Coupling-decoupling speakers

[KEW]

I have always been flummoxed by the contradiction of mounting philosophies for speakers and subs.
Auralex sells the Mopads and SubDude as isolation pads to decouple speakers.
Conversely, almost every speaker manufacturer sells their speakers with spikes often claiming they decouple a speaker, but penetrating through the padding offered by carpet to firmly contact the subfloor isn't really decoupling, is it!

Today, I came across this article here at Audioholics and thought I would bring it to the surface for any other suffering from teh same confusion I have been:

http://www.audioholics.com/education/loudspeaker-basics/speaker-spikes-and-cones-2013-what2019s-the-point

Once again, thanks to the gang at AH!

 

[FirstReflection]

The misguided notion that "spikes" or "cones" or "feet" of any kind work to decouple or isolate a speaker or subwoofer from the surface on which it is sitting is COMPLETELY BACKWARDS.

It's simple mechanical physics.

The mass (weight) of the speaker does not change. Nor does the force of gravity. Therefore, if you use a smaller surface area for the points of contact, all of that gravitational force is now being exerted via that much smaller surface area. The result is that the measured force at each point of contact will be much HIGHER than if there were no "spikes/cones/feet".

I've been trying to explain this simple fact to audio enthusiasts for years! The best "real world" example that I've been able to share has been the "cat or dog on your lap" explanation.

Anyone with a pet will be very familiar with this phenomenon.

Imagine that your cat or dog is sitting on your lap. That dog or cat can usually lay very comfortably on your lap - they don't feel heavy at all!

But now, imagine that your dog or cat stands up on your lap. All of a sudden, that very same pet has all of its weight being applied to your legs through only four much smaller points of contact (ie. the pet's paws).

Almost everyone has the experience where even a small, light-weight pet like a cat can induce discomfort or even pain when all of its weight is applied to your legs through only its four paws rather than when its weight is spread out over a large surface area when it is curled up, laying down on your lap.

So what happened? Did the cat or dog suddenly gain a bunch or weight when it stood up on your lap? Did the force of gravity suddenly increase? No! Of course not! All that happened is that your pet's weight is now being applied to your legs through only four points with MUCH less surface area. Therefore, all of that force is being exerted through those four small points (the pet's paws) and you FEEL a much greater force as a result - the pet's paws "dig" much deeper into your thighs!

So it's the exact same principle at work when you use spikes/cones/feet beneath your speakers. With spikes in place, the weight of your speakers being applied through only those four very small points means that those points "dig" much deeper into the surface beneath them.

Would you say that your pet is better "decoupled" from your leg when it is standing on its paws vs when it is laying down? No! In fact, you would say the exact opposite! Your pet is more obviously "coupled" to your lap when it is standing up!

Well it's the same thing with your speakers. Using spikes/cones/feet works to COUPLE your speakers/subwoofer to the floor or stand. The measured force at each point where the speaker feet make contact will be HIGHER. The downward force is not "spread out". Quite the opposite! The downward force is "focused" into those four tiny points! Same downward force, but MUCH LESS surface area over which that downward force is acting.

When that pet is standing on your lap, do you feel each little movement more or less? You feel each movement MORE, of course! Much more than each little movement when your pet is laying down on your lap with all of its weight spread out over a much larger surface area.

It's the same thing with your speakers!

With feet in place, each tiny movement of the speaker is "felt" much more strongly by the floor.

The whole idea of using spikes/cones/feet to "isolate" speakers or make them more inert is completely backwards and always has been! I don't know if everyone out there simply forgot 9th grade physics or what, but it's simple mechanics and very easy to explain in a scientific sense.

Would you rather lie down on a bed of 1000 nails or just four nails? In which situation do you think your would "couple" better to each of those nails? 1000 nails? Or just 4?

Simple stuff.

If you want to "isolate" your speakers and subwoofers, then you should NOT place all of their downward force into just four tiny little points with almost no surface area! You should do the opposite! You should try to spread the downward force over as much surface area as possible! Which is exactly what any "decoupling device" does through the use of a "cushion". A cushion simply being a device that displaces downward force by redirecting it in a horizontal direction.

 

[just-some-guy]

i agree. i have always known that.

i used to be of the theory that "coupling" the speakers to the floor gave a better sound. because, i figured, that the more solidly mounted the cabinets were, the less likely they would vibrate. and this is probably true to a minoot amount .
but, at the same time, this solid mounting also causes all kinds of things in the home to vibrate.

now, i decouple. but i don't get obsessed with it.

 

[sholling]

Spikes have their uses but decoupling isn't one of them. As the article points out they're probably better at minimizing the effect of Newtons 3rd law of motion.

 

[3db]

The whole idea of using spikes/cones/feet to "isolate" speakers or make them more inert is completely backwards and always has been! I don't know if everyone out there simply forgot 9th grade physics or what, but it's simple mechanics and very easy to explain in a scientific sense.

Would you rather lie down on a bed of 1000 nails or just four nails? In which situation do you think your would "couple" better to each of those nails? 1000 nails? Or just 4?

Simple stuff.

If you want to "isolate" your speakers and subwoofers, then you should NOT place all of their downward force into just four tiny little points with almost no surface area! You should do the opposite! You should try to spread the downward force over as much surface area as possible! Which is exactly what any "decoupling device" does through the use of a "cushion". A cushion simply being a device that displaces downward force by redirecting it in a horizontal direction.

I think the whole idea of the spikes/cones is to couple the speaker to the floor to reduce the amount of low frequency vibration from moving the cabinet around and thus interefering with the bass response of the speaker.

 

[KEW]

I think the whole idea of the spikes/cones is to couple the speaker to the floor to reduce the amount of low frequency vibration from moving the cabinet around and thus interefering with the bass response of the speaker.

I'm not sure I follow your wording, but coupling the speaker to the floor would better transmit low frequencies to the floor, using the floor as a sounding board to increase bass - assuming it is wood.

 

[sholling]

I'm not sure I follow your wording, but coupling the speaker to the floor would better transmit low frequencies to the floor, using the floor as a sounding board to increase bass - assuming it is wood.

Not coupling/decoupling - I think what he's referring to is using spikes to pin speakers in place so that they aren't moving even minutely in the opposite direction of the drivers (for every action there is an equal and opposite reaction). To the best of my limited knowledge that was the original sales pitch for spikes and something that the article saw as plausible. I saw an exaggerated example when I put my ULS-15 on a subdude - the darn thing was doing the hula. Needless to say I didn't leave it on the subdude.

 

[just-some-guy]

I saw an exaggerated example when I put my ULS-15 on a subdude - the darn thing was doing the hula.

was the sub moving on the subdude, or the subdude on the floor ?

 

[sholling]

was the sub moving on the subdude, or the subdude on the floor ?

The sub was moving on the subdude. Not a lot but it was an eyeopener.

 

[3db]

I'm not sure I follow your wording, but coupling the speaker to the floor would better transmit low frequencies to the floor, using the floor as a sounding board to increase bass - assuming it is wood.

My floor is a concrete basement floor which will not move. Even if its wood, it wood take alot of energy to buzz a properly constructed wooden floor

 

[FirstReflection]

And away we go!

Here come the oh-so-common, "concrete is inert and doesn't need decoupling", "coupling your subwoofer or speakers to the floor using spikes is good because it makes them more stable and thus, more inert" comments.

Sorry folks - those notions are completely backwards.

Concrete is not inert. Rather far from it, actually. Concrete shakes, bends, rolls and moves. Ever seen that famous film of the "rolling" bridge after the wind got it moving at its resonant frequency? Concrete is FAR from inert and it WILL move.

Concrete floors generally have more mass and are generally denser than wood construction. This means that it takes more energy to get them to move. But once they DO move, they transmit energy VERY effectively. Ever been in a concrete highrise? Yes, they are more "soundproof" than basic wood-frame construction. But if someone's subwoofer gets the concrete structure moving, you can here the bass thumping away throughout the entire building!

Concrete shakes and vibrates if you place your subwoofer on top of it without a decoupling device in between. If you have a concrete basement or live in a concrete building, it's extremely easy to witness. Try things out with the subwoofer on the floor. Then try things out with a decoupling device in place. It'll be very easy to notice the reduction in rattles and things vibrating (like windows). Anyone with a front projector that is ceiling mounted will easily notice that the image no longer shakes every time the subwoofer plays a strong bass note. Concrete is not inert. You still need to decouple, even if your building is concrete.

As for stability and making the speaker more inert by coupling it to the floor - it's the same notion as concrete: that by increasing the mass, you make the system inert. True enough, more mass requires more energy to get it to move. But just like concrete - once it DOES move, it transmits energy VERY WELL.

That swaying, rocking subwoofer on top of a SubDude? That's actually a GOOD thing. That subwoofer is obviously FAR from inert on its own. All of that shaking and rolling you are seeing when it is on top of a decoupling device would be transmitting energy directly into the floor otherwise! That's EXACTLY what a decoupling device is meant to do! It's meant to act as a cushion inbetween the movement of the subwoofer or speaker and the floor. The subwoofer or speaker can move all it wants, but the floor (and thus, also the walls and ceiling and adjacent rooms do NOT move because the decoulping device is acting as a "buffer".

Where exactly do you think all of that subwoofer's movement is going when you do not have the SubDude decouling device in place? Do you think all of that movement disappears? No! All of that movement is still happening, it's just being transmitted directly into the floor now! Your whole room and house is now shaking in sympathy with the sub - rather than the decoupling device absorbing all of that energy and distributing it over a much larger surface area and displacing much of it in differing directions.

Yes, it should be eye-opening. When you see a subwoofer or speaker rocking all over the place when there is a decouling device underneath it, that clearly indicates that it is ANYTHING but inert! It means that you desperately NEED decoupling in order to avoid having all of that movement being transmitted into your floor! And if it is moving so much that you are worried about it tipping over, that simply means that you need MORE surface area - ie. a larger decoupling pad and likely outriggers on the bottom of the speaker or sub so that the force is spread out over that larger decoupling pad's surface.

It's very unfortunate that people see a subwoofer or speaker moving around when it's on top of a decoupling device and conclude that it is "better" if that speaker is anchored to the floor so that it no longer visibly shakes! That's the exact opposite of what you should want! That speaker is the opposite of inert - it is producing visible movement. You should want to decouple it from your floor and avoid it transmitting that kinetic energy into your floor at all costs!

Backwards, backwards, backwards. But oh so common

 

[FirstReflection]

I realize how difficult it can be sometimes to wrap one's head around the whole decoupling thing. So I'd like to give a couple more examples of other "real world" situations that are more intuitive or easier to picture.

First, we need to agree upon the idea that it is preferable to have the energy of the speaker or subwoofer separated from the structure of the listening room. That is the principle axiom upon which everything else follows.

One way to better understand why you would want the energy of the speaker separated from the structure is to imagine that you are sitting in a car.

You are the observer. The car is the structure. And some moving object outside of the car is the speaker or subwoofer.

Now, would you rather that moving object outside of the car hit the car, move the structure of the car and therefore, move you as well? Or would you rather that moving object hit some sort of cushion or buffer, thereby allowing the car to remain pretty much still and therefore allow you to feel virtually nothing?

Since we're talking about audio, let's be even more clear. When that moving object hits the car, would you not agree that the car structure itself would make some sort of sound? If all you wanted to hear was the sound that the moving object makes, wouldn't it be objectionable for the car's structure to make sound of its own? Wouldn't that be distortion? Wouldn't that mask the sound that the moving object is making?

Let's be even more clear - you can still hear the sound that the moving object is making without it hitting the structure of your car. So how would it improve your ability to hear the sound of the moving object by having that moving object hit your car? Wouldn't it be better for the moving object to remain separated from your car so that you can continue to hear the sound of the moving object, but you don't get the sound that is created by the moving object hitting the car?

So let's go even further:

Say you are in a head-on collision. Would you rather have a spike come out of your steering wheel, or an air bag? Which one do you think would transmit more energy into your body?

Would you rather that your car have "crumple zones" or would you rather have it be extremely stiff and unable to "give" in any way? Which one would transmit more energy into your body?

Just because you can't SEE movement, doesn't mean that the energy disappears! That super stiff car frame with no "give" might not LOOK damaged, but YOU will be injured far worse than if your car has a "crumple zone" that deforms and absorbs the energy of the crash.

A spike that comes out of your steering wheel won't visibly move, but it's pretty darn easy to understand that you're going to be injured a heck of a lot worse by a spike coming out of your steering wheel rather than an air bag that deforms and cushions your movement.

So in audio, what we want is lower distortion, yes? We want to hear the sound that the speaker or subwoofer is making, yes? We do NOT want to hear other things in the room making sound when they are not supposed to, yes? Therefore, we want to separate the movement of the speaker or subwoofer from the room. We do not want the movement of the speaker or subwoofer to cause the room itself to make any sort of sound. We want that moving object outside of the car to never touch the car. We know that if it DOES touch the car, the car itself will make some sort of sound. It's the same thing with any speaker or subwoofer. The speaker/subwoofer is the moving object, the room is the car and you are still you

 

[sholling]

There is a time and a place where isolation is important but it isn't the be all and end all of speaker placement. When a front firing subwoofer is doing the hula on top of a subdude some small amount of energy that should be moving air is being wasted because the cabinet is moving in the opposite direction of the cone reducing the effective movement and velocity of the driver that's just simple Newtonian physics. On the other hand it's not an issue with a down firing sub and a subdude can do wonders in some situations. IMO a front firing subwoofer on a concrete benefits more from something that isolates while minimizing movement like the cork and hard rubber anti-vibration pads that I've suggested in the past. Carpet spikes are a different animal and are intended to lock a speaker or subwoofer in place and keep it from moving. By matching the length shape of the spike to the carpet and padding you can lock a speaker in place while letting the carpet isolate the speaker. How much spikes help is speculation, I've never seen measurement.

 

[3db]

And away we go!

Here come the oh-so-common, "concrete is inert and doesn't need decoupling", "coupling your subwoofer or speakers to the floor using spikes is good because it makes them more stable and thus, more inert" comments.

Sorry folks - those notions are completely backwards.

Come on over with an accelrometer and measure for yourself. I doubt very much that the amount of vibrations being transfered over to the concrete is goping to move it. Sure everything will shake give it enough force but from a loudpseaker. Give me a freaken break.!!!

Concrete is not inert. Rather far from it, actually. Concrete shakes, bends, rolls and moves. Ever seen that famous film of the "rolling" bridge after the wind got it moving at its resonant frequency? Concrete is FAR from inert and it WILL move.

Oh yes, I forgot. My speakers are capable of prodigous low frequency output that will cause a sympathetic vibration like the wind did on galloping Guerty. Reality check please!!

Concrete floors generally have more mass and are generally denser than wood construction. This means that it takes more energy to get them to move. But once they DO move, they transmit energy VERY effectively. Ever been in a concrete highrise? Yes, they are more "soundproof" than basic wood-frame construction. But if someone's subwoofer gets the concrete structure moving, you can here the bass thumping away throughout the entire building!

Concrete shakes and vibrates if you place your subwoofer on top of it without a decoupling device in between. If you have a concrete basement or live in a concrete building, it's extremely easy to witness. Try things out with the subwoofer on the floor. Then try things out with a decoupling device in place. It'll be very easy to notice the reduction in rattles and things vibrating (like windows). Anyone with a front projector that is ceiling mounted will easily notice that the image no longer shakes every time the subwoofer plays a strong bass note. Concrete is not inert. You still need to decouple, even if your building is concrete.


As for stability and making the speaker more inert by coupling it to the floor - it's the same notion as concrete: that by increasing the mass, you make the system inert. True enough, more mass requires more energy to get it to move. But just like concrete - once it DOES move, it transmits energy VERY WELL. .

Good grief man!! I don't know what they use in the concrete made in your area but I'll tell you that would take way more energy than what a sub can put out to get concrete transfer energy.

That swaying, rocking subwoofer on top of a SubDude? That's actually a GOOD thing. That subwoofer is obviously FAR from inert on its own. All of that shaking and rolling you are seeing when it is on top of a decoupling device would be transmitting energy directly into the floor otherwise! That's EXACTLY what a decoupling device is meant to do! It's meant to act as a cushion inbetween the movement of the subwoofer or speaker and the floor. The subwoofer or speaker can move all it wants, but the floor (and thus, also the walls and ceiling and adjacent rooms do NOT move because the decoulping device is acting as a "buffer".

Where exactly do you think all of that subwoofer's movement is going when you do not have the SubDude decouling device in place? Do you think all of that movement disappears? No! All of that movement is still happening, it's just being transmitted directly into the floor now! Your whole room and house is now shaking in sympathy with the sub - rather than the decoupling device absorbing all of that energy and distributing it over a much larger surface area and displacing much of it in differing directions.

Yes, let the sub rock back and forth and muddy up the bass response. Every audiohile's dream. I'd rather couple it to the concrete floor and let the density of teh concrete attenuate it quickly then have teh sub flopping around on a decoupling bad and interfer with driver excursion.

On a politer note, I agree with you that concrete can transmit energy but your scale of magnitude is way off. I' think it would be more detremental in sound quality to have a sub move around than to couple it to a concrete floor.

 

[billy p]

Some comedic releif before this starts to blow up. Will the size of the coin matter in all this(because size apparently matters) or is that a moot point and I love the fact they went so far as calling it a puck.....

Cheers, Bill...

 

[TLS Guy]

Come on over with an accelrometer and measure for yourself. I doubt very much that the amount of vibrations being transfered over to the concrete is goping to move it. Sure everything will shake give it enough force but from a loudpseaker. Give me a freaken break.!!!





Oh yes, I forgot. My speakers are capable of prodigous low frequency output that will cause a sympathetic vibration like the wind did on galloping Guerty. Reality check please!!



Good grief man!! I don't know what they use in the concrete made in your area but I'll tell you that would take way more energy than what a sub can put out to get concrete transfer energy.



Yes, let the sub rock back and forth and muddy up the bass response. Every audiohile's dream. I'd rather couple it to the concrete floor and let the density of teh concrete attenuate it quickly then have teh sub flopping around on a decoupling bad and interfer with driver excursion.

On a politer note, I agree with you that concrete can transmit energy but your scale of magnitude is way off. I' think it would be more detremental in sound quality to have a sub move around than to couple it to a concrete floor.

Sorry 3db, but there is lack of understanding of the physics of this issue all over this thread.

Sound travels through gas, liquids and solids, at varying speeds. Liquids and solids transmit sounds well, as a rule often better than gas.

The formula speed of sound = frequency X wave length holds for all mediums.

However there are two ways waves can travel.

The longitudinal wave, which is a pressure/pulse type of wave, and the traverse wave, which is like the waves at sea.

When we have a sub make the floor heave we think of the traverse wave. This can certainly occur in large span concrete structures and can lead to catastrophe, however it is unlikely to occur in your basement. However longitudinal waves can and do occur, which makes concrete basements less than ideal for sound reproduction. Certainly these longitudinal waves can transmit sounds over long distances within a concrete structure.

You may find this Wikipedia post informative.

 

[digicidal]

My floor is a concrete basement floor which will not move. Even if its wood, it wood take alot of energy to buzz a properly constructed wooden floor

It would depend greatly on the type of wood used and more importantly the density and how much insulation/airspace was underneath it. However, the problem (as I understand it - I'm not a physicist however) is not in the 'buzz' as this would most likely only occur at resonant frequencies for whatever materials were in direct contact. The issue is that transmission through a substrate (be it gas, liquid, solid) is not as dependent on those frequencies.

For example if there is a wave of 40Hz being transmitted to the air and a cement floor at the same time. I believe (again not a physicist here... just going from memory from college) it's entirely possible for this frequency to travel better through the floor than it did through the air. Air likes to get out of the way - and thus dissipates waves fairly quickly compared to denser substances.

So even though your floor is more than dense enough not to respond with it's own reflection into the air again from the vibrations travelling through it - it is very likely to carry that wave far enough that it can transmit up the walls and into your kitchen cupboards - where your dishes will definitely be able to make some sounds that will be audible.

This is why it is possible to often hear the sounds caused by the 'sympathetic vibrations' (my term here - probably not correctly used) resonating through the glasses/dishes long before you can actually hear the delivery truck pull up in front of your house. The engine rumble is actually better transmitted through the street, foundation, walls, etc... than through the air between the truck and your kitchen.

Maybe I'm wrong about this - but that's my limited knowledge coupled with some real-life observation.

EDIT: I didn't see that there was already a second page of responses - oops. TLS covered it much better and more scientifically than I - however, same concept. It should also be noted that BASS frequencies are of much more concern obviously than higher ones, since the waves are much, much longer.

 

[digicidal]

...Sound travels through gas, liquids and solids, at varying speeds. Liquids and solids transmit sounds well, as a rule often better than gas.

So the simple solution is not to decouple your device, but simply move your HT setup to the nearest mental hospital and set it up in an rubber room.

I guess it's a good thing I'm not a multi-billionaire oil baron with a penchant for the extravagant... because I think a diamond floor would be a nice aesthetic... but talk about transmission problems.

On the other hand, this chart clearly shows how similar the transmission rates of concrete are to wood - especially hardwoods. Great link TLS!

 

[TLS Guy]

So the simple solution is not to decouple your device, but simply move your HT setup to the nearest mental hospital and set it up in an rubber room.

I guess it's a good thing I'm not a multi-billionaire oil baron with a penchant for the extravagant... because I think a diamond floor would be a nice aesthetic... but talk about transmission problems.

On the other hand, this chart clearly shows how similar the transmission rates of concrete are to wood - especially hardwoods. Great link TLS!

It gets more complicated than that. All materials have a band pass effect on sound transmission, and it is different for different materials. Concrete has very unfortunate characteristics giving an unfortunate 1500 Hz ring to the sound it transmits. Wood is much kinder and warmer. So all concrete surfaces need well covering with sound impeding material.

 

[sholling]

Like anything coupling/decoupling theory can be taken to an extreme. I wouldn't want to have speakers on a bare concrete floor just like I wouldn't want bare concrete walls (HTIB as in HT In a Bunker? ) reflecting sound. But you don't want speakers shimmying either. A tower speaker sitting on 3/4" of carpet and padding is probably sufficiently decoupled and properly selected carpet spikes aren't going to transmit much if any energy - they may not even be penetrating all the way to concrete. On the other hand a down firing beast of a sub may need a SubDude or similar - carpet or no carpet.