Springs Under My Speakers: What's Happening?

[fineMen]

Commonsense dictates that in a properly designed and made speaker, only the diaphragms should move. Any movement (vibration) of the baffle or the enclosure would colour the sound. ... That's the physics of it, according to me.

Newton's or personally your's? First of all, it's not the movement that makes sound, but accelleration. Any move makes sound which makes coloration? Not quite. If move (accelleration) was same homogeniously over all frequency, no coloration and so forth ad nauseam.

Thing is, physics doesn't dictate, neither should common sense, but science gives mostly extremely good guidelines how to look at a situation and in case identify a problem as to find a solution. Many don't have this toolset at hand. The education in physics starts at not shorter than 4 years on university and may take longer. It may accompany you a whole lifetime.

To put it metaphorically, you try to hammer a nail into a wall just using your bare fist - autsch! The craftsman uses the appropriate tool and doesn't understand what exactly your problem is refusing it. You say it's common sense which is anyway o/k. But a short change of perspective may remind of the poor craftsman beside who willingly or not witnesses the massacre.

 

[Ken Tajalli]

Newton's or personally your's? First of all, it's not the movement that makes sound, but accelleration. Any move makes sound which makes coloration? Not quite. If move (accelleration) was same homogeniously over all frequency, no coloration and so forth ad nauseam.

Thing is, physics doesn't dictate, neither should common sense, but science gives mostly extremely good guidelines how to look at a situation and in case identify a problem as to find a solution. Many don't have this toolset at hand. The education in physics starts at not shorter than 4 years on university and may take longer. It may accompany you a whole lifetime.

To put it metaphorically, you try to hammer a nail into a wall just using your bare fist - autsch! The craftsman uses the appropriate tool and doesn't understand what exactly your problem is refusing it. You say it's common sense which is anyway o/k. But a short change of perspective may remind of the poor craftsman beside who willingly or not witnesses the massacre.

Perhaps you could dumb-down the above a bit for my benefit.
My level of education is not as high as yours.
Acceleration was same homo what?
How could a baffle or a cabinet react homogeneously over all frequency, if the diaphragm is emitting different frequencies at different times?
If you are objecting to the phrase "Move", replace it with "vibrate"., "resonate"

 

[fineMen]

Perhaps you could dumb-down the above a bit for my benefit.
My level of education is not as high as yours.
Acceleration was same homo what?
How could a baffle or a cabinet react homogeneously over all frequency, if the diaphragm is emitting different frequencies at different times?
If you are objecting to the phrase "Move", replace it with "vibrate"., "resonate"

I'm a native speaker, but in another language. Sorry for the massacre of misspellings.

 

[Thomas_A]

Obviously you have put some effort and thought for your experiment and measurements.
I applaud you for that. But your experiment and results can not be gospel that one could apply to every speaker, every situation.
Commonsense dictates that in a properly designed and made speaker, only the diaphragms should move. Any movement (vibration) of the baffle or the enclosure would colour the sound. That's why most quality speakers employ solid, damped enclosures with hefty solid feet or stand.
Any compliance on mounting allows the cabinet to move (vibrate) as a reaction to movement of the diaphragm.
The heavier and the more solid the enclosure, the less of an effect we experience.
A solidly built speaker, on a heavy solid floor is best.
If we don't have a solid floor, then a virtual one is best compromise .i.e. a massive solid slab.
That's the physics of it, according to me.

Well. I am far from the first one doing such experiments and I have yet not seen one that contradict Newton.

 

[Ken Tajalli]

....... have yet not seen one that contradict Newton.

I like that!
Thanx Issac .

 

[fineMen]

Thanx Issac .

He's dead, actually.

The membrane accelerates which it needs to do as to generate pulsating air pressure aka sound.
This needs a counterforce aka "actio equals reactio".
The counterforce is, in any and every case, no exception, the accelaration of another bulk of mass aka "force equals mass times acceleration".

Please let this sink in .. .. it is just so.

Regarding your question let's approximately think of two extremes.

(w) The other mass is all of the speaker, except for the membrane and nothing else, floating in space.
(y) The other mass is whole mother earth assumed to be rigid throughout. (Flat earth needs that, right?)

You see, in principal there is no difference, as earth is actually floating (y) as we assume it to be the case with the speaker alone shot into orbit (w).

(y) is easily related to a rigid coupling to the floor, which is rigidly coupled (hope so) to the ground ... down to the iron (audiophile grade) core.
(w) is understood as a weak, soft, wobbley stand; the forces the stand can and will relay to somewhere else are so weak, that they can be neglected. This will be exemplified further.

The relative acceleration of the other mass depends on the proportion of the masses. A heavy bass cone might weigh 100grams,. Calculating it for (w) the according speaker will weigh about 40kilograms. So the ratio is 1 : 400 and so will be the ratio of acceleration.

For the acoustical impact the surface areas have to be taken into account. The surface area of the membrane is about 550cm^2 that of the front baffle 100cm*40cm - cone area = 4000cm^2 - 550cm^2 = 3450cm^2. Related to the cone area this yields a ratio of 6.3 : 1.

Finally relating the acoustical output of cone versus front baffle taking acceleration and surface area into account (expressed in dB): 20*log10(6.3 / 400) = -36dB.

The baffle area's contribution, if and when it obeys to Newton's laws lies 36dB below the cones contribution, altering efficiency or frequency response by not more than 0.1dB (o-point-one).

A second thought may be that the backwall of the speaker radiates the same sound, but counterphase, cancelling the effect out a bit further.

Conclusively, even if you do not couple the speaker to a virtually infinte mass (y) the effect of the speaker moving is utterly neglegible!

So, question is, how to virtually shoot the speaker into orbit? A soft stand, springs, foam the like, but how soft?

Basically this question can be answered by application of very basic high school knowledge. But I won't explicate the calculations, just believe me, nobodies life depends on it.

Get some suspension, a sponge, springs, felt, what have you. If the speaker box, seated on that suspension sinks in by about 1mm, and is still a bit wobbley, then the suspension is sufficiently soft, regardless of the weight of the speaker, to simulate orbital freedom.

Another word of caution. For some mysterious reason audiophiles behave uninformed if they, what they do, use more than three 'spikes'. This makes rattle, necessarily and practically cannot be prevented, whatever one does!

Do we have an agreement that you and others please won't hurt themselves anymore? Don't try to hammer a nail into a wall with the naked fist of audiology. Thank you so much!

(courtesy of Europe's public education system)

 

[Thomas_A]

He's dead, actually.

The membrane accelerates which it needs to do as to generate pulsating air pressure aka sound.
This needs a counterforce aka "actio equals reactio".
The counterforce is, in any and every case, no exception, the accelaration of another bulk of mass aka "force equals mass times acceleration".

Please let this sink in .. .. it is just so.

Regarding your question let's approximately think of two extremes.

(w) The other mass is all of the speaker, except for the membrane and nothing else, floating in space.
(y) The other mass is whole mother earth assumed to be rigid throughout. (Flat earth needs that, right?)

You see, in principal there is no difference, as earth is actually floating (y) as we assume it to be the case with the speaker alone shot into orbit (w).

(y) is easily related to a rigid coupling to the floor, which is rigidly coupled (hope so) to the ground ... down to the iron (audiophile grade) core.
(w) is understood as a weak, soft, wobbley stand; the forces the stand can and will relay to somewhere else are so weak, that they can be neglected. This will be exemplified further.

The relative acceleration of the other mass depends on the proportion of the masses. A heavy bass cone might weigh 100grams,. Calculating it for (w) the according speaker will weigh about 40kilograms. So the ratio is 1 : 400 and so will be the ratio of acceleration.

For the acoustical impact the surface areas have to be taken into account. The surface area of the membrane is about 550cm^2 that of the front baffle 100cm*40cm - cone area = 4000cm^2 - 550cm^2 = 3450cm^2. Related to the cone area this yields a ratio of 6.3 : 1.

Finally relating the acoustical output of cone versus front baffle taking acceleration and surface area into account (expressed in dB): 20*log10(6.3 / 400) = -36dB.

The baffle area's contribution, if and when it obeys to Newton's laws lies 36dB below the cones contribution, altering efficiency or frequency response by not more than 0.1dB (o-point-one).

A second thought may be that the backwall of the speaker radiates the same sound, but counterphase, cancelling the effect out a bit further.

Conclusively, even if you do not couple the speaker to a virtually infinte mass (y) the effect of the speaker moving is utterly neglegible!

So, question is, how to virtually shoot the speaker into orbit? A soft stand, springs, foam the like, but how soft?

Basically this question can be answered by application of very basic high school knowledge. But I won't explicate the calculations, just believe me, nobodies life depends on it.

Get some suspension, a sponge, springs, felt, what have you. If the speaker box, seated on that suspension sinks in by about 1mm, and is still a bit wobbley, then the suspension is sufficiently soft, regardless of the weight of the speaker, to simulate orbital freedom.

Another word of caution. For some mysterious reason audiophiles behave uninformed if they, what they do, use more than three 'spikes'. This makes rattle, necessarily and practically cannot be prevented, whatever one does!

Do we have an agreement that you and others please won't hurt themselves anymore? Don't try to hammer a nail into a wall with the naked fist of audiology. Thank you so much!

(courtesy of Europe's public education system)

I just want to add that spiking the speaker to mother earth so that any resonant point would exceed the speaker output > 20 kHz, is not possible. There is a resonant point where the speaker movement will be multiplied even if "spikes" are used. The wobbly mouse pad is better.

 

[fineMen]

I just want to add that spiking the speaker to mother earth so that any resonant point would exceed the speaker output > 20 kHz, is not possible. There is a resonant point where the speaker movement will be multiplied even if "spikes" are used. The wobbly mouse pad is better.

Confirmed! Picking up the omitted calculation referenced in my post
=> #346
one might estimate the resonance of 'spike' versus speaker mass against the floor.

Even a 'spike' behaves elastically, it cannot be infinitely rigid. It will sink in by a tiny portion especially because it is pointy. That point is weak because it necessarily doesn't have much material to withstand pressuring forces, right?

If the 'spike' sinks in by a micrometer, a thousends of a millimeter, the resonance of the speaker versus ground lies at about 650Hz. If it was only 100 nano meter (!) the resonance would still be 2kiloHertz. Not the least, what is the 'spike' standing on ...?!

In case you don't believe that that micrometer magic can happen, think of this guy. It is used to measure metal items down to the micrometer. It order to not spoil the measurement by irregular forces, the clamping force is meticulously standardized by a screw drive and a clutch. They don't do it for no reason; they are not audiophiles ...

 

[Ken Tajalli]

I just want to add that spiking the speaker to mother earth so that any resonant point would exceed the speaker output > 20 kHz, is not possible. There is a resonant point where the speaker movement will be multiplied even if "spikes" are used. The wobbly mouse pad is better.

You are correct that speaker cabinet resonances can not be controlled by spikes, solid floor etc. But nobody had suggested that we could.
Also, let's not forget how this thread started, The need to isolate the speakers from a vibrating floor.
- If the speaker is sturdy enough and massive enough, then the cabinet's reaction to the diaphragm movements, would be minimal. (high mass inertia)
Almost all the energy of music is in the lower notes. Add to that, that the biggest and heaviest diaphragm happens to be the bass driver. As the large and heavy bass diaphragm moves back and forward in air, the counter reactive force on the cabinet becomes tangible. This is why if the cabinet is heavy enough, this effect becomes less. Now imagine, if the cabinet was lightweight, and mounted on very compliant foam pads. Something like this would happen:

An exaggeration! But true enough. The soft carpet (feet) under the stand becomes detrimental. Hence, Spikes were used to bypass the carpet, to steady up the assembly.
-However, If the floor itself, happens to be something like a suspended wooden flooring (as in the case of OP's), then the speaker vibrations would transmit to and from the floor to the speaker. The floor would have its own resonances, hence his need to decouple them.
So, how should we decouple from the floor, but at the same time stop the rocking phenomena as in the picture above?
- Choose a sturdy, heavy speaker, then use decoupling under them. The mass inertia of the speaker, would keep it from rocking.
- If the speaker is lightweight, add mass! Then decouple. To add mass, the easiest way is a heavy slab bolted to the cabinet, then use decoupling to float the slab.
If the speakers are not sturdy, buy something else . . .

Extra reading on the issue:

The physics of feet — Magico Loudspeakers

Magico gets more customer inquiries about loudspeaker feet than anything else. It’s only natural. Audiophiles are constantly looking to make that next big improvement. And few system tweaks are easier – or more rewarding – than a proper set of new feet. While we understand the importance of loudspea

www.magicoaudio.com

Constrained-layer damping - Wikipedia

en.wikipedia.org

 

[fineMen]

You are correct ...

Extra reading on the issue:

The physics of feet — Magico Loudspeakers

Magico gets more customer inquiries about loudspeaker feet than anything else. It’s only natural. Audiophiles are constantly looking to make that next big improvement. And few system tweaks are easier – or more rewarding – than a proper set of new feet. While we understand the importance of loudspea

www.magicoaudio.com

Constrained-layer damping - Wikipedia

en.wikipedia.org

And you are not in linking in the b/s from "magico"--name says it all. I gave you full explanation with calculations above (post #346). Grant yourself a reading on basic physics, this time basic elementary school physics, not audio physics from the marketing department.

You irritate me, making me feel like the "Upper Class Twit of the Year" (Monty Python, 1972). All that writing to no avail, c'mon. You win.

 

[Ken Tajalli]

And you are not in linking in the b/s from "magico"--name says it all. I gave you full explanation with calculations above (post #346). Grant yourself a reading on basic physics, this time basic elementary school physics, not audio physics from the marketing department.

You irritate me, making me feel like the "Upper Class Twit of the Year" (Monty Python, 1972). All that writing to no avail, c'mon. You win.

Cool my friend.
we are all friends here, may not agree on everything , but friends.
Sorry if I have irritated you.
not my intention .

 

[MattHooper]

Just an update.

Again, these are just my impressions from throwing together different material combinations under my speakers, so take it FWIW.

One constant I've held is the isoacoustic Gaia 2 footers on the back of the speakers, with the front of the speakers set on outriggers, which have spikes that sit upon
a hockey puck. The hockey puck is mostly there to raise the front speaker slightly higher than the rear (apparently sounds best this way in terms of crossover design per Stereophile. I have tried the speaker at various raised heights, aiming it more straight or tilted back slightly, and always find tilted back sounds best).

I've had these basic materials to play with under the speakers:

1 1/4" granite base
1" brass cone spikes.
Hockey Pucks
MDF platform - two pieces of 1/2" MDF sandwiching sorbothane damping layer

I've been playing with various combinations, sometimes deliberately keeping the height of the speaker constant but changing the materials beneath the speaker. Sometimes deliberately raising or lowering the speakers as well (I like the scale of the soundstage when raised). I've kept the general position of the speakers constant - re-measuring every time I change materials to ensure the speakers are the same angle/distance from the seating position (to 1/8" of an inch).

Sometimes I even just switch the placement of the same materials. For instance I might have:

Granite base -> hockey pucks -> Spikes in to floor

but then try:

Granite base -> Spikes -> hockey pucks on floor.

And I've been making notes about the sound on each set up, so I don't forget my impressions. Generally speaking, it seems I can get the sound to alter between
tighter but leaner bass, usually accompanied by a "lightening" or brightening of the general tone of the speaker, or thicker, deeper, punchier sounding bass with a "darker" less bright tonality. As well as sort of in between these sounds.

Two general trends seem to be occurring:

1. Raising the speakers (aside from raising the imaging/soundstage) tends to somewhat tighten the bass, lose a bit of bass impact, and lighten the tone.

2. Whenever I use the spikes - that is when the last component are spikes in to the floor - I get more "room feel" for bass, a greater sense of bass punch and impact, and that darker tonality.

So for instance if, beneath the granite bass, I place either hockey pucks or the MDF/sorbothane shelf on the floor, so the spikes are going in to those instead of directly in to the floor, I tend to get the tighter bass/lightened tone. When I switch them so the spikes go directly in to the floor, the MDF or pucks sitting atop the spikes (and atop those, the Granite), then the bass becomes heavier and more punchy and the tone "darker."

So, if it's accepted for sake of argument I'm hearing the type of sonic changes I describe, it suggests the spikes are always responsible for transmitting more vibration in to the floor, which could account for the perceptual changes in sound.

Again, I don't have measurements, but one reason this appears to be more than just my imagination is: At points I've been having a problem with one speaker grill rattling audibly with heavy bass content. (When I take it off the rattle disappears, but I often like to leave it on). The rattling seems to track changes I'm making cited above. So for instance the most bass-heavy sound was just the granite bass spiked right in to the floor. With that I was getting plenty of rattling from the speaker grill from heavy bass content. But with the speakers "more isolated" on pucks/MDF shelf/raised higher, I wasn't getting the rattling for the same content, at similar volumes.

Basically, from my throw-spaghetti-at-the-wall experiments, based on my impressions, I think I'm aiming for a combination of "raised speaker" which is ultimately spiked to the floor.

To that end, I'm actually making a new granite base - I'll be taking two 3/4" thick pieces of granite, and between them placing a sheet of steel, with wall damping material on each side of the metal holding it all together. So a sort of constrained layer idea. That will be thicker, hence raise the speaker height, and then I'll try
spikes (maybe higher spikes) under that granite bass.

I also hope to try something else, which will be screwing the speakers (coupling, hopefully) directly to that new granite base, and then perhaps placing the Isoacoustic Gaia footers between the bass and floor. Just to see what happens.

 

[MattHooper]

I just want to add that spiking the speaker to mother earth so that any resonant point would exceed the speaker output > 20 kHz, is not possible. There is a resonant point where the speaker movement will be multiplied even if "spikes" are used. The wobbly mouse pad is better.

You are correct that speaker cabinet resonances can not be controlled by spikes, solid floor etc. But nobody had suggested that we could.
Also, let's not forget how this thread started, The need to isolate the speakers from a vibrating floor.
- If the speaker is sturdy enough and massive enough, then the cabinet's reaction to the diaphragm movements, would be minimal. (high mass inertia)
Almost all the energy of music is in the lower notes. Add to that, that the biggest and heaviest diaphragm happens to be the bass driver. As the large and heavy bass diaphragm moves back and forward in air, the counter reactive force on the cabinet becomes tangible. This is why if the cabinet is heavy enough, this effect becomes less. Now imagine, if the cabinet was lightweight, and mounted on very compliant foam pads. Something like this would happen:

An exaggeration! But true enough. The soft carpet (feet) under the stand becomes detrimental. Hence, Spikes were used to bypass the carpet, to steady up the assembly.
-However, If the floor itself, happens to be something like a suspended wooden flooring (as in the case of OP's), then the speaker vibrations would transmit to and from the floor to the speaker. The floor would have its own resonances, hence his need to decouple them.
So, how should we decouple from the floor, but at the same time stop the rocking phenomena as in the picture above?
- Choose a sturdy, heavy speaker, then use decoupling under them. The mass inertia of the speaker, would keep it from rocking.
- If the speaker is lightweight, add mass! Then decouple. To add mass, the easiest way is a heavy slab bolted to the cabinet, then use decoupling to float the slab.
If the speakers are not sturdy, buy something else . . .

Extra reading on the issue:

The physics of feet — Magico Loudspeakers

Magico gets more customer inquiries about loudspeaker feet than anything else. It’s only natural. Audiophiles are constantly looking to make that next big improvement. And few system tweaks are easier – or more rewarding – than a proper set of new feet. While we understand the importance of loudspea

www.magicoaudio.com

Constrained-layer damping - Wikipedia

en.wikipedia.org

As I've mentioned in the post I just made: I'm building a new thicker version of a granite base (constrained layer type, with a sheet of metal and wall damping material between the sheets of granite).

Two possible approaches would be:

1. Have the granite sitting directly on my floor as a "new" and hopefully more solid bass for my speaker to sit upon. Then some form of (partial) isolation is employed between the speaker and that granite bass - e.g. the speaker wits upon isoacoustic Gaia or some other from of partial decoupling. The granite giving a sturdier base to allow the decoupling effect.

2. Have the speaker with NO footers, but instead screwed directly in to the new granite bass. Then between the granite and floor, place some partial decoupler, like the Gaia or whatever.

On general principles, which would likely be better in terms of reducing vibration-born distortion?

If I understand the principle behind #2, the idea if directly coupling the speaker to a heavy granite base would be a way of adding mass to the speaker, so as to reduce (or change) the vibrational behavior of the speaker - hopefully less vibrating. But, would it work this way? Is coupling the speaker to higher mass beneath it similar to, say, adding mass to the walls of the speaker to reduce vibrations?

Thanks.

 

[Purité Audio]

It’s just your imagination, although physically raising or lowering your speakers might make an actual real measurable difference .
Keith

 

[MattHooper]

It’s just your imagination, although physically raising or lowering your speakers might make an actual real measurable difference .
Keith

So...not everything I'm describing is necessarily my imagination.

And you believe that there can't be a sonic influence between coupling vs uncoupling of speakers to a surface?

(Also, as I mentioned, I'm experiencing differences in speaker grill rattling depending on what I place under the speakers).

 

[Emlin]

So...not everything I'm describing is necessarily my imagination.

And you believe that there can't be a sonic influence between coupling vs uncoupling of speakers to a surface?

(Also, as I mentioned, I'm experiencing differences in speaker grill rattling depending on what I place under the speakers).

Please understand that I say this with the very best of intentions, but I fear that that you may be quietly driving yourself mad with your subjectivity. Really. I'm concerned. Time to bring some objectivity back, I think.

 

[Thomas_A]

As I've mentioned in the post I just made: I'm building a new thicker version of a granite base (constrained layer type, with a sheet of metal and wall damping material between the sheets of granite).

Two possible approaches would be:

1. Have the granite sitting directly on my floor as a "new" and hopefully more solid bass for my speaker to sit upon. Then some form of (partial) isolation is employed between the speaker and that granite bass - e.g. the speaker wits upon isoacoustic Gaia or some other from of partial decoupling. The granite giving a sturdier base to allow the decoupling effect.

2. Have the speaker with NO footers, but instead screwed directly in to the new granite bass. Then between the granite and floor, place some partial decoupler, like the Gaia or whatever.

On general principles, which would likely be better in terms of reducing vibration-born distortion?

If I understand the principle behind #2, the idea if directly coupling the speaker to a heavy granite base would be a way of adding mass to the speaker, so as to reduce (or change) the vibrational behavior of the speaker - hopefully less vibrating. But, would it work this way? Is coupling the speaker to higher mass beneath it similar to, say, adding mass to the walls of the speaker to reduce vibrations?

Thanks.

It would not matter much.

As mentioned before. Hypothetically you might get more tactile sensing in the floor with coupling but also potentially increase distortion. Secondly, very heavy objects on a springy floor may create nodes (pressurised as a guitar string) and change in frequency when excited.

 

[MattHooper]

Please understand that I say this with the very best of intentions, but I fear that that you may be quietly driving yourself mad with your subjectivity. Really. I'm concerned. Time to bring some objectivity back, I think.

Much obliged.

It's ok, I'm having fun.

My overall approach has led me to a deeply rewarding sound system (as many a guest agree upon hearing it), so I'm good, thanks for the concern. ;-)

 

[MattHooper]

It would not matter much.

As mentioned before. Hypothetically you might get more tactile sensing in the floor with coupling but also potentially increase distortion. Secondly, very heavy objects on a springy floor may create nodes (pressurised as a guitar string) and change in frequency when excited.

Thanks. We've acknowledged the tricky layers of variables involved here, so I was most curious about general principles. Good point about the heavy object/new nodes).
I have presumed that insofar as I'd actually be hearing richer bass when coupled to the floor, that this can be a form of distortion (excitation from the floor/feeling the bass etc) that I happen to enjoy. So I'm just playing with combos to see which I enjoy most.

 

[Ken Tajalli]

As I've mentioned in the post I just made: I'm building a new thicker version of a granite base (constrained layer type, with a sheet of metal and wall damping material between the sheets of granite).

Two possible approaches would be:

1. Have the granite sitting directly on my floor as a "new" and hopefully more solid bass for my speaker to sit upon. Then some form of (partial) isolation is employed between the speaker and that granite bass - e.g. the speaker wits upon isoacoustic Gaia or some other from of partial decoupling. The granite giving a sturdier base to allow the decoupling effect.

2. Have the speaker with NO footers, but instead screwed directly in to the new granite bass. Then between the granite and floor, place some partial decoupler, like the Gaia or whatever.

On general principles, which would likely be better in terms of reducing vibration-born distortion?

If I understand the principle behind #2, the idea if directly coupling the speaker to a heavy granite base would be a way of adding mass to the speaker, so as to reduce (or change) the vibrational behavior of the speaker - hopefully less vibrating. But, would it work this way? Is coupling the speaker to higher mass beneath it similar to, say, adding mass to the walls of the speaker to reduce vibrations?

Thanks.

If you are asking me, I have already voiced my opinion and reasoning.
#2 would isolate speaker from or to the floor-boards . meaning vibrations from the speakers can not travel to and from the floor boards. Granite, by default is dead acoustically . its sheer mass means it requires a lot of energy to disturb its stationary inertia , and its particle construction should not have a resonance.
So, layering it with steel plates is not necessary, but a compliant isolation between the floor-boards and the granite is.
If the cabinet has resonances, this method may control some of the lower frequency ones, but it would not be a cure.
This method, allows you to hear the speakers, not the floor-boards !

FYI, suspended chasis turntables, isolate in similar manner.
A heavy platter solidly attached to a chassis and then suspended, means vibrations from outside can not disturb the platter. The mass of the platter/chassis provides the stationary inertia , springs are the isolation.