Marchman Technical College – Educational, Acoustical Absorption

Noise control and sound privacy within educational settings are imperative. During the design process, target STC’s for walls should be discussed and mandated by the architect, but oftentimes topical acoustical treatment for larger spaces is held until after construction is complete. With the hard, reflective surfaces present within gymnasiums, cafeterias, and auditoriums, acoustical absorption is needed to maintain speech intelligibility and reduce reverberation.

The architects for Marchman Technical College consulted with Commercial Acoustics for their cafeteria space, where we supplied them with 100 PVC-wrapped baffles to absorb soundwaves. After installing the baffles, reverberation in the cafeteria space was significantly reduced and sound privacy was finally reestablished.

Tampa Office Acoustics

An open office area was struggling with reverberation in their space and called Commercial Acoustics to help. We visited and found that unlike most open offices, that have issues with sound masking and speech privacy, this office setting did truly have unwanted echo in the space. This was due to a thin carpet, corrugated metal deck, and painted drywall.

Our team fabricated acoustic panels, baffles, and clouds, and used them in the space to deaden the excessive reverberation. We self-performed the install over a few hours, and finally provided their employees and staff the acoustical peace they were looking for.

 

 

Tropical Smoothie Case Study

As with many restaurants, Tropical Smoothie was suffering unwanted reverberation due to hard surfaces in their kitchen and dining area. We came on site and performed a reverberation test, then implemented a unique solution that improved their acoustics and aesthetics; a custom-printed absorption panel. The printing is done on acoustically-transparent fabric that allows the sound to transition into the absorbing core, made of mineral fiber.

The panel was custom-made over a 2-week timeframe, and installed on site in hours.

Lake House Acoustical Treatment

At the Lake House room in a luxury, master-planned community in Lake Nona, Florida, an unexpected issue arose.

The aesthetics of the room were impeccable. The room was adorned floor to ceiling windows along the walls, and custom chandeliers in the center. The hardwood floor was especially unique – charred in an oven for hours, then sand blasted to remove the marks – it felt more like tile than traditional hardwood. All of the mechanical devices were run by a single, wall-mounted flat-screen device, including the projector, room divider, and air conditioning.

However, regardless of the premium finishes and expensive electronics, one problem remained identified. With all of these hard surfaces, the reverberation time in the space was surprisingly long. While local residents use the room for meetings or yoga classes, it became very difficult to communicate with the echo that they experienced. A phenomenon known as “speech intelligibility”, this is a common issue experienced in gyms, auditoriums, and restaurants.

Unwanted reverberation or echo occurs when areas have large volumes and smooth, hard surfaces that reflect the sound back inward. When this happens, humans hear reflected noises as new words are being spoken, and have a difficult time identifying exactly what is being said.

The solution is to add soft, acoustical materials into the space, allowing the sound to be absorbed into its porous mass. The sound is then transformed into thermal energy and dissipated into the environment. The amount of absorption needed in a space is determined by the specific geometry and materials contained within.

For the Lake House, our production team custom-fabricated 100 2’ Wide x 4’ Long x 2” Thick Acoustical Panels, fabric-covered in the desired texture and color. Within 2 weeks the panels were delivered to site, and installed into the corrugated metal deck of the large room. Testing before and after the installation confirmed a drastic reduction in reverberation, from 1.5 seconds to 0.58 seconds.

This reduction resulted in a significant improvement in the perceived acoustic environment in the space. When previously conversation was strained, it was now smooth and neighbors had little difficulty understanding instructions and dialog.

Overall, the project took 3 weeks to complete, and the turn-key solution was provided at under $11,000.

Restaurant Acoustical Absorption

Cena Restauarant

While many restaurateurs struggle with acoustic issues, some are more critical than others. Take for instance, Tampa’s downtown Channelside restaurant Cena. A high-end Italian Cafe focused on upscale Mediterranean cuisine, the restaurant was a perfect storm of underlying acoustical concerns. The walls were painted gypsum with a significant square footage of windows. Meanwhile the tall ceilings created a large volume with little porous material to absorb the dinnertime conversation. The result – an echoey room that made conversing difficult.

With a limited budget and tight timeline before the holiday season, Cena management reached out to Commercial Acoustics for a cost effective solution. We measured their reverberation time of approximately 1.1 seconds, relatively high for a commercial dining space. After simulating the proper amount and type of absorption material, we proposed the solution to achieve 0.7 seconds, ideal for this type of restaurant. The solution included 2” thick fiberglass clouds and panels – capable of absorbing the low frequency discussions.

Within weeks we manufactured the ceiling clouds and panels in-house and coordinated installation. All fabric finishes were reviewed with the client and not only blended in but enhanced the existing décor. Installation occurred during closed business hours and was completed in a single afternoon. We measured reverb time afterwards and it met our target decay rates, but would it stand the true test? We met with Cena’s owner who was pleasantly surprised and stated “The panels really work! I had dinner with several friends and the place was packed and we had great ability to converse”.

We were able to provide this customized, acoustical solution before the busy holiday rush of patrons. Better yet, the manufacturing and installation took just over 3 weeks and we were able to deliver results to the client for under 6K.

Museum Acoustics

Acoustic Ceiling Cloud

We recently treated a small art museum in the city of St. Petersburg, Florida. The facility was moving from bamboo flooring to polished concrete, and the facility manager had concern for an increase in noise level (for a room that was already relatively loud). They host parties and gatherings as well, which leads to elevated speech and reverberation in the space.

Since artwork is on all of the walls, we needed to focus our acoustical treatment on the ceilings above. Acoustical Ceiling Clouds are an effective and aesthetic solution to absorbing unwanted noise in your enclosed space. While they may be more expensive than acoustical panels, they are also more flexible in their application – they may be hung along ceilings and exposed joists, up and out of the way.

The museum rooms had a moderate volume, and the measured reverberation time in the space was approximately 1.6 seconds prior to the floor retrofit. We calculated that the estimated reverb time would increase to 1.8 seconds with the concrete floor. Therefore, 2 moderate-sized clouds (4’x4’) were suggested for each room to bring the reverb back to the 1.4 second range. While still longer than preferred, the treatment would greatly reduce unwanted noise buildup during events and also make speech intelligibility more pleasant during smaller viewings.

We applied the 6 (total) ceiling clouds in a single morning, and the white light selected blended well with the white ceilings above. Overall, the project cost a total of approximately $3,000 and the lead time on the clouds was only a few weeks.

Acoustic Ceiling Cloud

Acoustic Ceiling Cloud

Acoustic Ceiling Cloud

Using Absorption for Noise Reduction (NR)

dB-reduction

I approach this article with caution, due to the vast amount of misinformation and confusion between the concepts of absorption and sound-blocking.

At Commercial Acoustics, we begin each of our architectural courses with a strong distinction between these pillars of the acoustical world, and even with our architect clients, there is typically still 1-2 attendees that ask additional questions.

At a high level, sound-blocking principles should be used when you have noise transferring from a noisy area to a quieter one and would like to reduce this transmission, while absorption is used in large areas with echoes and reverberation control issues. However, there are a few select scenarios where absorption in the source room may be used to lower the overall dB level, and by result, reduce the amount of sound spilling into adjacent units nearby.

For example, a bar-restaurant in St Pete that we consulted with several years ago was experiencing complaints from tenants upstairs that were constantly annoyed by the din on the bottom floor. The restaurant already had fire-proofing completed on their corrugated metal ceiling, and refinishing the ceiling with soundproofing membranes and going through the approvals process was cost-prohibitive. However, we noticed that there was very little absorption in the space, and therefore noise from the patrons was reverberating in the space and creating an unnecessarily noisy environment. The principle of Noise Reduction (NR) tells us:

 

NR=10log(a2/a1)

a2: absorption in treated space

a1: absorption in initial space

 

This means that increasing the absorption in a space by a sizeable amount can result in reducing the overall decibel level. Specifically, increasing the absorption by 300% can lower the noise level by 5dB. Since there was so little absorption in the space, increasing by 300% was possible at a fraction of the price of re-constructing the floor-ceiling system above.

dB-reduction

Ultimately, this approach may be used for significant improvement in areas with little absorption as well as loud noise and reverberation that leaks into adjacent spaces. This includes bars and restaurants with nearby dwellings. However, this will only treat reverberant noise, and should not be used to treat direct field sources such as a speaker or television right next to a neighbor’s wall.

How Much Sound Absorption Do I Need?

Acoustic Panels

At Commercial Acoustics, we approach every new absorption project with the same mindset – determine how much absorption is needed, then provide it in a cost-effective and timely manner. There are a few characteristics that typically demand some type of acoustic treatments – high vaulted ceilings, smooth walls, and no plush materials such as carpets and heavy drapes. When you notice an unwanted reverberation in your space, you can call an acoustical contractor, or just calculate your needed treatment.

Sabins Calculation Explained

To determine how much absorption you need in your space, follow the steps below:

First, calculate how many square feet the room is, and how tall the walls are. Multiply these units together, and you have the cubic volume of your space.

Then, add together the total square footage available in the room.

How absorptive is each surface? Check out our absorption coefficients here.

Total Surface Area = SA_floor + SA_walls + SA_Ceiling

The worst absorptive surfaces are hard, flat, and smooth. If they are parallel, that further worsens the situation.

The worst case scenario is a room of painted drywall that is a perfect cube, allowing resonant sound waves to reverberate continuously with minimal absorption or attenuation.

If there are no plush carpets or furntiture in the room, you are likely to have additional echo issues.

Sound Absorption Example Calculation

Example 1: You have a 20’ x 20’ room, with 16’ tall walls. The ceiling and walls are painted drywall, and the floor is painted concrete. This is a gym used for yoga, but the instructor has a difficult time talking to students due to the echo.

The area of the room is 20×20 = 400 sq ft. This is not exceptionally large, and usually would not be a problem if it weren’t for all of the hard surfaces.

Total area of the walls is 4 x (Area of Each Wall), or 4 x 20 x 16 = 1280 sq ft

Finally, the area of the ceiling is the same as the area of the floor, which is 400 sq ft.

Now, let’s determine the total volume of the room. Because it is a rectangular prism, it is simply 20x20x16, or 6400 cubic feet.

Finally, we just need to determine how much acoustic absorption space we have. In this case, painted drywall has an NRC, or acoustic coefficient, of 0.1. That means it reflects 90% of the sound that impacts against it, and absorbs only 10%. Likewise, painted concrete only absorbs approximately 10%.

To find the absorption area of the floor, we multiply the area of the floor by the NRC of the floor. 400 sq ft x 0.1 NRC = 40 Sabins.

The ceiling and the walls follow the same approach:

Ceiling = 400 sq ft x 0.1 NRC = 40 Sabins

Walls = 1280 sq ft x 0.1 NRC = 128 Sabins

Therefore, the Total Sabins, or acoustic absorption in the room is 208 Sabins.

Now, let’s plug this in to the Sabins Formula: RT = .049*V/A

We find that the reverb time in the space is 1.5 seconds, which explains why it is so poor. Compare that against the table of acceptable reverberation times here.

*There are other considerations, although this simplified model does give fairly accurate results.

For instance, is there furniture, which can often increase the NRC of the room?

Also, parallel walls allow standing waves to develop, which amplify the reverberation in the room.

Check out our proprietary acoustical calculator tool, and determine how much absorption you need in your space today!

Common Absorption Coefficients for Acoustical Treatments

Multi-Surface Acoustical Coefficient
Smooth Concrete – Unpainted 0.2
Smooth Concrete – Painted 0.05
Wood 0.15
Rubber 0.05
Plywood 0.25
Walls – Acoustical Coefficient
CMU – Unpainted 0.35
CMU – Painted 0.05
Brick – Unpainted 0.05
Brick – Painted 0.025
Steel – Structural 0.1
Plaster 0.05
Gypsum 0.1
Glass 0.05
Flooring – Acoustical Coefficient
Linoleum 0.05
Terrazo 0
Marble 0
Carpet on Foam Rubber 0.55
Carpet on Padding 0.3
Low Carpet 0.2
Hardwood 0.3
Treatments – Acoustical Coefficients
Cellulose Fibers (1″) 0.75
Polyurethane Foam 0.3
Semi Rigid Fiberglass (1″) 0.75
Cork Tiles 0.7
Acoustic Ceiling Tiles 0.5