Stonehenge

Ok somebody needs to explain this to me. The first part of this article suggests the model of Stonehenge amplified sound and may have been a place to hear music or speeches. The later part said it was a sound isolator ? I don’t get it. Also the material used to build the model was plaster and not the actual stone type. Idk, if the material, size and location was different how can they compare it to the real thing ? A clever idea but the experiment seems to have mixed results from what I read.