When a woofer is magnetically shielded the magnetic field is completely altered. There is a lot of information on the benefits of shielding, however, could this alter the actual performance of the woofer? Also, I am wondering how performance of drivers could be affected by metal enclosure which are becoming more popular. What if an enclosure if constructed from steel (which is very magnetic)? The magnetic field around drivers would have a different shape. Could this affect the way the magnet supplies force to the voicecoil? Thanks guys!
When bucking magnets are used to "shield" a driver the pole of the assisting magnet is the same polarity. This actually increases the motors strength a small amount while drawing in the external field lines so not to adversely affect the surrounding, eg purity banding that occurs when normal speakers are near to a crt TV. Effect on motor operation is nill in your case. BTW Mu metal is normally used for magnetic shielding of stray magnetic fields. Was common in higher end CRT TV's and computer monitors
I couldn't find where Troels has looked into this on his website DIY Loudspeakers
But do know it is there, somewhere. He has done this to improve some drivers, achieving 1dB or so increase in efficiency. Not much but better than not.
Within the motor itself is impossible to disrupt the field lines that could cause distortion to increase. It's a costly thing to add with marginal benefits for the end user. For a manufacture to do is cheap. An example of a good bucking magnet strengths is with a Vifa XT25BG60 dual ring radiator tweeter. The lesser versions of this tweeter are prone to many issues. With respect to the XT25BG60 it is nearly impossible to find a tweeter that matches it's performance when placed in a waveguide. Linear response, good low end capability and exceptionally low distortion.
Yes, but what happens if a woofer is mounted on a metal baffle (like steel which is very magnetic)? Unlike a shielding cup which encloses the entire magnet, the metal baffle would only go around the magnet but not cover the back of the woofer magnet. Could this affect the performance of the woofer in any way?
Steel, by its nature is not really a suitable material for speaker cabinets, so where might this be an issue?
countless paging speaker are all housed in metal enclosures no reported problems; several commercial enclosures using metal reinforced baffles for fly rigging purposes no reported effects there either.
the enclosures volume rather than material type will effect the driver but that's different.
short of what Greebster mentioned about the additional magnet potentially increasing the field strength of the motor no negative effects are known or reported at least from what i can tell after recently having studied up on the subject in order to solve a issue with a fullrange driver causing color distotion in a crt.
the enclosures volume rather than material type will effect the driver but that's different.
short of what Greebster mentioned about the additional magnet potentially increasing the field strength of the motor no negative effects are known or reported at least from what i can tell after recently having studied up on the subject in order to solve a issue with a fullrange driver causing color distotion in a crt.
and i don't know what speaker companies or types your looking at or have seen but most are aluminum (radio shack minimus 7 comes to mind)
being aluminum the material exhibits no magnetic effects.
being aluminum the material exhibits no magnetic effects.
I know a few people did DIY subwoofer with steel enclosures. But once again, I really just want to understand the theory and the physics behind what would happen. Does anyone know what would happen to the performance of a woofer that is mounted on a magnetic material like steel?
No ill effects, but as Cal has said not the best material for a baffle. If done would require alot of dampening and the mass of such would be to great, especially if large.
AFAIK Dynaudio and Morel drivers use magnets inside the larger 75-100mm voice coil with steel covering the outside to great advantage , but that limits the size of the magnet, so the motors are relatively weak. If they switched to rare earth magnets, that would be something.
which is probably why the paging/background music industry is moving away from metal back boxes to ABS enclosures less ringing smoother midrange and lighter to boot.
just because someone DIY'ed a metal enclosure doesn't make it a good idea (than again some have to try in order to learn) i just think of truck packing or hauling a metallic enclosure as no fun as my mangled digits still bear the scares inflicted by wooden boxes!
just because someone DIY'ed a metal enclosure doesn't make it a good idea (than again some have to try in order to learn) i just think of truck packing or hauling a metallic enclosure as no fun as my mangled digits still bear the scares inflicted by wooden boxes!
Hi,
ATC use steel baffles in some of their smaller speakers.
Steel sheet stuck to relative thin mdf walls by a damping
layer has been used to get a heavyweight miniature that
has decent internal volume for the external size.
Drivers with a "can" around the magnet require a
bucking magnet for the "can" not to saturate,
and basically do more harm than good.
The theory and the physics require a more detailed question.
The bucking magnet slightly concentrates the drivers
internal field by reducing flux leakage, a minor tweak
in terms of upgrading a driver, about a dB up.
rgds, sreten.
ATC use steel baffles in some of their smaller speakers.
Steel sheet stuck to relative thin mdf walls by a damping
layer has been used to get a heavyweight miniature that
has decent internal volume for the external size.
Drivers with a "can" around the magnet require a
bucking magnet for the "can" not to saturate,
and basically do more harm than good.
The theory and the physics require a more detailed question.
The bucking magnet slightly concentrates the drivers
internal field by reducing flux leakage, a minor tweak
in terms of upgrading a driver, about a dB up.
rgds, sreten.
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any sources you can link to
I thought saturating the magnetic structure near the gap was a good thing to withstand modulation effects. edit> I wonder if there is a Patent on that tech. so others have to throw stones at it.
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So would a steel front baffle become magnetized by the woofer magnet and would the magnet lose some of its magnetic force to the baffle? Come on, I know we got some physics majors here who know the answer.
My old Minimus 11's the big brother of the 7's where commonly referred to as "Toe Crushers" for good reason. Would jump back out of the way similar to the action when dropping a knife. Good thing the floor was carpeted with quality padding to absorb the shock. The back panel was made of steel plate. Once dampened they worked much better. Later gutted original baffle and replaced drivers. For no bigger than they are were quite heavy. Durability on the other hand was great. Even had them mounted to my motorcycle for a time complete with all the UV sand and salt spray you could throw at them worked quite well. Left them with my father to enjoy decades ago, he liked 🙂
Hi,
I'm talking about shielded bog standard ceramic magnet drivers.
I don't need any sources for that. Bucking magnet and "can".
rgds, sreten.
Hi,
Short answer is yes of course to some extent and no.
The steel baffle only really interacts with leakage flux.
Driver frames have been made with steel since ever.
rgds, sreten.
Magnetic force weakens quickly with distance. The acoustic properties of a steel baffle will have a much bigger influence on the speaker's performance than a few stray magnetic lines that may be deviated a little further away than they would be anyway.
The magnetic energy of a rare earth Neodymium magnet is directly related to the surface area of the exposed magnet in the direction of charge. Added mass has very little to nothing to do with any increased energy in the magnetic gap. So the overall increase in energy with a closed cup core magnetic system will come at the cost of an increase in diameter of the low carbon steel allowing for a larger diameter magnet internally with a larger surface area.
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