Trying to create a magnetic feild that is responsive to sound

[Sciart418]

I am an artist who has been creating work dealing with the visualization of sound waves. To best describe my latest piece, I am using ferrofluid and electromagnets to display the visualization. I have no background in physics so I don't know the technichal terms and formulas but so far with past works I have done pretty well with figuring out my ideas without all the technical stuff (just stating so that if you do respond please explain as thoroughly as possible). Basically what I am trying to do is create an electromagnet (electromagentic plate to be exact) that I can hook up to a stereo system or an amplifier. I understand that a speaker is a form of this (so I would hope this would be simple to do) but I am not trying to create the vibrations, just the magentic field and a very strong one as well. Can anyone please help me in anyway?

 

[schip666!]

Have you tried using a speaker voice coil, minus all the other speaker bits?

 

[Dadface]

Hello sciart.I really like schips idea and if it were me it would be the first thing I would try.Hello schip.

 

[Sciart418]

Thanks so much for the responses.

I definitely plan to try the speaker coil. I'm thinking it may be too weak of a magnetic field to really move the ferrofluid. Does anyone know if wrapping more wire around the coil (taking out the other speaker bits) to make it stronger can cause the stereo system, amp of computer, that it is hooked up to, to overheat or short in some way? I will probably be borrowing some equipment from others and don't have money to replace items that could get damaged.

 

[sophiecentaur]

I must point out that you are very unlikely to produce this effect over a large area (the "plate" you mention). You will only get a strong field across a relatively narrow gap - I am talking in terms of 1cm or less, probably.

I wouldn't say that a loudspeaker has no chance of working but, remember, there is a massive permanent (unvarying) magnetic field compared with a pretty tiny field from the voice coil. This is unlikely to produce a resulting field at the top of the gap which would vary 'visibly'. What is needed is soft iron with high permeability, rather than the high permanence of a speaker magnet.

I would suggest using a 'C core' transformer which has a single 'loop' made out of iron laminations (C shaped and interleaved to make a single loop of iron). If you cut a slot in one side, where the windings aren't, you should get a fairly strong field across the gap. You can try using the existing windings as it is a real pain to wind your own coils and I am not sure whether a 'kit' would be available.
afaik, these ferrofluids need some hefty fields to make them perform so you may need a pretty powerful amplifier for this effect to be visible. You may be able to pick up a scrap transformer from some old equipment. Ask a teckie or even your local scrapman and save money - at least for the experiment.

A note of warning / safety though: make sure that any other connections are covered with insulation. This is a transformer and the other windings can either produce shocking voltages or, if shorted together, they may affect the performance of the electromagnet (which is what you will have made). Btw, any ferrofluid that gets into the gap of a loudspeaker will NEVER come out! If you take the L/S magnet apart, you will have great difficulty in re-assembling it, too.

 

[Sciart418]

sophiecentaur: Thank you for your feedback. I have looked up this C core transformer you are talking about because I have never heard of it before this and it looks like I am going to have to find one and play around with it to completely understand what you mean by cutting where the widings aren't. How would this transfer to a plate?

I also had and idea of using a thin iron plate with a solid (or possibly hollow, which ever works better) post fixed to the bottom of the plate. This post would be fairly long so that I could wrap insulated copper wire many times around it to create an electromagnet. I was thinking then I could hook it up to a strong power source such as an amp. However I'm not sure if the magnetism will travel through the plate as well or just the area that the post is attached. Do you (or anyone else) have any thoughts or suggestions about this idea? Does this idea even have the possibility of working?

 

[sophiecentaur]

As I said before, you are very unlikely to get this effect to operate over a large region.
Perhaps I could illustrate why by considering the fact that everyone used to use horseshoe magnets rather than bar magnets when they wanted a strong force. That's because fields tend to spread out and rapidly become weaker with distance. By having the N and S poles close together, a horseshoe magnet has a much stronger effect.
Also, the field inside a loudspeaker needs to be as strong as possible. What do they do? They use the narrowest possible cylindrical slot to house the voice coil. In both cases you have a small gap in the 'magnetic circuit'.
Hence, I very much doubt that you will get a 'plate' to work.

I've been looking at links about ferrofluids and something I have noticed is that they are quite viscous. I think that must mean that they will not change shape quickly. A feasibility experiment is called for pretty quickly, I reckon.

This is a rough picture of what I had in mind. The magnetic field lines will be closest together (stronger field) right inside the gap and they spread out (weaken) as you get further away.