Surefire

[rhino]

What Episcopus says below agrees with my anecdotal evidence/personal experience.

I'm not sure that a meaningful numeric rating system is possible. We know sound intensity and sound level have a logarithmic relationship [sound level = 10 log (I/I_o) on the decibel scale], so to add the complications of the baffled plugs ... well, as a former US EPA employee, I am . . . not confident . . . that they or their contractors can do much of anything right.

The bottom line is that the Sonic Defenders work great for protecting your hearing from high intensity sounds with a sudden pressure/intensity spike like gunshots. They're not great for lower intensity, constant, but still potentially damaging noise. For the latter situations, good foamy earplugs rule!

I have these too. The NRR with them unplugged is 9, plugged is 16. The problem is that the attentuation in hearing protection like this is non-linear. The more intense the noise, the greater the reduction. I think the chart that comes with them shows something like a 36db reduction at 120db. I think the EPA is reworking the NRR scale to better test the non-linear systems, as plugs like these seem to be getting more popular.

I can shoot all day on the outdoor range with absolutely no discomfort. On the indoor range, I usually put the plugs in to up the protection, but I have gone with them out and not had any discomfort. I am very impressed with the protection these offer.

 

[Episcopus]

What Episcopus says below agrees with my anecdotal evidence/personal experience.

I'm not sure that a meaningful numeric rating system is possible. We know sound intensity and sound level have a logarithmic relationship [sound level = 10 log (I/I_o) on the decibel scale], so to add the complications of the baffled plugs ... well, as a former US EPA employee, I am . . . not confident . . . that they or their contractors can do much of anything right.

The bottom line is that the Sonic Defenders work great for protecting your hearing from high intensity sounds with a sudden pressure/intensity spike like gunshots. They're not great for lower intensity, constant, but still potentially damaging noise. For the latter situations, good foamy earplugs rule!

The way I understand the function of the Surefire plugs is that they aren't baffled, in the sense that something like the old Sonic ear valvs were. They have a filter that relies on acoustic energy and the laws of physics to dampen sound. I guess the filter distorts the high energy waves, killing them with interference. This lets low intensity through. They claim that the filter is tuned to the neighborhood of 85db, and anything over that is attentuated by the filter. Something like your lawn mower would be dampened, but not as drastically as something like a jet engine or sitting in front of the speaker stack at a concert. Impulse noises and constant noises are treated the same, but the difference is more noticeable on load impulse noise. Part of that could be that we don't typically hang out in 130db constant noise situations, so there is little frame of reference.

These are the filters they use. Hocks Noise Brakers® - How the Noise Braker® Works
This is an attenuation report. Hocks Hearing Health Products

It looks like lower frequency noises aren't blocked quite as well, but max attentuation is over 43db.

This page has a table showing the attenuation levels of different intensity noises. http://www.surefire.com/pdfs/ep3-ep4_tech_copy.pdf

The NRR isn't that important when it comes to non-linear plugs.

 

[rhino]

Thanks for the pointer to the Hocks Noise Brakers!

I'd still call that a baffle, though, although the geometry is different from what you'd see if you cut another brand in two to see what's inside.

 

[BE Mike]

Thanks soundslikejosh! No bemike i am not sure what nrr they are threw away the paper work.

The NRR is probably not that important; it is just the benchmark that I've gone by regarding ear plugs and ear muffs. Your real world experience is more valuable. I use muffs (sometimes muffs and plugs) when shooting the pistol, but I use ear plugs when shooting the rifle, because the ear muffs interfere with my head position on the stock. I'm always looking for something a little better. If I can find an ear plug that will reasonably protect my hearing, while allowing me to hear normal speech, I'm onboard.

 

[rhino]

I'm trying to understand "Accelerated Resonant Decay Principle" as it's used by Hocks. I can infer some from the words, but "the principles of physics" is so broad as to be meaningless as an explanation.

Judging from the graphic, I'm betting the impingement on the forward facing steps (what would be like baffles in a suppressor or a baffled ear plug) transforms some of the mechanical energy of the flow to heat. Since there also appears to be a reduction in the cross sectional area of the channel, the pressure will drop in exchange for an increase in velocity of the flow (think Bernoulli). If the pressure of the flow drops overall, I would expect the magnitude of the pressure maxima during the condensation part of the sound wave to be similarly reduced.

 

[Episcopus]

I'm trying to understand "Accelerated Resonant Decay Principle" as it's used by Hocks. I can infer some from the words, but "the principles of physics" is so broad as to be meaningless as an explanation.

Judging from the graphic, I'm betting the impingement on the forward facing steps (what would be like baffles in a suppressor or a baffled ear plug) transforms some of the mechanical energy of the flow to heat. Since there also appears to be a reduction in the cross sectional area of the channel, the pressure will drop in exchange for an increase in velocity of the flow (think Bernoulli). If the pressure of the flow drops overall, I would expect the magnitude of the pressure maxima during the condensation part of the sound wave to be similarly reduced.

I am not sure, but I think that part of it is using wave interference to cancel parts of the sound wave. It looks like the steps cause some rebounding of the incoming wave. As long as the sound waves meet when they are each in the proper portion of their phase, they will work to cancel each other, at least somewhat.

Physics was a long time ago, but won't an increase in velocity result in an increase in pressure? Though I guess that the smaller channel could be small enough that the increased velocity through it doesn't result in a pressure higher than the incomnig pressure.

 

[bigcraig]

GEEKS


I just order some of the ep4s.

 

[rhino]

I am not sure, but I think that part of it is using wave interference to cancel parts of the sound wave. It looks like the steps cause some rebounding of the incoming wave. As long as the sound waves meet when they are each in the proper portion of their phase, they will work to cancel each other, at least somewhat.

Physics was a long time ago, but won't an increase in velocity result in an increase in pressure? Though I guess that the smaller channel could be small enough that the increased velocity through it doesn't result in a pressure higher than the incomnig pressure.

I think you're absolutely correct that there will be some destructive interference inside the plugs. I don't think it's the primary mechansim of attentuation, however, as there would be no mention of converting the mechanical energy of the waves to heat.

The Bernoulli stuff was mostly me thinking out loud and reasoning an analog between a fluid dynamics situation (bulk motion of the fluid) vs. the acoustics/standing wave that would exist inside the plugs. I would expect the actual flow rate to be very low.

As far as pressure vs. velocity goes, it's an energy balance situation. Assuming the potential energy of the flow doesn't change significantly (no drastic changes in elevation) and that the fluid's density doesn't change much, you can reduce Bernoulli's Equation to:


P_1 + 1/2*rho*(v_1)^2 = P_2 + 1/2*rho*(v_2)^2

Where P_1, P_2 are pressures at points 1 and 2
rho = density
v_1, v_2 are the flow speed at points 1 and 2

We know from continuity that for a larger channel/pipe, the speed of the flow must be lower than for a smaller (in area) channel pipe because the mass flow rate into one end has to equal the rate out of the other. If the velocity drops in the bigger pipe, then the pressure has to increase in order to satisfy energy conservation. You trade pressure for kinetic energy and vice versa.

Of course, this is only vaguely related to the mechanism of the sound attentuation we're discussing, but it was fun to type it to make sure we can satisfy Craig's accusation!

 

[obijohn]

now boys, we all know that it's the thingies in your earholes simply won't let the loud bangbang noises in...and big craig is correct!

 

[Episcopus]

GEEKS

And proud of it