Testing The Speakers
Speakers are common components used in many products, therefore it is necessary to testing the speaker. When you check speakers, first make an inspection. Rattles and heavy vibration are often signs of a defective speaker. Visually inspect the speaker for cracks, dirt, and other faults.
The Purpose Of Testing The Speakers
If you are in doubt about the actual quality of a speaker, the best testing technique is substitution. Simply substitute a known good or similar-value speaker in its place. Many speakers will operate intermittently; by gently pressing on the speaker cone, it may begin operating. This is a good indication that the speaker is defective due to a bad voice coil, connection, etc.
When you are replacing a speaker, it is important to replace the speaker with one having the same impedance and power ratings. Primarily, the voice coil of the speaker determines the impedance and power rating of the speaker. The power rating, measured in watts, is the maximum power at which the speaker should be operated. The impedance (in ohms) of the speaker is used to electrically match the speaker input to the output of the receiver. The impedance of a speaker can be roughly approximated by measuring the resistance of the voice coil with an ohmmeter and then multiplying this value by 1.25. Some common speaker values are 3.2, 4, 8, 10, 16, and 20 Ω.
Methods Of Testing The Speakers
Another method used to check a speaker is to place an ohmmeter across the voice coil terminals. Listen and watch for a small “pop” and movement of the speaker cone. A defective speaker will show no movement or popping sound. Also, this method can be helpful in phasing two or more speakers together. Place the ohmmeter on the voice coil terminals, and note whether the cone moves in or out. Reversing the polarity of the ohmmeter will reverse the movement of the cone. Next, mark the positive side of each cone when it is in the out position (see the following picture). Then connect each speaker to the audio amplifier while observing the correct polarity. Sound reproduction should be improved since the speaker cones will move in and out together. The in-and-out movements of the speaker cones keep the speakers in phase, or in step with each other. If they are out of step, or opposing each other, at certain frequencies, the sound waves will be canceled.