[rbbert]

Well as I said, my speakers clearly sound better imperfectly decoupled, even raised 5/8" above my firm, rigid floor, than flat or with spikes and pennies.

I still think the forces generated by the woofers (pushing air away from the speakers) have to be either absorbed or reflected by the enclosure; if there is another option it is escaping me.  Your comment about the rigidity, etc. of the enclosure, or the coupled enclosure/floor combination, implies (to me) that those forces are sufficiently dampened by the enclosure material & design plus the added mass effect of the coupled floor and the enclosure's insulation (thus absorbed but sufficiently dampened to have no further adverse effects).  And I can also see where the passive radiators would have a positive effect here.  It seems to me, though, that elasticity in the horizontal plane (from ball/cup decoupling) could provide better  (and more elegant) dampening of those forces.

[John Casler]

Well as I said, my speakers clearly sound better imperfectly decoupled, even raised 5/8" above my firm, rigid floor, than flat or with spikes and pennies.

I still think the forces generated by the woofers (pushing air away from the speakers) have to be either absorbed or reflected by the enclosure; if there is another option it is escaping me.  Your comment about the rigidity, etc. of the enclosure, or the coupled enclosure/floor combination, implies (to me) that those forces are sufficiently dampened by the enclosure material & design plus the added mass effect of the coupled floor and the enclosure's insulation (thus absorbed but sufficiently dampened to have no further adverse effects).  And I can also see where the passive radiators would have a positive effect here.  It seems to me, though, that elasticity in the horizontal plane (from ball/cup decoupling) could provide better  (and more elegant) dampening of those forces.

IMO it is important to understand the differences between:

1) The reactive forces from the speaker driver that have the power, force and energy to cause the cabinet to resonate

2) The air pressure variations within the cabinet caused by the motion of the active drivers inside the cabinet

REACTIVE FORCES of the WOOFER(s)
This is quite simply the forces that are created when the woofer accelerates forward/backward against the air.  It is a combination of reactive forces from the air resistance to the cone, acceleration forces (in both directions) and momentums of the moving parts.

The IDEAL situation is that the basket and structure of the driver, and the cabinet are substantial enough to reduce ANY movement by them by not flexing or resonating by resisting.  This means they would need to have a resistive force equal or greater than the reactive forces produced by the driver.

Resisting the reactive forces causes the the system then to be more accurate in its wave launch and it will produce less distortion. 

This is why a Woven Carbon Fiber woofer cone will produce less distortion.  It is stiffer to reduce flexing (which is a type of deformation due to a lesser materials absorbing some of the energy and not translating it into sound energy).  It is lighter, which reduces the reactive forces that it creates so less resistance to those forces is needed.  It is also why "cast" baskets are often better than "stamped".  The resist deformation caused by reactive forces, and make the sound cleaner.

AIR PRESSURE VARIATION FORCES WITHIN THE CABINET

The second set of forces have little to do with reactive momentum of the drivers accelerations, but are created by the backside of the driver compressing and releasing internal air pressure within the cabinet.  While they are separate forces, they are also created by the active drivers and they might also have the potential to cause vibration resonance(s) to the cabinet.  The cabinet must also be sufficient to resisting these resonances.  In the case of VMPS speakers these forces are what causes the Passive Radiator to function.

So all that means that means that you will get a more accurate less distorted formation of a bass frequency the more rigid and resistive the cabinet is to reactive forces. It also means that damping/absorbing those forces will reduce that accuracy, by causing some of the energy to be dissipated from the task of creating the wave form.

However, why then would someone "decouple"?  Decoupling is sometimes a necessary evil "if" the resonances from the speaker cabinet are transmitted to the floor (usually wooden and suspended) to the degree that causes the floor or the combination of floor and cabinet, to actually also make a sound, which is also a distortion.  It really has no place is making a speaker itself sound better via absorption of resonances, since it would only serve to reduce the accuracy of the wave launch. 

I think some of the confusion with applying coupling and decoupling to components, is that with some components "decoupling" is certainly a preferred method of controlling vibrations.  A good example might be a Turntable.  It is certainly a good idea there.  Somehow the promoters of coupling/decoupling and damping devices have maybe been a little over the top on offering "either or" options for most all components and have not retained the actual and reasonable use for when and why to use them.

But as you said, there will always be a difference of opinion.  It is good however to know why one might be the better choice.

[rbbert]

... This means they would need to have a resistive force equal or greater than the reactive forces produced by the driver.

Resisting the reactive forces causes the the system then to be more accurate in its wave launch and it will produce less distortion...

This is a key point I think, but I also think you mean that the resistive force must be MUCH  greater than the reactive forces, and that's where the difficulty arises.  I don't know for sure, but it's possible that the horizontal elasticity in the ball/cup could increase that resistive force.  I'm afraid only experimentation could prove or disprove that (because it depends on the degree of elasticity), and I wish someone would have already done it.  The fact that there are some relatively new high-end speaker designs that utilize this system suggests that they have done that experimentation, but I certainly don't know that for sure.

[John Casler]

This is a key point I think, but I also think you mean that the resistive force must be MUCH  greater than the reactive forces, and that's where the difficulty arises.

You are 100% correct.  In order for one element to be placed in motion, the resistant element must have a greater resistive force to stay stationary.

  I don't know for sure, but it's possible that the horizontal elasticity in the ball/cup could increase that resistive force.

The more it increases the resistive force the greater the step toward coupling, and the further from decoupling.

I'm afraid only experimentation could prove or disprove that (because it depends on the degree of elasticity), and I wish someone would have already done it.  The fact that there are some relatively new high-end speaker designs that utilize this system suggests that they have done that experimentation, but I certainly don't know that for sure.

Often times a display of exotic resins, metals, woods and polymers tend to seem hi tech, but it you want to perform a simple decoupling experiment, simply cut a peice of thick carpet a little larger than the base of your RM40s.  Liberally Pledge the space on the wood floor where you will place the RM40.  Turn the carpet upside down so the pile is down and place the RM40 on the spot.  It will be a large step toward decoupling for a few days until the Pledge dissipates.  It will also allow you to hear if your floor is contributing resonances to your sound.

It is a fun experiment and very low tech, but might give you insight to whether or not to spend bigger $bucks$ to subdue wooden floor resonances passed from the speaker.

If you hear very little difference, then chances are no matter how high tech the materials, the benefits will likely not be there.  If you do hear improvements or even differences that might be improvements, then you might experiment with more decoupling means.

[rbbert]

Well I have the Herbie's Giant Fat Gliders (4 per RM-40) under them now.  Given the speaker's weight, I don't know how well decoupled they are, but they sound better than spikes/pennies or nothing.

Another AC manufacturer

http://herbiesaudiolab.net/spkrfeet.htm

[Roc]

I had this discussion with big John several years ago.  I too have RM-40's on carpet over concrete.  John advised to strongly couple the speakers to the floor by adding wts to the top of the cabinets.  So i put 200 lbs. on top of each.  This resulted in slighter tighter bass, but the real improvements were in the structure and clarity of mid's and trebble.
So i took the experiment one step further and made a new PR chamber with a heavy base plate, and much larger footprint.  Put pointed jack scews in the 4 corners and cranked then down onto the concrete, trying not to lift the speakers too much.  This made an even bigger improvement in the mids and trebble.  I was also able to level the speakers using this system.
The new PR chambers are completely different than stock, they are tuneable.  All 4 sides are closed, but have 5 large holes in each. By plugging 15 of the 20 holes the PR energy comes out on the side with the open holes.  This can make a big difference in bass response (having 2 bass paths) and can make the sound stage much wider/larger.  And with no PR energy aimed at the listener the sound is also more clear.

I use Herbies isolation devices under all of my electronics, and absolutely love them!  Tried the Square Flat Dots under my 626R's (HT system) with negative results.  Speakers wobble around and the sound got muddy and lost attack.  Removed them after a couple of days.

Just my 3 cents worth.

Dave

[rbbert]

As I emailed John a few weeks ago, I've settled on short (~1") spikes directly onto my floor.  Pretty good so far.  OTOH, with the (typical kind of) suspended floor in my home theater, decoupling definitely seems to work better.

[Roc]

Try the extra weights on top of the cabinets also.  You might like that too.

[dflee]

Just got around to reading and have time to reply.
I presently use an item made by Linn called Skeets. They're artificial concrete that have dimples for your spikes. My speakers weigh 110 lbs apiece and sound terrible on the wood floor suspended. The skeets work great. I am also looking at a product called Cerimax spike spotters.

Later
Don