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Automated In-situ Frequency Response
Optimisation of Active Loudspeakers
ABSTRACT
This paper presents a novel method for robust automatic selection of optimal in-situ acoustical frequency response
within a discrete-valued set of responses offered by room response controls on an active loudspeaker. A frequency
response measurement is used as the input data for the algorithm. The rationale of the room response control system
is described. The response controls are described for each supported loudspeaker type. The optimisation algorithm
is described. Examples of the optimisation process are given. The efficiency and performance of the algorithm are
discussed. The algorithm dramatically improves the speed of optimisation compared to an exhaustive search. It
improves the acoustical similarity between loudspeakers in one space and performs robustly and systematically in
widely varying acoustical environments. The algorithm is currently in active use by specialists who set up and tune
studios and listening rooms.
1. INTRODUCTION
This paper presents a system to optimally set the room
response controls currently found on full-range active
loudspeakers to achieve a desired in-room frequency
response.
The active loudspeakers [1] to be optimised are
designed and calibrated in anechoic conditions to have
a flat frequency response magnitude within the design
limits of ±2.5 dB. When a loudspeaker is placed into
1
Andrew Goldberg
Genelec Oy, Olvitie 5, 74100 Iisalmi, Finland.
1
1
and Aki Mäkivirta
the listening environment, response changes due to the
loudspeaker-room interaction. To help alleviate this,
these active loudspeakers incorporate a pragmatic set
of room response controls accounting for some
common acoustic issues found in professional
listening rooms.
Although many users have the facility to measure
loudspeaker in-situ frequency responses, they often do
not have the experience of calibrating active loud-
speakers. Even with experienced system calibrators a
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Summary of Contents for Genelec Optimisation of Active Loudspeakers
- Page 1 Optimisation of Active Loudspeakers Andrew Goldberg and Aki Mäkivirta Genelec Oy, Olvitie 5, 74100 Iisalmi, Finland. ABSTRACT This paper presents a novel method for robust automatic selection of optimal in-situ acoustical frequency response within a discrete-valued set of responses offered by room response controls on an active loudspeaker. A frequency response measurement is used as the input data for the algorithm.
- Page 2 GOLDBERG AND MÄKIVIRTA AUTOMATED IN-SITU EQUALISATION significant amount of variance between calibrations according to the in-situ transfer function measured in can be seen. With a number of different people this way [8] but the process can be so sensitive that a calibrating loudspeaker systems there will be an simple ‘press the button and everything will be OK’...
- Page 3 GOLDBERG AND MÄKIVIRTA AUTOMATED IN-SITU EQUALISATION loudspeaker can reproduce. This typically happens frequency f (typically 70…200 Hz in small spaces) is when the loudspeaker is mounted in the corner of a often dominated by room modes and comb filtering room where the loudspeaker is able to couple very caused by low-order discrete reflections from room efficiently to the room thereby exacerbating room boundaries.
- Page 4 GOLDBERG AND MÄKIVIRTA AUTOMATED IN-SITU EQUALISATION 3.1. Efficiency of Direct Search Table 7. Optimiser frequency ranges; f = 15 kHz; f is the frequency of the lower –3 dB limit of the The room response controls of an active loudspeaker frequency range.
- Page 5 GOLDBERG AND MÄKIVIRTA AUTOMATED IN-SITU EQUALISATION type objective function to be minimised is given in values are the –3 dB lower cut-off frequency of the Equation 3, loudspeaker and 15 kHz. This part of the optimisation algorithm takes 35 filtering steps. There are no driver level controls in ∫...
- Page 6 GOLDBERG AND MÄKIVIRTA AUTOMATED IN-SITU EQUALISATION Table 9. Number of filter evaluations needed by the 2. ‘Slope’ gives a user defined sloping target optimisation algorithm. response. There are two user defined knee fre- quencies and a dB drop/lift value. A positive slope Type of loudspeaker can also be set but is generally not desirable.
- Page 7 62.5 Hz, which shows some stepping caused by reflections. There is a high level 5 dB) reflection about 3 ms after the direct sound – Genelec 1031A [1] AES 114TH CONVENTION, AMSTERDAM, THE NETHERLANDS, 2003 MARCH 22-25...
- Page 8 Room acoustic measurements are shown in Appendix D (Figures 17-22). The octave and third octave reverberation times of the room were calculated according to ISO3382 [41]. The room is extremely Genelec S30D [1] AES 114TH CONVENTION, AMSTERDAM, THE NETHERLANDS, 2003 MARCH 22-25...
- Page 9 GOLDBERG AND MÄKIVIRTA AUTOMATED IN-SITU EQUALISATION After equalisation, the response (Figure 8) is closer to well damped having a T of about 0.2 s across the the target of a flat response. The broadband rms whole frequency range. The Schroeder curves indicate deviation between the original responses (2.8 dB) and a smooth, linear and very short decay in all octave the optimised responses (2.6 dB) shows a reduction of...
- Page 10 GOLDBERG AND MÄKIVIRTA AUTOMATED IN-SITU EQUALISATION Level, dB 1,000 10,000 100,000 Frequency, Hz Figure 7. Case study 2, room response control filter shape. 1,000 10,000 Frequency [Hz] Figure 8. Case study 2, equalised magnitude of the frequency response. Third octave smoothing. 5.
- Page 11 Point Equalisation in a Room Using Adaptive London) for the original inspirational idea, Lars Digital Filters”, Journal of the Acoustical Engi- Morset (Morset Sound Development) and Genelec neering Society, Vol 37(11), Nov 1989. Oy. This work is also presented in more detail as an [13] GREINER R.A.
- Page 12 GOLDBERG AND MÄKIVIRTA AUTOMATED IN-SITU EQUALISATION production”, IEEE Trans. Sp. and Audio Process- [31] MOORE B.C.J., GLASBERG B.R., PLACK C.J. ing, Vol 3, pp 185-192, May 1995. and BISWAS A.K., “The shape of the Ear’s Tem- poral Window”, Journal of the Acoustical Society [21] KIRKBY O., NELSON P.A., HAMADA H., of America, Vol 83, pp 1102-1116, Mar 1988.
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Page 13: Appendix A - Software Flow Chart
GOLDBERG AND MÄKIVIRTA AUTOMATED IN-SITU RESPONSE OPTIMISATION APPENDIX A – SOFTWARE FLOW CHART START START DIPtimiser Display GUI Reset GUI Variables and Graph Add Supported Models CLOSE Await User CLOSE DIPtimiser Inputs Reset Graph and Outputs Model Get Model Database Number Load Impulse Stored... - Page 14 GOLDBERG AND MÄKIVIRTA AUTOMATED IN-SITU EQUALISATION Load Filters Model Filters Preset BRO Is Large System? Find ML-TL Ratio Is Small System? Set BL & BT Set BT (wrt ML&TL) Reset BRO Is 3-way System? Set TT Display Final Tone Control Settings Display Final Frequency...
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Page 15: Appendix B - Software Graphical User Interface
GOLDBERG AND MÄKIVIRTA AUTOMATED IN-SITU EQUALISATION APPENDIX B – SOFTWARE GRAPHICAL USER INTERFACE Figure 10. Software graphical user interface at start up. AES 114TH CONVENTION, AMSTERDAM, THE NETHERLANDS, 2003 MARCH 22-25... -
Page 16: Appendix C - Case 1, Room Acoustics
GOLDBERG AND MÄKIVIRTA AUTOMATED IN-SITU EQUALISATION APPENDIX C – CASE 1, ROOM ACOUSTICS M a g n itu d e F req u en cy R esp o n s e 1,000 10,000 Frequency [Hz] Figure 11. Case 1, in-situ magnitude response. T im e D ata - F in lan d , H elsin ki D em o R o o m , 1 0 3 1 A , C en tre Time [ms] Figure 12. - Page 17 GOLDBERG AND MÄKIVIRTA AUTOMATED IN-SITU EQUALISATION En erg y-tim e C u rve - Fin lan d , H elsin ki D em o R o o m , 1 0 3 1 A , C en tre Time [ms] Figure 14.
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Page 18: Appendix D - Case 2, Room Acoustics
GOLDBERG AND MÄKIVIRTA AUTOMATED IN-SITU EQUALISATION APPENDIX D – CASE 2, ROOM ACOUSTICS M ag n itu d e Freq u en cy R esp o n se 1,000 10,000 Frequency [Hz] Figure 17. Case 2, anechoic frequency response. T im e D ata - F in lan d , G en elec Listen in g R o o m , S 3 0 D , R ig h t Time [ms] Figure 18. - Page 19 GOLDBERG AND MÄKIVIRTA AUTOMATED IN-SITU EQUALISATION En erg y-tim e C u rve - Fin lan d , G en elec Listen in g R o o m , S 3 0 D , R ig h t Time [ms] Figure 20.
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