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Author Topic: Binaural Mystery Solved - Dang Perplexing  (Read 494 times)

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Offline Moke

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Binaural Mystery Solved - Dang Perplexing
« on: January 03, 2018, 06:04:39 PM »
OK,... back in mid-December, I recorded a string quartet in a room that had been "off-limits" to me as a recordist for the better part of 7 or 8 years. I recorded in the larger concert venue, but, they didn't want me in the smaller room (just too small).
It is a very intimate venue, that is part of what was an old town mercantile, and its backroom storage warehouse. Now, the front of the store is the foyer, and the storage room warehouse is the venue.
When I say intimate,... 50 people packs the place. The venue measures maybe 15'dx35'w The stage front faces the 15' depth; parallel to the 35'wdith

The walls of the venue are all late 1800's brick masonry, which now sports the Cal Seismic Refitting standards, to keep 2 story masonry walls from collapsing under earthquake load.
This meant steel support posts, that were capped in a wood veneer, to be made to look like post_and_beam construction.
One of these posts was centered to the stage. So, I clamped to it. I ran my Gude Head MKE2002 headd, and CM3 pair clamped off of the same post clamp (see pic-1 dscn4320).
I pushed the clamp up to as high as I can reach which is just over 8', and mounted the head and cm3 pair.  I got a soundcheck, and everything seemed fine. So, I moved forward and dropped another rig within the Quartets U-shape presence, and, spent time soundchecking and listening to that mic pair (4060/baffle).
The stage in this hall is a temporary floating carpeted aluminum stage.
So, everything is rigged, and I'm tucked in literally into the branches of a christmas tree at the right rear corner.
The ensemble plays, and everything goes well, or at least by "appearance" (meaning, no overt issues arose).
I pack up, and leave the venue, and hoof it back up the hill to the parking structure (a block up the hill). On the way up the hill, I noticed an ice skating rink set up for the holiday, and make note, as Sarge likes to ice skate.
I get home, and start processing the recording from the day before (a choir concert), and did this until I went to bed.
I got up, and told Sarge about the skating rink, and, bam, she has her skates at the door, and the car warming up.
So, I grab the R09, cans, and the binaural recording, and, off to this same part of town, less than 12 hours later.

I listen to the entire binaural recording while she skates, and I'm really like what I'm hearing.
Sarge finishes skating, and off we go, back home.

I grabbed the binaural recording again, and settled down onto the couch, to give it a nice relaxed listen on the couch.  I settle in, and,....  WTF??
My perspective went from really enjoyable while down in town; but, now I'm at home, and my headphones feel like they're going to vibrate off of my head. But, not so much with an audible tone; I felt like I was being shaken by the head and shoulders, and really hard. It was very distressing.  I popped the headphones off, and, sat there really confused over what I had just experienced, distressing is not an inaccurate term for the feeling.
WTF just shook the hell out my head?

So, I got to thinking about the entire larger scene that had played out in that last 12 hours.
I was within the same 1 block vicinity on two different occasions in that time.  Once, while I was there recording (but, without headphones once the concert started). And then a very short time later, listening to a binaural recording, made in the same environment, mere hours prior.
Did the binaural recording somehow cancel out the same subsonic response that I should ahve been feeling in trip two, while listening to the bino track? My mind started to lead me in that direction,... just too much commonality, that would otherwise lead to something akin to a form of phase cancelling in recording (allow me this description, for lack of better one in my head right now).

I started thinking about the larger scene there, and, I thought I figured it out.
I speculated that the noise came from big-rig semis rolling down the Interstae-15 corridor, which in this case was the eastern boundary of the scenario. Just at the edge of the I-15 is the town center, City Hall, and all city services, a large building, and, terraced parking structure.  This building is large enough to block out, fliter the high frequencies of the road, and I speculated that it was the big rigs rolling by that caused the building wall, and post, to vibrate so much, as the venue is only two blocks, downhill of the freeway.

Problem solved, or, so I thought. HPF cleans out the vibration, music not touched.
That is until this morning. Sarge wanted to go skating again. So off we went.  The skate rink is just oustide of the city hall building, and that is all that separates the sakte rink, from the freeway.
I was sitting there, and, was aware of the freeway, but, was not getting this distressed feeling that I described.  Today would have a lot of big rigs rolling by, and I just asn't getting that sensation of shaking.

I decided to walk down into "old town", straight down from the sakte rink a block, which is also where the venue that I recorded in, that shook.
Old Town is an old west town from the late 1800's, with lots of era-proper masonry buildings, which makes them ancient buildings, as earthquakes knock down masonry buidlings here in Cali. These are era proper late 1800's masonry; antiquities.
So, I walk down past the venue, look into the windows, and continue past it.  There I find a bridge that has been constructed since my last recordings in the venue, from back around 2011.
That bridge crosses a wash that defined the western edge of town, since its inception, until whenever they built the bridge. Now, they have a new town center area on the other side of this wash. This bridge is a half block from the venue, but, I backdoored the venue, and didn't see it on the day of the recording.

So, I decide to walk across the bridege to see whats up on the other side, and see what they've done with their channeling of the wash (never a good thing; disaster waiting to happen).
I was standing at at the side, at mid-span, looking down into the wash, when a small 1/2ton import pickup drove over the bridge, and it scared the bejeezus out of me.  It was the exact same distressing frequency that I'd heard during the quartet.
To describe what happened on that bridge,....
You know those vibrating table football games, where the little plastic players move around on fine, sharp, plastic tipped bases, moving to the vibrating table?
I'm a really big guy. Its hard to make me feel like I'm moving by vibrations, but, I felt like I was on a vibrating table, and just being shaken inside out, and unabe to stop vibrating around.
I quickly walked off the bridge, and, gained composure.  Another car passed, and, because I was on the newly filled area at the foot of the bridge, it was less vibrating than on the bridge. So, another car was coming (these are just passenger cars), I stepped back onto the bridge, and, got that same violent shaking all over again.

That new bridge is going to kill that century+ year old building quicker than any earthquake, Hell, its 125 years old, and still standing. But the mortar dust that was on the floor below the brick wall, well, it was thick, and very telling.

So,... distressing binaural headhshaking recording mystery solved.

dscn4323 shows DPA4060 baffle on stage, as it relates to the binaural rear wall to the left.
« Last Edit: January 03, 2018, 10:01:17 PM by Moke »
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Offline Gutbucket

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Re: Binaural Mystery Solved - Dang Perplexing
« Reply #1 on: January 03, 2018, 06:44:11 PM »
Whoa.  Not quite Tacoma Narrows, but WTF?  Speculating that might overly fatigue the bridge structure or it's foundations over time as well.  What's it built out of- steel, reinforced concrete?

Looking at the bright-side, you've got a great mic-shock-mount test-rig there.
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Offline Moke

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Re: Binaural Mystery Solved - Dang Perplexing
« Reply #2 on: January 03, 2018, 07:11:38 PM »
Its a steel truss design, made to look old. It appeared to be bolted together, rather than riveted (confirmed). There were large hex heads at the joining point, with impact wrench marks on the shoulders.
It is maybe 75' wide? I think it would fit two cars width?
Truth be told, and in my home building experience (not civil engineeering by any stretch, but more than average,..) It shouldn't be anything more than a pedestrian bridge, or at most a single car at a time. It didn't appear to be any more than that.  I'm not an expert. I'm shutting up now.
They trenched out the natural wash, and made it like 30' deep right under the bridge, and 75' wide, at least..  The bridge abutments appeared to be of monolithic concrete, and, skirted by rip-rap of 1000lb+ boulders, thickly placed.
The walls of the wash were scraped to enarly vertical in that depth, and then gunite shot.  The only thing keeping people from falling off that face was a steel cable fence of maybe five cable strands tall? The concrete abutments have platers built onto them, that create "shoulders" for the bridge. This adds another 6 or so vertical feet to the fall into the wash, and, without any sort of fencing around the planter, just a warning sign to keep off.

Looking from the west side of the bridge (the newly opened land side), looking uphill to the city hall building.
The I-15 freeway is just the other side of the large city hall building. The concert venue is a half block from the opposite  end of the bridge view, all in the same slightly uphill linear view.



aerial view, but huge image. So, just linking,...
http://bomanite.com/wp-content/uploads/2016/06/TemeculaBridge_Imprint_14.jpg

It appears to be well built. But, the way it shook me this morning was way more than I feel that it should have. A small pickup had me bouncing around. A delivery truck? wow.
« Last Edit: January 03, 2018, 07:17:54 PM by Moke »
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Offline Gutbucket

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Re: Binaural Mystery Solved - Dang Perplexing
« Reply #3 on: January 03, 2018, 07:34:58 PM »
It's a mass-spring system with a problematic sympathetic resonance. If bad enough (and exceeding the design envelope) the city should may need to have an independant civil engineering outfit analyse the vibes and work up a damping arrangement.  That could be as simple as adding a calculated amount of mass to an appropriate location on the structure, or possibly a more complex refit requiring lossy dampers.   This is pretty much the microphone shock-mount problem, just on a different scale.
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Online heathen

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Re: Binaural Mystery Solved - Dang Perplexing
« Reply #4 on: January 03, 2018, 08:40:12 PM »
Gonna need some bigass Rycote Lyres for that bad boy.
Mics: Core Sound TetraMic | AT4031s | CA-14 omnis | AT853 cards | Line Audio CM3s | AKG 460/ck61 | Studio Projects CS5
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Offline Moke

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Re: Binaural Mystery Solved - Dang Perplexing
« Reply #5 on: January 03, 2018, 09:28:27 PM »
This is the theater I was recording in. The post I was clamped to (the seismic steel post), is the sidewall to the right. The bridge is a half block to the left.
It is called, the Merc.

another huge image:
https://southwestbackcountry.files.wordpress.com/2010/05/t12.jpg

The "Merc" is up front, on Main Street.  The larger theater, below, is the Old Town Temecula Community Theater. It sits behind the Merc. The two rooms are separated by a walkway between the rear of the Merc, and the Frpnt of the OTTCT. 
I recorded a good dozen shows a year in this one, for 7 or 8 years. I never once ehard such a deep subsonic rumble; lots of HVAC noise, yes, but never the body shaking rumble of the bridge.
This place is a fully proper acting and concert stage. The tall point of the building is the hoisted curtains/backdrop loft for the stage.
 
« Last Edit: January 03, 2018, 09:37:45 PM by Moke »
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