Spectrum Sweep Tracks

The Subwoofer Test Pattern Premium test suite includes six sets of sweep files. Each set contains an in-phase and an out-of-phase version of a particular sinusoidal wave. Each wave is a signal that varies its frequency from a minimum value to a maximum value. The minimum and maximum frequency values for each set are:

10-150hz in-phase.wav (track 56 on audio CD)
10-500hz in-phase.wav (track 58 on audio CD)
20hz-3000hz in-phase.wav (track 60 on audio CD)
100hz-5khz in-phase.wav (track 62 on audio CD)
1khz-10khz in-phase.wav (track 64 on audio CD)
3khz-15khz in-phase.wav (track 66 on audio CD)

The increment in frequency is linear (as opposed to logarithmic). The six sets of files cover the whole range of frequencies we are trying to test. The files overlap in some frequencies so that there will be no problem finding a file that can test a particular frequency range. Each file has duration of 1 minute, and they are recorded at 0 dBFS.

Usage

The objective of playing the sweep files is to test the limitations of your speakers. It will also give you information on how well your speakers reproduce an entire spectrum of frequencies. Your speaker system is comprised of subwoofer, woofer, midrange, and tweeter divisions. Each division specializes in reproducing a specific range within the total spectrum of audio frequencies.

Setup and Test

Start playing from the 10Hz-150Hz and 10Hz-500Hz sweep tracks and up. The sweep files will play a series of signals going continuously through the spectrum of frequencies; what you will hear is called a signature. A signature is the low and high amplitudes you hear when the signal sweeps a specific range of frequencies. The experiment is like dropping the same stone many times from a bridge to find out the depth of the pit underneath. If you hear a close sound you know it is not very deep; however when you hear no sound you know it is very deep. The experiment will help you find the profile or signature of the speaker's frequency response in an analogous way. When you hear too loud a signal it means your speakers have some resonance (or hotspot) at that frequency and when you hear a too low signal it means that your speakers have an attenuation (or drop-out) problem around that frequency.

The experiment can also show you your audio system's crossover frequencies: Crossover frequencies are the values where a section (tweeters, midranges, or woofers) yields the reproduction task to another better suited for the job. Take note of devices you may hear and draw on paper the signature for each speaker individually: disable the other channel with your equipment's balance knob.

Diagnose and Troubleshoot

First of all, it is important to check your speaker's manual about proper placement and configuration. For instance, some subwoofers benefit from being placed in the corner of a room, others benefit from a free-standing position.

If you have independent crossover equipment (that allows you to distribute certain frequencies to individual sections of the speaker) and you are experiencing any drop-outs, then the crossovers could be failing. Verify that the crossover frequencies are correctly assigned and make adjustments.

Adjust your equalizer (EQ) to reduce drop-outs and hotspots. You should always start with a flat EQ configuration. This adjustment should be in close agreement to the profile you drew above. Around the drop-out frequencies you should increase your EQ level. You should do the opposite, decreasing the EQ level around hotspots. Notice that the main purpose of this test is to find and resolve sound probelms caused by improper crossover configuration, other objects in the room, speaker placement, and to perform a preliminary adjust to the EQ settings. Frequencies around 1 kHz will help you to identify furniture that resonates in your listening room. You can move these objects out to solve the problem, but the room acoustics will change.

Out-of-phase versions of the sweeps tracks are also included. See the infomation about out-of-phase tones on the Tone Tracks page.

10-150hz out-of-phase.wav (track 57 on audio CD)
10-500hz out-of-phase.wav (track 59 on audio CD)
20hz-3000hz out-of-phase.wav (track 61 on audio CD)
100hz-5khz out-of-phase.wav (track 63 on audio CD)
1khz-10khz out-of-phase.wav (track 65 on audio CD)
3khz-15khz out-of-phase.wav (track 67 on audio CD)