Ustawienie cewek
Placement of coils in crossover networks
2x 0.56 mH in series = 1.12 mH
Measured value = 1.144 mH
 |
Fig. 1. Coils 20 cm
apart: 1.144 mH |
 |
Fig. 2. Coils 10 cm
apart: 1.137 mH |
 |
Fig. 3. Coils as close
as possible: 1.109 mH |
|
Fig. 4. Coils placed
close as seen on picture, one coil turned upside down: 1.181 mH Compare with fig. 3. |
 |
Fig. 5. Coils placed
close as seen on picture: 1.147 mH |
 |
Fig. 6. Coils placed
close as seen on picture: 1.175 mH |
 |
Fig. 7. Coils placed on
top on one another, same orientation: 1.312 mH |
 |
Fig. 8. Coils placed on
top on one another, reverse orientation: 1.015 mH |
Coils placed close to aluminium |
|
 |
Fig. 9. 3.3 mH cored coil, vertical orientation. Coil on plastic surface: 3.305 mH |
 |
Fig. 10. 3.3 mH cored coil, vertical orientation. Coil on 15 mm alu: 2.832 mH |
 |
Fig. 11. 3.3 mH cored coil, vertical orientation. Coil on 15 mm alu + 10 mm plywood: 3.055 mH |
 |
Fig. 12. 3.3 mH cored coil, vertical orientation. Coil on 15 mm alu + 15 mm plywood: 3.147 mH |
 |
Fig. 13. 3.3 mH cored coil, vertical orientation. Coil on 15 mm alu + 25 mm plywood: 3.232 mH |
 |
Fig. 14. 3.3 mH cored coil, horizontal orientation. Coil on 15 mm alu: 3.187 mH |
 |
Fig. 15. 3.3 mH cored coil, horizontal orientation. Coil on 15 mm alu + 15 mm plywood: 3.279 mH |
 |
Fig. 16. 3.3 mH cored coil, horizontal orientation. Coil on 15 mm alu + 25 mm plywood: 3.301 mH |
| Conclusion to
this small additional study: Coils placed vertically near to aluminium display a significant reduction in inductivity. Coils should at least be 5 cm/2 inches from nearest aluminium surface. More is recommended. Coils placed horizontally near to aluminium display only minor impact on inductivity, however 3-4 cm distance is recommended. |
|
| Dear Mr. Gravesen, As I think you don't have much time as you are designing excellent speakers at this very moment I will try to make it short: In my opinion, you measurements about the placement of coils won't show the whole truth or the real problem of placing coils next to each other. The real problem is the crosstalk, not the change in inductivity (although this is a little problem, too, even though the changes in inductivity stay below 10 %). It would be great if you cold do the measurements again, but this time measure the crosstalk, too. You could do this by giving one coil a 50 Hz signal with a defined voltage and measuring the output voltage on the other coil. Or you could at least give a hint on your page that the change in inductivity is not the only effect... I'm writing to you as in many internet boards people refer to your measurements and you are kind of a expert among the hobby loudspeaker designers... Best Regards, B.M. Dear
B.M. |