The focus of this thesis is the characterization of acoustic absorbers. Acoustic absorbers are employed to reduce noise and can be realized by means of numerous concepts. Active strategies aim to reduce noise by employing electro¿acoustical approaches while passive absorbers present a more cost¿efficient and robust alternative. Passive absorbers can be realized by either using resonant structures such as Helmholtz resonators or can be made from porous materials. Traditional porous absorbers are most commonly used for the reduction of noise with frequency components higher than 1 kHz. In porous absorbers, the acoustic energy is transformed into thermal energy by means of friction. Acoustic intensity probes are crucial tools for acoustic characterization. They consist of a sound pressure microphone and a 3D particle velocity sensor and enable determining the acoustic energy flow. In this thesis, the sound insertion loss of acoustic absorbers is analyzed by means of an acoustic intensity probe. Furthermore, a novel simulation aided calibration method is developed to calibrate all three components of the particle velocity sensor simultaneously by means of a reference sound field. The reference sound field, produced by a moving piston, is investigated by applying numerical calculation methods. The calibration method is then characterized and a validation of the method presented. In addition to this, two existing measurement methods for characterizing passive acoustic absorber materials under oblique angle of sound incidence are implemented and further improved. The first approach employs subtraction in the time domain, which allows for calculating the properties by separating an incoming and a reflecting impulse. The second method is based on a spatial Fourier transform. Here, the acoustic properties are calculated by decomposition of a sound field into plane wave components on several measurement planes. Both methods are characterized and subsequently improved. A characterization of passive acoustic absorbers in terms of the acoustic properties at oblique angles of sound incidence is performed and the absorption capability of the absorbers identified. The characterization is essential to gain the necessary understanding of where to place which absorber to achieve the optimum absorption of acoustic energy. Moreover, the material data can be used as boundary conditions for a precise simulation of realistic acoustic fields. Finally, development and characterization of an acoustic absorber for low frequencies is discussed. By applying a mass loaded membrane, acoustic energy can be transformed narrow-bandedly into mechanical energy, which produces an acoustic short circuit. As a consequence, the mechanical energy is not emitted efficiently in the free field, which results in a high sound transmission loss. The passive mechanical absorber is characterized and its application as an absorber array for absorbing narrow band acoustic energy in a frequency range below 300Hz presented.