Stacking magnets?
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I apologize if this has been discussed before. I searched & could not find anything on the topic, but there's no way I'm the first to think of it.

Has anyone ever tried stacking additional neodymium magnets (with opposite poles touching to effectively create a more powerful magnet) on the driver of their headphones? It would be a cheap, easy, and reversible mod to perform.

According to this site (http://www.kjmagnetics.com/blog.asp?p=doubled-forces), adding a 2nd, identically-sized neodymium magnet results in a magnetic force increase of ~169% (not 2x, due to the layers of plating on the magnets causing a slight reduction).

What effect does it have on sound? According to Fostex, higher magnetic flux density improves attack and decay for a crisper, more detailed sound signature. Headphones like the TH-X00 use magnets that exceed 1 tesla (1 tesla = 10,000 gauss).

Obviously, one would have to accommodate appropriately for drivers that have vent holes in the magnet. And I know that manufacturers design the drivers and magnets to work together as one 'unit'. But that doesn't mean there aren't room for improvements. Cost certainly has a large influence on product design, and manufacturers usually don't just grossly overengineer everything. Why use 2x oversized magnets or plastic that's twice as thick/rigid when it can be engineered to be 'just good enough' but a whole lot cheaper?

==================================================

Update 01/22/2018 - Be sure to read through all of the posts in this thread possible, as lots of good discussion going on. As promised, I will be keeping this 1st post updated with a 'running database' of magnets that work on particular headphones. To have magnet/headphone data added to this post, follow the guidelines** below
  • 1More MK801 - 20mm x 4mm round magnet (with hole)
  • Edifier H840 - 20mm x 5mm round magnet (with hole)
  • JVC HA-RX900 (placeholder)
  • Meizu HD50 - 15mm x 4mm round magnet (with hole). Stock driver is 15mm, & has (1) vent hole in center
  • Philips Fidelio X2/X2HR - 20mm x 5mm round magnet (with hole). Stock driver is 20mm, & has (1) vent hole in center
  • Philips SHL3300 - (placeholder)
  • Philips SHP9500 - 20mm x 7mm round magnet (with hole). Stock driver is 20mm, & has (1) vent hole in center
  • ISK MDH9000 - 20mm x 7mm round magnet (with hole). Stock driver is 20mm, & has (1) vent hole in center
  • Akai Project 50X - 20mm x 7mm round magnet (with hole). Stock driver is 20mm, & has (1) vent hole in center
  • Marantz MPH-2 - 20mm x 7mm round magnet (with hole). Stock driver is 20mm, & has (1) vent hole in center
  • LyxPro HAS-30 - 20mm x 7mm round magnet (with hole). Stock driver is 20mm, & has (1) vent hole in center
  • Freeboss MDH9000 - 20mm x 7mm round magnet (with hole). Stock driver is 20mm, & has (1) vent hole in center
  • Sivga SV007 - 20mm x 7mm round magnet (with hole). Stock driver is 20mm, & has (1) vent hole in center
  • Sony MDR-ZX100 (placeholder)
  • Sony MDR-ZX110 (placeholder)
  • SoundMAGIC HP150 (placeholder)
  • SoundMAGIC HP200 (placeholder)
  • Superlux HD-660 (placeholder)
Magnet mod is NOT possible on (at least) the following headphones:
  • 1More H1707 Triple Driver over-ears
  • JBL J55
  • Sennheiser Momentum v1 (over ear)
  • Sennheiser HD 630VB
  • Philips A5 Pro

** Database Guidelines:
  1. You must specify the diameter of the stock magnet. If the stock magnet has 2 or 4 vent holes, include the largest diameter magnet that will fit 100% inside of the vent holes (ie without obstructing the vent holes).
  2. You must specify the number and placement of the stock magnet vent holes (ie 1 vent in center, 4 vents in square pattern, 2 vents in straight line, etc).
  3. Please provide the maximum size magnet possible (not just "whatever works"). For example, the Fidelio X2 will accommodate a smaller magnet, but 20mm*5mm magnets are the same diameter as stock (and thus the largest diameter/most powerful magnet possible).
  4. Make sure you only list magnets that allow the cups to go back together without mods (it's not helpful to stack 6" of magnets on a driver if you can't put the headphones back together LOL).
  5. PM me the information and I will add it to the database.
 
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kkl10

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Digging up this thread because this is related to something that interests me too and would like to see it discussed more often.

I did play around with little neodymium magnets (~5mm cubes and such), letting them stick to the back of some GMP 50mm drivers (the pull was quite strong) to hear for any differences. There was a very apparent effect in sound. The frequency response changed (less bass) and the overall sound seemed indeed somewhat crisper and cleaner. I think I noticed that the sound tended to become more BA-like with progressively more magnets (or a more powerful magnet) sticked to the back of the driver. Frequency response effect didn't go in the desired direction at the time (as I expected), and it seemed to have decreased lower bass extention (unexpected.. but I'm not at all versed in the physics of it all), but I can imagine how this might be an interesting method to try to tighten up the sound of sluggish/slow sounding headphones. Definitely something to play with when modding cheapo headphones.

I played around with this years ago and there were no ill-effects on the drivers whatsoever. They still work flawlessly today. But I don't know if it's safe with all dynamic drivers.

EDIT: After testing a little more, I've realized that the FR and bass extension don't change at all. The sound simply becomes cleaner, clearer, faster.
 
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Slater

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Wow, I forgot all about this thread.

I run stacked magnets all of the time now (since I made this thread), and I have a selection of different "N" strengths, thicknesses, and diameters that I test out when modding headphones. As you discovered, it does have a noticeable effect on the sound.

They are so cheap to buy, it's easy to have a small collection of 4-5 different sizes on hand.

I exclusively use round magnets with holes in them, like this:

Magnets.jpg

Using magnets with holes also guarantees compatibility with stock magnets that are solid, as well as stock magnets that already have a single vent hole in the center (like the stock driver magnet in this photo):

driver with hole.jpg

You have to make sure to center the 2nd magnet when placing it on top of the stock magnet, so the magnetic field matches the stock magnet's field. How to do this depends on the setup of the stock magnet. For stock magnets that already have a single hole in the center (like the photo above), it's easy because you can set the 2nd magnet on top of the stock magnet and line the imaginary 'center' of the holes up with one another. For drivers that have 2 or 4 small vent holes or drivers with no vent holes whatsoever, I mark the exact center of the stock magnet with a fine sharpie (a cross shape works best). I then 'center' the 2nd magnet on the stock magnet by using the hole in the center of the 2nd magnet to line up the sharpie marks through the hole like a cross hair. Make sense?

As far as the diameter of the 2nd magnet, I try to match the diameter of the stock magnet as close as possible (but slightly smaller is OK too). So if the stock magnet has a diameter of 20mm (and has no vent holes or a single vent hole), I might use a magnet of between 15mm and 20mm. If the stock driver magnet has (2) or (4) small vent holes in them (like these photos)...

driver with hole 2.jpg
driver-before-tape.JPG

...then I need to make sure to use a 2nd magnet that is smaller than the space between the 2 or 4 small holes. In other words, if the distance between the 2 of the holes (opposite to one another) is 15mm, I just make sure I get a magnet with a diameter less than that. The idea is that the 2nd magnet, once installed and centered on top of the stock magnet, fits inside of the small vent holes and doesn't block any of the vent holes.

Update 01/24/18: Another user issued a reminder to make sure you orient the extra magnets the proper direction. If you attach them the wrong way, the sound can get WORSE not better. The details about how to install them the proper orientation is here: https://www.head-fi.org/threads/stacking-magnets.839878/page-3#post-13997758
 
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kkl10

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Just grabbed some of those little neodymium cubes and they definitely make the driver more resolving. Imaging, more minute detail from blacker background, faster decay, etc,. This is with the drivers out of the headphone cups. I'm not so sure about the diminished bass response anymore... I'll have to hear for that latter again. My ears are not at their most perceptive right now...

The back of the drivers I have feature four vent holes as shown in your third picture. I always make sure to never cover any of those vents and try to more or less center the magnets in place, but I'm not sure that having the driver perfectly centered makes much of a difference...
 
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The back of the drivers I have feature four vent holes as shown in your third picture. I always make sure to never cover any of those vents and try to more or less center the magnets in place, but I'm not sure that having the driver perfectly centered makes much of a difference...
I'm no physicist, but what you're trying to do when you center the 2nd magnet is to maintain an even magnetic field around the voice coil.

It's kind of similar to your wheels being balanced on your car. If you've ever driven with a wheel very out of balance, you'll agree that it's not fun to drive that way on the highway for instance. The stock magnet is perfectly centered for a reason. If it didn't matter, they would just slap the stock magnet on in any ol spot.

In other words, you are trying to enhance the stock magnet's magnetic field, not move it around or cause it to shift off-balance.

magnets2.png

The little cubes are cool to play around with and see how the sound is affected, but for permanent modding you may want to consider get the proper disc magnets.

If the magnetic field is off balance (by just using random magnets that aren't centered), in theory there could be the possibility for driver distortion or stress on the fragile voice coil wire. At what frequencies and at what what volume that could occur, and if it would be detectable by casual listening, depends on the individual case.

BTW, you could test this by taking an old junk driver and some iron/steel filings. You'll be able to visually see exactly how the stock vs stacked magnetic field is affected with the different sizes and shapes of magnets (as well as their placement on the driver).
 
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kkl10

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Yes, thought of that. Seems like a plausible issue.

Have you by any chance found that magnets affected bass extension in some way?
 
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Have you by any chance found that magnets affected bass extension in some way?
Not that I've noticed (at least, not during listening sessions).

Also, here's 2 photos I found of one of my early stacking mods. You can see the hole centering (the stock magnet had a single vent hole). The magnet used was a little small, but worked fine (it was just what I had on hand). I've since bought a number of different sizes of magnets to have on hand (they are only a few dollars for a bunch of them on Gearbest or Aliexpress).

DSCN0597 - Edited.jpg
DSCN0598 - Edited.jpg
 
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kkl10

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Just came across this interesting explanation of dynamic drivers by Tyll at innerfidelity. https://www.innerfidelity.com/content/how-headphone-dynamic-drivers-work

After playing around some more, I have to retract what I said about stacked magnets changing the FR. With the magnets I have, there's no such effect. Bass extension remains unchanged. There is simply a cleaner and faster sound.

I'm starting my modding efforts again, so I'll be getting stronger magnets than the N42 10 x 5mm neodymium disks I have now.

Would really love to see how this affects impulse response and THD in measurements. There has to be a significant effect. Somebody needs to give Tyll a shout about this.
 
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Just came across this interesting explanation of dynamic drivers by Tyll at innerfidelity. https://www.innerfidelity.com/content/how-headphone-dynamic-drivers-work

After playing around some more, I have to retract what I said about stacked magnets changing the FR. With the magnets I have, there's no such effect. Bass extension remains unchanged. There is simply a cleaner and faster sound.

I'm starting my modding efforts again, so I'll be getting stronger magnets than the N42 10 x 5mm neodymium disks I have now.

Would really love to see how this affects impulse response and THD in measurements. There has to be a significant effect. Somebody needs to give Tyll a shout about this.
That is definitely what I have found (cleaner, faster sound especially with drums).

Unfortunately, I have no way to measure the differences. But I stack magnets on a number of my headphones, and so far to my ears it has always seemed to provide improvements. I certainly haven't experienced any negative effects yet.

It should also be noted that the magnetic field has to remain as close to the voice coil as possible. So I have never stacked any more than ONE magnet on top of the stock magnet. I believe stacking 2 or 3 extra magnets on top of the stock magnet might start moving the magnetic field away from the voice coil, or somehow having an unwanted or unpredictable effect. If the goal is to get a stronger field without stacking 2-3 magnets, you can always buy a larger diameter magnet, a thicker magnet, or a magnet with higher N rating.

When I order my 'selection' of modding magnets, I always order the highest N rating possible between magnets of the same diameter and thickness.
 
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That is definitely what I have found (cleaner, faster sound especially with drums).


Unfortunately, I have no way to measure the differences. But I stack magnets on a number of my headphones, and so far to my ears it has always seemed to provide improvements. I certainly haven't experienced any negative effects yet.

It should also be noted that the magnetic field has to remain as close to the voice coil as possible. So I have never stacked any more than ONE magnet on top of the stock magnet. I believe stacking 2 or 3 extra magnets on top of the stock magnet might start moving the magnetic field away from the voice coil, or somehow having an unwanted or unpredictable effect. If the goal is to get a stronger field without stacking 2-3 magnets, you can always buy a larger diameter magnet, a thicker magnet, or a magnet with higher N rating.

When I order my 'selection' of modding magnets, I always order the highest N rating possible between magnets of the same diameter and thickness.
Okay, you got me! I’m curious. Can you link the magnets that you bought on Ali? So many magnets on there, it’s hard to choose. It would help me if you could link to a trusted seller of magnets that you are satisfied with. I’d like to try these with my pair of Sony Z7 which would seem to benefit from this mod. I’ll post my results and give you all the credit! :)
 
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Okay, you got me! I’m curious. Can you link the magnets that you bought on Ali? So many magnets on there, it’s hard to choose. It would help me if you could link to a trusted seller of magnets that you are satisfied with. I’d like to try these with my pair of Sony Z7 which would seem to benefit from this mod. I’ll post my results and give you all the credit! :)
It literally depends on YOUR magnet drivers, and any vent holes, all of which vary between headphones. There's literally no way for me to tell you what the best size magnets are for your Sony Z7s.

What you need to do is open your shells and measure your magnets, and whether or not they have any vent holes (and if so the distance between the vent holes). Then and only then can you go and search for magnets to mod with.

If you get that information and maybe take a few pics, I'll be happy to try and help you find some good magnets to use.

BTW, I also use the magnets with holes for all sorts of projects around the house. I screwed a bunch to a board that I hung on the wall and I use them to hang keys from when I walk in the house. I screwed some on my workbench to hold wrenches and other tools. I use them when making costumes and props for Halloween and comicons, to hold kitchen cabinet doors shut, to hold a bathroom door open when not in use, and even put them on my car's oil filter to catch metal particles before they damage my engine. They have a variety of uses, not just modding speaker drivers :)
 
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It should also be noted that the magnetic field has to remain as close to the voice coil as possible. So I have never stacked any more than ONE magnet on top of the stock magnet. I believe stacking 2 or 3 extra magnets on top of the stock magnet might start moving the magnetic field away from the voice coil, or somehow having an unwanted or unpredictable effect. If the goal is to get a stronger field without stacking 2-3 magnets, you can always buy a larger diameter magnet, a thicker magnet, or a magnet with higher N rating.
Only way to find out is to experiment until something dies. I've been very liberal with my experiments and stacked up multiple neodymium magnets behind each driver. As far as I can perceive, there is no negative side effect to this and nothing suggests that the magnetic field around the voice coil might be shifting in position/orientation and/or losing its grip over the diaphragm. If things were going wrong in some way, I reckon that the effect would be very audible and obvious. On the contrary, the more magnets I add the more the sound cleans and clears up and becomes smoother. However, I've only explored this to a limited degree because I don't have that many magnets to really go crazy big (can get the column behind each driver up to ~5cm in height... looks silly but sounds even better :p). There is also a point at which it's no longer worthwhile to add more height to the column of magnets behind the driver. A rod/column more or less three times as tall as it is wide might be enough for maximum gain in magnetic strength without redundant diminishing returns in sound quality. This could be impractical within many small headphone enclosures with relatively large drivers, though. On a truly open frame headphone, like mine currently is, it's very worthwhile to experiment.

Increasing the diameter of the additional magnets should provide a higher boost in magnetic strength than increasing the height. So it is indeed desirable to go for the largerst diameter and higher N grade to limit the column's height. In my drivers, there's an unfortunate limit of only ~13/14mm diameter because of the four vent holes on the back metal plate (currently using 10mm disk magnets).

I brought up Tyll's article because it's very educational about the anatomy of dynamic drivers in headphones. In my mind, this basic anatomy suggests that the effect of additional magnets tucked behind a headphone driver shouldn't affect the magnetic flux around the voice coil quite like you might be fearing. Take a look at the pics/illustrations on the article. It seems that the magnetic flux around the voice coil is guided by the metal pole pieces enclosing the permanent magnet of the speaker motor. There's one metal piece guiding the north pole of the magnet and another piece guiding the south. These pieces are static and independent from each other. One will always be the north and the other the south. Their arrangement seems to "shield" the voice coil from the direct effect of the magnetic field emanating from the permanent magnet itself. The points of strongest attraction of a magnet are its polar edges (correct?), and it's precisely these polar extremes that the metal plates guide to sandwich and trap the voice coil in place.

So placing the headphone driver (on its back) on the tip of an arbitrarily long rod magnet with similar diameter to the driver's north pole metal piece (as illustrated in some of the photos in Tyll's article, but maybe the exact diameter is not very relevant...) could shift the position of the whole magnetic field away from the voice coil. But since we only need the polar edges of the permanent magnet to trap the voice coil in place (and the polar edges of a magnet don't change when it comes together with other magnets) the magnetic field shift should not affect the speaker motor negatively. The added magnet should only contribute to increase even more the intensity of the magnetic flux at the polar edges around the voice coil, not to shift its orientation or position. Oh, now I see why it is indeed important to keep the axles aligned and centered. It's just like tucking two magnets together to form a larger one. The center of the magnetic field shifts to the center of the two magnets, but the magnetic flux at the polar edges intensifies.

Of course, I cannot exclude some sort of unpredictability in such a system. This is only my very limited understanding of the forces at play. In other words, I have no understanding of what I'm talking about and might have the wrong idea. Someone versed in the subject feel free to correct me...
 
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i just saw this thread and i put some magnets on my modded headphone for abusing and experiments (Hifiman HE350), there is a difference in the sound, they are a little bit faster for sure, i like the results
 
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i just saw this thread and i put some magnets on my modded headphone for abusing and experiments (Hifiman HE350), there is a difference in the sound, they are a little bit faster for sure, i like the results
Nice, spread the word to this post!
 
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