The ACS signal processing module:
ACS has recently launched the new ACS-D series processing module, that was developed in co-operation with the Delft technical university.
A very powerful digital processing module that in its normal configuration can contain a total of 96 audio inputs and 96 audio outputs.
Several modules can be connected together to make up even larger systems.The unique ACS concept for variable acoustics can now be applied with even more flexibility and at a moderate price.
ACS: A brief description
In a hall there will be sound reflections from walls, ceilings etc. The way sound reflects and re-reflects in relation to the position of the sound source and the position of a listener is what we call acoustics.
ACS changes acoustics by adding sound reflections to the natural ones.
To make sure this is done in a way that the listeners will perceive it as natural acoustics, it is very important that it happens at the correct place with the correct signal mix and timing. (speed of sound)
A number of microphones. (typically 8-30) are used to pick up sound. The recorded sound is processed, amplified and rendered using a number of strategically placed loudspeakers. (often all mounted invisibly)
Generally several acoustics presets are programmed and together with the original acoustics of the venue this will give a large freedom of selection.
ACS can for example change the very dry acoustics of the typical modern theatre (suited for speech) into the very lively acoustics of a good concert hall.
Or that of a dry sounding modern church into to the nice reverberant sound of that old basilica. All with a push on a button.
Because different venues require different solutions, modules of hard and software were developed. (listed below) One, or a combination of these modules are placed / installed in the main processing system and together they will form the system for variable acoustics
The function of these modules will be described in the paragraphs below.
Reverberation
Early Reflections
Foldback
Orchestra ShellACS systems are known for their natural sound.
Projects involving the installation of an ACS system often carried out in co-operation with the acoustics consultant of the principal and a local installation company. ACS engineers will support the whole process and check and tune system after the installation is completed. And also because ACS believes the best publicity comes from a satisfied user, our service and support does not end here!
Reverberation processing
This is generally the basis of an ACS system. It is common knowledge that the amount of reverberation desired is depending on the type performance.
Example:
You have to speak slowly in a reverberant environment like a cathedral to be intelligible, but a choir will sound great there.
The ACS reverberation processing adds reverberation in the amount necessary.
The length of reverberation is measured as the so called RT60 time. This is the time it takes in seconds for the sound level to decrease 60 dB after the sound source has stopped.
Below you see a list of generally accepted reverberation time requirements.
_____________________
Pop music /cinema
Speech
Drama
Comic and Baroque Opera
Grand Opera
Symphonic (Baroque)
Symphonic (Classical)
Symphonic (Romantic)
Organ, (Choir)RT 60 @ 500 Hz (sec.)
_______________________
1.0
0.7 - 1.1
1.0 - 1.4
1.2 - 1.4
1.4 - 1.6
1.2 - 1.5
1.5 - 1.8
1.8 - 2.5
> 2
Early Reflections processing
Another important part of acoustics are the early reflections.
Early reflections is sound arriving within 100 ms after the direct sound. (The first reflections from ceilings and walls)
Early reflections are amongst others important for clarity presence and spaciousness.
The correct amount of early reflections will make the audience feel closer to the performers, it will give a clear definition of sound and give a feeling about the size of the hall.
The example of the cathedral in the last paragraph makes it clear that reverberation doesn't improve clarity and presence, this is the reason why ACS has separate modules (control) for early reflections and reverberation (re-reflected later reflections)
In small shoe box shaped halls there are often sufficient naturally generated early reflections. In larger halls and for example the modern theatres with the typical diverging walls, you usually find a lack of early energy.
Of course the density of early reflections necessary is depended on the use of a venue.
In churches that like to have a more reverberant hall for hymn singing and choirs with an organ, early reflections are of minor importance. In larger churches or cathedrals you usually also find a limited amount of early energy. In concert halls on the contrary early reflections are of major importance to hear the pure "definition" of sound.
ACS delivers the early reflection unit to abolish the lack of early reflections.
Driving a number of loudspeakers, placed on suited locations, this unit can add reflections in a very flexible and accurate way.
In most projects we have done in theatres / concert halls a combination of processing for reverberation and early reflections is used.
Foldback Extension
In some venues the performance area is not a part of the acoustical environment where the audience is located. You often find situations like this in modern theatres where musicians will be seated on stage, in/under the stage tower. They are shielded from the acoustics of the hall by the proscenium opening.
For a good performance however it is important that the musicians know how their music is perceived by the audience. To solve this, an extension the reverberation processing was developed, named Foldback.
Foldback loudspeakers will radiate an image of the reverberation in the hall back to the performers on stage, making it an acoustical unity. Next to that, the nice reverberation will also let musician on stage play "lighter".
Orchestra Shell Extension
It is important for musicians to hear each other and themselves. Therefore there should be sufficient early reflections in the performance area. In theatres / concert halls often large mechanical orchestra shells are used for this purpose.
As an extension to the early reflection processing, ACS developed an electronic orchestra shell, an alternative for the mechanical shell.
A number of loudspeakers (typically 12-14) radiating early energy are placed in an U-shape around the performers.
The ACS orchestra shell will make sure one doesn't have to move the often large and heavy parts of a mechanical shell and compared to a mechanical shell it will save both initial expenses and later, labour costs.
A system rack with 24 power amplifier channels in the 2 lowest sub-racks.
For more extensive information we have several PDF documents available for download
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