Primacoustic Cumulus - Ceiling Corner Trap (Grey)


The Cumulus is a high-performance tri-corner bass trap that is designed to seamlessly integrate into most rooms without interfering with the natural room décor.

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Cumulus - Tri-Corner Bass Trap

The Cumulus is a high-performance tri-corner bass trap that is designed to seamlessly integrate into most rooms without interfering with the natural room décor.

Given the choice, acousticians will always employ corners for acoustic sound control. This is primarily due to the way sound propagates inside a room, whereby the walls and ceiling act as waveguides that drive sound to the corners where it gathers. The Cumulus nestles high, up into the tri-corner where the walls and ceiling intersect for maximum efficiency.

Made from high-density 6lb per cubic foot (96 kg/m³) glass wool, the Cumulus delivers exceptional sound absorption, is safe to handle, and has been tested to meet stringent Class-A/1 fire requirements for use anywhere. Front and back surfaces are bonded to micromesh and the edges are resin hardened to fully encapsulate the minute fibers. The panel is then wrapped in an acoustically transparent fabric to ensure maximum sound absorption. A unique spring tensioned clamping system securely holds the panel in place while making installation quick, easy and invisible.

At first view, the Cumulus appears to be quite large. But once the 24″ (60cm) panel snaps into position, it only extends down 17″ talking up very little wall space. This creates a 17″ deep air cavity behind the front facing panel that delivers broadband absorption down to 100Hz for control over model distortion in the problematic low-mid region. This makes the Cumulus the perfect acoustic starting point for home theaters and post production suites that have limited wall space and suffer from over-saturation of lower mid-range frequencies (boomy). For professional studios, the Cumulus helps eliminate standing waves and for voice-over booths, it provides an effective solution for the usual “chest-hump” that plagues most vocal booths in the 200Hz to 300Hz region.

The Cumulus tri-corner trap is a highly effective broadband absorber that comes in a choice of three architecturally neutral colors to match most room décors. The Cumulus comes complete with all of the installation hardware, saving valuable time.


In a Studio

This image shows the Cumulus in a typical project studio applications. The Cumulus is positioned high & out of the way to help control bass, making installation easy in any room.


In a Vocal Booth

Small rooms like vocal booths are plagued with problems in the 150Hz to 400Hz region. The Cumulus is extremely effective at absorbing these frequencies reducing chest hump.


In a Home Theater

Home theatres are not just about sound. Acoustic panels must integrate with the décor. The Cumulus seamlessly installs in any corner without interfering with art and furniture.



Even though acousticians have long identified the benefits of treating the tri-corner, the difficulty of mounting acoustic panels in corners and a lack of ideal mounting options have discouraged people from taking advantage of this prime room location.

The Primacoustic Cumulus presents a simple and elegant solution. It is a surprisingly basic acoustic device combined with ingenious mounting hardware. Once installed, the Cumulus looks terrific and is highly effective at reducing low-mid frequencies that are attributed to ‘boomyness’ in a room. The magic lies in both the quality of the acoustic panel, its innovative design and the corner mounting location.


The 24″ triangular Cumulus panel is made from high density 6lb per cubic foot (96 kg/m³) rigid fiberglass (A). The same material broadcasters and world-class studios have used for years to control room acoustics. The panel is fully encapsulated with micromesh (B) and employs resin hardened edges (D). These panel treatments combine to ensure the minute glass fibers cannot escape and produce pleasing architecturally straight lines. The 2″ thick panel is then covered in an acoustically transparent fabric (C). The edges of the Cumulus trap are reversed beveled and form a wedge shape (E) that flush-mounts and naturally transitions from the walls and ceilings to create an elegant corner trap.

The strategic corner placement combined with the high performance acoustic panel and cleverly created air cavity behind make the Cumulus a highly effective broadband absorber. The Cumulus is available in three neutral colors that will easily integrate with the most architecturally demanding room designs.

Each side is 24″ in length and, when in place, creates a 17″ deep air space cavity behind the panel that increases the bass absorption characteristics. Mounting Cumulus traps in a room will generally yield a significant reduction in the problematic low-mid region while leaving the architectural design of the room virtually intact. Invisible mounting is achieved using spring-tensioned clasps and a single eye-screw. Mounting literally takes minutes and because of the reverse beveled edges Cumulus traps flush mount ‘seamlessly’ into the room aesthetics.

Cumulus traps have been tested to meet stringent Class-A/1 fire ratings making them suitable for use in residential and commercial spaces.


Dimensions: 24” (60.96cm) x 2” (5.08cm) Edges are reverse beveled.
Panel Material: Formed, semirigid inorganic glass fibers; Density = 6lb per cubic foot (96 kg/m³)
Fabric Facing: Acoustically transparent polyester
Fabric Color Codes: Black=00, Beige=03, Grey=08
Order Number: Z840-1210-xx (xx denotes color code 00=Black; 03= Beige; 08=Grey)
Mounting Hardware: Eye hook, drywall anchor and spring clip included.
Quantity per box: 2 units
Weight: Shipping weight = 5 lbs (individual weight = 1.4 lbs (0.64 kg)



Absorption Coefficients

How to Use

Easy to install.

We often get asked why the Cumulus is so unique. The answer is not so much the concept of using the tri-corner, as this has been well known for years. What makes it unique is the combination of the high-performance panel with our innovative spring mounting system. For an acoustic panel to be used, it must first be presentable. If all kinds of screws or hardware is visible, it simply will not make it into the living space!


The mounting system is made up of five (5) components:

  • Corner claws to grab onto the panel edges
  • Springs that keep the claws tensioned
  • A key-chain ring to attach the springs
  • An eye hook to hold the Cumulus up into the corner
  • A zip-tie to tension the device and hold it in place


All you do is attach the claws and springs to the Cumulus, mount the eye-hook into the ceiling and then snap the whole assembly together in place. Once up, it nestles nicely and almost invisibly into any room décor. If ever you want to move it, you simply pull the edge of the cumulus away from the wall, cut the zip-tie and it will release.

As for colors, the Cumulus is available in beige, grey or black. Should you wish to change the color, all you need to do is re-wrap the panel with any breathable cloth and spray adhesive. Only thick vinyl will have an effect on the sound as high frequencies may reflect off the harder shiny surface. Woven cottons or polyesters will simply be invisible.


Cumulus Science

The Science & Development Of The Cumulus

  • Walls and ceilings act as waveguides to gather sound in corners
  • The Inverse Square Law: Double the distance = ¼ the energy
  • High density Broadway versus low density foam
  • Using air space to your advantage to increase bass absorption


Walls and ceilings act as waveguides to gather sound in corners

For years, acousticians have always employed corners as their starting point when absorbing sound energy. This is because the walls and ceilings (and floor for that matter) act as waveguides that work together to redirect sound into the corner. The ‘epicenter’ is the tri-corner where the walls and the ceiling intersect. This is without question, the eye of the hurricane. It therefore makes sense that this be the primary location for placing an absorbent panel. The Cumulus name comes from the cloud family and if you think of the ‘accumulation of sound waves’ the name certainly is well chosen.

The concept of waves accumulating or being guided also applies to PA systems and how these devices employ horns to direct sound waves. In Figure 1, you can see how a horn’s 90° walls disperse sound waves outward from the driver, directing the energy out the energy. The walls of your room do the same thing but in reverse. Sound waves are guided toward the corners as shown in figure-2. High frequencies are directional and reflect off of walls toward the corners while low frequencies travel along room surfaces, eventually finding the corners.

By positioning an acoustic panel like the Cumulus in the tri-corner, you not only capture the direct radiating field (Figure 3, red lines), but also capture the reflections from the ‘wall-to-wall’ junction and the two ‘wall-to-ceiling’ junctions. Thus the reason corners are extremely effective for acoustic panel placement.


The Inverse-Square Law: Double the distance = ¼ the energy

When designing a sound system, sound pressure levels are calculated based on a function known as the inverse-square law. What this basically means is that each time you double the distance; the sound pressure will be reduced by a factor of four (-6dB). This is because sound, for the most part, expands in a spherical manner.

This image illustrates sound emanating from a traditional horn. Notice how the acoustic energy spreads as sound travels away from the source.

Now, consider the same effect when we apply the concept to a reflected sound off a nearby wall. With acoustics, if you can capture the sound before it expands, it is easier to control. Thus another very important reason why corners are so beneficial; you essentially get more absorption for your money!


High Density Broadway Versus Low Density Foam

Another important aspect to the Cumulus is the quality of the acoustic material. Most folks do not realize that the density of the material plays a critical role in how well sound will be absorbed. In acoustics, we do not want to simply absorb high frequencies, but ultimately would like to absorb all frequencies evenly.

Technically speaking, acoustic absorbers work by converting sound energy into heat. This science is known as thermo-dynamics. The point here is that when something moves, even if ever so slightly, it requires energy and the energy will dissipate into heat.

The two most common materials used to control sound are glass wool fiber (fiberglass bat) and open-cell urethane foam. These come in various formulations and densities. Too high of a density, and the absorption suffers. Too low of a density and the product will not have any effect on bass frequencies.

The graph to the right compares high density Primacoustic 2″ Broadway panels to 2″ urethane acoustic foam. Notice that both are equally effective in the upper registers above 1000Hz. But as you go down to deeper and deeper bass, the foam product quickly looses its effectiveness below 500Hz. In fact, it has almost zero effect on some of the most troublesome frequencies of all.

For instance, urethane foam is only 30% effective at 250Hz while the Cumulus high density glass wool panel is 85% effective at that same frequency. Broadway panels deliver even absorption from about 250Hz all the way up. This results in a more natural sounding room that will sound more musical and transparent.


Using Air to Increase Absorption

A great way to increase the absorption of an acoustic panel is by creating an air space behind it. This works particularly well as you increase the panel’s density.

This graph compares a 2″ Broadway panel mounted directly to a wall surface to one that has a 2″ air cavity behind it. This results in a 20% increase of absorption at 400Hz just from moving the panel away from the wall surface by 2 inches.

The Cumulus with it’s corner location takes advantage of this well know acoustic trick. Sound waves that pass through the Cumulus are forced through a second time after reflecting off the walls and ceiling behind. More energy is absorbed each time the sound waves must pass through the high density material. A corner mounted panel like the Cumulus does the work of two panels for the price of one.


Calculating The Effect Of A Deep Air Cavity

Corner mounting the Cumulus creates a much deeper air cavity than a wall panel can achieve. The extra depth aids in the absorption of low frequencies making the Cumulus an effective mid-bass trap.

By applying the quarter-wavelength calculation, we can predict absorption attributed to the air cavity. When mounted, the 24″ sides create an air cavity behind the panel with a depth from 12 to 17 inches. It can be determined that the Cumulus will effectively attenuate frequencies between 100Hz and 500Hz while the acoustic panel surface will effectively absorb high frequency energy. This will help reduce troublesome mid-bass and be particularly helpful at eliminating standing waves from rooms with 8ft to 11ft ceilings that naturally resonate between 100Hz and 142Hz.


Putting it all together

The three absorption techniques discussed above are shown plotted individually and combined into a fourth composite chart for the Cumulus.




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