Centrefire Moderator Test and Review

[simonl]

It is worth being very, very careful with info available online as regards moderators and other shooting related "measurements" of sound pressure levels.

The gear to accurately measure the peak sound pressure level .....

Good post. Surely the most important criteria for the measuring kit is to be able to establish the potential extent of ear trauma? Doesn't the ear integrate too?
Also, as long as it's capturing the peak, does it matter if the measuring kit is non-linear? It should still put the moderators in the right order?

There's clearly been a lot of effort put into this evaluation and it's great to see, but it could be strengthened by adding more detail about the measuring technique.

 

[icerider]

Thanks, I believe you must be right, just did not pay enough attention to the equipment used. Somehow always had a chance compare existing moderator at a range, but as these lightweight had appeared I was considering ordering one without fitting and trying.

It is worth being very, very careful with info available online as regards moderators and other shooting related "measurements" of sound pressure levels.

The gear to accurately measure the peak sound pressure level produced by a rifle is very rare and extremely specialized indeed, typically it will be the size of a fridge or similar. It needs to cope with a very high SPL (in the order of 180dB SPL) and it also needs to be extremely "fast" as the peak SPL is present only for a very short period of time, this means it needs to be linear at very high frequencies. These circumstances also require extremely specialized microphones, they need to cope with frequencies over 80kHz and will be producing in excess of 40 Volts, maybe nearly 70V, at their output when subjected to a rifle shot, they also need to be physically small. For comparison most high quality microphones are linear to about 20kHz and will generally produce a fraction of a Volt at their output. Most meters for sound pressure level not only lack the high frequency performance necessary, and the high SPL performance necessary, but they also integrate - that is to say they sort of average the sound pressure over varying lengths of time. Again accurate recording requires data logging at hundreds kHz and this is not trivial. As a result accurate measurements of the SPL of a rifle shot are rare, as are accurate measurements of moderator performance. I've no idea how many suitable meters for this sort of work there might be in the UK, I'd guess there might be a few in a university here or there but it is possible there aren't any at all.

If the incorrect meters are used then it is impossible to predict how they might effect the outcome of any attempt to measure the attenuation provided by a moderator - it is possible a moderator which provides great reduction of the peak SPL might extend the time over which sound is present and so may appear to be "louder" to an integrating meter than another moderator which doesn't actually produce as much peak attenuation, such an error may appear consistent and repeatable and so give unfounded confidence in what is being measured. I have seen one expert shooting writer report the level of a rifle, as measured by his meter close to the shooter, as "98dB." Not only did he not know what it was referenced to (there is no such thing as a dB in isolation, a dB is a ratio and so must be referenced to some known fixed value) but he had no concept that if the meter was, as is likely, calibrated to measure dB(A) then 98dB(A) was probably approaching 70 - 80dB too low for the measurement concerned. As an example a link was recently posted on this forum to a moderator test which was carried out outwith the UK but which used a meter with, according to the maker, a maximum SPL of 140dB SPL and that was an integrating meter (i.e. it did a sort of averaging thing and so didn't measure peak SPL). I suspect most discussions of moderator performance are based upon measurements similar to this and, as such, are going to be incorrect in an almost completely unpredictable manner.

 

[caorach]

Good post. Surely the most important criteria for the measuring kit is to be able to establish the potential extent of ear trauma? Doesn't the ear integrate too?
Also, as long as it's capturing the peak, does it matter if the measuring kit is non-linear? It should still put the moderators in the right order?

The problem is that with non-linear kit you can't know what you are capturing - because a gun shot is a very "fast" sound so you need very high frequencies to give it that fast rise time and if you can't accurately record those high frequencies then it is possible you may not record the peak.

While the ear may integrate in terms of perception the problem with hearing damage is the energy in the sound, that's what does the work to do the damage, and so it is necessary to measure the peak - as mentioned I've seen people report peak figures of 98dB(A) (at least I believe it was A weighted though this was a concept beyond them) when they were probably seeing readings above 170dB(A) and when every 3dB increase is a doubling of power that means the correct figure has an awful lot more power to do damage than the 98dB(A) figure. So in this respect the measuring equipment does establish the potential for ear trauma as it can, if the right gear is used, establish the energy available to do work on the hair cells and there is some awareness of how impulse noise works in respect of damage.

If the measuring gear is non-linear then it is impossible to know if it will put the moderators in the right order or not, it is also impossible to know if each moderator will reduce the SPL below the magic 140dB SPL level above which instant damage is caused by an impulse and this is very important indeed as if the SPL is above this then you need hearing protection even if only exposed to a single shot whereas if it is below this threshold you are into the area of "dose" when considering potential for damage. With non linear or unsuitable gear you could simply be measuring distortion created by the failure of the capsule of the microphone, for example, and there is no reason to expect this to be correlated to the SPL of the gun shot and it is possible it could be of a lower level for higher level gun shots, you simply can't know this and so it makes any measurement worthless. It also makes publishing any measurement which is not correctly made a risky proposition if people are going to use it as the basis for decisions related to their safety.

 

[Edinburgh Rifles]

Very nice work indeed. I'm strongly considering Freyr-Devik either 196 or 269 for my Sako 6.5x55. Unfortunatelly they are not tested back to back in this review. I also have no chance to try them life on a rifle including balance. Which one of these would better suit for my 6.5 please? My rifle has standard factory barrel in 560mm.

Max sound attenuation -

It is worth being very, very careful with info available online as regards moderators and other shooting related "measurements" of sound pressure levels.

The gear to accurately measure the peak sound pressure level produced by a rifle is very rare and extremely specialized indeed, typically it will be the size of a fridge or similar. It needs to cope with a very high SPL (in the order of 180dB SPL) and it also needs to be extremely "fast" as the peak SPL is present only for a very short period of time, this means it needs to be linear at very high frequencies. These circumstances also require extremely specialized microphones, they need to cope with frequencies over 80kHz and will be producing in excess of 40 Volts, maybe nearly 70V, at their output when subjected to a rifle shot, they also need to be physically small. For comparison most high quality microphones are linear to about 20kHz and will generally produce a fraction of a Volt at their output. Most meters for sound pressure level not only lack the high frequency performance necessary, and the high SPL performance necessary, but they also integrate - that is to say they sort of average the sound pressure over varying lengths of time. Again accurate recording requires data logging at hundreds kHz and this is not trivial. As a result accurate measurements of the SPL of a rifle shot are rare, as are accurate measurements of moderator performance. I've no idea how many suitable meters for this sort of work there might be in the UK, I'd guess there might be a few in a university here or there but it is possible there aren't any at all.

If the incorrect meters are used then it is impossible to predict how they might effect the outcome of any attempt to measure the attenuation provided by a moderator - it is possible a moderator which provides great reduction of the peak SPL might extend the time over which sound is present and so may appear to be "louder" to an integrating meter than another moderator which doesn't actually produce as much peak attenuation, such an error may appear consistent and repeatable and so give unfounded confidence in what is being measured. I have seen one expert shooting writer report the level of a rifle, as measured by his meter close to the shooter, as "98dB." Not only did he not know what it was referenced to (there is no such thing as a dB in isolation, a dB is a ratio and so must be referenced to some known fixed value) but he had no concept that if the meter was, as is likely, calibrated to measure dB(A) then 98dB(A) was probably approaching 70 - 80dB too low for the measurement concerned. As an example a link was recently posted on this forum to a moderator test which was carried out outwith the UK but which used a meter with, according to the maker, a maximum SPL of 140dB SPL and that was an integrating meter (i.e. it did a sort of averaging thing and so didn't measure peak SPL). I suspect most discussions of moderator performance are based upon measurements similar to this and, as such, are going to be incorrect in an almost completely unpredictable manner.

I don't claim to know enough about the technical aspects of the sound meters required so took advice from several people who do.

The meter used ticks all the boxes:
B&K 2250-S analyzer
GRAS 40BF 1/4" Ext. Polarized Free-field Microphone
Freq range: 4 Hz to 100 kHz
Dyn range: 30 dB(A) to 172 dB
Sensitivity: 4 mV/Pa
The Analyser has a Rise time of 10 μs

The format of the test and the positioning of the mic in our test made no attempt to conform to US MIL-STD-1474D test format
I personally don't think it is applicable to sporting shooters many of whom shoot prone or seated.
The US military test is built around standing shots

The application of A (or C) weighted dB values is also incorrect in the recording of Max Peak of a gunshot
But again due to the US Military standard test has been adopted at the de facto standard by the moderator industry.


The purpose was to avoid any anomalies of testing mods on different days and trying to standardise recordings by trying to conform to a test format and using potentially different hardware.

By testing all the mods on the same day, same location, same rifle, same Ammo, taking mean readings on moderated and unmoderated to recalibrate through the test and rank them you remove any manufacturer interpretation of the test standards and get the unfiltered comparison

 

[simonl]

The problem is that with non-linear kit you can't know what you are capturing - because a gun shot is a very "fast" sound so you need very high frequencies to give it that fast rise time and if you can't accurately record those high frequencies then it is possible you may not record the peak.

While the ear may integrate in terms of perception the problem with hearing damage is the energy in the sound, that's what does the work to do the damage, and so it is necessary to measure the peak - as mentioned I've seen people report peak figures of 98dB(A) (at least I believe it was A weighted though this was a concept beyond them) when they were probably seeing readings above 170dB(A) and when every 3dB increase is a doubling of power that means the correct figure has an awful lot more power to do damage than the 98dB(A) figure. So in this respect the measuring equipment does establish the potential for ear trauma as it can, if the right gear is used, establish the energy available to do work on the hair cells and there is some awareness of how impulse noise works in respect of damage.

If the measuring gear is non-linear then it is impossible to know if it will put the moderators in the right order or not, it is also impossible to know if each moderator will reduce the SPL below the magic 140dB SPL level above which instant damage is caused by an impulse and this is very important indeed as if the SPL is above this then you need hearing protection even if only exposed to a single shot whereas if it is below this threshold you are into the area of "dose" when considering potential for damage. With non linear or unsuitable gear you could simply be measuring distortion created by the failure of the capsule of the microphone, for example, and there is no reason to expect this to be correlated to the SPL of the gun shot and it is possible it could be of a lower level for higher level gun shots, you simply can't know this and so it makes any measurement worthless. It also makes publishing any measurement which is not correctly made a risky proposition if people are going to use it as the basis for decisions related to their safety.

I agree you need adequate response time - but only to the point at which the ear is susceptible - from a damage perspective, not human perception.
I'm struggling to understand how a microphone could be so badly non-linear that it would exhibit a negative slope as you are suggesting - where a louder sounds gives a lower reading - unless it's in total saturation, which could be disproved by changing distance from source.
Edit: seeing ER's response doesn't the non moderated shot prove we're not in a significantly non-linear curve? Certainly non a negative slope.

 

[Edinburgh Rifles]

Very nice work indeed. I'm strongly considering Freyr-Devik either 196 or 269 for my Sako 6.5x55. Unfortunatelly they are not tested back to back in this review. I also have no chance to try them life on a rifle including balance. Which one of these would better suit for my 6.5 please? My rifle has standard factory barrel in 560mm.

269 max sound attenuation, longer form and more forward protrusion
196 shortest, lightest, less forward protrusion

Personal choice as they are both good at the key suppression factor

 

[caorach]

I agree you need adequate response time - but only to the point at which the ear is susceptible - from a damage perspective, not human perception.
I'm struggling to understand how a microphone could be so badly non-linear that it would exhibit a negative slope as you are suggesting - where a louder sounds gives a lower reading - unless it's in total saturation, which could be disproved by changing distance from source.

Yes, but if you change distance you still run into problems with rise time/slew rate. Initially it sounds like a good idea to get comparative readings by simply standing back a bit - you may not get a max (i.e. at the ear of the shooter) reading but you might get a good comparison between the options but of course if you aren't fast enough you can't win this one either.

If the mic ran out of mechanical travel, for example, then potentially it might produce no, or very little, output for very high SPLs as it could potentially be sitting on the end stops and we are not talking about anything approaching normal SPLs here so most mics, power supplies, amps and so on are going to be well beyond their design parameters. Depending on the slew times of your amps this might, or might not, have potential to give you a lower output for a higher input. Again though the key thing is that we can't really know exactly how this will work out as if there are so many aspects of our system that are "non linear" at the SPLs we require to measure then how might they interact? What happens if you drive the power supply to the rails?

We are not talking about what the ear hears here, we are talking about providing energy to it to cause damage. So what you are really asking is at what pulse length does the impedance coupling mechanism of the ear break down so that no energy is passed from the outside world to the inner ear and the truth is I've no idea but what we do know is that gunshot impulse noise causes damage and measuring gunshots requires you to be able to go from zero to many tens of volts in microseconds and this is not a common thing to have to do. So the adequate response time is very fast indeed and requires much higher frequencies than we can normally hear.

 

[Edinburgh Rifles]

No moderator on a centrefire rifle with supersonic ammunition reduces noise at the shooter's ear enough to negate ear/hearing protection

 

[Uncle Buck]

I take my hat off to you Ed you must have put some time in there....one question whatever happened to the humble T8 reckon it still a formidable player...?

Billy

??????

 

[Edinburgh Rifles]

It was unfortunate that on the day the only T8 in 14x1 I had was not a 30cal one
To be honest though with so many mods on the market the T8 isn't even a consideration for most people looking for a new mod

Would have been nice to see where they sat in the ranking though I agree

 

[Miki]

The problem is that with non-linear kit you can't know what you are capturing - because a gun shot is a very "fast" sound so you need very high frequencies to give it that fast rise time and if you can't accurately record those high frequencies then it is possible you may not record the peak. <snip>
.

I agree with a lot of what you are saying with regards to an absolute Noise Poser/Density measurement but that was not what Ed was trying to acheive. What he did was a 'relative' measurement using equipment that was able to give an accurate and repeatable meaurement, This 'equipment' included a high specification, calibrated noise meter/microphone, a table and a tape measure. The measurements were all taken on the same day in similar real-world conditions (ie outside) at the same place in a field facing a gentle slope with unchanging surrounding.. Each shot used the same gun and boxed ammunition, the microphone/meter was at the same 3D spot and was controlled in such a way that, to the best of Eds ability, the only difference was the moderator used.
I beleive it gave a clear indication of the performance of the different moderators, differences that are relative to each of the devices under test, the recoil distance was also measured and each moderator weighed.

Using this data you can pick a moderator from the list safe in the knowlege that it is either quieter, lighter or more capable in reducing felt recoil that another with the list of tested devices. Subjective matter (like does it look better on my rifle) and questions relating to moderators that were not tested are not relevant, catered for or wanted.

 

[G4ZZ]

Good work i bet that took some time to do.

 

[caorach]

I agree with a lot of what you are saying with regards to an absolute Noise Poser/Density measurement but that was not what Ed was trying to acheive. What he did was a 'relative' measurement using equipment that was able to give an accurate and repeatable meaurement, This 'equipment' included a high specification, calibrated noise meter/microphone, a table and a tape measure.

This is a very valid point and it is natural to assume that although the results may not be absolutely correct in relation to a fixed reference they may be valid on the basis of giving a relative comparison between the devices tested. However we don't know this as we don't know, by definition, how the testing gear behaves in the non-linear part of its range and with gun shots we are right at the edge of what we can physically measure. This is sort of the equivalent of measuring bullet velocity with a police speed gun that only records to 150mph - the speed you are measuring is way beyond the capabilities of the device in use but the speed gun might produce a figure on the display, the question is does that figure mean anything and could you use it to compare one bullet to another? A rifle shot produces an SPL of towards 180dB SPL while commonly available specialized meters will generally be linear to about 140dB SPL and it is hard to get people to understand the vast physical difference we are talking about here but, as you will be aware, a dB is a ratio and so you can measure anything in dBs so if you started off with a car at 30mph and increased its speed by 40dB (the difference between what we can measure and what we need to measure in this instance) it will be travelling at approx 2500mph. I don't know if that helps but it gives some "everyday" perspective on how huge this is as an engineering problem and may, therefore, allow us to understand why it is a problem that is very rarely solved.

In terms of the rise time then the front of the shock wave close to a gun is believed to be about 0.1um in width and it gets smaller with higher SPLs, the British Standard Human Hair (only joking) is about 1,000 times wider than this. This wave front is going past at a speed, in part, in excess of the speed of sound. So what we are trying to do is take a "picture" of 1,000th of a human hair passing us at about the speed of sound and, during the time it takes to pass, our electronics must record a swing in voltage of perhaps up to 200V plus the capsule of the microphone must overcome its inertia and move over its full travel. My understand is that we can't actually do this - that is to say no one can achieve this and the best we can hope for is a rise time in the order of 4 micro seconds - and so we have to compromise a bit. Again this gives some idea as to where making these measurements sits in terms of modern engineering - you simply don't do this stuff in your garden as it is way more complex than putting a man on the moon.

So Ed has clearly put a lot of work and thought into this and it is possible that his results allow a comparison between moderators, but it is also possible that they don't. As simonl has basically said what matters is the effect on your ear and he is correct as in the field this is a "does it do my hearing damage?" problem rather than an engineering problem. I deviate from Ed's position on this and also it is here that accurate and absolute measurement becomes important. Ed takes the stated position that even with a mod hearing protection is necessary and for the purposes of safety and liability this is a good place to be. My position is that the science says that below 140dB(A) impulse noise doesn't cause instant damage and so damage becomes related to "dose" and with a gunshot being of such short duration so the dose is actually quite low. Having studied the best data I can find I take the view that, on balance, my rifle is probably producing less than 140dB(A) at my ears so I'll fire one or two shots moderated without hearing protection when stalking over the period of a day. As stated, however, my position depends completely on knowing the absolute SPL of my rifle and the absolute and accurate reduction in this SPL provided by my moderator and it is, as we've established, extremely unlikely that I'm in possession of these two bits of info to the accuracy necessary to support shooting with a moderator and no hearing protection. So, although I maintain a position that the various tests of moderators may be completely meaningless you will note that I base my own position on some of these tests, in my defence I studied a lot of data and info to normalize what I was seeing but my own behaviour in the field is extremely flawed. Ed's position is the safest and most sensible, mine is based on 30 years experience in this area and good luck.

Once more this brings us back to what simonl said - "the ears have it." As SPL meters that are generally available to us, even the most specialized, are operating either completely randomly or in a very non-linear part of their range when recording gun shots we can't know if their relative readings are meaningful or completely meaningless even if we do know that the absolute readings are going to be wrong. However our ears remain the best bit of audio measuring gear we have and it may be possible to use them to check the results provided by an SPL meter - if you were to take several people and stand them a little way from the firearms being tested and get them to "score" each moderator for loudness then it would be very useful to compare this to the "absolute" but incorrect results produced by the meter. If there was a good statistical correlation between the people and the meter then you'd at least know the meter was giving the moderators their correct position relative to each other even if the absolute values were likely to be incorrect.

 

[Oh6]

@Edinburgh Rifles - What was the weight of the rifle (including scope & mounts etc) without a moderator attached?

Part of the analysis looks at the recoil reduction that the moderators being tested offer, what I am wondering is if the overall weight of the rifle was standardised, what this would do for the recoil reduction of each moderator.
So at it's simplest, the Predator 12 was the heaviest moderator on test at 0.808kg. So, if the rifle had additional weight added (i.e. in the stock, to aid balance), to increase it's weight for the other moderators to the total weight of the rifle when testing the Predator 12, what impact would that have on the recoil reduction table.

There appears to be calculators online, to assess the impact of additional weight on recoil, so this would potentially give a helpful extra column to the analysis.

 

[Miki]

This is a very valid point and it is natural to assume that although the results may not be absolutely correct in relation to a fixed reference they may be valid on the basis of giving a relative comparison between the devices tested. However we don't know this as we don't know, by definition, how the testing gear behaves in the non-linear part of its range and with gun shots we are right at the edge of what we can physically measure. <snip>.

I do understand where you are coming from but the testing provided a reference between the sound of a common rifle firing common ammunition in a common surrounding, unmoderated and then repeated with different moderators fitted. 5 shots were fired for reference and through each moderator. The fifle was left an equal time between 'tests' and was also fired unmoderated half way through to ensure continuity. The differences in sound levels are relative to the unmoderated firing and tabulated relative to each other. The bench mark wasn't rising (in volume/pressure) but falling (ie being moderated). The recoil was also measured against a maximum (ie fired without a moderator 5 times) and recorded the 'reduction' relative to this initial distance when a moderator was fitted. The 'constant' in all this was the rifle, ammunition, table, sound meter and location/surrounding. The relative variables were the moderators.

 

[icerider]

In very simple words what caorach is telling is, that almost no equipment is capable to record shot sound because of very, very short time interval it occours (rises and drops) in. Even with 5 times repeated and getting more or less same results doesn't mean they are to be tursted because of reason above. He also confirms that exposure to high(not jet sure how high) sound levels for a very, very short period of time couldn't cause hearing damage as it's cumulative (just like radiation, getting a dose). But of course it's better be safe than sorry so hearing protection is advisable.

Other good point Oh6 pointed out regading measured recoil. Mass between heaviest and lightest moderator is more that 600 grams, (808g vs 196g) which makes variable total mass recoil is moving (less with light mod, more with heavier). This should be taken into account when comparing recoil numbers in table.

I do understand where you are coming from but the testing provided a reference between the sound of a common rifle firing common ammunition in a common surrounding, unmoderated and then repeated with different moderators fitted. 5 shots were fired for reference and through each moderator. The fifle was left an equal time between 'tests' and was also fired unmoderated half way through to ensure continuity. The differences in sound levels are relative to the unmoderated firing and tabulated relative to each other. The bench mark wasn't rising (in volume/pressure) but falling (ie being moderated). The recoil was also measured against a maximum (ie fired without a moderator 5 times) and recorded the 'reduction' relative to this initial distance when a moderator was fitted. The 'constant' in all this was the rifle, ammunition, table, sound meter and location/surrounding. The relative variables were the moderators.

 

[Miki]

In very simple words what caorach is telling is, that almost no equipment is capable to record shot sound because of very, very short time interval it occours (rises and drops) in. Even with 5 times repeated and getting more or less same results doesn't mean they are to be tursted because of reason above.,<nip>

I think this is getting a little circular however I do disagree with what you have said.
What I understand @caorach is saying is that there is a limited set of circumstances and equipment that will 'accurately' measure shot sound because of the characteristics both you and he are at pains to mention. What I am saying is that if I have a piece of sound meqasuring equipment that measures the sound of an unmoderated rifle @ 150 bangs and that same piece of equipment measures the same rifle firing the same batch of ammunition under the same physical circumstance, with the addition of a moderator @ 120 bangs, then that moderator has reduced the sound by 30 bangs. If I repeat that "test" 5 times and each time the unmoderated bang is routinely the same level and the moderated bang is around 30 bangs less, then, with a degree of certainty I will state that moderator #1 provides 30 bangs of attenuation. If I then repeat the test with a different moderator (#2) under the same conditions, using the same equipment and that moderator shows a result of -27 bangs and I repeat this 'test' 6 times using 6 different moderators and halfway though this cycle I measure the sound of the rifle without a moderator (and the equipment shows me that this is still 150 bangs) then at the end of the test I can say with an element of certainty that some moderators are 'relatively better' than others at moderating the sound and all of them reduce the bang from the unmoderated rifle. If I list those results, the list is relative. #1 was better at reducing the sound than #2

For ease of comprehension you can substitute 'bangs' for 'apples' or even 'puffs'
This methology would also apply to recoil but does not account for your or my "ear" (a subjective psychological phenomenon) nor my eye (visual amenity) nor to a dBA or dBC scale relative to a weighted or unweighted level.

 

[SussexFallow]

So which moderator came out top ?

 

[Miki]

So which moderator came out top ?

have a look at the first post in this fred

 

[Edinburgh Rifles]

Recoil reduction and weight is not a linear correlation though.
As was shown
The heaviest mods were not always the best at recoil reduction
If you were to rebalance the overall weight of the test unit to make it the same for each moderator test it wouldn't be a fair and impartial test.

If a 700gr mod is less effective as a 500 or 300gr mod at reducing recoil then it demonstrates the lighter mods efficient internal brake design. Not just physical weight impacting recoil.


As to testing the actual peak noise
A 10 μs rise time is fast enough to accurately measure the peak of a gun shot.
Even if you discount the fact that they are all being tested eliminating a large number of other environmental and physical variable factors by doing it all at once on one single platform and one ammunition type.
You could argue that even I feel you are missing the fastest and highest frequency elements of the gunshot you are missing them consistently on all of the test shots

I also disagree that a single gunshot doesn't cause long term hearing damage.
Yes it is cumulative, more is worse.
But if you can get tinnitus from one shot then I would argue you have caused damage.
It's a direct symptom of the damage caused to the cochlea
In fact it's fairly universally accepted that a single very loud noise can damage hearing