Stealth aircraft use noise damping technology, and some of this might be appropriate even for this weird engine.
Is this true? I couldn't find any meaningful information via Google on stealth aircraft & and lower noise levels.
A stealth bomber overflew my house a few years ago (Boston area, after a July 4th flyover). It was by no means quiet - the "scream" from the engines is what alerted me to the fact that is was there.
The main application for this is, as far as I understand it, is high altitude to orbit engines. So any noise is too far up to make any difference anyway....
The article specifically mentions "subsonic jetliners," and "a supersonic airliner." The article also says: "Pulse detonation would also offer cheaper access to space, saving tons of liquid oxygen and fuel by powering vehicles from the ground to high altitude and hypersonic velocity, where conventional rocket engines would take over to lift them into orbit." So it looks like it is intended for conventional ground-to-low-altitude applications.
Of course it's a given that noise from pulse detonation engines at high altitudes won't be much of a problem to people on the ground (the same can be said now for conventional jetliners). The problems is that these vehicles have to take off and land at airports, and that's where you have noise problems.
FAA has limits on the noise level generated by an airport.
A lot (if not most) of the aviation authorities around the world set noise limits for aviation noise, including the EU and the U.K. What's interesting is that the FAA and various airports have more or less mandated the phase-out of noisier airplanes (Stage 1 & Stage 2 aircraft). If these planes wind up being noisier than the current Stage 3 aircraft, the U.S. air industry is gonna be tied up in lawsuits for a looong time.
Also, commercial supersonic flights over the continental U.S. are banned partly for noise reasons. Sonic booms are not good things for people and animals over the long term. I would assume that supersonic flights would be restricted to intercontinental travel.
It probably won't even be a military jet engine either, the military doesn't like their pilots deaf.
FYI, U.S. military jets tend to be much louder than commercial jets. Military jets are designed for performance, not environmental-friendliness.
None of these observations detract from the suggestion that reducing everyone's speed reduces the number and seriousness of accidents.
But similarly I've seen nothing to prove that reducing "everyone's" speeds actually reduces accidents. In fact, here in the Boston area traffic speeds are generally low due to the traffic congestion, but we have a lot of accidents! (few are fatalities of course due to the low speed). Clearly speed is one of many factors, and simply reducing overall speeds is not a panacea.
After a few hours of trying all kinds of things par the Knowledge Base and Apple Support I determined the power manger chip is completely dead (meaning it won't take power from an outlet and can't recharge the barrey.
Maybe you tried this, but I'll ask anyway: have you tried reseting NVRAM via OF? See here for details. It may not be the same problem, but it may be worth trying (assuming you can power on your machine!)
This assumes, of course, that they're talking about 100+ dB of sound pressure (SPL).
They likely are talking about dB SPL. Remember, pressure is force divided by area, and pressure is scaler. The headphone speaker diaphragm puts out a force. When you hold the headphone out in the open air, that force is divided by an (effectively) infinite area, and the resulting SPL is very low.
But when you put that speaker diaphragm into your ear, the total interior area of your ear canal is very small. Divide the diaphragm force by the small ear canal area, and you have a large pressure. Voila! High SPL.
Have you ever seen an acoustic calibrator or pistonphone? This is exactly how those devices work. They usually output 94 dB or 114 dB SPL. If you listen to them in the open air, you barely hear the signal, but if you put them against your ear, you could blow an eardrum.
Psychoaccoustics bears no relation to math or physics.
Sure it does - if you include "statistics" in "math." You give me a noise level, and I can give you a fairly good idea of how annoying that noise level is likely to be based on 30 years of statistical surveys.
You're talking about sound intensity (sound power through a unit area). When talking about sound, people usually refer to sound pressure. Sound pressure level (SPL) is 20*log10(pressure[Pascals]/20e-6[Pascals]).
You can of course convert from sound intensity to sound pressure using the approriate formula for your geometry.
Like, the fact that the application kills its own preferences if your drive runs out of space.
That's not a Mail.app bug, that's an OS X behavior. I've experienced this particular little "feature" with MT-Newswatcher, Safari/Chimera/MSIE, AlphaX, Preview, etc.
That said, I've been using Mail.app to handle email from 5 different accounts since 10.0 and I've had no problems with it.
Apple demanded $1.2 billion from Microsoft for alleged patent infringements...
The negotiations that resulted led to a strategic agreement between the two companies in August 1997, one part of which called for Microsoft to invest $150 million in Apple and for Apple to install Microsoft's Internet Explorer as the default Web browser for its customers... As part of his videotaped deposition, however, Microsoft Chairman and CEO Bill Gates testified repeatedly that his primary goal was to resolve the patent issues with Apple and obtain a patent cross license.
That remains to be seen. Everyone thought the Patriot worked well immediately after the first Gulf Wars. It took some time for the military to admit that the Patriot has a 100% miss rate.
If I put a subwoofer in a corner, pump 40 Hz through it, and stand blindfolded in the room with it, I can point it out. The omnidirectional nature of low frequency transducers is well documented, but the source point is very distinguishable.
I take issue with the word "very" (at least for most people) but I understand that pure tone sources can be identified in certain circumstances. I'm talking about identifying low frequencies in the context of reproducing music where the high-frequency cues dominate.
Problems begin to arise with very high frequencies in a reflective environment. If I take a HF horn, pump 12k through it, and stand blindfolded in the middle of a metal or glass room, I'd have a much harder time distinguishing the location.
You're essentially talking about a reverberant chamber. The size and shape of the room will affect the ease of distinguishing the source location because of various path-length differences.
In both cases, if you use a pulse instead of a constant sine wave, the ability to locate the sound is greatly enhanced.
True, but in the low frequency case you have high-frequency cues that help one to locate the sound, and in the high-frequency case, the reflections will have much less energy than the initial pulse so the source will be easier to identify.
Having worked on a contract for Neumann about 10 years ago or so developing the kunstkopf,
Did you work on Fritz?
I can tell you from personal experience and exhaustive testing, these observations are well documented, but never referenced by people using the satellite systems.
Okay, but everything you described above are not inherent problems with satellite systems, they are problems with all speaker systems.
Additionally, your statement about 80Hz being nondirectional can be easily debunked. Meyer has developed a subwoofer system which creates a cardiod pattern from a subwoofer. Also, placing two direct firing subwoofers in proximity to cause coupling, will exhibit lobing thereby becoming more directional.
When I said "non-directional" I meant in regards to perception, not source characteristics. You can obviously create beam-forming implementations as you describe, and one would be able to hear the difference if one stepped in and out of the main lobe(s). But it doesn't follow that once a person is in the lobe that they would be able to identify the source direction based solely on audio cues.
First, the subwoofer + satellite model is fundamentally flawed. 20Hz is directional. Bass doesn't "fill the room like fog" -- when a train's coming, you can hear the direction, right?
Umm while I would agree that Bose's implementation of satellites+bass module (to Bose's credit, they don't call it a "subwoofer") has flaws, the subwoofer + satellite principle is not necessarily flawed. If your satellites go low enough (80 Hz is the common figure), a sub/sat system is perfectly workable. See NHT.
Also, it's been pretty well established that frequencies below 80 Hz are non-directional. When you look at the wavelengths of those frequencies when compared with the typical human interaural spacing you can begin to see why. The reason you can hear the direction of a train is due to the high-frequency cues you get from the wheel/rail noise (disclaimer: I spent 7 years working as a noise consultant specializing in rail noise).
The cartoons could be there for the hard-core fans to view, and EPIII can still include references to those events. People who don't watch the cartoon won't miss anything, and those who watch the cartoon get a little bonus.
I asked a friend to show me the infamous "combat zone". It was three or four joints on a single block.
You do know that the "combat zone" hasn't really been the "combat zone" since 1991 or so? Much like Times Square, it's really been cleaned up over the last decade.
The Big Dig will probably be operational by summer or fall 2002, but the demolition of the old elevated artery won't be complete until 2005 so, so the project technically won't be "complete" by the time Macworld opens. Worst case only the northbound lanes would be open, but they're making pretty good progress.
FYI, the Silver Line extension to the convention center is not part of the Big Dig. The FEIS just went out to bid a couple of months ago (my firm was on one of the loosing teams) so don't expect to see the Silver Line at the converntion center before 2006.
Slashdot Mirror
Is this true? I couldn't find any meaningful information via Google on stealth aircraft & and lower noise levels.
A stealth bomber overflew my house a few years ago (Boston area, after a July 4th flyover). It was by no means quiet - the "scream" from the engines is what alerted me to the fact that is was there.
The article specifically mentions "subsonic jetliners," and "a supersonic airliner." The article also says: "Pulse detonation would also offer cheaper access to space, saving tons of liquid oxygen and fuel by powering vehicles from the ground to high altitude and hypersonic velocity, where conventional rocket engines would take over to lift them into orbit." So it looks like it is intended for conventional ground-to-low-altitude applications.
Of course it's a given that noise from pulse detonation engines at high altitudes won't be much of a problem to people on the ground (the same can be said now for conventional jetliners). The problems is that these vehicles have to take off and land at airports, and that's where you have noise problems.
A lot (if not most) of the aviation authorities around the world set noise limits for aviation noise, including the EU and the U.K. What's interesting is that the FAA and various airports have more or less mandated the phase-out of noisier airplanes (Stage 1 & Stage 2 aircraft). If these planes wind up being noisier than the current Stage 3 aircraft, the U.S. air industry is gonna be tied up in lawsuits for a looong time.
Also, commercial supersonic flights over the continental U.S. are banned partly for noise reasons. Sonic booms are not good things for people and animals over the long term. I would assume that supersonic flights would be restricted to intercontinental travel.
It probably won't even be a military jet engine either, the military doesn't like their pilots deaf.FYI, U.S. military jets tend to be much louder than commercial jets. Military jets are designed for performance, not environmental-friendliness.
But similarly I've seen nothing to prove that reducing "everyone's" speeds actually reduces accidents. In fact, here in the Boston area traffic speeds are generally low due to the traffic congestion, but we have a lot of accidents! (few are fatalities of course due to the low speed). Clearly speed is one of many factors, and simply reducing overall speeds is not a panacea.
Do tell me you accept that lower speeds save lives...
I accept that, all things considered, one is less likey to die if they are in a low-speed accident versus being in a higher speed accident.
I (and the U.S. FHWA) do not accept the general notion that you are less likely to get in an auto accident if you drive at a lower speed.
Great, so it's probably as accurate as "lower speed limits save lives!" normally parroted by police forces...
This is why the APSL is an Open Source license instead of a Free Software license.
Umm, APSL 2.0 is a "free software" license:
The Apple Public Source License (APSL) version 2.0 qualifies as a free software license.
Maybe you tried this, but I'll ask anyway: have you tried reseting NVRAM via OF? See here for details. It may not be the same problem, but it may be worth trying (assuming you can power on your machine!)
They likely are talking about dB SPL. Remember, pressure is force divided by area, and pressure is scaler. The headphone speaker diaphragm puts out a force. When you hold the headphone out in the open air, that force is divided by an (effectively) infinite area, and the resulting SPL is very low.
But when you put that speaker diaphragm into your ear, the total interior area of your ear canal is very small. Divide the diaphragm force by the small ear canal area, and you have a large pressure. Voila! High SPL.
Have you ever seen an acoustic calibrator or pistonphone? This is exactly how those devices work. They usually output 94 dB or 114 dB SPL. If you listen to them in the open air, you barely hear the signal, but if you put them against your ear, you could blow an eardrum.
Psychoaccoustics bears no relation to math or physics.
Sure it does - if you include "statistics" in "math." You give me a noise level, and I can give you a fairly good idea of how annoying that noise level is likely to be based on 30 years of statistical surveys.
As an example, Google for "schultz curve noise."
You're talking about sound intensity (sound power through a unit area). When talking about sound, people usually refer to sound pressure. Sound pressure level (SPL) is 20*log10(pressure[Pascals]/20e-6[Pascals]).
You can of course convert from sound intensity to sound pressure using the approriate formula for your geometry.
That's not a Mail.app bug, that's an OS X behavior. I've experienced this particular little "feature" with MT-Newswatcher, Safari/Chimera/MSIE, AlphaX, Preview, etc.
That said, I've been using Mail.app to handle email from 5 different accounts since 10.0 and I've had no problems with it.
Developed countries have regulations on noise level, the responsible personnel needs a simple and practical way to measure the level.
And the 5100 likely ain't it - is it ANSI/ISO/IEC certified? Is it a dosimeter? Does it give noise exposure metrics? How to you calibrate?
It may be a nice toy, but it's not a professional tool.
From an MS press release:
Apple demanded $1.2 billion from Microsoft for alleged patent infringements...
The negotiations that resulted led to a strategic agreement between the two companies in August 1997, one part of which called for Microsoft to invest $150 million in Apple and for Apple to install Microsoft's Internet Explorer as the default Web browser for its customers... As part of his videotaped deposition, however, Microsoft Chairman and CEO Bill Gates testified repeatedly that his primary goal was to resolve the patent issues with Apple and obtain a patent cross license.
Seemed to do well this time around
That remains to be seen. Everyone thought the Patriot worked well immediately after the first Gulf Wars. It took some time for the military to admit that the Patriot has a 100% miss rate.
If the record company had any brains they would start pushing newer technology like SACD and DVD audio. Superior sound quality, bonus features ...
...and DRM up the wazoo.
If I put a subwoofer in a corner, pump 40 Hz through it, and stand blindfolded in the room with it, I can point it out. The omnidirectional nature of low frequency transducers is well documented, but the source point is very distinguishable.
I take issue with the word "very" (at least for most people) but I understand that pure tone sources can be identified in certain circumstances. I'm talking about identifying low frequencies in the context of reproducing music where the high-frequency cues dominate.
Problems begin to arise with very high frequencies in a reflective environment. If I take a HF horn, pump 12k through it, and stand blindfolded in the middle of a metal or glass room, I'd have a much harder time distinguishing the location.
You're essentially talking about a reverberant chamber. The size and shape of the room will affect the ease of distinguishing the source location because of various path-length differences.
In both cases, if you use a pulse instead of a constant sine wave, the ability to locate the sound is greatly enhanced.
True, but in the low frequency case you have high-frequency cues that help one to locate the sound, and in the high-frequency case, the reflections will have much less energy than the initial pulse so the source will be easier to identify.
Having worked on a contract for Neumann about 10 years ago or so developing the kunstkopf,
Did you work on Fritz?
I can tell you from personal experience and exhaustive testing, these observations are well documented, but never referenced by people using the satellite systems.
Okay, but everything you described above are not inherent problems with satellite systems, they are problems with all speaker systems.
Additionally, your statement about 80Hz being nondirectional can be easily debunked. Meyer has developed a subwoofer system which creates a cardiod pattern from a subwoofer. Also, placing two direct firing subwoofers in proximity to cause coupling, will exhibit lobing thereby becoming more directional.
When I said "non-directional" I meant in regards to perception, not source characteristics. You can obviously create beam-forming implementations as you describe, and one would be able to hear the difference if one stepped in and out of the main lobe(s). But it doesn't follow that once a person is in the lobe that they would be able to identify the source direction based solely on audio cues.
First, the subwoofer + satellite model is fundamentally flawed. 20Hz is directional. Bass doesn't "fill the room like fog" -- when a train's coming, you can hear the direction, right?
Umm while I would agree that Bose's implementation of satellites+bass module (to Bose's credit, they don't call it a "subwoofer") has flaws, the subwoofer + satellite principle is not necessarily flawed. If your satellites go low enough (80 Hz is the common figure), a sub/sat system is perfectly workable. See NHT.
Also, it's been pretty well established that frequencies below 80 Hz are non-directional. When you look at the wavelengths of those frequencies when compared with the typical human interaural spacing you can begin to see why. The reason you can hear the direction of a train is due to the high-frequency cues you get from the wheel/rail noise (disclaimer: I spent 7 years working as a noise consultant specializing in rail noise).
What's to say that he can't do both?
The cartoons could be there for the hard-core fans to view, and EPIII can still include references to those events. People who don't watch the cartoon won't miss anything, and those who watch the cartoon get a little bonus.
(Okay, so that's not totally fair, but I couldn't resist)
Does Saint Leo University let you major in "Playing Video Games"?
Alas, FRA hasn't given us permission to release the results yet...
I will say that they are not as bad as jet planes, and they are comparable to the Acela Express trainsets.
I asked a friend to show me the infamous "combat zone". It was three or four joints on a single block.
You do know that the "combat zone" hasn't really been the "combat zone" since 1991 or so? Much like Times Square, it's really been cleaned up over the last decade.
The Big Dig will probably be operational by summer or fall 2002, but the demolition of the old elevated artery won't be complete until 2005 so, so the project technically won't be "complete" by the time Macworld opens. Worst case only the northbound lanes would be open, but they're making pretty good progress.
FYI, the Silver Line extension to the convention center is not part of the Big Dig. The FEIS just went out to bid a couple of months ago (my firm was on one of the loosing teams) so don't expect to see the Silver Line at the converntion center before 2006.
I think this is likely caused by the new gcc compilier in 10.2
My Octave install (form Fink) broke when I upgraded from 10.2. I downloaded the source files and recomplied, and now everything works fine.