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Amplifier making groaning noise even when engine off, chages pitch when I move subwoofer's cone.?
Pioneer GM8400M amplifier. Pioneer 12" subwoofer. It's the same oscillating groaning noise whether the engine is off or on. It's not a high pitched whine and not a low pitched hum. It oscillates up and down about 1 octave. The pitch of the noise changes when I press down on the subwoofer's cone. Pitch and volume of the noise does not change with engine speed. It does not change when I turn on accessories, like lights. The pitch and volume of the noise does not change when I adjust the gain, nor change the volume on the head unit. I have another Pioneer amp running the door speakers, which makes no such noise. Both amps share the same 2 gauge power wire and both are grounded at the same place, where I scraped the area to bare metal and used a copper washer on a bolt. I've swapped subs, same noise. Swapped in another amp (lower wattage) and no noise. What's the most common cause?
4 Answers
- yahoo sucksLv 710 years agoFavorite Answer
The amplifier is bad. The speaker outputs have shorted out.
Time for a new amplifier.
- Anonymous10 years ago
What you are describing sounds like 60 HZ hum, but it is not quite that.
A radio (or TV) that plugs into the wall in your house converts 120 V AC (60 Hz) to DC voltage. If the filter capacitors in the power supply are defective, there will be a low pitched hum.
I assume that your car amplifier uses some kind of square wave pulse as an input to a transformer to boost the AC voltage (that is, a low voltage square wave pulse produces a higher voltage AC).
Note: The square wave input to the transformer is changed to somewhat of a sine wave due to the high frequency losses in the transformer (particularly hysteresis loss).
The hum is produced by bad filter capacitors in your amplifier (those are the biggest capacitors that you see, and likely electrolytic).
WHY HUM PITCH CHANGES:
The pitch is independent of engine RPM because the square wave pulse is produced by the amplifier's electronics and it is independent of engine RPM.
The pitch changes when you touch the sub-woofer's cone because you are changing the harmonics of the cone. The original harmonics form a standing wave on the cone, and by touching it, you alter that standing wave (by putting a node where a node did not exist). A node is a point that stands still and doesn't vibrate. Thus, you change to a different harmonic by touching it (the pitch changes by an octave).
See the first link (says filter capacitors are easy to replace in your amplifier).
The second link is about hysteresis loss in transformers.
Source(s): http://torresengineering.stores.yahoo.net/filcapfo... http://en.wikipedia.org/wiki/Hysteresis - Anonymous10 years ago
It doesn't sound like an alternator issue, nor a speaker issue. Several things it might be, including wiring and connections. Try this for troubleshooting/reference:
- 10 years ago
over driving the speaker say 100watt amp an a 50 amp speaker??reverse hot an ground wires..wrong ohms of radio to speaker??? loose speaker vi-berating.....the new radios you dont ground to body ,must use ground from unit!!
