What is a frequency sweep?
A sweep is one tone that changes pitch over time. Instead of testing 440 Hz, then 500 Hz, then 560 Hz by hand, you set a start and an end and let the tone slide through everything in between. Anything wrong with a speaker or a room usually announces itself the moment the sweep reaches it.
Sweeps are the standard way to check frequency response. They're fast, they cover the whole range, and they make problems easy to place — you hear roughly where in the sweep the trouble happens, which tells you which frequency to go back and look at.
Linear or logarithmic — which one?
A linear sweep adds the same number of hertz every second. Over 20 Hz to 20 kHz, that means it spends nearly all its time in the treble and rushes through the bass in a fraction of a second.
A logarithmic sweep covers the same number of octaves per second instead, which matches how we hear pitch. It gives the low end real time and is the better default for almost any listening test. Use linear only when you specifically want even coverage in hertz — some measurement work calls for it.
What to listen for
- Rattles and buzzes. A loose grille, a car door panel or a badly seated driver will announce itself at one specific frequency.
- The bottom of the range. Start at 10 Hz and note where you first feel or hear anything. That's your speaker's real low limit, whatever the box says.
- Room modes. In a small room, some bass notes boom and others vanish. Walk around during a slow bass sweep and you'll hear them move.
- Your own hearing. Run 8 to 20 kHz and notice where the tone fades out for you. The upper limit drops with age for everyone.
- Crossover behaviour. On a multi-driver speaker, listen for a dip or a sudden change in character where one driver hands over to the next.
- Distortion. If a clean sine sweep starts sounding gritty, either the driver or the amp is being pushed past its limit.
How to run a useful test
Start with the volume low. A sweep passing through a resonance can get a lot louder than the rest of the run, and a 20 Hz tone at high level is hard on a woofer even though you barely hear it.
Pick a length of at least 15 seconds for a full-range sweep — anything faster and you can't tell where a problem sits. For hunting one specific rattle, narrow the range instead: a 20-second sweep across 40 to 90 Hz gives you plenty of time to move around and listen.
Use headphones for hearing checks and speakers for equipment checks. Judging a speaker through headphones tells you nothing about the speaker.