It's to actively surpress the explosive pressure
Lets be sure folks understand terms.
Electronic muffs are simply hearing protection muffs with a mic, some electronics, and speakers in the ear cups. They are just standard hearing protection ear muffs that insulate against noise with added electronics. All they do is shut the speakers off in the ear cup when the electronics detects the rapid rise in sound pressure level. They do nothing to the sound itself that isn't happening with passive muffs. They are not "noise canceling".
There are no active hearing protection devices that actively protects from gunfire. Active noise suppression (canceling) works with continuous noise by analyzing the waveform of the sound and applying a counter waveform so they cancel each other out. Great for shop/equipment noise, but they do nothing for high volume fast rise times of gunshots. To my knowledge there is nothing out there (or nothing affordable) that can actively suppress gunshot noise with the rapid rise times on the sound pressure level. The rise times are just too fast.
Many of you have noted that cheap yellow foam plugs seem to work better than custom molded plugs. This is the case when the foam plugs are properly inserted. The custom molded plugs allow for ease of insertion, but fundamentally lack the ability to expand into the ear canal as well as the foam plugs when they're properly used. It is a tradeoff between convenience and NRR.
High NRR foam plugs under muffs are the most effective personal protective equipment you can use to reduce exposure to noise from gunfire. You only gain 5db in equivalent hearing protection because plugs and muffs are effective over different sound frequencies. Their ranges overlap, but not across the entire hearing range. That's why you only credit 5 more dB on top of your plugs.
Another point - I've been a Health & Safety Professional for 30 years and the only hearing protection that I put my trust in comes from one of the major manufacturers of industrial hearing protection equipment. Other brands do not get my trust because unless I know that they're using the same testing and quality control required of the PPE manufacturers like 3M/Peltor, Howard Leight, Moldex, Sordin I don't know what standards they're producing to.
Lastly, I've bought hearing protection over the years just to test them. I've never found the major hearing PPE companies to overstate the performance of their muffs or plugs. I have almost always been disappointed about the test results of other manufactures.
Rant- If our government cared about our hearing they'd make suppressors readily and inexpensively available like Europe instead of causing the price to be artificially inflated and adding a $200 burden on top of it (along with months of delays). If you can, file an E-Form 1 and pay your $200 good guy tax and build your own suppressor when you get the permission back from the Fed. THIS with plugs and muffs will provide the best protection for hearing damage.
Bonus note -
not for shooting, but interesting https://www.3m.com/3M/en_US/p/d/v100765196/
