Is it the sheet metal of the duct shaking in and of itself, as in the traditional theatrical thunder machines, or is it two pieces of the same rattling where they join together? Is it making noise because of sound waves traveling through the air, or because the
subwoofer cabinet itself is shaking the floor and ductwork?
If it's the joints in the duct, it seems to me that one ought to be able to more solidly join the segments together somehow working from the inside of the duct without too much difficulty. If it's the whole of the duct that needs stiffening, that's somewhat of a harder problem. Likewise, if it's vibration from the
speaker cabinet, a different supporting strategy might solve things nicely (which could be as simple as sticking it on a chunk of foam or some other soft material).
@DrewE @Colin @Amiers @FMEng and
@BillConnerFASTC
I'd suspect the latter: The sub's output is rattling the building and its entirety. Herewith a 'Cole's Notes version of a previous (lengthier and more detailed) post: What feels like a decade and a half ago, I owed a favor to someone and the time came when payment was requested: I found myself generating a series of effects tracks to provide the sound and the
FEELING of DIY fireworks in the basement unexpectedly exploding simultaneously seemingly directly below the
stage. (There was no basement below the
stage, we were already in the 1870 odd basement.) This was true "church basement" dinner
theatre. The church was erected in the 1800's on the
edge of a farmer's property within approximately 10' of a steep ravine leading to a small bay. The church basement was dug into the previously undisturbed soil where every approximately 1,000 pound boulder in the area was rolled, stacked and mortared to form the
foundation for the original single story church; as the village and its parishioners grew, a second story was added; decades later, an attic
meeting room and a bell tower.
Cutting to the chase: The group didn't know me from Adam but I was able to borrow a key and access to the basement of the totally empty church for ONE midnight to 5:00 a.m. session as long as I left the place undisturbed, and returned any tables I moved to their original locations prior to the 6:00 a.m. cleaning person's arrival.
Picking up the pace: I borrowed one of the original
'Sen-surround' subs originally developed and built to travel with the film
"Earthquake!" as part of an optional equipment package to be received along with the 70 mm prints. For my one and only overnight session I lugged in the bare minimum for my purposes: A manually sweep-able audio oscillator capable of sweeping from appreciably below 20 Hz to slightly higher than 20KHz
in one continuous band, the Sen-surround cabinet (complete with its LARGE
'Sen-surround!!! logo stenciled in white paint on the cabinet's sides) and the largest stereo BGW solid state amp I owned. In a church basement
theatre there were a limited range of locations to 'lose' the sub without reducing the seat count nor occupying too much space in the cramped, near non existent, wings. I overran my 5:00 a.m. curfew but got to meet the caretaker as we passed in the parking lot.
In my five hours I'd tried several locations and chose two or three frequencies where the sub was truly vibrating anything /
EVERYTHING that would sympathetically resonate. Even though the patrons would be exclusively in the basement, I got into my task and checked the church directly above along with the entrance
lobby. I found frequencies you could hardly hear but could definitely feel. I stashed the sub then put the oscillator and my BGW back out in my van. At home, I added all the audible tracks that provided the appropriate sounds then laid down my sub tracks for the appropriate 'feelings'. When I auditioned various music and more standard effects for the director's selection and approval, I delayed demoing my final "product" until much closer to opening night when I could position the sub and
gaff my cables ONCE. As it happened, our final rehearsal was on the Thursday evening prior to the Friday opening. Immediately above us in the church were the organist and choir director along with their choir of dutiful members primarily between 70 and death. Below them our rehearsal was progressing per normal: The cast rehearsed with near performance projections saving a little in reserve for the crowd anticipated the next evening; door bells / chimes were the real deal and sounded at
level, as did real rotary dial phones of the era rang from a 25 Hz 90 volt source to sound 'right' when rung. Pre, interval and post music were played 'top 'n tail' at reduced levels for purposes of cuing then quickly faded out as we had no audience in attendance. The church and choir had become used to this approach anytime our rehearsals were going to collide with other rentals or church functions including wedding rehearsals.
Bottom Line: To say the organist and choir directly above us were unprepared for when we added the sub tracks and ran the explosion
cue at our anticipated performance
level would be an understatement at best. Unprepared; they dang near collectedly defecated their undies. So many people from various and sundry places in the building: Headed for the exits / stared down stairs for signs of
smoke or flames / bellowed 'Is everyone O.K. down there? I don't recall anyone above basement
level venturing down to actually see if everything / everyone was actually still intact.
Ya;
back to where this novel started: The sub rattling the building's got my vote / sitting it atop some manner of mechanical decoupling's likely urinating in the wind.
@MNicolai @TimMc @FMEng @Ancient Engineer : A devalued Canadian penny for your thoughts?
Toodleoo!
Ron Hebbard