Magnetism question

braunluver

braunluver

New Member
On a speaker with a vent hole in the pole piece. If I were to place a piece of ferrous metal in that hole would it affect the magnetic field?
Please bear with me on this. I am going somewhere with this.....
And,yes,before you say it.....I know that it will have an affect on cooling and thermal power handling of the coil.....
 
Damn, that wasn’t covered in engineering physics.

I “think” it will just become part of the field.

I wonder what Google knows about magnetic flux?

But, speaker magnets are not exactly laboratory grade calibrated flux devices so it probably doesn’t matter.

And the huge question everyone wants answered is “Just where are you going with this”?
 
It could affect the image of a wide screen TV if the speaker is near the screen, but you should be able to see that.
 
I'm thinking about turning a Peavey Black Widow 18 inch woofer into a coaxial

blhagstrom said:
Damn, that wasn’t covered in engineering physics.

I “think” it will just become part of the field.

I wonder what Google knows about magnetic flux?

But, speaker magnets are not exactly laboratory grade calibrated flux devices so it probably doesn’t matter.

And the huge question everyone wants answered is “Just where are you going with this”?
Click to expand...
 
Hmmm, interesting.

Now I’m wondering what the possible flux field interaction between the woofer and tweeter might be in close proximity.

FWIW, when they started worrying about TV and shielding speaker, they glued a can over the magnet to damped or deaden the flux. I’ve seem early and late model drivers from manufacturers. Some used the same basic driver and just added the can. But I have no idea what effect the can had and if they compensated at all.

I am thinking there are non-ferrous options for your idea.
 
I initially thought about aluminum, but then I wondered about the aluminum expanding more than the iron if I drove it hard and got it hot.
I have 2 of the black widows, and 2 or the 22xt compression drivers, and just thought this might be a cool project. I am by no means an engineer. Maybe the tried and true trial and error method may be the way to go?
blhagstrom said:
Hmmm, interesting.

Now I’m wondering what the possible flux field interaction between the woofer and tweeter might be in close proximity.

FWIW, when they started worrying about TV and shielding speaker, they glued a can over the magnet to damped or deaden the flux. I’ve seem early and late model drivers from manufacturers. Some used the same basic driver and just added the can. But I have no idea what effect the can had and if they compensated at all.

I am thinking there are non-ferrous options for your idea.
Click to expand...
 
It depends on the magnet design on the nearest speaker. Good magnets are designed to have very little magnetic field outside the small region in which the coil moves. You could make an experiment with a compass. If you see an effect nearby the location of the hole, then there is a significant magnetic field there and the ferromagnetic piece will amplify its strength by a factor 1000 or even larger, depending on the ferromagnetic material.
 
Could you put a sheet of (perhaps large??) paper over the driver. Sprinkle some iron filings onto it so you could physically see the patterns.... then...add your plug and redo the sprinkle.... see if/how the pattern changes?
 
Coytee said:
Could you put a sheet of (perhaps large??) paper over the driver. Sprinkle some iron filings onto it so you could physically see the patterns.... then...add your plug and redo the sprinkle.... see if/how the pattern changes?
Click to expand...

Bad idea. If the metal filings escape they will be attracted to the magnet. They will embed into the dust cap and cone. Don't do that.
 
Coytee said:
Uh....that is what the paper is for.... to hold the filings and keep them separate from the magnet...
Click to expand...

Sure. Until you bump it accidentally or cough or sneeze or something else that gets the metal filings on a speaker that you wish to remain undamaged. But, feel free to take any risks you wish on your speakers.
 
The Peavey Black Widows are FRB (field replaceable basket) speakers, so the magnet is not permanently mounted to the basket assembly (basket/cone/VC)--they are attached by three machine bolts, so that they can be separated "on the fly" to repair a damaged driver at a show/event. VC gap easily accessed for cleaning.
 
Ah!

Post #13 scooped me. As said in that reference.

Initially I was going to ask how large the pole hole :D is, but chances are it would not be too large/wide to affect the 'motor' working. In that sense it is unlikely that any ferrous material introduced there will affect the flux in the driver magnetic gap to any audible extent. As the reference said, relieving the pressure below the dust cap (which would raise Fp) is of primary importance, plus other factors mentioned there. [Air passing by through the voice coil gap will not appreciably relieve the below-dust-cap pressure because of the choke effect of the small gap.]
 
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