I'm starting to get back into car audio again, especially after seeing some high 170 and low 180 db readings! In 1989, I had a pair of 15" Kicker Comps driven by a small Alpine amp...and I thought 110 decibels was loud! How things have changed.
Anyway, I've been reading about PSI in some threads, and I had a question about converting PSI to SPL. I'm into high powered military rifles, and in some weapons, a peak pressure of over 60,000 psi is reached at the moment of powder ignition (such as the mighty M1 Garand, 30-06 rifle cartridge, 30 caliber).
If someone were to put a microphone inside the cartridge itself, and fired the gun, what SPL would 60,000 PSI generate? In firearms testing, they can directly measure these extremely high pressures using piezoelectric transducers (which can measure to 120,000 PSI). They do these tests to "proof" the gun design before manufacturing them. Since microphones have been made with piezo crystals, these piezo transducers could be used as "microphones".
Anyway, if any brainiacs could chime in, that would be great. I've been thinking about this conversion, since the loudest portion of a gun is inside the cartridge (not the muzzle), and no one has given a solid SPL reading in the cartridge, but definite PSI measurements have been provided. All I've read are SPL meaasurements at the shooter's ear, or from 5 feet away, etc. Thanks!
-------------------- I like loud sounds! Posts: 5 | From: KS | Registered: Oct 2007
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Not calling you incorrect crown cause you sound a bit more educated than myself on guns crown. But the reason I have a bit hard time seeing those figures eye to eye is for one I thought steel was only good to about 50,000 PSI approx. Also in theory. IF those did that much.. Lets say the surface area of the actual bullet (the leaving projectile only) is only 1/60th of a sqaure inch.. That would still me 1000lbs of force on the gun. Even with some sort of shock asorb.... I would still say it would have every bit of 200lbs of kick on the person firing. NOW again i am not an expert in guys in ANY way. I am only going off general knowledge and it doesn't add up. I am MORE than happy to listen if you can explain to me in a bit more detail how this is possible or measuring conditions
-------------------- KING KONG aint got **** on me. WOW have been gone a long time. But I am back baby. Former 2003 meca MR5 world record holder. UGLY 1991 brown explorer, BUT was able to do 151 on cert. lin x at the head rest at 42hz!(with cheap audiobahn 15s with about 60 percent of the power allowed that year. lol) Posts: 1120 | From: Indianapolis, In, USA | Registered: Jul 2001
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quote:Originally posted by OSTENTATIOUSJ: Not calling you incorrect crown cause you sound a bit more educated than myself on guns crown. But the reason I have a bit hard time seeing those figures eye to eye is for one I thought steel was only good to about 50,000 PSI approx. Also in theory. IF those did that much.. Lets say the surface area of the actual bullet (the leaving projectile only) is only 1/60th of a sqaure inch.. That would still me 1000lbs of force on the gun. Even with some sort of shock asorb.... I would still say it would have every bit of 200lbs of kick on the person firing. NOW again i am not an expert in guys in ANY way. I am only going off general knowledge and it doesn't add up. I am MORE than happy to listen if you can explain to me in a bit more detail how this is possible or measuring conditions
You made some good points! The info you're asking will require me to use lots of links, since guns and ammo discussions are very technical and elaborate. I'm planning to go to gunsmithing school so I can custom build my own precision rifles. I spent 13 years in the service, and I'm an armorer (gun mechanic) for the US Military's M107 50 caliber semi-auto sniper rifle. I can field strip that rifle in the dark in under a minute. I'm very experienced in weapons handling and shooting, having taken 1000 yard shooting courses with the 50 caliber platform.
Rifle / gun barrel steel is made of very strong steel alloys that have been either heat treated, cryogenically treated or carburized. They can have tensile strengths of 150,000 to over 200,000 psi. Click on the websites below:
A high powered rifle can generate tremendous instantaneous energy, since today's smokeless powder is essentially slow burning nitroglycerin. The 30-06 cartridge I mentioned earlier can generate nearly 3000 foot-pounds of energy at the muzzle, but since the combined weight of the gun and shooter far exceeds the weight of the bullet, their combined weight absorbs the energy over a large surface area, and the shooter feels a good "kick" (recoil), but not enough to knock them over. If you shoot a 700 Nitro Express with 10,000 foot-pounds of energy, yes, that can knock you down with recoil, if you're not ready. By the way, the M107 50 caliber rifle I mentioned earlier generates over 13,000 foot-pounds of energy.
Here's a table of recoil energy in popular calibers: recoil
I tried calculating 60,000 psi, and I got a number of around 260 decibels...has anyone else tried calculating it? I haven't done logs in a while.
Most of the high power rifles run at 60,000 psi chamber pressure. They need that high pressure, to accelerate that little bullet to over Mach 3 in about two feet of barrel. Here's the specs on a 300 Remington Ultra Magnum load, a really ferocious round, which at 1000 yards, has way more energy than a 44 Magnum at point blank, and can ruin someone's day:
For the piezo sensors that can handle these super high pressure loads, check the following site. They make sensors that can withstand blasts from heavy artillery and explosions:
I like figuring out how loud a rifle really is, since I shot a 338 Lapua without any ear protection one time, and my ears were ringing for days, and things seemed "quiet". I've always used earplugs / muffs since then. I've read that accurately measuring the short duration impulsive noise of a gun is difficult, and that most meters are not very accurate after 160 decibels or so, in impulsive meausurements, so I'm trying to calculate the decibels.
If someone says that measuring the noise inside a gun isn't practical since they're so small, I'll just tell them to crawl inside the chamber of a 16" diameter Navy gun, and have your SPL meter and earplugs ready, because that 600 pounds of powdered nitroglycerin will make a big bang!
-------------------- I like loud sounds! Posts: 5 | From: KS | Registered: Oct 2007
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I only really read the last part of your post becasue I am not very interested in guns. But there is 2 things I can tell you.
1. Your ear damage from shooting the 338 lapua without ear protection is probably caused from the higher pitched bang the rifle makes. I am not an ear expert but it seems I can listen to very loud sub bass for extended periods of time and it will not be as damaging to my ears as going to a concert is. It seems that higher pitched noises at the same SPL are much more damaging to your ears.
2. Measuring the noise inside of a gun is practical although like myself and team subgopoof already mentioned the common meters these days is made to pick up an oscillating movement of air. Also I dont think they measure anything above a certian frequency I think it is about 150hz.
quote:Originally posted by teamsplnoobs-kyle: I only really read the last part of your post becasue I am not very interested in guns. But there is 2 things I can tell you.
1. Your ear damage from shooting the 338 lapua without ear protection is probably caused from the higher pitched bang the rifle makes. I am not an ear expert but it seems I can listen to very loud sub bass for extended periods of time and it will not be as damaging to my ears as going to a concert is. It seems that higher pitched noises at the same SPL are much more damaging to your ears.
2. Measuring the noise inside of a gun is practical although like myself and team subgopoof already mentioned the common meters these days is made to pick up an oscillating movement of air. Also I dont think they measure anything above a certian frequency I think it is about 150hz.
I've also experienced the same thing, where loud, higher pitch noises felt more painful than loud, low pitch noises. I'm assuming the pain indicates more hearing damage is being done. Small caliber rifles (30 caliber), when shot up close, produce an intense "crack", and although it's only a few milliseconds in duration, it can hurt your ears bad, especially if it's done indoors without ear plugs. The bullet also produces it's own shock wave crack, since it's supersonic.
I'm not sure if my ears ever really recovered, since I still have low-level ringing that's never gone away after I shot the 338 (I was a fool for firing it beneath a metal awning, which reflects the sound back).
I've been around some loud booming car stereos (but not the ultra 170+ decibel types though), and they were loud, but they didn't hurt my ears. It felt more of a massage, deep inside the chest! And it makes your heart skip beats.
Has anyone been inside a car above 170 decibels?
-------------------- I like loud sounds! Posts: 5 | From: KS | Registered: Oct 2007
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Some people have been daring enough to sit in cars doing 170+, although they might be quieter then that with a passenger inside of them. I think the rifles you are speaking of are probably in the 130-140db range just at a high freqeuncy so it is very painful to hear.
posted
FREQ is a BIG player in how loud something feels. At least on the old lab I sat in a van that did over a 170. but was at like 80 hz. and honestly no BS I have sat in musical cars that did a 155 that sounded louder.
-------------------- KING KONG aint got **** on me. WOW have been gone a long time. But I am back baby. Former 2003 meca MR5 world record holder. UGLY 1991 brown explorer, BUT was able to do 151 on cert. lin x at the head rest at 42hz!(with cheap audiobahn 15s with about 60 percent of the power allowed that year. lol) Posts: 1120 | From: Indianapolis, In, USA | Registered: Jul 2001
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quote:Originally posted by TeamSubGoPoof: take an air compressor and blow directly into the sensor hole, with around 45psi blowing directly into it you'll only get around 135-140db.
Now if you take and pulse the air you can do over a 175 (176 and change was the loudest we got)
That's interesting info. Since these powerful 180-decibel cars are sealed and filled with cement, is it possible that the SPL meters are just measuring air pressure changes due to the large surface area of the woofers effectively "pushing and pulling" on the microphone's diaphragm in a confined space?
Is this similar to over-ear headphones having loud great bass due to efficient direct coupling to your eardrums? I'm sure most of you have noticed the excellent bass response from hi-end sealed over-ear headphones, but the second you break the seal over your ear, the bass volume disappears? I remember reading in Stereo Review (or Stereophile?) a long time ago that it wasn't bass sound waves you were hearing, but it was essentially your eardrum moving in unison with the headphone diaphragm due to pressure changes from the tight seal and confined space ("coupling").
Or are the SPL meters actually measuring the sound in these cars?
At the same time though, air pressure and sound are related...hmmm, I need to talk to my old physics professor to get this straight...
-------------------- I like loud sounds! Posts: 5 | From: KS | Registered: Oct 2007
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quote:Originally posted by TeamSubGoPoof: take an air compressor and blow directly into the sensor hole, with around 45psi blowing directly into it you'll only get around 135-140db.
Now if you take and pulse the air you can do over a 175 (176 and change was the loudest we got)
That's interesting info. Since these powerful 180-decibel cars are sealed and filled with cement, is it possible that the SPL meters are just measuring air pressure changes due to the large surface area of the woofers effectively "pushing and pulling" on the microphone's diaphragm in a confined space?
-------------------- Posts: 6496 | From: Russellville AL | Registered: Nov 2002
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I have no desire to get in depth in this topic, I will just point you to observe the differences between "A" weigting and "C" weighting for spl measurements...
Two weighting curves are commonly applied to measures of sound levels to account for the way the ear perceives the "loudness" of sounds.
A-weighting: A measurement scale that approximates the "loudness" of tones relative to a 40 dB SPL 1000 Hz reference tone. A-weighting has the added advantage of being correlated with annoyance measures and is most responsive to the mid frequencies, 500 to 4000 Hz..
C-weighting: A measurement scale that approximates the "loudness" of tones relative to a 90 dB SPL 1000 Hz reference tone. C-weighting has the added advantage of providing a relatively "flat" measurement scale which includes very low frequencies.
I believe that termlab uses "c" weighting for its measurements whereas gun manufacturers and organizations like nasa use "a" weighting...perhaps someone who knows a little more about this might chime in and give a more in depth picture here!
-------------------- Now, LEAVE ME ALONE... "Bigfoot, a figment of someone's imagination, or a mythical creature that is only seen in Ohio" has spoken!
my real email addy is shocker_mike@yahoo.com but wayne don't allow yahoo accounts so my account is working off of a dead email! Posts: 1758 | From: sherwood | Registered: Jul 1999
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I finally talked to an Army Ballistics specialist who in turn talked to a Contractor who does ballistics and explosives testing.
They said that 60,000 PSI inside the M1 rifle does convert to 266.31 decibels, but bear in mind this is a peak pressure inside the rifle chamber during powder ignition. They are using piezo sensors that are considered to be high intensity microphones with dynamic ranges way, way above standard microphones. Their range is 200 decibels to 275 decibels, and they essentially measure shock waves; "normal" sounds (below 194 db) will not register.
They also had data on a 25 mm caliber Bushmaster gun, used on the Army's Bradley Fighting Vehicle. At 20 feet in front of the muzzle, the discharge blast generates 208 decibels. I don't know of too many people who like to stand in front of gun muzzles to experience that noise!
Regarding the M1 30 caliber rifle from earlier, they said the minimum muzzle pressure is 2000 psi as the bullet exits; this translates to 236.77 decibels. So if someone were able to dodge the bullet and seal their ear to the muzzle right after the bullet passes, the blast impulse would rupture your eardrum, fracture the base of your skull, most certainly destroy your soft brain, and likely crack the top portion of your skull. And this is just blast pressure, not the bullet! The noise is directional, and concentrated to the front of the muzzle, so the shooter doesn't experience the brunt of the noise.
I asked what it would take for a car stereo to break 194 decibels, and they believe it will take speakers (and amps) that can emulate the blast velocity of high explosives, meaning the speaker must be able to generate a true shock wave by accelerating the cone to a velocity around 7000 meters per second (the blast velocity of nitroglycerin). That will take some serious power and subs! They aren't car stereo experts, but they think stereos will eventually reach 193.9 decibels in the future, and breaking 194 will require speakers that behave like an explosion. This will be fun to watch!
-------------------- I like loud sounds! Posts: 5 | From: KS | Registered: Oct 2007
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