Craig Sawyers

I've certainly toyed with the idea before. The problem is that you cannot passively magnetically levitate something (actually not true - see below), so all the audio feet have a tie-wire or guide rod to maintain stability. Which adds a bit of friction, so it is never truly maglev. The Japanese train uses dynamic control to keep it stable in the air - and you have to be darned sure of the control systems! The not true bit is that there is a bewildering property of superconductors called the Meissner effect. A piece of superconductor excludes external magnetic fields, the net effect being that the superconductor levitates above the magnets. Around 20 years ago I demonstrated this to my young kids. I brought home a magnet, a small dewar of liquid nitrogen and a piece of high temperature superconductor (or HTSC, which just looks like a small piece of coal). Cool the supeconductor in the liquid nitrogen and put it on top of the magnet - and it just pops into the air. You tube is your friend. This demo does the opposite thing - levitation of a magnet above a disc of HTSC

Can I ever forgive you for that vid - I just expelled coffee out my nose.

Yeah - they are weird objects. A star has to be greater than about 8 solar masses to gravitationally collapse into a neutron star at the end of its life. Much more than ~30 solar masses and you get a black hole rather than a neutron star. Both these exotic objects are supernova remnants. When a large star runs out of fuel, it collapses bewilderingly quickly - a few seconds - producing a huge amount of exceptionally hot material (mainly as a result of mechanical bounce - first the core collapses, then the outer shells of the star go inwards at about a quarter the speed of light, hits the collapsed core, bounces, and comes out again very hot indeed). Also, since a star spins (pretty slowly), as it collapses the spin speeds up, like a figure skater spinning on the ice can speed up, due to conservation of angular momentum. A neutron star can spin anywhere from once every few seconds up to about 1kHz, and emit a beam of radiation along its spin axis at the rotation speed. That was discovered in 1967 by a then research student called Jocelyn Bell in Cambridge UK using the radio telescope there. Initially tongue-in-cheek christened LGM for Little Green Men, she later figured out could be a spinning neutron star - now known as a pulsar. Her research supervisor Anthony Hewish won the Nobel prize for her work, and she got diddly squat. The fate of our star is different - since it is below something called the Chandrasekhar limit for formation of a white dwarf (>~1.44 solar masses; he figured that out aged 19, back in 1930) it will progressively bloat and cool when it runs out of fuel, swallowing up all the planets to earth and beyond, and becomes a red giant. Lucky for us not for quite a while yet, even though our sun destroys 5 million tons of material every second in nuclear fusion. To put that into context, a 10MT thermonuclear bomb destroys 0.05kg.

That same woman seems to have done a whole lot of you tube vids.

Yeah - I know what they meant. But if you knew nothing about a subject (which they clearly did not) you'd get someone who knew to check it; well I certainly would. And if they meant approximately, then either write the word, or an abbreviation like approx. Then there is no ambiguity. But then again, I'm just your regular pedantic asshole

That is what we used to use at Wharfedale. Actually it was speckle interferometry, which is what you have to use to map the resonances in rough surfaces. In the mid/late 1980's. Dunno what if anything they use now.

Plus *or minus* 20km??

A good way of subjectively seeing if anything is moving is the Beethoven trick. Put a stick (of a sort that will not damage the finish on the speaker) between the speaker and the pinna of your ear. You'll hear if anything moves.

The whole vibration thing is interesting. Suppose you put a mass on something that is springy, and the other end is coupled to something rigid, like a floor. What is the resonance frequency? It is dead easy to calculate - if the spring compresses by delta x metres, the resonance frequency is (1/2pi) x root(g/delta x). You do not need to know the mass and spring constant - just the deflection. So suppose the speaker compresses (say) sorbothane feet by 2mm, the resonant frequency is (1/2pi) x root(9.81/2E-3) = 11Hz. So at frequencies higher than 11Hz the speaker stays (vertically) stationary, and at frequencies lower than 11Hz, the speaker bounces up and down. Of course if it is actually sorbothane, there is high loss, so there is not a resonant peak, but the basic motion remains. Of course it is more complex than that, because the cones have substantial mass, so there will be a tendency for the speakers to rock like a pendulum as well as the cones move back and forth. In this case it depends on where the C of G of the speakers lie, where the drivers are (particularly the bass driver), and how far apart the springy bits (sorbothane for example) are. That in general will be a low frequency, certainly lower than the vertical 11Hz. Try rocking the speaker and see what happens - probably 1 to 2Hz. If you use spikes there is a gotcha. The spikes need to be very, very seriously locked in place. Because of the cone motion, particularly at low frequency, and tendency to pendulum rock, it the spikes are not locked absolutely solid, the speaker can rock on the spikes. Most easily diagnosed with swept sine. Got the badge on that one - testing a homebrew sub I wondered what the god awful noises were as I swept a sine wave - sounded like the worst sort of distortion. Loose spikes.

A rapid lithium battery induced disassembly incident at NASA. Oops.

About 50F here in the UK, and looking to cool down during November with night frosts and snow on high ground. Texas (30N) is on the same latitude as Egypt, Saudi Arabia and Kuwait. The UK (51-53N) corresponds to Southern Alaska. Factoid No:47b

RIP Bobby Vee, age 73. Early Alzheimer's. Far far too early.

Just catching up after a few days away, and am just reeling. Go for her jugular Steve - bring her as low as low can go. PS we get our cats from https://www.bluecross.org.uk/oxfordshire-burford-rehoming-centre , and fortunately these are the good guys. They give you a verbal third degree to make sure that you are the kind of person who can be trusted with a cat or dog from them.

Haven't heard anything since that post; but yes like you I'd be up for a bunch (provided they are genuine new old stock).

I'm just not sure where the silicon is in relation to the package. It *may* be much closer to one face than the other.

Happy Birthday!

Dog goes into the telegraph office (this is an old joke), puts his paws on the counter and goes "woof woof woof woof woof woof woof". The lady behind the counter says "You can have one more woof for the same money" The dog replies "That would be ridiculous, it wouldn't make sense with another woof"

That is the sort of faultless logic I use. "Hey - I've got all this free stuff. Let's use that fact that to spend lots of money to get the best value from the free stuff". Been there so many times.....

You can also get the Neutrik RCA's in an XLR housing, which looks kind of cool.

Hey man - have an absolutely great one!

The Naim Statement. About the same price as the boulder above, but at least you get a preamp (the middle slice).

Ooh - shiny

He doesn't say what the measurement bandwidth was. Which really makes it a very loose specification. The only hint is the very sharp mains harmonics in the noise plot, which are way sub-Hz in width. To get to -158dBV (-155.8dBu) from -107dBu on a 20kHz B/W you would need a measurement bandwidth of 0.25Hz, Shockingly badly specified.

The most significant issue with the THAT 1200 series of receivers is noise, -107dBu. It is dominated by the rather large values of noise-generating resistors inside (7k typical). With a good discrete design, or clever use of opamps you can get to -120dBu, which challenges measurement (<1uV in a 20kHz bandwidth).

Cooler is a relative term with the T2 Clone