[Big Red Machine]

I'm dabbling in thoughts and ideas while I start to ramp up toward building my next room.

I am looking at material densities right now for under the speakers and trying to decide if carving out separate platforms (on a concrete floor) of high density materials makes sense to place the speakers on.

Things like sand boxes, steel, Corian, concrete, etc. are all being considered and I have downloaded density tables, etc.

I would build the room's floor around these two spots allowing room for placement tweaks but they would not be influenced by the flooring materials and be "anchored" by the underlying concrete which is over 4.5 inches thick.

Do you think airborne vibrations are equal or higher than floor vibrations?
If you could do this, what would you do? I am open to $1000 expense to pull this off.
If it were to be accomplished, I wonder what the need for speaker "spikes" would be, if any.

[Big Red Machine]

Anybody?

[DaveC113]

Both floor and airborne vibration are issues, but the floor is obviously much easier to deal with. Even on concrete I think decoupling from the floor is far better and would suggest IsoAcoustics stands in that price range. I've tested them on a bunch of speakers and subs and they always result in better clarity in the bass through the midrange and a large decrease in sympathetic resonances from random stuff in the house.

[Big Red Machine]

I'm planning to make the floor inert under the speaker locations with MLV, MDF, sand, etc., so I don't have to go through too many gyrations above ground, so to speak.

[JLM]

Confused (not uncommon)...

Are you using floor-standing or stand-mounted speakers?

If floor is a concrete slab, why build up the floor from there? 

If you want to anchor floor-standing speakers directly to a concrete slab, consider doing what contractors do for connecting structural steel columns to concrete foundations: secure a wider baseplate to the speaker that you can fit anchors that would go directly into the concrete.  In the case of an existing slab you can use expansion bolts that ge hammered then tightened into holes predrilled in the concrete and baseplate.  The baseplate should be raised 1 inch above the slab, leveled, with grout added in-between to give good contact.  If you change your mind later the expansion anchors can be un-tightened and the grout chipped away.

If in addition you need to raise the speakers you can drill oversized holes into the slab, add reinforcing rods ("rebar") and form a pedestal to fill with concrete, and add conventional anchor bolts in the top then follow the above instructions for the baseplate/grouting.

If you want to isolate (I only recommend if the support is "soft" like a wooden floor) then any number of that style of speaker stands are available.  Adding a MLV/MDF/sand base is just a DIY variation of commercial products and you can expect results to vary.


Airborne vibrational energy always exceed floor vibrational energy in speakers using enclosures because the cone/diaphragm emits equal energy inside and outside the enclosure but the enclosure will leak energy (via cabinet walls or ports).  Grounding the cabinets to a huge mass (concrete slab) will only nominally reduce the vibrational energy from the enclosure (speakers rarely "dance").

There would be no need for spikes in these scenarios but this whole exercise iMO extends well into the "imaginary theory" end of the pond  and not worth your consideration.

[DaveC113]

I'm planning to make the floor inert under the speaker locations with MLV, MDF, sand, etc., so I don't have to go through too many gyrations above ground, so to speak.

Coupling speakers is a bad idea imo.

[JLM]

Wooden floors (especially if unfinished below and/or over a crawl space) can be nightmares as they can behave as giant resonators.  Adding insulation and plywood below would help.  The plywood would also help stiffen the floor.

[Big Red Machine]

Isolate the speaker section of floor from the concrete and the flooring of the room is my goal. Separate islands in the room as isolated from the concrete below and floor you walk on above.

I was thinking of a sand box with some density on of that like steel, then lead or MLV, and then floor boards to match the room but with a space between them and the room's flooring.

[mick wolfe]

I'm with JLM for the most part on this issue. A 4.5" concrete slab on a properly compacted sub base is ample mass loading for virtually any speaker or system. If you think that isn't massive enough, make it a 6" slab. Bottom line, I wouldn't commit to carving out dedicated areas for your speakers. Systems changes down the line could paint you in a corner in this regard. The big question is what will you cover the concrete with if anything? If it's carpet, I've had excellent results simply spiking through the carpet/pad directly to the concrete. Now if the floor is to be covered with wood, tile or just left as a stained finished concrete, I'd start with something as simple as Herbie's Gliders and experiment with various forms of decoupling from there. With wood, tile or concrete you'll probably still need an area rug of some ilk in the mix.

[Big Red Machine]

Both floor and airborne vibration are issues, but the floor is obviously much easier to deal with. Even on concrete I think decoupling from the floor is far better and would suggest IsoAcoustics stands in that price range. I've tested them on a bunch of speakers and subs and they always result in better clarity in the bass through the midrange and a large decrease in sympathetic resonances from random stuff in the house.

Yeah, Dave, was thinking about making the floor the equivalent of the Iso mount and if I pulled it off it would be out of sight and flush with the room flooring. If I make a large enough pad to allow for speaker movement side to side and in and out, then if different speakers come along I can still work with them (floorstanders).

[DaveC113]

Yeah, Dave, was thinking about making the floor the equivalent of the Iso mount and if I pulled it off it would be out of sight and flush with the room flooring. If I make a large enough pad to allow for speaker movement side to side and in and out, then if different speakers come along I can still work with them (floorstanders).

I suppose you could build the IsoAcoustics stands into the floor... they are too tall for some speakers for sure. I'd test a few things before making major changes though, IME the Iso stands do work really well though I've never tried the $$$ solutions like Stillpoints.

[charmerci]

Seems like the simplest, most effective method would be carpet over an inert bass (dense foam) and then spike the speakers through to the concrete.

[JLM]

Providing a separate slab on grade concrete pad from the rest of the concrete floor would theoretically be a step backwards as you'd be reducing the mass of what the speaker is supported by.  Reduced mass means higher resonant frequency and less energy needed for it to resonant. 

Yes you could do this and recess an isolating platform, but you'd be going from coupled to de-coupled support.  Your call but I can't believe it'd sound better.  Plus you'd be locked into a speaker location, size/weight of speakers, and would have to pull them out and patch the floor then repeat installation process when you make such changes/move.  And you'd have a joint in the floor even if you made it flush with the rest of the floor.

I'd worry way, way more about room size/shape and acoustic isolation of the room from the rest of the universe.

[Big Red Machine]

Seems like the simplest, most effective method would be carpet over an inert bass (dense foam) and then spike the speakers through to the concrete.

Yeah, like JLM mentioned, I wonder if construction adhesive would be an adequate anchor for something like concrete stepping stones or other material to bond the structure to the concrete floor? This would attach the speaker locations to something dense. I was trying to conceive of a way for the concrete to not transmit from one speaker to the other by having enough mass under each speaker to still act like "earth".

I was thinking an area wider and deeper than my speakers so that if some day I had some Wilson Alexandria's at 600 lbs each (or other massive speakers), I could support them but also keep the floor from vibrating deep down. But I would probably need footer depth concrete to make that happen.

[Bob2]

In one of the labs at the University where I worked the need for a vibration isolated floor was needed for Atomic Force Microscopy.
Engineers determined that the vibrations from vehicles on an adjacent road and a large vacuum pump about a block away were causing vibration problems in the lab. The floor was replaced and had a perimeter slab 10 inches thick. In the center of the lab was a slab that was 10 X 12 ft That was 8 feet thick.

To keep it out of contact with the rest of the floor at the perimeter a 1 inch gap was filled with a rubber compound.

Seemed to work. I have also seen this in stamping plants.

This is of course way overkill for your needs but why not isolate most of the floor in the room instead of transferring the energy to the rest of the house.
This would allow for placement of gear anywhere instead of only in a certain area.
Just a thought..

[JLM]

Please reread my posts, I didn't mention adhesive.

Good idea Bob, just isolate the slab of the entire room with saw cutting and installing a 1 inch expansion joint.  But this will cost well above $1,000.

[Bob2]

just isolate the slab of the entire room with saw cutting and installing a 1 inch expansion joint.  But this will cost well above $1,000.

Hey Jeff. Yeah that can get expensive but how can you put a price on great sound? 

Sorry I missed your get together. Seems I'm busier now than when I was working. Would like to get together when possible!

[JLM]

Will let you know when/where our next meeting is.

On second thought, saw cutting the slab at the room boundary provides for isolation from outside vibrations and in some tiny way could make isolation between speakers worse.  We live in a small country subdivision on 2.5 acres.  The only ground based vibrations we've ever felt was when I had gravel added to the driveway and asked that they roll/compact it.  50 feet away it shook the house enough to scare the cat.

For my study (dedicated audio front/office back basement man-cave) I used insulated staggered stud walls for interior partitions, insulated fiberglass exterior door with weather seals, and lined/insulated flexible ductwork - all of which work very well (practical and nearly no cost solutions).  My downfall was the ceiling (recessed light cans and drywall ceiling directly attached to bottom of floor trusses).  Builder balked at adding gauge metal furring strips and the cans, while rated air-tight and to be on contact with the insulation, allow sound to go up and down).  Could be fixed with track lighting and a second drywall layer with green glue if it bugged me too much.  But my initial impressions was an almost spooky level of sonic isolation.  Anyway, that's the kind of features where I'd put your $1,000 isolation budget (and probably have money left over).

[Big Red Machine]

I'm only concerned with the floor right now. Blank pallet and I start on the floor.
I always use a foam base and OSB over that then flooring. That's why I need to find a better way to anchor the speakers than on some flimsy sub-floor of foam and OSB.

I had considered cutting the concrete but that will mess up my footers for beam supports, so I'm not going there.

[Big Red Machine]

Please reread my posts, I didn't mention adhesive.

never said you did. you suggested using the concrete below for anchoring. i'm wondering how best to do that short of concrete lag bolts. today's adhesives are pretty darned good.