Sound Quality

Many would relate the “design” of a product to its visual appearance, but designing the sound of a product might well be as important. This might be obvious for products like loudspeakers, but have you ever wondered why some products sound noisy and annoying while others are more pleasant?

Let us enter the show room of a car dealer: Door open – close – tick or a solid clack? How much of the feel of a quality product is transmitted by its acoustic properties? How should the engine of a sports car sound and how should it sound in a luxury sedan? What are the various aspects of the sound that customers like in the acoustic appearance of the product? Can we develop computational models to determine the quality of an audio recording or a telephone transmission in order to aid the development of new products like “mp3” and mobile phones?

Such questions are central to the field of Sound Quality in which we look for objective measures and models for primarily subjective aspects relating to audio quality.

Perception-inspired testing for structural integrity of wind turbine rotor blades

Opting out of nuclear energy and the transition to the era of renewable energies are only possible with technological progress. Wind power plants contribute remarkably towards achieving an independent and green energy supply. In order to guarantee the reliability of those engineering structures over a lifetime of 20 years, they have to be checked on a regular basis. 

Finding defects in wind turbine rotor blades by tapping on the rotor blade

A very promising acoustic and non-destructive testing method is the (coin-) tap test, a standard procedure used for the inspection of wind turbine rotor blades. A skilled inspector utilizes a mallet to tap the material, thereby eliciting local body-born vibrations that emit audible acoustic signals. These acoustic signals reveal information about the integrity of the material and can be used by experienced inspectors while listening to them.

How and why Sound Quality methods are applied in Non-Destructive Testing

Non-destructive testing methods can quantify defects in wind turbine rotor blades in terms of type, size and location. But there is no such thing as free lunch – the results are at the expense of lengthy procedures and costly measurement equipment. An experienced inspector, however, can easily rely on the “trained ear”.

Figure 1: Sound pressure history of impact signals from tapping on a rotor blade with a mallet and specific loudness history for different frequency bands according to DIN 45631/A1.

A tap sound can be described as less impulsive and quieter than another, but does that mean there is a defect present? Sound Quality measures, such as subjective ratings of experienced inspectors in connection with psychoacoustic correlates, can help us understand which acoustic information is important for a robust identification of defects in materials. Moreover, models of the auditory system shed light into how humans process and make use of certain aspects of sounds. This interdisciplinary approach combines the knowledge of two research fields, and supports the development to more efficient methods for testing wind turbine rotor blades.

Selected Publications

Andreisek, G.; Große, C.U.; Seeber, B.U.: Attribute zur Beschreibung akustischer Unterschiede von Fehlstellen an Rotorblättern von Windenergieanlagen. Fortschritte der Akustik -- DAGA '15, Dt. Ges. f. Akustik e.V. (DEGA), pp. 513 – 515, 2015.