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Old 04-09-2002, 01:32 PM   #1
cantex
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Default crossover question

i am going to put in new front door speakers and tweeters and was thinking i should put in a crossover .

can anyone tell me the difference between a 12 and 18 db xover.
and which one i should go with.

thanks
vern
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Old 04-09-2002, 02:19 PM   #2
Concillian
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You should go with whatever comes with your components.

Crossovers are, quite possibly MORE important than speakers themselves, especially in the midrange.

Don't expect to throw on something not designed specifically for the speakers you have and have it sound right, unless you really know what you're doing.

To directly answer the 12dB vs. 18dB question, that is how much reduction in noise there is for every octave from the crossover frequency.

For instance, a low pass crossover has an 18dB ("third order") crossover slope. For frequencies one octave above the crossover frequency the crossover will reduce noise by 18dB, two octaves above, 36dB and so on. This will add on to any natural rolloff of the speaker itself.

For subs, it's very important to have a steep crossover slope, I find 12dB too shallow, and 6dB is ridiculously so for a sub. For a midrange though, a well matched 6dB crossover can sound very good, but it MUST be properly designed and incorporated. Higher order crossovers (steeper slopes) can, to SOME extent, mask poor crossover design/matching.
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Old 04-09-2002, 03:45 PM   #3
cantex
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Default 12 or 18

i have seen some component systems that have a 12db xover and some with a 18 db xover.

i guess my question is, do you think there is one better choice than the other, for the wrx interior?

my previous car (a 91 q45) there was a noticable difference between the 2 xovers, and i felt the 18bd gave me a better sound.

vern
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Old 04-09-2002, 04:22 PM   #4
6Pack
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Now you get into more complicated (mathmatical) things. This is going to be hard to describe without pictures.

Simple terms:
A 12db roll means the slope (rate) at which one source disappears per listening octave in listening frequency. A 18db slope is a steeper rate at which the source disappears per octave.

What really happens:
Staying within the same "type" of crossover (1st order for example)... (This is where the graph would come in handy): There is a peak before the crossover does it's thing and starts to "disappear" the source. Within this peak range the sound is actually amplified (sideeffect of how crossovers work). So the music in front of the crossover frequency is actually louder than the rest. The disadvantage to an 18dB slope is that this peak is a lot larger than the peak for the 12dB slope. In other words, the 12dB gives you more of flat frequency response (what you want). But the rolloff takes a lot longer (unwanted frequencies stay around longer) than 18dB xover. So there is no clear-cut winner. Now you can get more complicated crossovers, like 2nd, 3rd order etc. or even active crossovers. Just don't get too crazy. Remember for every component you add to your system the more distortion your adding. Producing quality audio with minimal amount of components should be your goal.

But definitely get the crossovers that are made for your speakers, they will probably sound the best and you don't have to put any effort into engineering/testing what works best because the manufactors have already done this for you.

For more info, I suggest getting a book or digging deeper on the Internet. Lots to learn.
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Old 04-09-2002, 06:14 PM   #5
Concillian
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Bottom line is:

Looking at 2 sets of components, if one advertises a 2nd order crossover (12dB per octave) and one a 3rd order crossover (18dB per octave) you have NO IDEA which is better until you listen to them.

It's all in how well the design is matched to the set of speakers. It's also in the design of the crossover, there are mutiple designs that give a 2nd or 3rd order rolloff.

Sorry, there's no simple answer to this one. As in most of audio, quality is in the ear of the listener. Sorry I can't be of more help.
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Old 04-09-2002, 07:25 PM   #6
cantex
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Smile thanks

you did answer my question.
i have some blaupunkt 6.5" and mb quart tweeters, and i'll experiment with different xovers.
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