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Speaker Spike Philosophy

This is a learning exercise for me.

I am a mechanics practitioner by training and by occupation, so I understand Newton’s Laws and structural mechanics and have a fairly effective BS-detector.

THE FOLLOWING THINGS PUZZLE ME, and I would be glad to hear from those who believe they understand so long as the responses are based on your actual experience or on sound mechanical arguments (or are labeled as conjecture). These are independent questions/musings, so feel free to weigh in on whichever ones you want, but please list the number(s) to which you are responding:

  1. Everything I have read recently ("Ask Richard" (Vandersteen) from 15 Feb, 2020, for instance) seems to indicate that the reason for speaker spikes is to hold the speaker fixed against movement induced by the drivers. I have seen in the past other explanations, most employing some use of the term "isolation" implying that they decouple the speaker (from what?) Evidently the "what?" is a floor that is fixed and not moving (let’s assume concrete slab foundation). So to decouple the speaker from the floor, which is fixed, is to . . . allow it to move (or not) as it wishes, (presumably in response to its drivers). These two objectives, "fixity" and "isolation" appear to me to be diametrically opposed to one another. Is the supposed function of spikes to couple the speaker to "fixed ground" so they don’t move, or is it to provide mechanical isolation so that they can move (which I do not think spikes actually do)? Or, is it to somehow provide some sort of "acoustic isolation" having to do with having some free space under the speaker? Regarding the mechanical isolation idea, I saw a treatment of this here: https://ledgernote.com/blog/q-and-a/speaker-spikes/ that seemed plausible until I got to the sentence, "The tip of a sphere or cone is so tiny that no vibration with a long waveform and high amplitude can pass through it." If you have a spike that is dug into a floor, I believe it will be capable of passing exactly this type of waveform. I also was skeptical of the author’s distinction between *speaker stand* spikes (meant to couple) and *speaker* spikes (meant to isolate/decouple, flying in the face of Richard Vandersteen’s explanation). Perhaps I am missing something, but my BS-detector was starting to resonate.
  2. Spikes on the bottoms of stands that support bookshelf speakers. The spikes may keep the the base of the stand quite still, but the primary mode of motion of such speakers in the plane of driver motion will be to rock forward and backward, pivoting about the base of the stand, and the spikes will do nothing about this that is not already done by the stand base without spikes. I have a hard time seeing these spikes as providing any value other than, if used on carpet, to get down to the floor beneath and add real stability to an otherwise unstable arrangement. (This is not a sound quality issue, but a serviceability and safety issue, especially if little ones are about.)
  3. I have a hard time believing that massive floor standers made of thick MDF/HDF/etc. and heavy magnets can be pushed around a meaningful amount by any speaker driver, spikes or no. (Only Rigid-body modes are in view here--I am not talking about cabinet flexing modes, which spikes will do nothing about) "It’s a simple question of weight (mass) ratios." (a la Holy Grail) "An 8-ounce speaker cone cannot push around a 100/200-lb speaker" (by a meaningful amount, and yes, I know that the air pressure loading on the cone comes into play as well; I stand by my skepticism). And I am skeptical that the amount of pushing around that does occur will be affected meaningfully by spikes or lack thereof. Furthermore, for tower speakers, there are overturning modes of motion (rocking) created by the driver forces that are not at all affected by the presence of spikes (similar to Item 1 above).
  4. Let’s assume I am wrong (happens all the time), and the speaker does need to be held in place. The use of feet that protect hardwood floors from spikes (Linn Skeets, etc.) seems counterproductive toward this end. If the point of spikes is to anchor the speaker laterally (they certainly do not do so vertically), then putting something under the spikes that keep the spikes from digging in (i.e., doing their supposed job) appears to defeat the whole value proposition of spikes in the first place. I have been told how much easier it is to position speakers on hardwood floors with the Skeets in place, because the speakers can be moved much more easily. I was thinking to myself, "yes, this is self-evident, and you have just taken away any benefit of the spikes unless you remove the Skeets once the speakers are located."
  5. I am making new, thick, hard-rock maple bases for my AV 5140s (lovely speakers in every sense), and I will probably bolt them to the bottom of the speakers using the female threaded inserts already provided on the bottoms of the speakers, and I will probably put threaded inserts into the bottom of my bases so they can be used with the Linn-provided spikes, and I have already ordered Skeets (they were a not even a blip on the radar compared to the Akurate Exaktbox-i and Akurate Hub that were part of the same order), and I will end up doing whatever sounds best to me. Still, I am curious about the mechanics of it all...Interested to hear informed, reasoned, and reasonable responses.
linnvolk
mitch2
3,969 posts
 
Discs under spikes are probably as close to decoupling as to coupling.  The KEF discs are 18mm in diameter or about 250 mm squared in area, which is probably about 100 times the area of the tip of a spike.
sokogear
1,095 posts
 
mitch2 - I'm talking about the tip of the spike going into a tiny indentation in the middle of the disc which is where it reacts with the floor. The weight of the speaker will go through that small area, not the entire disc because that is where the force is concentrated.
bachemar
14 posts
 
Might be easier to imagine the effects of different options (springs, spikes, sorbothane etc) by comparing it to something we can all relate to - Mattress shopping.

Imagine if you (speaker) were trying on different types of mattresses (footers) and were wriggling in place (speaker vibration) and how the mattress felt. Now imagine different types of mattresses and what exactly would happen to your wriggling efforts
  1. Cheap spring mattress, where you can feel the springs - The springs would absorb some of your wriggling, but it would still feel uncomfortable, because you can feel the "springiness" of the springs. This springiness is really the springs bouncing back from your wriggling but with a slight time delay. 
  2. You now add a pillowtop to the spring mattress (the Damping that was mentioned in an earlier post) - Ah much more comfortable, the pillowtop absorbs some of the low amplitude wriggling, and also absorbs some of the spring feedback, so it feels less bouncy
  3. An old school (non memory) foam mattress - slightly better, but still suffers from the springiness, although to a lesser extent
  4. You now try on a memory foam mattress (sorbothane, Herbie's discs etc.). There's no more force feedback from the mattress, and the memory foam, helps absorb and dampen your wriggling
  5. Sleep on the floor or a block of wood/stone/marble etc. that is lying on the floor - This would be fairly uncomfortable, the floor does nothing to absorb the wriggling, but doesn't impede it either. As you wriggle, you create multiple contact points between body and floor, which could create its own rattling sound.
  6. Now imagine if your skin was rigid, and had built spikes attached to your back, sleeping and wriggling on a concrete/stone floor - Similar to above, but the spikes might reduce the contact points making it slightly harder to wriggle and much more reduced rattling noise
  7. Now imagine sleeping with built in spikes, but these spikes have dug into the wooden floor - I imagine, the bonding of the spike with floor would create a damping effect making it harder for you to wriggle
mijostyn's avatar
mijostyn
8,570 posts
 
@audiopoint , That was a rather long winded dissertation. Although I believe there are resonance points at higher frequencies involving drivers, parts of drivers and speaker enclosures, the ones that are clearly audible and measurable by simple methods reside in the bass frequency range and are most difficult to control in subwoofers because of the mass of the drivers, the amount of air that has to be compressed on both sides of the driver transferring a lot of energy to both the environment and the enclosure. Subwoofers clearly shake in the direction the driver is moving which as I have shown can be measured with an accelerometer. Spiking the subwoofer clearly reduces this shaking/resonance because the mass of the loudspeaker is now fixed to a much larger mass. If you want to say that the resonance is drained away by the floor and house that is fine by me. Subwoofer enclosures also resonate in other ways but the big one besides shaking is expanding and contracting from the pressure differentials within the enclosure. Again this is easy to measure and clearly audible. This one is more difficult to deal with and requires some design cleverness. The frequencies at which these resonances occur depends on a number of physical factors like this stiffness and size of the enclosure walls and the overall mass of the enclosure. Any resonance in a speaker enclosure at any frequency is distortion whether or not it is audible is a different question. A subwoofer measurably generates less distortion when it is firmly spiked to the floor. I do not know if this is true for a full range loudspeaker that is crossed to a sub at say 100 Hz. At higher frequencies not near as much energy is transferred to the environment or the enclosure. Does vibration transferred to a purely electronic device cause audible distortion? I seriously doubt it but neither have I run that experiment so in truth I have to say I do not know.
Designing a decent speaker spike is child's play as is making a decent speaker stand. Locking the speaker to the stand is also child's play as long as you don't mind sinking a few screws into the enclosure. Designing and making a subwoofer enclosure that does not shake or resonate is not so easy. Do you have any siggestions?
mijostyn's avatar
mijostyn
8,570 posts
 
Suggestions:-)
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