Oops thats right...
Well how about measuring anyway but you have to do cut the foil in half first
but seriously what if you measured two short pieces against each other and multiplied this with the approximate length of the coil?
Looking at your graphs the phase lead reduced after removing the cap as well though, unless i'm looking at it the wrong way..
Well how about measuring anyway but you have to do cut the foil in half first
but seriously what if you measured two short pieces against each other and multiplied this with the approximate length of the coil?
Looking at your graphs the phase lead reduced after removing the cap as well though, unless i'm looking at it the wrong way..
Coolin said:Oops thats right...
Well how about measuring anyway but you have to do cut the foil in half first
but seriously what if you measured two short pieces against each other and multiplied this with the approximate length of the coil?
Looking at your graphs the phase lead reduced after removing the cap as well though, unless i'm looking at it the wrong way..
I'm not really sure how capacitance has to do with this, but it might be interaction between the wires and how they are layed out differently.
Yes, the phase lead was reduced after removing the cap. But it seems there are more complicated things involved.
capacitance
No offense, but I think this is an error of thought. The wire being parallel in all the turns does actually mean that they produce a capacitance. This capacitance of course does not work like a capacitor: this means the capacitor is not in series but in parallel (if you wish). But however you imagine it does not matter, what matters is what you measure! So if it has any effect on the phase or frequency response, then you must be able to measure this! If you cannot measure a phaseshift, then there is no noticable phase shift!
That does not mean however that there is no noticeable difference. Usually one uses sinewaves or pink noise to measure but this does not measure any impuls responses or shifts or distortion. It is therefor important to measure with signals that have more a nature like music (impulses, multiple frequencies simultaneously etc). There is actually such a signal, which a German measurement equipment manufacturer uses. Quite ingenius really.
No offense, but I think this is an error of thought. The wire being parallel in all the turns does actually mean that they produce a capacitance. This capacitance of course does not work like a capacitor: this means the capacitor is not in series but in parallel (if you wish). But however you imagine it does not matter, what matters is what you measure! So if it has any effect on the phase or frequency response, then you must be able to measure this! If you cannot measure a phaseshift, then there is no noticable phase shift!
That does not mean however that there is no noticeable difference. Usually one uses sinewaves or pink noise to measure but this does not measure any impuls responses or shifts or distortion. It is therefor important to measure with signals that have more a nature like music (impulses, multiple frequencies simultaneously etc). There is actually such a signal, which a German measurement equipment manufacturer uses. Quite ingenius really.
If one tries to model a foil inductor in very small increments, it certainly does seem there is a parallel capacitance. How interesting.
I wonder whether anyone has used the wire inductors from Duelund Coherent Audio? It certainly looks interesting, and possibly minimizes magnetic field influence on components nearby.
I wonder whether anyone has used the wire inductors from Duelund Coherent Audio? It certainly looks interesting, and possibly minimizes magnetic field influence on components nearby.
Ancient thread, I know.
I've finalized my outboard three way first order crossovers.
I'll be using Solen 14 gauge inductors, 1.5mH, 0.27mh. I've also ordered in some cast iron round transformer covers, to shield the inductors, as well as providing a basin to flood and encapsulate the inductors in epoxy resin.
I am hopeful this may reduce microphonics as much as in tightly wound foil inductors.
Anyone forsee any problems with tjis?
That cast iron will change the value of your inductors if in close proximity. You should actually place the coils in something non-ferrous, and then fill with epoxy. Duelund uses a kraft-paper tube of sorts, and Litz-wire coils. Aluminum will make the value of the coil go down if used, and iron will make it go up.
If you want reduced microphonics;
1- restrap the coils with steel barbed ty-wraps and remove the older loose ones. I use a zip-tie gun on all of my homemade or bought xover parts.
2- dunk your coils in polyurethane and let them dry. This will fill the voids inside and bond them rather nicely.
3- drop them into a PVC end-cap, or wooden crevice, or some other paper/plastic based housing with the leads extended up, and pour epoxy into the housing.
4- bore hole through center for use of a nylon bolt to mount the coil.
Over the last year and a half or so, I've built a comparator into a project to give the multiples of coil types a try. I made effort to keep magnetic fields unrelated, DCR minimally different, and used a switch based setup so I could hear the differences. I also used top-tier drivers. Tweeter DCR shunts were matched via the damping resistors required in the circuit individually.
In the following, the crowd did not know what I had in the circuit until after the test was over, but did know I was switching coils of some sort initially. This was a crowd of DIYers. This was done so I could switch all of the coils in the circuit to the same kind if I wanted to.
Crowd result said that steel-laminate had a bit more slam that was pleasing.
Litz on tweeter provided a BBC dip (for some unknown reason) that was also favorable at times.
The crowd did not like the foils or the P-cores (sintered core) as much as the regular round wire or Litz wire.
Ultimately, I settled on the Litz14 for the woofers, and regular air-core14 for the tweeters.
In the 3rd order tweeter shunt I had:
Wax foil 16 AWG
Foil 12AWG
Foil 14AWG
Air 22AWG
Air 14AWG
Litz 14AWG
On woofer in both LRC filter and LP coil I had:
Steel Laminate 18AWG
Air 14AWG
Litz 14AWG
Foil 14AWG
P-core 15AWG
I feel the Litz on the tweeter is not as good because the capacitance of the multi-strands can affect the FR. The Air-core did not suffer the same issues. The Air22 had the same issue as the Litz though, so I don't really know what happened there. The tweeter foils all seemed fine (no diff between gauge or wax vs tape), but the round Air14 sounded better. The Litz on the woofers had a little more detail than the Air, the P-core lost all of that detail and muddied it up. The Steel gave a bit of midbass slam that most will not be unhappy with, and the foils just seemed 'off' for lack of another explanation.
This was all subjective, but the homework was done.
Wolf
If you want reduced microphonics;
1- restrap the coils with steel barbed ty-wraps and remove the older loose ones. I use a zip-tie gun on all of my homemade or bought xover parts.
2- dunk your coils in polyurethane and let them dry. This will fill the voids inside and bond them rather nicely.
3- drop them into a PVC end-cap, or wooden crevice, or some other paper/plastic based housing with the leads extended up, and pour epoxy into the housing.
4- bore hole through center for use of a nylon bolt to mount the coil.
Over the last year and a half or so, I've built a comparator into a project to give the multiples of coil types a try. I made effort to keep magnetic fields unrelated, DCR minimally different, and used a switch based setup so I could hear the differences. I also used top-tier drivers. Tweeter DCR shunts were matched via the damping resistors required in the circuit individually.
In the following, the crowd did not know what I had in the circuit until after the test was over, but did know I was switching coils of some sort initially. This was a crowd of DIYers. This was done so I could switch all of the coils in the circuit to the same kind if I wanted to.
Crowd result said that steel-laminate had a bit more slam that was pleasing.
Litz on tweeter provided a BBC dip (for some unknown reason) that was also favorable at times.
The crowd did not like the foils or the P-cores (sintered core) as much as the regular round wire or Litz wire.
Ultimately, I settled on the Litz14 for the woofers, and regular air-core14 for the tweeters.
In the 3rd order tweeter shunt I had:
Wax foil 16 AWG
Foil 12AWG
Foil 14AWG
Air 22AWG
Air 14AWG
Litz 14AWG
On woofer in both LRC filter and LP coil I had:
Steel Laminate 18AWG
Air 14AWG
Litz 14AWG
Foil 14AWG
P-core 15AWG
I feel the Litz on the tweeter is not as good because the capacitance of the multi-strands can affect the FR. The Air-core did not suffer the same issues. The Air22 had the same issue as the Litz though, so I don't really know what happened there. The tweeter foils all seemed fine (no diff between gauge or wax vs tape), but the round Air14 sounded better. The Litz on the woofers had a little more detail than the Air, the P-core lost all of that detail and muddied it up. The Steel gave a bit of midbass slam that most will not be unhappy with, and the foils just seemed 'off' for lack of another explanation.
This was all subjective, but the homework was done.
Wolf
In cold weather the copper shrinks, and in hot weather it expands.
Many should have heard a fluorescent tube lamp's choke humming at 120Hz, and you might have been complaining that why didn't the choke makers do their job and wound the choke tightly? Well, they had done their best to wind the choke as tightly as possible, but when the choke heats up when energized, the copper wires will expand due to thermal expansion and it's unstoppable, and as a result the wound wires is loosen, so after several times of expanding and shrinking, the choke will make its space to hum. And if you are lucky (or unlucky) you will hear it singing at 120Hz.
Same to the crossover inductors, I think when a wire or foil coil is heated up, no matter how you tied it up, thermal expansion is unstoppable, and it gets worse for a multi-layer coil.
Copper is not elastic, it is soft metal and a wire will adapt and adjust itself if it's too tight, so in cold weather a tightly wound coil will shrink, but in fact it might be extending its length to release the force, so in winter the coil might still be tight, but in next summer it gets loosen.
And when current flows through a coil and heats it up, copper's thermal expansion will extend its length, the coil is likely to expand itself radially. As a result we might get a little bit loose coil singing along with the music, it might be trivial but I think it's there.
Maybe that's why when we hold a tight coil in hand we still can feel the vibration when AC current flows through it.
Thermal expansion is unstoppable. Not even with polyurethane or epoxy or varnish.
Many should have heard a fluorescent tube lamp's choke humming at 120Hz, and you might have been complaining that why didn't the choke makers do their job and wound the choke tightly? Well, they had done their best to wind the choke as tightly as possible, but when the choke heats up when energized, the copper wires will expand due to thermal expansion and it's unstoppable, and as a result the wound wires is loosen, so after several times of expanding and shrinking, the choke will make its space to hum. And if you are lucky (or unlucky) you will hear it singing at 120Hz.
Same to the crossover inductors, I think when a wire or foil coil is heated up, no matter how you tied it up, thermal expansion is unstoppable, and it gets worse for a multi-layer coil.
Copper is not elastic, it is soft metal and a wire will adapt and adjust itself if it's too tight, so in cold weather a tightly wound coil will shrink, but in fact it might be extending its length to release the force, so in winter the coil might still be tight, but in next summer it gets loosen.
And when current flows through a coil and heats it up, copper's thermal expansion will extend its length, the coil is likely to expand itself radially. As a result we might get a little bit loose coil singing along with the music, it might be trivial but I think it's there.
Maybe that's why when we hold a tight coil in hand we still can feel the vibration when AC current flows through it.
Thermal expansion is unstoppable. Not even with polyurethane or epoxy or varnish.
Thanks. I guess using the heaviest gauge inductor on a current demanding application, like a woofer, is the best way to limit thermal expansion then.
Less resistance to cause heat, and more mass to diffuse induced heat.
?
Yes, except the skin effect, less heat might be another reason for using higher gauge / lower DCR coils.
Well lets be more careful here. Copper, like every other metal is elastic, it has an elastic modulus. You can make springs from copper wire (not very good ones!)
However annealed copper has a _very_ low yield strain - it deforms permanently after only a small fraction (<< 1%) of stretch. This does indeed mean it can be stretched permanently even by small thermal expansions.
However humming chokes are usually due to magnetostriction in the iron/steel laminations, not winding movement. Windings are usually vacuum-impregnated with lacquer to fix the windings in place and help conduct heat and exclude moisture.
BTW if you want to make somewhat better copper springs you can stretch copper wire by about 5% first, work-hardening it. Changing to beryllium-copper alloy and you get extremely good springs, as used in nearly every switch and relay, as the yield strain is far higher in the alloy.
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From what I've read over the years in the Funniest Snake Oils Forum, skin effect doesn't matter at audio frequencies.
Skin effect can sometimes matter a bit, the skin-depth in copper at 10kHz is 0.65mm, so very heavy duty speaker cables will show an increase in resistance at the top end, not usually significant except for long runs. Its more significant to HF loss than the capacitance though, for what that's worth. The rest of the audio chain has conductors too thin for the skin effect to matter.
The skin effect is related to the screening ability of metals BTW, which is why steel screens better than aluminium for mains hum, as magnetic permeability contributes to the skin effect.
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