Tascam US-4x4HR: power output and what it will drive

The Tascam US-4x4HR is an audio interface at $249. It delivers 45 mW into 32Ω and 24 mW into 300Ω, which ranks it 253 of 280 for raw power among the sources in this database.

Measured at 100 dB SPL it has comfortable headroom on 454 of the 571 dynamic and planar headphones catalogued here, enough but not generous on 92, only marginal on 11 and not enough power for 14. Power is published at 32Ω; the rest of the table is derived from those figures. Output noise is not published, so the hiss estimate cannot be run.

The manufacturer publishes 45 mW into 32Ω. Everything else in the table above is worked out from those figures, and this table says which is which.

Derivation holds output voltage steady between and beyond the published loads rather than output power, because that is what an amplifier actually does. The full method is written up here.

Source: tascam.com.

Ordered from easiest to hardest to drive. Headroom is measured at 100 dB SPL, which is louder than almost anyone listens — a small negative number means the source still plays loud, just without reserve for peaks.

These figures come from each manufacturer's own sensitivity rating. A handful of planars — the HiFiMAN Susvara and HE-6se and the Abyss AB-1266 in particular — are widely reported to need far more than their published sensitivity implies, so treat a bare pass on those as optimistic rather than settled.

The manufacturer does not publish an output noise figure for this source, so the hiss estimate that runs on every other page here cannot be run on this one. Rather than substitute a plausible number, this page leaves the question open.

If you know the noise figure from a measurement you trust, the hiss calculator takes it directly and tells you where that noise lands in your own in-ears.

At 51.5 Ω output impedance, the one-eighth rule says this source suits headphones of 412.0Ω and above. 565 of the 571 models here fall below that. That is most of the database, not a niche — 222 of them multi-driver in-ears, and the mismatch tilts the frequency response audibly rather than subtly.

The rule is a rule of thumb, not physics: a source impedance below one eighth of the headphone's keeps the interaction under about 1 dB. The checker works it out for any pair.

Or put any two side by side in the source comparison tool, or run your own headphones through the amplifier matcher. Or see every Tascam source in the database, and how much of what this site says about them came from Tascam’s own documents.