# magnets against metal: bad?



## Alpine_9813 (Jul 28, 2018)

I have a truck. the rear speakers are in a box and it pushes them firmly against the metal wall. is that bad for the magnets? would they get de-magnetized or something?


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## Infinity99 (Jul 13, 2015)

They will not get "demagnetized" at all, however you are taking away from the efficiency of the speaker and maybe damaging it at the same time. The magnet is there to keep the coil in place and moving freely to allow wave forms to be produced (music, sound). 

If the magnet is touching a metal structure (outside force), then the magnetic force is being drawn to that instead of focusing its energy keeping the coil in its place or in motion if that make sense.

Laymen terms, its not a good idea. Build some spacers to push the speaker out farther away so that there is no magnetic force introduced to it. It may actually force your coil to one side producing a not so good sound and may damage the speakers coil.

Are the speakers in a box against a metal wall, Or are the speaker magnets actually touching metal.....


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## SkizeR (Apr 19, 2011)

I have a very strong feeling that the above is false, and that it doesnt effect it.

Sent from my SM-G950U1 using Tapatalk


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## ParDeus (May 10, 2014)

SkizeR said:


> I have a very strong feeling that the above is false, and that it doesnt effect it.
> 
> Sent from my SM-G950U1 using Tapatalk


I'm kinda with you here. For science sake, I'm going to a measure a sub with the DATS the proper way, and then try it with the sub stuck to 1/4 sheet steel.


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## JCsAudio (Jun 16, 2014)

ParDeus said:


> I'm kinda with you here. For science sake, I'm going to a measure a sub with the DATS the proper way, and then try it with the sub stuck to 1/4 sheet steel.


Interesting concept by infinity99. It will be interesting to see what you find out.


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## Grinder (Dec 18, 2016)

ParDeus said:


> I'm kinda with you here. For science sake, I'm going to a measure a sub with the DATS the proper way, and then try it with the sub stuck to 1/4 sheet steel.


Same here. Looking forward to your findings. :thumbsup:


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## DeltaB (Jun 17, 2017)

All magnets will loose some coercivity by placing it in a field. Some types are more susceptible to this. However, I wouldn't expect it to loose much more than -3dB over its life, or the manufacturer used the wrong type of material. Having said that, placing it next to the cab will do less to coercivity than the actually playing of the driver.


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## Donanon (Sep 13, 2013)

I was wondering about this myself a few weeks ago and found this information at: 

Do magnets ever lose their magnetism?

The answer appears to be, no.



D.


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## Alpine_9813 (Jul 28, 2018)

Infinity99 said:


> Are the speakers in a box against a metal wall, Or are the speaker magnets actually touching metal.....


speakers actually touching metal. albeit painted metal.

Ford Ranger rear speakers. factory setup. the aftermarket speakers have large magnets, would need smaller than normal magnets to not get pushed against the metal. such as the flimsy stock speakers.


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## Alpine_9813 (Jul 28, 2018)

I suppose, if one wanted to detect a loss in coercivity (magnetic strength) you could measure the magnet's strength before and after. what force does it have on an object at a defined distance.

like, bolt the speaker to a wood panel, set it on the floor, hang a steel object from a scale and make it exactly 1/8" from the magnet. record the weight.

or someone could make a gadget you simply hold on the back of the magnet and it measures what force it applies to a steel strip on the outside with an LED display.

or use a magnetic flux meter. (attachment to a gaussmeter)


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## diy.phil (May 23, 2011)

Sometimes they wrap steel all around the magnet and call it a shielded speaker!


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## JCsAudio (Jun 16, 2014)

diy.phil said:


> Sometimes they wrap steel all around the magnet and call it a shielded speaker!



Ferrous or nonferrous metal? 

Trick question.


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## ParDeus (May 10, 2014)

Alright, I got around to it. Didn't want to drag a 21" woofer upstairs, so a PE cheapo depot 6.5" mid is our subject. You can see my temperature controlled super duper science lab... I've nicknamed it "The Porch".




Here's the run of the speaker on glass. Ya, I know this isn't perfect, but it will show any relative difference.





And here's the speaker on some thick rusty steel. Being this thick (1/4"), it ought to "effect" the speaker more, assuming there is any.



These are the results from the run where the speaker is magnetically stuck to the steel.





I ran each version of the test 5 times to verify accuracy. All points were very close in each version. However, you can see a distinct difference between the runs. Now whether or not that has any effect and to what extent, I can't tell ya. Maybe one of the pro's around here can shed some light.

I will say this though, being near metal won't effect the voicecoil positioning as stated in the first reply, the suspension would have to be exceptionally weak and the metal would have to impart an additional magnetic field for that to happen.


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## ckirocz28 (Nov 29, 2017)

Donanon said:


> I was wondering about this myself a few weeks ago and found this information at:
> 
> Do magnets ever lose their magnetism?
> 
> ...


The answer is yes, if you heat them, otherwise no.

Sent from my SM-G935U using Tapatalk


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## DeltaB (Jun 17, 2017)

ckirocz28 said:


> The answer is yes, if you heat them, otherwise no.
> 
> Sent from my SM-G935U using Tapatalk


Actually, the answer is yes, especially for the intended purpose of usage of magnets in speaker motor usage.

For example, taking a high sensitivity driver for example, utilizing Alnico magnets, (Aluminum, Nickle, Cobalt) which at their designed power of Class A at 15~30 watts, you can drive them for some time, and not really worry about degaussing them, but take a SS amp with over a 100 watts and start driving them hard, and the field coil inside will start to degauss them. This is why professional shops who do the job right, at recone time will "regauss" Alnico V magnets. Always remember to make them magnets in the first place, you introduce them into a strong field, and the same can and will degauss them. (see item number 2 in the above mentioned webiste)


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## Oscar (Jun 20, 2010)

Looks like there is a loss of B in the gap when stuck to the steel plate, thus BL goes down, thus Qes goes up, thus Qts goes up. The loss in sensitivity would be small, and the shift in alignment would shift the EBP (Fs/Qes) lower towards the "sealed side" of the recommendations.

Having said that, you won't run into any 1/4" steel in any vehicle cabin, more like sheet metal around 40-65 thousandths thick (about 1/16" but usually much less). Even the frame rails in trucks are more like 1/8"-3/16" thick most of the time. And even then the speakers are still inside the box as per the OP, so there is the wood thickness between the magnets and the truck sheet metal, unless the scenario is elaborated by the OP.

Infinity99, 
As was said before, the magnet is _not _responsible for keeping the coil in-place, that is the job of the suspension system. The magnet is responsible for making the voice coil move when it is energized with an AC waveform signal.


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## ParDeus (May 10, 2014)

Oscar said:


> Looks like there is a loss of B in the gap when stuck to the steel plate, thus BL goes down, thus Qes goes up, thus Qts goes up. The loss in sensitivity would be small, and the shift in alignment would shift the EBP (Fs/Qes) lower towards the "sealed side" of the recommendations.
> 
> Having said that, you won't run into any 1/4" steel in any vehicle cabin, more like sheet metal around 40-65 thousandths thick (about 1/16" but usually much less). Even the frame rails in trucks are more like 1/8"-3/16" thick most of the time. And even then the speakers are still inside the box as per the OP, so there is the wood thickness between the magnets and the truck sheet metal, unless the scenario is elaborated by the OP.
> 
> ...


I may try this again tomorrow with the actual rear cab of my truck. I have a feeling 0.040" metal will have much less effect than a 10lb piece of steel.


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## JCsAudio (Jun 16, 2014)

Pardeus, thank you for doing that test.


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## SPLEclipse (Aug 17, 2012)

The little "blips" in the impedance graph usually happen because the driver is moving or rattling. If the piece of steel wasn't flat or wobbled even slightly during the test that would cause the little anomalies. As for if that would cause the higher qes/qts - I have no idea, but theoretically if there was energy wasted on the rocking or wobbling I'd imagine it _could_ result in that.

Thank you for actually doing that though - this thread could be a hundred pages long with nothing but "what ifs" so it's good to have solid, real data!


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## ParDeus (May 10, 2014)

SPLEclipse said:


> The little "blips" in the impedance graph usually happen because the driver is moving or rattling. If the piece of steel wasn't flat or wobbled even slightly during the test that would cause the little anomalies. As for if that would cause the higher qes/qts - I have no idea, but theoretically if there was energy wasted on the rocking or wobbling I'd imagine it _could_ result in that.
> 
> Thank you for actually doing that though - this thread could be a hundred pages long with nothing but "what ifs" so it's good to have solid, real data!


Ya, I noticed that little blip in the beginning of the sweep during the "on steel" test. I did that test several times, and none of the other runs had the blip, but the numbers were still very close.

Honestly, the only reason I used the run with the blip is because it had the least-worse sun glare in the photo lol.

My tech skills need a little brushing up- I tested the driver with my laptop, took pictures with my phone, and posted the info with my tablet. I've got a feeling I could have condensed my device usage a little haha.


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## JH1973 (Apr 21, 2017)

Glad this topic came up because in the build I'm currently doing the tweeter magnets are resting up against the A-pillar sheet metal due to space constraints.They literally just barely fit.They don't have a pull to the metal though and I'm kinda puzzled by that.Could it be that the sheet metal is painted?


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## miniSQ (Aug 4, 2009)

i wonder what the effect of constant contact with the steel would be after a month? a year?

And did the OP ever clarify how the magnet would contact the steel if it was inside a box?


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## Oscar (Jun 20, 2010)

JH1973 said:


> Glad this topic came up because in the build I'm currently doing the tweeter magnets are resting up against the A-pillar sheet metal due to space constraints.They literally just barely fit.They don't have a pull to the metal though and I'm kinda puzzled by that.Could it be that the sheet metal is painted?


Paint will not redirect a magnetic field.


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## seafish (Aug 1, 2012)

JH1973 said:


> Glad this topic came up because in the build I'm currently doing the tweeter magnets are resting up against the A-pillar sheet metal due to space constraints.They literally just barely fit.They don't have a pull to the metal though and I'm kinda puzzled by that.Could it be that the sheet metal is painted?


Your tweeter is enclosed and likely shielded unlike the OPs mids.


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## Alpine_9813 (Jul 28, 2018)

miniSQ said:


> i wonder what the effect of constant contact with the steel would be after a month? a year?
> 
> And did the OP ever clarify how the magnet would contact the steel if it was inside a box?





Alpine_9813 said:


> speakers actually touching metal. albeit painted metal.
> 
> Ford Ranger rear speakers. factory setup. the aftermarket speakers have large magnets, would need smaller than normal magnets to not get pushed against the metal. such as the flimsy stock speakers.


they are mounted like stock speakers but the magnet isn't small like stock speakers, so they get smushed against the wall of the cab.


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## Infinity99 (Jul 13, 2015)

Infinity99 said:


> They will not get "demagnetized" at all, however you are taking away from the efficiency of the speaker and maybe damaging it at the same time. The magnet is there to keep the coil in place and moving freely to allow wave forms to be produced (music, sound).
> 
> If the magnet is touching a metal structure (outside force), then the magnetic force is being drawn to that instead of focusing its energy keeping the coil in its place or in motion if that make sense.
> 
> ...



Well call me out, fair enough, thanks to everyone who took the time to test this! I learned something new! I can appreciate that if anything, but what I appreciate more is no one bashed the hell out of me in the process. My theory is shot to hell mostly, but great work to take the time to test it! SCIENCE = WIN!


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## JCsAudio (Jun 16, 2014)

Infinity99 said:


> Well call me out, fair enough, thanks to everyone who took the time to test this! I learned something new! I can appreciate that if anything, but what I appreciate more is no one bashed the hell out of me in the process. My theory is shot to hell mostly, but great work to take the time to test it! SCIENCE = WIN!


And this is what I like about this forum, way less egotistical flame bashing going on here than most forums. People actually discuss things like intelligent educated people do and use supporting data/facts to debate, not call each other names because they disagree like some kids do. :surprised:


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## Grinder (Dec 18, 2016)

V8toilet said:


> And this is what I like about this forum, way less egotistical flame bashing going on here than most forums. People actually discuss things like intelligent educated people do and use supporting data/facts to debate, not call each other names because they disagree like some kids do. :surprised:


Agreed. It really is a pleasure to interact with many of our fellow DIYMA members. However, while there seems to be fewer of them now than when I first came here, we still have our share of a-holes who seem to love nothing more than to stir the pot ...and not just in OT, LOL.


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