🔧 INSTALLER LEVEL: Three-Way and Active System Design
Three-Way Crossover Planning
A three-way active system needs: - Tweeter high-pass filter (HPF at crossover 1) - Midrange band-pass filter (HPF at crossover 2, LPF at crossover 1) - Midbass low-pass filter (LPF at crossover 2) - Subwoofer low-pass filter (LPF at crossover 3) - All driver high-pass filters (subsonic protection)
Selecting crossover frequencies:
Tweeter crossover (Crossover 1): Must be at least 2–3× the tweeter's Fs. For a tweeter with Fs = 900 Hz, minimum crossover is 1,800–2,700 Hz. Set at 2,500–3,500 Hz for most quality tweeters.
Midrange/Midbass crossover (Crossover 2): Depends on midbass capability. Typical 6.5" midbass reproduces to 500–600 Hz smoothly. Cross at 300–500 Hz.
Subwoofer crossover (Crossover 3): Standard 80 Hz for full-range fronts. 100–120 Hz if front speakers are small.
Example for quality 3-way + sub:
| Output | Filter | Frequency | Slope |
|---|---|---|---|
| Tweeter L/R | HPF | 3,000 Hz | LR24 |
| Midrange L/R | HPF | 300 Hz | LR24 |
| Midrange L/R | LPF | 3,000 Hz | LR24 |
| Midbass L/R | HPF | 80 Hz | LR24 |
| Midbass L/R | LPF | 300 Hz | LR24 |
| Subwoofer | HPF (subsonic) | 25 Hz | LR24 |
| Subwoofer | LPF | 80 Hz | LR24 |
Driver Protection and Acoustic Rolloff Interaction
Physical drivers don't have infinite bandwidth — they have natural acoustic rolloffs. A tweeter's response may already be falling at 2 kHz even without a crossover filter. The DSP filter combines with this natural rolloff:
H_total(f) = H_DSP_filter(f) × H_driver_response(f)
Why this matters:
If your tweeter is already −6 dB at 3 kHz due to its natural Fs rolloff, and you set your HPF at 3 kHz, the effective cutoff appears lower than intended — the natural rolloff and DSP filter compound.
Compensation: Set the DSP crossover slightly above where the natural rolloff begins. Measure the full system with crossover active to confirm actual acoustic crossover point. The measured −6 dB point (in an LR24 system) is what matters, not the filter setting alone.