dBA - dBC for EDM in an old castle

[karel.will]

Hi,

I've been asked to advise on an EDM event in an old european castle with fragile stucco ceilings. These are not yet restored...
Last year they had a 90dBA limit, as an average over 60 minutes.
However, the people responsible for the castle feel that this didn't protect the castle enough.

So, this year I suggested they require the use of cardioid subs, that will drastically reduce the amount of sub energy inside the castle. The castle's court is a horseshoe form, and the stage will be aimed directly to the open side of the castle's court, and away from the delicate ceilings. So there won't even be any reflections from the subs. (hurray!)

But, just to be sure, I would like to add a dBC limit to avoid visiting techs turning up the amount of sub to try and circumvent the dBA limit.

So, finally my question: what would be a reasonable dB C limit to accompany the legally imposed 90dBA limit? Remember, this is just to avoid excesses. The genre isn't the commercial boom boom boom type, but more of an electronic arts type.

You can find more info about the artists performing here: http://www.horstartsandmusic.com

Thanks!

If you need more info, please ask!

Charlie

 

[Ivan Beaver]

Re: dBA - dBC for EDM in an old castle

Hi,

I've been asked to advise on an EDM event in an old european castle with fragile stucco ceilings. These are not yet restored...
Last year they had a 90dBA limit, as an average over 60 minutes.
However, the people responsible for the castle feel that this didn't protect the castle enough.

So, this year I suggested they require the use of cardioid subs, that will drastically reduce the amount of sub energy inside the castle. The castle's court is a horseshoe form, and the stage will be aimed directly to the open side of the castle's court, and away from the delicate ceilings. So there won't even be any reflections from the subs. (hurray!)

But, just to be sure, I would like to add a dBC limit to avoid visiting techs turning up the amount of sub to try and circumvent the dBA limit.

So, finally my question: what would be a reasonable dB C limit to accompany the legally imposed 90dBA limit? Remember, this is just to avoid excesses. The genre isn't the commercial boom boom boom type, but more of an electronic arts type.

You can find more info about the artists performing here: http://www.horstartsandmusic.com

Thanks!

If you need more info, please ask!

Charlie

It is not uncommon for the C weighting to be 20-25dB or more than the A weighting.

I would say the "limit" would be when the ceiling starts to come down.

Seriously though-it is not just a simple number, but rather the resonant freq of the ceiling that will start to cause problems.

I would run as FAR FAR away as I could from stating a number-because then YOU could liable for that.

"Well Karel said that XdB C was fine and we were below that".

If you get the resonance correct-often it will be much less than you think. Other freq can be quite a bit louder without any damage.

 

[Art Welter]

Re: dBA - dBC for EDM in an old castle

Last year they had a 90dBA limit, as an average over 60 minutes.
However, the people responsible for the castle feel that this didn't protect the castle enough.

So, finally my question: what would be a reasonable dB C limit to accompany the legally imposed 90dBA limit? Remember, this is just to avoid excesses. The genre isn't the commercial boom boom boom type, but more of an electronic arts type.

Charlie,

It only takes seconds for low frequency content to cause structural damage if the resonant frequency of the "delicate ceilings" is excited, so a 90dBA limit, as an average over 60 minutes, tells nothing about the SPL energy delivered to the structure down low, as dBA is -40 dB at 20 Hz. If an electronic drone 20 Hz tone read 90 dBA, it would actually be 120 dB SPL, which could potentially cause structural damage. I know from experience that short impulses of kick drum of around 120 dB definitely can cause plaster to crack and fall off ceilings.

DBC also rolls off below 100 Hz, it is about -6 dB at 20 Hz. You really need a dB meter flat to 20 Hz for what you want to measure.

I have found in my home studio that around 100 dB SPL somewhere between 15-20 Hz can make the 5/8" drywall (sheet rock panels) "flap", if that level was continued for more than a few seconds, screws would be pulled out and joints would crack.

To actually determine what frequencies excite the various portions of the castle ceiling, and what level at what frequencies and duration will cause damage would require destructive testing.

Art

 

[Jeff Babcock]

Re: dBA - dBC for EDM in an old castle

Karel,
Sorry for the slow response. FYI Waves Maxxbass processing works really well for this sort of thing. It can be used to replace actual bass frequencies with higher frequency harmonics which fools the ear into thinking low bass is there when in reality it is not.

I have done this in some situations where flown subs cause unwanted structural vibration noise or particles to fall from the ceiling etc. It would work well for the situation you describe.

 

[Ivan Beaver]

Re: dBA - dBC for EDM in an old castle

Karel,
Sorry for the slow response. FYI Waves Maxxbass processing works really well for this sort of thing. It can be used to replace actual bass frequencies with higher frequency harmonics which fools the ear into thinking low bass is there when in reality it is not.

I have done this in some situations where flown subs cause unwanted structural vibration noise or particles to fall from the ceiling etc. It would work well for the situation you describe.

Except at EDM shows people want to FEEL the bass-not just hear it.

And just because it is a low freq does not mean it will cause any damage. It is the resonant freq of the "object in question" that causes the most damage.

Yes generally it is lower in freq (for building size damage) and the higher freq are not loud enough to set things into oscillation, but it can be done at higher freq.

The problem is that the only way to find the "problem freq" is to actually cause the damage. It is to late then

 

[Jason Lavoie]

Re: dBA - dBC for EDM in an old castle

The problem is that the only way to find the "problem freq" is to actually cause the damage. It is to late then

If I were the owner, I would think about maybe some vibration sensors on the sensitive pieces and monitor actual potential damage. I would think a resonance would show up pretty easily.
Just throwing the idea out there, not sure how it would be accomplished in real life

Jason

 

[Ivan Beaver]

Re: dBA - dBC for EDM in an old castle

If I were the owner, I would think about maybe some vibration sensors on the sensitive pieces and monitor actual potential damage. I would think a resonance would show up pretty easily.
Just throwing the idea out there, not sure how it would be accomplished in real life

Jason

So how do you know how much vibration a particular piece of "sensitive piece" can take before damage?

Until that is determined-there is no way to know when you might be getting close to the limit.

It is like saying you put speed sensors on the road.

Unless you know what speed is safe for the road-a sensor means nothing. Is 20mph to fast? what about 80MPH? On some roads 20MPH will send you in a ditch. On others 100MPH is just fine.

It varies

 

[John Roberts]

Re: dBA - dBC for EDM in an old castle

Would EDM stand for "electronic DANCE music"? Thousands of humans bouncing around rhythmically could impart larger stresses on physical structures than air wiggling back and forth.

Resonances are important and some serious structural evaluation seems in order.

JR

 

[Jason Lavoie]

Re: dBA - dBC for EDM in an old castle

So how do you know how much vibration a particular piece of "sensitive piece" can take before damage?

Until that is determined-there is no way to know when you might be getting close to the limit.

It is like saying you put speed sensors on the road.

Unless you know what speed is safe for the road-a sensor means nothing. Is 20mph to fast? what about 80MPH? On some roads 20MPH will send you in a ditch. On others 100MPH is just fine.

It varies

I was thinking more like if something started to resonate it would stand out as a spike, kind of like a feedback detector.
Obviously as you said before we won't know the threshold until plaster starts to fall but it could be useful to know if parts are resonating

Jason

 

[Ivan Beaver]

Re: dBA - dBC for EDM in an old castle

Would EDM stand for "electronic DANCE music"? Thousands of humans bouncing around rhythmically could impart larger stresses on physical structures than air wiggling back and forth.

Resonances are important and some serious structural evaluation seems in order.

JR

I have been at shows that got scary due to the people all moving together and actually causing the floor to bounce.

I did a gig with "All Time Low" once that We had to actually hold the stacks to keep them from falling as the floor moved up and down.

 

[Ivan Beaver]

Re: dBA - dBC for EDM in an old castle

I was thinking more like if something started to resonate it would stand out as a spike, kind of like a feedback detector.
Obviously as you said before we won't know the threshold until plaster starts to fall but it could be useful to know if parts are resonating

Jason

It could be a fine line between when something starts to resonate and failure.

How could you monitor all of the "vital items" at one time?

Let's say something has a resonate freq of 38Hz. But the DJ is not playing anything that has 38Hz in it. But the next guy comes on plays 38hz real loud. Before you can react-the damage is already done.

It is not like they will slowly turn the level up.

 

[frank kayser]

Re: dBA - dBC for EDM in an old castle

90db over 60 minutes - That could include some absurd peaks or even extended periods well above 90, that when averaged in with, say a break, still make that 90db number. Sure you want to go with a long average like that?

wow...
frank

 

[Timo Ulkuniemi]

Re: dBA - dBC for EDM in an old castle

Hello

Back when I had bigger set than now - I rented a system for techno-rave evening, that was held in old building. Somehow they managed to get a crack on the floor - must have been a weak spot just waiting for final tap - when bringing the stuff back they were VERY eager about it and asked, if they could get bigger system next time...

Perhaps for them "Dying with your boots on" means "Dying while building collapses on you"

 

[Ivan Beaver]

Re: dBA - dBC for EDM in an old castle

Hello

Back when I had bigger set than now - I rented a system for techno-rave evening, that was held in old building. Somehow they managed to get a crack on the floor - must have been a weak spot just waiting for final tap - when bringing the stuff back they were VERY eager about it and asked, if they could get bigger system next time...

Perhaps for them "Dying with your boots on" means "Dying while building collapses on you"

We were doing a demo/show in a very popular EDM club in Atlanta.

The owner came up to us and asked us to turn it down, because stuff was starting to fall off the ceiling and he did not want any damage to occur to the club.

Different people want different things

We were doing another EDM show in NC and the owner kept asking us to turn it up. The sound guy said it was more than enough and totally happy. We had a good bit of "room left" in the system.

But the owner just kept asking for it to be turned up.

When we pressured him for why-he said that he WANTED to be arrested for noise complaints!!!!!!!!!!!

So he could make the papers the next day.

They had never had a system in there that came close and he wanted the publicity for being LOUD.

You never know what is behind why some people want something

 

[karel.will]

Re: dBA - dBC for EDM in an old castle

Hi Guys,

Sorry I didn't reply sooner, festival season...
The festival was a big succes, with the folks from the castle very happy. They told me there was a lot less rumble inside the castle, and the public still had a great time. Cardioid subs, gotta love 'em!

Thanks!

K.

 

[Steve Kirby]

Re: dBA - dBC for EDM in an old castle

I have been at shows that got scary due to the people all moving together and actually causing the floor to bounce.

I did a gig with "All Time Low" once that We had to actually hold the stacks to keep them from falling as the floor moved up and down.

This reminds me of a party at a ski lodge some years ago. Big amateur ski race and they threw an awards party at the end of the weekend. People would start pogo dancing and the floor on the 2nd story of the lodge would literally move several inches. If you tried to stand still you would get kicked into the air. One year they hired in a large local corporate event band who set up portable staging and put up their Harbinger PA. This was back when Harbinger was a legitimate set up. I think they were dual 15 + horn over dual 15 sub trap cabs. About 5 or 6 wide. I went up and warned them that the floor was spongy. They thought about it for a bit and decided to strap the arc of cabs together. When things got going they still had to hold on to them but thanked me later for the warning. Without the straps individual cabs were definitely going to fall on people.

 

[David Buckley]

Re: dBA - dBC for EDM in an old castle

I have been at shows that got scary due to the people all moving together and actually causing the floor to bounce..

A chap who used to post on another forum who related a yarn about when he worked as a tech at a holiday camp in the UK, and they had a two story building, the upper floor of which had concerts and the like. Get a bunch of people moving and the fire doors on the lower floor were blown open by air pressure. Eeek.

 

[gordon mcgregor]

Re: dBA - dBC for EDM in an old castle

I remember doing a gig in one of those holiday camps and the dancing and sound from the speakers destroyed the ceiling below and the organisers of the event being handed a big bill. G