoams.com/construction/dryvit.htm

Have them cut up as many 7 inch blocks as you need. They will have a special tool that will cut Styrofoam easily. Hopefully, this will not take more than a 4 hours of there time. $100 to $300 perhaps? Maybe he would let you rent the machine for the weekend.

Then take the blocks and set them on top the one panel that you have makeup, gluing the blocks together as you go. Take these glued up blocks back to the Dryvit guy and have him cut them in half. Now you have 2 panels for every set of blocks that you have glued up. 6 inch will be the longest block with ½ inch above the edge of the grid.

Paint the panels.
Install the panels in the ceiling.
Place insulation over the panels as you go.

The finished product gives you a ceiling that acts like a bass trap, has a great deal of diffusion and looks absolutely awesome. I think you can stay within your $1200 budget.

I hope this is clear. Hope you like projects.

[dknightd]

I think the OP's plan is sound. Most ceiling tiles are absorbant mostly in the trebble. Having the cavities filled with loose glass makes the ceiling more of a broadband absorber. Broadband is good. If you don't think your room is too dead as is, then adding more absorbing mass above what you have is always a good thing. Your plan to replace the existing ceiling panels with thicker ones will help them absorb in a broader freqhency range. 4" of compressed glass in the corners, backed by loose glass, will help with bass absorbtion. But to really absorb low frequencies, you need more depth. If you can make soffits out of solid 3lb/ft**3 fiberglass about 24" square it will likely help you with your peaks and valleys. You could just put 6" of dense stuff below your existing ceiling in the corners and gain quite a bit. You shoudl also consider putting 6" dense fiberglass on your wall-wall corners. Pretty much the more broadband absorption the better. My expereince has been you cannot absorb too much bass frequencies in a typical room. You do have to watch out for too much trebble absorbtion.

[Terry Montlick]

One thing to keep in mind is that a ceiling bass absorber will do very little to help lengthwise and widthwise low frequency room modes. And because room length and width are typically greater than room height, these will be the first (lowest frequency) room modes that can give you problems.

- Terry

[Ethan Winer]

Terry,

> a ceiling bass absorber will do very little to help lengthwise and widthwise low frequency room modes. And because room length and width are typically greater than room height, these will be the first (lowest frequency) room modes that can give you problems. <

I agree the length mode is the worst offender, with the width and height probably equal for second place. Non-axial modes are way down the list of importance.

But trapping the ceiling does help the length and width, at least if you treat around the ceiling perimeter, because that treats those wall-ceiling corners. So even trapping just those parts of the joists will still help a lot. Fluffy fiberglass between the joists is also useful at the first reflection points. Another advantage of treating all of the joist spaces is to reduce the intrusion from foot steps above, and also to minimize potential squeaks and rattles.

--Ethan

[craig john]

Ethan,

I have a nasty length mode at 40 Hz. Room Response at LP. How much improvement would you expect with the combo of fluffy fiberglass and the 2" ceiling tiles around the perimeter? Thanks.

Craig

[David French]

Just for an idea, here's a measurement of a small room with and without a one foot drop ceiling made from one inch 703.


A drop ceiling probably won't do too much to a powerful 40 Hz mode.

[Ethan Winer]

Craig,

> I have a nasty length mode at 40 Hz <

That's a little too low to target with "soft" absorption like fiberglass. The good news is that a peak at 40 Hz is nowhere near as damaging musically as all the other peaks and deep nulls you surely have at higher bass frequencies.

> How much improvement would you expect with the combo of fluffy fiberglass and the 2" ceiling tiles around the perimeter? <

A lot. But again, most of the improvement will be above 40 Hz. You should still do this.

--Ethan

[Killroy44]

Originally Posted by Ethan Winer

Craig,

> I'm thinking about replacing the whole thing with black ceiling tiles and black gridwork. <

Even better is to just pull out the grid, which will give you more height, and pack the cavities between joists entirely with fluffy fiberglass. Then you can staple fabric to the joist bottoms, and add thin wood trim strips to cover the staples. This will be much more absorbent at high frequencies than any ceiling tile, and all that fiberglass will give a nice amount of bass trapping. It will also cost less than replacing one grid with another, and is probably less work too.

--Ethan

Wow this sounds awesome and easy to do, does anyone have any pictures of something like this??? This seems too easy, yet could be cost effective vs. the $100's of dollars in high NRC score ceiling tiles. I suppose one could make frames and staple the fabric to them I'm very intrigued by this idea. Any more detail on how to do this would be greatly appreciated!

Thanks Ethan!
Kevin

[Ethan Winer]

Kevin,

> Any more detail on how to do this would be greatly appreciated! <

I talk a bit more about that in the MiniTraps Demo video on my company's web site. But there's not much more to it than what I already described!

--Ethan

[BasementBob]

Here's what I did - stuffing the joists full of insulation.
http://www.bobgolds.com/AbsorberCeilingJoist/home.htm
Obviously variations are possible.

[windwaves]

Originally Posted by Ethan Winer

Craig,

Even better is to just pull out the grid, which will give you more height, and pack the cavities between joists entirely with fluffy fiberglass. Then you can staple fabric to the joist bottoms, and add thin wood trim strips to cover the staples. This will be much more absorbent at high frequencies than any ceiling tile, and all that fiberglass will give a nice amount of bass trapping. It will also cost less than replacing one grid with another, and is probably less work too.

--Ethan

What kind of fabric should one consider here ?

thx,
ww.

[windwaves]

Originally Posted by Ethan Winer

Craig,

Even better is to just pull out the grid, which will give you more height, and pack the cavities between joists entirely with fluffy fiberglass. Then you can staple fabric to the joist bottoms, and add thin wood trim strips to cover the staples. This will be much more absorbent at high frequencies than any ceiling tile, and all that fiberglass will give a nice amount of bass trapping. It will also cost less than replacing one grid with another, and is probably less work too.

--Ethan

What kind of fabric should one consider here ?

thx,
ww.

[Ethan Winer]

Originally Posted by windwaves

What kind of fabric should one consider here ?

The following explanation is from my Acoustics FAQ.

--Ethan

Nearly any porous fabric is appropriate, and one popular brand is Guilford type FR701. Unfortunately, it's very expensive. One key feature of FR701 is that it's made of polyester so it won't shrink or loosen with changes in humidity when stretched on a frame. But polyester is a common material available in many styles and patterns at any local fabric store. Another feature of FR701 is that it's one of the few commercial fabrics rated to be acoustically transparent. But since you're not using it as speaker grill cloth to place in front of a tweeter, that feature too is not necessary.

Shiny fabrics having a tight weave should be avoided because they reflect higher frequencies. The standard test for acoustic fabric is to hold it to your mouth and try to blow air through it. If you can blow through it easily, it will pass sound into the fiberglass. Burlap and Muslin are two inexpensive options, but nearly any soft fabric will work and also keep the glass fibers safely in place.

[windwaves]

Thx !

[windwaves]

has anyone heard of QuietZone® SOLSERENE Fabric Ceiling System ?

I am thinking about this as a fabric for the type of application introduced here by Ethan. I would guess it has some interesting soundproofing properties.

This seems to be a very interesting product, but can't find many references about it.

[Basspig]

Originally Posted by craig john

Thanks Bryan,

I didn't mention the *other* reason I'm considering this. I'm hearing some rattles, squeaks and groans from the ceiling, especially in the corners during deep bass passages. I can't tell if the tiles are rattling in the gridwork or if the gridwork itself is rattling. Nonetheless, I think the higher mass ceiling tiles will be less likely to vibrate and will keep the gridwork from rattling also.

Anyway, do you think this combo of ceiling tiles and SelectSound will make a serviceable bass trap? I'm probably going to do the ceiling tiles anyway, but if you think I'm wasting my time with the SelectSound between the joists, I won't bother with it.

Craig

Suspended ceilings do make good shock absorbers when coupled with layers of insulation.
Some thoughts:
You'll want to put 3-1/2" fiberglass 24" wide batts on top of each tile to keep it from bouncing around.
If you plan to run really powerful infrasound, then you'll need to vent the ceiling. I took out the corner tiles. A grid diffuser could go into the vented areas for aesthetic reasons. This will reduce problems with tiles getting sucked out or broken by excessive movement.
The bass trap theory works--only problem is that it traps very low frequencies and makes the room starved for deep bass.
My own ceiling has insulation batts between joists, but also 3/4" thick hard fiberglass tiles (got these in 1968 when the building codes outlawed hard fiberglass tiles) nailed to the joists, which alone have a surprising amount of attenuation. Then I've got 6" of soft 24" batts in the air gap between the panels and the drop ceiling.
It's pretty effective at isolating sound from upstairs, but deep bass leakage is always a problem. Most of it goes straight up.
That's my two cents on suspended ceilings.

[rynberg]

I wish I would have seen this thread before....much cheaper solution than those Acoustical Solutions tiles would be the Capaul Open Plan tile, which is available in black with an NRC of 0.95.

From the OPs description of his original tiles, they are mineral fiber which have poor mid-frequency absorption as compared to fiberglass tiles. Painting a tile with a roller will pretty much completely kill the mid and high frequency absorption.

A grid should not rattle unless there are wires touching other objects, as Scott mentioned.