FiiO K11 with the Sennheiser HD 600 — and why the HD 650 is a different question
Same 300 ohms, same family, 6 dB apart — and the K11 is exactly the source where those 6 dB flip the verdict. HD 650: 115.5 dB, comfortable. HD 600: 109.5 dB, target reached with nothing to spare. The catch is that the deficit is in volts, and the K11's headline 520 mW says nothing about volts.
Signal Chain Compatibility Matrix
Select gear and parameters for live gain, impedance and SPL calculations.
Input Equipment Setup
PASS: Optimal Signal Chain
Requires minimum +60dB of clean pre-amp gain. Most budget entry interfaces max out at +50dB to +56dB and introduce hiss at max pot. An inline preamp booster (Cloudlifter CL-1 / FetHead) is strongly recommended.
The interface preamp provides sufficient headroom.
$538
$405
-25%Tonal & acoustic characteristics: Flat, wide-range frequency response for clean music and speech. Smooth, warm acoustic character with air-suspension shock isolation.
Technical advisory: With +69dB max gain, the Gen 4 Solo can drive demanding dynamics like the Shure SM7B natively without requiring an external inline booster.
Physical Interconnect Topology
Shure SM7B
Direct Cable Connection (No Intermediate Box)
1x Shielded Balanced XLR Cable (3-Pin XLR Male to XLR Female)
Focusrite Scarlett Solo (Gen 4)
Host: Apple MacBook Pro (M1/M2/M3/M4)
The HD 600 reaches the target and stops there; the HD 650 clears it by 5.5 dB. One DAC, one impedance, two verdicts.
Both headphones are 300 Ω. Sennheiser publishes the HD 600 at 97 dB/V and the HD 650 at 103 dB/V — six decibels, which is four times the power. For a 110 dB peak the HD 600 needs 4.467 V, 66.51 mW, 14.89 mA; the HD 650 needs 2.239 V and 16.71 mW.
The FiiO K11 publishes 4.24 V with a 1.2 Ω output impedance. After the divider the HD 600 sees 4.223 V and reaches 109.5 dB — half a decibel under target, while the HD 650 reaches 115.5 dB. Damping is a non-issue for both: 300 / 1.2 = 250, well past the ratio of 8.
| Source | HD 600 | HD 650 | |---|---|---| | FiiO K11 (4.24 V) | 109.5 dB (−0.5) | 115.5 dB (+5.5) | | FiiO KA13 dongle (1.22 V) | 98.7 dB (−11.3) | 104.7 dB (−5.3) | | SSL 2 MkII (3.46 V) | 107.8 dB (−2.2) | 113.8 dB (+3.8) |
The pearl: the K11's headline number is measured at the wrong impedance to answer this question. FiiO publishes 520 mW — at 32 Ω. The HD 600 asks for 66.5 mW, which looks like an eighth of that and therefore trivially easy. It is not, because at 300 Ω the K11 cannot deliver 520 mW at all: 4.24 V into 300 Ω is 60 mW, and that is the ceiling. Power figures do not travel across impedances; volts do. Read the voltage, not the milliwatts — the HD 600 wants 4.467 V and the box has 4.24, and that 5 % shortfall in volts is the entire verdict.
So the practical reading: on a K11 the HD 650 has room for a dynamic recording; the HD 600 will be sitting at maximum volume on quiet material, and every 6 dB the mastering engineer left below full scale comes straight out of your listening level.