Perhaps the most common symptom among disengaged employees is their sense of being ‘cogs in the machine’, simply performing perfunctory tasks and unable to take real ownership of their work. As such, companies that want to improve employee engagement may need to rethink their techniques from the bottom up, creating more empowered employees who take an active role within the firm.
Open Celled Foams
Acoustic foams or foam that absorb energy usually above 125 cycles are technically called open celled foams. Open celled foams have just what the name implies, open cells. If you look at an open celled foam closely you would see each one of these cells arranged cell to cell with no cap on the end. The cell structure is open in order to allow air movement hopefully carrying sound to enter each cell. The cells in most open celled foams are irregularly shaped.
The goal of acoustic foam is to provide for absorption in a portable and lightweight technology. It is also less expensive than building cabinets or boxes. Absorption is the goal and it begins for foams that are at least two inches thick around 125 cycles. The design goal after these variables are met is to provide as much absorption as one can within that 2 inches of foam and provide it quickly. Most acoustic foams begin absorbing around 100 Hz. and climb through 4,000 – 7,500 Hz.
There are two general types of sound absorbers. They are broken down into two main categories based on how they function. Our active absorbers is termed active because it will have a front panel or wall some call it a membrane. Air can also be part of an active absorber such as in the case of a Helmholtz resonator. An example of a Helmholtz resonator is a coke bottle. If you blow across the neck of the bottle you will recreate a resonating system that starts at 185 Hz.
A passive absorber will have no “moving parts”. Well, maybe some kinetic energy working with normal air flow across the surface of our passive absorber material. Examples of porous, passive, absorbing materials would be drapes, couches, or acoustical foam. Air flow through the porous material causes friction between the fibers or cells and acoustic energy is converted heat and transformed forever.
The term sound absorption coefficient is a number we use to denote the amount of absorption a material exhibits. If 50% of the energy is absorbed by the material, then we would assign it an absorbing coefficient of .50. One square foot of the material would be assigned an absorption coefficient of .50 which would equate to .50 absorption units or sabins. An open window is a perfect absorber. Sound leaves the room through the window and never returns. Each square foot of the window would be assigned an absorption coefficient of 1.00.
Auralex is a company that is well known. It offers many room acoustic products that range from low frequency absorbers through middle and high frequency absorption. Lets look at their two inch foam as our example:
TABLE HERE 125 at 11%, 250 at 30%, 500 at 91%, 1,000 at 100%, 2,000 at 100%, 4,000 at 100%.
Sonex is a second well known company that also has many sound absorbing products. One of their foam technologies is termed Super Sonex. Here are the numbers:
TABLE HERE 5% at 125, 30% at 250, 80% at 500, 90% at 1,000 95% at 2,000 and 99% at 4,000.
Acoustic Fields is a new company that also has its own foam. Here is the data:
TABLE HERE 125Hz.at 30% 250 at 64% 500 at 90%, 1,000 at 1,000Hz.
Three Foam Comparison
Lets look at all three sets of data. At 125 Hz. Aurelex is 11% and Sonex is at 5%. Acoustic Fields is at 30%. Both Auralex and Sonex are at 30% for 250 Hz. Acoustic Fields is at 64% more than twice as much absorption. All are around 90% at 500 cycles and close to 100 % after 1,000 Hz.
Acoustic Field’s Difference
Aurelex and Sonex perform basically the same from 125 Hz. – 1,000 Hz. but Acoustic Fields’s foam performs differently. It absorbs at higher rates starting at 125 Hz. At 125 Hz. Aurelex is at 11%, Sonex at 5% and Acoustic Fields is 30%. Acoustic Fields foam is 6 times more powerful at 125Hz. than Sonex and 3 times more powerful than Aurelex. At 250 Hz, the trend continues. Aurelex is at 30%, Sonex is at 30% and Acoustic Fields is at 64%. This is twice the absorption at 250 cycles than either Aurelex or Sonex.
ALL THREE IN ONE TABLE HERE
Critical Band: 125Hz.-250Hz.
The 125 Hz. – 250 Hz. band is a critical band for vocals and guitars. It is critical for piano and brass. Our mixes build up in this low middle frequency area and extra absorption is always welcome for clarity and definition. This frequency range is also very problematic in today’s smaller recording studios. Smaller room dimensions create unwanted resonances within the 125 Hz.- 250 Hz. ranges. A smooth even absorption rate and level goes along way to clarity and reduces mid range “muddiness” both in playback and recording environments.
New Foam On The Block
All foams are not created equal. Acoustic Field’s foam technology absorbs at higher rates than other open celled acoustic foams. This increased absorption is centered in the 125Hz. – 250Hz. which is a critical band for our middle frequencies that affect our vocals, guitars, and pianos. This 125 – 250 cycle range is also critical in small room acoustical environments. Our physically smaller project studios almost generate resonances within this area. We need all the absorption help we can get in this frequency range.
Acoustic Fields 1″ foam: 15 30 65 92 90
I’m helping a friend with his studio. He’s got a live room which is roughly 25″x8″x9″. It’s pretty much a square concrete tube with acoustic foam in some spaces but not enough to cover all. Any suggestions on how to treat the tube resonance issues? Would rock wool traps help? Any ideas or tips would be greatly appreciated.
The 25′ dimension is good but the 8′ or 9′ width or height is not. The axial mode issues between the short side walls will require at least a 12″ space loss on each wall in order to provide the necessary real estate to minimize them or lower their nuisance value at the mixing or listening position, leaving a 6′ horizontal wall dimension. This is not exceptable in any acoustic sense. There will be many axial modal resonances and they will all possess lots of power at their respective room mode positions with in the room. They will overpower your middle frequencies and you will always be working around them in the mix.
Try to find a room that has at least a 12′ width. We really need a minimum of 12′ to fully accept a 100 Hz. wavelength. Hopefully, you can keep the 25″ length. Rock wool traps will not provide the rates and levels of absorption needed for your room size. They will work within their design parameters. There design parameters will not go low enough to handle your issues.
I’m converting a bedroom into a control room and I could really do with your advice. The dimensions are 12ft by 7ft and I’d like to split it in two using a false build wall. Budget’s not really an issue. The floor is concrete and the walls are stud brick. Basically I’m looking to produce the best listening environment. What should I do? Is the space big enough and worth all the effort of putting in the wall?
I want to make sure I understand your question. You want to take a room that measure 12’x 7′ and divide it into two equal rooms of 6′ x 3 1/2′?
I am assuming a room height of 8′.
If this is true, neither of your new rooms will work for a listening environment and definitely not for a control room. A room that is 3 1/2′ wide and 6′ long is about the size of a closet.The original size of 12′ x 7′ would work for a listening room and or a monitor room if you could get the acoustical issues under control. This will be no easy task, no matter what the acoustic foam companies tell you.
Since your room size is so small, you will have to control all room boundary reflections with a minimum of 2″ of acoustic foam. We will have to leave the bass issues alone for now. There is no room to deal with them in these room sizes unless we can build into the walls themselves. you will have to give up 12″ on each wall space to achieve satisfactory levels of low frequency absorption.
I would strongly consider finding a larger room. You will be fighting less in your mixes with a larger room. You can keep the 12′ room dimension but the 7′ has got to go from any acoustical perspective considered.
I want to soundproof my home recording studio from scratch. It measures 35 ft by 38 ft and has a 10 ft. ceiling. I’ll need to soundproof the walls, floor and ceiling as it’s in a residential complex in NYC. I’ve only ever used foam and didn’t cover the whole space so what kind of costs am I looking at? Also to what degree can I solve the sound bleed issue so I don’t annoy the neighbors?
You will need barrier technology that achieves a STC rating of 65 or better if you have neighbors and you are going to be playing music at the pressure levels most studios I know play at. Your room is huge and low pressure energy will have room to move without causing noticeable resonances. However, you must isolate your existing room from the rest of the building to avoid sound “bleed” into your neighbor’s rooms. You have no choice but to build a room within a room and mechanically decouple your new floating room from your existing room. Your new room will float on vibrational isolators and be a sealed unit inside but not touching your existing room.
You can build the room out of block or frame. You can use 2″ x 10″ stud and frame out 3″ from the existing wall from all four walls and then the ceiling. This will be your new room basic foot print. Barrier techniques and materials will then be applied systematically on this 2″ x 10″ frame. The Internal wall cavity can be filled with a blend of activated carbon and specialty mineral wool.
If you have certain neighbors that are sound sensitive more so than others, you may need additional barrier technology on the shared surface area between you and your neighbors. This is a difficult project and you must spend time and energy in the design, material choice, and definitely the construction methodology for success to occur. Without a professionally supervised installation you are wasting time and money.
I’m adapting the front room of my apartment so it can be used as a home studio. The problem is the sound is awful at present with an annoying long boom in the 50Hz range and strong mode issues between 100 and 150 or so.
I believe it is because of the brick walls which are 12ft distance from each other and which the speakers directly fire at. Because it is also my lounge I don’t want it to be too covered in thick tube traps (12 to 17cm would be max). Also I don’t own the property so I can’t really go about mashing up the walls or ceilings too much with screws, etc. I have some space available either side of the speakers for traps.
Do you have any recommendations of what I can do with this situation?
You will have to trade real estate to minimize your acoustical issues. To deal with your particular situation, you will need some frequency specific low frequency absorbers and you will also need some broadband absorbers to cover the 100 – 150 cycle range. Acoustic foams do go down to 100 Hz. but their rate and level of absorption will be lower than you will probably require. You need serious low frequency absorption to deal with a 50 Hz. resonances.
Since you do not own the property, you can get freestanding absorbers that will assist you but you will have to provide places for them to go into. These places are not places of convenience or because you have the room for them in this or that location, but they need to be placed where the resonances are within the room to have maximum impact. The side walls at 12′ present axial modal issues that must be addressed with low frequency absorbers that have the necessary rates and levels of absorption to deal with their magnitude.
Space next to your speakers can be a good place to start with low frequency absorption because the speaker is a pressure source and placing low frequency next to the pressure source is advisable when you are trying to reduce low frequency pressure issues. This is no place for foam. Use diaphragmatic absorption because it works well in regions and areas of high pressure. In fact, diaphragmatic absorption needs sound pressure to operate at its best. You can add foam to the low frequency absorber to handle middle and high frequencies.
And welcome to my new weekly Monday mailbag where I’m going to answer the many questions that come in via email to us so as to help out fellow home studio designers and audiophiles. I’ll be here every Monday with answers to all your latest questions. So if you’ve got something you need answered in relation to sound diffussion, home studio and theatre sound design and more then please feel free to send them into firstname.lastname@example.org.
To get us started this week I thought I’d answer this message that came in from Todd in Atlanta, Georgia.
Been reading the blog for a while now and thought you were the perfect brain to pick before I get started with my studio installation. I really want to know what’s the best bang for my buck – acoustic foam or acoustic panels?
I’m almost done installing my vocal booth. I jusy need to finish the door and window plus I need to add the insulators but my funds are running out. Would I be better off getting foams or panels? In the long run what will be the difference in the sound recordings?
It is nice to see someone taking on a vocal booth project. It is no easy task.
Window – Laminated Glass
Lets examine the window first. Always use a laminated window that has laminated glass on at least one side of your vocal booth window. A laminated window has a layer of plastic melted onto its surface and thus adhering to the glass pane itself. Remember, sound isolation technology is all about minimizing vibrations. Since you are on a budget, use 1/4″ thick laminated glass as a minimum thickness.
Position the glass into a frame and then secure the frame into the window opening. Use an acoustic sealant between the laminated glass and the window frame and also the vocal booth window opening and the frame itself. For better results, place another piece of laminated glass, 1/4″ thick, leaving a 1″ air space between both 1/4″ laminated pieces into the window frame. This dual pane method is worth the extra cost in materials, since it appears that you are doing all the labor.
Mass Layered Door
For the door, you can take two pieces of 1″ MDF or multiple density fiberboard. Make sure it is the commercial grade MDF, it will be smoother and easier to finish if you desire. on top of 1″ MDF door piece, glue a vibrational damping sheet of at least 1/8″ thickness to one of the MDF sides. Make sure there is more glue applied to the exposed damping compound. Place the second MDF piece on top of the glued damping compound. You must place an acoustic glue or sealant on both sides of the damping compound. You are making a sandwich of two – 1″ pieces of MDF with a thin slice of vibrational damping compound glued between them.
Place self tapping deck screws that are 1/1/2″ long, 12″ on center throughout the door surface area. This is a heavy door. make sure your hinges can support the weight. You will be at 10 lbs/sq.ft. Do not forget to include a heavy duty weatherstrip between all edges of the door to door frame contact ares. A small air hole is like a leak in a high pressure dam. It will leak lots of sound energy.
Inside Booth Foam
Treating the inside of your vocal booth with foam absorbing technology is the most economical way to cover the vocal frequency ranges you will be dealing with which start around 150 Hz. and go past 4,000 Hz. Make sure you choose a foam that absorbs at the proper rates and levels that are necessary for you to achieve whatever vocal sound you are going for. A closed cell foam will give you those necessary rates and levels of absorption in your vocal booth. Thicker closed cell foams will produce higher rates and levels than thinner foam of the same type. I would suggest starting with 1″ thick closed cell foam.