martin clark said:
I haven't spent much time looking at harmonic motion, so I'm having to engage the brain a bit to picture what you're saying.
Although, something seems wrong with this picture, maybe I'm thinking about it incorrectly. But if you have two springs, one soft and one stiff, and the same force acting on each, the softer one will extend further. For a given force on the platter, I'd then expect the softer spring to compress more.
Change in spring length is related to applied force and the spring's constant. If I load a soft spring with a low weight it might extend to 1 unit. Then I load a stiff spring with a heavy weight and it extends to 1 unit as well. But at these points, changes in the spring length will be determined by delta force, which is the groove modulation force in this example. Assuming delta F remains the same, the stiffer spring will change less.
So deflection wouldn't be the same, although I think period would, as you've said.
I'm open to being wrong on that one but it seems right, maybe I'm missing something.
graeme uk said:
Excellent, £5 is cheaper than I expected.
Eeka chu - you're right, and I'd read the proposition wrong.
If the 'springs' had different rates and different free lengths, but were squished down to the same length by different masses, then yes, the periods will differ.
But I still think if you try it with magnets, and a constant levitation height for different masses, I think you'll find the period of oscillation is rather closer due to the 1/d^3 field strength effect. In effect, a very non-Hookean spring.
If the 'springs' had different rates and different free lengths, but were squished down to the same length by different masses, then yes, the periods will differ.
But I still think if you try it with magnets, and a constant levitation height for different masses, I think you'll find the period of oscillation is rather closer due to the 1/d^3 field strength effect. In effect, a very non-Hookean spring.
graeme uk said:
Last I heard they were still working it out. I was offering to arrange for it to be held here at York University since the university is empty and the physics / electronics building rented out for such events during the holidays (you can even stay in the colleges), but they wanted to go with something smaller at first. It's the first UK version, trying to catch up with the US guys who seem to have 'em all the time. There's a massive thread somewhere on here about it....
http://www.diyaudio.com/forums/showthread.php?s=&threadid=94337&highlight=
I might try to get along to it but I'm so busy at the moment it's untrue.
martin clark said:
No problem, it's not easy to picture exactly what would happen. I'm pretty sure about the amount of deflection being different for the same force (whether or not it would be a linear change with platter weight / magnetic field strength I'm not sure just now - if it wasn't it'd be handy, since there might be an 'ideal' point to aim for where extra weight and field strength does next to nothing), but now that you've mentioned period I think I'm going to have to work out what would happen.
Quantifying that effect might involve integration / differentiation since the 'spring constant' of the field is going to be far from linear.
I'll have to think about it tomorrow though, I have a night's worth of differential equations and integration stuff to work on at the moment. I hate maths....
Ok - I've re-designed the bearing because of a specific problem. I've discovered that there is indeed a magnetic field projected beyond the upper surface of the platter. I should add that this field is quite localised to imediatly either side of the circle formed by the magnet array. As the magnet array is of a diameter that falls within the unplayed centre section of the platter I'm not sure how relevant this is in real life but I'm not happy with it. As a result I have re-designed the bearing to move the magnets further from the underside of the platter and to incorporate a shielding disk between the magnets and the platter. I have added the shielding disk to my MK! design and this seems to have solved the problem completely (I'm very pleased to say). Materials have arrived to make the MK2 version which will move the magnets further from the platter surface and I will have a go at making it next week - pics to follow.
graeme uk said:Out of interest, what exactly was your amp/speaker combo the other day? I know it was naim amplification, but thats all i remember.
Just wondered
OK, here goes:
Avondale Audio Phono stage using modified Naim 323 K boards run from a modified Naim Snaps power supply into Naim Nac 72 Pre-amp run from a NAim Hi-Cap power supply. 2 X Naim 135 mono block power amps to modified Epos ES14 speakers on custom Origin Live stands via Linn K400 speaker cable - also a REL Stadium sub-woofer
Bit of a mouthfull
Ive been tuneless since your house. When i got home and set the TT up i plugged my phono stage in the wrong way round and blew something. Ive ordered a new one, should be here tomorrow.
I had to buy another one the same as ive made arm changes and i need a fair comparison.
Oh well.
Ive been tuneless since your house. When i got home and set the TT up i plugged my phono stage in the wrong way round and blew something. Ive ordered a new one, should be here tomorrow.
I had to buy another one the same as ive made arm changes and i need a fair comparison.
Oh well.
don't forget your little black pods....
as key to the sound of your system as any of your components i'd venture.
Mark, give me a shout when you think you are going to redo the sub chasis and i'll speakto Simon Sanderson and see if he has any offcuts of carbon/nomex board left from the speedboat we did.
as key to the sound of your system as any of your components i'd venture.
Mark, give me a shout when you think you are going to redo the sub chasis and i'll speakto Simon Sanderson and see if he has any offcuts of carbon/nomex board left from the speedboat we did.
sq225917 said:
That would be great - many thanks. Sorry I've not been in touch but I had to do some actual business - also one of my speakers has decided to 'go all funny'; to be precise - one of the bass drivers has become de-centred so my system has not been working for the last few days :-( . I have managed to source a spare mid/bass driver now...but it wasn't easy. Everything should be back on song by early next week (I hope).
Oh I forgot, Graeme, I'm really sorry to hear about your phono stage probs....I'm not sure how connecting it up the wrong way round could damage it though.
Oh, hang on "little black pods", you mean the ones on top of the speakers. Yeah they seem like total nonsense don't they but once you've heard the difference with and without, they definately sounf better with. It's most odd, but I've never had anyone not be able to hear the difference.
I did notice those cones, i should have asked as im not a believer (but open minded about it). Whats the explanation? I cant see how it can be a soundwave thing, so must be a cabinet resonance thing?
I connected the inputs and outputs the wrong way round. Now it equalizes the sound but doesnt amplify it. No big beal, there only £15, but an inconvenience all the same.
What happened to your driver? What do you mean by de-centered? Not heard of that before. Sounds nasty!
I connected the inputs and outputs the wrong way round. Now it equalizes the sound but doesnt amplify it. No big beal, there only £15, but an inconvenience all the same.
What happened to your driver? What do you mean by de-centered? Not heard of that before. Sounds nasty!
It looks like the rear spider may have sagged a bit over time and now the voice coil makes contact intermittently with either the phase plug or the magnet; anyway, the result is that it now 'buzzes' at certain frequencies.
With regards to the black cone/bullet things; I believe that the explanation (as far as it goes) is to do with high frequency dispersion. I think 'Audio Physics' (but I could well be wrong on this) first came up with the idea. Hi-Fi+ had an article on it a few years ago and I had some spare cones lying about so I tried it (didn't expect to hear anything) - I liked it so much I made some better quality ones; they just rest on the cabinet so can easily be removed. I will play you the difference next week when my system is working again. You can also hear a difference when you put them on the inside corners instead of the outside. Simon has heard the difference perhaps he will comment?
With regards to the black cone/bullet things; I believe that the explanation (as far as it goes) is to do with high frequency dispersion. I think 'Audio Physics' (but I could well be wrong on this) first came up with the idea. Hi-Fi+ had an article on it a few years ago and I had some spare cones lying about so I tried it (didn't expect to hear anything) - I liked it so much I made some better quality ones; they just rest on the cabinet so can easily be removed. I will play you the difference next week when my system is working again. You can also hear a difference when you put them on the inside corners instead of the outside. Simon has heard the difference perhaps he will comment?
sounds interesting. Braking up the high frequency sound waves as they eminate from the baffle?
Were sort of wavering from thred topic here, probably my fault
As for the cone, you mean sagging of the actual metal spider of the driver chassis? Thats a bit poor!
maybe they need some reinforcement?
maybe thses are conversations for another day.
Good luck with mag lev mk2
Were sort of wavering from thred topic here, probably my fault
As for the cone, you mean sagging of the actual metal spider of the driver chassis? Thats a bit poor!
maybe they need some reinforcement?
maybe thses are conversations for another day.
Good luck with mag lev mk2
re the little black pods on the speakers.
the effect, but the effect is noticable in the first few seconds of a track.
having them present or not present alters the position and width of the sound stage. you can widen and contract the image size, it also sounded like it brought the treble forward slightly.
the effect sounds similar to increasing the baffle size around the treble unit, if you've ever done that with stick on foam blocks.
it seems like a part remedy for sharp edged loudspeakers, if anyone has modified their baffles to remove sharp edges and applied radiused edges, then the effect is very similar, though apparently directional due to the corber positioning of the pods above one corner of the bafffle.
the effect, but the effect is noticable in the first few seconds of a track.
having them present or not present alters the position and width of the sound stage. you can widen and contract the image size, it also sounded like it brought the treble forward slightly.
the effect sounds similar to increasing the baffle size around the treble unit, if you've ever done that with stick on foam blocks.
it seems like a part remedy for sharp edged loudspeakers, if anyone has modified their baffles to remove sharp edges and applied radiused edges, then the effect is very similar, though apparently directional due to the corber positioning of the pods above one corner of the bafffle.
YNWOAN said:
Interesting, I had an idea for how to remove that problem using carefully positioned bits of mu-metal, but where abouts did you end up putting the metal plate?
The first thing I thought of was to just fix it to the platter, but then it's rotating with the field. It would also need grounding to short out the maximum amount of any AC field trying to get through it.
But for some neodynium magnets with a gigantic OD and ID to go round the perimeter of the platter. That would help keep the field away from the playing area and also improve the stability of the platter.
I know you can have neodymium magnets customs made, if enough people were interested maybe it could be a group buy.
What did you use to track down the field in the end?
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