h a l f b a k e r y
Tip your server.
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
or get an account
Music, and suction cups. Arguably two of mankinds's
Yet both have their flaws. Music - very nice to listen to,
yes, but it doesn't actually do anything. Suction cups -
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
this speaker, instead of being conical and flexible, is flat
and rigid. A narrow rubber gasket connects its edge to
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
or other flat, vertical surface. You let go and - dash! -
entire contraption falls to the floor.
Now, replace the speaker against the surface, but this
connect its leads to a suitable source of amplified music.
Once again, release your grip and - gadulka! - the
remains mysteriously in place.
How, I hear you enquire, is this possible???!!!
Well, consider the speaker when it is first held against
surface. As the music plays, the speaker's flat diaphragm
moves to and fro. As it move to, it tends to compress
cushion of air between it and the surface. This would
to push the speaker away from the surface but,
auntie Inertia is your friend and secret lover. The inertia
the speaker means that it will not move significantly in
fraction of a second it takes the diaphram to move
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
The silicone lip now seals itself tightly against the
At each "to" movement, the diaphragm will fart out a
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)
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-
will stay in place much like a regular suction cup.
However, a periodic burst of music will restore its failing
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
of sound would offset this leak, allowing the suction to
turned on and off at will. One could construct,
a window-climbing robot, whose suction-feet would play
carefully-synchronised piece of polyphonic music as they
gripped and released.
No doubt the waveform and frequency of the sound
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
in place by Van der Valk's forces.
"...Nick, I can't knock success...but you still put me through too many changes..."
No, it has nothing to do with Nick Danger - just the google searches that [MaxwellBuchanan] makes me do... [normzone, Dec 05 2011]
The Singing Detective
More appropriate music this device could play... [normzone, Dec 05 2011]
||"Your music really sucks." [+]
||[ ] not convinced that it would fart instead of just pushing off.
||Then you should repeat the thought experiment
more closely, and take notes.
||perhaps, but the inertia that you're counting on to make it fart outwards would also serve to make it fart inwards.
||Hmm, the frequency may affect its effectiveness.
||My fish are not going to like this.
||//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.
||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.
||// 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).
||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.
||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.
||//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
||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).
||//it doesn't act like a valve until you push it.//
The speaker is initially held in contact with the
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.
||And I contend that it is only necessary to provide
sufficient force to bring the sucker into contact with
||If you used a sawtooth waveform to drive the speaker, you could use the power of Arrr! to force it closer to the glass.
||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.
||// 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-
||//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
||*since this is a thought experiment, I thought I could
splash out a little on the raw materials.
||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.
||// wildly distend the waveform coming out the
front// It's all handled in software.
||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. +