iPhone 16 and AKG K371: the cheapest USB-C dongle is already 5.3 dB more than enough
The K371 needs 0.63 V for a 110 dB peak. A $76 FiiO KA13 on phone power delivers 1.158 V into 32 Ω — 115.3 dB, 5.3 dB of headroom. The real constraint here is not the amplifier but the phone's power contract.
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)
Yes, with 5.3 dB spare — and the interesting question is not loudness but whether the phone will feed the dongle at all.
The iPhone 16 has no headphone jack, so the chain is phone → USB-C dongle → headphones and the dongle is the entire amplifier. AKG publishes 114 dB SPL/V at 32 Ω for the K371, one of the most sensitive over-ears in this catalogue: only the Sony 7506, the MDR-MV1 and the Philips SHP9500 sit higher. A 110 dB peak needs V = 10^((110 − 114)/20) = 0.63 V, that is 12.44 mW and 19.72 mA. The KA13 on phone power makes 1.22 V; after its own <1.7 Ω output impedance takes its share of a 32 Ω load, 1.158 V arrive at the headphone, which is 115.3 dB SPL.
The pearl: the iPhone 16's 4.5 W is conditional, and the non-Pro is the one that pays. Apple's Accessory Design Guidelines, Table 25-1, give the iPhone 16 as 500 mA at USB Type-C Default and 900 mA (4.5 W) only under a USB Power Delivery contract. The iPhone 16 Pro advertises 900 mA even at Default. Same connector, same year, different budget — and an accessory that does not negotiate PD lives on 2.5 W. FiiO publishes no consumption figure for the KA13 at all, so the catalogue records the USB 2.0 default allotment of 500 mA at 5 V as a ceiling rather than inventing one. On the level side this changes nothing: at 0.63 V into 32 Ω the headphone itself asks for 12 mW.
Damping, for once verifiable. FiiO publishes «<1.7 Ω» for the 3.5 mm output. Against 32 Ω that is a ratio of 18.8, comfortably past the 8 that the 1/8 rule wants, so the K371's frequency response is not being bent by the source. Worth keeping in mind that this same 1.7 Ω would be a problem with a multi-driver in-ear of 8-16 Ω, where the ratio falls below 8 — the rule is about the pair, not about the dongle alone.
The practical catch is the opposite of «not loud enough». 115.3 dB of peak capability means normal listening sits far down the control's travel, and on iOS that control is the system volume acting on the dongle. Use the phone's hearing-safety limit rather than the last three steps of the slider: with this pairing, everything above about a third of full scale is already past any sane long-term exposure.