sub freq sweeping

Hi Dave, I had a look at your pics and I must say, GOOD JOB!!

It's clear that you have passion for perfection and I think it came out real nice. I've been thinking about your sweeping description and was wondering if you could describe it more precisely; is it air movement, a noise or is the centre of the sound moving while you adjust gain, etc ?

In the pic of the woofers, there appears to be a glass reflection (looks like a cover {I don't mean at/over the amps, higher up}) - is this glass on there permanently ? Also, is there any air flow between the boot and the cabin ?

Another question re your settings:

On the GTR9001::   off/12/24db - subsonic filter; 40hz boost; off/12/24db - low-pass filter

On the GTR1252:: 40hz boost; 80hz - LP/off/HP

Are you running any active x-over in your system, or anything else important to know about the sub setup ?

Thanks bro.

To give some anwsers: The GTR9001's are one to each sub, set at LP, no subsonic (off), Subs are divided in air space inside the box, at the top of the box there is a boot between the box and top of trunk that has an opening about 3" tall and 18" wide to allow opening into the cabin, and the glass is there permanently but about 4" out from subs to allow excursion, and is open on all sides. for air flow. I know it probably affects my waves but the USACi requirements say that the judge can't touch my subs anywhere with a ball-point pen or the subs aren't protected.

The 1252's are on the highs. 1 2-channel for front, and 1 2-channel rears. The XM1S slimline amp is on the front 8" sub at 2 ohms. The 3 amps are running LP on all subs but with nothing external just the F/R/S adjustments and parametric on the head unit. Doing everything else with speaker placement and enclosure volume and position. Notice the tweeters in the doors? I used that placement to widen my stage. They hit the side windows and open the stage WAY boyond the A pillars! There are also tweets in the A pillars aimed up and toward the center of the galss raising my stage to the center glass about 8" above the dash.

As for the sweeping: It's not air; it seems to be moving the bass from behind me to infront of the headrests toward the hood. I think, now, from what has been explained to me; i'm completing a wave between the two sub positions (F/R). A friend helped me test it with a mic and an oscilascope last night; and we think that when the top of the front wave overlaps, ever so slightly, the bottom of the back wave that's what seems to the ear to be that sweet spot. Kind of like filling a hole in the front seat area.

I'm learning as I go; and having fun doing it. I mean; that's what it's all about right? Allways open to suggestions; or anything anyone can toss at me to help me make it better. Thanks for the good word man. I really appreciate it.

Dave

What do you mean by the timing is a little off? 

You say there is a sweet spot with the dial.  What happens when you move past the sweet spot?  Does it move to the back once more?  What frequency is your subs crossed over at?  If I had to guess, the subs are causing resonances within pannels in the rear that you are localizing making it sound like the bass is in the back.  When you turn up the 8, it masks these resonances and now your localization is dominated by frequencies in the front.  There could be other reasons as well, especially if the sub and 8 are overlaping any. 

I may be telling you something you already know; but keep in mind that there is a difference between electrical phase and acoustic phase.  Electrically all the speakers might be in phase, but due to their different locations within the vehicle they might be out of phase with one another causing constructive and destructive interference.  This is especially problematic when more than one speaker is producing the same frequencies on one of the stereo channels.  The results are what is known as lobing (or comb filtering).  The best solution is to eliminate these overlaping frequencies, but without causing a dip in the response.  Usually this can be achieved with steeper crossover slopes.

Just a quick correction; there is no lower harmonic below the fundamental.  Harmonics only show up higher in frequency than the fundamental.  Or am I misreading what you are saying?

It really is too bad too as they used to make some of the best processors on the market.  Now I am forced to run an 8 year old deck just so I can enjoy the 4000X processor. 

Sure it is possible to use your ears to tune your system.  But you will be your limit on how good it can sound.  Psychoacoustics and other limits of your hearing will effect your results.  And it will take you huge amounts of time and money to get there.  However precision measuring equipment with much higher accuracy than your ears and a good processor can fix things that you would never find by using your ears and I can guarantee you the differences will be very audible and benificial.  And you will do it in MUCH less time.  So to answer your question, before processors they either lived with mediocricy or spent heaps of time training their ears and learning how to change the signal to match what they want to hear.  As an example, I know the great speaker engineers like Arty Newdell (sp?) will spend weeks upon weeks on a crossover design using his highly trained ears and years of experience.  However I've watched my old boss Dan Wiggins many times design incredible crossovers in just a couple hours with the help of measurement equipment.  And this included an impressive imaging speaker setup using a cheap 6$ Goldwood midrange and a $12 Audax tweeter.  I don't mean to sound too negative with this, especially since there is a great deal of satisfaction to do something great yourself after great effort. Just understand processors are tools to make things easier for you if you let them.

There was mention earlier about group delay.  If you are looking into working with this any, it is good to know what to look for ahead of time.  Here's a great link discussing group delay by Dan Wiggins and Dr. David Hyre: http://www.trueaudio.com/basslst2.htm  And here's a quote by Dan Wiggins explaining what to look for with group delay when designing an enclosure:

"it's just a measure of time through the system at a given frequency. How much is too much? I try to keep the product of group delay and frequency below 400, and when it's lower than 3 msec (latent time of fusion) it's a non issue.

Thus at 20 Hz I try to stay at or below 20 msec. At 40 Hz, 10 msec. At 80 Hz, 5 msec. Once I've dropped the group delay below 3 msec or so it no longer matters.

Note that this implies that 50 msec at 8 Hz isn't a problem; 50 msec at 50 Hz is... There isn't one "good" or "bad" number - it's a continuum that you want to stay below.

Dan Wiggins

Adire Audio"

Link for the above quote: http://forum.carstereos.org/group-delay-t33736p4.html

Thanks Steven. As allways, i very much respect your opinion and help. I'll look into some sort of processor and group delay. Any sugestions on a processor (not to outrageous $ please)?