Here is a copy of a presentation I made recently to our local AIA chapter, when it says refer to handout it's the ABC's of acoustics I used as a handout for this meeting and can be found on this blog as "Alphabet Soup of Acoustics".  Once again - my opinion only based on experience.

NRC refer to handout

Ceilings:

The most common method of adding acoustical absorption to a space is through the use of acoustical ceiling tile but remember – just because it’s in the book doesn’t mean it absorbs sound.  When picking a tile look for the NRC, 55 is a middle of the road rating however you can get up to a 70 with mineral fiber tile.  If you want to get a higher rating you need to look at fiberglass tiles, you can get 90-100 with them.  Be aware of some tiles that have a very smooth, hard face – often they have no NRC.  Tiles suitable for kitchen areas don’t have acoustics.

Metal tiles can have acoustical value if they are perforated and backloaded with fiberglass.  The same is true with wood.  No perforation – no acoustical absorption

With the trend of leaving ceilings open to the metal deck acoustics can get overlooked until the space is occupied, then it’s really costly to fix.  There are a variety of products available to add acoustical absorption into spaces like this; clouds for spot absorption, adding material to the bottom of the deck between the joists where it’s not so noticeable and can be done in black.  There are sprays that can offer acoustical properties sometimes fairly low so read the literature. 

Acoustics on the ceiling doesn’t always have to be tile and grid.  There are stretch ceiling systems that can add acoustics while giving you a fairly monolithic look, depending on the size of the room.   Then there are acoustical plasters, these products usually get applied to fiberglass and result in a clean, monolithic look while offering the function you need.  Always asses the need for access before deciding on a ceiling.

Walls:

·       Fiberglass is the best for reverberation NRC

·       Durability for gyms – Tectum, fiberglass behind it doubles the NRC

·       Mineral fiber has lower NRC but higher tackability

·       Adding 1/8” layer of 20 lb. density fiberglass improves the impact resistance and increases the tackability

·       Copolymer facing can be very expensive and be more difficult to handle than fabric

           

Picking the right fabric:

·       Please don’t leave it TBD unless you have no choice – it makes a huge difference when bidding, price can be $10.00 yd - $80.00 yd

·       Decide up front if you are using multiple colors and communicate that clearly,  it makes a difference in the amount of fabric needed

·       know the lead time – if it’s 12 weeks there may be a problem

·        know the width the fabric comes in and don’t design panels larger than the fabric can cover, allow for thickness of the panel and figure 4-5” for wrapping the back

·       Be careful of fabric with backing, a quick test to see if a fabric is acoustically transparent is to blow through it – if you feel the air on the other side then sound can get through it as well

·       Does the fabric have a directional pattern, if so these are likely to cost more because there will be more waste when laying out panels.  Fabric can be “railroaded” or run the “long” way on the panels.  Just be sure you understand the pattern and how it is laid out

How design of sound panels affects the schedule:

If you design panels floor to ceiling, corner to corner the wall cannot be measured until it is actually built.  This is very likely to cause a delay.  The order has to be placed with accurate measurements, the manufacturer does a set of drawings and returns them for approval, the drawings are checked over and returned approved – and then production is scheduled.  If there is a long lead time on fabric things get worse.  Ways to deal with the situation: fabric can be ordered ahead of time but someone (not me) has to take the responsibility for the quantity of fabric since there aren’t final measurements.  By designing “island” panels, sizes independent of the built wall, the panels can be ordered at any time so they can be delivered when they are needed

Stretch panel systems can help with the schedule in some cases, still have the fabric lead time.  If you want a complex design then perhaps stretch systems are the way to go.  Keep in mind you are not likely to get as many bids since it is not something just everyone installs but it can be a problem solver and offers some additional design flexibility.

When trying to figure out how much absorption to put in a space there are some on-line tools that can help.  Some of it is common sense to a degree, how much will the design allow.  If you are limited by space and/or budget put absorption on two adjacent walls rather than opposite walls.  The results will be better.  Feel free to ask me about a tool I use frequently to help determine how much and where to put panels.

STC refer to handout

Sound Transission Class – sound that goes through the wall, from space to space.  It is important to remember STC is the result of an assembly, not an individual product.

Things such as off-set stud walls and resilient channel have been around a long time and certainly do work when installed correctly.  Sound board has been around for a long time as well.  It is basically mineral fiber in a large sheet, think 4’x8’ ceiling tile, and installed behind the drywall.  See manufacturer’s literature for ratings by assembly.

Of course an extra layer of drywall often times works, don’t let the seams line up.  Another product that has been around awhile and is very effective is vinyl loaded noise barrier.  The material is approximately 3/16” thick and comes in rolls and it weighs one pound per square foot.  This can be applied to the studs behind one side of the drywall or for very severe cases woven between the studs in an off-set stud construction.

One of the newer products on the market these days are drywalls that have a layer of material in the middle that will help stop sound transfer.  These products are more expensive than regular drywall of course but do a good job.  These can be added to an existing wall, the board can be finished just like standard drywall.  See the manufacturer’s literature for assemblies

Important things to know when designing a wall to stop sound: back to back electrical boxes are a super highway for sound – if you have them in an existing wall there are pads that can be put between them to help stop the transmission.  Sound caulk should be used where the wall meets the floor, ceiling and corners.  A room designed with all the best sound control in the world won’t make up for a door that doesn’t stop sound, or an open window.  Sound through a small opening fans out into the opposite space.

CAC refer to handout

Ceiling Attenuation Class

This typically comes into play when you have an open plenum and sound can carry from office to office. Acoustical ceilings with good NRC ratings will not automatically result in a good CAC rating.  There are ceiling tiles with CAC backing, often times foil.  Many times with tile and grid batt insulation will be put along the edge of the dividing wall to help stop sound transfer.  This is one of those common practices that isn’t officially endorsed by tile manufacturers.  When doing this it is important to remember to put the weight of the batts on the mains, not on the cross tees.

Drywall lids don’t usually cause a problem in this area.

AC refer to handout

 Articulation class, this refers to open office areas and the sound that carries over the partitions.  As the issue of daylighting becomes more prevalent partitions are getting lower and/or have glass at the top.  These things will have an effect on the acoustical function of the space.  When designing an open plan office using a high NRC tile will help.  Sound masking can also come into play but that is an area I know nothing about so I won’t go there. 

SABIN refer to handout 

This term often comes up when using things such as hanging baffles or cantenary banners – product that can absorb noise from both sides.  Still comes down to NRC, how much sound is kept from being reflected back into the space.

So when it comes to acoustics, please always consider it in any design, you may find you don’t need to do anything extra but you may also find you do need to do something.  It is always more expensive to do it later.

1.    Figure out the specific problem you need to solve – NRC, STC

2.    How bad is the problem likely to be

3.    Look for the right solution, remember often times it’s a combination of solutions

4.    Don’t waste money on overkill but don’t leave it out either