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#1
Posted to rec.audio.tech
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Need suggestions for equipment for generating greater than 135dB SPL
Hello,
I am testing a sound protection and recording system that will withstand very loud sounds. I need to test in a sound field that is at least 135dB or better. I'm performing real world testing at 135 to 153dB SPL and need to simulate those levels in a room in my office building. Can someone suggests a combination of components (speakers, amplifiers, etc) and manufacturers that can get me close to these ranges. The sounds that I am wishing to replicate are from jet aircraft engines. I have make recordings at 44HKz, but am unclear about how to play them back at levels similar to the actual recording levels. The majority of the energy is below 12 kHz in the recordings I have. I don't believe exact replication of the sound fidelity is critical for my testing, but the amplitide is important. Also, what might I use to keep the sound from getting too loud outside of my test room? Thanks, Edward |
#2
Posted to rec.audio.tech
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Need suggestions for equipment for generating greater than 135dB SPL
"edward" wrote ...
I am testing a sound protection and recording system that will withstand very loud sounds. I need to test in a sound field that is at least 135dB or better. I'm performing real world testing at 135 to 153dB SPL and need to simulate those levels in a room in my office building. Dosen't seem practical to attempt this in "a room in my office building". Unless the building is scheduled for demolition soon and you conduct the tests only at night or weekends when others are absent. :-) Can someone suggests a combination of components (speakers, amplifiers, etc) and manufacturers that can get me close to these ranges. The sounds that I am wishing to replicate are from jet aircraft engines. I have make recordings at 44HKz, but am unclear about how to play them back at levels similar to the actual recording levels. The majority of the energy is below 12 kHz in the recordings I have. I don't believe exact replication of the sound fidelity is critical for my testing, but the amplitide is important. There are a number of manufacturers/vendors of large speaker systems which are used in live music events (i.e. head-banging rock concerts) Some of their more heavy-duty industrial-strength products may be able to produce these sound levels in a small enclosed space. The people over on another newsgroup deal with these speaker and amplifier systems every day. Check out... news:alt.audio.pro.live-sound Beware, they can be a rough crowd, but there are several experts there. Also, what might I use to keep the sound from getting too loud outside of my test room? I doubt there is anything practical you can do in existing construction to even eliminate the problem of the SPL causing damage to the structure. Trying to contain it without a foot or two of solid concrete and/or lead seems impossible. Why not investigate the facilities that are already set up for this kind of experimentation? Seems quite likely that there are several across the US and in many western countries. |
#3
Posted to rec.audio.tech
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Need suggestions for equipment for generating greater than 135dB SPL
In article .com, "edward" wrote:
Hello, I am testing a sound protection and recording system that will withstand very loud sounds. I need to test in a sound field that is at least 135dB or better. I'm performing real world testing at 135 to 153dB SPL and need to simulate those levels in a room in my office building. Can someone suggests a combination of components (speakers, amplifiers, etc) and manufacturers that can get me close to these ranges. The sounds that I am wishing to replicate are from jet aircraft engines. I have make recordings at 44HKz, but am unclear about how to play them back at levels similar to the actual recording levels. The majority of the energy is below 12 kHz in the recordings I have. I don't believe exact replication of the sound fidelity is critical for my testing, but the amplitide is important. Also, what might I use to keep the sound from getting too loud outside of my test room? Thanks, Edward You need to build a sealed chamber to contain the equipment. The exact frequencies? There could be extreme low frequency components that might be hard to deal with . Some powerful mid to high range driver should work. greg |
#4
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Need suggestions for equipment for generating greater than 135dB SPL
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#6
Posted to rec.audio.tech
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Need suggestions for equipment for generating greater than 135dB SPL
In article , (GregS) wrote:
In article , (GregS) wrote: In article , (GregS) wrote: In article .com, "edward" wrote: Hello, I am testing a sound protection and recording system that will withstand very loud sounds. I need to test in a sound field that is at least 135dB or better. I'm performing real world testing at 135 to 153dB SPL and need to simulate those levels in a room in my office building. Can someone suggests a combination of components (speakers, amplifiers, etc) and manufacturers that can get me close to these ranges. The sounds that I am wishing to replicate are from jet aircraft You might be able to get the levels and relative bandwidth using a horn driven by an air gun of some sort. I'm crossposting this message. Group at alt.sci.physics.acoustics greg |
#7
Posted to rec.audio.tech
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Need suggestions for equipment for generating greater than 135dB SPL
Thanks to All,
You've pointed me in the right direction. And I'll plan on doing my testing out in my barn rather than in my office. I'm close enough to an airport that noone will be certain where the sound is coming from. Edward |
#8
Posted to rec.audio.tech
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Need suggestions for equipment for generating greater than 135dB SPL
In article , Per Stromgren wrote:
On 26 Mar 2006 14:51:20 -0800, "edward" wrote: Hello, I am testing a sound protection and recording system that will withstand very loud sounds. I need to test in a sound field that is at least 135dB or better. I'm performing real world testing at 135 to 153dB SPL and need to simulate those levels in a room in my office building. Can someone suggests a combination of components (speakers, amplifiers, etc) and manufacturers that can get me close to these ranges. Perhaps you can get that sort of SPL:s inside a loudspeaker enclosure? I know that the levels inside is a lot higher than on the outside, but not how much higher. 10-20 dB is my educated guess. That sound kinda sounds like my oil fired furnace, without the bearing whine. Also a little like some torches I've heard. greg |
#9
Posted to rec.audio.tech
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Need suggestions for equipment for generating greater than 135dB SPL
Per Stromgren wrote: On 26 Mar 2006 14:51:20 -0800, "edward" wrote: Hello, I am testing a sound protection and recording system that will withstand very loud sounds. I need to test in a sound field that is at least 135dB or better. I'm performing real world testing at 135 to 153dB SPL and need to simulate those levels in a room in my office building. Can someone suggests a combination of components (speakers, amplifiers, etc) and manufacturers that can get me close to these ranges. Perhaps you can get that sort of SPL:s inside a loudspeaker enclosure? I know that the levels inside is a lot higher than on the outside, but not how much higher. 10-20 dB is my educated guess. The Bruel & Kjaer 4220 pistonphone calibrator achieves a 127 dB SPL in a volume of about 19 cm^3 using nothing more than two pistons about 4 mm in diameter with a total peak-to-peak ex- cursion of all of 0.5 mm (that's a displacement volume of 6 billionths of a cubic meter, smaller than most 1" done tweeters), all powered by a 9-volt battery. The total displacement ratio is about 0.033%. To get to anSPL of 135 dB would require a change in displacement ratio only about 2.5 times that, or all of about 0.08%. Achieving very high sound pressure levels at one specific point is not very difficult at all: it requires simply that the pressure change at that point by the requisite amount. You want 135 dB? make the air pressure there chage rapidly enough by only 0.08%, and you have 135 dB. So, inside a speaker enclosure, all you need to do is change the volume by 0.08% at the right frequency to get an SPL of 135 dB. Say you have a speaker with an internal volume of 1 cubic foot, about 42 liter. You have to change its volume by 0.08% of that, or about 0.034 liters, or 3.4 x 10^-5 cubic meters. Using a 10" woofer, with a piston diameter of, say, 22 cm, you need only a whopping excursion of 0.9 mm, a wee more than 1/32", to get there. Of course, there are some caveats: for this to work, the largest dimension of the enclosure needs to be substantially smaller than the smallest wavelength, so the the pressure is essentially the same every- where in the enclosure (for a 1.5 cubic foot box, this limits the experiment to about 100 Hz or lower), the enclosure has to be sealed and essentially loss- less, and the item being subjected to the sound has to, obviously, fit in said enclosure. Enclosure too small? Make it bigger! And therein lies the rub: The total displacement RATIO will remain the same regardless of the size of the enclosure, so that the displacement volume must go as the total volume. Make it the size of a room (42 cubic meters, a room only 8' high, 12' wide and 16' long), since it's 10,000 times the size of our enclosure, requires 10,000 times the displacement volume to achieve 135 dB at every point in the room (again, assuming the room is sealed, etc). Or get something that plays pretty loud, and just get as close to it as needed. A speaker that's capable of producing 105 dB at 10 meters will produce 125 dB at 1 meter., and 135 dB at about a third of a meter (1 foot) from the source. Again, there are some constraints, the neat inverse square ratio works fine untilm you're in the near field, defined here as the point where the distance from the driver is no longer substantially larger than the driver itself. |
#10
Posted to rec.audio.tech
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Need suggestions for equipment for generating greater than 135dB SPL
There are definitely some restraints in my testing configurations that
lend themselves to this approach. At present, I have a system that can generate about 128dB. During the test, I am wearing a protective helmet, a lexan mask, ear muffs, and ear plugs. I stand at about 1 foot from two speakers. My amplifier is only a 125W/channel Sony unit, so I know I can go farther. Theoretically, I could make an enclosure that would allow me to place just my helmeted head into a box mounted on the ceiling. One aspect that is a bit unusual about the actual noise environment around the jet engines is that the sound pressure wave tends to come primarily from one direction. Edward |
#11
Posted to rec.audio.tech
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Need suggestions for equipment for generating greater than 135dB SPL
"edward" wrote in message oups.com... There are definitely some restraints in my testing configurations that lend themselves to this approach. At present, I have a system that can generate about 128dB. During the test, I am wearing a protective helmet, a lexan mask, ear muffs, and ear plugs. I stand at about 1 foot from two speakers. My amplifier is only a 125W/channel Sony unit, so I know I can go farther. Theoretically, I could make an enclosure that would allow me to place just my helmeted head into a box mounted on the ceiling. One aspect that is a bit unusual about the actual noise environment around the jet engines is that the sound pressure wave tends to come primarily from one direction. Edward do not most sound/noise sources come primarily from one direction? discounting echo/reflections. |
#12
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Need suggestions for equipment for generating greater than 135dB SPL
"TimPerry" wrote -
do not most sound/noise sources come primarily from one direction? discounting echo/reflections. At those kinds of SPLs, who would notice? :-) "Edward" didn't mention the SIZE of the desired test area, but it is certainly easier to develop that kind of SPL in a small enclosed space than in a large area, particularly outdoors (except with an actual jet engine, etc. :-) |
#13
Posted to rec.audio.tech
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Need suggestions for equipment for generating greater than 135dBSPL
Peter Larsen wrote:
edward wrote: Hello, I am testing a sound protection and recording system that will withstand very loud sounds. I need to test in a sound field that is at least 135dB or better. I'm performing real world testing at 135 to 153dB SPL and need to simulate those levels in a room in my office building. Can someone suggests a combination of components (speakers, amplifiers, etc) and manufacturers that can get me close to these ranges. The sounds that I am wishing to replicate are from jet aircraft engines. I have make recordings at 44HKz, but am unclear about how to play them back at levels similar to the actual recording levels. This question was vaguely hinted at by Greg, how did you make the recordings and how did you ensure that nothing clipped when making them? Edward Kind regards Peter Larsen Four, maybe three, 70's vintage Marshall stacks and one finely tuned fender strat should do the trick. (sorry I couldn't resist) |
#14
Posted to rec.audio.tech
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Need suggestions for equipment for generating greater than 135dBSPL
edward wrote:
Hello, I am testing a sound protection and recording system that will withstand very loud sounds. I need to test in a sound field that is at least 135dB or better. I'm performing real world testing at 135 to 153dB SPL and need to simulate those levels in a room in my office building. Can someone suggests a combination of components (speakers, amplifiers, etc) and manufacturers that can get me close to these ranges. The sounds that I am wishing to replicate are from jet aircraft engines. I have make recordings at 44HKz, but am unclear about how to play them back at levels similar to the actual recording levels. The majority of the energy is below 12 kHz in the recordings I have. I don't believe exact replication of the sound fidelity is critical for my testing, but the amplitide is important. Also, what might I use to keep the sound from getting too loud outside of my test room? Thanks, Edward - Perhaps a little thinking outside the (speaker) box would help. The most efficient means of producing extreme and sustained SPLs would be a compressed air or steam whistle, which would be far cheaper than any electronic approach. It would require some capacity for metalworking for fab and tuning, however. -- ______________________________________________ Insanity is the inability to either tolerate or create ambiguity. |