Here is an interesting scientific study of Muffs and Plugs. The benefits of Muffs and Plugs may be far more than typically estimated, within certain frequency ranges. As a general rule, safety agencies say that, by using quality plugs and muffs together, you can get +5 dB more protection than the highest-rated device. So, with 32 dB NRR plugs and top-quality muffs you might get 37 dB NRR effective. But this study says the benefits may be signficantly greater for some frequencies:
https://apps.dtic.mil/dtic/tr/fulltext/u2/a507742.pdf
From Page 903:
As demonstrated previously,
sound attenuation increased significantly when wearing the muff and plug in combination (4,10,12). Compared with the Muff alone (and without regard to the size of plug used), the benefit due to the combination was an additional 20dB at 0.25kHz and 0.5kHz, and 10—13dB from 3.15—8kHz. Compared with the Plug alone, the benefit was an additional 10—17dB from0.25—1kHz and 3—8dB beyond. Below 2kHz, these observed values exceed the often quoted 5dB rule-of-thumb prediction, which suggests that the combination will yield 5dB more attenuation than the higher attenuation of the pair of devices worn singly.
This study was conducted for the Canadian Military.
