NC and NR curves are at best not relevant and at worst disastrous in recording studios

These curves describe acceptable background noise in rooms. They are empirically derived to approximate human hearing sensitivity (which varies with frequency) and represent annoyance or interference with the activity in the room e.g. hearing on the telephone in an office or call centre.

Most importantly, the curves rise at lower frequencies because our hearing is less sensitive to low frequencies and increasingly so at overall lower levels. So if the background noise were louder at low frequency, we may perceive it as at a similar level to the overall. In other words, in an office we can accept more low frequency noise relative to the overall level.

However, in a recording studio there are MICROPHONES and they DO NOT hear like humans. Their sensitivity is essentially flat. Rooms designed with increasing noise at low frequency DO NOT work because the microphone will record this and the recording chain will amplify it. This generally causes monitors to have excessive excursion at low frequency and causes modulation artifacts in the audible range.

It is not reasonable to high pass filter the sound to remove the low frequency because of other effects this has on the recorded audio.