The 9/11 Forum

David B. Benson wrote:
By the way, notice what happens when you clap your hands together.

What happens? Does one hand one-way crush the other?

David B. Benson wrote:

Trippy wrote:Taking into account the reduced volume, and the fact that the perimeter columns were 1'-2" in the appropriate ddirection, and the void space in the cores, yields a cross sectional area of 1,067 m^2 - both window space and core void space to escape, and gives us a flow velocity of 15.2 m/s which is still Force 7 on the Beaufort Scale.

That's close to what I calculated some time ago.

And yes, assuming all the windows already broken is quite reasoanble for the initiation floor 97. See NCSTAR1--5A.

no_body --- Poster Trippy is offering what I take to be valid criticisms and in a responsible manner.

By the way, notice what happens when you clap your hands together.

That's reassuring.

i hate to be the one to point out the painfully obvious, but if the sound of the first impact is what is recorded, and then the building continues "collapsing" by the same mechanism, then the increase in mass and energy expenditure will be reflected in the soundwave.
in other words, the sound will start small, ramp UP from there, and then ramp back down as the debris settles and the descent slows at the bottom.
as the mass is accelerating, and the amount of breakage and banging increases, the sound of the bangin also increase, and the alleged booms of "pancaking" should be nearly the same for each floor, accept increasingly louder as the velocity increases.

david, what happens when you clap your hands together in rapid succession louder and louder?
do you get one anomalous peak at the initiation of applause?

newton wrote:i hate to be the one to point out the painfully obvious, but if the sound of the first impact is what is recorded, and then the building continues "collapsing" by the same mechanism, then the increase in mass and energy expenditure will be reflected in the soundwave.
in other words, the sound will start small, ramp UP from there, and then ramp back down as the debris settles and the descent slows at the bottom.

Absolutely so, but see last paragraph. This is why I asked about the intensity. I'm not fit for this sort of analysis, but I will offer my impression. I can't really hear anything pronounced, I'm not sure I hear anything distinct. Looking at the waveforms in the display, I was to unable to identify this sound as being anything other than what you describe above. Just the first sound of collapse and ramping up of intensity. If I missed the obvious, sorry.

That's why I would only judge based on numbers (spectral energy density over specific intervals) that could be explained reasonably. Subjectively, I don't hear anything weird. I've listened to that audio track many times, long before this thread, and I never heard anything that caught my attention. And, yes, I was well aware of the delay in reaching the camera. To say that now I hear something, since it's been suggested that I should hear something, is dishonest.

david, what happens when you clap your hands together in rapid succession louder and louder? do you get one anomalous peak at the initiation of applause?

Sometimes one person starts clapping first and others join in! But it's only the intensity of one clap as compared to many. If the first impact - for example, should there even be such a thing - is nearly axial as Tony Szamboti suggests, the first clap may well be the loudest. It's like the first person clapping squarely once, then being joined immediately by a room full of people hitting thumb against thumb, palm against fingertips and so on.

i see, but, as a total waveform output based on energy expended, the total sound output would be greater.
i do not see nor hear the ramping up of sound.
and, in fact, most cameras have built in compressors.
there is a phenomena known as "ducking". what happens is, if you imagine the compressor to be a pipe of fixed diameter, and the sound being something forced through the pipe, then, the compressor will shirnk the entire sound wave into a space that will fit through the pipe. however, this is not dome linearly. the loudest sounds and lowest frequencies will be less squished than the quieter sounds.
the helicopter is a good litmus. i really don't think it flew away quickly, and then flew back. it is more likely that it was in about the same general area, and the OTHER sounds caused the helicopter to be suppressed as all the sound was "squished through the pipe", so i would guess the loudest sound was happening while the helicopter is muted

i hear a low rumble BEFORE the building starts moving (my speakers go down to 5Hz and up to 40 000Hz).

i also notice that the cameras microphone doesn't go that low. there's a "hole" in the spectrum at around 160Hz. and, there is not much energy below that line. i would say that's the filter cutoff point, and any low frequencies that managed to still get recorded in the below 160 range must have been quite loud indeed. basically, though, the subsonic spectrum where all the action is was filtered out by the camera' mic. this "collapse" would have put out ample energy right down to less than 10 hz, i'm sure.
i'd be curious to know where the crowd was standing, and how their reaction correlates to the action of the tower. did they react to the rumble, or the visual? also, where was the helicopter, and what was it's flight pattern (as this would determine how much the cameras compressor was kicking in)?
obviously, the crowd is somewhere between the source and mic, and the helicopter could be anywhere, but fairly close, as it is quite loud.

A most informative post, newton. I see what you're saying. I probably need to bow out of this, there's very little I can contribute. Too many concerts for the eardrums, too.

I once made a compilation of the sound

http://www.youtube.com/watch?v=g_GpPdgAGwk

At physorg we noce did an analysis of the sound of the south tower, check at 1:13. my conclusion (which of course hasn't been peer reviewed but also not peer rejected) was that the rumbling started before the tilting section hits the next floor.

newton wrote:i see, but, as a total waveform output based on energy expended, the total sound output would be greater.
i do not see nor hear the ramping up of sound.
and, in fact, most cameras have built in compressors.
there is a phenomena known as "ducking". what happens is, if you imagine the compressor to be a pipe of fixed diameter, and the sound being something forced through the pipe, then, the compressor will shirnk the entire sound wave into a space that will fit through the pipe. however, this is not dome linearly. the loudest sounds and lowest frequencies will be less squished than the quieter sounds.
the helicopter is a good litmus. i really don't think it flew away quickly, and then flew back. it is more likely that it was in about the same general area, and the OTHER sounds caused the helicopter to be suppressed as all the sound was "squished through the pipe", so i would guess the loudest sound was happening while the helicopter is muted

i hear a low rumble BEFORE the building starts moving (my speakers go down to 5Hz and up to 40 000Hz).

i also notice that the cameras microphone doesn't go that low. there's a "hole" in the spectrum at around 160Hz. and, there is not much energy below that line. i would say that's the filter cutoff point, and any low frequencies that managed to still get recorded in the below 160 range must have been quite loud indeed. basically, though, the subsonic spectrum where all the action is was filtered out by the camera' mic. this "collapse" would have put out ample energy right down to less than 10 hz, i'm sure.
i'd be curious to know where the crowd was standing, and how their reaction correlates to the action of the tower. did they react to the rumble, or the visual? also, where was the helicopter, and what was it's flight pattern (as this would determine how much the cameras compressor was kicking in)?
obviously, the crowd is somewhere between the source and mic, and the helicopter could be anywhere, but fairly close, as it is quite loud.

Hi Newton

OWE said

"A most informative post, newton."

Yes wins the prize for best and most relevant

I agree the people are likely to be in the street close by as well as possibly on the roof near the mic. Their sounds are present in the very high frequency range along with the birds. I think the camera or mic has a cut off above 17kHz.

They react to the visuals mostly. The tower has dropped to the point where the roof line is about to enter the airborne debris. They seem to shut up when the distant bang is heard,

The helicopter is the predominant sound and fills a lot of the low frequency range above the 160 Hz cut of and is an annoying presence in all bands. It has an oscillating pattern with two pitches. It sounds like it 'reacts' to the demolition and turns, the pitch slowly drops as in a Doppler shift. I would say the Helicopter is near but not close, there is definite presence in the high Hz, but not all the time. One way to find out what's close and not is to use a high pass filter and slowly let more bass through. The people and the birds mostly.

Another source of 'pollution' are the screaming sirens, there are many and they're present almost continuously, they fill the mid -high frequencies.

As for ducking and compression I can't hear much evidence, except possibly with the rumble towards the end, heavy compression attenuates high frequencies, and they seem to be there intact throughout.

There are some fast attack short duration sub bass peaks through out, One associated with the first mast movement.

There have been problems syncing video and sound in the desktop recorder my colleague is using, he's looking for a solution.

Here's the thing - and feel free to ignore this if it suits your agenda, but do so at your own peril.
I found some video footage taken from about a third of the distance of the Sauret footage (about 500 yards) looking more or less dead on at the corner with the window washer on.
What we saw - Bob and Bri
I stripped the audio track between 19minutes and 20minutes, and passed it through a sonogram, and do you know what I found?

Not a damn thing!

Look for yourselves:
19.00 - 21.00 Sonogram
19.20 - 19.45 Sonogram

There is no indication of anything resembling the rumble whatsoever. So it's loud enough to (according to posts in this thread) survive 126db of attentuation, and yet a microphone 1/3rd the distance shows no indication of it whatsoever.

This suggests (to me at least) that the rumble is prehaps a redherring that is local to the Sauret footage (a gust of wind perhaps) it might be worth checking how the rumble fits in with OWE's displacement data, see if it coincides with one of the periods with lots of oscilation (remembering that there is an unknown disturbance earlier in the footage), this might indicate that the rumble and the apparent motion of the tower are linked (eg both caused by a gust of wind).

Don't forget. Correlation does not imply causation (if it did, then storks really do drop babies at the doorstep, and eating chocolate causes car accidents).

PS - Don't start on the factors that I haven't considered like ducking and microphone response, remember, i've been reading the thread to, and yes sonogram indicates some ducking, however, this seems to occur after the sound of the rumble should have reached them, and if the rumble is as loud as has been suggested, should be visible in spite of it (were it to have occured during the possible ducking).

Addendum:
It occurs to me that there is another possibility which may be testable, however that test may be inconclusive as a negative result could have one of two or three possible causes.

The Bob and Bri footage does not include the portion of audio we're discussing "Oh my God" says Bob or is it Bri? then there's a jump cut and the next thing is the tower is half way down. The bang on initiation is going to take close to a second to reach B&B's apartment, the cut in the video must be close to 7 seconds?.

So what relevance does posting a comment about a video that does not contain the audio we're discussing have?

OED,

obfuscate, v.

3. a. trans. Of a person: to make (a subject, etc.) unclear, obscure, confused, or difficult to understand.

Now it might be deliberate or it might be a personality trait, either way......
Would obfuscaters kindly leave the thread? you know who you are!

The sound we're discussing does not have the characteristic of wind.
It's a loud distant sound that reverberates. It has a fast attack and short duration, most of the rest is early reflection and reverberation.

no_body wrote:The Bob and Bri footage does not include the portion of audio we're discussing "Oh my God" says Bob or is it Bri? then there's a jump cut and the next thing is the tower is half way down. The bang on initiation is going to take close to a second to reach B&B's apartment, the cut in the video must be close to 7 seconds?.

No.
To the best of my knowledge the only potential cut in that area is before the area considered.
There is a potential cut at 19.19, where the sound is muted for a moment, but this is before the sound of the rumble should have arrived, however, every other cut in the video is faded (the video is 22minutes long, and covers a period of slightly more than 29 minutes, and every other cut in the video is faded in and out. This period however represents a muting of the sound, but no sudden jumps in the footage, and occurs just after what sounds like a knock at the door, so seems to me to be more likely that they've muted out a friends name at their request.

The camera is focused on the events on the ground, and then pans upwards as the building starts coming down.

Now. I will grant you that there is one seemingly ambiguous part at around 19.41, where in retrospect (and after listening to it repeatedly half a dozen times in quick succession), where there might be a poorly timed cut, I grant you this on the basis that it sounds like Bri says "Oh my G--" and is cut off, however, this would appear to me to be after the building started moving.

However, I find no evidence of a cut between 19.20 and 19.40 which is where, based on what's in the footage, I was expecting the rumble to manifest itself.

no_body wrote:So what relevance does posting a comment about a video that does not contain the audio we're discussing have?

OED,[sic]

Oxford English Dictionary?
Or was this supposed to be QED (Quod Errat Demonstratum).

no_body wrote:obfuscate, v.

3. a. trans. Of a person: to make (a subject, etc.) unclear, obscure, confused, or difficult to understand.

Now it might be deliberate or it might be a personality trait, either way......
Would obfuscaters kindly leave the thread? you know who you are!

Ad Hominem attacks will get you nowhere, and this is the third or fourth time you have accused me of deliberate dishonesty.

no_body wrote:The sound we're discussing does not have the characteristic of wind.

Proof?

no_body wrote:It's a loud distant sound that reverberates. It has a fast attack and short duration, most of the rest is early reflection and reverberation.

Proof?
I've already demonstrated that a collision can produce these characteristics, where's you're proof that it's anything more than that (if we assume it is indeed a global, rather than local phenomenom as you claim).

There is a video with audio taken by a Dr. Mark (Marc?) X(don't recall family name) from West Street. Poster shagster has listened to it and commented on PhysOrgForum about the timing of the last loud bang (which I take to be the west wall of WTC 1 falling flat onto West Street and use for timing purposes). Poster einsteen has listened too it, but wrote on PhysOrgForum that he could not here that final bang.

I mention this because it is yet another video, taken fairly close up, which will be yet another record of sounds at collapse initiation and thereafter.

Let's look at the B&B audio from around 19.41 from the cut that begins with a brief discussion of the Mariot hotel and ends with

Male "Oh my God"
Female 'Oh my G"

Cut...
In fact I'd say there are two cuts, the second comes after about 5 frames of the first. Now why would some one do an edit like that, maybe to fool the Trippys of this world?

I also think the jerky camera is fake it looks like the same frame repeated and rotated, because everything suddenly freezes - the car, the smoke stop moving while the camera jerks about, weird.

Oh and by some strange coincidence the cut happens just as the large boom on the initiation should come in.

Now we're ready for that first large piece of debris to enter the frame. How far do you think it's moved from not being in frame to being in the frame, toggle between frames, What do you think its acceleration is?

It should be in free fall, shouldn't it move further in the next frame? does it?.

As for there not being any rumble, from the spectrum of the audio I'd say it is "A" weighted that's -40dB at the bottom end, turn up the bass (below around 80 Hz) by +40dB,

Notice also the AGC kicking in when the people in the room speak, the AGC has fast attack and release.

There is a close correlation between the Sauret audio and the audio from B&B in the sub bass level, booms coincide, therefore the booms are not local. Turn up the Bass!, video to follow, Proof! (still some gremlins in the desktop recorder, be patient)

The first rumble coincides with the camera shaking in the Sauret video the part where someone or some thing falls from the tower, female B then says "People are jumping now they're..." She must have seen the falling object I guess.

There is an anomaly with the audio, it appears to be running at 96% speed, it looks like its been time stretched. I say this because my audio colleague has been comparing the sub bass, using side chained gates to pick up the peaks, and there's a close correlation between the two, but only if the B&B video is sped up. It's all very perplexing.....

It's like they've done this edit job with the sole purpose of hiding that initial bang, me and my suspicious mind.

How short sited of me.
Of course these civillians are in on it.
Either that or 'the man' hacked google videos and edited it post upload.

who says they're civilians? "bri and bob". too cute. how many other videos come with cute little white bread names attached?
this video was hidden from the public for a few years before it surfaced. lots of time to edit and manipulate.
i'm not sayin', i'm just sayin'.
and, hundreds or even thousands ARE in on it, trippy. only a few at the top, but lots of scared or ambitious little pawns and knights and rooks underneath. many are unwittingly helping.

things like sibel edmonds testimony aren't going away. bin laden worked for the CIA right up to 9/11.