What happens, if anything, when an extra magnet is added to the rear of a speaker. I know it has been mentioned in here somewhere but I can't find it. If it has any advantage is the magnet held in place by its own attracti0n or is it glued. Thanks for any reply.
jamikl
jamikl
Piggyback magnets are aligned with both magnetic fields in same direction.
Bucking magnets have fields reversed, in both cases they are usually glued on.
bucking magnets are used for shielding purposes, piggyback magnets to alter T/S parameters, although bucking magnets also alter T/S parameters, opinions divided on the efficacy of doing so, I tried it once and could hear no difference so never tried it again, Sreten says it is a bad idea, others have used it but I can't find the old links.
A well designed speaker shouldn't need any extra magnets and bad / cheap designs are probably beyond help anyway.
BUT all speaker builders wind up with lots of spare magnets so why not try it and see if you can measure any difference????
Bucking magnets have fields reversed, in both cases they are usually glued on.
bucking magnets are used for shielding purposes, piggyback magnets to alter T/S parameters, although bucking magnets also alter T/S parameters, opinions divided on the efficacy of doing so, I tried it once and could hear no difference so never tried it again, Sreten says it is a bad idea, others have used it but I can't find the old links.
A well designed speaker shouldn't need any extra magnets and bad / cheap designs are probably beyond help anyway.
BUT all speaker builders wind up with lots of spare magnets so why not try it and see if you can measure any difference????
I have some Eminence Beta 15s and some ruined Pioneer 12" car subs which I picked up roadside. I am wondering whether adding the Pioneer magnets to the Eminence will make any difference.
jamikl
jamikl
First off are the car subs worth rebuilding??
I wouldn't ruin a good cast frame just to scavenge a magnet.
Do you have any measuring equipment? as this isn't something I would imagine you can hear easily.
If it is just a magnet or two I can supply plenty of those, save throwing them in the bin when we move next month
I wouldn't ruin a good cast frame just to scavenge a magnet.
Do you have any measuring equipment? as this isn't something I would imagine you can hear easily.
If it is just a magnet or two I can supply plenty of those, save throwing them in the bin when we move next month
" I have some Eminence Beta 15s and some ruined Pioneer 12" car subs which I picked up roadside. I am wondering whether adding the Pioneer magnets to the Eminence will make any difference "
Adding a magnet results in a decrease in qes.....u won't here any diff though..... the polarity should be same..that is while attaching the spare magnet u should feel that the speaker's magnet is repelling the other magnet and not attracting it. Otherwise qes might increase....
Adding a magnet results in a decrease in qes.....u won't here any diff though..... the polarity should be same..that is while attaching the spare magnet u should feel that the speaker's magnet is repelling the other magnet and not attracting it. Otherwise qes might increase....
It's hard to generalize but all things being equal an extra magnet attached with opposite polarity will:
- increase sensivity slightly by bucking stray magnetic field back and thereby increasing force factor.
- lower Qts slightly by lowering Qes for the same reason as above.
- dramatically decrease stray magnetic fields, not as effeciently as a proper shielding but for most purposes this is the primary benefit.
Attaching a magnet with equal polarity will:
- increase sensitivity and decrease Qts for the same reasons as above but it will have more effect because you're adding extra magnetic field strength and not just focusing the already existing.
- dramatically increase stray magnetic fields which in itself can be a major drawback.
It should be noted that except for the increase/decrease in stray magnetic fields the benefits are minor to minute. And that the more well designed the drivers magnet motor system is in the first place the less benefit you will see.
- increase sensivity slightly by bucking stray magnetic field back and thereby increasing force factor.
- lower Qts slightly by lowering Qes for the same reason as above.
- dramatically decrease stray magnetic fields, not as effeciently as a proper shielding but for most purposes this is the primary benefit.
Attaching a magnet with equal polarity will:
- increase sensitivity and decrease Qts for the same reasons as above but it will have more effect because you're adding extra magnetic field strength and not just focusing the already existing.
- dramatically increase stray magnetic fields which in itself can be a major drawback.
It should be noted that except for the increase/decrease in stray magnetic fields the benefits are minor to minute. And that the more well designed the drivers magnet motor system is in the first place the less benefit you will see.
Only way to do it is to add in bucking style. This forces more of the outside stray flux back into the center increasing the Bl of the driver (putting more B in the usable gap). If the speaker has a steel basket and/or a motor with metal plates the same size or larger than the magnet then the effect will be greater since these usually have larger stray fields.
Moondog55 said:
Hi,
Not sure what I said was a bad idea, piggyback perhaps ?
That basically can only make things worse ....
Bucking magnets do work it terms of bucking magnetic fields.
Neither way works very well in terms of efectively using the
additional magnet because its not placed in the magnetic
circuit, in other words buy a driver with a bigger magnet
in the first place.
An externally hosted image should be here but it was not working when we last tested it.
The extra full size magnet (used bucking style) makes a 10%
difference, not very cost effective compared to enlarging the
"proper" magnet.
🙂/sreten.
The problem with ceramic is that you need to go wider to get more real strength and judging by that picture those are as wide as they can go. Going taller with ceramic even inside the motor doesn't get you anywhere near as much as wider.
As Saturnus pointed out earlier the changes will be slight. I believe there was a long discussion on the Single Driver website
about this along with some measurements and it looked like
you could sometimes pick up another 1/2 db eficency.
Sometimes you don't even get this but lose a little sensitivity instead. One thing I have noted on comercial examples of this
is that the bucking magnets used are much smaller than the main
magnet.
about this along with some measurements and it looked like
you could sometimes pick up another 1/2 db eficency.
Sometimes you don't even get this but lose a little sensitivity instead. One thing I have noted on comercial examples of this
is that the bucking magnets used are much smaller than the main
magnet.
sreten said:
woody said:
Yeah, about ½ dB effeciency is maximum you could normally expect. However, as I demostrated in my Boominator build, when you have 2 identical drivers mounted magnet to magnet and playing bipolar that combines the best of both worlds, and I even found the increase in sensitivity to be even higher, just under 1 dB but I'm thinking the last bit of effeciency increase comes from the design of the drivers used. They have a ventilation hole through the middle but at the same time a fine mesh dustcap that allows full breathing through, I guess that construction kills a little effeciency to get a higher power tolerance which is not needed in my Boominator anyways.
I have double SS 8" in my 3way speaker, closed design
At some time I mounted exstra magnets
I have later found that it sounds best with both exstra magnets mounted on bottom woofer...and none on the upper one
At some time I mounted exstra magnets
I have later found that it sounds best with both exstra magnets mounted on bottom woofer...and none on the upper one
tinitus said:I have later found that it sounds best with both exstra magnets mounted on bottom woofer...and none on the upper one
I'm guessing the bottom woofer is significantly closer to the x-over and therefore the reduction in stray magnetic field will have an influence on that.
You could have been right, but in that case I reckin the result would have been the same with one magnet on each woofer
My design is a pyramid. and I found out that upper and lower woofer didnt sound exactly the same...they cover the same frequency
Tendency was equal on both channels...so it neither related to one driver being a bit off
I reckon it due to upper and lower woofer having just slightly different acoustic condition inside the box, because of the pyramid design
If it rally only was related to influence on xo components, it would have the same impact on both woofers
Im quite certain its related to the assymmetric design I seem to like "mr Scratcher" a lot lately 😀
My design is a pyramid. and I found out that upper and lower woofer didnt sound exactly the same...they cover the same frequency
Tendency was equal on both channels...so it neither related to one driver being a bit off
I reckon it due to upper and lower woofer having just slightly different acoustic condition inside the box, because of the pyramid design
If it rally only was related to influence on xo components, it would have the same impact on both woofers
Im quite certain its related to the assymmetric design
I seem to like "mr Scratcher" a lot lately 😀Thanks for the responses. I wouldn't buy a magnet to use this idea but as I said I have these ruined car subs, Pioneer, with rather large magnets on them which I hoisted from hard rubbish collection. Pioneer do not make cones for them but I suppose I could try any cone and surround with same size voice coil openeing and see what happens. What is left of t
he cones look like thin polystyrene foam.
jamikl
he cones look like thin polystyrene foam.
jamikl
It would take less time for the coil to reach a certain position,it means it will provide better separation.
piggy back decreaces your perfomance and magnet strength
I did a expriement with piggy backing I get only 51.2db at 155hz
without any magnets added i get 52.7db at 155hz
with 26pices of 10x20x2mm n52 magnets added to the side of the 6.5inch speaker iget 52.95db at 155hz
the enviroment and position of the funriture had been kep the same during the expriment as this effects the volume level from the pickup
I did a expriement with piggy backing I get only 51.2db at 155hz
without any magnets added i get 52.7db at 155hz
with 26pices of 10x20x2mm n52 magnets added to the side of the 6.5inch speaker iget 52.95db at 155hz
the enviroment and position of the funriture had been kep the same during the expriment as this effects the volume level from the pickup
Attachments
Tacking onto a 10 year old post...
I meddle about with guitar speakers quite a bit and find that the increase in BL product from a correctly added backing magnet often has a beneficial effect. This is because they usually start off a bit under damped. The decrease in Qes coupled with the slight efficiency increase seems to improve the consistency of note to note volume at the low end.
Some very inexpensive speakers were very responsive to the addition. Now the daughter's keyboard has hardly any bass and is much louder. Sort of a win as the transition across the keyboard is a smooth increase in the volume of the fundamental note frequencies. But thre effect is a bit too pronounced. Shouldn't have used glue...
A better win was adding neodymium slugs to the back if the bass/mid range drivers in some B&W 601s. This improved the efficiency sufficiently to enable the tweeters attenuating resistor to be removed. The slightly smoother bass roll off was augmented with extra dampening fluff and a slight lowering of the bass port resonant frequency. Some stiffening of the case occurred to. Overall result is quite pleasing and works really well in thre small room with brick walls that system resides in. Rather think the magnet mod was essential for the recipe.
Is anyone else tinkering with such?
I meddle about with guitar speakers quite a bit and find that the increase in BL product from a correctly added backing magnet often has a beneficial effect. This is because they usually start off a bit under damped. The decrease in Qes coupled with the slight efficiency increase seems to improve the consistency of note to note volume at the low end.
Some very inexpensive speakers were very responsive to the addition. Now the daughter's keyboard has hardly any bass and is much louder. Sort of a win as the transition across the keyboard is a smooth increase in the volume of the fundamental note frequencies. But thre effect is a bit too pronounced. Shouldn't have used glue...
A better win was adding neodymium slugs to the back if the bass/mid range drivers in some B&W 601s. This improved the efficiency sufficiently to enable the tweeters attenuating resistor to be removed. The slightly smoother bass roll off was augmented with extra dampening fluff and a slight lowering of the bass port resonant frequency. Some stiffening of the case occurred to. Overall result is quite pleasing and works really well in thre small room with brick walls that system resides in. Rather think the magnet mod was essential for the recipe.
Is anyone else tinkering with such?
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