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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
linnvolk OP
88 posts
 
@ausaudio,

You caught me in some less-than-clear writing.

The second quote is based on a tacit assumption that we are talking about hard floors.  This is what I have, and I tend to default to it without necessarily giving the reader the appropriate cues.  My bad.  The point here is that putting spikes on a speaker that would otherwise be sitting directly on a hard floor does nothing to help the stabilize the speaker against the rocking mode.  They actually will destabilize this mode, because the spikes have to be inboard of the periphery of the speaker base in order to have something to screw into.  This reduces the footprint and thus the resistance to rocking.

The first quote addresses, as stated, the case of tower speakers on thick carpet.     It is equally or even more applicable to bookshelf speakers on stands (which are likely a more top-heavy arrangement). In this case, the speaker will want to rock back and forth on the springy carpet, pivoting about its base, due to the carpet's compressibility.  Here, using spikes lets you bridge across the mushy carpet and get "seated" on hard floor.

I agree with your accelerometer statement.  My life is not long enough nor my pockets deep enough to head down that road.  Though not part of my practice area, my company could actually do this for several thousand dollars. 

I think the "hand on speaker test" with some thumping bass would provide a substantial clue regarding whether spikes or springs are either one changing the game as far as speaker vibration is concerned.  I suspect that neither will show any difference in that test, though here, as in listening, perception bias will play a part unless you enlist at least one other person in a blind test so that you do not yourself know which is which.  Even there, the speaker on springs will have some perceptible wobble in response to just your touch which you won't be able to ignore/forget.
ausaudio
90 posts
 
I would suggest light pressure of a finger at the upper back edge of the speaker to detect movement as opposed to cabinet flex. Thoughts?
aschuh's avatar
aschuh
42 posts
 
@ausaudio - At 92 g x 8 ounces mass you are looking at a force equal to a weight of 736 ounces or 46 pounds.
It is very possible that a horizontal force directed towards a 100 pound sub, sitting on springs with minimal horizontal stability, moves the sub horizontally.
linnvolk OP
88 posts
 
@aschuh, that would be quite true if the force were static.  In your example, that force is reversing direction 60 times per second.  No problem for an 8-oz woofer cone.  The displacement (vibration) response of the 100-lb sub in rigid-body mode at that frequency will be of very small magnitude as it is nowhere near the natural frequency for that mode.  Whether there is enough magnitude to matter and whether the magnitude is attenuated by the use of spikes or springs (and whether that attenuation is good, bad, or indifferent) IMHO would best be addressed by running the test and using your hands/ears...or accelerometers.  For the accelerometer testing, please hire my company, have them spend several days on testing (I will write the test report), and send @ausaudio the bill.
linnvolk OP
88 posts
 
@ausaudio, I agree with the light finger pressure at the upper back edge of the speaker, to ID rigid body rocking response.  As for rigid body translational response, the bottom of the speaker might be better.  I don't know though if we can conclude that what we feel in either location is free of flexural modes, though it ought to be more free than anywhere else on the speaker.  Best to place accelerometers at multiple places and post-process for modes; the rigid-body components should be easy to identify for an experienced dynamicist.  Glad you are paying for all this.
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