Industrial noise, whether generated by a printing press or steel punch, travels in the form of sound waves from the offending machine through the air, reflecting off the various wall and ceiling surfaces back into the room causing a never ending clatter.

The problem with industrial noise is that it not only causes ear damage; the brain has to work all the harder to discern 'important sound' such as instructions, safety announcements or task monitors such as beeper or buzzers. The greater degree the distraction; the more 'work' the brain must do. This is a form of ear fatigue. The more employees are subjected to offensive noise, the less attentive they are and it follows that productivity suffers.

To reduce noise in these environments, there are basically two actions that can be taken: The first is to contain the offending machine by building an acoustically designed room around it. The second is to introduce acoustical panels throughout the facility.

Reducing noise in large industrial rooms

Sound expands spherically at a rate of 4 every time you double the distance. If it is impossible to contain the sound locally, then the most effective method of controlling sound in large industrial buildings is to create 'traps' that capture sound as it tries to expand. These traps are in fact, corners and treating corners is the most effective place to apply acoustic panels.

It is important to note that the performance of acoustic treatment follows a bell curve whereby the more you put in, the more noise you will absorb. For instance, a couple of 2'x4' acoustic panels on a wall in a 12,000 sq-ft facility will do little to control the noise. At the other extreme, applying acoustic panels to every surface will do wonders but will cause the accountant to have a heart attack!

The logic is simple: measure the surface area (walls and ceiling). For instance, a 12,000 Sq-Ft tilt-up facility would measure 23,750 sq-ft of surface area. A practical target is 25% coverage or about 6000 sq-ft of absorptive surface area.

Walls 1 and 2: 75ft x 25ft = 1875 each (total 3750 sq/ft)
Walls 3 and 4: 160ft x 25ft = 4000 each (total 8000 sq/ft)
Ceiling surface: 160ft x 75ft = 12,000 sq/ft
Total: 23,750 sq/ft
Acoustic material target (25%): 23,750 x 25% = 5937 sq/ft

As mentioned, corners are the most effective place to apply absorptive panels. This is because sound that strikes an untreated surface, in this case an adjacent wall, reflects off the wall and is absorbed before it has a chance to expand. We can create even more corners by hanging baffles in a tic-tac-toe grid in between the ceiling joists. Baffles are particularly effective as they are open on two sides. This makes the twice as effective as wall mounted panels and therefore can significantly lower the panel count and cost!

Containing offending machines
There are various levels of containment that must be considered before building a room around a particular machine. The most obvious question is whether the machine can be contained at all. For instance, incoming and outgoing process materials may make containing a machine impractical. This TecNote will look at three options to consider:

(a) Full containment - building a room inside a room
(b) Partial containment - using the maze concept
(c) Constructing barriers - to limit sound exposure

Full Containment
To stop sound, you must eliminate transmission lines. Sound travels through vibrations in the air, walls and even the floor. The louder the noise and the lower the frequency, the more difficult it is to contain. To contain sound, you need mass or heavy walls and ceilings. Sheetrock (drywall) is cost effective, easy to build with and is heavy. This makes it ideal for containing sound. Two or three sheets on top of each other will build up a lot of mass and can be very effective. To take the process up a notch, building offset stud walls reduces the coupling as sound hits the inside wall and causes the outer wall to vibrate. Varying the mass of one of the walls by applying an extra sheet of drywall will cause the two walls to vibrate at different frequencies, further improving the performance. Using heavy, double and triple glazed windows and heavy exterior doors will help reduce noise from escaping. Insulating all seams around doors, windows, air vents, and electrical outlets will help. Remember - where air passes; so does sound. Once the room is built, treating the inside of the room with acoustic panels is essential. Thicker 3" material is best as it will absorb frequencies down to 500Hz. The more material you install inside the room walls and ceilings, the better. This of course will be determined by your budget.

Partial containment
For machines that require constant access for incoming and outgoing process materials, strategically placed 'walls, tunnels and canopies' can help contain the noise. These are typically constructed using plywood and can be hung on top of the machine or be self-supporting. All inner surfaces should be treated with acoustic panels to capture the noise. As sound expands by a factor of 4 every time you double the distance, placing the panels as close as possible to the offending machine is best.

Barriers
Simple barriers made from plywood and covered with acoustic material can help reduce noise considerably as the direct sound is usually significantly louder than reflected energy. These barriers are easy to construct and are generally positioned using line of sight. The reason for this is that high frequencies above 250Hz are much more directional than low frequencies which for all practical purposes, will simply pass through or go around a barrier.

Primacoustic Broadway panels are made from high-density fiberglass and are covered in a durable fabric. They are Class-A fire rated making them safe for use in public places and available in a variety of sizes and basic colors. They are easy to install, and are well priced! This makes them a great choice for industrial noise applications.