Don't know if this has been covered before: I just got an Alpine - 7894 and was thinking about how to use the adjustable time correction. Since the S2000 only has front speakers, but the 02 has separate tweeters and woofers, I figured I would wire the tweeters up to the front amp and the woofers up to the rear amp. That way, I get more power and woofer / tweeter level control with the fader, but more importantly, I get adjustable time correction on each driver.

After staring at the manual for a while and fumbling with a tape measure on my head, I decided the speakers were the following distances from my head:
L Tweet 23"
L Woofer 33"
R Tweet 43"
R Woofer 49"

That corresponds to a time correction of:

L Tweet 1.9 msec
L Woofer 1.2 msec
R Tweet 0.5 msec
R Woofer 0 msec

I was pretty dubious that it would make much of a difference, but MAN O MAN, did it ever! All of a sudden, I had a half way decent soundstage. It felt like I jumped out of the car and sat in front of a home stereo. I didn't think something so simple could fix such a sad stock stereo.

I started wondering about what made such a difference. Was it the side to side time correction, the woofer / tweeter? After playing with the time correction / fader / balance, it seemed like the side to side correction made the big difference. No correction: sounds stock. Correction: it has a soundstage. The difference wasn't nearly so big with the woofer / tweeter correction. Without the correction (woofer and tweeter with the same correction) there seemed like a dip in the response at 2 or 4 kHz, but not much.

So, has anyone done this? I have noticed that there are lots of Alpine owners that have this feature, but I don't remember seeing anyone talk about it.

Many thanks to MacGyver for posting the simple way to run speaker wires in the doors on his web page. It saved me a bunch of time.

 

I do not believe that your time correction with the woofers and tweeters is going to have much of an effect. In fact high frequencies travel faster that lower frequencies.
This is why some speaker manufacturers place the tweeter behind the woofer. Tweeters use very little power compared to woofers and subwoofers. Also it is not difficult to blow out a tweeter. I hope you are using a high pass filter with this set-up. In my opinion, you should use the front amp for the fronts and the rear amp for Lucid's rear speaker system ( or install your own). I have this set-up and delay the rear speakers by 25 microseconds. This adds some depth and ambience to the sound stage.

 

Otter,

You'll most likely notice a difference in side to side time delays, but not in the tweeter/woofer delays. Why? Look at the two speakers in the driver's door...quite a bit of the sound you hear from them are actually by way of reflected waves coming back off of the passenger door and window. Try playing around with the values, such as making the delay for the passenger side twice as much as that for the driver's side speakers...you'll start to hear some really interesting stages.

Also, make ABSOLUTELY SURE the time correction adjustement circuitry is not making any other changes to your music. Quite a few circuits such as that one will actually modify the frequency response, not just the timing, to give the perception it's doing more than a stock system. I'm not saying that's what Alpine is doing, just saying to watch out for it when thinking "Wow, this sounds so much better than stock!"

 

[QUOTE]Originally posted by JPit
[B]I do not believe that your time correction with the woofers and tweeters is going to have much of an effect.

 

Modifry,
Thanks for the examples of why different sound frequencies move at the same speed. I couldn't think of a good example without an equation (always a thread killer ). I wasn't sure how much practical difference it was going to make at first. I did know that a soundstage completely disappears if a speaker is wired with incorrect polarity. I know that isn't exactly the same as 180 degrees out of phase unless the signal is repeating, but it isn't hard to imagine a 0.5 msec delay being about the same at 2 kHz as a reversed polarity on a speaker.
That being said, the proof is in the listening. The sound with no delays sounds like a stock setup (no soundstage effect to speak of). With delays, there is a pretty good soundstage effect going on. It's among the best I've heard in a car, and that is with stock speakers, no external amps, no fancy anything other than the head unit. Not mind boggling compared to what stereo can do, but pretty good for inside a car (an S2000, no less).
As far as speaker distances go, I can hear a foot. I have built enough speakers to say that with some confidence.
But to put it in a more objective way, the speed of sound is ~1 msec / 1 foot. That means two 500 Hz sound waves originating with one source one foot in front of the other puts them ~180 degrees out of phase. That's not hard to hear.
Having touted my ear's distance gauging abilities, I couldn't hear the woofer / tweeter delay very dramatically. I could hear a suckout come and go with changing delay, but it was real subtile. Take that for what it is worth (nothing).

MacGyver,
I suppose Alpine could be doing some response shaping without me knowing, seeing as I haven't measured any responses. But that brings up a very interesting subject. I think I will try to measure the response of the system with different adjustments. I have a decent mike that I have used on other projects and will try to use my laptop to make measurements.

Everybody,
I have seen software that will do anywhere from simple FFTs to full blown system characterization with a sound card. Anyone have a favorite that is reasonably priced for curiosity rather than a rabid hobby / professional market? I certainly will post any findings after I get off my rear and make some measurements.

 

modifry: Oops, sorry...I said Otter wouldn't notice a difference in woofer/tweeter delays, but forgot to give a reason why. Thanks for taking care of that one. Besides, cut me some slack, when I posted that I had just walked in the door an hour or so before from my trip to D.C. My brain only works when it's had sleep


Otter: I just reread your post, and JPit has a good point...if you're using one of the amp channels to power just the tweeters, you had better make sure the high-pass filter is engaged on the head or build one of your own...you'll eventually blow the tweeter otherwise.

Also, if you use a mic to do a frequency response check, make sure either the mic has a flat frequency response over the audio range, or your analyser can take any non-linearities into account. When using standard PC soundcards to analyze audio, note that most consumer cards out there aren't flat at all when it comes to sampling...the high-frequency response starts to droop quite a bit, and all too often the bass response can out and out suck. They're usually pretty careful about output DACs, but input ADCs are given significantly less attention since most cards are used for playing sound, not recording it. For free/really-cheap software, just do a Google search.