Dear Dr Almagro
Many thanks for your constructive comments on this version of the preprint. I have already submitted a revised version which is soon posted here.
I do understand your concerns on the accuracy, particularly at low levels. Since I could not bring out the Ckass 1 SLM from our lab, I did not have any other choice but a mobile devices.
The accuracy of the SLM apps on the devices depends on (1) the device (in many cases, so called noise floor or internal noise); (2) App's design. When the same app is used, the accuracy depends on the device; on the contrary if the device is the same different apps can show different accuracy. (Please see ref 11)
Regarding NoiseCapture, I also checked its measured value with that measured by SLA app on iPhome XS and obtained fairly good agreement. Also, by using the device and app used in this submission I had checked that noise levels around 35 dBA could be obtained. Considering that the measured results in this survey are all greater than 39dBA ca, at least, the relative difference which is required for qualitative discussions, which was rather important in this work, may be obtained even by these methods.
As mentioned above, even though the device is the same, the accuracy may vary with apps. Considering this fact, I shall add some data on the accuracy to address your comments. Please wait for a while until I can have a professional SLM at hand: I will make a further revision.
Once again, many thanks for your thoughtful comments, I appreciate it very much.
Kind regards
Kimihiro Sakagami