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- Barkefors, Annea, et al.
(författare)
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Design and Analysis of Linear Quadratic Gaussian Feedforward Controllers for Active Noise Control
- 2014
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Ingår i: IEEE Transactions on Audio, Speech, and Language Processing. - 1558-7916 .- 1558-7924. ; 22:12, s. 1777-1791
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Tidskriftsartikel (refereegranskat)abstract
- A method for sound field control applied to active noise control is presented and evaluated. The method uses Linear Quadratic Gaussian (LQG) feedforward control to find a Minimal Mean Square Error (MMSE)-optimal linear sound field controller under a causality constraint. It is obtained by solving a polynomial matrix spectral factorization and a linear (Diophantine) polynomial matrix equation. An important component in the design is the control signal penalty term of the criterion. Its use and influence is here discussed and evaluated using measured room impulse responses. The results indicate that the use of a relatively simple, frequency-weighted penalty on individual control signals provides most of the benefits obtainable by the considered more advanced alternative. We also introduce and illustrate several tools for performance analysis. An analytical expression for the attainable performance clearly reveals the performance loss generated by having to use a causal controller instead of the ideal noncausal controller. This loss is largest at low frequencies. Furthermore, we introduce a measure of the reproducibility of the target noise sound field with given control loudspeaker setups and room transfer functions. It describes how well a controller that uses an input subspace of dimension equal to the effective rank of the system is able to reproduce a target sound field. This performance measure can e.g. be used to support the selection of good combinations of placements of control loudspeakers.
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| 2. |
- Barkefors, Annea
(författare)
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Linear Quadratic Gaussian Controllers for Feedforward Active Noise Control : Pushing Performance and Moving Towards Adaptive Control
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Active noise control is a research area focused on using destructive interference of sound fields to attenuate undesired noise. Methods for active noise control are best suited for low frequency noise, as the complexity of the problem grows rapidly with frequency. Coincidentally, passive means of damping have the opposite quality in that they work better for higher frequencies and become bulky and impractical for low frequencies. Applications for active noise control range from fan noise in ducts, noise-cancelling headphones and noise in cars to propeller induced aircraft cabin noise. In this comprehensive summary, the underlying principles of active noise control are presented and the control problem is discussed. Several aspects of the control system are introduced to give an introduction to the research papers that are the basis of this licentiate thesis. The work behind the thesis is focused on a Multiple-Input Multiple-Output (MIMO) Minimal Mean Square Error (MMSE) Linear Quadratic Gaussian (LQG) feedforward controller. This controller is shown to achieve uniform damping in an extended region in space and push the upper frequency that can be controlled. The influence of different design variables has been investigated, and the properties of the control path analyzed with consideration of its ability to suppress noise of prescribed spectral properties over an extended region. In this context, it has been shown how to use the reproducibility of the primary noise path by the control path as an indication of achievable performance for a given control system. Finally, the controller has been adapted to follow changes in the primary noise statistics, an approach that seems promising to considerably raise the performance of the controller.
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| 5. |
- Brännmark, Lars-Johan, 1974-
(författare)
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Robust Sound Field Control for Audio Reproduction : A Polynomial Approach to Discrete-Time Acoustic Modeling and Filter Design
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is concerned with the design and analysis of robust discrete-time filters for audio equalization and sound field control in real reverberant environments. Inspired by methods in polynomial control theory, a unified framework for acoustic modeling and filter design is developed. The work on modeling is centered around three main themes: First, the acoustic channel between a loudspeaker and a point in space is studied in time, frequency and space, and a polynomial matrix fraction description with diagonal denominator is selected as a physically motivated channel model. As a means for representing channel uncertainties, a probabilistic design model is proposed. Second, the concept of sound field dimensionality, based on the Karhunen-Loève expansion of the sound field, is explored and integrated into the polynomial systems context. Third, a method for spatial interpolation of acoustic transfer functions is proposed and evaluated. Interpolation errors are accounted for by applying the probabilistic uncertainty model to the interpolated data. The work on filter design can be categorized into single- and multichannel methods. The single-channel problem concerns the improvement of the impulse and frequency responses of a single loudspeaker over a region in space, by means of a scalar prefilter. This problem is posed in a SIMO (single-input multiple-output) feedforward control setting, and is solved using polynomial methods. The solution offers several useful insights and results. In particular, new results are derived regarding the adverse pre-ringing problem associated with mixed phase filters. Based on the new results, a refined mixed phase method is proposed that is practically free from pre-ringing artifacts. In the multichannel problem, a desired spatio-temporal sound field is approximated by the joint use of several loudspeakers. This problem is initially formulated and solved by feedforward control over a continuous spatial domain, assuming full knowledge of the spatial field. To obtain a practically feasible design, the control criterion is then spatially discretized, resulting in a standard MIMO(multiple-input multiple-output) linear quadratic feedforward control problem. Since information is generally lost in the discretization process, a robust design based on spatial interpolation and probabilistic error modeling is proposed. The multichannel designs are assessed in an automotive setting, using practical measurements of a nine-channel sound system in a car.
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| 6. |
- Brännmark, Mikael, et al.
(författare)
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A Proposed Model for Evaluating the Sustainability of Continuous Change Programmes
- 2012
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Ingår i: Journal of Change Management. - : Informa UK Limited. - 1469-7017 .- 1479-1811. ; 12:2, s. 231-245
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Tidskriftsartikel (refereegranskat)abstract
- Many studies report that it is difficult to sustain change. This article focuses on how an organization can initiate and sustain a continuous change process. A theoretical model is proposed as a fusion of two previous models for evaluating the sustainability of a change programme; the first is based on analysing stakeholder interest balance as a prerequisite for organizational sustainability, the second on analysing the design of the implementation, indicating whether long-term effects will be achieved. It is argued that the combination of these factors provides a more comprehensive perspective, since it allows us to evaluate both the ‘form’ and the ‘direction’ of the programme. To assess stakeholder interest balance, the goal for the change programme is analysed, utilizing the broad stakeholder interest balance perspective. To assess the design of the implementation, four preconditions for long-term effects should be analysed: management's ownership of the change initiative, professional steering, competent leadership and participation. Reference is given to the management concept Lean Production, which is claimed to engage the organization in continuous change. Application of the model highlights the mismatch between narrowly focused change programmes such as Lean Production and sustainable change.
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| 9. |
- Brännmark, Mikael
(författare)
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Implementering av Lean i medelstora företag : En lärande utvärdering om hållbarutveckling
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Denna rapport är ett av delresultaten från det interaktiva forskningsprojektet Produktionslyftet, inom HELIX VINN Excellence Centre. Projektet genomförs i samarbete med Produktionslyftet, ett nationellt program för spridande av managementkonceptet Lean produktion. Syftet med forskningsprojektet är att öka kunskapen om hur hållbart utvecklingsarbete kan bedrivas, både utifrån ett program- och företagsperspektiv. Rapporten beskriver två delstudier, en kvalitativ och en kvantitativ, som genomförts i samarbete med elva av företagen i Produktionslyftet, tio av dem pilotföretag för programmet. Den första delstudien genomfördes under sommaren 2008, genom en intervjustudie med programmets pilotföretag, medan den andra genomfördes under våren 2009, i formen av en enkätstudie med sju av företagen i programmet. Då en interaktiv forskningsansats har använts, så har i båda fallen den insamlade empirin från de båda delstudierna återkopplats till representanter från Produktionslyftet, samt programmets finansiärer, och en gemensam tolkning och analys av empirin har gjorts. Denna gemensamma tolkning har sedan analyserats utifrån modeller kring hållbart utvecklingsarbete och resultatet från detta arbete har sedan sammanfattats i två arbetsrapporter, som har återkopplats till programmet och dess finansiärer. Resultaten i delstudierna, samt den gemensamma tolkningen och analysen av empirin, fokuserar Produktionslyftets coacher, samt deras arbete med företagen. Dels spelar coacherna uppenbarligen en central roll i programmets arbete med företagen, och dels är coacherna mycket uppskattade av företagen. Coachernas arbetssätt, samt hur deras arbete påverkar möjligheten för företagen att skapa en hållbar utveckling, upptar också en central del i rapporten. Detta kan sammanfattas, som att om coacherna driver på arbetet för hårt, få finns det risk att det uppstår problem för företagen, men om coacherna inte är pådrivande så finns risken att åtminstone vissa av företagen inte tar sitt ansvar för Lean-arbetet. Med andra ord, coachernas arbete med företagen utgör en svår balansgång mellan att uppfylla företagens målsättningar med Lean-arbetet, i vägning mot Produktionslyftets mål och syfte. Men resultaten pekar också på vikten av att företagen har ett tydligt ägarskap och driv i utvecklingsarbetet. Slutsatsen i denna rapport blir därför att om programmets utvecklingsarbete skall bli hållbart, så hänger det troligen på dels att man har duktiga och kompetenta coacher, men också att man har en väl fungerande företagsrekryteringsprocess, där företag med ett internt driv för Lean-arbetet väljs till programmet.
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| 10. |
- Brännmark, Mikael, et al.
(författare)
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Implementing Lean in Swedish Municipalities and Hospitals : Initial effects on the work system
- 2011
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Ingår i: FALF2011:Det nya arbetslivet. - Luleå : FALF.
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Konferensbidrag (refereegranskat)abstract
- This paper is the first preliminary product of a three year interactive research project, studying the effects of Lean when introduced in Swedish municipalities and hospitals. Focus of the paper is the implementation process (more specifically, employee participationand facilitated learning) and changes in the work system (focusing on work content, organization and work environment). The empirical data has been collected through interviews and group interviews in three municipalities and one hospital. These results, together with the discussion and analysis, shows firstly that the implementation processes of the studied units are characterized by a medium or high level of opportunities for employee participation and learning, although this is produced in different ways. Second, the changes in the work systems mostly affect the organization of the work, through reorganization and redistribution of the work tasks, rather than changes in how the work tasks are performed.This has lead to more orderly and structured work processes. Lastly, the employees’ reactions to these changes have been mostly positive, although not exclusively so. However, it is important to stress that the employee reactions are most likely as much a result of the implementation process, as of the changes in the work systems. Longitudinal studies are therefore needed to study the long term changes in the work system and the effects on employee health, which will be the next step of this research project.
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