Audio Upgrade Follow-Up
Questions and Answers, Part 4

> I just finished reading your installation notes, and I'm wondering if
> you are aware of a couple of things.

> 1) The stock tweeters are not fed full signal. There is a capacitor
> (high-pass crossover) mounted to the 5.25" that filters bass from them.

Really? Oops, I missed that. The old 5 1/4" are in my garage. I'll look at them later. If so, I'll have to update the schematics.

> 2) The trunk is the worst place to put line-level converters. They
> should be as close (electrically) to the head unit is possible. This
> lowers the amount of EMI and RFI that can enter the signal.

I actually spent some time considering just where to put them. If you put them in the front it's true that there is less chance for EMI, but then long RCA cables will be required to get to the amp in the trunk. (I had already decided that I wanted the amp in the trunk). The downside with this is that the long RCA cables would have been pretty expensive. Plus at the time I was concerned about routing relatively fat RCA cables in the door channels under the carpet retainers.

With the line-level converters in the trunk, I figured that the speaker cables that I routed to them would carry speaker level inputs, so the signal to noise ratio of any picked up EMI would have been relatively small anyway. This is one of the reasons I intentionaly routed the amp power cable down the other side of the car.

You raise an excellent point, that should not be overlooked. On the other hand, I've been a EE for about 16 years now, so the potential of some noise pickup doesn't bother me as much as some people. It's just one more thing to fix . But seriously, I can't detect any noise pickup like alternator whine, popping, or whatever.

> 3) You should never put a crossover (or other audio elecronic
> component) near a light bulb. The coil can pick up a lot of noise. I
> realize the lights in the doors only turn on when the door is open, but
> if you ever listen to the stereo while, say, playing basketball with the
> doors open, it could (potentially) cause noise problems.

You know, that's a good point, and it never occured to me. Later, I'll listen to the front speakers carefully with the door open, and see if they're picking anything up.

> 4) Why are you firing your sub through the rear seats? Turn the box
> around and fire it off the back of the trunk. This generally yields
> lower F3's and increased output.

This is the second time this has been suggested to me. I'm going to try it. By the way, what are F3s?

> I was also wondering why you put 4" coaxes in the rear, rather than
> using the same setup, but feeding 5.25" separates mounted in the 6x9
> space. Crutchfield even sells the adapter plate.

Boy, I like the way you think. I actually thought long and hard about putting in 5 1/4" and separate tweeters in the back, using the Crutchfield adapters you're referring to. The only reason I didn't do it was the cost. I felt that would have been overkill for just getting rear-fill. This upgrade cost me $1200 as it is.

> I'm not trying to be a know-it-all, and this information is FYI, but
> these are some things that commonly cause trouble, and if you ever have
> problems, check those out first. I've been installing car stereo for 4
> years professionally, and countless years before, and I'm just offering
> some suggestions.

> By the way, despite the aforementioned items, I think your install was
> pretty damn good.

You made some excellent points. Thanks for the input, it sounds like you've got some great experience we can all learn from.