One of the most common questions that you will hear in active room acoustics is: “what would be the best reverberation time for my room and how do I get there?”. The counterquestion needs to be: “what do you want to do in your room?”. And therein lies one of the common problems for room acoustics in modern performance spaces: It needs to be good at everything!
The community hall needs to host the local choir, the comedy night, the theatre group and be a ballroom. But nowadays also bigger venues like opera/concert houses feel the financial need to fill every night of the week with acts. Take for example the König Albert Theater in Bad Elster (which has an Amadeus system). There is a theater production followed by a rock and a pop concert to be continued by an operetta the next day.
Active room acoustics
All those different kinds of performances need different room acoustics to work. One solution for this is adaptive room acoustics through passive means like extra absorbers (curtains, …). Or adding extra volume to a room. But those systems barely get used even if they are present in a room because most of the time they can be impractical.
That is where active room acoustics through electroacoustics like the system by Amadeus Active Acoustics come into play. Founded in 2018 in Vienna, Austria by Thorsten Rohde, Volker Werner and Fabio Kaiser the mission of Amadeus is “We shape sound”. They achieve this by looking at the main acoustic influences of the sound field (direct sound, background sound and reverberation). And controlling the latter two by capturing and processing the former.
Source by Amadeus Acoustics AES2020
Amadeus active Acoustics
The idea of actively altering the room acoustics using electroacoustics is nothing new. It has been around since experimentations with these systems in 1950 in the Royal Festival Hall in London (Parkin, Morgan 1970). Active room acoustic systems can be categorized into three main categories: In-Line, Regenerative (Non-In-Line) and a hybrid approach of the former two (like the Amadeus system).
While In-Line systems use a few directive microphones placed usually within the critical distance of the sound source and loudspeakers distributed in the auditorium, regenerative systems use a high number of microphones and loudspeakers. It is important that the signal from the loudspeakers back to the microphones (HLM) doesn’t exceed the one from the source to the microphones (HSM) to stay within stable conditions for the loop gain (g) and the system not to display audible feedback (artifacts like ringing tones).
The way In-Line systems accomplish this is by said placement of microphones and loudspeakers. Regenerative systems use the signal loop between microphones and loudspeakers to accomplish the change in room acoustics. For them to not get unstable (ringing tones) there needs to be a be a good number of microphones, loudspeakers and some smart processing (Svensson 1995).
Altering Reverberation Time
While his presentation at the EIAS 2023, Fabio Kaiser of Amadeus Acoustics explained that the hybrid approach of their active room acoustic system Amadeus is capable of not only altering the reverberation time of a space. With Amadeus it is possible to change room acoustic parameters like clarity (C50), early decay time (EDT) and the center time (ts) independently from the reverberation time (Kaiser et al. 2019).
Change in Center Time with different presets of Amadeus at Convention Center Suhl, Germany (ebd.)
3D immersive sound installations
While this possibility is very interesting for concert spaces, the Amadeus system can do even more. It is possible to build 3D immersive sound installations like the James Bond Experience – 007 Elements installation in Sölden Austria.
To experience the Amadeus system in person, we visited the Amadeus Showroom in Vienna together with the students of the University of Vienna. There we were able to hear the subjective difference an active room acoustic system can make to a room. And also experience the immersive 3D functions of the system. This is especially impressive since the audience can be immersed in the same room acoustics as the sounds that are played through the system.
So, if choral music in a church setting is played through the system, it will also immerse the audience into the same acoustics. If one then for example claps, the clap can have the same reverb as the music that is played. All this works so seamlessly and realistically sounding, that Amadeus can fool the students into thinking it was turned off when it in fact was working its magic.
To experience the Amadeus system, one can ask for a tour of the showroom in Vienna or visit one of the projects already built with active room acoustics system.
Parkin PH, Morgan K. “Assisted Resonance” in The Royal Festival Hall, London: 1965–1969. JASA 1970;48(5A):1025–1035.
Svensson PU. Computer simulations of periodically time-varying filters for acoustic feedback control. J Audio Eng Soc. 1995;43(9):667–677.
Kaiser F, Frischmann C, Werner V, Rohde T. Room acoustic evaluation of active acoustics systems – results from measurements. Proceedings of the International Symposium on Room Acoustics 2019, Amsterdam, Netherlands