Component/system/vehicle airborne sensitivity

From one generation to the next car generation, or version, many small changes in design and materials affect the airborne and vibro-acoustic isolation. For example isolation of noise emission from the leading edge of the tires to the interior. Or HVAC ventilator noises passing through the tubing and dashboard to passenger ears. These can be quantified accurately using volume acceleration sound sources. And using reciprocity and small microphones the excitation can be done from the ear location, measuring the response at the noise radiating surface. Airborne transfer functions reproduce well and allow differences in sensitivity or isolation down to 1 dB to be measured. Sound sources, typically applied for automotive acoustic and vibro-acoustic sensitivity, from low to high frequency:

Component/system/vehicle structural sensitivity

Road noise sensitivity, for example, requires verification of vibro-acoustic transfer, local stiffness, cross vibration transfer, and component modes. From the wheels through the suspension, frames and body, all have a major impact on the low-mid frequency comfort. Even smaller changes can improve or degrade effectiveness requiring verification system input and transfer testing. But also the numerical simulation models used to limit high sensitivity risks need regular verification. The self-suspending self aligning Qsources shakers allow faster more reliable verification of components and assemblies. These devices fit well in locations and orientations that cannot be handled by an impact hammer or traditional supported shaker. Shakers typically used on these applications from very-low to high frequency:

Acoustic and vibro-acoustic modal analysis

Standing wave or acoustic modes in the interior of the car, in the tires, in HVAC units,…These “airborne” modes can couple well to the structure and cause significantly higher vehicle noise levels. The volume acceleration and volume displacement signals of the Qsources volume sources allow well controlled airborne modal identification for troubleshooting applications. Combined with the right processing software these also allow scaled (vibro) acoustic modal analysis to improve numerical models both in enclosed (cabin) or open (under floormodes) situations.

Typically applied sound sources for this application from low to high frequency:

Component/system/vehicle, experimental modal analysis

Experimental modal analysis is often applied for numerical model correlation with the purpose of improvement of the modelling capability. It supports improved material models, improved interface modelling, etc. Experimental modal analysis is also applied to better understand the natural vibration or coupled-acoustic-structural behavior. Trimmed body modal analysis, dashboard-carrier modal analysis, steering wheel modes, cabin acoustic modes, rear-view camera or mirror modes,….

Typically applied self-suspending shakers from very-low to high frequency:

Transfer path analysis (TPA) and inverse identification of interface loads

New sound or noise phenomena arise with new electric systems and known sound become more prominent in the absence of combustion engine noises. Some of these phenomena are for a significant part structure borne. Diagnostic measurements like transfer path analysis (TPA) help understand the phenomena and help quantify the requirements to control noises. TPA in almost all various forms relay on a combination of operational testing and artificial excitation testing. The identification of the interface loads is an essential step in the process. And once interface loads are better known, they can be used with nummical component and system ( like car body) models to asses suitability and set requirements. Better software support and many published experiences have helped make TPA a feasible approach. Some of the Qsources shakers typically used in TPA analysis, from low to higher frequencies:

Modular noise development

Although mostly fairly quiet modules are involved, the new configurations with electric motors, battery cooling units, high power heat pumps, etc. bring challenges for integration without loss in sound quality. FE models with test-bed extracted measured loads help to do early analysis. And coupling an FE model to measured FRF matrices of the surrounding structure (body and frames) allows to set sensible targets for the vibration levels of the units and for the sensitivity of the supporting structures.

The mostly inverse load identification of blocked forces, or interface forces, require efficient and reliable FRF (or transfer function) measurements. And mobility FRF matrix based analysis (FBS) also require large numbers of accurate transfer functions. The tight spacing at the interfaces often does not allow access with instrumented hammer measurement, nor external supported shakers with load cells. The patented solutions from Qsources for highly compact self-suspending and self-aligning shakers support both the process of testing for load identification and for testing large numbers of interface FRF in an efficient way. Some shakers, and couplers, used for such applications:

Airborne Source Quantification (ASQ) and other airborne diagnosis/analysis

Not all phenomena are significantly structure borne, many are mostly air borne. In that case the parallel of TPA, Airborne Source Quantification (ASQ) becomes useful as a diagnostic technique. There various approaches and similar techniques under other names to address airborne transfer. Most benefit from the use of volume acceleration (volume velocit, or volume displacement) as airborne source strength. But sound power can also be used to quantify source strength with system airborne transfer or isolation or insertion loss etc. Better software support, practical-stable volume sound sources and many published experiences have helped make ASQ and variants a feasible approach. Some of the Qsources sound sources typically used in ASQ analysis, for dircet or reciprocal excitation, from low to higher frequencies: