Discussion in 'Speakers' started by Justin_T, Mar 16, 2004.

1. ### Justin_T Stunt Coordinator

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Hello,

A while back it was suggested to me to use "anti-vibration" pads for my sub since I am on a 2nd floor apartment. I will eventually get a larger apartment on the first floor, however, until then I have to consider isolating the vibration for consideration of the neighbor below. I've placed the sub on mdf board...3 of them to be exact. Have also tried placing it like 2-3 feet off the ground on a stand and it STILL vibrates down to the ground brutally shaking it. The apartments are built well too. Do these anti-vibration pads make the difference to stop the boom on the floor. I mean the sub is extremely powerful and the bass is thunderous without it having to shake the floor. Where can I find these anti-vibration pads? How do they work? Any info would be greatly appreciated.

Thanks,
Justin

2. ### Andrew Testa Second Unit

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Justin,

Two thing to consider here to keep the downstairs neighbor happy: Sir Newton and panda thumb audio. Panda Thumb Audio is run by a forum member and sells custom sorbothane pads for vibration absorption tuned to your application. However, you don't want to go there first. The first stop is a visit with Sir Newton. There's some basic physics at work here that you can use to improve your sub's performance as well as reduce the vibration. As any advanced physics book will say on the first page, F=ma, and the rest of the book is an exercise thereof! The reason your cabinet is vibrating so much is the action/reaction law of motion: the signal applies a force on the cone via the voice coil to make the cone move. There must be an equal and opposite force applied to the cabinet through the driver magnet. So the more thunderous the signal, the more force applied to the cabinet. This makes your cabinet vibrate so much, and that vibration is transmitted through to the floor.

One consequence of this is that your sub's performance is suffering due to the energy lost by the reaction of the cabinet. If the cabinet rocks back from a particularly heavy signal, the cone rocks back with it while trying to push air in the other direction. With the cabinet vibration the cone loses the benefit of a solid base and the air displaced (your bass) is reduced in intensity and muddied. Ideally you want the driver to have an immovable base to react against. You can get this by mass loading the cabinet. Anything heavy that can be placed on or under the sub will help. If placed under, make sure the sub is securely coupled to it to maximize the energy transfer. I don't know what sub you have or what your SAF situation is, but an attractive slab of slate, limestone, or granite would be ideal.

So what does this do for your neighbor? Well, from F=ma, it's clear that if the mass goes up, then the acceleration must go down for a constant force. That means that for the same signal, the accelerations of the cabinet in reaction to the driver are reduced. This also should result in better performance since the driver has a more solid base to react against. This should reduce considerably the energy transfered to the floor, but it doesn't eliminate it entirely. NOW is the time to look at a vibration isolation technique. Something like the sorbothane or a DIY bicycle tube will absorb the remaining vibration energy and convert it to heat,decoupling the sub from the floor, and eliminating the energy transfer.

I mention all of this because if you only use an isolation device, you lose a lot of the energy being dumped into the cabinet by the driver reaction. If fact you'd lose even more since an isolation device would remove what coupling there is with the floor that currently provides some mass loading to the cabinet. The cabinet would still vibrate as much as it ever did and the performance wouldn't get any better. If you mass load the cabinet first, you gain the performance back and reduce the amount of vibrational energy that needs to be absorbed.

So my recommendation would be to find a way to mass load first, then contact Gary at Panda Thumb audio (pandathumbaudio.com) about the sorbothane, or try some of the DIY tricks like the bike tube.

Andy

3. ### Justin_T Stunt Coordinator

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Awesome response Andrew! Many thanks!

4. ### Alex_P Stunt Coordinator

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One thing about adding more weight to the sub is that you definitely reduce the vibration between your sub and the floor, but then you gain the shaking on the floor (like the floor is moving with the sub). Of course this will give you a tighter and cleaner sound. This is what I've noticed when I add +100lb sub to my apartment. Either way, your neighbor will not going to be happy about it. Let me know if you come up w/ something cuz' I am in the same boat as you. Thanks.

Alex,

5. ### Andrew Testa Second Unit

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Alex,

yes, the added weight does couple you to the floor more efficiently. That's why once you reduce the vibrations with the weight, look into a an isolation device between the sub and floor. The residual vibration will be converted to heat and you're decoupled from the floor. Something like this:

Subwoofer
Big ol' slab
sorbothane
'nother slab
Floor

It'd be a pretty thick piece of sorbothane, but it would do the job.

Andy

6. ### Justin_T Stunt Coordinator

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I think I will go with the:

Subwoofer
Big ol' slab
sorbothane
'nother slab
Floor

Sounds to me if the vibration can get through two slabs of granite or limestone I need to wait to use my sub until I get a freakin house Will keep everyone posted on how it turns out.

Thanks for the suggestions!

7. ### Andrew Testa Second Unit

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Great! I can't wait to hear how it turns out.

I've been posting to a lot of threads recently about vibration and isolation and was trying to think of a cheap way to cobble together some kind of accelerometer to try and quantify the changes in vibration. Last night I was reading through the Loudspeaker Design Cookbook and there it was right in front of me: a DIY accelerometer for cheap! Here's the recipe:

from Radio Shack buy the dirt-cheapest piezo tweeters they have. Should be \$5 to \$10 tops. Rip off the grill, cut the cone away from the frame, and gently pull the cone base off the piezo disk. Unsolder the leads to the piezo disk. Glue the disk to a short piece of dowel and there you have an accelerometer! fix the dowel to whatever you're measuring, use blue tac or whatever sticky stuff is required, then a voltmeter connects to the piezo disk leads. You may need some additional amplification to read a voltage, so it would be piezo leads to pre-amp in, voltmeter to pre-amp out. the voltage will give a relative measure of acceleration for comparison purposes. I had some piezo tweeters and demolished them last night, and tried it out on the clothes dryer which was conveniently right there and vibrating away. I could see a very small voltage change, so I need to try the amplification. I have a real cheap voltmeter though. If yours is more sensitive to small voltages you won't need the extra step.

I'm going to try the amplifier and if it works I'll make a report. Good luck with the sub tweaking!

Andy

8. ### Justin_T Stunt Coordinator

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HAH!!! Got it my friends! I went with the method Andrew suggested:

Subwoofer
Big ol' slab
sorbothane
'nother slab
Floor

Amazing! The bass is still thick, punchful, and powerful yet the floor remains solid. It use to literally shake the floor on the smallest bass cues, now the room just reacts instead of the floor. Went downstairs to check with my neighbor and he was like, "Nope, I don't hear it...you're cool man" This while playing the THX demo disc at above normal volume level. SWEEEEET! Thanks for your help guys. I think I will invite him up sometime for being so cool!

9. ### Chu Gai Lead Actor

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Decoupling such as Andrew suggested seems like your best bet but it is a bet as the low frequencies can propagate in other ways and still piss your neighbor off. Since you've got 3 MDF boards you could try something like putting an inflated bicycle tube in between and see if that improves matters any.
Cute idea on that accelerometer Andrew.

10. ### Alex_P Stunt Coordinator

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Andrew and Justin, What do you meant by

I don't quite get it.

Justin,
If your sub won't shake/vibrate the building, isn't it reduce the LFE? I want to hear and as well as feel the bass. I don't know just to hear it. Thanks.

Alex,

11. ### Justin_T Stunt Coordinator

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Hey Alex,

My sub reaches frequencies down to 23 so I still feel everything. The only difference is now the room basses and not the floor. It's hard to explain. It's like the bass is trapped in my apartment and not being lost through the ground. Trust me, you can still feel it. When we say big ol' slab we mean granite, limestone, or cement...whichever is better looking for you. Sorbothane can be found here (pandathumbaudio.com), however if you have rubber pads that would go inbetween the slabs I think that would work just as effectively. I too worried about the loss of bass from the sub being on a very sturdy surface. Wasn't the case. I test out HULK which we all know has huge bass and a THX demo disc and was amazed at the response I got. Hope this helps.

12. ### Mark Murphy Supporting Actor

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I was worried about my floor resonating too much when I went from a Jensen POS sub to a 25-31PCi. I live on the 3rd floor and I didn't want to upset my neighbors. I have my sub on two pieces of 3/4" MDF and on the bottom are 8 rubber "anti-vibration" pads used for washers and dryers. The sub is located in the rear left corner of the room about six feet away from where I sit. I can "feel" the LFE just fine and the floor doesn't shake too much, at least not enough to bother my neighbors.

13. ### Andrew Testa Second Unit

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Alex,

My first post in the thread detailed the reasoning behind this approach. In short, if the floor is shaking, that means energy from the sub is shaking the floor and NOT making sound waves, which is what you 'feel' in the LFE. If you eliminate the energy transfer to the floor, all that previously lost energy is now making sound waves, and the LFE experience should improve.

Mark,

If you'd like to experiment, add a couple of cheap cement slabs to the MDF under your sub to increase the total mass. The MDF isn't adding very much weight to the total, so the pads underneath are probably trying to absorb a lot of energy. You may find the floor shaking reduced further, and some improvement in the bass with more mass on top of the pads.

Justin,

Cripes that was fast! What materials did you end up using? I'm really glad it worked so well. And Chu is (always) right, that just because the sub is no longer energizing the floor, the sound can still transfer out of the apartment through other avenues. But it sounds like the floor was the main problem for you. Glad to have helped!

Andy

14. ### Mark Murphy Supporting Actor

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Andrew,
I will give that a try. Do you know the best kind of place to get the concrete slabs? I did get an improvement in my sub's performance when I put it on the mdf/pads. I could feel more of the vibration in my couch than I could before. I was thinking of getting some shakers but after I put the sub on the mdf/pads I realized that I don't need them. I get plenty of tactile response on the couch from the sub alone. It probably helps that I have it tuned to 22hz and the rooms is pretty small. The gain on the amp is only turned up 3/8, calibrated w/Avia and a RS SPL meter.

15. ### Andrew Testa Second Unit

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Mark,

Probably your closest home depot/Lowes type home store. The garden department should have a bunch of square concrete pavers or such that you can use.

Andy

16. ### Alex_P Stunt Coordinator

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Andrew + Tustin,

Thanks for the tips regarding how to reduce vibration. It really improved my sub on LFE. Getting more tight and clean LFE. This is what I did. I went to OSH and bought a piece of rubber. Cut 4 lil pieces for sub's legs and glued underneath them. I also got 8 pieces of concrete pavers (1ft square each). I laid 4 pieces of concrete pavers underneath and cut out the rubber pad and place it on top of the concrete pavers. Then placed the last 4 pieces of concrete pavers on top. Then placed my sub w/ rubber padded legs on top of the pavers. Re-calibrated my sub. After all that, I popped in "The Haunting". Cranked it on -10db below reference. All I can say is "WOOOOWWWW..." Feel like somebody is pounding on my chest. And I noticed that the floor doesn't vibrate as much. It's definitely reduce the vibration, most of it probably goes to me instead of the floor I will probably adding some more weight on top of my sub this weekend see how it goes. Not that my sub isn't heavy enuf, it's +100lbs sub. It's DIY Tempest. This is awesome. All these only cost me ~\$10.

Thanks once again...
Alex,

17. ### Andrew Testa Second Unit

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Alex,

I'm glad it worked well for you! Sometimes little tweaks CAN make a big difference if you know the physics behind them. Enjoy your sub!

Andy

18. ### doteagle Auditioning

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I live in a 100 year old 6 brick think urban condo. My medium subwoffer disturbes neighbors below on the second and first floors.

I used household items to moderate the floor vibration.

Underneath the subwoffer I placed two packs of copy paper. On top of these I placeed a big hard cover table top history of baseball book. The feet of the subwoffer stand on the big baseball book allowing the subwoffer to operate.

Great improvment