quote:

Originally posted by tnekkcc:
I can get you any measurement you want from any source if I can control the reflection co efficient of the environment.

So, what would your preferred "reflection co efficient of the environment" generally be when measuring the SPLs of impulse type sounds such as a gunshot and what influence would that have on your methods?

Saeed,

Good luck in your experiments. I hope they appear on the site alongside the other useful information.

My minor experience in moderators has shown that charge weight, powder burn rate and peak pressure all have an effect on noise of moderated rifles. Barrel length therefore introduces a variable too.

Regarding moderator efficiency volume is a great help but can be made up for by efficient design and machining to tight tolerances.

What designs is Walter coming up with - over barrel or cans that are only in front of the muzzle.

Finally (especialy being Walter) beware shooting large charge weights of slow powder out of short barrels - there is the potential for powder build up and subsequent risk.

There is comfort and joy in working with sub sonic .22s. I have been down this road over and over for forty years plus. Once you perfect your design ( which is easy) you will be able to fire a bolt action, or shotgun break type action, and all you will hear is the slug hitting the target. The effective and accurate range will only be 25 yards.
Larger caliber guns produce a larger volume of gas at higher velocities and the larger the caliber, the less effective the silencing. Silencing is one thing and suppression is another.Re-read tnekkcc for he is on the money.
But all this is sort of fun isn't it?

quote:

Originally posted by nvreloader:
Seead,
Be sure and try little 22 Jet, model 53 83/4" bbl, It feels like some one is sticking a needle thru both ears at the same time, the 30 Ruger carbine is not far behind.
Don.

Even the .22 WRM is painful in a short-barreled handgun.....

yes, the NAA mini revolvers were a rude surprise.

It would seem to me that the chamber in which the sound is measured would have to adhere to some kind of standard so that the results could be duplicated at another location by different people, else you really don't have anything. A shot may sound like an A-bomb going off in your shooting room, Saeed, but not sound like much more than good belch on an expansive desert plain. Maybe you can build a box of one cubic meter, line it with foam rubber of some thickness that can be purchased in most developed countries around the world, then situate the microphone at a specific distance from the muzzle and blast away.

As if things aren't complicated enough...

Measuring noise for the purpose of evaluating silencer/suppressor design is going to be tricky. Along with factors already discussed, you have to consider the geometric distribution of noise around the muzzle. In other words, measuring the noise level at a single point away from the muzzle with and without the "can" may be misleading. Without the can, the peak level might occur in the direction perpendicular to the boreline, with the can it might be 70 degrees from the boreline.

Another thing to consider is what part of the problem you are trying to minimize. That is, are you trying to minimize noise at the shooter's ear, the game's ear, or the neighbor's? Things change with distance. Over long distances, higher frequencies are attenuated by air more than lower frequencies, which is why distant thunder is a low "boom" while close thunder is a "crack". So a suppressor design which is best for saving the shooter's ears may not be the best for keeping the neighbors from complaining.

Maddening, isn't it?

You are, in my view, spot on the money CouchTater. My take on it, from the perspective of a hunting rifle, is that your aim would be to reduce the levels at the shooters position. I would base this on two assumptions which, while they may be flawed, will hold sort of true. One is that hunters often shoot alone and the other is that anyone with a hunter is likely to be behind the hunter and so at approx the same angle from the muzzle as the hunter himself. Assuming this then any moderator which protects the hunter would also tend to protect someone standing beside him and, probably, slightly behind him.

I suspect that the issue you raise homebrewer is not valid if you are using a meter with the correct response time to measure the peak SPL of a firearm. If you were integrating with respect to time, and I suspect many meters do this to some very small extent, then reflections from the environment would be an issue and the total "dose" received by the human ear or an integrating meter would increase in, say, a hard room. However, in order to measure the peak SPL of a firearm I figure you need a meter with a response time in the order of 25us or better and such a unit is likely to be able to easily differentiate between the primary gunshot and any reflections, sound moves about 1 foot per millisecond so at 25us you have a spatial resolution in fractions of an inch. There are some additional confounding factors in this situation which would still make measurement in a free field more appropriate but I would assert that even in a hard room, such as Saeed's shooting room, with a suitable meter you will get results which are repeatable and reasonable from the approx position of the shooters head.

Certainly it has been interesting to consider such things and I have a friend who is a bit of an authority on such matters to I must discuss the matter with him when I get the chance. I can't help but imagine that he will have cause to put me right on a few things but it will be interesting to explore the topic.

quote:

Originally posted by caorach:

quote:

Originally posted by tnekkcc:
I can get you any measurement you want from any source if I can control the reflection co efficient of the environment.

So, what would your preferred "reflection co efficient of the environment" generally be when measuring the SPLs of impulse type sounds such as a gunshot and what influence would that have on your methods?

The field theory for sound looks an awful lot like the field theory for electromagnetic radiation.
The wavelengths are similar and the chambers used for measuring emission look similar.
The anechoic chambers I have seen for sound look just like the chambers for EMI [electro magnetic interference] where I have often worked.

Just becuase I make fun of amateur posters here over out of control and pointless chamber pressure or spl measurements, does not mean I have not made fun of giant high tech cooperations for out of control measurements of sound, emi, lightning, etc and then sent them an invoice.

What does it all mean?
If someone wants to play with a strain gauge or spl meter, I should not be a spoil sport.

quote:

Originally posted by tnekkcc:
The field theory for sound looks an awful lot like the field theory for electromagnetic radiation.

As sound is a longitudinal wave it would seem reasonable that the linear wave equations would be related to elements like the elasticity of fluids and so would be derived from Newton's equations for motion. Sound is, after all, just molecules in motion. With electromagnetic waves being somewhat different I would imagine the derivation of the fundamental equations would also be radically different, RF theory really makes my head sore. However, perhaps you would care to provide us some background and outline the parallels you see between the two and how this impacts upon measuring the peak SPLs of gunshots? I can't quite see how this all ties together so a detailed treatment would be most useful to me and while I appreciate it might be a little boring for others without specialist knowledge in this area I am sure they would humour us for a little while and we might be able to reach some general conclusions which would be useful to everyone.

Sound waves and radio frequency waves get attenuated, bend around corners, and get reflected.

Your TV rabbit ears and the ears on your head are sensitive to 2 meter wavelenths.

Your gun and your cell phone are into shorter wavelengths.

quote:

Originally posted by tnekkcc:
Sound waves and radio frequency waves get attenuated, bend around corners, and get reflected.

Your TV rabbit ears and the ears on your head are sensitive to 2 meter wavelenths.

Your gun and your cell phone are into shorter wavelengths.

I think you are being coy now, there is no need to hide your obvious knowledge of the matter or to simplify matters as while I'm far from an expert on anything both myself and others are most interested to see your detailed treatment of this matter. As an audio engineer I am especially keen on your ability to get any measurement we might want if we can control the "co efficient of reflection of the environment." You hint that you have considerable practical experience of this but, perhaps, in the first instance you could humour us and produce a theoretical treatment to allow us to develop our own practical approaches to the theory. I was never that smart when it came to tricky maths and so this is an area that I must have entirely overlooked but they say you learn something new every day and I tend to find that I learn about 100 new things every day. I'm sure you must be aware that most on this forum will be happy with the concept of wavelength and with basic Newtonian physics so if you would care to start there and derive the maths from such simple foundations I'm sure most of us will be able to follow. As you have demonstrated a willingness to explain things in the most simple of terms in your postings in this thread I'm sure you will easily be able to help us with the bits we don't understand.

Then, perhaps, you could expand the theory to tie sound and electromagnetic radiation together. Do you think, for example, that as they both have similar wavelengths they interact and could you detail a way we might quantify such interaction? For example if my cell phone is about to ring and so is handshaking with the mast could this impact upon how my rifle sounds?

quote:

Originally posted by caorach:
As an audio engineer I am especially keen on your ability to get any measurement we might want if we can control the "co efficient of reflection of the environment."

If that number is greater than one, it amplifies.
If it is less than one, it attenuates.
You start with a signal, vary the reflection with respect to frequency and transform the signal and it's noise into any profile, and amplitude desired. I suppose the unreflected signal, if it is a straight line to the SPL, will alway show a little something. Like radio wavers, in the near field that should fall off as 1/r and in the far field as 1/r^2.

What does it all mean?
The gun will measure louder in a concrete bunker than in a closet full of clothes.
Same gun, same SPL meter, very different measurement.

quote:

Originally posted by tnekkcc:
If that number is greater than one, it amplifies.

That's amazing. So, the nature of the room actually modifies the sound coming out of the muzzle of the rifle? Am I correct in this or am I misunderstanding?

quote:

Originally posted by tnekkcc:
If it is less than one, it attenuates.
You start with a signal, vary the reflection with respect to frequency and transform the signal and it's noise into any profile, and amplitude desired.

Ah, just when I thought I was getting the hang of this it gets complicated again. Exactly what does a transform to a profile involve doing? Is this a transform like Laplace or FFT or is it something different? Also when you say vary the reflection (I assume you mean reflectivity) with respect to frequency what does that involve and why do you do it?

[

quote:

Originally posted by tnekkcc:
What does it all mean?
The gun will measure louder in a concrete bunker than in a closet full of clothes.
Same gun, same SPL meter, very different measurement.

So, in summary the sound pressure leaving the muzzle of a rifle will depend upon the nature of the space where the rifle is fired and, potentially, the sound might actually be made louder by certain types of room, for example?

quote:

Originally posted by caorach:
the sound might actually be made louder by certain types of room, for example?

An exponential horn, a parabolic focus, and active surface, etc.

quote:

Originally posted by tnekkcc:
An exponential horn, a parabolic focus, and active surface, etc.

It would be useful if you addressed some of the other questions raised as well as I think we might be getting to the crux of this matter. I am still keen to understand how we go about this transforming the signal and its noise into any profile for example. I would imagine others are interested in your parallels between sound and electromagnetic radiation and, especially, in your views on whether they interact if, say, we let them both loose in the same room.

Now, the objects you outline above are hardly rooms in which a gun will be fired and I think your suggestion that a parabolic horn, say, in some way amplifies sound is a misunderstanding as it merely matches impdedances like the horn on a brass instrument; so let's try to stick to rooms in which a gun could reasonably be fired by a reasonable person. Are you saying that the nature of such a room will increase the SPL leaving the muzzle of the rifle? Do you expect the laws of thermodynamics to have a role to play here?

I think the point is that the SPL measurement depends on the environment.

I have had one acoustic field theory course and one electro magnetic fields and waves in college 32 years ago and I am not as handy with eetothejayomegatee as I was then. I made money on audio for aircraft in the 70s and built some antennas in the 90's. I still have some equipment for calibrating microphones left over from the 747/767 public address amplifier and we use very tight coupling, so the environment does not get involved.

What does it all mean?
You are not going to get me very far from "How loud are gunshots?"