Several kW speaker inside an apartment - what would happen?

[Red Squirrel]

We were tuning the equalizer at my church since we got a new sound system so we used a sine wave generator to try to find the resonant frequency of the room.  Once we hit it, very interesting things happened.   Stuff like wood strips on the walls started to vibrate and depending on where you walked you could feel it in your head, like some places were more intense than others.   I imagine if we had actual kw worth of speakers pumping that for a long time things would start to break and it would probably be dangerous to the ears.   The speaker we have is "rated" at 1000w (a fairly standard size for large PA systems) and the amp is higher, though we did not have it anywhere near it's max, and we all know those ratings are mostly BS anyway.    But if you were to actually do that with several kw I'm pretty sure it could start to cause things to break, loosen up etc, maybe even take out windows. 

[CatalinaWOW]

Interesting bit in here about the satellite shake and bake testing that ESA does to the commercial sattelite s they manufacture.

http://omegataupodcast.net/242-satellite-testing-at-estec/

Pics also there of the facility and the equipment, plus some very interesting discussion as well. Yes an hour and a half of audio to listen to, but well worth it in conjunction with the photos from there.

I once got to participate in a publicity tour of a similar facility.  They had a 100 kW tRMS amplifier driving an electromagnetic shaker.  The amp was huge, perhaps 3 meters wide, 2 meters tall and a couple of meters deep.  We walked onto the driven platform while they drove it with the audio from a local radio station.   That had to be one of the least efficient speakers ever used.  even at max power it wasn't rock concert level.  I later worked at a facility that had another copy of that 100 kW amplifier driving a shaker.  It was seldom used because maintenance and calibration were such a PITA.

So the two keys are efficiency in converting input power to acoustic power and resonance for coupling with the target.  Since resonance is often key to efficiency in acoustic power conversion there could be interesting problems in getting the whole thing to work.

[DenzilPenberthy]

Bear in mind that, depending on the design of the building, you can remove a wall with a surprisingly low pressure - as little as 2.5psi. Removing a wall from half way up a tower block is not good!

https://en.wikipedia.org/wiki/Ronan_Point

[james_s]

That's actually not very surprising, I mean if you think of how many square inches of area the wall in even a small bedroom is, multiply that by 2.5 pounds and you've got quite a lot of force.

[SeanB]

I once got to participate in a publicity tour of a similar facility.  They had a 100 kW tRMS amplifier driving an electromagnetic shaker.  The amp was huge, perhaps 3 meters wide, 2 meters tall and a couple of meters deep.  We walked onto the driven platform while they drove it with the audio from a local radio station.   That had to be one of the least efficient speakers ever used.  even at max power it wasn't rock concert level.  I later worked at a facility that had another copy of that 100 kW amplifier driving a shaker.  It was seldom used because maintenance and calibration were such a PITA.

So the two keys are efficiency in converting input power to acoustic power and resonance for coupling with the target.  Since resonance is often key to efficiency in acoustic power conversion there could be interesting problems in getting the whole thing to work.

Nothing compares in fuel to noise efficiency than a jet engine at full afterburner on a ground test bed. 150dB 100m away, and we were behind the sound baffles, the collection of scraggly trees and the entire complex as well. might be partly responsible for some of my hearing loss that, plus just the regular noise from the non afterburner jet engines as well.

[Simon]

Immediate issues:  Hearing loss..... and expect the Police to kick down your door.  You won't hear them knock.


Potential issues include other physiological damage and structural stresses.  Get some resonance happening and you never know what will happen.

Speaking of resonance, I seem to remember hearing about some experiments with large structures using a comparatively small device.  The device set a relatively small mass oscillating at the resonant frequency of the structure.  It did not show any ill effects quickly, but over time, the structure(s) also exhibited oscillation at noticeable and then troubling intensities.

So, as long as the input energy from a resonant source exceeded the losses from the resonant system, you could end up with some pretty dramatic results.

Not so much in the UK, if the source of noise in in the house the police are powerless

I do remember tell of someone doing low frequency experiments in a building and the sounds ending up in the ventilation system and causing problems. Not sure if this is an urban myth though. Of course we have walls of Jerico

[schmitt trigger]

[

Nothing compares in fuel to noise efficiency than a jet engine at full afterburner on a ground test bed. 150dB 100m away, and we were behind the sound baffles, the collection of scraggly trees and the entire complex as well. might be partly responsible for some of my hearing loss that, plus just the regular noise from the non afterburner jet engines as well.

Indeed! a jet engine on afterburner is beyond loud.

Similarly....The loudest continuous man made sound (A-bombs are far louder, but they are not continuous) is the one made by a Saturn V rocket during liftoff.

[james_s]

Nothing compares in fuel to noise efficiency than a jet engine at full afterburner on a ground test bed. 150dB 100m away, and we were behind the sound baffles, the collection of scraggly trees and the entire complex as well. might be partly responsible for some of my hearing loss that, plus just the regular noise from the non afterburner jet engines as well.

It is indeed extremely loud, but I'm not sure how it compares in terms of fuel to noise efficiency. Something like the LM1500 which is an industrial turboshaft version of the J79 without afterburner produces 10,000 HP which is about 7.5MW and that's extracting about 30% of the energy from the fuel into mechanical energy. That means around 22MW of fuel energy being fed into the machine, and I'll conservatively estimate that an afterburner is going to more than double that. How loud is a 50 Megawatt amplifier driving an enormous array of speakers? That's starting to sound like a Spinal Tap concert.

I really can't think of any practical devices that produce more sustained noise than an old fashioned turbojet engine though.

[DenzilPenberthy]

... unless you take advantage of the inverse square law and just stand a bit closer.  Long story but I had the opportunity to help out ringing an extremely large bell a few moths ago. The regular folks I went with who are keen bell-ringers say they've measured it at 145dB and it's rung by two people swinging it back and forth by hand...

I was sceptical about the 145dB claim because I understand how logarithmic scales work but I was there wearing -35dB earplugs and it still felt about as loud as using an angle grinder without ear protection so I can believe it. My ears were distorting the sound and were ringing for quite some time after.   I'm used to being vibrated to bits by bass-bins at music events but it's a very strange feeling getting the same physical effect in the high 100s of Hz...

Edit:  you don't get a sense of just how loud it is on the video but it's surprising how little energy you have to put in to it. It weighs nearly 10 tonnes.

https://youtu.be/Y8gHziy278Q?t=2m40s

[WastelandTek]

It weighs nearly 10 tonnes.

https://youtu.be/Y8gHziy278Q?t=2m40s

egad!  that one lass is jumping off the ground to grab and pull...wow

[babysitter]

sound level causes a pissing contest often...
Just recently I had a wannabee stage techie bragging about "Company XYZ sells a 180 dB system yadda yadda yadda"
I was short before pointing to the ESA ESTEC/LEAF facility, able to test at around 156 dB levels, and Project Pluto which was expected to kill not just with its nukes and radionuclide-spewing emissions of the drive, but also with its 162 dB noise.