Rupert Till (Huddersfield) and Bruno Fazenda (Salford) also explored Stonehenge's acoustics. At a 2011 conference, Steven Waller argued that acoustics interference patterns were used to design the blueprint of Stonehenge. Almost a decade later, in a detailed study described in a 2020 journal article of the Journal of Archaeological Science, a team led by Trevor Cox and Bruno Fazenda (Salford) employed an acoustic scale model reconstruction of Stonehenge to examine the acoustics within and around the site at different historical stages of the monument, applying sophisticated architectural acoustics methods and knowledge to studies on prehistoric archaeology, offering novel insight into how speech and musical sounds were altered by the acoustics of Stonehenge. Chavín de Huantar Miriam Kolar and colleagues (Stanford) studied various spatial and perceptual attributes of Chavín de Huantar. They identified within the site held the same resonance produced by pututu shells (also used as instruments in the Chavín culture). Chichen Itza Scientific research led since 1998 suggests that the Kukulkan pyramid in Chichen Itza mimics the chirping sound of the quetzal bird when humans clap their hands around it. The researchers argue that this phenomenon is not accidental, that the builders of this pyramid felt divinely rewarded by the echoing effect of this structure. Technically, the clapping noise rings out and scatters against the temple's high and narrow limestone steps, producing a chirp-like tone that declines in frequency. Artifacts Archaeologist Paul Devereux's work (2001) has looked at ringing rocks, Avebury and various other subjects, that he details in his book Stone Age Soundtracks. Ian Cross of University of Cambridge has explored lithoacoustics, the use of stones as musical instruments. Archaeologist Cornelia Kleinitz has studied the sound of a rock gongs in Sudan with Rupert Till and Brenda Baker. Panagiotis Karampatzakis and Vasilios Zafranas investigated the acoustic properties of the Necromanteion of Acheron, Aristoxenus acoustic vases, and the evolution of acoustics in the ancient Greek and Roman odea. Study groups The activity of research groups in the field of archaeoacoustics (sometimes called "acoustic heritage") and the related field of music archaeology is determined by the availability of funding, though some groups maintain a long term presence in the field. In the past twenty years, many researchers have undertaken both seminal work in developing methods to identify, conserve, or recreate aspects of historical acoustic environments, as well as case studies at relevant heritage sites. The Acoustics and Music of British