tanstaafl, what are the keys to good imaging?



keys to the bank vault would be my guess

Actually... it's like real estate: Location, Location, Location.

When we installed my system, we removed the windshield to gain access to the top of the dash, and cut holes and installed some very good speakers (Diamond Audio Hex series 4.5"/1" separates) way up in the very corners, right next to the glass. We then cut a hole right in the center of the dash, and installed a 4"/1" coaxial speaker (with titanium dome tweeter) as a dedicated center channel. All six of these speakers (if you count the coaxial center channel as two speakers) are aimed right up into the windshield, where the sound is then reflected back to the passengers.

The door speakers (front doors only) are located very high up in the doors -- a matter of a couple of inches below where the glass starts. These are also good speakers -- 6.5" Diamond Audio Hex series again. This eliminates the problem I see with many installations where the mid range speakers are located in kick panels down by the feet, dragging the whole sound stage down to knee level.

My subwoofers (two Diamond Audio 10") are located where the spare tire used to be -- clear in the farthest rear corner on the left side of the car. They are molded right into the side of the car, and the spare tire cover goes over them so that there is no evidence that the speakers are there when it is in place. The full size spare tire was replaced by a space saver spare which now resides in the under-floor storage compartment (station wagon, remember), and then the spare tire was covered by a 1/4" thick aluminum plate 31" on a side, hinged at the front. Mounted on top of this plate are the amplfiers, crossovers, equalizer, power blocks, amp turn-on relays, etc. Then the storage compartment door closes over all that, leaving a totally stealth installation with nothing other than the head units and the remote gain controls (built into the armrest) visible. There is about 1/4" clearance between the bottom of the amp rack (the aluminum sheet) and the spare tire, and about 1/4" clearance between the bottom of the "floor door" and the components on the rack. Remember that the amplifiers are Class T amps, far more power efficient than the normal class A/B amps, thus throwing off far less waste heat. It's a 1400 watt system and on a six hour road trip the components get noticeably warm, but not hot. I'd guess no more than 115 degrees F.

The subwoofers' imaging I cannot take credit for -- it is a freak of the acoustics of the Taurus wagon. For whatever reason, those subs sound like they are in front of me, even though they are about 7 feet back. I have no explanation.

Finally, there are the speakers in the stock location in the roof, clear in the back of the car. These are not DIamond Audio speakers, but Boston Acoustics. The stereo shop gave them to me for free because he had no use for them. Some kid brought his slammed Civic into the shop and told Dave (the stereo guy) to pull his old speakers out and replace them with Alpine, because Alpine was really hot sh*t. So, Dave pulled out about $300-$400 worth of high end Boston Acoustic speakers and put in probably about $150 worth of Alpine junk. The kid was happy. I was happy. Dave was happy.

Having the remote gain controls for each speaker pair lets me do two things: I can move the sound around to wherever I want it by adjusting the gains on the individual amplifiers; and I can change the character, the tonality of the sound the same way. All I have to do is bring up that titanium dome tweeter in the center channel a bit, and the sound gets noticeably brighter, at the expense of a narrowed sound stage. Want a bit more warmth and presence? Add a bit to the 6.5" door speakers and you're there, along with a wider stage. More ambience is available with the roof speakers, the subwoofers will make you think someone's kicking the back of your seat. I have a Crystal Method demo track I use that literally moves the car on its suspension. The two 10's are in a common enclosure, where acoustic coupling takes effect, giving me lower than normal frequencies for 10" at the expense of maximum decibels, which I don't care about at all -- the car isn't loud, it'll hit maybe 130 decibels max.

It takes months to tune a system like that. Oh, I could RTA it on a pink noise track -- but a perfectly flat pink noise curve, while impressive to the technopiles, doesn't sound all that good. One thing I've learned over the years tweaking stereos is that you can only tune it for about 20 minutes at a time. After that, anything you do to it makes it sound better -- lots better -- until the next morning you get back in the car with "fresh" ears and realize just how badly you screwed it up. I've gotten to where I don't tune by ear at all any more, at least not in the sense of turning knobs while I listen to it play. Instead, I live with it for a few days, decide that, yeah, I need some more mid-bass in the 800-1000 Hz area, and then (with the stereo off) adjust the appropriate control by the amount I guess will do what I want. Then, I listen for a few more days and repeat the process. Takes time and determination.

I do have sort of a picture I can place here. It is a .jpg of my signal path diagram, and on it there is a tiny picture of the amp rack before i changed over to the 5-amp system, so it doesn't look much like it any more, but will give you some small idea of the general layout. See attached.

Wow, looking at this post, you'd never guess that I enjoyed bragging about my stereo, would you?

tanstaafl.