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What frequencies does this material dampen?
Follow Ups:
When you use compressive materials for damping, such as sorbothane etc, you are setting up a spring system. To be effective it must be properly loaded or it will not function as a damper. An analogy : putting Cadillac shock absorbers on a VW & visa-versa. The best way to reduce shelfborne vibration input to equipment is to isolate the unit from its' shelf. A good method is using archery target arrow points for a 3-point isolation instead of the stock 'legs' of the unit. The contact area of the unit with the shelf then becomes the total area of the arrow points, which is miniscule. The arrow points should rest on metal disks so they do not dig into the shelf. This does not address airborne vibration, but neither do the other materials such as sorbothane, etc.Happy Listening !
Cones and archery points (a great idea I have used myself) cannot *isolate* a component from its shelf--they *couple* the component to the shelf.This often (though not always) sounds better, probably because the shelf and unit are more rigidly coupled together and the unit behaves as if it were more massive than it is. You are simply trading one form of vibration for another, and the new one might sound better.
Sorbothane is a proprietery material that actually transforms vibrations into heat. (It's used a lot in bike seats, etc.) Therefore, it does islolate to some degree. I have actually used Sorbothane pucks under the boombox by my son's drumset--it skips less that way!
An inner-tube type platform will do better, as it will isollate down to a lower frequency.
Well, here we go again. If you REDUCE the contact area between two items you are ISOLATING the two items; if you INCREASE the contact area between two items you are COUPLING them. It's simple High School level physics, think about it. If you use an inner tube as a cushion you are again setting up a 'spring system' and the 'firmness' of the inner tube MUST be closely adjusted to the weight of the load or the 'spring system' will not function properly.Happy Isolating !
If low frequencies can travel across the contact point, regardless of how small it is, there is no isolation.Of course a spring must be adjusted to the load in order to create an effective mechanical low pass filter. Such a device, regardless of how large it is will *not* couple the low frequencies, it will isolate them.
I suggest reading Doug Blackburn's excellent piece on cone footers over at soundstage.net.
Springs do isolate but that isolation is frequency dependent.From 0 Hz to the spring system's resonant frequency, the system passes all vibration, and actually increases the amount of vibration it is passing as the frequency increases, reaching a maximum at the resonant frequency - after all, that's what "resonance" means. At resonance it can actually be passing many times the level of vibration actually entering the system. From the resonant frequency on up, the amount of vibration passed starts to reduce finally reaching unity - passing the same level of vibration entering the system - at a frequency approximately 1.4 times that of the resonant frequency. As frequency continues to increase, the amount of vibration passed continues to reduce so we finally start to get some isolation, with the degree of isolation provided increasing as frequency continues to increase.
Coupling devices like cones don't have a mechanism or process for shedding vibrational energy so they pass whatever vibration gets into the cone. However the vibration entering the cone is dependent on things like contact area and that introduces an element of frequency dependence. My feeling is that the smaller the contact area, the more the lower frequencies have difficulty entering the cone. That's why there is often an observed difference in sound when someone reverses the vertical orientation of the cone, and the reason some manufacturers recommend that the point be placed in contact with the surface (platform or component) exhibiting the most vibration. Cones will pass whatever gets into them so they are couplers.
But it's worth noting that we don't call springs 'couplers' because they transmit perfectly at frequencies below 1.4 times their resonant frequency and that we don't call cones 'isolators' because they fail to transmit all vibration in the surface they are in contact with. We call springs 'isolators' because they isolate when they're working properly, and we call cones 'couplers' because that's what they do when they're working properly. There are no perfect isolators or couplers, but to regard one kind of device as the other simply because it doesn't work perfectly and, at frequencies outside of its operational bandwidth, it passes some vibration we would prefer it didn't, or blocks some that we would prefer it did, is missing the point.
It's also worth noting that isolation isn't necessarily a good thing and coupling isn't necessarily a bad thing. Shannon Dickson makes the point in his excellent "Bad Vibes" article (see Paul Tobin's post for a link) that perfect coupling would actually give the best results we could achieve - at that point the component and the supporting shelf or rack would actually be at rest in relation to each other. We can't achieve that and so we strive for the best result we can achieve, noting always that what we're after is a result that we find pleasing which means there is an element of personal taste involved.
I think what works best probably usually involves passing a minimum of vibration in each direction and, depending on frequency, it can sometimes be easier to achieve that with isolation and sometimes with coupling. I'd rather couple than try to isolate if the problem frequency of vibration was close to the resonant frequency of the spring system I had available to use for isolation, simply because it's better to pass the vibration unamplified through a coupling device than amplified through a spring system at resonance.
David Aiken
Springs do isolate but that isolation is frequency dependent.I understood this. A good audio "spring" will start operatining (i.e. acting as a filter) at very low frequencies. If 1 or 2Hz becomes an issue, we're probably talking about an earthquake and audio considerations will no doubt rapidly become inconsequential.
;-}The point I was trying to make was to counter the suggestion that cones provide isolation due to the small contact surface. Which brings us to...
...My feeling is that the smaller the contact area, the more the lower frequencies have difficulty entering the cone.
With cones (or spikes, etc) between a shelf and a component, if you cause the shelf to move vertically at a very low frequency, the rigidity of the cone will pass this motion to the component, regardless of how small the contact surface is. It is the rigidity that passes the vibration.
This is easily demonstrable by raising and lowering the shelf in your hands (as similarly pointed out by Doug Blackburn in his excellenct "The Myth of the Cone Footer". The component will match the motion of the shelf exactly.
There may well be benefits to using cones or at least they may provide a change in sonics the listener appreciates. I do not however, believe isolation from low frequencies is the reason.
Anything rigid, whether it be a cone or a cylinder or a cube, provides a vertical link between the component and the shelf that vibration can enter from either side and travel through to the other side.2 things are at play.
First, not all vibration is in the vertical plane and I actually suspect most isn't. The rigid object will transfer a vector force of any vibration present on one side to the other, but the size of the vector force decreases as the axis of the vibration shifts from vertical to horizontal. Most of a vertical vibrationary force will be transmitted but very little of a horizontal force will. I suspect the bulk of the vibration causing us problems is more horizontal than vertical in axis, especially in shelves, since it will tend to propagate along the long axis which allows more flexing.
Second, contact area does make a difference. Consider the effect of a large wave striking a flat breakwater with a large, exposed contact area vs the same wave striking a pier support which has a small exposed contact area. The wave wraps around the pier support which absorbs very little energy from the wave because the width of the support is very small in relation to the wavelength of the wave. On the other hand, the breakwater which has a contact width which is much larger and may even be larger than the wavelength of the wave, cops it full on. I suspect that what happens when a vibratory wave contacts the tip of the cone has some similarities to what happens when a wave strikes the pier support, and what happens at the flat of the cone which is much wider and has a larger contact area, is closer to what happens in the breakwater example. We also see this sort of behaviour with sound striking an obstacle - the result depends on the width of the object relative to the wavelength of the soundwave. Given that vibration is a wave phenomenon, I see no reason to believe that similar behaviour won't occur and I suspect that kind of thing is the explanation for the observable difference in result that comes with reversing cone orientation.
Put the 2 together and you have a combination of vector and wavelength factors affecting how much vibration will enter the cone to be transferred to the other side.
Dickson also makes the obvious comment in his "Bad Vibes" article that one can influence the results with cones by placing them at points on the shelf which are 'null areas' - areas where the amplitude of flexing is lowest - because there is minimum vibration to be transferred at those points.
David Aiken
Dave,In order for relative motion between the spike/cone and shelf to happen in the horizontal plane, the vibration forces have to overcome static friction, and the frictional force is not directly dependent on contact area. Remember your high school physics. The frictional force is just the product of the friction coefficient (material dependent) and the perpendicular (vertical) force holding the surfaces together.
There can be a secondary dependence on the contact area if one of the surfaces deforms under load, producing mechanical grip that adds to the frictional forces. This happens with rubber tires on the road, for example. This could also happen with a spike or a cone, depending on the hardness of the material it's sitting on. So if you compare a metal spike or cone (small contact area) to a round metal puck (large contact area), the spike or cone will have an equal or greater static friction force that must be overcome before there can be any relative motion.
Second, contact area does make a difference. Consider the effect of a large wave striking a flat breakwater with a large, exposed contact area vs the same wave striking a pier support which has a small exposed contact area. The wave wraps around the pier support which absorbs very little energy from the wave because the width of the support is very small in relation to the wavelength of the wave. On the other hand, the breakwater which has a contact width which is much larger and may even be larger than the wavelength of the wave, cops it full on. I suspect that what happens when a vibratory wave contacts the tip of the cone has some similarities to what happens when a wave strikes the pier support, and what happens at the flat of the cone which is much wider and has a larger contact area, is closer to what happens in the breakwater example. We also see this sort of behaviour with sound striking an obstacle - the result depends on the width of the object relative to the wavelength of the soundwave. Given that vibration is a wave phenomenon, I see no reason to believe that similar behaviour won't occur and I suspect that kind of thing is the explanation for the observable difference in result that comes with reversing cone orientation.
Your analogy doesn't really hold up for two reasons. One is static friction, as described above. But also, the wavelengths are very long at typical frequencies of vibration. The propagation velocity in typical shelf materials (wood, glass, steel) is 4000-6000 m/s. Typical sources of vibration include motors, refrigerator compressors, and transformers, which produce 60 Hz and harmonics. Also CD and DVD transports, with frequencies in the 200-1600 rpm range. And bass frequencies which couple from the air and floor during playback. That means the wavelengths are anywhere from a few meters to 100m. So I think it's safe to say that under most vibrational forces, the whole shelf moves as a unit.
Dave
We really are getting beyond my physics at this point, but I don't think the whole picture is as simple as you're painting it.Accepting what you say about propagation speeds and the frequencies/wavelengths concerned, I still think the assertion that the "whole shelf moves as a unit" is a simplification. The whole shelf is definitely moving as a unit if, by that, we mean that the movement at any point in it is related to the movement at any other point. Given that the movement involves flexing, not all of the shelf is moving in the same direction at the same time, or even at the same speed. We don't have a rigid structure simply shifting back and forth uniformly at all points so whatever motion it imparts to a component resting upon it and coupled to it by 3 or 4 cones is also going to be a bit more complex. There's also the point that the shelf is effectively anchored at it's own points of support and its motion at those points is going to be different to it's motion elsewhere where it isn't anchored.
The shelf is moving as a unit and all aspects of the shelf's motion are definitely related to each other, but we don't have movement in unison at all points in the shelf.
Given that the mass of the component is acting vertically on the cone and we have a minimal area contact, the tendency is going to be for the cone to remain aligned vertically as the shelf flexes. There will be a tendency for a given cone to slide as the shelf flexes under it, but not all points of the shelf are going to be flexing in the same direction at the same time. And since we have at least 3 cones located at different points on the shelf, and the cones are constrained at both ends due to contact with the component as well as the shelf, and the shelf motion is one of flexing, there is going to be movement of the cones in relation to at least one of the 2 surfaces they are in contact with, and possibly both. If all 3 shelf contact points are flexing in the same direction, the tendency will definitely be for the cones and component to slide in that direction but it's unlikely that all three shelf contact points are flexing in the same direction simultaneously so the tendency will be for each cone to slide in a different direction but their freedom to do so is limited by their contact with the component. The end result of that is that the ability of the cones to move in conjunction with the shelf is constrained to some degree.
Which is what we would expect since we can't achieve perfect coupling. Without perfect coupling the shelf/cones/component simply aren't going to move in unison.
And we also have to consider that the shelf isn't the only thing moving. The component has its own vibratory state and the cones are coupling that state to the shelf just as they are coupling the shelf's state to the component. Once again it's unlikely that the vibratory state of the shelf and the component are going to match perfectly so at some times they will be working against each other and at other times in concert with each other. The cone's tendency to move in conjunction to the shelf will be modified by its other tendency to move in conjunction with the component, and vice versa.
Upshot of all that: we have imperfect coupling and the combination of factors affecting what is going on is messy. It simply isn't as simple as CD wants or as you suggest and I still believe there are definitely frequency dependent aspects to what happens. My wave/pier support analogy may not be correct, but that doesn't mean that my belief that there is frequency dependent behaviour is wrong - it would simply mean that if there is frequency dependent behaviour, the explanation is different. Even if there is nothing frequency dependent going on, things aren't going to be as simple as you suggest once you factor in shelf flexing, at least 3 cones, contact at both ends of the cone, and the different rates/directions of vibration in the component and the shelf.
There are simply more forces and factors involved than the coefficient of friction between cone tip and shelf, surface area of contact and any deformation aspects, and the vertical force arising from the mass of the component supported by the cone. We also have to consider, at the very least, those same factors at the cone/component interface, angular displacement in both shelf and component due to vibratory flexing, the change in the coefficients of friction with angular displacement, possible flexing in the cone itself, and the influence of at least 3 cones with movement constraints top and bottom. Your account of the forces operating at the cone tip is most definitely incomplete and overly simplified.
I've said it before and I'll say it again now: I'd really like to see a good account of what actually is happening in a real life situation with cones. I've seen some explanations that are patently wrong, and some that are right as far as they go but simply incomplete, which is where I'm placing your posts. And among the things that account should deal with are the observations of many including myself that different cone materials and shapes have an impact on the results that we hear. It's those differences, plus the difference that more than a few of us hear when we reverse the cone orientation, that have me convinced that something frequency dependent is going on. I could be wrong and those differences may well be the result of something else, but I'd really like to get an understanding of what is contributing to those differences. Nothing in this thread has helped me there.
David Aiken
I used to sell high end scientific scales. We recommended a marble platform with cones to the floor, and cones to an intermediate shelf and cones to the scale. And the scale would be hooded to prevent air from further vibrating the scales.A single layer of cones can only mass load the equipment above it to a very small surface area contacting the lower mass. Each mass will vibrate based upon its own material characteristics and the energy acting upon it.
I built a Viola in high school and the front and back of the Viola is what vibrates. The thickness varies across the surface meaning it is in no way uniform. This allows the best mixture of frequencies to be excited by the strings action upon the bridge soundpost and bass bar.
The idea that vibrations are limited to vertical or horizontal movement seems to be simple nonsense to me. I expect objects to have 3 dimensional energy impact upon them and react in kind.
Different materials have different resonance patterns so I would expect no two materials of cones to sound the same, nor cones of differing mass of the same material to sound the same.
Cheers!
but I used to play classical guitar, knew a guitar and lute maker, and had him build a guitar for me. I watched numerous instruments being built, including soundboards being voiced by shaving and strutting.You're right - it isn't all horizontal and vertical motion or, rather, it is but it's movement that has to be defined in 6 degrees of freedom (up/down, left/right, and front back) and the movement is even more complex because the shelf/soundboard is relatively fixed at some points and flexing elsewhere. There's a lot going on, especially when the soundboard or shelf or whatever is being excited by vibration from a number of different frequencies, and also excited at different points by different frequencies.
I saw a quote somewhere recently - it may have been on another board here - where someone had said something like "In theory there is no difference between theory and practice, but in practice there is a difference." Good accounts that are really useful explain that difference also.
David Aiken
I appreciate your discourse on this issue. I do have a question, prompted by the discussion of materials and their properties. Where can I find a description of the properties of different materials used in audio to couple, uncouple, or absorb/translate vibrational energy? Are there materials better at deflecting or absorbing energy relative to a certain band of frequencies vs another material? If certain materials convert mechanical energy into thermal energy, wouldn't that be preferable? Thanks in advance for your replies.
As far as uncoupling or isolating goes, probably the simplest criterion is the resonant frequency of the spring system being used. Isolation will commence at a frequency 1.4 times the resonant frequency of the spring system and improve as frequency increases. For that reason it is desirable to get the resonant frequency of the spring system as low as possible so that isolation starts as low as possible.There's endless argument here over materials and properties. You'll find the people who like heavy materials - lead fills for stands and racks, and granite/marble/stone slabs for placing things on, and then you'll find people who believe the ideal is the use of structures which are light and rigid. I have a leaning towards the light and rigid side of things but the Dynaudio stands I use for my speakers come from the heavy school and work very well with the speakers. I use a Grand Prix Audio Monaco rack which in many ways is quite light and rigid but Grand Prix Audio recommend mass loading the vertical columns. While I didn't use lead for health-related reasons, I did use a steel fill which is a bit over twice as heavy as sand and that works fine too. I think you can get success with either approach, and probably with hybrids as well, provided you know what you're doing and do it well.
There's also endless argument over the use of 'tone woods' like maple which sustain and can add their own resonance to the sound, imparting a richness that you would otherwise not get, and the use of dead materials which add little or nothing.
While one can argue endlessly over which approach is better and why, and a lot of that seems to come down to which theory you want to believe, at the end of the day we're playing with something that affects musical sound and we all have our own ideas of what that should sound like. There's an element of personal preference at play here and not everyone likes the same thing. I doubt there is any overall agreement.
And I say that knowing that a majority of people talk about 'isolation' but many seem to have no idea of what that really means since they talk about cones isolating when what they do is to couple, which is the reverse of isolation. Life might be a lot easier if we talked in general terms about 'resonace control' instead of using 'isolation' as a general term for what is going on. Then perhaps we could start to use the term 'isolation' more correctly and more uniformly and also have some kind of intelligent discussion about what we're all trying to do and even acknowledge that there is an element of personal preference in which particular result we each individually think is best.
I can't refer you to a document that gives details of the properties of various substances which are relevant to their sonic performance, nor can I even give you a list of which properties are the most important. I don't have the technical knowledge in the area to be able to do either and, as I said, I doubt there's any real agreement as to which properties/substances are better since not everyone is chasing the same result.
All I can suggest is that you take the time to experiment with a few different sorts of cones and soft footers like Vibrapods and the like, and also some of the bearing type feet, and also see if you can listen to a few systems on different sorts of racks and platforms to start to get a feel for things yourself. You should start to get a feel for things and also a feel for which style of approach you like. Then decide whether you want to try a DIY approach or simply buy commercial products that use that particular approach.
I know that sounds like a lot of effort but I really think it's worth while in the long run. If you put in a bit of time and effort you will learn a lot about what you like and which aspects of your system's sound and performance you consider are most important in advancing your enjoyment of listening to music. Not only will that help you a lot in developing your own resonant control strategy, but it's invaluable knowledge to have any time you go shopping for new components and you're trying to sort out which of a number of competing products would best fit into your system and enhance the sound of it.
David Aiken
(a) "very little of a horizontal force will"if you are using a roller or something horizontally compliant, sure, but a sharp spike sticking into a shelf will normally *not* allow horizontal movement of shelf relative to spike.
(b) "The wave wraps around the pier support which absorbs very little energy..."
A patently inapt analogy to a spike supporting a shelf or resting on one. With wave-pier it's obvious where the extra energy is going -- into to shore. Spike-shelf, on the other hand, is no different from any rigid structure which incorporates slender pillars.
It's not like this is a matter of seculation either -- this is well-understood at the theoretical and practical level, and vibration it measurable.
The amount of folk-science on this board, stated with quackish confidence, is just unbelievable.
Re: "(a) "very little of a horizontal force will"if you are using a roller or something horizontally compliant, sure, but a sharp spike sticking into a shelf will normally *not* allow horizontal movement of shelf relative to spike."
First it's worth while noting that the tips of many cones are not "sharp spikes", they are much more rounded, and they don't "stick into the shelf". The relatively flat original Tiptoes had a hemispherical section tip, as do the Black Diamond Racing cones I have used and many other cone designs. Such 'blunt pointed" designs do allow for some degree of motion between the cone tip and the shelf.
And second, as I said, energy is transferred to the cone as a vector force and the vertical vector component of a horizontal force is significantly less than the horizontal vector component.
Re: "(b) "The wave wraps around the pier support which absorbs very little energy..."A patently inapt analogy to a spike supporting a shelf or resting on one. With wave-pier it's obvious where the extra energy is going -- into to shore. Spike-shelf, on the other hand, is no different from any rigid structure which incorporates slender pillars."
Well, I would have thought that it was obvious where the extra energy was going if my analogy was correct - it's remaining in the shelf and being conducted from the shelf via the shelf supports, whatever they are. Small contact areas aren't going to work equally well for energy transfer at all frequencies and, as I said, it's a vector transfer so not all of it can be transferred anyway.And I think there is are significant differences between a cone point resting on a shelf and slender pillars supported by a rigid structure. A shelf is often not a particularly rigid structure in a lot of ways - much less rigid than a solid floor, for instance. More importantly, support pillars don't simply rest on their supporting structure - they're actually physically connected to that structure in a much more substantial manner and to a much greater depth than any penetration by a cone, especially a cone with a rounded rather than a pointed tip, plus there's a much greater contact area as a result. The mechanics of energy tranfer to a pillar are going to be different to those of a cone resting on a shelf. I'm not so sure that the analogy is all that inept.
Also, don't forget that *ALL* of the vibrational energy present in the shelf is not flowing into the cone. I never suggested that there was any energy disappearing into thin air - vibrational energy is dissipated by conversion to heat or other forms of energy or it flows via physical conduction into other objects where it is dissipated by conversion into other forms of energy. Cones supporting a component are only one pathway that the vibration has for conduction elsewhere from the shelf - there are also the shelf supports to be considered - and some energy is most definitely converted into heat and movement within the shelf. Energy seeks the most efficient method of dissipation and transmission through cones may well not be the most efficient pathway in a given situation. What isn't transmitted through the cones is simply dissipated more effectively elsewhere.
All I have said in my previous posts is that there are reasons why a cone is not a perfect conductor and why it may have some frequency dependent behaviour. I don't think you'd want to argue that they are perfect conductors which operate equally well at all frequencies. I most definitely wasn't suggesting that cones were isolators. In fact, in my first post I said "There are no perfect isolators or couplers, but to regard one kind of device as the other simply because it doesn't work perfectly and, at frequencies outside of its operational bandwidth, it passes some vibration we would prefer it didn't, or blocks some that we would prefer it did, is missing the point."
Further,in my second post I said "Put the 2" -ie the vector force and the impact of contact area on transmission - "together and you have a combination of vector and wavelength factors affecting how much vibration will enter the cone to be transferred to the other side." I think that remains a fair and accurate statement and I see nothing in your comments that could be used to suggest otherwise unless you want to suggest that all vibrational energy in a shelf will be dissipated via conduction through cones if cones are present, and I would argue most strongly against that.
"It's not like this is a matter of seculation either -- this is well-understood at the theoretical and practical level, and vibration it measurable.""Seculation" - do you mean "speculation"? And yes, vibration is measurable but I've yet to see a reliable study on what effect cones have on vibration transfer in a real life situation and in the absence of some actual measured results, about all we can do is speculate to some degree. If you know of such an account, I'd be most happy to see a reference. I am prepared to bet however, even without reading it if you know of such a study, that cones don't transfer equally well at all frequencies, that they don't transfer all of the energy from whatever the tip is in contact with to whatever the flat side is in contact with and vice versa, and that how effectively they do transfer vibrational energy depends on the axis of vibration relative to the cone's vertical alignment. That's what I've claimed is happening and you've said nothing to indicate that any of those claims is wrong.
David Aiken
The context from the original poster was arrowheads used as spikes which will definitely couple very thoroughly. I could imagine a rounded teflon ball making contact with a flat teflon surface or something like that, and then *maybe* it would function like a roller, but if that's what you want why not just get rollers?The more effectively you couple, the more the shelf that the thing coupled to the shelf will behave as a single unit, especially if the component is heavy, and all this business about vibrations passing or not is silly. If you really want to change how vibrations transmit try something like sorbothane.
And your description of the whole system gets murkier and murkier. Make it simple. We have a table, let's say, atop of which sits, say, a record player or whatever you like. The table rests on the floor. The question is whether we should put something in between the component and table, presumably to isolate it from the table (though this wants to be specified because sometimes people are trying to damp vibration produced in the component). Assuming that the table is not possessed by spirits that give it its own vibrational energy, any additional vibrations are coming from the floor (or perhaps the air). It's not like vibrations are going to come into the table, look around for something to pass into, give up and wander back down into the floor or air.
That's one reason what follows "Well, I would have thought..." is silly. More generally your surf analogy is inapt because water is. well, liquid, and will flow past the pier to hit the shore and transfer energy there, so of course a wide pier will absorb more energy than a narrow one. That particular system has slmost nothing to do with the problem under discussion.
"More generally your surf analogy is inapt because water is. well, liquid, and will flow past the pier to hit the shore and transfer energy there, so of course a wide pier will absorb more energy than a narrow one. That particular system has slmost nothing to do with the problem under discussion."Well, the cone tip is a relatively small object in the "sea" of the shelf and the vibration is a wave phenomenon that is occurring throughout the shelf. Most of the wave flows past the cone tip simply because it would flow past that point whether or not anything was there. We're talking about what happens at a point of interuption to the wave motion and I can assure you that all of the vibrational energy doesn't congregate and flow into that point.
So the question becomes what happens with that part of the vibration wave that does flow through the point of contact and what happens is that not all of the energy in that part of the wave flows up and into the cone. If the vibration is in the horizontal plane, most of it is going to continue to flow through the shelf and pass by right under the cone tip. If it's vertical, then more of it will pass into the cone tip and what happens if the plane of vibration is somewhere in between vertical and horizontal is that more will be transmitted to the cone than if the vibration was horizontal and less than if it was vertical. Change of direction always involves vector transmission.
And there's still the point of frequency and contact area - the size of the obstruction to the unimpeded flow of the vibration. It does have an effect - you've produced no evidence to show it doesn't.
You say that my description gets "murkier and murkier" but there are a number of factors at play and it isn't as if the cone, just because it happens to be a coupling device, is going to act as a perfect conduit and that vibration that isn't travelling in the vertical plane is going to change direction to flow up or down the cone with the same amount of energy that it was travelling in it's original direction. Forces don't work that way.
It's all very well to want a simple description of what is happening, but you can't ignore the facts of force direction and what happens when that force is channeled in a different direction, nor can you ignore vibratory behaviour in the shelf as a whole and the fact that the point of contact is a small part of the shelf area and that, at the least, you would need a contact area equivalent to the whole of the shelf area if you were to even attempt to get a total transfer of energy via an ideal coupling device. Reducing contact area effectively imposes a 'filter' on the transfer of energy and that filter is going to affect both frequency and effectiveness of transfer.
David Aiken
When a longitudinal pressure wave moves the shelf horizontally under the cone tip, the cone tip moves equally since it is coupled to the shelf by static friction. The amount of energy tranferred through the cone is dependent only on the mass supported by the cone. That mass has to be accelerated by the force trasferred through the cone. As long as the magnitude of the vibration is below the threshold where the acceleration force overcomes static friction, the shelf/cone/component interface behaves as one rigid body. And if the magnitude of the vibration is above that threshold, then the cone "breaks loose" from the shelf and the maximum force transmitted through the cone (and thus the maximum energy transfer) is limited by the coefficient of dynamic friction.It really is that simple. The contact area has nothing to do with any of this unless you want to consider the effect of surface deformation on the coefficient of friction.
Dave
Coupling devices like cones don't have a mechanism or process for shedding vibrational energy so they pass whatever vibration gets into the cone. However the vibration entering the cone is dependent on things like contact area and that introduces an element of frequency dependence. My feeling is that the smaller the contact area, the more the lower frequencies have difficulty entering the cone.
Cones ought to be near perfect couplers as long as the vibration forces don't overcome static friction, and once they do the cone will float on the surface. I don't know whether low frequency vibrations would be likely to generate larger forces, but it seems plausible.
It's also worth noting that isolation isn't necessarily a good thing and coupling isn't necessarily a bad thing. Shannon Dickson makes the point in his excellent "Bad Vibes" article (see Paul Tobin's post for a link) that perfect coupling would actually give the best results we could achieve - at that point the component and the supporting shelf or rack would actually be at rest in relation to each other.
Theoretically, perfect coupling should give the best results if the primary source of vibration is in the component itself (e.g. a vibrating CD transport or a humming transformer). Coupling then provides a path for vibrational energy to drain out of the component into a suitable sink. Coupling the component to something massive can also lower its resonant frequencies. Conversely, isolation should give the best results when the primary source of vibration is external to the component.
YMMV of course. We know how component and system dependent these things are. I like the idea of using a stethoscope as part of the tuning process, but I've yet to try that.
Dave
Stereophile 'Bad Vibes' article
System Details
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We appreciate your efforts.And you have to admit pkell44 shows admirable consistency in being totally wrong about *both* sorbothane *and* spikes, with capital letters and condescension to boot!
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nt
Many but it depends on the grade and thickness of the Sorbothane as well as the load on it.Kal
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