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Posted: 3/22/2011 6:38:23 AM EDT
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I'm doing a little research on recording Sound Pressure Levels (SPL) for firearms with and without suppressors, muzzle brakes, and flash hiders. I've learned that an AR15 could generate an SPL in excess of 160db. All the commercial, inexpensive sound meters I've come across max out at 130db and are not designed to be able to process the short, impulse-type sound wave of a gunshot. Does anyone here have experience in recording and measuring rifle SPLs? If so, how do you do it? Oscilloscope with a high SPL microphone? Thanks! |
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There are B&K's on the market occasionally, used in working order for around $1000. The 1/4" mic costs about $1250 by itself, but you may get lucky and find one on the used market as well. Mic adapters and calibrators are other costs of course.
The equipment is expensive but doesn't have to cost $10K. Obviously the tripods in the above photo are $50 walmart style. If someone paid $10K for equipment I would expect him to think it belonged on tripods worth at least $150 Some of the operations have really expensive equipment like GRAS stuff and electronic equipment piping the data into a computer, but the results are similar. You get data either way. The people in the industry will tell you digital equipment doesn't have the rise time to compete with old analog stuff. So there are only two meters I believe that will do industry work, and they are both older models. One is Larson Davis, the other B&K. Put $14,000 or better of equipment together, and it still tells you the same thing that a B&K 2209 will tell you (but maybe with a little less legwork and shooting if you're talking about multiple meters in one settup). A lot of industry jazz in firearms is wow factor. Get a bikini babe, a minigun, a HUMMER, or a Duece and a half for a picture and what do you have? Something totally unrelated to what you're doing that makes people think big things are happening. That's about where I think the $10,000 + settups come from. People are trying to buy credibility. |
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For field portable, both the B&K 2209 and the Larson Davis 800B are hard to beat for a number of reasons. Both are out of production. The LD meter is in the same price range as the B&K. If purchasing either used, you absolutely MUST return it to the factory for re-certification. Not all are in perfect working condition. We recently obtained a LD 800B for our Michigan location, and it needed about $600 in repairs.
Besides the microphone (around $900-1,000 new from LD), you will need a calibrator. Plan on around $500-700, and I would suggest a new one. Used ones may or may not be able to hold calibration, and they are worthless unless re-certified by the manufacturer. The correct microphone is a 1/4 inch pressure mic, and the B&K and LD versions are interchangeable. Both of these meters have analog detectors with digital processing. As such, they will meet the requirements of MIL-STD-1474D of a 20 microsecond (or better) rise (response) time. All of the rest of the portable meters have digital detectors, which cannot meet the rise time specs (28 µsec is about the limit for digital detectors). Non-suppressed peaks are fairly broad (>100 µsec) and most meters will be reasonably accurate if the response time is under 50 µsec. Suppressed peaks are very short, and even at 20 µsec rise time, some of the peak may be missed. With slow response, the suppressed peak may well have passed, and the reading will be abnormally low. While this may look good in the marketplace ("oh wow, look at all those DBs"), the results are not believable to folks who actually understand the issues. It is not a simple process. At issue is believability (both to you and to your peers). With good used equipment certified and a calibrator, you can probably do a decent job for around $3,500. |
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Wow, all very good information. Thank you so much for the info and leads. I might look in to renting some equipment for our first test or maybe hiring someone to come out for the day with their equipment. At this time, I don't need to purchase a full setup to get the data we need for this run. Is there anyone in the Southern California area known for sound testing?
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