Subwoofer Crossover Calculator

About This Tool

The Subwoofer Crossover Calculator recommends an appropriate crossover frequency in Hz based on the size of your main speakers' mid/bass driver and your subwoofer driver. While professional setup uses room measurements at the listening position, this tool gives you a sensible starting point that works in 80% of home theater and stereo setups.

Why Crossovers Matter

A subwoofer-and-mains system has two devices reproducing the bass region. Without a crossover, both play overlapping content — leading to comb filtering, phase issues, and uneven response. A crossover splits the spectrum: sub gets lows, mains get mids and highs. Properly aligned, the two blend seamlessly into a single coherent system. Misaligned, you get holes or peaks in the response that no amount of EQ can fully fix.

The 80 Hz Standard

THX and Dolby established 80 Hz as the standard home theater crossover for satellite and bookshelf speakers, for two reasons. First, most 5-inch+ speakers can play down to 80 Hz with reasonable output. Second, the human ear loses directional hearing below 80 Hz, so it doesn't matter where the sub is in the room — bass under 80 Hz feels like it comes from everywhere. With a 24 dB/octave Linkwitz-Riley filter (standard in AV receivers), the sub and mains overlap by an octave near 80 Hz and sum cleanly to flat response.

Speaker Size Determines Lower Limit

Physics dictates that small drivers can't move enough air to reproduce low frequencies cleanly. A 4-inch driver might roll off at 100-150 Hz. A 5.25-inch driver typically reaches 70-90 Hz. A 6.5-inch driver gets to 50-70 Hz. An 8-inch driver can hit 40-50 Hz. A 12-inch driver might reach 35 Hz. These are rough rules — actual roll-off depends on cabinet design, tuning, driver Thiele-Small parameters, and intended SPL. But driver size is the dominant factor.

Setting Crossover by Ear vs Measurement

By ear: play music with strong bass. Adjust the crossover until the transition between sub and mains is seamless — no "hole" in the upper bass, no boomy hump where the two overlap. By measurement: use REW (Room EQ Wizard) with a calibrated USB mic. Measure the mains alone, the sub alone, and both together. Adjust crossover and phase until the combined response is flat across the transition region. The measurement approach takes an hour but produces dramatically better results than guessing.

Phase and Time Alignment

Even with a perfect crossover, sub and mains can fight if their phase is misaligned at the crossover point. Most subs have a phase control (continuous or 0/180°) and many AV receivers offer subwoofer delay (millisecond adjustment to compensate for the sub being closer or farther from the listener than the mains). After setting crossover, sweep the phase control while playing pink noise and watch your meter — pick the phase that maximizes output at the crossover frequency.

Pair With Other Tools

Use our Decibel Distance Calculator for SPL planning, the Speaker Impedance Calculator for amp matching, the Headphone Impedance Matching tool for personal listening, the Reverb Time Calculator for room acoustics, the Note Frequency Calculator for wavelength math, or the Audio Bandwidth Calculator for streaming planning.