Music, and suction cups. Arguably two of mankinds's greatest inventions.
Yet both have their flaws. Music - very nice to listen to, yes, but it doesn't actually do anything. Suction cups - jolly useful, but not very exciting to listen to; worse yet, they eventually lose suction and have to be re-positioned.
Come with me, if you will, on a thought experiment that combines the best attributes of music and suction cups.
Imagine a loudspeaker, perhaps two inches across. It has the usual metal frame and voice-coil, but the diaphragm of this speaker, instead of being conical and flexible, is flat and rigid. A narrow rubber gasket connects its edge to the metal rim of the speaker, allowing it move to and fro in the usual speaker-like manner.
Also imagine (if I may ask you), a lip of flexible silicone rubber around the edge of this contraption.
Now, take this odd speaker and place it against a window or other flat, vertical surface. You let go and - dash! - the entire contraption falls to the floor.
Now, replace the speaker against the surface, but this time connect its leads to a suitable source of amplified music. Once again, release your grip and - gadulka! - the speaker remains mysteriously in place.
How, I hear you enquire, is this possible???!!!
Well, consider the speaker when it is first held against the surface. As the music plays, the speaker's flat diaphragm moves to and fro. As it move to, it tends to compress the cushion of air between it and the surface. This would tend to push the speaker away from the surface but, remember, auntie Inertia is your friend and secret lover. The inertia of the speaker means that it will not move significantly in the fraction of a second it takes the diaphram to move forward.
Instead, the air between the diaphragm and the surface will be momentarily compressed, and will escape in a farting manner from between the surface and the soft silicone lip of the speaker.
The diaphragm now moves fro, creating a partial vacuum. The silicone lip now seals itself tightly against the surface.
At each "to" movement, the diaphragm will fart out a small volume of air; at each "fro" movement, the silicone lip prevents that air from returning.
As a result, the speaker will, after a few sound-cycles, suck itself quite firmly onto the surface. Of course, the limit of the suction is determined by the travel of the diaphragm in relation to the distance between the diaphragm and the front edge of the speaker; it may also be limited by the power of the speaker's coil. Howevertheless, a substantial fraction of the air can be expelled, and a vacuum of perhaps 20% (about 3psi) might be thus created. This modest vacuum will hold the two- inch speaker-sucker with a force of about 10 pounds.
The music can then be turned off, and the speaker- sucker will stay in place much like a regular suction cup. However, a periodic burst of music will restore its failing grip.
The possibilities are unlimitless. For instance, we could also make a very small hole in the speaker diaphragm, so that it would lose suction quite quickly (say, in under a second) if left alone. However, the continuous application of sound would offset this leak, allowing the suction to be turned on and off at will. One could construct, therefore, a window-climbing robot, whose suction-feet would play a carefully-synchronised piece of polyphonic music as they gripped and released.
No doubt the waveform and frequency of the sound would have to be optimised, but I suggest that one could start with a recording of a flute playing the theme tune to a well-known Dutch detective series of the 1970s. This would allow one to point out that the suction cup was held in place by Van der Valk's forces.-- MaxwellBuchanan, Dec 04 2011 "...Nick, I can't knock success...but you still put me through too many changes..." http://en.wikipedia...alk_%28TV_series%29No, it has nothing to do with Nick Danger - just the google searches that [MaxwellBuchanan] makes me do... [normzone, Dec 05 2011] The Singing Detective http://en.wikipedia...e_Singing_DetectiveMore appropriate music this device could play... [normzone, Dec 05 2011] "Your music really sucks." [+]-- baconbrain, Dec 04 2011 [ ] not convinced that it would fart instead of just pushing off.-- FlyingToaster, Dec 04 2011 Then you should repeat the thought experiment more closely, and take notes.-- MaxwellBuchanan, Dec 04 2011 perhaps, but the inertia that you're counting on to make it fart outwards would also serve to make it fart inwards.-- FlyingToaster, Dec 05 2011 Hmm, the frequency may affect its effectiveness.-- mitxela, Dec 05 2011 My fish are not going to like this.-- 2 fries shy of a happy meal, Dec 05 2011 //Not one mention of a valve.//
The silicone lip acts as a valve, in the same way that the rim of a common-or-garden suction cup does.-- MaxwellBuchanan, Dec 05 2011 The silicone lip will let air out of the speaker when the speaker cone volume is reduced, but it will also let air in when the speaker cone volume is increased - and then the speaker will fall to the ground and break. Note that 'pumping' a regular suction cup does not create a vacuum.-- hippo, Dec 05 2011 // but it will also let air in when the speaker cone volume is increased//
No it won't, because it is a lip at a shallow angle to the surface (like the peripherymost part of a regular suction cup). As on a normal suction cup, it acts as a flap-valve - air can be squeezed out (pushing the lip up to let air escape), but not in (the pressure in that case simply squashes the lip to the surface).-- MaxwellBuchanan, Dec 05 2011 Hmmm - I wonder if you're asking your speaker suction cup to do two contradictory things: (1) be sufficiently strong to not collapse under a vacuum sufficient to carry its own weight, and (2) be flexible enough to 'fart' out air through the rim. Also, even with the 'ideal' suction cup speaker, will any 'farting' occur? Say a large movement of the speaker cone reduces its volume by 5% and (in an ideal world, again) 5% of the air is expelled, then when the speaker ruturns to a 'neutral' position the internal air pressure will be 95% of the external pressure. Then, suppose another movement of the speaker cone reduces the volume by 5% no more air will be expelled as the internal and external pressures will be the same.-- hippo, Dec 05 2011 I agree with [hippo]; a sustained musical tone will not cause the attenuation you desire. but, a pulse or click will do, if it is of sufficient amplitude.-- pocmloc, Dec 05 2011 //a sustained musical tone will not cause the attenuation you desire. but, a pulse or click will do, if it is of sufficient amplitude.//
OK - step by step. Imagine first a normal suction cup. You place it in contact with the surface, press slightly (which farts out some air), then release, and it holds.
A speaker system will achieve the same result, assuming that the inertia of the speaker body (magnet, voicecoil, frame) is sufficient to hold the whole shebang in place for a millisecond or two.
Now, as to the volume displaced and the effect of repeated cycles. I said the speaker cone was flat, expressly so that the displaced volume can be large relative to the initial volume. Imagine a flat speaker cone with a travel of, say, 2mm (which is perfectly feasible, if anyone wanted to fease it). Assume also that it starts out 3mm from the surface (again, no problem). You would be able to displace 2/3rds the air with a single pulse.
As for the repeated cycles, it's true that they will not remove more air than the initial swept volume. However, I'm assuming that, in a single rapid pulse, not all of the transient positive pressure is released by farting. In other words, some positive pressure remains after the speaker cone (disc) has reached its maximum forward position. Repeated cycles will allow this air to be released in a series of diminishing farts, until the internal pressure is as low as it can get (in this example, 2/3rds atmospheric), whereupon no further vacuum will be produced.
If it's simpler to imagine, consider a regular suction cup which you tap repeatedly with a small hammer (never compressing the cup fully).-- MaxwellBuchanan, Dec 05 2011 //it doesn't act like a valve until you push it.// The speaker is initially held in contact with the surface. Hence, if the air pressure inside the enclosed volume rises (as it will, when the speaker cone/diaphragm moves forward), air will be expelled fartwise through the lip. When the speaker cone/diaphragm moves backwards, it reduces the internal pressure below ambient, whereupon the lip will seal.
I contend that this is no different mechanistically, and ileum alter panesque, to placing a regular suction cup on the surface and tapping it lightly.
Eppur si sugere.-- MaxwellBuchanan, Dec 05 2011 And I contend that it is only necessary to provide sufficient force to bring the sucker into contact with the surface.-- MaxwellBuchanan, Dec 05 2011 If you used a sawtooth waveform to drive the speaker, you could use the power of Arrr! to force it closer to the glass.-- pocmloc, Dec 05 2011 On the one hand I can see it working for a person, armed with a plunger, trying to stick themself to a glossy high ceiling after being launched from a seesaw by the sudden vertical arrival of several trained bears.
Or untrained, the only difference being the willpower to remain stuck to the ceiling.
But I'm unable to grok it with a loudspeaker.-- FlyingToaster, Dec 05 2011 // I can see it working for a person, armed with a plunger, trying to stick themself to a glossy high ceiling after being launched from a seesaw by the sudden vertical arrival of several trained bears. //
Unfortunately, this is way too long to be [marked-for- tagline]-- Alterother, Dec 05 2011 //But I'm unable to grok it with a loudspeaker.//
OK - maybe it'll work if we do it in stages. First of all, if a regular suction cup is held up to a window (just in contact), and then tapped briefly with a small jade* hammer, will the suction cup stick to the window?
*since this is a thought experiment, I thought I could splash out a little on the raw materials.-- MaxwellBuchanan, Dec 05 2011 mmm, at the risk of a second nested "even if it did work...", putting a closed low-pressure chamber at back of the cone is going to wildly distend the waveform coming out the front.-- FlyingToaster, Dec 05 2011 // wildly distend the waveform coming out the front// It's all handled in software.-- MaxwellBuchanan, Dec 05 2011 Somehow, I imagined this to be a series of chromatically-tuned suction cups driven by voicecoils. The cups and drivers would be radially mounted on a wheel, and sequential activation of the coils would produce rotary "wall-walking." The cups would be chosen for their resonant frequencies to produce chromatic scales.
Or the whole thing could be turned on its side, allowing random activation, and possible chords. +-- csea, Dec 06 2011 random, halfbakery