Sound insulation at Wasdale Head

 These barriers were in operation around a generator at Wasdale Head. 

I was very interested in the set of symbols that went with it. I'm not sure whether it adds kN to the load or is resistant to forces in the kN range. Also, does it reduce by 43dB or is what comes through less than 43dB?

So I tried their website. I really liked the frequency graphs lower down. This seems to show 43dB REDUCTION but at high frequencies only. This is important because I know from experience that it is the frequencies around 4000Hz that are most sensitive to the ear.