Spikes versus wall coupling

Newbee way back when my oldest sister had a senior class prom party at my parents house, I remember my father being really pissed off the morning after..Reason was the new hardwood floors were dented from all the young ladies who wore 4 inch heels the nite before..You didn't see footprints from the soles of the shoes the guys wore even though the guys weighed twice as much. The young ladies' weight were more effectivly coupled to the wood floor than their much heavier male counterparts. A speaker cabinet while playing is not resting at a standstill.In fact the cone motion is modulating the whole cabinet.This cabinet motion can be as large as the exsursion of the tweeter of that same speaker..The most effective way to limit this loss of energy, this out of phase energy, this self perpetuating generation of resonance is to direct couple the speaker to the floor as described. Some coupling devices I know of are designed to limit the entrance of frequency's below 4 hz, so mother nature's blowups are less imposing on ones audio..Tom

MarkPhD Thank you for your detailed response. I may be dense but if you are trying to decouple the speakers by using spikes, could you not also decouple using cork, felt or rubber, or combination products such as (VIBRATION ISOLATION PADS or Klein Tech Systems Iso-Damp Discs vibration isolation pad - both from the tweeks page) and get the same result without damaging the wood floors and still being able to move speakers more easily.
I assume these absorbant materials do not pass vibrations easily. Are you saying that spikes are better becuase they also anchor the cabinet and prevent the small cabinet movements that rubber etc might allow?

Gammajo, you can decouple using anything. It is the small surface area that makes spikes good as this is what increases the mechanical impedence. If you use a product with a larger surface area, you will get less impedence and more energy transfer. How much less, and whether it is audible would have to be the subject of further debate add experimentation. I don't quite know what to make of little rubbery decouplers like isobearings or pucks. With a larger surface area compared to spikes, they are not as efficient as decouplers. On the other hand, if they wiggle a bit, the movement may damp vibrations. So you may be losing a little bit of decoupling, but gaining a little bit of damping. Remember that isolation and coupling can both do the same thing. I really don't know how to answer the questions in your latter post. We're pretty close to my limits of knowledge on this particular subject. I was hoping that the Bright_star_audio person who posted might kick in a few words. Bright Star make reputable products and should be able to add some insight. Sorry I can't help further.

MarkPHD thank you and all others who have posted. I am clearer now on the issue. For me logically it makes sense for the speakers to have something very solid to push against so that the movement of the drivers is all in the correct direction, and spikes also isolate due to their small surface - cork, felt and rubber would tend to compress under 185 lbs speakers and behave more like a solid and transmit vibration, and therefore the spikes are most apprropiate.
For underneath lighter components with less intrinsic vibration I think these materials might be more appropiate to isolate the components, absoring vibration both from the component and from the shelf.

Hi All,

Even though there may be asymmetrical mechanical impedence between the point interface and the opposite interface of the spike there is still significant mechanical transfer occurring in BOTH directions. This pathway does not provide isolation. It allows vibration to flow up the rigid point or spike into the component that is placed on top of it. This problem is quite significant when components are placed on a rigid mounting but is still an important issue when speakers are placed on a rigid point.

Points have been a relatively popular method of mounting a speaker. Is it the best method for mounting a speaker? No. It does provide sonic improvements as compared to having a speaker sitting directly on carpet because the carpet does not support the cabinet effectively and allows it to deflect in reaction to the drivers’ movements. This creates Doppler shift as well as allowing some of the drivers’ energy to be diverted from the main task of making sound to making the cabinet move. A speaker resting directly on a hard floor does not usually sit as flat as we assume it will. Both the floor and the bottom of the speaker cabinet are not truly flat and “chatter” between the two does occur. Again, wasted energy. Placing three points under the cabinet does help the speaker become much more rigid and that is the main reason for their relative popularity. Three points does define a plane and that will naturally make the mounting more stable than without the points in place. Unfortunately, the spikes are not nearly as effective as other methods of transferring vibration out of the cabinet and they also do not support the rear two corners of the cabinet which allows them to be much more susceptible to internal resonance. The rigid mounting for the speaker also allows external sources of vibration to enter into the cabinet from the floor which causes a different source of Doppler shift contamination. This vibration is not sourced from the speaker and therefore has no relation to the music signal in the recording – it is exhibited as a general displacement of the speaker cabinet which lowers the overall dynamic range and interferes with pace and rhythm.

The fact that the support and interface we place under a speaker perceptively changes the sound clearly illustrates the insidious nature of vibration as it relates to an audio system. Almost every aspect of sound reproduction - tonality, spatiality, dynamics, coherence, etc. - is compromised by unwanted vibrational energy. That is the result of a disturbance in the relationship between frequency, amplitude and phase of the original signal that the audio system is reproducing.

As the speaker drivers are radiating acoustic energy into the room (the energy that we want - music) they are also sending energy into the speaker cabinet because of air pressure from the inward motion of the cone and by conducted energy through the frame and mounting flange which becomes unwanted stored energy (USE). This USE causes the cabinet walls, the crossover components, the connected speaker cable, etc. to vibrate (the drivers are also subject to compromise by their own vibrational energy that they've sent into the cabinet that is then reflected back towards them after a delay in time). The cabinet vibration has the most consequence towards corrupting the speaker's performance. If we were able to quiet the driver's acoustic output into the room and just hear the result of the cabinet walls vibrating I think we would be shocked as to just how much audible acoustic energy the cabinet would be radiating! THIS version of the audio signal would have a different frequency balance than the driver's output (it would sound muffled being dominated by the primary and secondary resonance frequencies of the cabinet) it would be lower in amplitude (but not uniformly lower because of the non-linear nature of the cabinet materials) and would be delayed in time (the amount of time it would take for the energy to leave the drivers, be absorbed by the cabinet and then be released into the air) thus affecting phase integrity. If we think about this 'smeared' version of the signal (which contains corrupted frequency, amplitude and phase) being mixed back into the original signal it is no wonder that USE significantly affects the reproduction and that altering the USE has an audible effect!

Now, just imagine if we make a significant reduction of USE in the speaker cabinet. The amount of audible difference would be profound. Placing high mass on top of the speaker cabinet will significantly increase the resonance frequency (a good thing) and decrease the amplitude (also a good thing) of the top panel. The weight load will then be translated onto the side panels with a related change in their resonance frequencies. Furthermore, the added mass will more effectively couple the speaker bottom to the top plate of the speaker support, the floor or more suitably to a high-mass high-absorption platform so the USE can be drained from the speaker cabinet.

If we used laser infrarometry to measure the displacement of the speaker panel we would see a noticeable reduction in displacement (vibration) when high mass is set on top. In addition, if a high-mass high-absorption platform is placed under the speaker, this multi-stage vibration control system forces the speaker to be more effective in its main task of reproducing music - the drivers do not waste their energy in making the cabinet or internal parts vibrate because the cabinet is far more resistant to displacement. The drivers have no choice but to use their energy more efficiently in creating music.

The most effective method for supporting a speaker would be a high mass element on top of the cabinet, a high-mass high-absorption platform directly under the speaker (on top of a rigid and strong stand for a mini-monitor) and a pneumatic base on the floor to decouple the speaker's energy from entering the floor and being transmitted to the equipment rack (the pneumatic mount must be designed in the correct manner so that it does support the speaker without allowing Doppler shift to occur). This configuration is highly successful in eliciting the peak performance from the speaker without a redesign of the cabinet or the component parts.

The other components in an audio system will also benefit by a reduction of USE in their chassis. Besides speakers, turntables exhibit the largest degree of improvement by proper vibration control. Since they are electro-mechanical devices it is almost intuitive to us that this be so but the purely electronic devices also benefit: tubes are microphonic, the master and sub-clocks (which are based on oscillating crystals) in digital devices are affected, a spinning disc inside a digital player will exhibit non-linear movement, all component parts (transistors, ICs, capacitors, resistors, wire, diodes, etc.) that process the signal become microphonic, motors, fans and buzzing transformers induce vibration into surrounding parts, and the list goes on.

What are the sonic results of vibration contamination? As we discussed, frequency, amplitude and phase are corrupted. Frequency balance is skewed: one portion of the spectrum is highlighted or diminished as compared with another. Brightness may increase, midrange may become too forward, and bass may bloat and become ill defined. Amplitude of the signal is changed: the dynamic range of an instrument and indeed the dynamic relationships between the instruments are altered. Phase integrity of the signal is deteriorated: the spatial relationship of the instrument with its environment and the spatial relationships between the instruments are altered. In fact, frequency, amplitude and phase are interrelated and changing any one affects the other two. If all three are affected at the same time (by the presence of unwanted vibration) the resulting cacophony significantly reduces the ability of the system to convey what is actually contained in the recording - and that's what audio is all about. Not just what sounds pleasing because it makes someone feel fuzzy all over but what is musically and emotionally fulfilling because it reflects the actual sound of the instruments as they have been captured in the recording.

When we eliminate the sonic results of vibration contamination we more accurately hear what the individual components in a system are doing. It is possible that these results might be misinterpreted by some individuals. For example: if a speaker is providing excess out-of-phase elements the size of the soundfield might INCREASE beyond what is actually in the recording. Bigger is not always. This individual will have adjusted speaker placement and acoustic room treatment based on this exaggerated sonic view of the soundfield. Once the out-of-phase elements are properly controlled by reducing vibration the size of the soundfield may become smaller in this incorrect set-up and the listener may say, "Oh, this is not as good as it was before because things are not as large." What they should be doing is reevaluating speaker position and room treatment to optimize the now correctly operating speaker. Once that is accomplished they will find that not only is the soundfield as large, if not larger than before, but the instruments are in proper relationship with one another and ambience is cohesive instead of exaggerated. Frequency changes can also be misinterpreted: in a vibration plagued system a too forward midrange during transients is a typical symptom. Some people might misinterpret this as the system exhibiting "good presence" or a forward brightness region is often described erroneously by some listeners as "good detail". The removal of the vibration will eliminate these effects. Some may feel at first, that the removal of these exaggerated artifacts is a step backward in reproduction, but what they are hearing in the now vibration free system are the possible cumulative effects of previous tweaking and/or component choices made with a vibration drenched palette. Once the problems caused by unwanted stored energy are removed some system choices may need to be reevaluated.

Best Regards,

Barry Kohan
President
Bright Star Audio

Disclaimer: I am a manufacturer of vibration control products.