MSA Sordin Supreme performance: the misleading “NRR=18dB” rating

When you bring up MSA Sordin Supreme ear-pro among folks who are serious about shooting sports, it’s pretty much guaranteed that you’ll hear spec-sheet-based performance objections from at least one person.  After all, what self-respecting gear whore (myself included) doesn’t review the spec sheets when making a buying decision?  Actual quote from a recent discussion on pistol-forum.com:

These [MSA Sordin Supreme Pro-X’s] have a woefully low NRR rating of 19. I wear a pair of {OtherProducts} rated 25 outdoors and another pair of 33 indoors. I tried on a pair of these Sordins and they were also rather small fitting for those with large brain boxes.

How do we reconcile these objections with the fact that MSA Sordin is, as far as I can tell, the alpha dog supplier of mission-critical ear-pro to hardass pipe hitting bearded trigger-pullers from every NATO country and then some? One might think that the special forces teams do a little more than read the promotional flyer before buying $300/pair ear pro for their hitters. Resolving this will require looking a little deeper than the spec sheet…

Short Attention Span Theater Version

MSA Sordin Supreme Pro-X Neckband (OD Green)

MSA Sordin Supreme active-electronic hearing protectors are labeled with an NRR of 19dB.  This figure is worthless.  In the frequency range where you find most of the sound energy from a pistol/rifle/shotgun blast, the Sordins are actually good for a 27dB (averaged over range) sound reduction when worn correctly.  Certain guns, such as a full-comp Open gun in USPSA or a short-barreled/comped-or-braked carbine, will bark higher-frequency blast noise that the Sordins will cut by over 35dB. While the occasional shooter can get away with wearing either plugs or muffs at an indoor range, those who go shooting on the regular are very strongly recommended to double up on the ear pro.  Indoor ranges, and certain covered outdoor ranges, expose the shooter to very high sound pressure levels which will cause damage over time if only plugs or muffs are worn.  This is true for every make and model of ear-pro on the market short of full-isolation helmets.  If you’re shooting indoors, or you’re at multi-hour carbine/rifle class, wear plugs under your muffs.

Interested in the full story?  Continue onwards, intrepid reader!

In an ideal world, hearing protection would work equally well across the human-audible frequency range of 20Hz to 20kHz.  The reality is that sound waves behave differently as you move down the frequency range.  Sounds in the high-pitched 16-20kHz range are, with rare exception, only audible to people under 25 years old, and are easily blocked by earplugs. The very lowest frequencies, in the sub-100Hz range, transmit easily through solid materials such as muscle and bone.  As the frequency gets down towards 20Hz, the sound energy is felt more than heard.  As a result, hearing protection products decline rapidly in effectiveness for deep-pitched sounds with frequencies below 100Hz, and in fact start to drop off around 250Hz.  Fortunately, the vast majority of pistol, rifle, and shotgun blast noise is concentrated in frequencies well above the crossover into bass frequencies.

As with any other products, hearing protection works perfectly as designed until you introduce actual live human beings into the situation.  I am shocked, shocked I tell you, to learn that people don’t use hearing protection equipment properly every time they put it on.  (That’s sarcasm, folks.)  Earplugs get put in wrong, earmuffs are worn with a hat which breaks the seal against the head, sound-absorbing foam isn’t replaced on schedule, etc etc.

In a bid to make life even more complicated than it already is, OSHA came up with NRR (noise reduction rating) formulas to de-rate (reduce) the theoretical effectiveness of hearing protection products to allow for idiot, excuse me, “average” users who can’t follow instructions.  Wait, it gets better… not to be outdone, NIOSH came up with a related, more-realistic version of the standards for de-rating effective noise reduction.

Here comes the punch line: it’s basically impossible to tell at a glance which standard was used in calculating the NRR of a given product. The solution is to seek out the test data published by top-tier ear-pro manufacturers, which shows noise reduction performance at 125/250/500/1000/2000/4000/8000 Hz, and compare it to the peak frequencies of the kind of noise we’re trying to block.

MSA Sordin Supreme performance specs

Some ear-pro makers put noise-reduction labels on their products by picking the frequency range with the greatest reduction, then calling that the noise-reduction rating.  By those standards, what rating would we give the Sordins?

If I were a marketing guy, I’d look at this chart, shout “38.7dB noise reduction!” and rush off to get stickers printed to slap on all of the boxes.  That’s quite a difference from the 18dB NRR shown on the lower part of the chart, isn’t it?  Let’s get to the bottom of this!

Gunshot Noise Characteristics

While writing this review, I searched out and read a half-dozen scientific studies (or abstracts containing all of the info I needed) which examined the frequencies and effects of gunshot noise.  Because I’m all about spreading knowledge without making you do the legwork, here’s everything you need to know about gunshot noise:

1. Gunshot noise is very substantially louder and more damaging if you are in the peak pressure zone from the shockwave generated by expanding gases, 10-12 feet forward of the gun’s muzzle, when it goes off.  (Experienced shooters will recognize this as being obvious.  Bear with me as we get to the meat of the question.)
2. Rifles with muzzle devices which redirect the expanding gases to reduce recoil change the situation dramatically: shooters next to you will receive the same blast and concussive effect as standing in the peak pressure zone 10 feet downrange from an uncomped gun.  The difference is roughly equivalent to shooting with closed-cell foam earplugs (uncomped gun) vs shooting with earplugs removed (comped gun).
3. Compensated pistols produce a similar phenomenon, although with a much lower SPL penalty to folks nearby due to the lower gas expansion pressures of pistol ammo.
4. Indoor-type environments, i.e. those with a solid wall to either side and a roof overhead, ensure that you, the shooter, get exposed to much more sound energy when the gun goes off compared to shooting outdoors in an open environment.
5. Centerfire non-magnum gunshots produce sonic energy from 750 Hz out to 8 kHz
6. Centerfire magnum rifles and pistols extend the sound energy produced all the way down to 200 Hz and move the peak energy down into the 500 Hz range
7. Popular-caliber rifle gunshots (5.45/5.56 through 7.62 mm) generate peak sonic energy in the 1.5-2.0 kHz range, and that peak is VERY loud due to the high pressure gas generated by rifle ammunition.
8. Pistol gunshots generate peak sonic energy around 1 kHz but the impulse is more diffuse than rifle fire (boom vs crack)

Too much to chew on?  Skip over a bunch of that?

Yeah, I don’t blame you, it’s a lot to think about.  Here’s the really short version:

• Critical frequency range for hearing protection against gunshot noise is 1 kHz through 8 kHz, dropping off as you go up the spectrum from 1 kHz
• If you want a single number for comparisons, average the ratings for 1 kHz and 2 kHz (matches up with 1.5 kHz peak SPL)
• If you’re shooting or working around short-barreled rifles and/or guns with compensators, look at the 2 and 4 kHz ratings
• Magnums? Check out the 500 Hz rating, and may Odin smite you if you shoot them at an indoor range with anyone in the lanes around you…

So how do the Sordins actually perform?

First, I’ll just note that there’s not a single ear-pro product on the planet that I would shoot for a full 2+ hour session at an indoor range without wearing some form of plugs underneath.  If I’m by myself, I’ll wear a pair of in-ear headphones with Comply foam tips, yielding the same ~20 dB noise reduction effect as a pair of throwaway foam plugs.  If I’m with others, I’ll wear plain foam plugs — but in both cases, I will turn up my electronic ear-pro amplification until it’s loud enough that I can hear normally with the plugs in.

The MSA Sordin Supreme family is good for a ~30 dB reduction across the spectral frequency range of pistol gunshot noise, sufficient for shooting rifle, pistol, or shotgun in an outdoor environment.  With earplugs, they’re good for at least 40 dB of reduction, more than sufficient for all-day sessions at indoor ranges.  If I were in an indoor/outdoor combat environment (which thankfully is not my daily existence) I would be wearing Earasers Musicians Hi-Fi Earplugs to reduce all sounds by 19dB while keeping things crystal-clear, with my MSA Sordin Supreme Pro-X muffs over the top.  I’ve used this combination recently, and if you need maximum hearing protection because your dumbass hunting partner tends to fire off his .300 Win Mag compensated rifle just a little to close to you, then you owe it to yourself to give it a try.