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Mr. Lee. I have a couple of questions that I really haven't gotten any answers on from other people. I hope you can help me out. My first question is about amplifier clipping. What exactly is it when an amp clips and how do I know if my amp is clipping? I heard that that is one of the biggest reasons subwoofers are blown.
Thank you for your time. I am sure you are extremely busy but I would really like to have some answers from someone who knows their stuff.
Again thank you and keep up the great work.Brian Walker
The term "clipping" is a simplified description of what happens when an amplifier tries to amplify a musical signal that exceeds its maximum output voltage limit. The signal is not really "clipped", but it is flattened as if the top and bottom of the waveform were neatly sliced off. It is a bit like jumping on a trampoline in a room with a low 8-foot ceiling. Jumping up and down to a height of just less than 8 feet will be no problem, but if you jump to a height of 10 feet, you will be "clipped" by 2 feet. That hurts!
Incidentally, that is how your speakers feel when they receive this incomplete signal. The subwoofer's (or any speaker's) job is to move in and out in a proportional distance to the voltage of the signal it receives. If the speaker was on the way out to something resembling 28 volts, and the amplifier clips at 20 volts, the speaker will wait until the signal falls back down to 20 volts for it to continue the journey. While it waits, it expends 100% of the power it is receiving as heat only, not sound. This is a bit like hitting your 8-foot ceiling and instead of bouncing off, you stick there until your imaginary self has gone to the 10-foot level and passes back through 8 feet on the way down. That really hurts! This is probably the greatest cause of speaker failure.
You can usually hear the effects of clipping when you exceed about 5% distortion. It sounds similar to when you play any factory stereo system too loud. Anything below that requires an oscilloscope to see the signal.
How do you prevent clipping, you ask? Recognize that your head unit typically distorts when it hits about 80% of the volume control's range. This applies to head units with readouts that count up with volume. For instance, as the numbers on the display get larger, the volume increases as well. If the highest number your head unit displays on the volume scale is "30", then your head unit is probably distorting at about 23 and above, so don't go there. The exception is if your volume readout counts backwards, where "0" is full volume and "20" is much quieter. This usually means an attenuator controlled preamp head unit.
Also, never turn up the gain control adjustments on an amplifier. It will appear to make your system play louder, but will almost guarantee noise, poor dynamics, excess hiss, smoking speakers and often amplifier failure.
How does the subwoofers' positioning affect the amount of perceived bass in relation to its phase? Allow me to elaborate, and feel free to rephrase the question if you publish this letter.
Drivers are placed in the doors and fired inward. This causes the main speakers to be 90 degrees out of alignment, uncorrectable except by realigning the speakers directly at the listener if I am not mistaken. Drivers are also placed in the back for fill in either the deck facing upward and reflecting off of the rear windshield (also 90 degrees out of phase) or in the doors facing inward. Now if the subs are placed facing directly at the back of the drivers head, when they reflect off of the front windshield will they be 270 degrees out of phase? Will pointing subs at each other make them sound more correct? Will pointing the rear fill toward the driver 180 out of phase make them more correct? Is the only way to know to try it?Brian M. Boswell