Some of my crossover design have parallel notch filter using several small value inductors(under 100uH)
Most of audio inductor brands usually have above 100uH so small values need custom order and it will cost some times also a little pricey.
I would like to ask if the industrial inductor could be bought from Mouser like this https://www.mouser.jp/datasheet/2/212/1/KEM_LF0062_SNG-1608324.pdf
or this https://www.mouser.jp/datasheet/2/445/74437529203470-1721700.pdf could be used for the crossover.
Thanks a lot!
Most of audio inductor brands usually have above 100uH so small values need custom order and it will cost some times also a little pricey.
I would like to ask if the industrial inductor could be bought from Mouser like this https://www.mouser.jp/datasheet/2/212/1/KEM_LF0062_SNG-1608324.pdf
or this https://www.mouser.jp/datasheet/2/445/74437529203470-1721700.pdf could be used for the crossover.
Thanks a lot!
I assume that the small inductor values are largely due to the low Q-factors (rather than high resonant frequencies) of the notches. If so, you may use the second one (Wurth) without any problems.
However, it would be nice to recall that smaller notch inductors would require smaller resistors for the same Q-factor at the same resonant frequency when compared to larger ones.
All the best.
However, it would be nice to recall that smaller notch inductors would require smaller resistors for the same Q-factor at the same resonant frequency when compared to larger ones.
All the best.
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I would wind them myself being they are such small values. i would stay away from cored inductors, mainly because they can introduce distortions of their own when they saturate and some ferrite core materials are pretty bad that way.
Profiguy,
The OP says "several small value inductors", which is probably why he wants them ready-made, instead of hand-wound.
I think the ferrite is OK for shunting (rejection) purposes, as long as it doesn't saturate. However, it wouldn't be the best choice if the choke were directly in the signal path, like in a low-pass filter, as you have already mentioned.
To OP:
Note that the low Q-factor is a very important point to check, since the reduction in inductance value with current would also shift the resonant frequency in high Q-factor applications.
The OP says "several small value inductors", which is probably why he wants them ready-made, instead of hand-wound.
I think the ferrite is OK for shunting (rejection) purposes, as long as it doesn't saturate. However, it wouldn't be the best choice if the choke were directly in the signal path, like in a low-pass filter, as you have already mentioned.
To OP:
Note that the low Q-factor is a very important point to check, since the reduction in inductance value with current would also shift the resonant frequency in high Q-factor applications.
Inductors most suitable for hifi speaker crossovers, especially of such low value inductance, are air core inductors. They are easily made or they can be bought as higher L values, then unwound to desired spec.
The Wurth inductor would work, as it's saturation current (Isat) is fairly high - 13Amps (13^2*8=1350Watts into 8ohm). The Kemet one I'm not sure about - it's application is listed as an earthing inductor, which usually don't carry heavy currents so I would guess it's saturation current is fairly low. When the core saturates the inductance drops as the core is no longer helping to boost the value of inductance above that of an air core. This results in non-linear distortion as the filtered signal amplitude becomes modulated by signal amplitude causing a non-linear response. For hifi usage you typically want to keep Isat above 10A (for an ~8ohm system) as it doesn't just suddenly saturate, the effect is more gradual - i.e. at 5A there will still be mild saturation. If you have Isat>10A then it'll probably be essentially linear at <1A which is normal listening levels.
You can make air-core inductors by just winding enameled wire around a non-ferrous and non-conductive bobbin. Air core inductors can't saturate, the only disadvantage is that you need more turns of wire, so you'll need heavier gauge wire if you need low DC resistance also. That is mainly why ferrous cored inductors exist as they achieve lower DCR for the same volume of wire (or the same DCR while being smaller/cheaper) and they don't leak as much magnetic field.
I have used solid wooden dowels or old plastic solder spools to wind air core inductors. You can also buy a higher value inductor and unwind it to the value you need. Inductance follows the square of the number of turns so if you buy a 0.4mH inductor and remove half of the turns it will be around 0.1uH.
Air Cored Inductor Calculator – M0UKD – Amateur Radio Blog
You can make air-core inductors by just winding enameled wire around a non-ferrous and non-conductive bobbin. Air core inductors can't saturate, the only disadvantage is that you need more turns of wire, so you'll need heavier gauge wire if you need low DC resistance also. That is mainly why ferrous cored inductors exist as they achieve lower DCR for the same volume of wire (or the same DCR while being smaller/cheaper) and they don't leak as much magnetic field.
I have used solid wooden dowels or old plastic solder spools to wind air core inductors. You can also buy a higher value inductor and unwind it to the value you need. Inductance follows the square of the number of turns so if you buy a 0.4mH inductor and remove half of the turns it will be around 0.1uH.
Air Cored Inductor Calculator – M0UKD – Amateur Radio Blog
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The saturation current limit isnt the whole issue. If the inductor core material doesn't behave very linear, it will audibly distort well before its saturation point. Most ferrite cores don't sound good in the signal path of a crosover and even when the inductor is part of a paralleled circuit.
The core saturating is exactly what makes the inductor non linear. Imagine you've got a cored inductor which is part of a 1kHz lowpass filter. You play a 1kHz tone, so it's at -6dB. Then, a big bass note comes along and on the peaks of the bass sine wave it pushes the current up to several amps, the core starts to saturate and the effective inductance drops, pushing the crossover frequency up to 5kHz. Now during this saturation the 1kHz tone plays at 0dB instead of -6dB due to it now being in the pass band. Effectively the bass note is modulating the 1kHz tone, which is intermodulation distortion. The same thing would happen if the amplitude of the 1kHz was large enough to push the core into saturation at it's peaks - it would amplitude modulate itself which would be harmonic distortion.
The stated Isat is where there is a knee in the current-inductance curve, and typically if you stay 10x under this the amount of core saturation and therefore change in inductance and therefore distortion will be insignificant. Most home hifi drivers will be distorting quite a bit when pushed to several amps of current. A sine wave peaking at 5Amps into an 8ohm speaker is 100Watts rms. For speaker drivers under 8", typically distortion is plainly audible at tens of watts if not a handful of watts.
Ferrite cores have high permeability (often >50) but low saturation point. You need hardly any turns of copper to achieve a certain inductance, the core is easy to saturate and when it does it effectively becomes an air core with hardly any turns so the inductance will drop to almost nothing. Basically garbage for speaker crossovers unless the speakers are very low powered or the inductors are used in a way that very little current flows. That is why you find ferrites in cheaply manufactured speakers as they save a lot of copper, and the speaker drivers are garbage anyway so you probably won't notice the inductor distortion over the speaker driver distortion when you turn them up too loud, but they still sound ok at low volumes.
Steel laminate has much lower permeability (<20) but much higher saturation point and is much better suited for hifi speaker crossovers. When sized correctly, the distortion can be completely negligible compared to even decent speaker drivers at a given power level, and be far more cost effective (by using less copper wire) than an equivalent DCR air core. See:
Test of a couple of iron core inductors | HiFiCompass
The stated Isat is where there is a knee in the current-inductance curve, and typically if you stay 10x under this the amount of core saturation and therefore change in inductance and therefore distortion will be insignificant. Most home hifi drivers will be distorting quite a bit when pushed to several amps of current. A sine wave peaking at 5Amps into an 8ohm speaker is 100Watts rms. For speaker drivers under 8", typically distortion is plainly audible at tens of watts if not a handful of watts.
Ferrite cores have high permeability (often >50) but low saturation point. You need hardly any turns of copper to achieve a certain inductance, the core is easy to saturate and when it does it effectively becomes an air core with hardly any turns so the inductance will drop to almost nothing. Basically garbage for speaker crossovers unless the speakers are very low powered or the inductors are used in a way that very little current flows. That is why you find ferrites in cheaply manufactured speakers as they save a lot of copper, and the speaker drivers are garbage anyway so you probably won't notice the inductor distortion over the speaker driver distortion when you turn them up too loud, but they still sound ok at low volumes.
Steel laminate has much lower permeability (<20) but much higher saturation point and is much better suited for hifi speaker crossovers. When sized correctly, the distortion can be completely negligible compared to even decent speaker drivers at a given power level, and be far more cost effective (by using less copper wire) than an equivalent DCR air core. See:
Test of a couple of iron core inductors | HiFiCompass
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