Anyone tried, or can point to work on "tuning" a barrel for sound?

[wolff]

     I'm curious about something.  Has anyone tried or perhaps read up on adjusting cannon barrel length and/or diameter of a Salute Cannon to improve its tone and volume at a given charge?
     The tuning of "tubular bells" is something I have some experience with.  I've used a simple program that roughly calculates where the "sweet spot" ought to be, or where to drill a hole to hang the tube up, plus optimal length based on tube diameter.  It's not perfect science, since metallurgy controls much it, but you get the picture.
     I was looking at my 15FC Big Bang Cannon yesterday, and wondered if the barrel length (or diameter, for that matter) could make the little bugger sound like a BIG one.

Sound Off!

bw 
 

[GGaskill]

Just to be sure, you are asking about making the report of the small gun sound like a large gun, not about making the barrel ring from the shot.

[RocklockI]

This something I have wondered about as well . I'm thinking of making a thunder mug ,and would seem like there would be a ideal bore size to length ratio ,or at least one just B4 the law of diminishing returns kicks in big time .

I'm thinking 5x bore dia. ....for no good reason .

[Cat Whisperer]

Some basic principles here.

The shorter the barrel the more intense the muzzle blast.  (more powder burning/expanding as it exits)

The larger ID of the barrel the lower the frequency of the blast that is best 'coupled' to the atmosphere.  For example, a given speaker will sound louder in the bass notes if one makes a cone (often is exponentially curved) that goes from a small diameter (speaker) to a large diameter (exits to the air).  These principles are greatly adapted by speaker-enclosure manufacturers.

The frequencies from any explosion (black-powder, automotive engine, etc.) are primarily high frequency, but the repetitive rate (engines) is low. 

SO, make it look like a blunderbuss!

[gulfcoastblackpowder]

Cat Whisperer is right that a blunderbuss style barrel would be the best way to optimize the sound to being closer to a large gun.  Think of a cannon like a horn (trumpet or even better, a compression driven loudspeaker horn).

I'm no acoustical engineer, but from what I can tell, here's how I understand it (some of this may be extraneous and/or inaccurate, but it's just my take and worth what you paid for it):

We can model a cannon for noise purposes as a compression driven horn loudspeaker.

According to horn theory, the length of a horn is key to producing the frequency desired, and must be at least 1/4 of the wavelength of the frequency to be produced, and preferably at least 1/2.  

The wavelength of a sound wave is the speed of sound (343m/s) divided by the frequency.  For a low frequency, say 80Hz, you'd need a length of at least 1.07m [343(m/s) / 80(1/s)]/4.  

Conversely, if you want to find out the lowest frequency your length "horn" can produce, you would use the following formula:

f = c  / (4*L),

where c = 343m/s, where the length is in meters,
or c = 1125ft/s, where length is in feet,
or c = 13500in/s, where length is in inches

If you have a .33m tube (~1ft.), about the lowest frequency you will be able to produce is about 258Hz.  This is still a low frequency, but 258Hz will never sound like 80Hz.

Similarly, the mouth (muzzle) area is a factor in the frequency achievable according to the following formula:

A_fm = (c/F_o)²/4pi

A_fm is the free mouth area (m²)
c is the speed of sound (344 m/s)
F_o is the flare frequency (or cutoff frequency) in Hz

Because we are using a circular cross section, A = pi*d²/4

This solves to:

F_o = c/(d*pi)

Using this, if we assume we have a .0127m bore (.5in), the cutoff frequency would be ~8.6kHz.  As you can see if you look at the formula, the cutoff frequency is linearly inversely proportional to the bore size.  If you were to increase the bore to 1in (.0254m), you would halve the cutoff frequency to 4.3kHz.  A 3" bore would be capable of producing lows to ~1.43kHz.

This means that by opening up the muzzle using some form of curve - be it conical, exponential, hyperbolic, tractrix, or what have you - you can get closer to the frequency of a larger bore gun.  Of course, sound pressure is just as important as frequency, which is why when you have greater pressure in the bore, you have a louder boom.  That said, I wouldn't recommend a conical muzzle, at least not for the whole length, as it would remove too much material for my liking, and it wouldn't allow the wadding to expand as smoothly as the bore enlarges.  I would actually recommend a combined shape of a straight bore running most of the length of the gun, say 2/3 or more, with a curve from there to the muzzle.  This would allow you to use the barrel for shooting live rounds in addition to salutes.  Of course, the longer the straight bore, the more accurate the gun will be when firing live rounds, while the longer the curve, the smoother and the more effective it will be in increasing the effective bore size.  

Selection of wadding material would also become a factor, because that expansion I think would play a big factor in how much effect the barrel flare would impact the sound.  To understand what I mean by this, consider a blunderbuss.  When shooting a solid ball out of a blunderbuss, the flare has no effect on the accuracy of the gun (only your ability to sight it), while when shooting shot, it will allow the shot to spread a little more than a gun with the same primary bore size without the flare.  Though there is only a small difference here, as the flare on a blunderbuss is more to serve in easing the loading of the gun, since it is a short range - often called "coach" - gun, the impact on the sound wave would be significant.  I would think some powder wadding, such as flour or corn meal (perhaps mixed with a little Cremora for a nice flame) would lend itself well to this type of muzzle, as it would tend to expand smoothly throughout the curve in the muzzle.

Of course, now that I finished typing this I notice you are not even asking about a blackpowder cannon, but a toy (http://www.bigbangcannons.com/product.aspx?i=1&c=4) that uses calcium carbide and water to, as I understand it, produce essentially trace amounts of acetylene to burn up in a flash: http://en.wikipedia.org/wiki/Calcium_carbide.  It also doesn't appear to have enough wall thickness to even try modifying in the form described above.  I don't think I'd bother trying to make that thing sound more like a real cannon - you'd probably be asking for problems.

[Cat Whisperer]

I LOVE detailed answers with detailed principles, theory and formulas.  GREAT RESPONSE!

But in simple terms (Li'l Abner: "as any fool can plainly see."):

My beer-can caliber mortar 'sounds' bigger than my golf-ball caliber mortars, and
my 4.5" mortar 'sound's bigger than all the others.  

Cannons may be different, but it's easier to achieve 'big-bore' with a mortar than with a cannon.

[RocklockI]

Jeez Gulfcoast I think you said it all !

[gulfcoastblackpowder]

The problem with a large bore mortar is that is doesn't have the necessary length.  They will almost always sound more like a whoompf than a boom.  If you could get enough compression in one, you'd get a better sound out of it.  A Howitzer would be the best compromise between large bore and manageable length (which is after all, why they were designed in the first place).  As the old quote goes that suits another interest of mine: "There's no replacement for displacement."

[Cat Whisperer]

My 4.5 goes BOOM not whomf.  1.5x1.5 ish powder chamber under 7.5 lbs of concrete filled 4"pvc pipe - .050 clearance.

Long barrel mortars with light charges don't have the muzzle blast and have more of muffled thunk.

[RocklockI]

I think you guys might be talking blanks vs live ammo shooting

[gulfcoastblackpowder]

Really, it doesn't matter too much is it's used for blank or live fire - compression is compression however it's achieved.  The compression, and therefore the pressure wave, can change differently depending on how it's achieved, though.  7.5lbs of concrete slug is almost certainly sufficient compression for that size powder chamber.  That's why you get a good boom. 

The charge will always play a big role too.  Keep in mind, if you hold up a megaphone and whisper into it, people won't be able to hear you as well as if you yelled through it (or without it).  Of course, yelling with it would typically give you more than yelling without.  That's the principle I was talking about in referencing horn theory.  All else being equal, a longer barrel (to a point) will produce a fuller sound, unless it is undercharged (think of the difference between the sound your mortar makes and the sound a 12 pound Napoleon would make).

Most of the shooting I do is with blanks (both cannon and firearms) and often it's louder than a live round would be, and no, I don't use more powder - again, it's about compression.

[RocklockI]

Then what do you use to "compress the air" with a blank load ? If it as loud as a live ...wieghted shot .

what is your "wad" ? ................ No dont go there !

  I used to ...in my earlier days would use soggy wet newspaper in a bubble of saranwrap or something to keep the charge from being spoiled . Sometimes we would put the powder in a balloon mush it into the chamber then sooggy paper ........

OH yea it was GOD AWFULL LOUD and thank goodness the southbend 2 1/4" held fast !   On fourth of July 83' the house kitty corrner to us in the back was brand new it was hardly finished .....

So I used their backyard as a landing zone for the shredded newspaper !!!

So after a night of disregaurding the rules of decency and common sence in more than one way ,,,,,"its a tradition"   (I was bad in those days )  I was picking up pieces of  paper and tossing it into the vacant lot kitty corner cause ...what the heck it would be gone into the soil by the time someone moved in ......

JUST THEN the sliding glass door opened and a guy emerged from it said "Hi!" ....well I was startled by his being there .... so I thought quick ....real quick ......he looked bedraggled and not happy ! and in his bathrobe .

I thought so quick I asked him "if he had heard my cannon last night ?" He asked "Is that what it was ? "

and also that "Yes He Did Hear It And So Did His Wife And She Spent The Night Under The Bed ........"

Knowing I only make a first impression once ..... I gave him a hearty wave . He left ,I left . Then They left ....the nieghborhood .

I think he said he was laid off and had to leave right off !  

Just kiddin he never said a mummbling word to me after that and they did just ....disappear .

Now I'm getting a new nieghbor next door . the old ones are leaving , and the 4th of July is comming up so as this neighborhood "lights up" that night I will eastablish my rights on the subject right off .

Hope it wont be a cop ...... or a nut .

 Gary

And DO NOT THE THINGS I HAVE DONE WITH THE PAPER , AS IT DOES MAKE EXCESIVE PRESSUERS and YoU cOUlD Be KILt DeAd . I would never do it agian .

[Double D]

.

what is your "wad" ? ................ No dont go there !
 

 Gary

 Box of cream of wheat.

Click on the picture...



Standard 300 grain FG, over powder chamber card board wad, pour in box of cream of wheat, another card board wad.  Use fuse and not quill.

The only load we have shot from that gun that lets you feel the concussion.

[gulfcoastblackpowder]

It's a trade secret, but let's just say...I like my hot dogs plain...no ketchup, no mustard, etc., so no need for a bun...those are better served as cannon fodder!

Seriously, they fit a 1.5-1.75" bore nicely, and half a bun will give you really good compression while a whole will literally knock boards off the dock you're shooting from (been there, brought home the drift wood)!  What's better - no debris left after firing but what seagulls happily eat - powdered toast.  This is a big deal because we often shoot over water for various organizations and municipalities, and having an environmentally friendly discharge is important to them. 

Other people have used bread in the past, and there was a story I read or heard of a while back where someone left an obscene amount of bread in their cannon for a very long time, and the yeast reacted and made the pressures dangerous.  Nice thing about cheap hot dog buns is they don't have much yeast in them, so that's not a concern (besides, if a cannon is loaded...discharge it!)...and it's really cheap.  If you want a nice addition to the flame, add a little Cremora brand coffee creamer, but this should only be done at night.

I guess I just gave away my trade secret...though most of it had already been in print elsewhere.

[RocklockI]

  I wont breath a word .

[Double D]

Creamora makes a sticky mess...bread-hot dog bun, like wadded newspaper make solid slugs and you have to have a safe impact zone. Grass clippings and leaves do break windows across the street.  Sand scours the bore and works like bird shot. 

When using card board wads, be sure down range is not dry grass or have fire fight equipment handy.  Flour works  like cream of wheat. 

A standard foil wrapped cartridge with no projectile makes a good blank.

...based on my experinece.

[wolff]

Excellent Thread!

My apologies if I confused things by mentioning Big Bang Cannons at the end of the post.  I ought to have started a separate thread about the toy cannons (if they're even germaine to this Forum).  I did open it with mention about Salute Cannons, which was my main point, sorry if I messed anyone up

   The Horn Speaker example was perfect, and to make matters worse, making a bell or chime (tubular bell) sound "pleasing" is a horribly complex combination of everything from metallurgy, the right physical dimensions, where the tube is supported or struck, and whether you're looking for a pure note or notes with overtones...  All I can say is that having experimented with tubes made from fire extinguishers, to 1/4" thick walled aluminum home O2 tanks, up to 8" an dia. x 55" tall steel tube, is that "striking" that balance aint easy!

     I appreciated reading the Physics of Sound generation and propagation, along with the Physics of "Selected" Wad Usage designed to safely increase pressure to achieve the most pleasing output for a given tube.  I intend to digest this material and do what I believe many innately, or deliberately do:  Look for a safe, safer load/wad that delivers the safest and loudest ring and/or BOOM!
 
regards all,

Wolff
 

[gulfcoastblackpowder]

Creamora makes a sticky mess...bread-hot dog bun, like wadded newspaper make solid slugs and you have to have a safe impact zone. Grass clippings and leaves do break windows across the street.  Sand scours the bore and works like bird shot. 

When using card board wads, be sure down range is not dry grass or have fire fight equipment handy.  Flour works  like cream of wheat. 

A standard foil wrapped cartridge with no projectile makes a good blank.

...based on my experinece.

I didn't say Cremora wouldn't make a mess - which is why you only use it when you need the effect, and only as a mixture.  I wouldn't recommend it in anything rifled or small bore, as it would just be a headache to clean.

The nice thing about the hot dog buns is they do break up as long as they aren't wet.  Let them get slightly stale if you use good ones (though I don't know why you'd choose to buy good ones for this purpose).  They will still compress, but they will completely break up upon firing.  I know someone who happened to be down range when this combination was shot by a different group, and they were just wearing a layer of bread ash.

Newspaper is something a lot of people use.  I don't like it.  Sure, it's cheap, but the paper doesn't burn well, and will smolder.  If firing in the middle of nowhere, this may not be a big deal (though it can set the ground on fire), but at one point when I was just starting to get into cannon, I was at a show and we ran out of buns, so a more experienced shooter scrounged up some newspaper.  It worked ok at getting compression, but when it was shot, little bits of smouldering newsprint filled the air, some of which drifted onto a nearby tent.  All you could do was watch as a little pin-hole from one of these bits opened to about 1 foot wide.

I recommend having at minimum a fire extinguisher handy any time you're shooting BP - regardless of load (and not just to shoot at).

[Victor3]

 And of course, a logical thing to do to prevent newspaper from burning would be to soak it in water before ramming it.

 But don't ever do that; it will make a loud boom but can turn into a bore plug that could burst a barrel...

[dan610324]

just another little warning here

a few pages of wet newspaper rammed into a 1.5" cannon did actually penetrate a 55 gallon oil barrel
both sides
so please dont use it


a foil wrapped charge and 2 cardboard wads is perfect

if you soak the wads in a mixture of baking soda and water and let them dry they will not burn

[Double D]

Excellent Thread!
 I ought to have started a separate thread about the toy cannons (if they're even germaine to this Forum). 
 

They are germaine here per our original charter, as are punt guns.

 
I didn't say Cremora wouldn't make a mess - which is why you only use it when you need the effect, and only as a mixture.  I wouldn't recommend it in anything rifled or small bore, as it would just be a headache to clean.

I know you didn't, I did.

The nice thing about the hot dog buns is they do break up as long as they aren't wet.  Let them get slightly stale if you use good ones (though I don't know why you'd choose to buy good ones for this purpose).  They will still compress, but they will completely break up upon firing.  I know someone who happened to be down range when this combination was shot by a different group, and they were just wearing a layer of bread ash.

Stale, makes sense.  Never heard of a stale hot dog bun in this house.

Newspaper is something a lot of people use.  I don't like it.  Sure, it's cheap, but the paper doesn't burn well, and will smolder.  If firing in the middle of nowhere, this may not be a big deal (though it can set the ground on fire), but at one point when I was just starting to get into cannon, I was at a show and we ran out of buns, so a more experienced shooter scrounged up some newspaper.  It worked ok at getting compression, but when it was shot, little bits of smouldering newsprint filled the air, some of which drifted onto a nearby tent.  All you could do was watch as a little pin-hole from one of these bits opened to about 1 foot wide.

Lots of stories around this one.  Like soaking in saltpetre to make it burn quicker.  It works, just doesn't all burn in bore or before it hits the ground .

Although newspaper is biodegradable, people prefer you clean it up before it becomes one with the soil.  One sheet of dry wadded newspaper will shred into little tiny particle and will cover several acre's...or so it seems.

I recommend having at minimum a fire extinguisher handy any time you're shooting BP - regardless of load (and not just to shoot at).

Yes of course, but I was thinking of a cow pasture up the Applegate river about 25 or 30 years ago and said firefighting equipment.

And of course, a logical thing to do to prevent newspaper from burning would be to soak it in water before ramming it.

 But don't ever do that; it will make a loud boom but can turn into a bore plug that could burst a barrel...

And you can get some pretty incredible range.



 

[gulfcoastblackpowder]

Usually when my crew goes out shooting, we just buy a supply of the cheapest buns we can find, and in the FL heat, they dry out quickly.  Plus, they're not too doughy in the first place.  You don't want them fully stale, just about half way, or they will just crumble as you try to load them, and wont give you near as good compression.

An alternative to newsprint that I forgot to mention earlier is rice paper or cheap napkins.  These won't smoulder like the newsprint, so they pose much less risk of fire.

I wouldn't want to put soaked paper of any form down a cannon barrel.  It just doesn't seem like a great idea.  Kind of like when I once knew a goofball that put half a banana down the barrel of his cannon.  You really have no idea how bad a slurry of banana and BP can smell until you've been around it!