QuestionI want to check it out and get some answers to your questions. The problem is quite interesting, and it might in fact be the amp. First, to explain the noise: it is constant and loud bassy buzzing (motorboating, I guess), and begins with a loud popping sound. The noise is independant of the volume setting of the head unit.
When it first began, it was quite sparadic; however, I adjusted the gain on the amp down and the buzzing stopped. At that precise point in the gain setting, I can control the noise - when I adjust the gain above the point, I get the pop and buzz, below, I get music.
It is intersting you talked about the impedance, since the new rear speakers are Orion C63s @ 3 ohms. I wonder if that messes with the amp (though the owner's manual states that the amp supports 2-8 ohms in stereo). Could they have sold me speakers that are incompatible with my amp? Or do you think that my amp is having some sort of crazy problem at a certain point in the gain? One thing I didn't do was connect my front speakers to the rear channel. Do you think I should go and buy a resistor @ radio shack?
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Followup To
Question -
I have an aftermarket system installed in my '02 Maxima (not a factory Bose system). My head unit is a Clarion ProAudio 9175 wired to a Precision Power PC4400 (50Wx4) amp. I have MB Quart speakers installed in the front, wired through the existing dash front speaker wiring. A custom stereo store recently installed two Orion 6.5" speakers in the rear doors, wired directly to my amp. Previously, I had no rear speakers connected (just factory speakers installed). Ever since they installed the speakers, I get this resonating full volume bass blast thorugh all speakers @ startup (no music), an on accasion as I am driving. Sometimes it goes away after a second, sometimes it remains until I turn off my head unit. When the rear speakers are unplugged from the amp, there is no feedback. The retailer says that it is my amp, but I dont think he is blowing smoke cuase he doesn't want to troubleshoot the problem on his dime. Do you have any other ideas? The last time it happened, I smelled a faint hint of smoke, like when a wire overheats. I think it may be my wiring, but I don't want to unnecessarily take everything apart.
Answer -
Without hearing the sound and how it is provoked I cannot be sure. Does the bass relate to music or is it constant once it starts? And what triggers it to go into bass growl? You said on startup, but will increased volume settings make it worse or effect it?
My first guess is you have a feedback problem; either wires running too close together or the new speakers are too low impedance and setting the amp off into motorboating.
1. Here is what to do for just checking the causes. Disconnect the two rear door speakers and make sure it is no longer growling.
2. Now, connect just one of them, say the drivers side door. Does it do it with only one speaker connected?
3. Now, try the passenger side speaker. Does it growl with only that one connected?
4. Go to Radio Shack - or any electronics parts store - and purchase a 10W wirewound 4.7 ohm resistor and connect in series with the speaker in each door. Does that kill the growling? If so, you can leave them in or continue to try finding the cause of the bass blast (or growl or motorboating).
Let me know how it goes this far. If you need more help.
Cleggsan
AnswerI think this is electronic feedback. It is probably due to the big current in the speaker wires inductively interfering with either the head unit or the amp. Redressing wires away from each other often will solve this problem.
The low impedance speakers draw more current for a given setting and that may be a contributor.
Switching fronts and backs is a useful experiement, for sure; not only are the impedances different maybe, but the wiring to the fronts may be a different loop.
And, yes, adding the series resistors will tell us without doubt the problem is current feedback. These resistors should only cost about $1.59 each or less - so it is not an expensive test to conduct.
Thanks for the feedback,
cleggsan
