I got bored of trying to explain this once a week over messages so I thought i'd make a video! tl;dr:
1) Coil moves in magnet creating current which opposes that coming from amplifier.
2) Amplifier sees opposing current as resistance.
3) Things that cause higher resistance due to higher opposing current: high excursion, strong motor, tight coil gap, many coil windings, large boxes, playing outside of tuning frequency.
3.5) In free air, Fs yields highest impedance. In a ported box, tuning frequency yields lowest impedance.
4) Best (ported) box design is one that holds the cone still enough to prevent over-excursion before the coil has reached its power capacity over the whole desired frequency range.
5) High box rise is a sign of an efficient system and can be used to wire amps lower to yield more power.
6) A strong motor doesnt suddenly give you dB gains, you need to combine it with wiring lower and/or more amp power.
7) Playing too far either side of box tuning frequency is like playing in a leaky sealed box (higher than tuning) or free air (lower than port tuning). This is why large port area = huge peak and steep roll off either side, and small port area = lower peak but shallower roll off either side (more flat response).
8) The BEST box design in the world is infinite baffle. The problem is that woofers do not have infinite excursion. If they did, you wouldn't need a box, only a baffle to completely isolate the front and rear waves. (rotary woofers kind of do this but they have other limitations)
9) T-lines work differently in that they have modes along the line that load the cone, then in between they let go, so you alternate between listening to the cone then the line then the cone etc. Ill do a video on this later.
10) Impedance rise can be seen every day with electrical household items that use some kind of coil/magnet/motor setup.
I am planning to expand on this video soon with some real life examples and footage using the SPL LAB LCD unit, to show the resistance at DC, then free air, then playing in a box. This should be pretty cool to see.
18 фев 2017
