Whereas standard boundary element calculations focus on the forward problem of computing the radiated acoustic field from a vibrating structure, the aim in this work is to reverse the process, i.e., to determine vibration from acoustic field data. This inverse problem is brought on a form suited for solution by means of an inverse boundary element method. Since the numerical treatment of the inverse source reconstruction results in a discrete ill-posed problem, regularization is imposed to avoid unstable solutions dominated by errors. In the present work the emphasis is on Tikhonov regularization and parameter-choice methods not requiring an error-norm estimate for choosing the right amount of regularization. Several parameter-choice strategies have been presented lately, but it still remains to be seen how well these can handle industrial applications with real measurement data. In the present work it is demonstrated that the L-curve criterion is robust with respect to the errors in a real measurement situation. In particular, it is shown that the L-curve criterion is superior to the more conventional generalized cross-validation ͑GCV͒ approach for the present tire noise studies.

The backward region of the H1 detector has been upgraded in order to provide improved measurement of the scattered electron in deep inelastic scattering events. The centerpiece of the upgrade is a high{resolution lead/scintillating{ bre calorimeter.The main design goals of the calorimeter are: good coverage of the region close to the beam pipe, high angular resolution and energy resolution of better than 2% for 30 GeV electrons. The calorimeter should be capable of providing coarse hadronic energy measurement and precise time information to suppress out{of{time background events at the rst trigger level. It must be compact due to space restrictions.These requirements were ful lled by constructing two separate calorimeter sections. The inner electromagnetic section is made of 0.5 mm scintillating plastic bres embedded in a lead matrix. Its lead{to{ bre ratio is 2.3:1 by volume. The outer hadronic section consists of 1.0 mm diameter bres with a lead{to{ bre ratio of 3.4:1.The mechanical construction of the new calorimeter and its assembly in the H1 detector are described.

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