Enclosures can Amplify Escaping Noise

Recently, an Acoustical Solutions customer asked the following about acoustical enclosures:

“What do you recommend to reduce the noise from my neighbor’s swimming pool equipment? The equipment is up against the exterior stucco wall of his home and is also enclosed be a 3-sided concrete block walls with a wooden door. There is no top on the enclosure…”

First of all, doesn’t it seem like noisy machinery should be quieted by the surrounding block and stucco walls? If noise is escaping, it would be going up out of the top of the machinery and straight up into space, not bothering neighbors, right? Unfortunately, this is not the case.

Only a few things can happen when sound waves reach a surface. The sound can either be absorbed, reflected, or a combination of the two. This depends on the type of surface the sound waves are coming into contact with. Hard, flat surfaces will reflect the most sound, whereas porous, soft surfaces generally are more absorptive.

So, returning to our customer’s dilemma, we can now understand why although the equipment was surrounded by dense walls, the neighbors were still bothered by sound. The block walls ‘block’ noise from passing through, no pun intended, but they do nothing to absorb sound, therefore noise is reflecting back and forth in the enclosure until it eventually shoots out the top at multiple angles.

Here is the situation explained by Acoustical Solutions Sales Rep Kevin McIver: “The neighbor did well in surrounding the pump to block the sound, but the hard surfaces around it are now amplifying the sound before it blasts out the open top of the enclosure and bounces off his house towards other homes. I’d either recommend acoustical blankets to line all of the walls or 2″ PolySorpt^® Acoustical Panels. The blankets or panels will provide an absorptive layer inside the enclosure which will greatly reduce the amount of sound trying to escape”.

Now it all makes sense. You don’t necessarily need a top on an enclosure unless what you are trying to keep sound away from is directly above the source, all you need is for the inside of the enclosure to be absorptive and much less noise will escape.

This same principle applies to enclosures of a much larger sort, actual rooms.

Colonial Williamsburg is a popular historical attraction in Virginia. One of their most impressive facilities is the Williamsburg Lodge and the upscale Lodge Restaurant with a state of the art kitchen, which is open to the dining room for guests to see.

The problem is, whatever noise is made in the kitchen seems to be amplified in the dining room.

Sound familiar? The kitchen, surrounded by all hard surfaces save one, has noise being reflected about the room and amplified before it shoots out into the dining room. It is essentially behaving as the block wall enclosure, just turned on its side.

The Williamsburg Lodge contacted Gary Hudson at Acoustical Solutions, LLC., who found the source of the problem: “Kitchens have a lot of reflective surfaces, so all the noise being made there is being reflected around and shot out the only unblocked space — into the dining room”.

Hudson recommended the ceiling tiles be replaced with acoustical ceiling tiles, and that acoustical wall panels be installed. AlphaEnviro^® Wall Panels were installed strategically along the perimeter of the kitchen, and 2″ thick AlphaEnviro^® PVC Ceiling Tiles were used to replace the existing ceiling.

After the acoustical products were installed, echo and reverberation decreased in the kitchen allowing for increased speech intelligibility and a more pleasant work environment for those preparing meals. More importantly, however, patrons seated in the dining hall no longer heard every clatter and bang made in the neighboring area.

“The Kitchen turned out really well,” said Lee Anderson of the Colonial Williamsburg Foundation, “we received many compliments from the first day it was up”.

The key point to remember about acoustical enclosures then, is that if there are openings, it is best that the inside of the enclosure has absorptive surfaces.