  Rendering objects invisible to impinging acoustic waves (cloaking) and
creating acoustic illusions (holography) has been attempted using active and
passive approaches. While passive methods are applicable only to narrow
frequency bands, active approaches attempt to respond dynamically, interfering
with broadband incident or scattered wavefields by emitting secondary waves.
Without prior knowledge of the primary wavefield, the signals for the secondary
sources need to be estimated and adapted in real-time. This has thus far
impeded active cloaking and holography for broadband wavefields. We present
experimental results of active acoustic cloaking and holography without prior
knowledge of the wavefield so that objects remain invisible and illusions
intact even for broadband moving sources. This opens novel research directions
and facilitates practical applications including architectural acoustics, and
stealth.
