The influence of the reproduction system on the results of the listening tests in building acoustics

The way humans perceive sound has become an important factor in building acoustics, thus 
opening a path to subjective evaluation of sound insulation properties of building elements 
through listening tests. Different approaches have been taken in order to present the sound stimuli 
to listeners in the most realistic way possible. 
The reproduction of sound stimuli during listening tests related to building acoustics is usually 
carried out over headphones, being a very convenient way for the reproduction of acoustic stimuli 
in general. Nevertheless, in some cases a realistic reproduction over headphones is impossible. On 
the other hand, loudspeaker systems allow the subject to perceive the sound in a more natural way, 
related first and foremost to source localization. However, the use of a loudspeaker system implies 
the interaction of the system with the listening room; a problem that can be minimized provided 
that the listening room has been properly treated in the acoustic sense. 
To examine the influence the sound reproduction system itself has on the results of the listening 
tests carried out in building acoustics, a listening test was designed and executed with the stimuli 
reproduced over two different reproduction systems. The same sound stimuli was reproduced once 
over the headphones, and in the second experiment a stereo listening setup made of two 
bookshelf-size studio monitor loudspeakers aided by a subwoofer was used. The listening test 
itself was designed to assess the quality of airborne sound insulation of different building elements 
through loudness judgements. Namely, the test compared the sound insulation properties of a 
typical lightweight and massive inner wall, as well as a typical outer wall with and without an 
ETICS façade (external thermal insulation composite system). Pink noise, music and traffic noise 
were filtered using the sound reduction index vs. frequency curve, and then used as the stimuli in 
the experiment.