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In Reply to: RE: Your best tweaks for fullrange posted by Dryginger2 on May 08, 2015 at 06:21:35
Well that's a very impressive tweak!!!
But I don't understand why shielding the speaker is good for sound?
You have to constrain magnetic fields to maximize power?
Follow Ups:
DG is NOT shielding the speaker. The flux fields will stretch out forwards and backwards. To shield the speaker you need to completely enclose the magnet and to be honest regular iron will work just as well,
Magnetically conductive material tends to capture the "lines" of magnetic force and within that material moves faster than through air speeding up magnetic efficiency.
MJ has a point : since we are working with magnetic fields there is an associated E field generated by the magnetic induction. Mumetal manufacturers recommend layering the mu metal with copper foil and it speeds up the magnetic field even more.
Even when wrapping the magnet, it is important to eliminate sharp corners. Even a small radius on the corners seems to "sweeten" the sound.
two decades ago I was attempting to build shielding for some of my favorite speakers for use as center channels. It was a great learning experience.
One of the best tweaks was to imagine two lines tangent to the magnet of , say the tweeter and midrange. Now place a few layers of mumetal and copper perpendicular to the centerline of the magnets but within the tangents (sorry scanner is down, but I will send a picture later), and halfway between the drivers. ACtually placement is similar to how I recommended the putty be placed on the front baffle, except the mu metal strips should be placed parallel to the magnets and in the line of sight of them.
There is a tremendous increase in detail within the crossover points. The magnetic fields of each driver is actually affecting each other and a lot of what we consider crossover distortion disappears, even though we may have not even noticed it before
Of course YMMV and FWIW
Hi Stu
You mean iron works good in theory or you actually used iron for capture the magnetic lines?
Would be iron useful in right place?
please send the photo if you can.
thank you
mehrdad
tweaker
A good source is old transformers. Normally silicon steel, they are highly permeable and can direct magnetic fields quite nicely. A bit more work, but I like to cut off the coil windings and just use the laminated sheets. It enables me to experiment with more precise placement of the lamination orientation. You can also simply short out the windings ( For me it depends on the size of the transformers).
Over motors or under, I often used to use large steel washers. These will absorb the magnetic fields and work well but even better with copper tape bonded to the top and bottom. Works well for TT's and CD spin motors.
If you use the copper tape I like to run a ground wire to the component
Hi
Silicon steel of old Transformers is very good idea.
Thanks so much
tweaker
Stu,
"DG is NOT shielding the speaker. The flux fields will stretch out forwards and backwards. To shield the speaker you need to completely enclose the magnet"
Four layers of 'MagnetShield' wrapped around the side and back of each of my mid-range and woofer magnets has resulted in a 25+% increase in dynamics and slam so, if it's not the magnet-shield minimizing the 'fringing-effect', what else does your testing suggest is energizing their drivers?
DG
Going back to physics class:
Remember those magnetic lines of force when sprinkling ferrite powder on a piece of paper above a magnet? They would rather travel through ferrous metal rather than through air, and you could demonstrate this by placing a piece of ferrous metal above the magnet on the paper. The lines of force want to move towards the ferrous metal.
In fact, you can greatly extend the range of the magnetic field this way.
In using concentric layers of magnetic material around the speaker magnet, the lines of force move closer together, thus simulating a more powerful magnet. A comparison of ceramic magnets to something like neodymium will show many more and denser "lines of magnetic force.
I would prefer the layers of magnetically conductive material to be as close as possible (think laminations in a transformers). In such a case, I use the copper foil only on inner most and outermost layers and ground them to gain a a bit more "speed" to the drivers. Actually, come to think of it, alternating copper and mumetal will provide magnetic isolation between the mu metal layers. You wouldn't want the magnetic field of one layer bleeding into the adjacent ones.
Thinking of magnetic fields and their interactions was very difficult for me. Voltage and resistance is much more easier to comprehend and measure. Although eventually I did get a gaussmeter, by that time I had sort of started to comprehend magnetic fields. Incidentally you can use a simple compass as a sort of gaussmeter
YMMV and FWIW
Stu,
So differentiating between 'shielding' and 'enclosing' is largely semantics since it's impossible to 'seal' the front of the speaker?
Emil Detoffol of LessEMF Inc. advised that the effect of MagnetShield or MuMetal was virtually doubled when leaving a gap between each layer. That was the reason for the cork strips but copper foil sounds like an excellent idea. The only limitation is the space restriction in re-installing the speaker through its hole in the cabinet. Certainly blocking the central air hole at the back completely throttles the driver.
All I know is that wrapping the sides and back with layers of MagnetShield puts the performance of my speakers (that have a good reputation) on steroids.
DG
Magnets are weird things
Alnico drivers basically use slugs, and the Alnico elements are located where the pole pieces are normally located. The Outer shell of the magnet structure forms a sort of "keeper" like what you are making pulling the magnetic field closer to the slug and thus increasing the magnetic intensity.
Funny budget alnicos like in TV sets use a u shaped keeper with two ends open. Still work but not very efficient Just slapping on a couple pieces of steel to the open sides helps a lot. The good drivers, Altec, Bozak, etc. use rings ( looks like steel pipe to me), and afford better shielding ans well as stronger magnets.
Less emf is correct, you don't want direct contact with the magnetic material as the "lines " of force can cross over and muddle the field intensity. In pulling the lines closer together, you are reducing the overall magnetic field extension, and increasing the intensity at the same time, at least at the magnet core.
There's a paragraph in the Lessemf catalog which states you should be directing magnetic fields not necessarily trying to eliminate them. That fact took me many years to sink in. so now I work on redirecting the magnetic fields and achieve much better results
YMMV
and FWIW
Too bad Radio Shack closed down. About 15 years ago they had a number of raw drivers, cheap and fairly good. RS 1354, IIRC a 5 inch full range with whizzer with tight voice coil spacing. Bought a dozen to play around with. They actually sounded pretty good. I cut off the dust caps, drilled the pole pieces, built phase plugs since at $7 each they were pretty much expendable. It was a great learning experience, since what I heard often contradicted standard wisdom and advice
unclestu,
FWIW
Too bad Radio Shack closed down. About 15 years ago they had a number of raw drivers, cheap and fairly good. RS 1354, IIRC a 5 inch full range with whizzer with tight voice coil spacing. Bought a dozen to play around with. They actually sounded pretty good. I cut off the dust caps, drilled the pole pieces, built phase plugs since at $7 each they were pretty much expendable. It was a great learning experience, since what I heard often contradicted standard wisdom and advice
I was wondering if I could contact you concerning the tweaks on that speaker. I have 5 or 6 of them. I dropped a lot of money on their selloff
of those and several other speakers often at a dollar apiece.
DagW00d
contact me at unclestu52@gmail.com
Aupiho,
Look at the first picture of the 'fringe effect' where there is all that magnetic flow outside the area between the two metals. Now visualize the loss of magnetism to the driver that exists when magnetism escapes from the sides and back... Wouldn't you want to stop a clutch from slipping and preventing a car engine from delivering its full performance? This is somewhat similar for coil speakers whose manufacturers have not enclosed their magnets.
DG
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