The investigation of the noise contributions of vehicle interior targets has become standard practice for vehicle manufacturers to gain insight in noise contributions, interface forces and system sensitivities. Because new technologies are being implemented and available time for testing time reduces, the need for dedicated testing devices increases. LMS uses its experience in NVH technology to continuously develop new acoustic and structural exciters under the brand name LMS Qsources. These enable NVH departments to expand and improve their testing processes and reduce the measurement time. All LMS Qsources seamlessly work within the LMS testing software suites.
All LMS Qsources serve very particular purposes and can be used in conditions in which traditional exciters may be impractical, inaccurate or even impossible to apply.
For instance: Transfer Path Analysis (TPA) based on matrix inversion requires Frequency Response Function measurements from body force inputs to local overdetermination points. Traditionally, only a restricted number of paths could be excited with a standard modal hammer. For those apparent unreachable excitation locations, LMS developed the miniature and integral shakers. They do not need any support as they are self-aligning and they are miniaturized to the maximum. Do not let their small size fool you: they have enough power to not only obtain local transfer functions but also to measure Body Noise Transfer Functions (BNTF) in a reliable way.
Another application is Airborne Source Quantification (ASQ). The aim is to analyze all acoustic sound sources that are contributing to the occupant ear pressure. This investigation requires a large set of Transfer Functions. To reduce measurement time the reciprocity principle can be used. Instead of exciting at every discrete noise source, like engine surface patches of a vehicle, excitation is done at ear location by a calibrated sound source. There can be a significant advantage in instrumentation, accuracy and efficiency by using the reciprocity principle in a measurement setup. In this case, the LMS Qsources Low Frequency Volume Source and the Mid High Frequency Volume Source are used. A third source, the Miniature Volume Source is designed so that local FRFs in case of a source strength identification based on matrix inversion can be measured while minimally disturbing the sound field.
In case of a Panel Contribution Analysis, artificial operational loads, identified during TPA, are applied on the force input locations. These inputs can be suspension supports or engine mounts in case of a vehicle. The LMS Qsources shakers are ideal to introduce such spectrum shaped loads. In this way the response is measured on the different panels. The transfer function from panel to target (ear) location can be measured in a reciprocal way, gaining a huge amount of time.
Another application of the calibrated sound sources are evaluation of the body isolation. The stable p/Q guarantee results, far less independent from the acoustical environment than p/p FRFs traditionally measured.
Based on the diverse hybrid (combined test & CAE) technology projects, new exciters are continuously being developed. For instance: a new exciter will allow to, based on local Transfer Functions measured in a full vehicle, to obtain acoustic trim impedance without having to remove the trim from the vehicle or structure instead of making a time consuming sample, necessary for a transmission loss measurement with an impedance tube. The resulting data can also serve as input data for CAE models.
