tonistry.

Sound

Diffuse-field

Also called diffuse-field target, DF curve

Diffuse-field is a headphone measurement target that describes how a flat sound source would measure at the eardrum if it arrived evenly from every direction. It is a reference for what "neutral" should look like on a headphone measurement rig.

0+6+12dB20 Hz1001k10k20kat the eardrumrise near 3 kHzflat source
A flat sound arriving evenly from every direction measures at the eardrum with a broad rise peaking near 3 kHz, because the outer ear and canal boost those frequencies. The diffuse-field target is that shape, shown here illustratively.

A microphone inside an ear simulator does not measure flat even for a flat sound, because the outer ear and canal boost some frequencies. The diffuse-field curve removes that effect so a measurement can be read as a tonal balance. Free-field is the same idea for a source directly in front.

Headphones tuned strictly to diffuse-field tend to sound lean and bright to most listeners, which is one reason the Harman target, with its added bass, became more common. Some measurement sites plot against a tilted diffuse-field curve as a compromise.

The term matters mostly when reading Frequency response graphs: the same headphone looks different against each target, and neither is a verdict on sound quality.

Related terms