🔧 INSTALLER LEVEL: Professional System Calibration

Gain Staging Across the Entire Chain

Proper gain staging means no clipping, maximum signal-to-noise ratio, at any link in the chain.

Illustration in preparation Description: Signal flow from head unit through DSP to amplifier, with level meters at each stage showing proper levels (near max, not clipping)

Stage 1 — Head unit output:

Most head units output 2–5V RMS at maximum volume. The spec sheet will state this as "preamp output voltage." Higher is better (less noise from subsequent stages).

Stage 2 — DSP input:

Set DSP input sensitivity to match head unit output. Play 0 dB test tone at reference volume. Input meter should read 95–99% — near maximum but not clipping. Never let it clip.

Stage 3 — DSP internal processing:

EQ boosts increase internal signal level. A +6 dB boost doubles voltage. If you have several boosts, check internal clip indicators or reduce input trim to compensate.

Stage 4 — DSP output to amplifier:

Set DSP output level so amplifier gain can be set to a point roughly mid-range on its adjustment. If gain is maxed out with DSP at full output, the amplifier is being driven too hard relative to its noise floor. If gain is near minimum, the DSP output is unnecessarily high.

Stage 5 — Amplifier gain:

As calculated by target voltage method above.

Verification:

At every stage, clip indicators (or DMM) should show signal approaching but never reaching maximum. This is proper gain staging.

Time Alignment Calibration — Full System

Illustration in preparation Description: Side profile of car with distances drawn from each driver to listener's ear position, with a table of calculated delays beside it

Step 1: Measure acoustic distances

Use a measuring tape from the acoustic center of each driver to the listener's ear position (not just the mounting hole — aim for the dust cap center or horn mouth):

Step 2: Find reference (furthest driver)

Subwoofer at 68 inches — this receives 0 ms delay.

Step 3: Calculate delays

Delay (ms) = (D_ref − D_driver) × (1000 / 13,500)

Step 4: Enter into DSP

Program calculated delays per channel. Enable alignment.

Step 5: Fine-tune by ear

Play a track with a strong, clear center vocal — Norah Jones, Diana Krall, or acoustic guitar works well. Adjust left/right tweeter delays in 0.1 ms steps, listening for the image to lock to center. When correct, the vocalist should appear to be sitting directly in front of you, not biased left or right.

Then adjust midbass delays for maximum warmth and body in vocals. Finally, adjust subwoofer for tightest bass impact (often requires ±3–5 ms from calculated value due to acoustic wavelength effects).

Target Curve Application

Illustration in preparation Description: REW graph showing measured response (irregular), target curve (smooth slope), and the resulting EQ correction curve that bridges them

Recommended starting target:

The Harman-derived preference curve for automotive listening: - +6 dB at 20 Hz - Slopes linearly to 0 dB at 300 Hz - Flat from 300 Hz to 2 kHz - Gentle rolloff: −2 dB at 10 kHz, −4 dB at 20 kHz

In REW: EQ → Target Settings → Load target or draw manually.

Applying EQ to match target:

Work in priority order:

1. Major peaks >8 dB: Cut first, narrow Q (8–12)
2. Broad dips >6 dB: Consider leaving — boosting is risky and reflections may fill them in
3. Tonal slope errors: Broad, low-Q adjustments (0.5–1.0) to shape overall tilt
4. Fine-tuning: Medium corrections (Q = 2–4) for residual errors

Listen after every 2–3 EQ adjustments. Measurements guide, ears decide.