DIY Sub Riser Feet

[grimmace19]

I don't know whether it was on here or another audio site but I was inspired by the DIY sub riser someone built with slabs of granite. By a stroke of dumb luck a new employee at my store has a part time job at a marble and granite shop. With this, he said they throw away plenty of scrap in the size I need to put under my sub 12s. The place I saw the original riser with the granite sheet used hockey pucks as the feet and I was thinking of doing the same. However, via parts express there are plenty of rubber cabinet feet to choose from at little cost 60-75 cents per.

With these options in mind does anyone have recommendations as to which would be better? I think the hockey pucks would possibly work better but look worse. The rubber would be thicker, heavier, and have a flatter surface for supporting the 3cm heavy sheet of rock compared to the other feet available. However, the option of very cheap rubber feet from parts express would allow me to buy more of them and place them in say 6 different pressure points.

The last part of all of this is attaching either the pucks or feet to the granite. Any suggestions for an adhesive to use on either one of these things?

Thanks for the help.

[louhamilton]

I don't know whether it was on here or another audio site but I was inspired by the DIY sub riser someone built with slabs of granite. By a stroke of dumb luck a new employee at my store has a part time job at a marble and granite shop. With this, he said they throw away plenty of scrap in the size I need to put under my sub 12s. The place I saw the original riser with the granite sheet used hockey pucks as the feet and I was thinking of doing the same. However, via parts express there are plenty of rubber cabinet feet to choose from at little cost 60-75 cents per.

With these options in mind does anyone have recommendations as to which would be better? I think the hockey pucks would possibly work better but look worse. The rubber would be thicker, heavier, and have a flatter surface for supporting the 3cm heavy sheet of rock compared to the other feet available. However, the option of very cheap rubber feet from parts express would allow me to buy more of them and place them in say 6 different pressure points.

The last part of all of this is attaching either the pucks or feet to the granite. Any suggestions for an adhesive to use on either one of these things?

Thanks for the help.

Sub risers can be used for isolation as well as just raising the sub off the floor. I would think granite would cause more resonation and reflections. A carpeted surface should be better, IMO.

I would get a 3/4 - 1 inch thick solid sheet of wood, use either 2x4 or 2x6 as the legs, carpet everything, add some polyfill to the underside of the riser. Additionally, I would add spikes to the bottom of your sub for isolation from the riser.

This is how I started mine. I have since removed it from my setup for a rebuild. I just need to get upgraded spikes and finish the rebuild (looking for new carpeting but have not had the chance to get to a carpet remnant store).

I also plan on adding permanent "moving sliders" so I can adjust the sub placement during movie watching versus WAF placement.

[ShinAce]

My advice, use three feet. A tripod is inherently stable.

If your floor and or the slab don't match perfectly, there will always be a loose foot to introduce vibrations.

[kcoc321]

I would go with spikes. They are adjustable for any uneveness in the floor. PE has some inexpensive ones. Just epoxy set some threaded inserts. That's what I am going to use once I get a wet saw to cut the 'scrap' granite slab I got. I am also spiking the subs to the granite and put a small 1/8"d divit for the sub spikes into the granite to make sure they don't 'walk' on the granite slab.

I would go with 4 feet, but no more. I feel better about that than having a 70 pound chunk of rock only on three feet. I looked at commercially available granite platforms and that is what they all have.

[kcoc321]

I searching for some pictures I found this information regarding the resonance or lack thereof, of granite speaker platforms.

For speaker stands, isolation is largely absent from all designs. Cones actually provide no isolation, but a direct positive coupling to the floor. THis is not bad, as it reduced independent motion of the stand, and thus the speaker, but if the floor accelerates upward, the stand and speaker does too, and conversely. The majority of designs of good stands combat this by mass, reducing acceleration of the stand in any given vector, and also by rigidity, preventing internal distortion of the stand that amplifies a vibration with the release of stored elastic strain, when the stand is stressed. A solid chunk of granite does this better than most alternative designs. It has very high mass and is thus resistant to acceleration, it has high rigidity and requires very high energies to undergo elastic strain. On top of this, its heterogeneous granular nature means it has very good properties with respect to internal resonance. P-waves (all sound is a form of primary or secondary P-wave), propogate by standard wave laws, reflection, refraction etc. In a material like granite, waves are refracted and reflected chaotically as they pass through effectively unlimited numbers of constrained boundry layers between grains of varying density. In simple, since every grain is a different size and shape, and in contact chaotically with its neighbours of different properties, no standing waves function, or large scale resonance can exist. It gets a bit more complex, since a granite block can support L-waves, as can any object with a high shear modulus, and thus Love wave type resonance is possible, but is extremely low, and orders of magnitude lower than any structure made of metal shapes irrespective of filling or geometry. L-wave disipation is also extremely rapid, due to energy loss as heat generated through surface interaction of the miriad grains.

[grimmace19]

^ Even with a college education I can't follow that paragraph at all. Someone with a masters or better please fill me in on whether that statement speaks highly or poorly of granite slabs.

[kcoc321]

hehe....yeh it look at least a couple of cups of coffee to follow it. Here is the cruks of the paragraphs.

A solid chunk of granite does this better than most alternative designs.

The rest is for the techno-geeks :D

[grimmace19]

My thoughts on my own question are coming down to this... I will most likely just go with some "cabinet feet" from parts express. With the 60+ pound sheet of rock along with my sub weighing in at 47, there shouldn't be any problem with vibration being introduced when they are smashed into the carpet so hard. By not having a smooth design like a hockey puck, the silicone should bond better and they will look better. Once the project is finished (Thursday afternoon) I will give an update of how things worked for me. For a grand total of what will be under 10 bucks, any sort of improvement (even visually) will be worth it to me.

[Amherst]

The silicone should bond better and they will look better.

Silicone is actually a poor adhesive, it's main purpose is to create a seal, water or air.
If you are joining a masonry product (granite) to rubber or plastic the better bet would be to use a urethane adhesive such as PL for wood projects. Read the label it will indicate for use on masonry. For any visible over gluing use lacquer thinner on a rag to clean up around the joint before it sets. Wear a disposable glove when applying glue and cleaner.

[grimmace19]

Project Complete!

Alright, after I finally got the granite from my co-worker I slid the pieces under the subs without any feet. Because the granite pieces were around 60 pounds they sunk into the carpet quite nicely. After a good listen, the pieces alone eliminated all vibration from my fireplace and some from the upper vents. This not being good enough however, I took a wrench and tightened up the vents as much as possible. This stopped it a bit more but still had some rattle. I decided then to put the feet I ordered onto the granite. Using the silicone as originally planned worked quite well. The granite went back into place and like magic stopped all vibrations. The granite is so heavy that even though the feet are about 3/4 of an inch you cant even see them, the granite looks like it just hovers at carpet level.

Now for the sub sound itself. There wasn't much of a noticeable difference. The bass may be a bit more pronounced but nothing to write home about.

All in all, the sub feet cost me 5 dollars from parts express and the silicone tube was 3 bucks... for 8 dollars, it was well worth it. For all the vibrations I was able to eliminate you can't go wrong for under 10 bucks.