Speaker Diagnosis
Tools Required
J 39916-A Audio System Diagnostic Kit
Important: Always compare the front speakers to the front and the rear speakers to the rear. Do not compare a front speaker to a rear speaker because they could be different speakers or their mounting environment could cause them to sound different.
The diagnostic tape in J 39916-A contains a section of tones for the purpose of testing and evaluating coaxial speaker or other complex speaker system operation. The following three basic tones are used for this check, in addition to a combination tone (which is a blend of the three tones):
| • | 50 Hz sine tone |
| • | 500 Hz warble tone |
| • | 9 kHz spectral tone |
Bass/Sub-woofer Test (50 Hz sine tone)
Use the 50 Hz sine tone on the diagnostic tape to evaluate the bass response of the audio system. This tone is also helpful in evaluating audio systems which have separate subwoofer amplifiers and speakers.
Midrange Speaker Test (500 Hz warble tone)
Use the 500 Hz warble tone on the diagnostic tape to evaluate midrange speaker response. This tone is qualified as a warble tone because it has different audio characteristics than a sine tone and produces a warble sound. At these tone midrange frequencies, it is better to use a warble tone than a sine wave because the location of a warble tone source, such as a speaker, is easier to identify. A normal sine tone can set-up a standing wave within a vehicle which can make it difficult to determine its source location.
Tweeter Test (9 kHz spectral tone)
Use the 9 Hz spectral tone on the diagnostic tape to evaluate tweeter or high frequency response. This tone is a section of frequencies of equal amplitudes ranging from 8.5 kHz to 9.5 kHz. This sounds like a group of crickets chirping. This type of tone is used for the following two reasons:
| • | Much like the warble tone, it is easy to locate its source. |
| • | This type of tone is easier to identify for those people with high end hearing loss problems. |
All Speaker Test
Use the combination tone on the diagnostic tape to evaluate numerous audio concerns such as distorted or no sound from speaker(s). When using the combination tone, comparative AC voltage measurements can be made on the speaker terminals, provided the fade and balance controls are in the detent position. Using these voltage measurements, a determination can be made in the diagnosis of speaker or amplifier.
Speaker/Grill Rattle Test (50 Hz to 8 kHz swept sine)
Use the next portion of the diagnostic tape to diagnose speaker and grill rattles. The first test is made up of two tones played back-to-back. The second test is a variable frequency tone, but the frequency change is at a much slower rate. Both tests can be used to repair a speaker rattle or buzz. If the problem has already been isolated, the fade and balance controls can be set to the proper location and the test tones can by played in the specific problem area.
Motor Speed Test
The diagnostic tape contains a two-minute time-period section marked for the purpose of checking the cassette tape motor playing speed. This portion of the diagnostic tape can be used to verify concerns of abnormal sound from the cassette tape player. In some cases, improper tape motor speed can cause audio abnormalities.
The tape motor speed is within tolerance, if the time taken for this test is between one minute and fifty-six seconds to two minutes and one second.
Noise Diagnosis (Dead Space)
The diagnostic tape contains a section of dead space. Use this section for diagnosis of noise such as alternator whine, switch pops, etc. which can be more easily detected during dead space (blank space in-between songs).
