# Auralex Gramma?'s



## chrapladm (Jun 17, 2009)

I am just wondering if there is an easier DIY option to basically take my sub off of the floor. It will be placed on the floor but I was wanting some isolation to the floor is all. The Auralex seemed to be an option but I thought of just using a 12mm thick rubber mat under neath but figured I best just ask here. Bryan usually chimes in with the best advice so thanks to any and everyone.

Here is the Auralex but I was only thinking of trying to copy something like that.
http://www.auralex.com/sound_isolation_gramma/sound_isolation_gramma.asp

Thanks


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## Jason_Nolan (Jul 4, 2008)

a 12mm thick rubber mat wont work. For one, this is less than half an inch and the rubber is denser than the open celled foam they use in the Grama.


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## bpape (Sep 14, 2006)

For cheap isolation - just use a piece of something like 1/2" plywood or MDF to allow you to still spike the sub to something. Cut 2 tennis balls in half and place them in the 4 corners under the wood.

Back in the day, we used to use something like this for turntable isolation.

Bryan


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## chrapladm (Jun 17, 2009)

I have seen the tennis ball thing before on turntable stands.

So if I use a sheet MDF and spike that to another sheet of mdf that is laying flat on the floor will this work?

I would just use a sheet of ply and add spikes but I didn't want the 100lb sub digging into the hardwood floors. 

Using tennis balls wouldn't I have to use about 8 of them because of the weight?

I wouldn't mind the spikes as long as I can lay a sheet of something under the spikes for protection of the floor.


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## bpape (Sep 14, 2006)

If that's all you're concerned about and not the isolation, you can actually get metal disks with indents in them specifically for that purpose. Put the disks down with the indent up, then the spikes from the sub sit in the indent.

You still get the concentration of weight from the spiking but you protect the floors.

Here is a kit that has the inserts, spikes, disks, etc.

http://www.parts-express.com/pe/pshowdetl.cfm?&DID=7&Partnumber=240-718&ctab=14


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## tesseract (Aug 9, 2010)

Will coupling the sub to the floor with spikes work as well as decoupling with an isolation device?


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## bpape (Sep 14, 2006)

Coupling and decoupling are 2 very different goals. You decouple to avoid vibration transmission to the structure but at the expense of not holding the sub tight so nothing moves but the driver. Coupling via spikes deliberately ties the box to the structure allowing the sub to be a bit cleaner by not having any other movement than the driver.


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## tesseract (Aug 9, 2010)

I couple my stand mounted monitors with spikes, top plate and floor. I have hesitated on the Gramma solution because of what you outlined above, the sub won't be stationary anymore. 

I am concerned about cabinet movement, I do want only the driver to move. Wouldn't tennis balls under a board still enable the sub to move even if the sub is spiked to the board above the tennis balls?



> For cheap isolation - just use a piece of something like 1/2" plywood or MDF to allow you to still spike the sub to
> something. Cut 2 tennis balls in half and place them in the 4 corners under the wood.


Just curious, because I will be looking at isolation soon and I want the most effective method.


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## chrapladm (Jun 17, 2009)

How much does a box filled with sand absorb vibrations?

My sub doesn't much because of it being dual opposed but there is still some and thats why I was going top try and get rid of those small vibrations. But if not a sand box then I will just stick with the spikes for now.


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## bpape (Sep 14, 2006)

A box filled with sand will help a bit in isolating the sub from the structure provided there is enough mass.

Just also remember that you're changing the position of the sub in the vertical axis which can impact frequency response.


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## chrapladm (Jun 17, 2009)

Yah I figured the change in height would change things but I figured I would ask. After seeing so many people building stages for their HT I thought this could be an option but maybe not really justified in my situation.

BUT what type of mass would be needed?

I think if I did do a structure with sand I would have to just make a sort of stage for everything to go on which would be 24"d x 13.5ft wide x 6"h. Now the height I would be sure on but that would be as minimal as I can make it but big enough that it had an effect on things.

That being said there would be 4 subs cabinets in total going on it. And they would all be dual opposed cabinets.


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## bpape (Sep 14, 2006)

6" will be fine if you do the whole thing. Just remember that the top plate, you'll also want to make 2 layers of 3/4" MDF or plywood.


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## ozar (Feb 12, 2012)

This thread is getting some age on it, but I've got to tell you guys that these things really work, and they are working very well in my particular case.

My pair of Hsu VTF-2 MK4 subs were sitting on carpet installed over hardwood flooring and they would really make quite a rumble during heavy bass audio tracks, so I purchased a couple of the Auralex GRAMMA isolators and slipped one under each sub and they made a huge difference. No more rumbling, vibrating floors, and bass tones sound much cleaner having all that rumbling removed.

After seeing the materials used for construction and seeing how they were assembled, I do feel like they wouldn't have been too hard to have manufactured myself, but I'm not regretting spending $50 each for them one little bit. :T


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