The voice coils depend on the inside diameter size (mm) minute ∮13.28, ∮14.28, ∮16.4, ∮19.43, ∮20.4, ∮25.5, ∮25.9, ∮30.5, ∮38.5, ∮35.5, ∮44.3, ∮49.5, ∮50.5, ∮51.5, ∮60, ∮64.5, ∮75.5, ∮76.5, ∮78.6, ∮99.2, ∮100.2 and so on. The speaker supplier may divide into, the intermediate frequency, the tweeter voice coil low frequency according to the frequency sound. Has PL, PSV, AL, ASV, KSV according to voice coil's material minute and so on, the first letter will be the voice coil framework material code number, P represents the paper tube, A represents the aluminium sheet, L is the heat resistant 135℃ wire rod, SV (heat resistance refers to rubber on behalf of the heat resistant 180℃ wire rod which wire rod surface will attach under this temperature not to expire ageing), K will be one exotic material (glass fiber), English name will be KAPTON, the heat resistance in 220℃ above. Circles the system according to the voice coil the layer to be possible to divide into the monolayer, two, four, six. Voice coil's quality, first from the outward appearance looked that circles the system the wire rod to be whether smooth, be clean, whether there is to jump the line, loosens, overlaps, whether the line superficial insulating layer does flake bumps into and injuries, whether there is does the extra thin noodle upward label blow up, turns upwards, the voice coil inside diameter wall is whether smooth, whether there is burr, moreover whether is its resistance number standard and so on.