Effects of modifying an existing passive crossover - diyAudio
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Old 27th December 2005, 02:27 PM   #1
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Default Effects of modifying an existing passive crossover

For my winter beater, I built a big 12dB/octave passive crossover network (mounted in my headliner!), to run my subwoofer, midbass drivers, and a component set - all from a 2 channel amp. I used nice components, tried to use good design - fun little project.

The amp, Xover, speakers etc. are just pieces I've had around.

I have a few issues though, and I would like to modify the crossover - but I'm unsure of the results I'll get.

Most fundamentally, I put my subwoofer/midbass crossover point at about 80hz.
I was trying to strike the balance between
1) "not being able to locate my subwoofer" (bass-up-front)
and
2) "able to crank it loud without bottoming the midbasses"

Unfortunately, I can somewhat locate the subwoofer as coming from behind me, and I can bottom out my midbass if I bring them up to a respectable level (I have a 2/3 octave EQ installed in the hatch as well) and really try to crank it hard on rock.

It's probably not that my Xover point is wrong (since I'm getting both symptoms I'm trying to avoid ), but rather that the Xover simply isn't steep enough.

I'd like to avoid messing with the sub's LP filter for now anyway - it's really not that bad, from a location standpoint.

My midbass drivers really are just 5.25" Parts Express speakers - I have two per door (phase aligned by location, sort of a mini-array). They worked real nice in an old install that I had, but I may not have been playing them as low.

So I think two things could help me:
1)
make my midbass high-pass steeper - probably go right to a 24dB/oct to avoid phase issues (if that is possible with a mix of slopes ).
2) pick up some higher-excursion 5.25" midbass drivers (if anyone knows of any that are decent but cheap).

So..If I made my midbass high-pass steeper - could that be as simple as duplicating the existing 12dB/oct HP Xover, and putting that in-line with my original one?

That would be ideal, because I wouldn't have to unmount my big Xover from my car headliner - I could install the secondary Xover behind the door panel, like a standard passive Xover.

Would I be changing the Xover point, in using this strategy - or would I be just changing the slope?
(obviously I'd be changing the response and phase characteristics around the Xover point, but being so low, I'm hoping that won't be an issue with respect to the benefit I'd get - this isn't a mid-to-tweet Xover, right?)

I don't have any tools for Xover design on this computer, unfortunately.
Any help is appreciated!
(even if it's just to point me to a higher throw 5.25" )
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Old 28th December 2005, 05:07 PM   #2
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Any help?

Passive crossover design a dead art here?

I'd like to put a filter in-line with the existing filter, if that is possible.

Unmounting this behemoth and fundamentally building a new, steeper filter is probably prohibitively time consuming.

(and of course - higher excursion 5.25's would help too, although I doubt to the degree that I wouldn't need to steepen my HP filter)
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Old 28th December 2005, 05:34 PM   #3
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Car audio is really a different ball game. I think you will always hear the sub comming from the back if you listen to music that has strong beat. Just basic physics.
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Old 28th December 2005, 06:46 PM   #4
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hey geo a couple of 5.25,s id reccomend around the price range are the peerless csx-x car driver model 850517 avail from madisound 2.5-3 mm x-max -4-ohm-good driver for around 35.00, and if you can wait pe- dayton is coming out with a 4-ohm-car lineup in a month or two ,perf should be very similar to their 8 ohm alum cone versions avail now- 5.25 i believe should be in the 25-30.00 range,excellent drivers and the price cant be beat!
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Old 28th December 2005, 09:40 PM   #5
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I'd go for the new drivers myself, but if you don't, the values will change on a 24 dB so use a calculator, like this one. It may that the drivers are cheaper unless you have a lot of caps and coils laying around.

http://www.mhsoft.nl/spk_calc.asp
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Old 29th December 2005, 06:30 AM   #6
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good piont cal ,he would end up spending as much or more on decent to hi-q passive parts in the end,i would def look at new inexp. drivers save the time and cash on the x-over,an x-over , going from an 12db-24 db slope wont improve the parameters of the speakers improve the area in wich is lacking
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Old 30th December 2005, 04:58 PM   #7
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I'm not optimistic that it's really an 'either/or' sort of thing.

The 5.25's that I have now are cheap, but work well as midbass drivers - at least down to some point. I only used them in this install because I had great luck with them in an old install - but in that install, I was cutting them off at about 100hz (possibly even higher) with the filter built into my amp at the time. And they didn't bottom at all.

In this install, my Xover point is about 75hz, and I'm not so much noticing them bottoming even in the 75-100hz range - I'm noticing them bottoming when I'm getting strong stuff in the 40hz, 50hz, 60hz range.
...hence my inquiry into steepening my Xover slope.

I'm sure upgrading the 5.25's would definitely buy me a little more output before they bottom out, if I can find a driver with enough excursion capability...
Maybe I'm pessimistic, but I can't think of a 5.25 that could have such great throw to completely eliminate the problem.

It WOULD be great, ideally, if that was the case - because then I'd still have that 50hz, 60hz presence up front - that would ideally help keep the bass image up front.
5.25" high-throw midbass drivers aren't too common.

But I also wouldn't mind experimenting at least with steepening the Xover slope - but if I did that, I'd like to build another 12dB/oct module to put in-line with the existing one (I could tuck it into the door for this one), if that's possible.
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Old 30th December 2005, 05:02 PM   #8
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And no, I don't have a lot of caps and coils lying around.

The components I used in my main Xover are decent, midgrade components. No exotic components, but no cheap components.

I think I ended up spending around $250-$300 for my parts, in total, to build a 3-way... so I was figuring maybe $75 or so to build this "add-on" Xover - again stressing the 'if that is possible' side.

I think you guys are right ideally, if a 5.25" driver is available, that is the best solution - but remember, I need four of them.

I'd spring for it though, if they were good. I have power to spare, if efficiency need be sacrificed.
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Old 30th December 2005, 05:05 PM   #9
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Quote:
Originally posted by dodgerblue
hey geo a couple of 5.25,s id reccomend around the price range are the peerless csx-x car driver model 850517 avail from madisound 2.5-3 mm x-max -4-ohm-good driver for around 35.00, and if you can wait pe- dayton is coming out with a 4-ohm-car lineup in a month or two ,perf should be very similar to their 8 ohm alum cone versions avail now- 5.25 i believe should be in the 25-30.00 range,excellent drivers and the price cant be beat!
I've had good luck with the Peerless stuff I've owned in the past... but I don't know if that excursion capability really beats the throw of what I have here. That's the kicker.

I could wait for the PE stuff - I'm not really hurting, stereo is working, just not as much impact as I'd like, since I have to EQ down my midbass a touch.

Probably a post-CES release?

Thanks!

...I guess ultimately something like a 6mm 5.25 would give me more comfort than a 3mm one - and that might be asking too much.
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Old 30th December 2005, 09:59 PM   #10
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dont know wich diy drivers you are using or if they are mounted in the doors of your veh,but drivers that made specifically for the ib-door locations can perform much better than a driver built for example a sealed environment due to the parameters of the driver,unless you did work to your doors-dynamat etc. for instance,you cant expect any driver to perform well,if your drivers is built for another app. might explain the bottoming out prematurly or be suspesion noise ,most aftermarket 6 in speakers have less than 3 mm linear x-max,so for an good 5.25 built for ib-door locations to have 2.5 - 3mm linear is pretty good ,and may not give have the bottoming out or suspension noises you are exp. just a thought , i dont have any extra passives or parts or i would send them to ya! i do know some of the older mb quart passives for their 5.25 in and or 4 inch model seperates did have an 12 db 100hz hp option on them if you find a set on ebay might help- woops forgot you had 4 of them 4-8 ohm or 4 -4ohm 5.25,s?
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