Part of our Lightweight PA Systems Guide

How to Set Up an Active Crossover for Your PA Subwoofer (2025 Guide)

Dial in tighter low end, protect your tops, and get more usable headroom—this step-by-step guide shows you how to wire and tune an active crossover for your PA subwoofer with pro-level results.

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Why use an active crossover?

Small tops waste power trying to reproduce deep bass. An active crossover splits the spectrum, sending only lows to the sub and only mids/highs to your tops. Result: better clarity, more headroom, and reduced distortion.

Gear you need

• Small format mixer with L/R main outputs (XLR or 1/4" TRS)
• Analog active crossover (2-way stereo / 3-way mono)
• Power amp for passive sub(s), or powered subs
• Appropriate cables: XLR or 1/4" TRS patch cables; Speakon speaker cables for amp→sub
• (Optional but recommended) Measurement mic + pink noise or RTA app for quick verification

Step-by-step wiring

1. Mixer → Crossover inputs: Connect L/R main outs to the crossover inputs (XLR or TRS; match what your mixer provides).
2. Crossover LF outs → Sub amp: Run the LF outputs to your power amp’s inputs. Amp speaker outputs go to your passive sub via Speakon.
3. Crossover HF outs → Tops: For powered tops, go directly from crossover HF outs to each top. For passive tops, route HF outs to a second amp, then to tops.
4. Set initial levels: Start with crossover output gains at unity, amps turned down. Bring up amp gains slowly while playing music at show level.
5. Polarity check: If bass is hollow near the crossover point, flip sub polarity (180°) and keep the position with more punch.

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Starter crossover settings

• High-pass (sub): 30–40 Hz (protects the driver from ultra-low content)
• Low-pass (sub): 90–110 Hz is a solid starting range with most 8–12" tops
• High-pass (tops): Match the sub’s low-pass (e.g., 100 Hz) so the bands meet cleanly
• Slopes: 24 dB/oct Linkwitz-Riley is a reliable default for smooth summation
• Balance: Use LF/HF output trims to balance sub/top levels—aim for punch without boom

Mono vs. stereo subs

Mono sub bass is typical for live sound and simplifies placement/phase. Run both mixer L/R into the crossover, then send summed LF to one sub amp channel (or to multiple subs fed the same mono LF). Stereo tops still run normally from the HF outputs.

Troubleshooting & quick tips

• Hollow/phasey low end: Flip sub polarity; nudge crossover point; check cabling.
• Over-boomy: Lower sub level a couple dB; raise the sub HPF a touch; verify room placement.
• Weak kick: Try lowering the crossover from 110 → 90 Hz; adjust attack with minimal EQ.
• Clipping lights: Turn down mixer bus; let amps do the heavy lifting; keep gains staged sensibly.

Related reads:
Auto-EQ a Room with a Midas MR12 ·
Best 5 – 8″ Powered PA Speakers (2025) ·
Best Battery-Powered PA Speakers
Best Lightweight Powered PA Subwoofers of 2025

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Recommended gear (hand-picked)

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Quick reference: typical starting points

FAQ

Do I need an external crossover if my powered sub has one built in?

Usually not. Many powered subs include a low-pass filter for the sub plus a high-passed “thru” for your tops. Use an external crossover when you want finer control, different slopes, or you’re driving passive subs/tops.

Where should I set sub level?

Start with sub output at unity on the crossover. Increase until the low end supports the mix without masking vocals/kick definition. If the room gets boomy as people leave, trim a dB or two from the subs.

Can I run stereo tops with a mono sub feed?

Yes—very common in live sound. Sum LF to mono for the sub channel and keep HF/MF stereo to the tops.

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