## 1 Introduction  
The acoustic properties of surfaces are essential to estimate and calculate sound propagation within an enclosed space [1, 2]. The acoustic scattering from surfaces and sound absorption characteristics are very important in all aspects of room acoustics, e.g., in opera houses, concert halls, industrial workplaces and reverberation chambers.  
The sound scattering mechanism is activated by the corrugations of the walls with a sufficiently rough structure or by single elements such as columns, statues, etc., or by diffraction effects along the edges of panels. For example, concert halls or theatres could present focalization of the sound, so diffusing panels are inserted to solve this problem [3, 4]. Many measurement methods have been developed to quantify the various types of sound scattering coefficients and to determine the sound diffusion mechanisms. For many years, acoustical surface scattering has been deeply studied by researchers worldwide [5, 6, 7], and its standard definition is the ratio of the energy reflected outside the specular zone to the total reflected energy.  
[PERSON] suggested quantifying the diffusion by means of the standard deviation of the reflected energy distribution [8; 9]. A similar approach was proposed using a new diffusion uniformity coefficient based on the circular autocorrelation function of the polar reflected energy diagram [10; 11]. Moreover, different techniques depending on the type of incident sound field (free field or diffuse field) were proposed to measure the sound scattering coefficient [12; 13]. Contrastingly, the Audio Engineering Society (AES) proposed a measuring technique of the diffusion uniformity coefficient [14].  
Continuous studies in this field [15; 16] brought the introduction of the standards ISO 17497-1:2004 [17], which refers to the measurement of the random-incidence scattering coefficient, and ISO 17947-2:2012 [18], which refers to the measurement of the directional diffusion coefficient.  
In this paper, two diffusion measures are introduced with somewhat different applications. One measure was performed in a semi-anechoic chamber (Room A) and the second in a large reverberant room (Room B). To determine the sound diffusion coefficient, two QRD panels made of different materials were tested following ISO 17947-2:2012 regulation. The success and the failure of the measuring methodologies being used are highlighted by the contribution of extraneous reflections recorded inside Room A that compromised the scattering results, which have been discarded because they were considered to not be affordable values. The results of the panels tested inside Room B instead have been compared with the reference curves of a theoretical model based on the principle of free field sound propagation, while data analysis consisted of a polar distribution of the scattered field through the use of the Fast Fourier Transform (FFT).  
This concept could be extended to the correct architectural design of a room with regard to the purpose of its appropriate use that sometimes, in the context of cost reduction, is wrongly used for other types of sound tests by facing unexpected objectives.