(I posted this in part of a reply, but felt it worth of being posted because it made such an improvement):

As you know the S2000s decks have powered-outputs (Speaker-Level), '00 and '01 models output 20watts max, '02 models output 30watts max.

To drive an AMP, this speaker-level output needs to be converted to pre-amp levels (typically under 4volts). Many devices are available to do this from just about anywhere that sells car-audio (BestBuy, Circuit City, etc..) In this example, I'll talk about using a PAC model (but all are pretty much the same).

---------Speaker In L--------: [ Pot L ]
*********************: [PAC UNIT] ===== 2 RCA connectors for pre-amp out
---------Speaker In R--------: [ Pot R ]

Each PAC (or similar) until has a Potentiometer (Pot) which adjustes the output signal (pre-amp levels) such that at 'maximum' power, you do not cause a 'square wave' (clipping) to the AMP.

There are 3 items you will need:
(1) An oscilliscope (set it at 1mega ohm, .5 volts/div, set to AC) [This can be rented, borrowed from work, etc...]
(2) A 'test' CD (Make this yourself using CoolEdit (www.cooledit.com).
(A) Make a 5minute 80hz full-scale sine-wave
(B) Make a 5minutes 660hz full-scale sine-wave.

 

Aaron,

I created both a 120 hz and a 660 hz test tone, not 80 hz so if you need me to do another just let me know and I will burn it before I come over.

Kirk

 

I don't get this part. If the PAC unit has "gains" then I would attach the o-scope to the speakers leads first, find the point of distortion, turn the deck volume down a hair, then attach the PAC and adjust the gains on the PAC to the point of "just before" distortion. Then do the same procedure with the speaker out leads from the amplifier and adjust the gains on the amp. Am I missing something here?

 

[QUOTE]Originally posted by rstark
[B]

 

I found that even with the RCA leads from the head unit itself, there is distortion at high volume (at least the ones I've worked with). I'm not trying to be a smart ass here, your write up was very good and will be helpful to those tuning their systems!

 

[QUOTE]Originally posted by rstark
[B]
I found that even with the RCA leads from the head unit itself, there is distortion at high volume (at least the ones I've worked with).

 

The deck will most likely clip at high output, but this would be passed right on to the PAC; regardless of who the "limiting factor" is, you will see it on the scope. You just might find that you need to reduce the deck's output as well to fix it (though amartin's finding indicate otherwise).

I'd also suggest using two probes in a Ch1-Ch2 arrangement across the RCA leads, or using a ground isolator/cheater (3 to 2 prong adapter). If you attach the scope ground to the RCA's shield/ground, you'll end up grounding the RCA's ground to earth (AC) ground (check it, they are always tied). This could intriduce noise, distortion, and possibly even level shifting to the output of the PAC. Not likely to matter much, but it's worth at least putting a "cheater" on the cord to open the scope/AC ground path.

 

...and another question- why 80 and 660? Why not something lower, or points with more range between them? Like 30 or 40, 1k, and 10 or 15k? Something closer to the limits, where the deck/PAC might be a little more "distortion-challenged"? I'd stay away from 60 (since you will now have AC present in/near the car) and <30 or >15k (since you are at the limits of the hardware, anyhow). But why not a little more of a sweep on the tones?

 

There's a write up on the rec.audio.car newsgroup FAQ that suggests turning your bass, treble and fader to center (or zero) and using a 1KHz test tone to find the clipping point of the head unit. I would assume that 1KHz is more in the center of all the common frequencies, and that should be your starting point. It also suggests that if you're testing a subwoofer output, and if it's crossed at 80 Hz, to use a 40Hz tone (center of the frequency that's crossed). Testing the clipping points for a system with an EQ, you would use more frequencies to match the EQ's number of bands. There's some good reading on the FAQ and can be found here:
http://www.mobileaudio.com/rac-faq/rac-faq...q_5.html#SEC102

 

I picked 80hz because thats where my sub should filter off (low pass) at, and my mids in the rear should just begin around there (HP at around 100hz)... The 660hz was for the mids-- middle "C", so if I end up hearing it, I doesn't kill my ears (like 1K does)...but I'm sure 1k is just fine... As far as like a 10k sample-- why bother? Most of the power consumption happens below 1k... Its not like the amp works hard to make a 10k+ audio sample loud. It might be useful if you have a 3-way crossover where you absolutly want to have the tweeters swperate from your mid-range. Up to you... hell, if you are making the CD, might as well make 80/120/660/1k/2k/4k/8k/16k

(Since my friend was making the CD for me, I didn't want to bother him into making all the extra frequencies).

-- Aaron