Many of us in our daily experience have already encountered such systems. Who hasn't happened to buy headphones / earphones to listen to music / talk while on the street, in the subway or in very noisy contexts?
These devices do nothing but cancel the background noise as much as possible to allow optimal listening. They are really useful and practical audio systems, but there is also their use in other contexts. Imagine if the same concept could be used to improve the sound of an entire room, or maybe even influence its acoustics?
Wouldn't that be great?
Well this type of application exists and goes by the name of "Active Acoustic Enhancement Systems" or active acoustic improvement systems. Follow me and let's start by understanding how they work.
The problem
While I am talking to a person in a room, the sound waves that start from my mouth reach the ears of my possible interlocutor.
In fact, not only my voice reaches the ear of the friend, but also the reflected waves that my voice has generated in the surrounding environment.
Solution
To improve my friend's listening we should try to reduce all those reflected waves that ruin the acoustics of the original sound. Practically this can be achieved by modifying the acoustic characteristics of the rooms, acting on the walls, using curtains and panels to dampen reflections, with good results, even some limitations and in any case with high costs. A more technological solution is to use an electronic system that is capable of dampening reflections.
This solution is certainly easier to use: by pressing a button we can change the acoustic behavior of a room without having to make expensive physical changes to the room.
operation
Essentially, the improvement of the acoustic behavior of a room can be achieved in two types of systems: In-Line or Regenerative. Both methods work on the management of annoying reflected waves.
In-line systems
An in-line system (in-line or SF-2) works on direct sound, creating “synthesized” reflections and reproducing them with a speaker system. If the environment is very absorbent, the result can be almost completely controlled. However, if the room already has reflections, the result is the sum of the original reflections and the synthesized reflections. An inline system offers a one-way response, generating acoustic energy from the performer area to the listener area. Therefore, if the performer leaves his area, eg. the stage, the system no longer works. Furthermore, the acoustic energy from the audience response is not included in the system response and it is difficult to improve the acoustics of the performer space.
Assuming the inline systems have no feedback, any reverb pattern can be added to the existing acoustic file. If the existing acoustics are “dry” (low energy / low reverberation time), the result depends almost entirely on the active system, which is ideal for being able to make multiple uses. A disadvantage of inline systems is that only the area covered by the directional microphones is improved, such as the stage. Sound from other areas, from the public for example, is not enhanced unless there is another dedicated system in that area. It is very difficult for inline systems to sustain a natural acoustic behavior that covers an entire room.
VIVACE system example
The heart of the sound system consists of two redundant units, the internal signal processing can handle up to 40 microphone signals on several independent processing levels. Convolution algorithms running on four major processors are used to create natural sound fields of up to 192 different output signals, each individually and in detail adjustable. The high processing capacity allows a VIVACE to simultaneously generate up to four acoustic spaces with independent characteristics, thus being able to acoustically treat different areas of the concert hall or theater according to artistic requirements.
Regenerative systems
A regenerative type system works by adding reflections based on the room's original reflections. This type of system is sometimes referred to as “Assistance of Sound Field”(A-SF“ sound field assistance ”, or more commonly as“ regenerative ”). In this mode, different combinations of microphone / amplifier / speaker are used to regenerate the reflections in the room.
Regenerative systems have a very natural result, but rely entirely on the nature and tone of the existing room acoustics, leaving limited freedom to change the character of the acoustics.
CarmenCita system example
The technological solution consists in completing the acoustic matrix of natural sound paths with an electronic matrix. To provide quality acoustic immersion Carmen Quote uses active electroacoustic cells, composed of microphones and speakers. The digital processing of the signals allows to halve the number of electro-acoustic cells that equip the show room.
A homogeneous distribution of these cells in the walls and ceiling allows you to naturally control the duration of the reverberation in the room, also thanks to a wireless tactile remote control, which controls the acoustic characteristics of the room in real time to instantly adapt it to the type of performance.
Furthermore, all the electro-acoustic cells can be used as a spatialized diffusion system, the position of multiple sound sources can be controlled in real time during a performance.
Hybrid systems
By combining the concepts of inline and regenerative system we obtain a “hybrid regenerative”. The system can be built with fewer channels than pure regenerative systems, eg. with 16 microphones and 16 speakers, which make up 16 independent channels. In medium and large rooms, this is probably insufficient to significantly increase the acoustic energy required to improve reverberation time using only regenerative techniques. By applying one digital reverb per channel, the reverberation time can be increased without adding energy, while the number of 16 independent channels is just enough to boost the acoustic energy to an appropriate level. In this way, the system allows more freedom in modifying the acoustic response than using purely many independent channels.
An example of this approach is the Yamaha AFC system.
It uses 4 microphones and DSP to lower the frequencies that most create problems for the acoustics of the room (resonances at certain frequencies)
Conclusions
Thanks to the improved performance and affordability of DSP and electro-acoustic equipment, the use of active sound enhancement systems has increased significantly over the past decade. The general trend of adoption or acceptance tends towards the application of hybrid regenerative, which are able to provide both regenerative and online modes of operation, achieving a natural and powerful sound without the constraints of singlemode systems. The most obvious benefit is the improved audience listening experience, but perhaps most importantly, it also improves the artists' listening experience on stage. So if the improved acoustics benefit the performance, the audience listening experience will be great!
