Hi All.
I recently purchased 10 three way crossovers that were originally used in a local theatre's sound system. They are identical, and contain a total of ten air core inductors each of .56, 1.3, 1.5, 2.4, and 3.6mH at 16 gauge, and ten air core inductors each of .51 and 2mH at 18 gauge.
I have a few different crossovers that I would like to build for a couple of projects and, in some cases, the values that I require would be easiest to achieve by using two inductors in parallel. For example, I need a pair of 1.8mH inductors, one for each crossover's low pass for the woofer, and a pair of 1mH inductors in the high pass portion. Using two 3.6mH (@ 1.5 Ohms DCR) in parallel will give me 1.8mH (@ .75 Ohms DCR). Two 2mH (@ 1 Ohm DCR) in parallel will give me 1mH (@ .5 Ohms DCR).
I know that putting two identical inductors in parallel will halve both the inductance and the DCR of a single inductor, but are there any other factors that I need to consider when doing this?
Also, if I end up using 20 gauge inductors in the crossovers without paralleling them, and I also have resistors in series in that portion of the circuit, can I make up for their higher than desirable DCR by reducing the value of the series resistors accordingly?
Thanks in advance for your input!
I recently purchased 10 three way crossovers that were originally used in a local theatre's sound system. They are identical, and contain a total of ten air core inductors each of .56, 1.3, 1.5, 2.4, and 3.6mH at 16 gauge, and ten air core inductors each of .51 and 2mH at 18 gauge.
I have a few different crossovers that I would like to build for a couple of projects and, in some cases, the values that I require would be easiest to achieve by using two inductors in parallel. For example, I need a pair of 1.8mH inductors, one for each crossover's low pass for the woofer, and a pair of 1mH inductors in the high pass portion. Using two 3.6mH (@ 1.5 Ohms DCR) in parallel will give me 1.8mH (@ .75 Ohms DCR). Two 2mH (@ 1 Ohm DCR) in parallel will give me 1mH (@ .5 Ohms DCR).
I know that putting two identical inductors in parallel will halve both the inductance and the DCR of a single inductor, but are there any other factors that I need to consider when doing this?
Also, if I end up using 20 gauge inductors in the crossovers without paralleling them, and I also have resistors in series in that portion of the circuit, can I make up for their higher than desirable DCR by reducing the value of the series resistors accordingly?
Thanks in advance for your input!
Putting two identical inductors into the same physical space also increases the inductance by four compared to one of them.
That would be the case if I put them in series? If I stack two 2mH inductors on top of each other and parallel them, do I get a 2mH inductor at half the DCR?
If I were going to return to passive crossover design (went active long ago and won't go back) I would consider one of these essential to the process:
Dayton Audio DATS V2 Computer Based Audio Component Test System
Useful for accurately measuring inductors, low value resistors, capacitors, and of course speaker drivers and systems. It's extremely versatile, accurate, and super easy to use. And understand, I have no vested interest in this device other than personal experience.
Mike
Dayton Audio DATS V2 Computer Based Audio Component Test System
Useful for accurately measuring inductors, low value resistors, capacitors, and of course speaker drivers and systems. It's extremely versatile, accurate, and super easy to use. And understand, I have no vested interest in this device other than personal experience.
Mike
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With windings in the same direction, yes, except that it is not possible to line the centres up perfectly because the bobbins are stacked.
Very interesting. Assuming that I am able to permanently fix the relative positions of two stacked and paralleled inductors, shouldn't it be possible to vary the degree to which they are coupled by moving them around until I get an inductance reading that I want? For example, if I have two 2.5mH inductors and I parallel them, I should be able to get a range of mH values between half (1.25mH) when they are far enough apart, and somewhere close to 2.5mH (minus losses) when they are perfectly stacked and coupled.
I am in the unusual situation where I have many inductors, and I can use two or more to get appropriate mH values by "wasting" inductors while also reducing the DCR of the combined inductors as compared to using a single one.
Also, for example, if I need 3mH and I have two 3.6mH inductors, I should be able to get that value by stacking two 3.6mH inductors so that they couple imperfectly. This will save me from unwinding inductors to get to the correct value.
Does this all make sense?
I am in the unusual situation where I have many inductors, and I can use two or more to get appropriate mH values by "wasting" inductors while also reducing the DCR of the combined inductors as compared to using a single one.
Also, for example, if I need 3mH and I have two 3.6mH inductors, I should be able to get that value by stacking two 3.6mH inductors so that they couple imperfectly. This will save me from unwinding inductors to get to the correct value.
Does this all make sense?
Yes but it is rather impractical, as I suggested it is best to use an LCR meter, they are not overly expensive and are surprisingly accurate. The thing with variable coupling is that it is not particularly controllable over a wide frequency range, it may be detrimental to say the tweeter's high pass filter through mutual inductance, that is, the tweeter's filter coil and with that vice versa. It's always best to keep any stray magnetic fields confined to a small perimeter.
C.M
C.M
Thanks Tweet. I have an inductance meter and will play around with the inductors. They are currently attached to their respective crossover PCBs, but I will harvest them soon.
The crossovers that I intend on building have large resistances in series and in parallel with the inductors in the high pass sections, as they combine very efficient mid/high compression drivers/horns with substantially less efficient horn loaded direct radiators in the bass sections. I am therefore less concerned about DCR in the mid/high sections than I am with DCR in the bass section of the crossovers. If I stack and parallel inductors, it will only be for the bass sections of the crossovers.
It is unneccesary to know the value of an inductor to the last digit. You have to measure the frequency response anyway, while building a x-over. The values you need are dictated by the single drivers. So don´t waste time and money on measuring the components values, even moving the box a little in the room has more influence than the tolerance of two identical coils, resistors or capacitors.
So, look for a good microphone and get to know your measuring software. The components come last. If you build up your speaker system, and have designed an x-over, just build it twice and test it on the same speaker for identical response. Any huge mistake with a componens value will be obvious.
Anyway, a tester from China for 7-18 $ should do. These Meters have come very cheap.
So, look for a good microphone and get to know your measuring software. The components come last. If you build up your speaker system, and have designed an x-over, just build it twice and test it on the same speaker for identical response. Any huge mistake with a componens value will be obvious.
Anyway, a tester from China for 7-18 $ should do. These Meters have come very cheap.
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This is referred to as 'leakage inductance'.
I'd like to learn about this if you have a reference?
Leakage inductance is going to be centred between the bobbins so no additional issue there.
The inductors I have on hand are air core. They can be stacked fairly neatly, and I can use a bit of Goop and a few ties to secure them in place. I need to pull them off the PCBs and experiment a bit. I’ll report back when I try it out.
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