The Hasseris Gymnasium & IB World School is a high-school founded in 1970 in Aalborg, Denmark.
Designed in the modernist style, it has approximately 800 students each school year.
The main issue
Inside the school there is a multi-purpose hall whose sloped design is iconic and features in the school’s logo, being a central point for many activities and presentations like music shows, exams or graduation ceremonies. But that slanted design comes with a set of acoustic problems, with its high ceiling producing lots of reverberation. The RT60 measured before the acoustic treatment was in place was 1.84 seconds.
To solve the issues in this room, Claus Hansen from AudioExperts found a simple yet unique solution. He created a wedge made of mid and high frequency absorbers with low frequency absorption inside the custom made frame.
The proposed solution
Claus Hansen started as an Electronics Engineer and has more than 30 years of experience with professional audio loudspeaker systems, sound and acoustics, being a JOCAVI partner since 2006. An expert in our products, Hansen proposed some of JOCAVI’s ADDSORB REV absorber panels, mounted on the side walls in an angled design, and BASSLAYER panels on the back wall.
The ADDSORB REV was mounted in specially made aluminum stands to create an effective noise reduction solution and a balanced sound, enhancing both human communication and musical sound. These special stands were also designed to accommodate tuned panels inside the triangle shape to absorb the more problematic frequencies measured before treatment.
This solution completely supported and designed with JOCAVI created a very balanced noise reduction spectrum, achieving 1.08 seconds of RT60 average and a staggering 41% of RT reduction. Below you can see the measured frequencies before and after inside the space. Note the huge difference around the 1000Hz.
JOCAVI has over 27 years of experience in acoustic treatment projects for large spaces, always finding an aesthetically pleasant solution with cost in mind. You can find our products in auditoriums all around the world, from east to west, north to south, and every project is unlike any other.
"Acoustics is the branch of physics that studies sound. Sound is a wave phenomenon caused by a wide range of objects and sound sources, which is propagated through the different physical states of matter.
In acoustics we can generally divide between sectors: sound generators and means of sound transmission, propagation and reception.
Acoustics analyzes these means, creates instruments and tools, quantitative tables, etc. in order to provide the necessary data or solutions for a variety of branches of intervention so that the means of sound propagation and any defects are envisaged and contemplated through duly studied solutions.
The chain of acoustic emission and reception of sound (noise) includes the person who receives the sound effect and the event that gives rise to the phenomenon. Acoustics is considered a science that covers diverse disciplines and which is also covered by them."
These are some words from the upcoming book written by the CEO and founder of JOCAVI, João Carlos Vieira, explaining the basics of acoustics. JOCAVI is an expert in the field, with over 27 years of experience and completed projects all around the world, so you can rely on our knowledge to make your own project come to life.
That is why JOCAVI developed its own Acoustic Simulator (JAS) where you can make a room simulation and see what quality acoustic treatment can do. You just have to know your room measurements and materials and then you can test the difference in reverberation time (RT60). Note these are merely estimates to help you understand the huge impact professional acoustic treatment materials can have in leveling the noise in your room of choice.
Of course you don't even have to know a thing about acoustics! Just contact us and our project and sales teams will build you a custom solution or refer you to one of our nearest partners that can help you to make your dreams come to life.
If you want to build a home cinema you need to correctly address your room acoustics. There is no use in buying top-of-the-line equipment without controlling your flutter echoes and balancing noise levels.
SmartAV has been working with JOCAVI for 20 years, designing and building custom home cinemas and Hi-Fi listening rooms for clients that with high demands that want the best materials and products.
Nuno Teixeira, audiovisual and electroacoustics consultant at SmartAV, says that JOCAVI’s know-how, project solutions and designs have added value to the clients, because they know they have a tailored project matching their expectations.
We went to SmartAV’s new home cinema showroom, built with four products from our range that show some of the different options JOCAVI can provide.
As always in an acoustic treatment, the idea is to balance the room and provide a pleasant listening experience, but in this case, we also wanted to showcase different types of products and finishings you can choose, from over 1100 possible options made by JOCAVI.
The products in use were BASSLAYER® bass traps, tuned to 160Hz with fabric finishing, ADDSORB REV®, a wood veneer panel to improve absorption on mid-range frequencies, SEAFOAM® absorbers with velvety finish that maintain physical properties over a wide temperature range and LIGHTWALLTRAP® with MOTIF® custom prints, a bespoke solution to achieve a unique look to every project.
These and many more product designs and options are available at jocavi.net
Check out the video below.
This year we'll be partnering with Professional Audio Design in a larger, more visible and integrated booth where you'll be able to see our products being used in real enviroments!
It will be a booth with a closed space simulating a studio where you'll be find JOCAVI's eye-catching acoustic panels, Augspurger's impressive speakers, AMS Neve's amazing consoles and Sontronics world class british design microphones, all wrapped up with Professional Audio Design's knowledge of studio development and implementation.
AES Conventions are held annually in both the United States and Europe and are the largest gatherings of audio professionals in the world. Workshops, tutorials, technical papers and the trade show floor provide attendees with a wealth of learning, networking and business opportunities.
From October 16th to the 19th meet us at AES New York.
The filtering function that arises when a signal is added to itself after having delayed in time is called a comb filter. The resulting frequency response resembles a comb, hence the name.
Two 500Hz sinusoidal tones added. The second is delayed by 1ms, hence the sum is zero. Two 1kHz sinusoidal tones added. The second tone is delayed by 1ms, hence the sum is the double (+6dB).
The comb filter function is almost never intentional, but it is heard all the time in sound productions, where it can arise both acoustically and electrically. Acoustically, it typically occurs when the sound on its way from source to receipient takes in part a direct path and in part an indirect path via a single reflective surface. The reflection must be attenuated at least 10dB and preferably 15dB in order for it to not have an effect on the sound field at the recipient position. Electrically, the phenomenon arises when two microphones with a certain distance between them capture the same signal at the level from each microphone is of the same order of magnitude.
Two typical situations in which comb filters arise, either acoustically or electrically.
In genera: All digital signal processing takes time. Thie means in practice that comb filter effects can arise if you loop a signal via, for example, a compressor and combine this signal with the original.
dB Level Frequency - Hz
An example of a comb filter created by the combining of two signals with the same amplitude, but with a time delay between them of just 1ms.
It can be seen in a dip occurs due to cancellation at 500Hz, 1.5kHz, 2.5kHz, etc. It can also be seen that the two signals add to double their value (+6dB) at low frequencies and with a full wavelength's delay at 1kHz, 2kHz, 3kHz, etc.
Cancellation occurs for a comb filter at all the frequencies where the two signals are in opposite phase. This occurs when the time delay comprises duration of , 1 , 2 , etc, periods. At 1kHz the period is 1ms. Half of the period is 0.5ms. If a time delay of precisely 0.5ms occurs, it means that cancellation will arise, not just at 1kHz, but also at 2kHz, 3kHz, 4kHz and so on.
The maxima of the standing waves are shown in the figure. The curve expresses the area of the room where the actual frequency is audible. At the minima the frequency is represented at a much lower level (sometimes – 40 dB compared to the maximum).
If the room has the same dimensions as length, width, and even height it is very problematic to obtain an even sound distribution.
How to prohibit standing waves?
Parallel walls in the room should be prevented. Then the strongest modes are suppressed. When placing the monitors it is important that as few modes as possible are excited. This is why the monitors should not be placed in a maximum of a standing wave. At low frequencies a monitor can be considered as to radiate the sound energy in all directions.
Also known as radiation.
When placing the monitor close to a solid boundary – for instance a wall – the sound energy that should have been radiated in the direction of the wall instead is radiated into the free half space. Hence the sound pressure is doubled in the half space, which yields +6 dB.
Placing the monitor against two boundaries – for instance in a corner limited by two walls – it is now radiating to the quarter space. Now the sound pressure is doubled twice, which yields +12 dB.
In practice, the placing by barrier walls, or ground, influence the frequency range below 125-150 Hz.
The special frequencies are also called room modes. Standing waves between parallel walls are called axial modes. Other modes exit. For instance tangential and radical modes. (See the illustration). Normally the axial modes are the strongest.
The standing waves are characterized by having a maximum sound pressure at the boundaries of the room. Depending on the frequency there are one or more dips across the room. In a box shaped room the frequencies can be calculated as follows:
f = frequency in Hz
c =speed of sound (approx. 340 m/s or 1130 ft/s)
l = length of the room
w = width of the room
h = height of the room
n = integer from 0 and up
Wallace Clement Sabine is the father of modem acoustics. He found that reverberation time is described by a relationship between the room size and the amount of absorption in the room. Larger rooms – longer reverberation. More absorption – shorter reverberation.
Note: One square meter (1 m2) Sabine is comparable to an open window with an area of one square meter:
The sound that hits the window will disappear and never return. One square meter Sabine is one square meter with full absorption. The basic formula sounds simple, but the problem is that the materials in the room will absorb differently at different frequencies. The absorption may range from nothing (fully reflective) to total absorption.
A proper reverb time should be constant with frequency, but this is not always the case because of the behaviour of the materials in the room. The low frequencies are the most difficult to control.
This is why the reverberation time against frequency in practice may look like this:
Reverberation time measured in a control room. From 250 Hz and above the curve is nicely placed around 0.3 sec. But bellow the reverb time rises to 0.75 sec. which is too much.
The reverberation time measurement is defined by the time it takes a sound to attenuate 60 dB after the source is stopped. In the real life we can experience reverb times from approximately 0 sec. (outdoors or in anechoic chambers) to something like 10 – 12 sec. In special reverb chambers the time may exceed 20 sec. Control rooms normally should have a reverb time around 0.2 – 0.3 sec.
Why do we have reverberation? The speed of the propagating sound wave is very slow – at least compared to light: approx. 1130 ft. or 340 m per sec.
If there are no reflecting surfaces between the sound source and our ears, only the direct sound is heard and there is no reverberation.
If there is a single reflecting surface we may hear the reflected sound in one way or another, but there is still no reverberation.
If the sound is generated in a room, there are a whole lot of reflections. Each of these travels different paths with different distances on the wayto the receiver. Each time the sound hits a surface it may loose some energy if the surface is absorbing.
One sound source, one receiver and no room.
Only the direct sound is received.
One sound source, one receiver and one reflecting surface. The sound is received twice. (In the control room this is normally experienced as comb filtering, see later).
One sound source and one receiver in a room. The sound impulse is reflected in many surfaces. All the reflections are melting together and heard as reverberation.