2004-2007 Cadillac CTS-V General Discussion Discussion, BOSE noise comp mic in Cadillac CTS-V Series Forum - 2004 - 2007; I've seen this little bugger in the wiring schematics listed in the FAQ. here
I wonder if this has anything ...
I've seen this little bugger in the wiring schematics listed in the FAQ. here
I wonder if this has anything to do with the bass reduction at higher volume levels. I'd like to play around with it to see if there's any difference with it or without it. When the car is off and there is no ambient noise the stereo sounds great. With the engine running it goes to crap.
Has anyone done this or tried it? And where is it?
As far as I know, that mic only adjusts audio gain, not EQ (loudness curve). What you are hearing is the monstrous noise floor of our cars when driving down the road. The stock sub just doesn't have enough power to manage it.
It's the loudness curve. As you crank up the gain to compensate for road noise, the loudness curve compensates less and less, which gives the impression of decreasing bass as you turn the volume up. Set the volume at an appropriate level with the car off. Note the bass and overall sound. Now, without changing the volume (or the source if you have control over it), start the car and go drive around. It will sound like there is less bass, and in fact the overall sound level will need to be increased, which puts you at a different point at the loudness curve, further contributing to the impression of decreasing bass response.
I'm not sure how this is generally handled by OEM audio solutions, but in our case, I think the stock sub actually limits what the gain is to the sub channel. I have also noticed that the bass which goes to the interior speakers (I assume there is some kind of high pass filter), increases a lot more linearly with the volume, whereas the sub seems to level off (possibly as a protection). That gain is mapped to the loudness curve, so even if you beef up that whole system, if you are using the stock sub channel output, you'll still be stuck with the relative gain of the sub channel vs the rest of it. The amp itself may also do some limiting, to avoid clipping. In that case, replacing the sub AND amp would eliminate any self-limiting imposed by the sub-amp itself, but it would not help any limiting pertaining to the loudness curve used by the head unit.
Generally, loudness is used particularly in car audio so that at low system volumes, you still perceive a fairly flat response from lows to highs. This helps compensate, particularly, for road noise. As you turn up the volume, the effects of loudness (from your psycho-acoustic perception) are less necessary. In layman's terms, it means there is less bass boost as you turn the volume up, because at high sound pressure levels, your brain/ears essentially "hear" bass better.
Loudness has been the bain of all those who have tied aftermarket systems to stock head units, often requiring remote gain controls at the driver's fingertips, or, devices that attempt to compensate for loudness. If I can find one, I'll link it.