Toward a new sound metering standard.

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Toward a new sound metering standard.

Post by silencertalk »

So this post is based on what I wrote about sound metering here:

http://www.silencertests.com/standards.htm

To sum it up -- the mil-std is for hearing risk assessment and not for loudness measurement. It has two flaws for human perception of loudness:

1. It is based on peak sound level rather than total sound power.

2. It is based on A-Weighting, which is a crude approximation of the 40 Phon (dB at 1000 Hz) equal loudness curve (rather than the 120 Phon curve which would be the best single curve).

So what is the solution? Well, C-weighting is clearly better than A, because it is the 90-100 Phon curve.

But I really want to measure in units of Sone.

Sone calculations use the REAL equal loudness curves at 1/3 octave intervals, not some simple parametric equation of it. And furthermore, it uses the specific curve for whatever the sound level is!

It has one more advantage -- it is not logrithmic but rather they rescaled it so that 5 Sone would sound five times as loud as 1 Sone. When you see the numbers they are easy to digest and compare.

The 20 microsecond rise time in the mil-std is not needed if you do not care about their hearing-risk-assessment criteria. A slower rise-time IS useful for comparing silencers (I will debate this more with Al Paulson in person because I know his book says otherwise). Yes, there are those which will call me a heretic, etc -- but they are members of the flat-earth society. At least I hope. I have to think outside the box. I never got ahead by following other people.

Trust me on this -- when the military switches to units of Sone everyone who blasted me for daring to say this now will pretend they always thought it was a good idea and in the future when others start to propose this it won't seem so daring that I am saying it now. Some say that only 'recognized standards' are useful and do not support testing silencers outside the military standard -- which is to say -- those people do not support testing silencers for human loudness perception.

The military only does sound testing to protect the hearing of their members -- not to find out which silencer sounds best and is the neatest one to buy. I am interesting in testing to know what works the best and pretty much know all of the major products are already hearing-safe.


Back to Sone units: There are Larson-Davis sound meters which directly measure in Sone (the model 2900). I found another brand also called the Cel-553C http://www.enviro-equipment.com/product ... s_sla.html although I am not clear on if it can handle the unsuppressed sound levels.

One could also do it on a PC with a sound card and some spectrum analyzer software using this program:

http://www.xlnoise.com/products/productloud.php

but that would be really painful to do 10 shot averages. I will try it as I made a cable to go from the output of my 2209 meter into my 40Khz bandwidth sound card. That way I can use the good micrphone with my PC.


What I would like to do is MIL-STD-1474D because people want it, and then in units of Sone because I think it will be best for comparison. Since I don't have a Sone meter now, I should probably do C-weighted results as that is the best I can do with my 2209 meter.
Last edited by silencertalk on Mon May 30, 2005 8:52 am, edited 1 time in total.
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Post by renegade »

FWIW, I do not buy into the current MIL-STD either (it is a measure of intensity and not loudness), but it is a standard.

The major problem I saw with you not using A-weight was you still reported results in dB, so most folks would compare your dB to MFG dB and think they were apples to apples when they were not.

When I bought a recent set of muffs, it reported net reductions over a range of frequencies. That is what I would like to see. Trying to report performance of a silencer as a single number is as silly as trying to report performance of a car as a single number.

Phon or sones is definitely an improvement.
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Post by William Perkins »

I have been suprised at who has contributed to the discussion and who has remained silent. Since I am not interested in throwing anyone in front of a bus I will let the following quote remain anonymous. I only offer it as an interesting viewpoint. Realize that this comment was made over 1 year before Robert presented his site to the public.

"There has been some comment on the value of sound pressure level measurements and the statement that actual measurements have little meaning when compared to subjective observation at a demonstration. I can agree in part with this opinion.

Personal observation and comparison are exceptionally important when choosing a suppressor. The only problem is that what may seem quiet to one observer is not necessarily quiet to another. The reason is usually related to individual hearing acuity and both the degree and range of that individual’s hearing loss. Additionally, many differing suppressor designs treat different portions of the audio spectrum differently. Some act as a low pass filter, attenuation the higher frequencies selectively while others shift a lot of the sound energy toward the upper range of human hearing or into the ultrasonic range. If examples of both type suppressors have the same peak sound pressure level measurement, the tonal quality will be significantly different, and one may be more pleasing to one observer while the opposite is true for another. Which is more quiet is a subjective observation.

Sound Pressure Level (SPL) measurements with a meter that meets MIL-STD-1474D will give an objective (Measurable) evaluation. Meters meeting these specifications will record the highest single peak between approximately 30 Hertz and 60 kiloHertz, regardless of whether this peak is within the range of human hearing (below about 15,000 Hertz) or in the ultrasonic region. Unfortunately, using a filter will too frequently cause the meter to miss the major pulse. Sadly, this is about the only objective method of evaluation a sound reduction device.
The one thing that is important about SPL measurements is long-term hearing damage. MIL-STD-1474D specifies that hearing protection must be used if the SPL is 140 dB or louder.

The MIL-STD currently specifies A-weighting (which slightly attenuates the high frequencies rather than unweighted, which will not be as favorable for advertising purposes. My experience is that for the same weapon, unweighted is about 5-7 dB worse than A-weighting.

The bottom line is that for hearing protection issues, as long as the actual measured SPL is below 140 dB, choice of a suppressor should be made on other factors, including intended use (urban, rural, etc), appearance, reputation, cost, longevity, and what sounds best to you, the customer. Whether a given can measures reductions of 41 or 38 or 30 dB on a given day (assuming accurate measurements), changing atmospheric/weapon/ammo conditions will cause differing measurements on different days and locations. Sadly, too many advertising claims of SPL reduction are made on the basis subjective rather than objective observations or one-upmanship. Further measurements made at sea level in the summer may not be reproducible at 10,000 ft in the winter.

MIL-STD-1474 is indeed about hearing damage protection. The reasons MIL-STD-1474D are even referenced (in addition to hearing protection issues) are twofold,

1. Ascertain the sound meter meets the standards suitable for firearm sound measurements (20 microsecond rise time) and that it won’t miss the main pulse (as a Radio Shack meter will), and
2. Provide a repeatable location for measuring.

What would be of real benefit to the industry would be if everyone could agree on one (or possibly two) locations to be a standard and then everyone used these."


Emphasis in ORANGE is mine, not the authors. It is interesting that some of what Robert is trying to accomplish was publically expressed by one of the industry giants yet there is much resistance.

The Manufacturers seem to fall into several categories.
1. Manufacturers that make outrageous claims don't want the public to know that their products don't perform up to their imagination.
2. Some manufacturers that I hold in high regard and believe are credible but are suspicious and silent.
3. Manufacturers who really don't care because civilians are not their customers.
4. The manufacturers who are participating. An open (public) dialogue does a lot to build trust with existing customers and develop new customers.

Some of the criticism HAS been justified. But it seems that efforts are made to address those concerns and respond/correct them. Unfortunately, without feedback, those who have concerns but fail to voice them will not be part of the solution.

In retrospect, this was to be expected. Those who have been around for a while will remember the SAR supressor trials from years ago and how that self-destructed despite the best efforts of well respected individuals in the industry. Offering to use one location, all testing would be done with the manufacturer present, unbiased witnesses validating the testing procedures, and using accepted MIL-STD-1474D protocol. Despite all these efforts, Ka-boom. Nothing to show for it.
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Post by silencertalk »

Well I am pretty sure there is stuff to show for the suppressor trials -- but they probably chose not to show it. I am not sure why. I would guess it is because all of the attacks I have received would have been directed at them and they were unwilling to weather the storm. It has not been hard for me because I have been through bigger issues in the past with some very powerful name-brand opponents.
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Post by PCArms »

Good for you Robert.

Data is so subjective, and once you carve the numbers in STONE, you better be able to BACK THEM UP, and REPEAT THEM!

I think you have done a great job DOCUMENTING your procedures.
(Although there has been some questions as to numbers changing after the fact????)

Most people don't keep track of the minuet details,
so it's easy to say, "My Can drops the level, 84dB and your data only shows a 23dB drop????"
Ha. :lol:
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Post by silencertalk »

[quote=
(Although there has been some questions as to numbers changing after the [/quote]

Two things changed. One was that I thought I was testing a SpecWar2 with an AAC mount and had that in the table. Later after talking to my testing partner I discovered that it was a Wolverine that had an AAC mount. I changed the name in the table to "Wolverine with AAC mount."

When others saw the SpecWar2 disappear from the table, they accused me to being in bed with SWR and deleting a result SWR was not happy with.

The other thing that changed was upon re-examing the raw data I saw that the mic was clipping on an M4 at 1 meter for the unsuppressed shots. I did some experiments and learned that was the only situation where the mic was clipping (handguns did not do it). So I retested the M4 at 2 meters and added 6dB to the result, and then updated that number. When I did this, rather than keep quiet about it, I posted to everyone what happened and how I fixed it. Several people have used that against me but their claims have no merit. Would everyone prefer that I just not fix the mistake?

Those people who are complaining about a number changing do not really have a problem with it -- it it just the biggest problem they could find to try to discredit me so they grasped at straws and tried to sell their position to others. It is kind of like how the liberals are trying to get President Bush's Juditial nominations killed -- by repeating half-truths over and over hoping some will stick or at least chip away.

Let me put it this way -- after testing all of these cans, *I* am learning a lot about what can to buy. If I am learning a lot, people who have no time or resources to test cans can benefit from what I have learned either from reading the stuff on this site or asking for an opinion. One thing I have learned is there is a huge difference between my opinions of cans based on what I have heard or read before, and what I know now.
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Post by PCArms »

Thanks for the DETAILED, (and quick) explanation.

Now GET OFF the computer and do more TESTING, (hahahaha)

So when is the Trip to see Kevin?
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Post by silencertalk »

In less than two weeks.
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