How does one measure frequency response?

[quincy]

how do you measure it in speakers? can you just get a bunch of tones in sound files that are completely one frequency? should i try and find some of these? or should i just play notes on a sawtooth synth on my keyboard until the speaker wont play them?
and on a different note, how are capacitors used in crossovers to seperate the frequencies?
im obviously a bit lost on FR.
please help me learn something

[audioguru]

Hi Quincy,
Depending on how and how much your hearing has been overloaded, the frequency response of your hearing might be good or might be terrible. It is difficult to judge how much the levels are different between two frequencies.

My hearing has always been pretty good because I avoided exposure to loud sounds.

I measured the frequency response of many speakers by using fixed frequency sine-waves, using sine-waves with a frequency sweep and using pink noise with a real-time analyser.

When measuring the frequency response of speakers then echoes must be avoided. I layed a speaker box on its back on the ground outside pointing straight up to avoid echoes, then suspended a good quality and calibrated microphone above it. Speaker manufacturers use an anechoic room.
If you try to measure the frequency response of a speaker indoors then the echoes will make peaks and cancellations all over the place. If the speaker is one meter above the floor then there is a direct path and a longer path cause by sound bouncing one time off the floor. They cause a cancellation at a mid-range frequency. Echoes are also from walls and the ceiling.

The frequency response of speakers changes if the angle changes. The best response is directly on-axis.

[audioguru]

The frequency response of a modern audio power amplifier is absolutely flat from 20Hz to about 100kHz.
The frequency response of good speakers is within 3dB from 40Hz to 18kHz.
The frequency response of poor speakers is all over the place and is not flat. Poor speakers have a few resonant peaks and a few frequencies that are at a very low level. Usually cheap speakers do not produce deep bass nor sizzling highs. Just a boom and a squeak.
A good speaker makes music sound great.