AdubsDJService

Good evening!

I've noticed on more than one occasion that my ZV28s produce enough low-frequency energy to make the floor "wobble" or "wave," essentially move up and down quite a bit. It Made me think.

If the floor in a venue is “flexible” enough. Can it negatively affect the frequency response of subwoofers?



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Glen Allan

I'm often curious how much of this is actually the floor "waving" or how much of it is some kind of visual distortion due to the intense air pressures effecting what we see. I've had all 4 of my ZV18s going on wood floors and shake the hell out of the entire house without that happen, but i've also hit he right frequencies and had it difficult to not see stuff moving due to eye wobbling. Concrete for instance obviously cannot wave without cracking, but it sure can look like it is. Almost like the rolling shutter effect we see when doing vids of speaker drivers going or even the fun ones like people's car doors waving, but instead of the issue of being one of frame rate issues in the capture, it's a visual interrupt of our actual eyes.

My take on it effecting sound would be that if the floor is not very rigid, there will be some loss of energy going into the floor, but this kind of naturally compensates for itself by adding the visceral effect of standing on the vibrations, giving it a pretty rad feeling as well. I guess it could then take some of the energy out of the air, but i'd have to guess it's minimal. Or to say it in a another way, the boxes are operating properly and themselves aren't losing output capacity, but as with all audio reproduction, the room will effect everything. Not sure how much that specifically would effect the response above very low frequencies though. Even then the issue is more what's being absorbed vs what's reflecting based on material density and reflectivity. This would change anywhere different you go.

Often i find the problem not so much a matter of changes in response, but that audible vibrations in different objects or walls kind of kill the clean and effortless sound the boxes are putting out, adding unpleasant distortions. I've actually opted for configurations which are less bass producing to minimize this effect in certain venues.

If you are finding the issue with the floor exceedingly problematic at a venue you do shows at often i'd think some kind of extra isolation from the ground would be a good option. Rubber pads or whatever will decouple it from the floor. Even running the subs on the wheel carts with the locks not engaged could help (if they aren't also rolling due to the bass).

My favorite venue so far is all concrete walls and cinderblock walls with an open roof, so no vibration and corner boundary loading really enhances low frequency output. Actually it's a fine balance for some music as it can be overwhelming and make the other frequencies harder to hear even with the tops going full. That just comes down to managing the output at the source then, and i'm not even remotely complaining!

I'm curious to hear David break down the actual physics of this!

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Glen Allan
In a similar vein i have had issues with DJs using vinyl on wood floors due to the bass feeding back through the needle. Getting them to better isolate and decouple their turntable from the floor is vital. Or getting them off of the same surface as the subs are on.
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AdubsDJService
Hey Glen!

I wasn't necessarily mentioning it as a problem. I apologize if it seemed that way. 

I am more or less curious. Oddly enough, the only time ive had visual distortions in front of my ZV28s was two of them horizontal side by side outdoors. 

In my scenario its definitely a physical movement of the floor. Concrete walls, solid yet weirdly shaped celling but a wooden floor with a basement under it. Like you said, its more like "standing on the vibrations" which is its own cool effect, because nobody has ever experienced it unless they are in front of my system lol. Depending on the venue of course. 

I should have asked/said "how/does a more flexible venue floor affect low end frequency response" :-)

Im always finding that there is a hole 10-15 feet in front of the system that I can never get rid of. Acoustics are so crazy!

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audible vibrations in different objects or walls kind of kill

Definitely! It makes me want to show up with a caulk gun and some rubber cement and walk around the venue and attack anything that buzzes! lol 



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Glen Allan

Hello! Oh no apology needed. I'm curious as well. Not sure how much we can do to fix other people's venues when they didn't even know there was a problem till we brought out these ridiculous subs!!! The place i'm most often doing shows now has a ton of fluorescent light fixtures on the ceiling and they can vibrate horribly. Really sucks since i also live record the shows with a RØDE NT4, which totally can pick up that metal vibration sound.

I've had the visual distortions when i put mine in a cube configuration to optimize the most bass output. I think your side by side on the floor would be like when i do mine all four across, which definitely gives the lowest frequencies the most chance to get out. it also really depends on the kind of music. I do experimental sound and noise based shows which really dip low at times... Got the whole can't speak properly thing going as well when the low frequencies hit your vocal cords [tongue]

By hole do you mean cancellation? I would guess that has to depend on your systems physical configuration/arrangement and the venue itself. The trick i have now is if i'm going to play the same venue a lot i try 3 or four different setups to see how the bass response works out. Annoyingly i find i end up doing a split config because the places just can't handle the amount of bass when the subs are clustered. Do you have the option to totally change where the subs are located in the space? Any chance you have to move them around will tell you best placement. But if you are getting a hole that close to the system there's some kind of phase cancellation happening. Hard to really say how much the venue is causing it, but changing the placement of speakers can completely change that if you can.

I'd be concerned about the floor integrity, lol. Have you been in the basement while the bass is pounding? It might give you an idea of where the vibrations are focused the most and let you see how much is actually moving! Might even be good to sketch out your configuration and basic layout of the space.

We'll have to let David chime in on the best approach.

And yeah, i'd love to rip out all those light fixtures! A caulk gun would be great as well!

[biggrin]

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jeffl
I too would like to hear David's deep thoughts on this.  No pun intended.

My thought, is that some of the energy is being consumed as heat as the wood structure moves and absorbs and dampens the energy.  Part of it though, as it is moving, wouldn't be dampening the sound but creating sounds, by making the air touching the floor move.  Would it be in phase with everything?  Probably not as it would be vibrating on a horizontal plane rather than with the incoming waveform on the vertical.  It would definitely add to room vibe as mentioned, but I expect it would add to low frequency rumble, reducing clarity and increasing distortion.  But hey, not everything is about perfection as distortion isn't always a bad thing, and if it produces 3rd order harmonics some way some how... man... that venue might just sound majestic.
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jeffl
I also forgot to include the speed of sound through wood as opposed to air, which is much faster as it is a solid medium, but varies depending on the wood.  So you should feel the floor shake ahead of the incoming direct sound from the speaker, which depending on the size of the venue might feel neat.  Interesting thing to ponder over though.
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