What Is the Bass / Subwoofer Frequency Sweep?
A bass frequency sweep generates a continuously changing or static low-frequency tone that lets you evaluate your subwoofer's or bass speaker's performance across its rated frequency range. By listening for changes in volume, distortion, or cabinet vibration as the frequency changes, you can identify resonance peaks, crossover points, room modes, and driver rolloff frequencies. This tool uses the Web Audio API OscillatorNode for phase-accurate, sample-perfect tone generation across all four standard waveforms.
How It Works
The tool creates a Web Audio API OscillatorNode connected through a GainNode to your system's audio output (AudioContext.destination). The oscillator frequency is updated either manually via the slider or automatically via a requestAnimationFrame-driven logarithmic sweep from 20 Hz to 200 Hz over 15 seconds. Logarithmic sweeping matches perceptual hearing — each octave covers the same amount of time, matching musical pitch perception.
Step-by-Step Instructions
Technique Tips & Hardware Facts
Room Modes & Standing Waves
When sweeping, you'll notice the bass sounds dramatically louder or quieter at specific frequencies — these are room modes (resonances). Bass sounds louder at modal frequencies where room dimensions create standing waves. Acoustic treatment or subwoofer placement changes can address these.
Port Tuning Frequency
Most ported subwoofer enclosures have a tuning frequency (typically 25–40 Hz) where bass output peaks. Below this frequency, output drops rapidly. Sweep slowly in this range to hear your sub's tuning point.
Distortion Test
At excessive playback levels, subwoofer drivers produce audible distortion — a buzzing or rattling quality distinct from the clean fundamental tone. Distortion indicates the driver is exceeding its excursion limit (Xmax). Back off the volume immediately.
Crossover Alignment
Use 60–120 Hz tones to verify your AV receiver or speaker crossover is routing bass correctly. If you hear the tone from your satellite speakers instead of the subwoofer at 80 Hz, your crossover settings may be misconfigured.
Infrasonic Range (20–40 Hz)
Very few consumer systems reproduce below 30 Hz. Many subwoofers roll off steeply below 40 Hz. You'll feel infrasonic frequencies as physical vibration more than hearing them as a musical pitch.
Frequently Asked Questions
What frequency should I set to test my subwoofer?
Start with your subwoofer's rated -3dB cutoff frequency (check specifications). For most 10-inch and 12-inch subwoofers this is between 25–40 Hz. Then test at the crossover point (typically 80 Hz) and at 120 Hz where the handoff to satellites occurs.
Is it safe to run a sweep at full volume?
No. High-volume sweeps can mechanically damage subwoofer drivers. Start at 20–30% volume and increase cautiously. Distortion (buzzing sound) means you've exceeded safe excursion limits — stop immediately.
What does the sine waveform test vs. sawtooth?
Sine waves test a pure single frequency with no harmonics. Sawtooth waves contain all harmonics of the fundamental, making them harsher sounding and more revealing of distortion at lower volumes. Square waves contain only odd harmonics.
My laptop speakers can't reproduce 40 Hz — is the tool broken?
No. Most laptop speakers are physically incapable of reproducing below 100–150 Hz at any meaningful volume. The oscillator generates the correct waveform; your speakers simply can't move enough air to produce that sound level at low frequencies.
Can I use this to tune my car audio subwoofer?
Yes. Set your head unit or amplifier to a flat EQ curve and sweep through 20–200 Hz. The frequencies where output drops or distorts reveal the system's limitations and help you tune bass boost, subsonic filters, and crossover points.