F-15 Eagle
New Member
Anytime.
Question on comparing the F-35 with the F-15/F-16.
- Thread starter AICfan1989
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F-15 Eagle
New Member
Actually lower frequencies carry farther than higher ones and they tend to go through walls and houses and what not more and you can feel them more like someone is shacking your internal organs, so the F-35 at 1000 ft will be louder due t the lower frequency and it will be harder to escape from. Up close the F-35 is within 2 dB of the F-22 and it sounds like a screech according to people who have heard them and because of the low pitch sound 50ft away the F-35 is like having your body ripped apart due to the high intensity low pitch sound waves.
Actually, meat_helmet ist right: The human ear is much more sensitive to higher frequncies, that's because we're designed to hear things like speech and a baby crying- see table below-. Low frequency noise in general is much more comfortable to the human ear than high frequency noise. You have to differentiate between sound pressure and loudness.
As a production engineer everytime I set up a machine I have to deal with this phenomenon. And it's a complicated matter indeed. However, it's an urban myth that whatever powerful jet engines can rip tissue apart due to the sound they emit - that would require extremely low frequencies and enormous energies- Both can not be found on jet engines like the F135. Due to principles of construction certain frequencies result, thats the same as in every man made machine- there are bearings, gears, compressed gas and other things that together emit what we call noise. And at 50ft every jet engine makes you feel like your body is disintegrating.
Attention here, a dBA level is already a weighted sound pressure level that takes into account human hearing.
localhost127
Member
general rule is +10dB for humans to perceive as "twice as loud" ... +3dB for twice the acoustic power, and +6dB for twice the amplitude (within tolerances...).
now, regarding pitches and frequencies and why some freq's sound louder at +3dB than others - that is because of the frequency response of the human ear, etc...it's not flat-response. a human isn't going to perceive 95dB at 25Hz and 4000Hz as the same (although his/her internals might say otherwise!
)i would find highly dubious if anyone can claim they can tell 2dB difference.
harder to escape from what? a person on the ground hearing it?
again, human hearing isn't perfectly flat...so just because low (approaching sub-sonic) frequencies travel further than mid/high freq ranges, that doesn't mean a human will perceive it to be louder or notice it any sooner.
and we haven't even taken into account the most important factor: the extremely (relatively) slow speed of sound in atmosphere.
is there a document i missed about frequency response / output of this engine, versus other platforms? or how did this come to be the discussion?
humans don't have built in FFT logic...i highly doubt most if not all humans can produce a spectrogram in their head while sitting 50ft from an f-35. a human is going to feel like his body is ripped apart at 50ft from any jet engine, not just the f-35.
im not sure what relevance any of this discussion has at all.
you're arguing lower frequencies in the human audible spectrum travel further - and they do ... and are you insinuating that as a result of that, and if the f-35 produces these low frequencies at a higher dB rating than other platforms, that it will travel further and somehow become a disadvantage?
if so, could you please detail to me how this might be noticeably different than current operating platforms? for example, if the f-35 engine does produce a waveform +2dB greater (say, at 40Hz), how could an enemy capitalize on this?
also, lower frequencies are omni-directional ... so you cannot pin-point them like you can mid-high range frequencies...so having one platform/engine louder at lower frequencies may not be a disadvantage as it may seem at first thought.
seems like creating a mountain of discussion out of a molehill of rather irrelevant information/specs...but im open to new insight.
edit: Falstaff replied as i was typing and pretty much hit it spot-on.
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F-15 Eagle
New Member
Oh I agree I have no doubt higher pitch sounds are a lot harder on the ears than lower ones, from personal experience high pitch sounds are horrible on my hearing.
However that being said lower frequency sounds still carry farther than high ones even if the dB level is the same.
Thats why rifle shots which are relatively high in pitch and have a dB level of +165 dB will only carry for 1-2 miles but the roar of an F-35 with a dB level of 148-152 will carry for at least 10 miles.
meat_helmet
New Member
Oops, you got me there. Its been a while since I did anything on acoustics - getting dB mixed up with dBA, what a rookie mistake!
Info from an Aussie perspective
From Australian Aviation weekly news email:
RAAF USE OF SALT ASH RANGE TO BE REDUCED: Use of the Salt Ash Air Weapons range near RAAF Base Williamtown will be halved when the F-35A JSF enters RAAF service.
The ADF says it has completed its review into the way the JSF will use the range and the aircraft’s anticipated noise footprint, expected to be far greater than the F/A-18 Hornets it will replace, and has determined the use of the range can be halved by the increased “use of training simulation.”
“Through this review of our proposed JSF training activities we have assessed that we can make a significant difference to levels of aircraft noise near the range which will in turn refine the Australian Noise Exposure Forecast in that area,” Deputy Chief of Air Force, AVM Geoff Brown, said in a statement. “RAAF Williamtown has long been part of the Hunter region. Air Force has worked with the Port Stephens Council and the local community to find a way to decrease the noise footprint of the JSF, while still achieving essential training.”
AVM Brown stressed that the reduced requirement for the Salt Ash range didn’t change the anticipated noise “contours” in other areas surrounding RAAF Williamtown, “where we have no room to move on our requirement to get aircraft into and out of the Williamtown base.”
From Australian Aviation weekly news email:
RAAF USE OF SALT ASH RANGE TO BE REDUCED: Use of the Salt Ash Air Weapons range near RAAF Base Williamtown will be halved when the F-35A JSF enters RAAF service.
The ADF says it has completed its review into the way the JSF will use the range and the aircraft’s anticipated noise footprint, expected to be far greater than the F/A-18 Hornets it will replace, and has determined the use of the range can be halved by the increased “use of training simulation.”
“Through this review of our proposed JSF training activities we have assessed that we can make a significant difference to levels of aircraft noise near the range which will in turn refine the Australian Noise Exposure Forecast in that area,” Deputy Chief of Air Force, AVM Geoff Brown, said in a statement. “RAAF Williamtown has long been part of the Hunter region. Air Force has worked with the Port Stephens Council and the local community to find a way to decrease the noise footprint of the JSF, while still achieving essential training.”
AVM Brown stressed that the reduced requirement for the Salt Ash range didn’t change the anticipated noise “contours” in other areas surrounding RAAF Williamtown, “where we have no room to move on our requirement to get aircraft into and out of the Williamtown base.”
F-15 Eagle
New Member
Admin: Text deleted. One liner + an agenda issue
You've been cut a fair bit of slack up to now because you're a long serving member. However, your broken record sniping is wearing very very thin.
I suggest that you pause and think about how you want to re-engage in this thread.
You've been cut a fair bit of slack up to now because you're a long serving member. However, your broken record sniping is wearing very very thin.
I suggest that you pause and think about how you want to re-engage in this thread.
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