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The Primacoustic Australis is an effective studio bass trap designed to control low frequency energy and help reduce modal distortion in studios.
The Australis measures a full 12" x 36" and is made from a solid block of high-density 1.7 lb open-cell acoustic foam. The large size and high density combine to deliver optimal absorption in the all important bass region.
The Australis works by trapping the random omni-directional bass energy that tends to cluster in corners and overwhelm the room. Quarter-wavelength calculations prove that Australis is particularly effective for studios that have modal problems in the 75Hz to 200Hz range. Once in place, it has the positive effect of reducing smear, giving bass more definition and punch while allowing recordings to translate better to other rooms.
The attractive wedge design allows easy placement in corners using the supplied impalers. For even greater bass absorption, Australis can be stacked, grouped to form a wall cluster, or placed edge-to-edge at the wall and ceiling seam. And as with all Primacoustic foam products, Australis employs a fire retardant to meet California 117 code. This makes the Australis an excellent choice for use in home studios, home theatre and music practice rooms.
The Science of the Australis Bass Trap
The Australis bass trap is particularly functional in that it is compact and therefore easy to place in almost any room. Although there are installations all over the world where Australis is used in large rooms, it is actually most effective in rooms that are common to most homes.
The reason we say it 'is designed for regular rooms', is that when it comes to bass traps that are made from a material such as foam, it is the physical depth or size of the device that dictates how deep - or the lowest frequency it will absorb. The density of the material is also important as this will dictate how much the bass trap will attenuate in the low frequency region.
Room modes are locations in the room where certain low frequencies will either amplify or cancel each other out as they bounce around. The most prevalent of these are caused by the resonant frequencies that occur between parallel surfaces when the room is excited shown below
The fundamental resonant frequencies are calculated by dividing the speed of sound (1130 ft/sec) by the length of the room. A typical room that measures 12ft x 14ft with an 8ft ceiling will resonate at 94Hz, 80Kz, and 141Hz respectively. Depending on where you are standing in the room, when these frequencies come together, they will either combine when they are in phase, or cancel each other out when they are out of phase.
If you happen to be seated where two 94Hz waves combine ‘in phase’, you will find this frequency sounds louder and you will naturally want to reduce it using an equalizer. Then, when you listen to your recording in another room, you will find the 100Hz region to be lacking. Why? You used your EQ to compensate for the modal distortion in your studio. The obvious solution is to reduce modal distortion with a bass trap.
Common room sizes and room modes:
Wall to wall length (feet) 8 9 10 11 12 13 14 15
Resonant frequency* (Hz) 141.25 125.56 113.00 102.73 94.17 86.92 80.71 75.33
Bass trap depth needed (inches) 12 13.5 15 16.5 18 19.5 21 22.5
* There are many room modes and resonant frequencies in addition to the primary ones discussed here such as armonics and modal concerns from tangents. By searching the web, you can find pages of detailed information to assist.
Building a neutral listening space
A functional studio design is one that does not have severe peaks and valleys. It is neutral. And of course, when you record in a neutral room, the music translates better when you listen to it in other rooms, on your i-Phone, or in your car.
Using quarter-wavelength calculations, we can predict how a bass trap will generally perform. Because the Australis measures 12" x 36" we know it will be very effective at 140Hz, will likely be 85% effective at 90Hz and provide about 50% efficiency down to 47Hz.
It is important to note that the higher the density the material, the more even the absorption will be, particularly in the low end bass region. This is where you have to be careful. Primacoustic Australis is made from 1.7lb per cubic foot foam while competitors use 1.3lb. Less density means less chemical which of course means lower price. But less density means less performance, particularly in the low end.
The science behind the absorption is called thermo-dynamics. It is basically an energy transfer whereby sound waves cause the open cell structure of the foam to vibrate. Once in motion, the vibration causes the minute walls that make up the cellular structure in the panel to heat up, thus a thermal energy conversion occurs.
Where things really get interesting is when you compare the physical design of some products, you will find that many have large air gaps on the front surface. Air does not absorb sound as it has very little density. In fact, sound travels through the air quite well and is why we can converse with other people and amplify it to ear splitting levels. So one can easily conclude that the more absorptive material the better!
Using corners to your advantage
Acousticians always use corners if they are available. This is because sound tends to travel along the walls, floor and ceiling using the boundaries as waveguides. Ultimately, this means that the sound will migrate into the corners. The Australis is designed to easily fit into a corner by simply hanging it like a picture. Once in place, it will absorb sound throughout the audio range right down into the bass region.
Once bass is attenuated, less of it is echoing around the room which means there is less of it causing modal disruptions. Will using Australis bass traps turn your bedroom into a million dollar studio? No, but they will help solve some of the primary room problems that plague most studios and do it without breaking the piggy bank!
How To Use The Australis
The Australis bass trap is a corner mounted device that hangs in place using the supplied impalers. Installation is easy: All you do is screw the impalers into the wall surfaces using standard wall anchors then 'push' the Australis down so that it impales itself.
Once in place you will immediately notice the bass tightening up and a more even frequency response as you move around the room. For larger spaces or for those that want more bass attenuation, you can stack Australis traps on top of each other. The larger size not only increases low frequency absorption, but also lowers the effective cutoff point.
In spaces where wall to wall corners may not be available, you can mount Australis bass traps up high at the wall and ceiling junction. This requires using the impalers on the wall and then gluing the Australis to the ceiling using any standard construction adhesive.
The Australis can be mounted anywhere. And even though this is a bass trap, the Australis is very effective at also absorbing mid and high frequencies. This is why most people will mount the Australis at ear level where it will also serve to attenuate powerful primary reflections.
Application 1 – Stacked Traps In Front Corners
The Australis bass trap is designed for corner mounting. But it does not just absorb bass… it also absorbs all frequencies above. This makes it an excellent mid and high frequency to combine with other acoustic panels to control powerful first order reflections and attenuate flutter echo. Stacking two Australis bass traps will extend the low frequency performance below 50Hz and increase the attenuation of all frequencies.
Application 2 – Stacked Traps In Four Corners
Corners are the acoustician’s best friend. Sound naturally gathers in corners following the natural wave guide created by the walls and ceiling. Stacking two Australis in each corner will not only help reduce modal distortion, but also aid in reducing primary reflections and work with other panels to increase control over primary reflections and flutter echo. Start by mounting the lower panel using the supplied Impalers, then mount the second on top. No messy glue is required!
Application 3 – Using The Ceiling And Wall Joint
Sometimes, corners are simply unavailable due to doors, windows, equipment or room size. Because the Australis is relatively light, it can easily be mounted high, up and out of the way by positioning it up in the ceiling & wall joint. In this case, you can use the impalers to hold it in place but you will likely need to use some type of construction adhesive to hold them there. The benefit is that they are still in a corner which means you get optimal performance.