Using 6" x 1" neodynium magnets as drivers in custom headphones. Emotiva XPA-2 as amplification. No paper cone, just neodymium!!!!
May 14, 2015 at 3:30 AM Thread Starter Post #1 of 4

MagnetMadness

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Preface
 
I'm a high school physics / computer / robotics teacher.
 
I've enjoyed making "headphones" with 2" sphere neodymium spheres hooked up to some hand-wound coils of copper magnet wire (10 gauge AWG or something like that, so they can take a TON of current without getting too hot). Kids love them. Then they become speakers easily.
 
Question:
 
I think it would be fun to make some headphones using two of these 6" x 1" Neodymium Discs. They'd have to be reinforced, housed, and aligned to not fracture the users skull in an accident, but it'd be awesome. 
 
2" x 2" neodynium spheres sound pretty darn good. Again, high gauge wire, powered with a massive home thearter amplifier. 
 
Does anyone else do this for fun? Any suggestions? Any encouragement? 
 
Thanks!
 
First time poster, so trying to get some cred
 
Grado RS-1
Sennheiser PX - 100 
FiiO Amps / DACs
HiFiman tube dac/ amps
Grado RA-1 Amp
Grado 60s
Grado 80s
Sony SA-5000
Sony SA-1000
AT - 50Ms
 
but I love me some think copper wire, some, giant magnets, and 3 15-Amp circuits worth of huge amplifiers driving the most inefficient things imaginable. 
 
Example:  Wrapping a 2" neodymium sphere of N45 quality (http://unitednuclear.com/index.php?main_page=product_info&cPath=70_71&products_id=281) in about 30 loops of 16awg copper wire and running it through a cheap receiver sounded pretty darn good. It was almost straight-to-the-bone, as in if you pushed it hard against your ear (effectively covering your ear so you can't hear anything else, the high frequencies still got in and the bass was joyfully violent. "Better than beats!!" I got a 18 year old inner city kid who wanted Beats by Dre more than anything. 
 
Anyway, have at me. Thanks for taking the time to humor me. 
 
May 15, 2015 at 11:55 AM Post #2 of 4

jcx

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definite safety issues with big Ne magnets - cuts, even broken bones are real issues when they fly together or at any Fe nearby
 
I really can't see your school safety officer allowing such large magnets without serious supervision, shop inspections for loose tools, handling precautions if they had the slightest clue how much force, energy product are involved - and how non-intuitive the risks are - humans aren't expecting lumps of stuff to suddenly fly
 
 
as far as making good audio transducers yourself  - you should look at ribbon speakers and flat diaphragm magnetic planar types - many diy sites will have worked out projects with pics
 
the ribbon speaker style is particularly simple mechanically - just some Al foil in a strong mag field - driving them safely requires a power resistor in series to be safe for a ordinary audio power amp - a step down transformer really needed for more current, louder sound
 
May 15, 2015 at 1:21 PM Post #3 of 4

MagnetMadness

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Safety issues are a major concern, but very preventable with proper engineering and safety procedures, but I appreciate and share your concern for potentially extreme hazards. Though I've never worked at a school with anyone who checks the safety of anything. I'm trusted not to be an idiot (which I appreciate, I know my physics / chemistry safety!). 
 
I do appreciate your insight into planar design, as I didn't know planar speakers were that simple ---- I've made a lot of them but I usually just called it 'awesome' and don't bother looking up the proper terminology.
 
Still, It would be fun building a speaker where the magnets are large enough that a speaker cone would be totally optional. I think 6" radius would do it. If more volume is needed one simply throws things at the magnet increases its surface area!  (or stick it to a metal door / locker / car / metal chair / etc and have an 4' x 10' driver  ---- It worlds pretty well with smaller neodymium magnets. 
 
thanks again for the reply. 
 
May 15, 2015 at 4:39 PM Post #4 of 4

jcx

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voice coil motors are just a efficient geometry for coupling the current in a wire to a concentrated mag field to generate a force/motion over a restricted range
 
 
for sound radiation you have to add some solid surface to push the air - sometimes this is just a cap, a dome/inverted dish the same diameter as the voice coil, there are also ring radiators, the common cone you see everywhere...
 
the relation of sound wave generation and desire for decent loudness and wide response dictate the popular ways of coupling the motor motion to the air with different size/shape diaphragms
 
the motor has to be designed for some range motor linear travel and available force before melting the glue holding things together and meet the acoustic radiation requirements too
 
quite a bit of engineering goes into what we use today in commercial loudspeakers - over a century of development
 
 
for demoing principles in science class you don't need all of that but you also have to accept the resulting performance limits being way behind current technology, what you can buy for lunch money
 

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