@ worthman,Welcome to the forum
. Glad to see a pro joining us.
Can't you say the same things more gentle?
How the heck do you know if C isn't used in the UK for aircraft noise?
You say that D is sometimes used instead. Where, by who, with what?
I'm not going to check exact standards now, but the D-weighting disappeared ages ago from the standards. The only reason you find this D still in lots of graphs is that people like to copy info from one another because it looks learned (and hardly bother what they copy or where it comes from or stands for).
90% has no idea idea it disappeared ages (decades) ago and isn't representative for modern planes and related traffic anymore (which is why it disappeared from the standards VERY long ago, I have to search real antique data just to find it).
Also dB(B) disappeared from modern standards (which I pitty, since it can be a useful weighting), which is why modern SLMs, in accordance with current standards mostly only show dB(A), and dB(C) + the linear ones..
And C is maybe the standard for you and in your surroundings for theater and studio levels, but where does ISO tells that? It's better to use C than A, that's evident (not only for the level relationship, but because of the high low frequent content for studio purposes).
ISO 717-1 gives a weighting for traffic and Music.
In Belgium and the Netherlands we give specific weightings for different types of music. And a C-weighting can also be useful at low levels for music isolation single number ratings.
What I mean is: please doing science, be a bit more more careful with your absolutes.
worthman wrote:"The reference curves are found in several standards including BS EN ISO 8233:1999."
Just a question: Is your Standard code correct or is that BS 8233:1999
As far as I know the NR curves were only shown in ISO/R 1996:1971 (withdrawn 1982)
A lot of countries toke these curves over in own National norms (back then the ISO number wasn't preserved). But the NR curves got a second live outside the ISO standards.
Your Standard code tells that this is a British, European and ISO standard, which can't be true: ISO 8233 has no relation with sound.
Hence I guess it's a typical British Standard BS 8233:1999
, without the EN ISO.