Your speakers claim 20 Hz to 20 kHz on the box. Every speaker claims that. In ten minutes with a tone generator you'll know what yours actually deliver — where the bass really starts, where the treble really ends, and which frequency makes the left cabinet buzz like a trapped wasp.
No measurement mic, no spreadsheet. Your ears are enough for this, as long as you test in the right order. One warning before we start: keep the volume moderate through all of this. Test tones concentrate all their energy at one frequency, which is harder on tweeters (and ears) than music at the same perceived loudness.
1 – Open the generator, pick sine, set 200 Hz, and set a comfortable volume. Everything reproduces 200 Hz; this is your reference for "what a clean tone sounds like on this system."
2 – Walk downward: 150, 100, 80, 60, 50, 40, 30. At each stop, listen for the moment the tone stops being a NOTE you hear and becomes either silence or a papery flutter. That transition is your bass floor.
3 – Write the number down. Decent bookshelf speakers manage 50–60 Hz. A real subwoofer keeps going to 30 and below. A laptop taps out near 150–200, and phone speakers — bless them — around 400–500.
One trap here: at the edge of its range a speaker often plays the harmonics of a note instead of the note. If 40 Hz sounds oddly thin but still "there," you may be hearing 80 and 120 Hz ghosts. The flutter-or-note test catches most of this.
This end has a complication the bass end doesn't: your own hearing rolls off up here too, and you can't tell by listening whether the speaker quit or you did.
1 – Climb from 8 kHz: 10, 12, 14, 15, 16, 17, 18. Stop where the tone disappears.
2 – Now run the generator's built-in speaker reality check. It plays those same steps and listens through your mic — if 19 kHz registers on the meter, the speaker produced it and the disappearance was your ears. If nothing registers past 16 kHz, the hardware quit first. Ten seconds, mystery solved. No other tone generator does this, which is exactly why we built it in.
3 – If you have a teenager available, they make an acceptable backup instrument for the 17–19 kHz region.
Frequency response is only half of what you'll find. The other half is buzzes — panel resonances, loose grilles, that one shelf ornament with opinions.
Switch to sweep mode, 20 to 200 Hz over 30 seconds, and just listen to the room. Anything that joins in — a door panel, a picture frame, the speaker's own cabinet — announces itself at its resonant frequency. Note the number, then play that exact tone steadily while you walk around and press on things until the buzz stops. Congratulations, you are now the kind of person who fixes rattles with a tone generator.
Your speakers go from, say, 55 Hz to 17 kHz. Useful in three ways. If you're shopping for a subwoofer, you now know the crossover point to aim for. If a mix sounds different in the car, you know which octaves your room speakers simply aren't showing you. And if the marketing said "20 Hz – 20 kHz," you now know precisely how optimistic that was — the box means the speaker emits SOMETHING at those frequencies, not something you'd call music.
Save your floor and ceiling as presets in the generator. Next time you rearrange the room or buy new speakers, re-run the test and compare. Takes two minutes the second time.