Sennheiser IE 200 impedance: 16 or 18 ohms? Sennheiser publishes both, and shows what everyone else hides
«Impedance (without cable / with cable) 16 Ohm / 18 Ohm» — almost nobody separates these. On a Lewitt CONNECT 2 the two numbers differ by 0.1 dB in level and move the damping ratio from 9.5 to 8.4, straddling the 1/8 rule. That is what a single low figure hides.
This is the opposite case to every other claim in this catalogue: nothing here is ambiguous. Sennheiser prints both numbers and labels its sensitivity too. The value of the entry is what it reveals about the makers who print one.
The IE 200 page gives «Impedance (without cable / with cable) 16 Ohm / 18 Ohm» and «Sound pressure level (SPL) 119dB (1kHz, 1Vrms)». Two ohms of difference are the cable's series resistance. The source is connected to the cable, not to the transducer, so 18 Ω is the load that matters and 16 Ω is a property of the driver alone. We store 18 Ω.
With the cable — 18 Ω. 119 dB/V needs 0.355 V for a 110 dB peak, i.e. 19.71 mA and 6.99 mW. Lewitt publishes «Max output level 6.8 dBV (high impedance mode)» — 2.19 V — and «Impedance 1.9 Ω». Result: 124.9 dB SPL, +14.9 dB, damping ratio 9.5, verdict comfortable.
Without the cable — 16 Ω. The same 0.355 V is required, because the sensitivity is expressed per volt and the voltage does not care about the load. What changes is 22.18 mA and 7.87 mW drawn, a level of 124.8 dB SPL, +14.8 dB, and a damping ratio of 8.4. Two ohms cost 0.1 dB of level and 1.1 of damping ratio.
Why the damping number is the point. The 1/8 rule wants a source impedance at or below one eighth of the load: 2.25 Ω for the 18 Ω figure, 2.0 Ω for the 16 Ω one. The CONNECT 2's published 1.9 Ω clears both, but only just — and the margin is smaller than the difference between the two published impedances. Move the same earphone to a Focusrite Vocaster One (5 Ω) and both readings fail: +11.2 dB with a ratio of 3.6, or +10.9 dB at 3.2. On an Audient EVO 4 (50 Ω) the ratios are 0.4 and 0.3.
How to judge, and what to carry away. Here there is nothing to judge — take 18 Ω, because that is what the plug presents. The reason to record the claim is the case you will meet everywhere else: a brand prints a single «16 Ω» and you have no way to tell whether it is the driver or the finished product. Two ohms is 12 % of the load on a 16 Ω in-ear, and it lands exactly where low-impedance in-ears are most sensitive to the source. The pearl: Sennheiser also labels its sensitivity — «119dB (1kHz, 1Vrms)» — and that label is worth 17.4 dB. Read the same 119 as dB/mW and the required voltage falls from 0.355 V to 0.048 V, the level rises to 142.4 dB SPL, +32.4 dB. One sheet, two labels, and every number on it usable without a second document.