The just noticeable differences (JND) of room acoustics parameters are useful quantities in design and research, as these values provide a guideline as to when a design change will result in a subjectively noticeable difference. The clarity index for music (C80) JND has been studied previously by Cox et al (1993) and Bradley et al (1999), who found C80 JNDs of 0.7 dB and 0.9 dB, respectively. These studies had limitations in that Cox et al had a relatively small subject pool and Bradley et al's study used speech signals rather than music, as the focus was C50. Two new studies have been conducted to further investigate the C80 JND. In Study 1, 51 musically trained subjects were exposed to a total of 54 AB paired comparisons producing results suggesting a higher JND of 1.6 dB. A pilot study, Study 2, was conducted to compare two testing methods: Test Method 1, which was used in Study 1, required the 11 subjects to listen to all of signal A and then all of signal B before giving a response, while Test Method 2 allowed subjects to switch in real-time between the two signals, as it was hypothesized that Test Method 2 would yield a lower JND similar to previous work. However, this study yielded an even higher C80 JND of 3.8 dB averaged over both test methods. In particular, an interaction effect was found with test method and the order in which the subjects received each test method. The results that most closely matched the predicted trendline were obtained when the subjects completed the first half of the test using Test Method 1 and the second half using Test Method 2. If the first half of the test was considered a training period, then the results in this case from only Test Method 2 gave a C80 JND of 4.4 dB, which was much higher than found in previous work.