The 9/11 Forum

We have gone to the only source available UTube and selected 6 videos, the sound quality isn't great in some of them, but, it's as good as B&B. The ones we've chosen are 3 collapses one that seems to include a column snap, though it might be re-bar in the concrete support beams, 3 are of demo's from similar (but currently unknown) distances from the camera as WTC.

So there is a collection of audio that contains each of the above. The demolitions chosen have a significant portion of collapse audio after the detonations. It'll take some time to sort these out, give us a week, meanwhile any other suggested sources for comparison.

Fire induced collapse with column re-bar snap
http://www.youtube.com/watch?v=p22OkclAU3

This ones apparently due to fire but looks a bit like a pull. Collapse sounds only
http://www.youtube.com/watch?v=1h9TOFP7ViY

High rise collapse Manilla some problems here, the TV channel have pumped (multi band compressed) this audio. but there is a clear portion of collapse sounds (I'm not sure if the electricity explosion isn't dubbed in after, along with some screams for added spice)
http://www.youtube.com/watch?v=uKeENdyIluI

Everglades Hotel Implosion
http://www.youtube.com/watch?v=7XG-l3N1YfQ

Beirut Hilton hotel implosion
http://www.youtube.com/watch?v=vdJTDuYB_h8

Demolition of the Philips building - in Oslo
http://www.youtube.com/watch?v=ZAyyHQQXX_0

Oh and this one for its sheer pointless grandeur.

New Frontier Hotel Implosion Las Vegas
http://www.youtube.com/watch?v=h3K3kEDEAN4

no_body wrote:We have gone to the only source available UTube and selected 6 videos, the sound quality isn't great in some of them, but, it's as good as B&B.

You didn't check Google videos?

Google Videos at least gives you the option of downloading the videos directly, rather than having to go through a third party.

Trippy wrote:You didn't check Google videos?

Google Videos at least gives you the option of downloading the videos directly, rather than having to go through a third party.

Please feel free to include any additional video resource links you think may be useful to progress this thread. I'll include a couple for WTC 2 asap.

Just a little something for the weekend...

From the initial analysis ( looking at some of the bangs in the sonograph) there do appear to be noticeable differences brtween collision bangs and explosive bangs.

First the difference in amplitude is large and difficult to estimate from the 3 videos that feature demolitions. After the explosions stop, the collapse of the entire building seems very quiet, I'm afraid I can't put a number of dBs to it. All the video cameras could not cope with the difference in amplitude, In one case the sound of the reverberation of the explosions is louder than the collapse.

The next difference is in harmonic content,

In collisions after the air burst, the sound energy emanates from the objects impacted, and there is resonance (I would suggest the same is true in column snaps, tho there's no data to verify this intuition), the pitch of which depends on the dimensions of said colliding objects.

This is a high frequency containing 'crack and bang' from a collision. We've noticed this harmony, a chord if you like, in one or two other places we looked at noticeable bangs in collapses.



In the explosion there is pitch modulation starting very low, with relatively low amplitude and rising to a crack where maximum energy is released and then falling again with a modulation in the tail These are two shots of the same sample looped.

Here from WTC1 Sauret Two versions of one of the 5 'Chimes' (+36dB bass restoration)



And here from the initial blast from one (sorry I haven't got that information to hand) of the demolitions.



Collapses are very random.
Here from the fire induced collapse

.

Collapse bangs don't always sound the same they have different pitches and generally don't modulate in pitch, rather they resonate harmonically, Explosions have much more energy in the high band, collisions tend to be duller, though we've found one exception, the general rule seems to be dullness, accounted for in part by the sudden appearance of suspended material after the explosion.

Any thoughts?

Comparison of Roof movement coincident sound from 4 videos.

The bang that coincides with the first movement of the roof appears in the audio from 4 videos.

Sauret
Bob and Bri
Andres Barrila
and Rick Segal


Large scale image

Using this data, an analysis was made syncing Sauret and Segal audio.
In the image below Segal is panned extreme right (Bottom) and Sauret extreme left (top)


Large scale image

Segal's audio was already boosted in the bass end. This image was produced by using a very short envelope sidechained gate. (see previous videos for the technique) i.e. hold= 0.04 ms and a release of 24ms. The background is attenuated by 12dB and the sidechain frequency is set to 43Hz.

There is a close correlation between the two audio files, and this analysis was made to give timings for the various events we see in the demolition.


Large scale image

Segal was ~3.6 km from the source, giving an attenuation due to the inverse square of around -134 dB. Both wind conditions (all videos upwind of the source) and temperature profile, add additional attenuation which with out PE modelling is difficult to quantify. These sounds can only be detonations of varying size.

Edit:
Three 'phases' can be identified. Initiation of top block demolition, Starting with a bang that coincides with the first movement of the antenna, followed by 3-4 rapid detonations as the roof begins to move, ending with 3 bangs (marked B01, B02, B03 in the 2 images above) that coincide with the large cloud ejections. Phase 2 is the 'zipper' many rapid detonations including at least 5 large booms approximately spaced at 1 second intervals. The final 3rd phase starts with 3 bangs, followed 2 seconds later with the demolition of the lower tower, these explosions are the largest. Relative silence ensues even though large pieces of outer wall have yet to hit the ground.

These events have been checked against 3 videos of the collapse and everything seems consistent with a top down controlled demolition ending with the demise of the lower portion of the tower