Crossover points

This may have been covered elsewhere, but I don't really want to wade through all the one-sentence responses to Stephen's (and other's) postings on sound quality installation.  At any rate:

I would like some input on crossover points.  I am running Polk db650s (temporarily - see my signature) in all four speaker positions (FL,FR,RL,RR) and will soon be adding my Focal 25A1 subwoofers to extend bass response of my system.  The Amplifier I'm currently using (Blaupunkt GTA4) has a fixed high pass at 80Hz (the Memphis Belle I will eventually use has fully variable crossovers from 40Hz on up).  Based on the frequency response graph of the subs, I will want to low pass them at around 100-110Hz.  Will the overlap in coverage cause the staging to be "pulled" toward the rear of the car (the subs will be in the rear)?  I realize the range from 80Hz to 110Hz isn't that wide, and vocals are going to be higher in the spectrum than that (except for some Barry White, maybe... lol).  Short of adding a subwoofer in the front of the car to counter this, how can I best apply the crossovers to affect the best sound imaging?

Thanks for any help!

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One sentence responces  .....they go ON FOREVER.....   I DO respect his knowledge.

I wouldn't play the sub that high....90 cycles tops. You focals up front....are you using the xo's that came with them? I would shut them down before their low freq. respose...say 70, 75 cycles. Focal claims 60. Done this way...no gap.

Someone will post on this SLAMMING my suggestions. This is why I post in the security section. There are nothing but facts presented there.  The audio section has too much "I would do it this way"  "I like the way this sounds...." Other than the definitive aspects of some of the electrical theory's....it's all personal preferance.

just my opinion.

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I will use them but only to separate mid-bass from tweet.  The high pass will occur at the amp.  I totally agree about setting the points higher than suggested.  When you don't "strain" the drivers, they perform so much better for a lot longer.  And you think I won't be under utilising the quality of my subs by limiting them to a 90Hz LP?  That's interesting - I've never done that (probably because I've used smaller, quality subs in the past).  I'll definitely play with it.  By the way... I think your suggestions are completely valid, so anybody that feels like slamming them can jump off.  Thanks! 

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NoBody Slams KarTuneMan.

Tweak your crossover points for a few sessions after the install is all settled in.  It doesn't really matter what the actual numbers end up being as long as you start at reasonable points and so are in the ballpark.  Standard starting point is 80 Hz crossover from sub to mids.  Use test tones, at least initially.

Note:  what you don't see in the frequency response graphs is your car's cabin gain.  You can't rely too heavily on those response charts.  Thus, the tweaking by ear.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Nobody....NOBODY slams KarTuneMan......    I really got a laugh

what you don't see in the frequency response graphs is your car's cabin gain.  I really like this.....

Happy New Year.....

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Since I'm mainly in the planning stage (it sucks having to wait for things to be shipped - damn the holidays!), I haven't yet wondered what my cabin gain and cabin shaping will do to the imaging.  I have also read Stephen's post about front end set-ups where he mentioned that a flat response sounds very different than what you might expect because we've all "pre-disposed" ourselves to a certain type of EQ enjoyment.  Therefore, I'd like to have an objective way to achieve the system flatness.  Where is a good place to obtain a RTA and what would be a good way to learn how to use one?  I'm assuming they are outrageously expensive??  Are good local shops generally equipped with this tool and should they be willing to allow me to use it? 

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True RTA is great.  You will need also need a test microphone like the Behringer ECM8000 and mic preamp.

BTW, I suggest matching your crossover points and slopes @ 80Hz.

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I checked out TrueRTA... it would indeed be nice to spend $100 versus $2000. 

Okay... to further the subject -  to a casual listener, does this really make any true difference?  How much of a competition difference does it make to step up (for example) from 12db/octave crossovers set at overlapping points - LP100Hz for the sub and HP80Hz for the mids, etc - to 18db/octave set at matching points so that there is virtually no overlap making it darn near seamless?  Does this make any "real" difference to the judge sitting in my car for 30 minutes judging my SQ? 

This deep of a Tweaking will only occur for me in the distant future as I upgrade, but it would be cool to gather this knowledge sooner rather than later.  Thanks!

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