AKG K-518LE, heavily modified.



Mods:

1. Silver-plated teflon-coated high-purity copper shielded recable. There are no headphones known on the market with shielded cables. There're some custom replacement cables that're shielded, like Sweetcome​ cables for AKG headphones, who had sent some three samples ages ago. Anyway, shielded cables have a sound that's more focused/wholesome/defined than unshielded cables. Silver-plated copper is the cheap alternative to pure silver, and it's still a lot quicker/more lifelike than regular copper (headphones often have low-grade copper wiring by the way). Besides, the stock AKG cable was only 80 cm.

2. Capacitor buffering. The final solution for horrid transient intermodulation distortion of the K-518/K-81. It's that which makes them sound horribly muddy, not the bassy foamies! The problem is twofold: driver excessive reactivity, and insufficient electric/mass damping of the driver (nominal impedance is only 32 ohm). Another possible solution was resistor impedance boost (to increase electric damping in higher frequencies), but the resistors also washed out/chilled sound, so capacitors it is. Capacitors filter/smoothe out the current fed to the drivers (110-uf/10V high-quality tantalium electrolytics).

3. Dual damping, with Dynamat Superlight and Blu-tack, on both the driver backs and inside cups. This makes the cups and drivers more rigid and less prone to parasitic feedback distortion, which blurs transients and makes everything horribly muddy and blurry even in the midrange (which is a shame for an AKG design). Dynamat and Blu-tack damping also improves noise isolation.

4. Deflated pads. The original pads had foam doughnuts inside which made them too "fat", stealing impact power and, worst of all, killing off middle midrange harmonics. The result was an overly glassy sonic tint and lack of detail on strings and midrangey instruments.

5. Silicon glue seals for wire strain relief, necessary to prevent any internal wire movement, which could threaten capacitor joints. Capacitors could just blow up if return wiring was torn off or worn out.

The result is a pretty much transparent, very slightly bassy sound. Quick, lifelike. The headphones are sensitive enough and have enough extra isolation from Dynamat/Blu-tack lining to block all street noise, even tube train noise. AKG's sensitivity figure is 115 dB/mW, presumably pad deflation and shielded wiring have improved that by at least 3 dB.

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