Group delay
How long a given frequency takes to get out of the speaker, measured in milliseconds and plotted against frequency. A system with flat group delay passes every frequency with the same lag, so the shape of a transient survives. Where group delay rises, that band arrives late relative to the rest, and the leading edge of a kick drum or a plucked string is smeared across time even though the frequency response looks fine.
It is one of the four curves an enclosure calculator predicts before anything is built — the others being frequency response, impedance, and step response (micka-enclosure-calculator).
Why bass is where it bites
Group delay is a delay in absolute time, so a few milliseconds is nothing at 2 kHz (many cycles) and a lot at 30 Hz (a fraction of one). Every mechanism that extends bass output — a port, a passive radiator, a high-pass filter, an EQ boost — is a resonant mechanism, and resonance stores energy and gives it back late. That is the standing bargain of low-frequency design: extension and output are bought with time.
- Sealed boxes roll off gently (2nd-order) and keep group delay low across the range.
- Vented/ported boxes gain output near tuning and a steeper (4th-order) rolloff below it, and pay with phase rotation and group delay around the tuning frequency.
- Per svs-sealed-vs-ported, the penalty tracks where the box is tuned: tune below ~20 Hz and the rotation sits under the music band, with the two alignments’ curves said to converge above 30 Hz. Vendor claim, not yet independently checked here.
”Tight bass”
The listening-room phrase for low group delay and a well-damped rolloff. It is not a property of the driver alone — the same driver in a sealed box and a ported box produces different group delay, which is the concrete version of this spoke’s “the same driver in two boxes is two different speakers” (synthesis).
Open question: the corpus still has no measured group-delay comparison from a neutral party — the figures circulating online (order-of-magnitude: single-digit ms sealed vs. tens of ms ported at 30 Hz) come from SEO content farms and are recorded here as unverified.
Related
loudspeaker-enclosure · room-gain · passive-radiator · audio-dsp · micka-enclosure-calculator · svs-sealed-vs-ported