Why can excellent drivers still sound mismatched? This workshop explores basic electrical filters, acoustic summation and how to turn measurements into documented crossover decisions.
about 100–130 minutes6 lessonsNo login
Learning outcome: Distinguish electrical and acoustic slopes, spot common measurement mistakes and document a crossover revision.
LESSON 01 / 06
Electrical filters are not acoustic slopes
A capacitor in series with an ideal resistor forms a first-order electrical high-pass. A real tweeter has frequency-dependent impedance and its own acoustic transfer function. The acoustic result combines driver and crossover.
Worked example
With R = 8 Ω and C = 10 µF, the ideal RC high-pass -3 dB frequency is 1/(2πRC) ≈ 1,989 Hz. This is not an approved tweeter crossover point.
Your turn
Why is this formula not a complete crossover design?
Reveal solution
It ignores real impedance, response, phase and power-handling constraints.
LESSON 02 / 06
Match levels before choosing slopes
Woofers and tweeters often have different sensitivities. Resistor networks can reduce tweeter output. A simple series resistor also changes the filter load; a correctly designed L-pad keeps impedance closer to a chosen target.
Worked example
A 90 dB tweeter and 86 dB woofer do not automatically match with an arbitrary series resistor.
Your turn
What should you know first?
Reveal solution
Measured response in the cabinet and branch impedance.
LESSON 03 / 06
Phase controls summation
For coherent sound fields, relative phase matters alongside level. Equal in-phase pressures sum to +6 dB at a point compared with one branch; perfect opposition can cancel at that point.
Worked example
Pressure amplitudes 1 and 1 in phase sum to 2: 20 log10(2) ≈ +6.02 dB.
Your turn
Why can’t we just add two dB curves?
Reveal solution
Sound pressures must be combined as complex quantities including phase.
LESSON 04 / 06
Baffle effects and directivity
The front baffle causes diffraction. Transition from half-space to full-space radiation changes energy distribution. The baffle step depends on shape, driver position and placement. Directivity also constrains the crossover region.
Worked example
A 20 cm baffle may show a broad transition across several hundred hertz depending on geometry and room, not a universal filter frequency.
Your turn
Why measure off axis?
Reveal solution
A flat on-axis trace does not guarantee smooth directivity.
LESSON 05 / 06
Useful and safe REW measurements
A calibrated measurement microphone and suitable interface provide useful data. Measure drivers separately on the intended cabinet, preserve a common timing reference and choose a reasonable distance. Time gating reduces room reflections but sacrifices low-frequency resolution.
Worked example
A 5 ms gate gives only roughly 200 Hz frequency resolution. Near-field and impedance measurements can complement bass data.
Your turn
What does a shorter time window do?
Reveal solution
Suppresses reflections but reduces low-frequency resolution.
LESSON 06 / 06
From measurements to crossover revisions
Crossover design is iterative: measure each branch, identify usable overlap, simulate filters, verify complex summation, check polarity and several angles. Follow with listening and power-handling checks.
Worked example
Record component values, measuring distance, microphone position, smoothing, level, filter version and actual summed responses.
Your turn
Why log component values and measurements?
Reveal solution
Otherwise comparisons across revisions are not reliably repeatable.
INTERAKTIVES LABOR / INTERACTIVE LAB
RC high-pass: ideal model
Only a capacitor in series with an ideal resistor. Real crossovers require impedance and acoustic measurements.
