Papasteack, do you see a difference in impedance as function of frequency when you add the magnets?
"Speaker heat origin", is interesting, but would need it own topic. 😛
This thread is about experimenting the addition of neo-magnet around loosy ferrite of a speaker to get back original B and so BL, qes/qts.
I have choosen from available and cheap neo magnet format (a bit longer them ferrite magnet), and put them around the ferrite magnet intuitively, but maybe there would have been better way to place them, or more appropriate format to choose ? It cost me around 34 € with shipping from germany.
Can someone try to explain what happen to magnetic field doing how i did ? To recall, I have put neo magnet so that it repulse ferrite magnet, to get same pole orientation.
I feel it increase the intensity of the flux, and at the same time, concentrate it to the center (ie to the airgap). What do you think ?
Does assembly of different strenght of magnet have been used commercially, does it make any sense (concentrating the flux seems intuitively interesting) ?
This thread is about experimenting the addition of neo-magnet around loosy ferrite of a speaker to get back original B and so BL, qes/qts.
I have choosen from available and cheap neo magnet format (a bit longer them ferrite magnet), and put them around the ferrite magnet intuitively, but maybe there would have been better way to place them, or more appropriate format to choose ? It cost me around 34 € with shipping from germany.
Can someone try to explain what happen to magnetic field doing how i did ? To recall, I have put neo magnet so that it repulse ferrite magnet, to get same pole orientation.
I feel it increase the intensity of the flux, and at the same time, concentrate it to the center (ie to the airgap). What do you think ?
Does assembly of different strenght of magnet have been used commercially, does it make any sense (concentrating the flux seems intuitively interesting) ?
Off course, qes/qms beeing measured from impedance curves... But at the same time, Fmin remains conform to datasheet around 135hz. I found using SBacoustic measuring paper 1,8mH instead of 3,4mH from datasheet, but i'm not confident in how i did. SBacoustic paper is not as "plug&play" as diysubwoofer thiele measurement sheet (Brian member).
Would be interesting measuring impedance at Fmin & let say 1khz with and without magnets.
I'll maybe try, but i have really hard time getting so much magnets in place, and i fear a lot from collar to break for my fingers safety (when some magnets jump out the collar, it is sometime a bit violent). I suspect from sum of repulsing force of neo magnet from ferrite, and force needed to hold it tight, not far from collar breaking point (cannot grip more the screw with my screwdriver).
Ideally, i'd like to get a dayton dats, but it's too much cost.
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Too lazy for technical explanations...
Concentrating the flux seems intuitively interesting until the airgap is saturated
https://en.wikipedia.org/wiki/Permeability_(electromagnetism)
You shoud improve your mod by closing your magnetic circuit.
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Good idea !
2 circle of soft iron pieces from neo pole to pole plate and same for back plate ?
Silver Prout : (beeing in France) do you think standard iron from leroy merlin should do the trick ?
EDIT : would be easier for experimenting with multiple little pieces...
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Ok, ok, i stop myself, closing magnetic field seems interesting to experiment, seems doable, but i don't see how i could pratically do it without too much work, moreover, i already have a sufisant effect for my needs.
Instead of adding a lot more neo magnet as i did, i would have better to keep around 10 magnet, and close the magnetic field. But it would have need to much work, cutting iron, adjusting, and keeping in place. Here i stop my experimentation. From a pratical point of view, i got enough result, without too much work.
Now, i'll simply measure the frequency response in simple closed box at different level to see how it react, compared to sim.
Still i'd be really interested if there were other experiment like this done, and if someone should explain me simply what it involve.
Instead of adding a lot more neo magnet as i did, i would have better to keep around 10 magnet, and close the magnetic field. But it would have need to much work, cutting iron, adjusting, and keeping in place. Here i stop my experimentation. From a pratical point of view, i got enough result, without too much work.
Now, i'll simply measure the frequency response in simple closed box at different level to see how it react, compared to sim.
Still i'd be really interested if there were other experiment like this done, and if someone should explain me simply what it involve.
these wide pancake ferrite magnets need to extend beyond the poles to prevent the flux short circuiting instead of passing through the gap.
The old fashioned alnico that were tall cylinders did not have this problem, so their pole pieces could come right out to the edge.
Adding the neos as he has done is just increasing the route length that the shorting flux would need to take. i.e. it forces the ferrite to not short circuit and may add a little more flux between the pole pieces.
It does not look pretty but there could be a useful increase in the gap flux. The fact that he has measured some changes in performance indicates that the magnetic circuit has changed.
The old fashioned alnico that were tall cylinders did not have this problem, so their pole pieces could come right out to the edge.
Adding the neos as he has done is just increasing the route length that the shorting flux would need to take. i.e. it forces the ferrite to not short circuit and may add a little more flux between the pole pieces.
It does not look pretty but there could be a useful increase in the gap flux. The fact that he has measured some changes in performance indicates that the magnetic circuit has changed.
I needed time, reading, and reading again what you said. You explain really well, but it's not something intuitive (shorting route lengh). I understood at the moment i looked at some femm sims.
The fact i use neo magnet a bit longer than the ferrite make this effect even more pronounced if i imagine it well.
How neo field is added to the full field is something harder to imagine, moreover, contact between neo and ferrite is small since neo are round => what let me think i got so a big effect of reducing shorting flux beyond the poles, and a not ideal add of magnetic field from neo contact to ferrite...
Talking of this kind of stuff even in my native french would be hard, so in english, i won't probably be understood...sorry...
The fact i use neo magnet a bit longer than the ferrite make this effect even more pronounced if i imagine it well.
How neo field is added to the full field is something harder to imagine, moreover, contact between neo and ferrite is small since neo are round => what let me think i got so a big effect of reducing shorting flux beyond the poles, and a not ideal add of magnetic field from neo contact to ferrite...
Talking of this kind of stuff even in my native french would be hard, so in english, i won't probably be understood...sorry...
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I knew driver waited 2 years in a humid garage, cone facing up, wasn't a good idea...looking at real life excusion, driver was bottoming back plate at +/-6mm (whereas even Xmax is said to be +/- 7mm).
So, I had some other experiment... I felt xmech was not so far seeing flat black plate, but this is not normal.
Looking at it, spider was not flat at steady state, as if cone were pushed. So i put the driver cone down, pushed the cone down, applicated some acetone to spider, and surround, blocked it like that and finally, now at rest, spider (and surround) are flat. I added liquid latex from beyma to surround and spider to "block" this new standby position, and add some elasticity to this new position. To compensate for spider isolation, i put it some little cut. Bottoming is now at +/-8mm. It seems voicecoil is better centered, qes is now at 0,27. Not so much change, but in the good and coherent direction.
Overall not so much change in parameters, but everything is coherent. FS is now 33hz, vas=85L, qms=3,16, qes=0,27, re is still 6,25. So with qes and qms lowering, it is now qts=0,25 !
Having fun, but next step will be to adjust neo-magnet to get around qts=0,31 for a bit more low end extension in it future bandpass cab.
So, I had some other experiment... I felt xmech was not so far seeing flat black plate, but this is not normal.
Looking at it, spider was not flat at steady state, as if cone were pushed. So i put the driver cone down, pushed the cone down, applicated some acetone to spider, and surround, blocked it like that and finally, now at rest, spider (and surround) are flat. I added liquid latex from beyma to surround and spider to "block" this new standby position, and add some elasticity to this new position. To compensate for spider isolation, i put it some little cut. Bottoming is now at +/-8mm. It seems voicecoil is better centered, qes is now at 0,27. Not so much change, but in the good and coherent direction.
Overall not so much change in parameters, but everything is coherent. FS is now 33hz, vas=85L, qms=3,16, qes=0,27, re is still 6,25. So with qes and qms lowering, it is now qts=0,25 !
Having fun, but next step will be to adjust neo-magnet to get around qts=0,31 for a bit more low end extension in it future bandpass cab.
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Playing again, adding latex again (to the cone too), with 10 less magnet, got now fs=30, VAS=120L, qms=2,3 qes=0,36 qts=0,31. Perfect for my hornresp sim target ^^
Funny to see how all mods work so well
Funny to see how all mods work so well
Your magnets are perhaps lobing very far in your room and it should harm sensitive devices ?
Are you sure that a horn is the best impedance matching for your room ?
From very approximative calcul from specs, neo total magnetic field is only around 3 time the equivalent of the ferrite. Still less power than some 18"... Not so much a concern. It would be to use mostly in a specific room in the garage...
I never said it was for a horn. I just said i used hornresp to sim. It can sim whatever kind of cabinet loading you want. And i've precisely said this sub will be use in a specific 4th order bandpass enclosure.
Hornresp
"This Windows-based application calculates the theoretical acoustical impedance, acoustical power, electrical impedance, diaphragm displacement, phase response and group delay versus frequency characteristics of finite and infinite horn loaded loudspeakers"
Since you like to split hairs, and i have nothing to hide...
Hornresp give more or less the same total power response as akabak. Here akabak 3 ways on axis sim with this sub in green for <150hz. Total impulse response bellow. Red is a 8" of the unity horn, not seen the 4" at throat and not seen a bullet horn for >~5khz.
Kind of frankeinstein unity horn cabinet around total 100 liter (with all taken account), 4 way active project, with composite damped horn (silicone/foam/glass fiber) done, outside box of a oak squeleton with polystyrene, glass fiber, silicone damping, hard fiber wood outside...minidsp + 4 remote sensing bridged amp + some passive shaping for the 4" fullrange. Outside finish will be guitar cabinet western vinyl.
The 4th bandpass (bellow in green) for this sub is easy to simulate, with around 33L rear chamber, 9 liters heavily stuffed front chamber, and around 20cm 50cm² vent heavily rounded 4cm to 300cm².
I show akabak sim to show i took in account delay, phase, and ringing to get a not so bad target impulse response (it's often worst even in sim).
Hornresp give more or less the same total power response as akabak. Here akabak 3 ways on axis sim with this sub in green for <150hz. Total impulse response bellow. Red is a 8" of the unity horn, not seen the 4" at throat and not seen a bullet horn for >~5khz.
Kind of frankeinstein unity horn cabinet around total 100 liter (with all taken account), 4 way active project, with composite damped horn (silicone/foam/glass fiber) done, outside box of a oak squeleton with polystyrene, glass fiber, silicone damping, hard fiber wood outside...minidsp + 4 remote sensing bridged amp + some passive shaping for the 4" fullrange. Outside finish will be guitar cabinet western vinyl.
The 4th bandpass (bellow in green) for this sub is easy to simulate, with around 33L rear chamber, 9 liters heavily stuffed front chamber, and around 20cm 50cm² vent heavily rounded 4cm to 300cm².
I show akabak sim to show i took in account delay, phase, and ringing to get a not so bad target impulse response (it's often worst even in sim).
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