Think of it like the wake of a boat, except that instead of producing a visible wave, it’s an audible wave. At any one point, an observer is only going to hear one boom, but it is in fact a long booooooooooooooooooooooooooooom that moves past the observer.
At least, this his how it was explained to me.
OK I think I get it now, Thanks. I found this site and the ships bow wave analogy, as K2K said, made it all suddenly make sense.
Whoa, was unprepared for how funny I’d find jb’s little vignette.
Anyway, so how do whales feel about this boom carpet business? It sounds like the ocean is just lashed with these things all the way across.
About hearing the booms “before they had been banned” – commercial aircraft are not allowed to exceed the speed of sound over the US, but military aircraft can do this, although they’re restricted to certain areas. However, before this law was passed, there were no commercial planes capable of going that fast.
Military planes can and do exceed the speed of sound, as CnoteChris points out. They used to do it more - I recall when I was a kid in the 1960s that I would hear the booms frequently over East Texas. It’s similar to the concussion you feel after a cannon is shot - a boom that you can feel in your gut. The boat wake analogy is the best way for me to think about it. As a boat goes across the lake, it makes a wake anytime it’s travelling faster than the wave speed, not just at the instant it passes through that speed.
Didn’t the Concorde fly to the west coast once?
When I lived in LA, and the Space Shuttle was landing at Edwards, we would hear the doulble booms. It never seemed that loud to me.
Another time the BlackBird (SR-71) left Edwards for the east coast, I only remember hearing one boom.
Maybe it’s just me. 
I grew up in western Colorado, and I also remember sonic booms happening 1-3 times a day. We had a lamp pole in our living room with a cylindrical shade that would rattle after a boom hit our house. I thought they were cool!
The shock wave dissipates so with long distance it’s softer and longer in duration. To really know sonic boom you have to get up close and personal. When the Connie was near Central Americal in the fall of '83 we put on weapons demonstrations as a show of force for visiting heads of state. We’d helo aboard the visitors then launch an alpha strike. Once the planes were launched we set up folding chairs on the edge of the flight deck - at leat the first time we did. The hight point of the show was a supersonic flyby of an F-14. The pilots loved to hot dog so they’d pass by at flight deck level, 65 feet or so off the water, about fifty yards from the ship at about 1,000 knots TAS. The shockwave knocked just about everyone on his ass, hilarious. I found that I could be grabbing chow inside the ship near the water line on the 2 deck and still feel the shock wave. The shock wave is pretty neat but the eerie part is watching a plane hurtle almost directly at you in absolute silence.
Here is a diagram that shows the Mach cones and boom carpet of a sonic boom. The site explains why there are two booms (one caused by the nose of the plane, one by the tail). How loud is it?
The supersonic aircraft is likely to be tens of thousands of meters away, yet to a person on the ground, it its sonic boom will sound (very briefly) louder than a jet engine only 50 meters away.
“Anyway, so how do whales feel about this boom carpet business? It sounds like the ocean is just lashed with these things all the way across.”
Reading that triggered a question in my mind:
Considering that most supersonic flight is done by military aircraft, and considering the resources the U.S. (and other countries’) Navy puts into sonar and sound detection equipment to detect submarines and ships, has anyone ever used sonic booms as a means of detecting supersonic flight over water? Or at least seriously proposed it to the relevant office of the Navy?
I was watching a PBS show about jets. It said that the Air Force did an experiment on the public’s reaction to the booms. They had a supersonic jet fly over at several preset times a day. People accepted it for a while, but when they increase the frequency of the flights and the intensity (flying lower i assume), things (like windows) shattered and people got pissed.
Absolutely!
I saw the Thunderbirds do this in Wichita, outside of McConnell AFB. They came at us, completely silent, and after they shot past us it took until about the count of two before there was this Crash! that knocked us off of our feet.
When the SR-71 flew over KC, we all heard the boom. It was like a continuous roll of thunder.
I caught a show on Discovery’s Wings channel about the Blue Angels and their airshows… when discussing their need for precise timing, they mentioned one pilot who had to boost his speed to rejoin formation with the others, inadvertantly breaching supersonic speeds. The result was the shattering of windows for eight blocks of a business district. :eek:
Think of sonic booms as thunder, which they essentially are. When you are close to lightning, the thunder is ear shattering. When it’s far away, it’s a low rumble. Same with a sonic boom. Same principle as “travelling”. When a lightning bolt hits, not everyone hears the thunder at the same time. Why? Because sound moves, hence…the speed of sound:)
One thing to keep in mind concerning sonic booms is that generally, the larger the object, the larger the boom. Since the Concorde is about twice as large as most supersonic military aircraft (rarities like the B1, Backfire, and Blackjack excluded), its sonic boom is more intense.
When I was at Berkeley, some of my colleagues studied this fairly extensively. They were really concerned with shock-shock interactions and shock wave impingement on surfaces such as bow shocks hitting wings or engine mounts, but I remember at least one study of shockwaves over water. IIRC the result was that the shocks diffused relatively quickly in water due to the higher speed of sound, higher viscosity, and/or lower compressibility. That’s a vague memory so YMMV, but I can dig up cites if you’re interested.
Even if the shockwaves diffuse quickly, marine animals like whales and dolphin are much more sensitive to sound than humans so there’s more risk of harming them. Of course, these were engineers and not biologists doing the study, so they weren’t specifically looking at the effects on marine life, but I remember the comment that this would make any dolphin in the area really uncomfortable.
Nonetheless, I think the general argument is that the population density of sound-sensitive mammals near the surface in the open ocean is relatively low, so the damage done is mimimal. Even if the damage is high, dolphin with tinnitus are less photogenic than oil-soaked seals, so the environmentalist lobby picks the battles it can win.
I used to work in building that was just past the westernmost end of Miramar NAS (in San Diego) and we regularly had broken windows on the upper floors due to sonic booms.
I became so used to the booms that the one time I was in the office when there was a perceptable (to me) earthquake, I thought it was just another plane, FWIW.
Another thing to add is that even without the sonic booms, the Concorde is may be the loudest thing that the average airport would ever see. For some reason, it landed in Toronto five or six times last year. (AFAIK, there were no scheduled flights to Toronto, so I’m not sure why it was there.)
I work directly under the western flight path to the northern runway at Pearson Airport, 10 km west of the airport grounds. If the sun is at the right angle, plane shadows pass over my desk.
The Concorde was easily three times louder than the other plandes that went over, even the big ones like 747s. It was mindbogglingly loud. I can only imaginbe what it was like on the runway at takeoff…
Another thing to add is that even without the sonic booms, the Concorde is may be the loudest thing that the average airport would ever see. For some reason, it landed in Toronto five or six times last year. (AFAIK, there were no scheduled flights to Toronto, so I’m not sure why it was there.)
I work directly under the western flight path to the northern runway at Pearson Airport, 10 km west of the airport grounds. If the sun is at the right angle, plane shadows pass over my desk.
The Concorde was easily three times louder than the other planes that went over, even the big ones like 747s. It was mindbogglingly loud. I can only imaginbe what it was like on the runway at takeoff…
The first (and only time) I saw the Concorde was in Rio DJ, Brazil. No idea if it was regular service to Europe or just a special run; it was dark and I couldn’t read the painted logo.
At any rate, our mission (VP) was cancelled just before takeoff, so our BAF (Brazilian Air Force) contact advised that we might want to wait a few minutes to watch the Concorde take off. Damn glad I did; the usual F-14/15/16s (and not so usual SR-71s) I’ve seen just can’t touch this thing.
This was about midnight and the only noise on the field was the the Concorde and frogs croaking. Fairly quiet during its taxi to the active and line-up for take-off. Then the roll… still quiet until it got fairly close (we were mid field about 50yds from the active runway) and then all hell broke loose.
There was a few seconds of a ripping ungodly racket and the upper red strobe… and then it was gone; simply gone.
(I wonder what one of these things would sound like at flight-deck level at about 200yds to port at full tilt cruise (M2.2)?
I think Sunspace hit the nail on the head - the sonic booms aren’t the problem, it’s the unearthly noise the thing makes during take-off (I know, I live 20 miles west of Heathrow, and boy was it loud). The sonic booms aren’t so bad, in my experience, since Concorde cruises at 60,000 feet. Startling, but not really loud. A bit like a distant gunshot. Surely you Americans should be used to that?
(nitpick) By the way, it’s “Concorde”, not “the Concorde”.