Crossover advice needed

[Bwap]

Hello everyone, I have a dilema with my crossover wiring that I am hoping someone will be able to help me out with. Thank you for your advice and knowledge. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

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[Bwap]

I have been working on a frontstage for my car and was planning on building my own crossovers, but have ran into a few walls there. So I have been thinking about wiring in a supertweeter before the crossover in a component set(or the crossover inputs).I plan on wiring some speakers to my RockfordFosgate that pushes 300@2x4. This method would be wiring the 4 ohm woofer to an 8 ohm tweeter with a passive crossover, using one that makes the load the amp sees at this point 4 ohms(like a component set). I then would wire my 8 ohm supertweeter into the inputs of the crossover(paralell), resulting in an impedance of 2.66 ohms. This option is not ideal because it would be sending 130watts to the midrange and 65watts to each of the tweeters, while 150watts to the midrange and 75watts to each tweet is best.. At two ohms the power split with them all wired in paralell is optimal, ratings being exactly at said wattages. Also I am planning on wiring an on/off switch in before the supertweeter. If I turn the tweeter off while they are all wired in paralell it will leave a 2.66 ohm load. That is about 160 watts to the midrange and 80 watts to the silk tweeter which is fine. Although if I have them wired in before a crossover, turning off the supertweeter will result in a 4 ohm load.. leaving 100 watts for the midrange and 50 watts for the tweeter, which is less than I would like for these drivers.

Basicly I would really like to run 150 watts to a mid range woofer(low pass), 75 watts to a silk dome(high pass) and the remaining 75 watts to a supertweeter(high pass) wired all in paralell with proper filtering. As I said above, a 4 ohm woofer and two 8 ohm tweeters wired in paralell, result in a two ohm impedance. I have a diagram on how i was planning on wiring this, hopefully you can tell me if it achieves a two ohm impedance while still being a successfull crossover, or tell me a way I can do this/do it better.

These are the speakers I plan on using:

Crescendo pwx-6.5 - http://store.crescendoaudio.com/pwx-6-5-mid-range/

Amp High pass - Meeting my 8"s at 50%@ undecided hz.. thinking 450-500hz?

Low pass - 4,000-5,600hz

Thinking 4,000hz

Morel MDT 12 - http://www.parts-express.com/pe/showdetl.cfm?partnumber=277-060

High pass - 1,800-3,800hz

Thinking 2,500hz

Crescendo FT1 - http://store.crescendoaudio.com/ft1-black-series/

High pass - 3,800-5,000hz

Thinking 4,000hz

Any opinion on the crossover points would also be appreciated, thanks.

 

[Bwap]

Is this the right section?.. im hoping the right person sees this.

 

[maylar 10+ year member]

Seems like a lot of tweeter to me. The problem with a passive hookup is that you don't get to adjust the level or crossover points, and trial & error passive experiments can get expensive. What do you do if you get it all connected and find that there's too much 2000 Hz from the supertweet?

I would persue an active solution, or back off to one tweeter crossed to the same point as the mid. That way your EQ is split between 2 distinct drivers.

As for hipass on the mid, it's capable of going below 400 hz easily. What range is the 8 covering?

 

[keep_hope_alive Premium Member]

this was my response in a PM

Power isn't split the way you describe. The amp doesn't allocate power that way.
What happens is the amp sees an impedance load at each frequency and delivers a voltage and sources current.

that means at the given output voltage (at that moment) the current is determined by the impedance (at that frequency) and thus the power is determined by the combination of voltage and current (P=V*I)

Power output is dynamic and constantly changes every fraction of a second. higher frequencies usually have much lower amplitude (voltage) and thus see only a few watts at any time. Lower frequencies are usually mixed louder and will see more power during musical peaks.

Audio power - Wikipedia, the free encyclopedia

When wiring a tweeter in parallel, the amp will only see the parallel combination above the crossover point. So the amp will see the combination of 8 ohms and 8 ohms which is 4 ohms, for high frequencies, and will see the woofer at 4 ohms below the crossover point.

i think you run the FT1 from 8kHz and up. That's what a super tweeter is for - frequencies above 10kHz

there is a bit more to it than that, but you have the diagram right. the amp will see no less than 4 ohms given a 4 ohm woofer and two 8 ohm tweeters per side.

you just need to make sure the crossovers are properly sized for the impedance load. impedance affects crossover point/sizing.

Parts Express Crossover Guide

 

[nudels 10+ year member]

i suggest prototyping a breadboard with l-pads and slide switches for designing selectable freq/slope passive crossovers if that's desired.

it is totally possible to get the right sound out of two drivers one would not normally think to combine, it just takes some dedicated reading and a bit of trial-and-error. the only real fickle problem ive had with building passive crossovers is calculating and aligning the phase of two completely different drivers based on their free-air imp. plots. (when applicable)