Active Field Control (AFC) Reverberation Enhancement System Using Acoustical Feedback Control

Transcription

1 Active Field Control (AFC) Reverberation Enhancement System Using Acoustical Feedback Control

2 What is AFC? Active Field Control Electro-acoustical sound field enhancement system *Enhancement of RT and SPL reverberance, loudness Early reflections spaciousness * Improvement of undesirable acoustic conditions Under-balcony uniformity Stage acoustics Easiness of playing Under development at Yamaha for more than 15 years Installed in approximately 50 venues in Japan New device AFC-1 has been released in the US

3 Definition of three categories developed in the field of Sound Field Control A-SF P-SF S-SF Categories Assistance of Sound Field Production of Sound Field Synthesis of Sound Field Definition Control of room acoustic condition based on the given room condition Production of spatial sound effects, mainly for a theater, movie, etc. Synthesis of requested condition in a given, or highly absorbent, room Yamaha AFC System

4 AFC Key Features 1. Conservation of original acoustics in the room because it uses an acoustic feedback loop 2. Wide range controllability using a FIR filter 3. Effective at any position in the room 4. Stability against coloration using Time Varying Control 5. Two separate systems, Rev. and ER 6. Easy operation

5 Conservation of original acoustics

6 Two ways to increase Reverb Time Less absorptive Absorptive Room size Larger room size

7 (db) Wide range of controllability using FIR filter AFC has two ways of enhancing reverberation (db) 0 adding energy to each FIR tap extending RT with increasing SPL Decreasing absorption (Sec) 0 (Sec) expanding gaps between FIR taps extending RT without increasing SPL Increasing room volume

8 Time Varying Control Using feedback is essential for AFC Loop gain control for maintaining stability is the key for AFC Two types of Time Varying Control are included in AFC to ensure smooth loop gain They ensure enough margin against instability

9 TVC :EMR (Electronic Microphone Rotator) I/O combination is changed periodically

10 TVC : fluctuate-fir Each FIR tap moves periodically on time axis (Tdi,Fi) Tdi: variable time range(msec) Fi: modulation frequency(hz) time

11 Closed loop gain with TVC

12 Stability against the increase of Loop Gain

13 Basic Idea for Speaker and Microphone Placements 5-6m (16-20ft)

14 Effective at any position in the room Yamaha AFC Conventional way Reverberation is controlled using feedback Effective area is limited

15 Block diagram of AFC system

16 Core Device: AFC1

17 Block diagram using AFC1

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21 AFC Tuning Process Architectural condition is fixed Equalization of frequency characteristic of each speaker Adjustment and measurement of loop gain Adjustment and measurement of reverberation Confirmation of acoustical condition by listening to the sound using instruments actually

22 Loop Gain Monitor (LGM) Microphone HA Loop Gain Monitor EQ SFP EQ SP AFC1(1) AFC1(2) PC Pink noise FFT or RTA LGM has been developed based on DME32 Digitally connected with AFC1 To change the loop on/off of each channel To select the oscillator signal and its input channel

23 Application of AFC

24 Easy Operation

25 Example of RT Characteristics

26 Experimental Project Yamaha Hall A total solution for the system including AFC, SR, surround effects, etc. is realized utilizing digital network m-lan.

27 YAMAHA HALL 524 seats, Original RT 500Hz =0.7s Finished by wooden slats which caused high absorption Too dead for acoustical instruments AFC has been installed in order to realize the sound field optimum for both cinema and classical music. Experimental project using AFC1 & m-lan,, which have been installed at the first time in the world.

28 System configuration AFC and SR system are digitally connected. The system located in different spaces are also connected with m-lan.

29 pattern change control panel for AFC AFC1 Optical mlan converter AFC / Amplifiers rack

30 T 60 measurement results

31 Conclusion The development of TVC and utilization of digital equipment improve sound quality. AFC is gaining acceptance by classical musicians, who typically have had some reservation about the use of electro-acoustics. As the next phase of development, a total solution for the system including AFC, SR surround effects should be proposed utilizing digital network.

32 Thank you very much!