Just a thought about the Filed coil drivers that how many turns and gauge of wire used for the field coil drivers. I mean mostly observed for an 8 inch filed coil drivers. I read somewhere on the forum that there will be approx 4000 turns which is quite large count. I agree the fact as different drivers have different number of turns but in general would like to know.
What is the observed resistance of the coils for example take Feastrex drivers what is the resistance of the feild coil not the impedance of the voice coil.
What is the observed resistance of the coils for example take Feastrex drivers what is the resistance of the feild coil not the impedance of the voice coil.
A raw turns number tells you nothing.
The actual magnetic "push" into the gap comes from Current times Turns:
You can have fewer turns with lots of current or viceversa.
There´s 2 ways to connect field coils:
* the old one was to get them do double duty, to act as filter chokes *and* as electromagnets, win win situation, only problems is that different amps have different idle and average current needs so sometimes they did not match.
Also some hum was injected into the sound, and coils are relatively low resistance
* the other way, used in higher quality devices (think Hammond organs) was to feed them their own supply, which in general meant higher resistance.
As a rule of thumb, calculate windings and turns so current through field coil dissipates between 5W (small speakers) up to 15 or 20W (large 12" and 15" speakers)
Want accurate results? : start FEMM and calculate Ampere-Turns to get 8000 to 10000 Gauss at the voice coil gap.
The actual magnetic "push" into the gap comes from Current times Turns:
You can have fewer turns with lots of current or viceversa.
There´s 2 ways to connect field coils:
* the old one was to get them do double duty, to act as filter chokes *and* as electromagnets, win win situation, only problems is that different amps have different idle and average current needs so sometimes they did not match.
Also some hum was injected into the sound, and coils are relatively low resistance
* the other way, used in higher quality devices (think Hammond organs) was to feed them their own supply, which in general meant higher resistance.
As a rule of thumb, calculate windings and turns so current through field coil dissipates between 5W (small speakers) up to 15 or 20W (large 12" and 15" speakers)
Want accurate results? : start FEMM and calculate Ampere-Turns to get 8000 to 10000 Gauss at the voice coil gap.
Just a version 1 FEMM analysis:
Coil diameter 18AWG
Number of turns 1000turns
Voltage applied 10VDC
Magnetic material CR10.
Preliminary results: Flux density in the gap is 2.14T
Observations: CR10 in general cannot take alot of flux So need to reduce the voltage or reduce the number of turns.
any inputs will be appreciated.
I agree the geometry of the magnetic circuit needs to be optimized but yes atleast we are getting decent values in the beginning.
Coil diameter 18AWG
Number of turns 1000turns
Voltage applied 10VDC
Magnetic material CR10.
Preliminary results: Flux density in the gap is 2.14T
Observations: CR10 in general cannot take alot of flux So need to reduce the voltage or reduce the number of turns.
any inputs will be appreciated.
I agree the geometry of the magnetic circuit needs to be optimized but yes atleast we are getting decent values in the beginning.
Attachments
DC Resistance 6.35 Ohms
Wire Gauge 18 AWG
Wire Diameter 40.3 mils (1 mil = .001 in)
Coil Length 6 in
Coil Inner Diameter 3.5 in
Coil Outer Diameter 4.06 in
Average Turn Diameter 3.73 in
Wire Length 974.78 feet
Copper Weight 4.79 pounds
Turns 998
Levels 6.7
Turns/Level 148.88
Current through the wire 1.57Amps
Power dissipation approx 15W
Wire Gauge 18 AWG
Wire Diameter 40.3 mils (1 mil = .001 in)
Coil Length 6 in
Coil Inner Diameter 3.5 in
Coil Outer Diameter 4.06 in
Average Turn Diameter 3.73 in
Wire Length 974.78 feet
Copper Weight 4.79 pounds
Turns 998
Levels 6.7
Turns/Level 148.88
Current through the wire 1.57Amps
Power dissipation approx 15W
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