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Discussion Starter #1
shinjohn, I've been meaning to experiment with flipping the rear 6x9's 180 degrees out of phase relative to the fronts, but I haven't gotten around to it yet. What do you think, just wasting my time or worth a try?
Dorhn

[This message has been edited by dlh2 (edited 11-01-2001).]
 

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<font face="Verdana, Arial" size="2">Originally posted by dlh2:
shinjohn, I've been meaning to experiment with flipping the rear 6x9's 180 degrees out of phase relative to the fronts, but I haven't gotten around to it yet. What do you think, just wasting my time or worth a try?
Dorhn
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Hey Dorhn, assuming that you are considering this on a bass performance standpoint, yes, it's worth a shot. I imagine this is the case, since the 6x9s are pretty low on the door, and you can't hear them directly anyways. If you had the speakers firing full range, directly at your ears, you could get some strange effects though...

Getting optimal bass response in a car is tough, even if you know all the basics/rules/theory of acoustic spaces, etc.. Give it a try, and please report back on your results!

If you get a little confused because of the tweeter/mid, you may try: 1)disconnecting those drivers, or 2) covering them up with something, or 3) using an inductor as a low pass filter on them.

Good Luck!
-SJ

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Discussion Starter #3
John, precisely, I'm looking at this from a low frequency cancellation/reinforcement standpoint. When I have the Pioneer head unit installed, I dial back on the high & mid response of the rear 6x9's, independent of the fronts, and use them for low feq. fill with the soundstage up front. (that's what cool about that head unit. I can click them back to full range when needed) I know from experience the importance of phasing from playing around with my M&K sub in my home theater setup but I never really considered that aspect in car audio until I discovered by accident that the rear package shelf speakers in my S-class MB were out of phase with the fronts. I can easily access the rear speaker leads under the driver's side door threshold, and I've got an old speaker selector switch in my junk, so I think I will temporarily hook it up in reverse so I can simply sit in the van and A/B the 6x9's in and out of phase with the fronts. I'll let you know the outcome.
Dorhn

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That's cool Dorhn. So do you switch between the head units or keep either the Pioneer or Blau installed primarily?

An M&K at home, sweet. I really like those push-pulls, esp the 5000 MKII. That baby has some output capability....

Anyhow, bass cancellation/reinforcement is an interesting thing, and just so hard to predict due to so many different effects in a closed space environment. We could calculate and try to make some predictions based on dimensions of the Ody, air volume inside, etc... but in reality, you just gotta try it out.

I myself am still trying to get a feel for things in this vehicle. I've got a good sense on how to get good, flat bass response in a sedan, but the volume in the Ody is just so much greater, I'm at a bit of a loss. It's a great learning experience though, and as I figure out stuff, I'll be sure to post my findings too. I'll be eager to see how your test works out! BTW, got an SPL meter and test CDs?

-SJ

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Discussion Starter #6
Yea John, I've got a RS SPL meter and a Stereophile test CD. I hope to have time this weekend to run my little phasing experiment. I've been using the Blau for a few weeks now but I'm going to reinstall the Pioneer to confirm my suspicion that it kicks the Blau's butt sonically. Just wish the Pioneer was more user friendly and had station scan, then it would be a no-brainer. BTW, I haven't disconnected the factory tweeters yet. I was waiting to hear the outcome of Odyfox's with & without comparison.

Have you done much in the way of attacking the road/tire noise that enters the cabin? I've done a lot of de-rattling, but still haven't tackled this problem since, to do it right, it's probably going to require removing all the interior panels, seats and carpeting. Sounds like Tomhan may do it right though! Hell, if he can quieten down an 81 Econoline this should be easy for him. Tomhan, if you're listening, keep us posted. With pictures if possible.

Dorhn

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Hey Dorhn,
Sounds good. The tweeter thig, again, a matter of personal preference. And I myself dislike the interface of Pioneer head units, so I completely understand.
Oops. Gotta go now. More later..
-SJ

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Discussion Starter #8
Shinjohn, this was both an interesting but frustrating experiment! See the SPL readings in my pics. I consistently got higher readings at 125 to 200 Hz and 25 to 50 Hz when IN phase, but between 63 and 100 Hz I got higher readings OUT of phase. This was using the Stereophile Test CD#2-track 16-low freq warble test tones. The Fender bass guitar track gave me a higher reading OUT of phase. Most of that energy must be in the 63 to 100 Hz range. When listening to music CDs with a lot of low freq energy, I got higher SPL readings OUT of phase, but, subjectively, they sounded deeper IN phase. That jives with my SPL test tone readings. All this was done with the fader control centered, the rear seat down and parked in the driveway. Anyway, I left the quick disconnects in the speaker leads so I can flip-flop the polarity and do a subjective listening test the next time we take a trip.

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[This message has been edited by dlh2 (edited 11-03-2001).]
 

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<font face="Verdana, Arial" size="2">Originally posted by dlh2:
this was both an interesting but frustrating experiment! </font>
Ah. I've located your problem. I find that a much heavier beer than Bud Light gives more accurate SPL readings.



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-= Darell =-
2001 Civic EX (ULEV)- currently the BIG car.
1997 EV1 (ZEV) in process - "This is NOT your father's golf cart"
 

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Discussion Starter #10
LOL Darell! Yea, that Bud Light can's natural frequency is somewhere between 80 & 100 HZ.
 

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Sorry. I'll stop. Back to your regularly-scheduled program....

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2001 Civic EX (ULEV)- currently the BIG car.
1997 EV1 (ZEV) in process - "This is NOT your father's golf cart"
 

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Nice work Dorhn!
Just plopped your data in excel for you..



The low volume and higher volumes followed the same trends, so just plotted one set of data.

The graph of the in phase measurements are telling. You're getting LOTS of dropout in the 60-140Hz range. This is in part due to the cancellation we were talking about, but also likely due to the location of the rear speaks and that of the SPL meter. Given the length of the passenger compartment, frequency/depth of the dip, and location of speaks vs. SPL meter, I'd say node.

Ultimately, what you decide in terms of how you end up configuring your rear speaks comes to your own perception of the sound. Here's my guess on subjecively, how the different setups sound:

0 deg (in-phase): excellent transient response and attack, low end fullness, time-correct phase perception, lack of mid bass warmth.

180 deg (out-of phase): punchier mid-bass sound, transient response compromised a bit, sense of slight "delay" on certain bass passages.

And how I might look at it on a music preference/recommendation standpoint:

The 0 deg case would be better for the purist, listening to acoustic music (classical, jazz, etc..), where coherence is most important.

The 180 deg case would be better for those looking for a warmer sound, and higher output. Rock, pop, rap, etc...

Now, I think for the 180 deg case, you need to get those speaks crossed over @ 100Hz or lower, else it will sound kinda weird.

Seeing that Marley disk, I really can't make a good judgement on what you would prefer. Marley is kinda middle ground... (or all over, depending on how you look at it!)

Anyhow, time for bed. Thanks for posting this data Dorhn! Great job! This is really loads of fun too!

Oh, and on the topic of NVH, I'll have to chime in later. I could write alot on my thoughts re: this subject (used to do NVH analysis back at Ford when I lived in Michigan, believe it or not!)... I've read the other threads on this subject, and don't wanna start another huge chain of discussion in the A/V, Sec, Navi forum...

'nite!

-SJ

p.s.- you should get a copy of the Autosound 2000 CDs. I used to use Stereophile's but I really dislike the warbles. The AS2000 has pure sine waves....

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[This message has been edited by shinjohn (edited 11-04-2001).]
 

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Discussion Starter #13
SJ, thanks for taking a look at the data. That in phase dip really bothered me when I looked at the SPL results, but you hit the nail on the head with regards to my subjective listening test. Most music sounded better with the rears in phase, but that punchier mid-bass when out of phase was certainly noticeable with pop and rock! My guess is that all this will be out the window when driving and the cabin noise factor is introduced. It's fun though, and I'll probably drive the wife crazy on our next trip listening to test tones and getting her to chart SPL readings.
 
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