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Genelec Proceedings of Institute of Ac, Introduction Manual

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Genelec Proceedings of Institute of Ac Introduction Manual Download Page 17

Proceedings of the Institute of Acoustics

 

 
 

 

 
 

Is Large 
System?

Is Small 
System?

Load Filters

Model Filters

Preset BRO

Find ML-TL 

Ratio

Set BL & BT 

(wrt ML&TL)

Reset BRO

Set TT

Display Final 

Tone Control 

Settings

Display Final 

Frequency 

Response

Set BT

Is 3-way 

System?

1

2

 

Figure 6 continued. Software flow chart, part 2. 
 
 

Y

N

N

Y

Summary of Contents for Proceedings of Institute of Ac

Page 1: ... the optimisation algorithm is then investigated by studying the statistical properties of frequency responses before and after equalisa tion 2 IN SITU EQUALISATION AND ROOM RESPONSE CONTROLS 2 1 Equalisation Techniques The purpose of room equalisation is to improve the perceived quality of sound reproduction in a lis tening environment not to convert the listening room anechoic In fact listeners ...

Page 2: ... from colora tion Also despite the widespread use of equalisation it is still hard to provide exact timbre match ing between different environments Several methods have been proposed for more exact inversion of the frequency response to achieve a close approximation of unity transfer function no change to magnitude or phase within a certain bandwidth of interest16 24 Some researchers have also sho...

Page 3: ...n parameters x ℜn Multi objective optimisation is concerned with the minimisation of a vector of objectives E x that may be subject to constraints or bounds Several robust methods exist for optimising functions with design parameters x having a continuous value range37 3 1 Efficiency of Direct Search The room response controls of an active loudspeaker form a discrete valued set of frequency re spo...

Page 4: ...d less or no bass roll off is eventually required The min max type objective function to be minimised is given by Equation 2 3 2 2 1 0 0 max max min f f f f f f f x f x f a f x f x f a E b a m b f m a f m 2 where x f is the smoothed magnitude of the in situ frequency response of the system am f is the bass roll off setting m currently being tested x0 f is the target response fa defines the bass ro...

Page 5: ... The least squares type objective function to be minimised is the same as shown in Equation 3 However am f is the bass tilt and bass level combination m currently being tested together with the fixed midrange and treble level ratio setting found in the previous stage Also f1 and f2 now define the loudspeaker pass band Table 7 The user can select both values The default values are the 3 dB lower cu...

Page 6: ...response around fLF when off axis loudspeaker location reduces significantly the high frequency level when a loudspeaker is positioned behind a screen or when the measuring distance is very long It is naturally preferable to remove such causes of problems if possible 3 4 2 Target for Optimisation There are five target curves from which to select 1 Flat is the default setting for a studio monitor T...

Page 7: ...system parameters Parameter Equipment Setting Measurement System WinMLS200039 Microphone Neutrik 3382 40 Sample rate fs 48 kHz MLS sequence order 14 16 Averages 1 Impulse response length 0 341 s 1 36 s Time window Half cosine FFT size 16384 65536 Frequency resolution 2 93 Hz 0 733 Hz 4 1 Statistical Data Analysis Statistical analysis was conducted to assess the ability of the equalisation algorith...

Page 8: ... band of equalisation crosses are indicated on the graphical output The proposed room response control settings are shown and the effect of these settings is visualised in the response plot The treble tilt midrange level and bass tilt controls have been set The equalisation corrects the low frequency alignment and improves the linearity across the whole passband The optimised result is displayed i...

Page 9: ... green background as well as the error function value and processing time Figure 2 Case example statistical analysis output 4 3 Results 63 loudspeakers were measured before and after equalisation 12 small two way 22 two way 30 three way and three large systems Depending on the product type not all of the room response controls are available Tables 1 4 Table 12 shows the number times a control was ...

Page 10: ...in terms of quartile difference and RMS deviation in the sub band analysis This was not evident in the broadband metrics indicating that the arbitrary definition of subband frequency division introduced some error The cases where this happened originally suf fered from severe response anomalies due to extremely bad room acoustics The equalisation was not designed to compensate for such problems Su...

Page 11: ...is heuristics is the order in which these choices should be taken A considerable improvement in the speed of optimisation was achieved relative to an exhaustive search The optimisation algorithm is robust to a wide variety of situations such as variations of room acoustics differently sized loudspeakers with differing anechoic responses and varying in situ responses42 The optimisation is sufficien...

Page 12: ...to 75 Percentile Difference Change due to Equalisation Small models 3 2 1 0 1 Broadband LF MF HF Level dB RMS Deviation Change due to Equalisation Small models 5 4 3 2 1 0 1 Broadband LF MF HF Level dB 25 to 75 Percentile Difference Change due to Equalisation 2 way models 3 2 1 0 1 Broadband LF MF HF Level dB RMS Deviation Change due to Equalisation 2 way models 5 4 3 2 1 0 1 Broadband LF MF HF Le...

Page 13: ...nd tune studios and listening rooms 7 ACKNOWLEDGEMENTS The authors would like to thank Mr Steve Fisher SCV London for the original inspirational idea and some of the measurements used in the statistical analysis Mr Olli Salmensaari Finnish Broadcasting Corporation for additional measurements Mr Lars Morset Morset Sound Develop ment and Genelec Oy Parts of this work are presented in more detail as ...

Page 14: ... Regularisation IEEE Trans Speech Audio Proc vol 6 pp 189 194 1998 Mar 22 Johansen L G and Rubak P Listening Test Results from a new Loudspeaker Room Cor rection System presented at 110th Conv Audio Eng Soc preprint 5323 2001 May 23 Johansen L G and Rubak P Design and Evaluation of Digital Filters Applied to Loud speaker Room Equalisation presented at 108th Conv Audio Eng Soc preprint 5172 2000 Fe...

Page 15: ...Conv Audio Eng Soc preprint 5730 2003 Mar 39 Morset Sound Development WinMLS2000 http www winmls com 2003 Feb 40 NTI AG Neutrik Test Instruments 3382 Microphone http www nt instruments com 2003 Feb 41 Goldberg A P Mäkivirta A Statistical Analysis of an Automated In Situ Frequency Re sponse Optimisation Algorithm for Active Loudspeakers proceedings of the 23rd Conf Au dio Eng Soc 2003 May 42 Goldbe...

Page 16: ...red Measurement Microphone Compensation CTRL M Measurement Dump Reset Graph and Outputs Get Model Number Apply Mic Compensation Remove DC Window FFT and Smooth Load Impulse Response Set DIPtimisation Range Display Original Freq Response Display Target Response Calculate Target Resp Stored Measurement CLOSE DIPtimiser 1 2 Figure 6 Software flow chart part 1 CLOSE Set Frequency Range START ...

Page 17: ... Is Small System Load Filters Model Filters Preset BRO Find ML TL Ratio Set BL BT wrt ML TL Reset BRO Set TT Display Final Tone Control Settings Display Final Frequency Response Set BT Is 3 way System 1 2 Figure 6 continued Software flow chart part 2 Y N N Y ...

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