Sciencemadness Discussion Board

Why is FP louder than fast detonation?

golfpro - 1-8-2013 at 08:34


so I have done a few small scale ETN detonations, I made little firecrackers for the 4th that were .3 grams of ETN, w/ silicon/KNO3 on top of foil separating them. These were kind of loud, but not much louder than the little "M-80's" which have supposedly .05 grams FP as the legal limit.. I could practically hammer .3 grams of this ETN without earplugs and be just fine. So I just decided to get about 5 grams in a small cup and stuck a cap in the middle, set it on the curb and that was pretty loud, it took a little chip out of the cement and you can still see where the blast was. It sounds a lot faster than fireworks, like a sharp crack, but if I would have watched a 3" aerial burst charge and 6 grams of ETN explode back to back, I would say no way that's only .13g of FP! I realize the size and loudness of an explosion is a factor of logarithms, and not twice the amount of material is twice the noise level. My erythritol used for nitration is from "Truvia" which is supposedly not pure erythritol, would this provide a reason for lower yields or less power (Impure ETN) or both?

I haven't ventured just yet into +100g ANNM or AN based charges, but I'd like to when I find a good spot for a test, and I don't know where to go. I want to experience a large explosion eventually (1kg-20kg ANFO charge), and then I'll probably just give up the hobby, work my way up in a step ladder. But now that I am capable of making SA*DS for caps, it takes some of the anxiety away.

energetic.material - 1-8-2013 at 09:06

hey man im new too but not the place to ask these questions. Those are pyrotechnical and have to do with confinement and shaping of the "charge". If someone wants to give a detailed response be my guest i suggest you try . Good luck.

CaliusOptimus - 1-8-2013 at 11:04

I believe this has to do with the duration of the pressure wave. Contained flash powder explodes much slower than high order etn, creating a longer and less intense wave. This seems to register as louder on your eardrums.

golfpro - 1-8-2013 at 11:35

That is not a pyrotechnic question, KCLO4/Al is an energetic material...??? It's not misplaced either. It has nothing to do with shaping of the charge I can say that, shaping of any charge is irrelevant here, we assume we're using a clyindrical/round container

So, a cast bit of ETN (20 grams say) would produce a much more dense shockwave than 20 grams loose ETN powder, but I wonder what the difference in sound would be like. I bet the loose ETN would be louder or seem louder. Would be neat to watch this happen

As soon as I find a spot to try some of this out....

[Edited on 1-8-2013 by golfpro]

[Edited on 1-8-2013 by golfpro]

Praxichys - 1-8-2013 at 11:45

I'm no physicist, but:

Consider the wavelength of the sound generated. A long, slow release of pressure will generate a much larger wavelength of sound than a short, sharp release. A short wavelength pressure wave has a higher energy density per unit volume than a long, low pressure wave of the same energy. Since air is a lossy medium, waves with a higher energy density will compress the air more than a low frequency wave and therefore dissappate their energy as heat much more quickly. This is why low frequency sound travels so much farther than high frequency sound.

Since we can guess the average spectral components of more brisant explosives to be of higher frequency than that of a lesser explosion, it is expected that for two explosions of the same energy the slower of the two will deliver the most energy to the ears of a distant observer, barring effects of the lowest audible frequency, etc.

Another factor is the diffraction of sound around objects. Sound with a higher wavelength (in the order of cm) is much more quickly scattered and reflected by small objects than sound with a wavelength in the order of a couple meters. Think about why one needs to place mid-range speakers carefully but remain basically indescriminant about the placement of the woofer.

Antiswat - 1-8-2013 at 12:08

i must say you are surely wrong on this one.. i dont know if theres something different of locations you tested, you cant say ''what i remember a fireworks shell as sounding like''

theres massive difference whether 5g goes off in air, or on the ground few metres from you..

i could perhaps illustrate better with say 0.5g mass of the discussed organic compound
compared to 1.2g KClO4 MgAl
thereafter if any doubt should still hang around, comparings between different types of Al with KClO4, MgAl and Mg

i would like to see you film 1g FP and 1g ETN going off at the same place, and same day, aswell as same time, not exactly same time tho
same distance to camera etc.

Hennig Brand - 1-8-2013 at 14:43

About 5-6 years ago I build black powder rockets for a time. Once I had rockets that worked reliably I immediately started putting exploding headers on them. These where just large bottle rockets basically. I would saw out long straight strips of light wood on the table saw for the stabilizing stick. I used to mess with TATP quite a bit because I was just starting to learn. I also made a lot of flash powder. My rockets would go at least a few hundred feet up I estimated. I can tell you with certainty that 1 g of TATP going off up there puts 1g of any flash going off up there to shame in terms of the perception of sound and the distance away the sound can be heard. One gram of ETN would show an even greater effect by far, though I never tried it.

Motherload - 1-8-2013 at 17:33

The duration of the blast is longer for a cardboard tube FP charge.
That's why it is perceived as louder even though the decibel output of the HE is higher.

Kinda like this analogy of thermobaric devices.
The PSI generated is lower than a straight HE charge but the duration during which the pressure is maintained is longer resulting in more damage.

golfpro - 1-8-2013 at 20:00

Praxichys that would make sense then.

I've always thought of a model rocket and at the very tail end of the thrusting fuel, as it burns out, a primary (.5g SA-DS) and then some 5-25 grams of ETN all in the same motor. This would be the first thing on my list if I was into rockets.

So an explosion in the air is louder, say we had a 5gal. bucket of ANFO and hung this on a tree 7 feet up. BTW, ANFO is almost half the speed of ETN, so there is a more drawn out, not as sharp shockwave probably, simulating a louder sound.

BTW, is ANFO (powdered AN, maybe slightly moist from the air, (or dense prills which is preferable))/ Fuel Oil (Sunflower Oil) 94/6... Can this be reliably detonated at amounts around 1kg with a nice 20-50 gram Cast ETN booster? This would be with no confinement other than the plastic container. Otherwise I'll dig a hole and try it.

Practicaler - 1-8-2013 at 22:45

I don't think firecrackers can give more louder sound than etn. I am not going to mention any physics theoryjust telling u practically from my experience . I kept 30 grams of etn in steel pipe 3 inch long one inch diameter of 3mm thickness and in one pipe30 grams of flash powder then the etn gave much much louder sound than flash powder

Praxichys - 2-8-2013 at 04:38

@ Practicaler, Antiswat, Hennig Brand - I believe your observations are valid. To make a 1:1 comparison, the charges must be matched in blast wave energy, not weight.

[Edited on 2-8-2013 by Praxichys]

Antiswat - 2-8-2013 at 07:27

i dont think a 1:1 comparison is needed, if the ETN can be shown as being much louder than an given amount of flashpowder, twice the amount

let me put some conclusive evidence to this post :P

the third more dull bang was 3g KClO4 MgAl packed in a tight papertube, different location however, but still not as loud (dB) but due to the different location it might sound as being louder, its basically just the heavy frequencies hitting back

the comparison was acceptable, as there was by extremes a difference of 2 m/s wind at test / comparison site

the FP charges was 1.15 and 1.20g, sound was nearly identical
the HE charge was 0.6g, at a even longer distance than to the FP charges (few metres) the person had ringing ears, due to high frequencies, which is this ''snapping'' sound some might describe highly brisant HE's as sounding like

bring up relevant material with same type of test site if this seems unrealistic / modified by software somehow

Trotsky - 2-8-2013 at 20:54

How much rebiana is in TruVia? I wonder if partially nitrated rebiana analogues might account for some of that. I have nitrated a few Stevia components. They had a habit of rapidly breaking down if not kept completely dry.