9.5 Frequency and Crossover Reference Charts
The Frequency Spectrum in Context
Illustration in preparation Description: Full audio spectrum 20 Hz–20 kHz on logarithmic scale with labeled regions: sub-bass (20–60 Hz), bass (60–250 Hz), upper bass/lower midrange (250–500 Hz), midrange (500–2000 Hz), upper midrange (2–4 kHz), presence (4–8 kHz), brilliance/air (8–20 kHz); instrument ranges shown as horizontal bars below the spectrum
What lives where:
| Range | Frequencies | Perception | Speaker type |
|---|---|---|---|
| Sub-bass | 20–60 Hz | Felt more than heard; chest pressure | Subwoofer only |
| Bass | 60–160 Hz | Bass guitar, kick drum, bass weight | Subwoofer + midbass |
| Upper bass | 160–300 Hz | Bass guitar body, male voice fundamental | Midbass woofer |
| Lower midrange | 300–800 Hz | Voice clarity, piano body, guitar | Midrange driver |
| Midrange | 800–2500 Hz | Vocal presence, most instruments | Midrange driver |
| Upper midrange | 2.5–5 kHz | Consonants, attack, sibilance edge | Tweeter lower range |
| Presence | 5–10 kHz | Detail, air, "sparkle" | Tweeter |
| Brilliance | 10–20 kHz | Cymbal shimmer, reverb tails, "air" | Tweeter (if capable) |
Crossover Frequency Quick Reference
Illustration in preparation Description: Visual guide showing speaker types on left, recommended crossover ranges as colored bars spanning the frequency axis, with notes on slope at each transition
Recommended crossover points:
| Transition | Typical Range | Slope | Notes |
|---|---|---|---|
| Sub → Midbass | 60–100 Hz | 24 dB/oct | 80 Hz most common (THX standard) |
| Sub subsonic filter | 15–25 Hz | 24 dB/oct minimum | Below box tuning for ported |
| Midbass → Midrange | 200–500 Hz | 12–24 dB/oct | Depends on driver capabilities |
| Midrange → Tweeter | 2000–5000 Hz | 12–24 dB/oct | Check tweeter Fs; cross at min 2× Fs |
Rules for tweeter crossover:
- Minimum: 2–3× tweeter Fs (e.g., Fs = 800 Hz → minimum 1,600–2,400 Hz crossover)
- Recommended: 2,500–4,000 Hz for most quality tweeters
- Slope: 12 dB/octave minimum; 24 dB/octave for better protection
Filter Slope Comparison Chart
Illustration in preparation Description: Four frequency response curves on same axes showing 6, 12, 18, 24 dB/octave high-pass filters from same crossover frequency; rolloff rates, -3 dB points, and phase shift labeled for each
Attenuation below crossover:
| Slope | 1 octave below | 2 octaves below | 3 octaves below |
|---|---|---|---|
| 6 dB/oct | -6 dB | -12 dB | -18 dB |
| 12 dB/oct | -12 dB | -24 dB | -36 dB |
| 18 dB/oct | -18 dB | -36 dB | -54 dB |
| 24 dB/oct | -24 dB | -48 dB | -72 dB |
Example: 80 Hz crossover, 24 dB/oct slope: - At 40 Hz (1 octave below): -24 dB attenuation - At 20 Hz (2 octaves below): -48 dB — almost inaudible
Phase Shift Reference
Illustration in preparation Description: Phase response curves for 1st through 4th order Butterworth and Linkwitz-Riley filters, showing phase at crossover frequency for each
Phase at crossover frequency:
| Filter order | Type | Phase at Fc |
|---|---|---|
| 1st (6 dB/oct) | Butterworth | ±45° |
| 2nd (12 dB/oct) | Butterworth | ±90° |
| 2nd (12 dB/oct) | Linkwitz-Riley | ±90° |
| 3rd (18 dB/oct) | Butterworth | ±135° |
| 4th (24 dB/oct) | Butterworth | ±180° |
| 4th (24 dB/oct) | Linkwitz-Riley | ±180° |
Why LR4 is preferred: Both HPF and LPF are -6 dB at Fc (not -3 dB like Butterworth). The sum of both is flat. Phase is identical for both — no cancellation. Industry standard for professional active crossovers.