I have two questions which have popped into my brain recently and wondered if anyone could enlighten me. Apologies but they're not car related really.

First question......if a silencer on a gun can make it relatively quiet (I appreciate it's not like the films and does still make a noise) despite it's size, why does it take an enormous silencer to keep a car quiet(ish). I assume there's a fairly sensible answer to this one.

Second question......those metal coffee pots that you put directly on the stove and are sort of octagonal at the base and split in the middle, well how on earth does the coffee all of a sudden transfer to the top section when it's ready?

For size of silences question I'd imagine its because the chamber of a gun is a lot smaller than that of a car engine therefore a lot less volume. Bigger engines need bigger silencer.

A silencer as you are picturing it is just from movies (or at least it was when I was interested in that stuff).
All a silencer actually does is direct the sound forward so ears to each side hear less, the people in front actually hear it full volume.
When I was looking into an exhaust silencer for track days, Merlin told me that it is the thickness that can kill sound, the length to a lesser extent. The baffles and paddings absorb the sound energy, so I guess the more baffles the more absorbtion?

The coffee pot IIRC initially has the water in the bottom when cold. When it heats up and boils, it bubbles up a spout in the middle all the way to the very top, and percolates down through the coffee grinds (in the top in a perforated basket) by gravity, but it is stuck in the top half as it is sealed from the bottom. Periodically air is sucked down to replace the water and then more boils up the spout. (the spout end is close to the bottom of the lower sealed half so it keeps going till nearly all is used up)!

I type with one finger so I bet someone has posted a better reply by now, but E for effort as all my teachers used to say!

For the silencer, I would assume its down to the length of time, speed of the air and volume of air. The gun only needs to be silenced for a mili second or 2. It also only has a small bore and a single (ish) speed of air.
The exhaust is a lot larger, needs to deal with constant/sustained air flow, and is also designed to work with varible flow rates.

[Edited on 18/12/10 by loggyboy]

http://www.youtube.com/watch?v=qZU5TGljAmw

Above bares out Bitsillys comments on directin the sound, the gun is quieter, but the echo is the same!

[Edited on 18/12/10 by loggyboy]

the stove top coffee maker has a funnel which fits internally and holds the coffee grounds, the pipe from this goes into the water reservoir . When the top is screwed on the funnel makes an air tight seal. as the water boils in the lower section the steam expands this air gap and thus forces the boiling water up through the funnel, through the grounds and up into the upper 'pot'. the pipe in the upper pot it above the final water level and wont run back down. You get a hissing noise as the steam directly escapes telling you coffees ready. Unlike the cona system, which realises the creation of a vacuum in the lower reservoir to pull the coffee back down.

Cheers

Moss
the cona fascinated me as a child and wish i had one to impress my kids

this give a visual of what happens
cona in action


[Edited on 18/12/10 by LoMoss]

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Originally posted by bitsilly
A silencer as you are picturing it is just from movies (or at least it was when I was interested in that stuff).
All a silencer actually does is direct the sound forward so ears to each side hear less, the people in front actually hear it full volume.

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They are sound moderators as defined on your FAC (fire arms cert). The tubular body contains loose fitting corrugated washers about 10mm appart. The round travels through the washer holes. They work best with sub sonic rounds.

What is not true?

I will take what you mysteriously imply (on a public forum??) as fact, and that you do indeed have a working knowledge.

However, regarding how I was led to believe what I wrote, it came from two very different ex military people who both had field experience.

Please don't shoot the messenger, I'd much rather you could argue it out with them!

I am still in contact with one of them.

Nice chap but totally mucked up.

I know him and of his experience, so please grant that I may stick with his understanding rather than yours.

Thinking about it, the rounds they used would have been super sonic, which changes things quite a bit!

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Originally posted by bitsilly
Thinking about it, the rounds they used would have been super sonic, which changes things quite a bit!

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Lots to learn!

The point my mates made to me at the time was that from the propulsive explosion there is a direct line of sight to the victim. Along that path the sound is unaffected by the silencer as the path is clear (if it wasn't thebullet would hit it). So foward of the gun there is little you can do. The sound also has a tendancy to spread out rather than stay in a coherent beam of sound.
For the sound that travels to the side it is a different matter.

Lastly I cannot see how this can be disproven by saying it is like someone hearing petrol exploding at full volume when standing behind a car, as there is a lot of work gone into making that sound pass around baffles, through wadding and around corners etc. but hey I am not the expert! (BIG SMILY FACE).

Hi bitsilly, firstly there is no point in using a silencer unless your ammunition is sub-sonic.
If using super-sonic ammunition and a silencer, the noise that you hear from in front of the weapon is the balistic 'crack' of the bullet pasing by [unless it hits you, then you don't hear anything]. This is a sonic boom not unlike that produced by aircraft but on a much smaller scale. Not the sound of the propellant exhaust, produced by the gun firing, coming out of the front of the silencer.
Secondly. my analogy of a car exhaust pipe holds true, if a straight through 'sports' silencer is used on the car. This would not be too dissimilar in design from a firearms silencer. Although not all firearms silencers are actually open at the end. Some ammunition does not need a silencer at all, as it is inherently silent but exotic ammunition is another topic all together.
Finally, I have no problems discussing the operation of firearms/silencers etc. on a public forum. It's just low order technology, mostly already in the public domain. What I am not prepared to discuss, is where or how I obtained my working knowlege of them. As that is not relevant to this thread.
The bit about the lack of a smiley face, was meant to be dry humour. This obviously failed massively.
I'll get my camo.

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Originally posted by LoMoss

quote:

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Originally posted by bitsilly
Thinking about it, the rounds they used would have been super sonic, which changes things quite a bit!

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Very similar to exhaust design as well
All you ever wanted to know about sound moderators

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quote:

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Originally posted by Confused but excited.

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Originally posted by LoMoss

quote:

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Originally posted by bitsilly
Thinking about it, the rounds they used would have been super sonic, which changes things quite a bit!

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Very similar to exhaust design as well
All you ever wanted to know about sound moderators

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Interesting, but don't believe everthing that you read on t'web.
A rather sweeping statement posted on an open resourse site

Certainly not 'All you ever wanted to know'
I should have put a smilie face after this.

about silencers/supressors/moderators but probably enough to satisfy the average casual internet browser.
And some incorrect information.
Interesting, may have to put my world domination plans on hold

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Humour usually passes WAY over my head!

But the 'I'll get my camo' bit worked! lol

Ed

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Originally posted by bitsilly
Humour usually passes WAY over my head!

But the 'I'll get my camo' bit worked! lol

Ed

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