Passive X-overs

Discussion in 'General Car Audio Discussions' started by TheViking, Oct 1, 2006.

  1. TheViking

    TheViking Well-Known Member

    I would like to make this a sticky, but............

    Anyway, some of you folks have wondered about passive x-overs. They are a wonderful way to get great results from the mobile audio enviorment. Lots of guys think that the only way to go is with electronic x-overs and thats it. Well, the truth of the matter is this.....If you want accurate sound, with proper phasing, and a realistic soundstage, passives are the way to go.

    Lets think about this for a minute........ up.....passives are what are used in almost ALL home audio speakers. You know, those things that sit on your living room floor with a 15 inch woofer, 4 inch mid and 1 inch dome tweet.....well, guess what, they run off an amp, just like your car speakers do, and they sound great doing it with passive X-overs! why does car audio have to be different?

    First off, what is sound?????? i will break it down into 3 seperate areas for simplicity.

    well, its a set of frequencies that the human ear can hear. from 20 Hz up to 20,000Hz (in theory) 20 Hz is the low stuff that shakes the hell out of stuff. as a matter of fact, you watch a woofer at 20 Hz an it just seems to bounce back and forth without doing much in the way of sound, thats normal... i wont get into the science of things here too much frequencies up to around 100 Hz are what are considered sub bass, things like the kick drums, synthsizers, bass guiars, etc...thats the sounds that make your mirrors shake and gets your girlfriend wet when she sits on the trunk. Oh, and there is NO imaging or stereo information in this range of sound, especially in the car audio world.( for all intents and purposes) it?

    Then we have the mid bass. This is a critical part of the sound. it cover from about 100Hz up to around 3KHz. this spectrum covers the sounds of the critical stereo and imaging "stuff"..... the mid bass contains sounds from kick drums, guitars, vocals, piano, toms, cymabals and things like that.... It is in this area that things get critical. we want to do as little as possible to "smear" the sound.....

    then we have the high frequencies.....yep, the stuff your tweeters take care of and get abused with..... tweeters are the unsung heros of the speaker world, they take an incredible amount abuse and power with lots of clipping and keeep on ticking.... but thats another topic.. the tweeters handle the range of sound from about 3KHz on up to beyond what the human ear can hear. (in reality, most of us really cant hear much beyond 15Khz, and it gets worse as we get older, FYI) These frequencis handle the "high" stuff, like cymbals, upper vocals, all the upper registers, again, these ae critical sounds for proper imaging....

    Now, what does this have to do with X-overs you may ask? simple...since a single speaker cannot effectively play the entire sound spectrum from 20- 20KHZ with any type of realism, we have designed speakers that play certain sounds with the greatest of ease. Low frequncies like to move lots of air, so they have the greatest size, more size = more air movement...simple, thats why subs are big and move back and forth alot (xmax)....

    mid bass is a tricky area, its a sound that needs to be addressed in a critical area. If I remember right, 5 inchers are good to about 4Khz, and 6 inchers are good to about 2.5 KHZ as far as upper fequncy extension, this is due to the cone diameter and the effective wavelengths they produce......... Another area of another topic, just take my word for it so i dont have to get drunk and remember all this stuff too much!

    Tweeters...Oh boy.......thats like a ford/dodge/chevy thing .......

    They cover the upper registers, they dont move much as far as air goes, they have to be litghtning quick in response and they are so damned delicate that even a slight amount of clipping from the amp can toast them like char brolied burgers. anyway, these little drivers range in size from 2 inch down to half an inch. why so small? cause the less mass they have, and the smaller the surface area, the better they respond to the upper frequencies (in theory)........ again, wavelength propogation and localized standing waves in the area of the tweeter can make or break it...........

    So, now we have a defined set of frequencies that need to be delivered to 3 different types of speakers, subbass, mid-bass, and tweeters... simple enough right??? LOL!!!!!! NOT!

    will continue this on here in a bit.........stay tuned, need to get a beer and clear my head of the porn i was just looking at......dam the net......Oh, and any particular questions along the line of this? please wait till I am finished, this is going to be a long drawn out boring thing to most, but intersting to those that want to learn about sound and how to make there cars sound good.....
  2. TheViking

    TheViking Well-Known Member

    So, why passives and not electronic X-overs?

    Simple....With elecronic x-overs, you have a set variable, with passives, you are UNLIMITED in your choice of frequencis and phasing......

    OK, lets talk about phasing here for a second.......

    What is phasing?

    It is the arrival time of a signal in reference to an original signal (reference signal)

    what happens when to signals meet that are not in phase? you get phase cancelation. this is true from the lowest sounds of subbass to the limits of the RF spectrum and beyond..... and Is CRITICAL to the accurate reproduction of sound. Example. the subs in your trunk are playing the lows. from 100Hz on down, the midbass is playing form 100Hz on up, all sounds good till one day you rewire you r amp and finds that you accidently hooked up the subs polarity backwards, and the sound is different....why????wel, its simple, even though each speaker is playin a different set of sounds, there is an overlap in the range of frequencis that they play. If the subs are set at 100 Hz on down at 12 dB per octave, and the midbass are set to play 100Hz on up at 12 dB per octave, then guess what, each set of speaker is playing a set of sounds that they are not designed for, albeit at a lower want to see some real phase cancellation!!!! take and wire up a dual voice coil sub out of phase, IT MAKES NO BASS!!!! this is what I am talking about!!

    X-overs are NOT a wall, they DO NOT STOP ALL frequencies at the x-over point!!!!!


    100Hz Low pass for a sub, guess what...It plays 200Hz also!!!! and 400Hz!!! and 800Hz!!! not as loud as the 100Hz, but its there... this is where we get into octaves, and Db per octaves.....crap i am biting off morte than I can chew, cause my writing skills suck!!!

    Lets look at a 6 dB per octave X-over..... for a 100 Hz.......with the woofer playing at exactly 120 decibals to keep it simple.......

    at the x-over frequency of 100Hz, the sound is 3 decibals quieter or 117 dB .... at twice that frequency, or 200Hz, or ONE octave above the sound of 100 Hz, the sound is 6 decibals quieter. or 114 dB..... at 400Hz, or 2 octaves above 100Hz the sound is 12 decibals quieter or 800 Hz or 3 octaves higher, the sound is 18 decibals quieter or 102 dB...... are you following me on this??????? am i even making sense???? i explain things in a hard to unserstand method at times.....let me know if yall are in tune here.......thanks.
  3. aznboi3644

    aznboi3644 Full Member

    In Tune indeed...and I VOTE FOR THIS TO BECOME A STICKY

    Caddy...get your ass on it
  4. pedro quiroga

    pedro quiroga Well-Known Member listening.eerrr can you tell me or show me how to make a nice 3 way.i have that 4 ch(m44) running my doors and dash,and would like to run those 6 off of only 2 ch' get rid of the other 4ch i have running my 6x9s in 2 ch i can run them off of the same amp.
    Last edited: Oct 2, 2006
  5. TheViking

    TheViking Well-Known Member

    OK, seems like some of you are following what i am saying, good deal.....

    I just discussed the 6dB per octave x-over slope in the previous post. Now lets move on to the 12, 18, and 24 dB per octave slopes. If you understand the operation and theory of how 6 dB slopes work then this is easy.....

    At 12 dB per octave, the volume of the sound decreases at a rate of 12 decibals per octave, this is twice as much as the 6 dB slope, therefore the the subs play less of the nid bass and the tweeters play less of teh midbass. At 18 and 24 dB per octave, this rate of decrease is even more intenese!!!!!

    Now, with these different slopes, we have a few other things happening besides just the roll off of the unwanted frequencies. An interesting thing happens here. The Phasing of the sound becomes different. Rmember Phasing? When two speakers move back and forth in unison, they are in phase, when they are moving opposite of each other, they are out of phase. When passive x-overs are introduced into the system, the phasing also changes! At a rate of 12 dB per octave x-over, the signal going to the speaker becomes 180 degrees out of phase with the input!!!!!! At 18dB per octave, the signal to the speaker is 270 degrees out of phase with the input signal!. what does this mean to you? Lets say you are building a set of x-overs for an 8 inch mid bass and a 1 inch tweeter. you want the woofer to play from 20Hz on up to whervever is naturally rolls off on its own, so no x-over on it, the tweeter you want to roll off at 3kHz @ 12 dB per octave. You build the x-over and get everything hooked up. As you listen to it, something doesnt sound quite right, the upper midrange soujnds a little odd and not vey natural......You go back and look at your wiring, everything is hooked up as it should be...all positve and negative connections are correct, but guess what. even though the tweeter is hooked up properly with positive to positive, and negative to negative, It is OUT OF PHASE with the woofer!!! This is because the 12 dB x-over has inverted the phase 180 degrees! So simply reconnect the tweeter out of phase by reversing the leads.. very simple. You go back and listen to the system, and the midrange has become open, dynamic, and natural sounding!!!!!

    Now, same set up, using 18 dB per octave on the tweeter......what happens this time? It is 270 degrees out of phase with the woofer!!!! But wait, You ask, If i reiwre the tweeter and hook it up with the polarity reversed, it will still be out of phase with the woofer ???? yes it will, but only by 90 degrees......Still not in pperfect unison with the woofer, but closer....How can we mmake up for the additional 90 degrees of? a few things can be done...One off the easiest is to simply move the tweeter a little closer to you than the woofer, are a little farther away from you...Because DISTANCE also effects phase!!!!! Just what you wanted to hear, right?!!!!!!!!!

    Yep, simply moving speakers that play different frequencies at different distances from your ears cause's lots of phasing issues!!!!!! thats why it is so hard to get an accurate soundstage and imaging n the car as opposed to the home audio enviorment!

    Ok, now what? well, lets rembember what we have talked about as I coninue on.

    In the car audio world, what we want to do is create a simple and effective reproduction of the original performance. Key word here is simple! The more drivers you put in your car that handle the range of sound from 100 Hz on up, the more difficult it will be to obtain good SQ. So simplicity is paramount. This means a nice set of components speakers in the front, and the subs wherever you can get them! Rear speakers are Ok if not over done, but we will not discuss them right now, lots of controversy on that subject..

    So youve got your nice new components for the front stage!!!! great!!!! Lets start looking at the speakers and the ways to make them perform their best.

    You open the boxes and pull out a nice new set of tweeters and a set of mid bass drivers and a pair of Subs Now, what kind are they you may ask, they are VIKING model XX6.5r mid bass drivers, and VIKING model XX1.5r 1 inch soft domes and VIKING model XX12r 12 inch subs. (Always wanted my own speaker company!!!!)... these speakers are top of the line! cast baskets, cones made out of alien technology secret stuff and the tweeters are even more awesome with liquid cooled voice coils!!! LOL!!!! And since i have a speaker company now, i also make my own amps!!!!! I want to run this system on a single VIKING model XX2500r. this baby does 250 watts per channel @ 4 ohms and 1000 watts Mono @ 4 ohms!!! Its a simple 2 channel amp, and it will run the ENTIRE system!!!!

    So lets look at a few things here. I want the midbass and tweeter up front, and the subs in back, simple enough. The components up front will run stereo off the amp with the subs run mono on the amp. I want the subs to play from 100Hz on down @ a rate of 12 dB/octave. I want the 6 inchers to play from 200 Hz up to 3kHz, again at a rate of 12dB/octave. Now the tweeter, i want them to run from 3.5kHz on up to as far as they can go @ 18dB/oct. Now, you are probably asking a question right now....why are there gaps in the frequency's that are be crossed over??? Heres why......the subs are playing from 100 Hz on down, at a rate of 12dB/oct. this means that they wll still play quite a bit of sound from 100 Hz on up to 200Hz!!! thats within the range of the midbass driver! the mid bass driver will be playing also down in to the range of the sub!!! remember, x0overs are not a "wall" to stop frequencies. so we want them to roll off into each others x-over range a little bit, not alot, or we run into....phasing issues!!! same principle applies to the tweeter! You also probaly notices that I am xing it over at a rate of 18dB/oct. this is due to the fact that tweeters really dont like to play things much below their resonant frequency, and any sound that gets to them that is in the low midrange region will toast them very quickly!!!!!!!! Also, we dont want alot of phasing issues happening in the critical midrange so as not to destroy the imaging So a fast roll off is being called for here........

    Next, i will discuus the x-overs and the implementation of them into the system, and how they effect the speakers.....till next time!
  6. pedro quiroga

    pedro quiroga Well-Known Member

    this is better than a magazine.cause we get the new issue every other day or so.LOL.i cant wait for drawings and the like.
  7. TheViking

    TheViking Well-Known Member

    OK, the x-overs themselves, here we go!

    First off a little electrical theory here, what is the type of voltage that your amplifier puts out? It is AC voltage, unless you drive the amp into clipping then it sends out DC voltage from the power supply! (DC voltage is a VERY bad thing for speakers BTW) Ok, so AC voltage is used to drive the speakers, pretty simple really. Now how do we make certain speakers play certain sounds? We use passive x-overs......

    They are nothing more than a capacitor of a certain value or an Inductor of a certain value. caps use the term microfarads (mF) to denote value. Inductors use the term MilliHenries (mH) to denote the value. so how do these things work? I will keep the explanation here rather simple to understand.......... Capacitors store and realease energy at a particular rate given the value. What is happening is the caps resist low frequencies, that is, there impedance, or resistance to flow of current rises the as the frequency lowers. Thats why caps stop the bass from getting to your speakers. Inductors, or coils as some term it, do just the opposite, they limit the passage of high frequencies, the higher the freq. the higher the reistance to those frequencies.. A few other components are also in x-overs, including resistors and light bulbs. But not that import right at this moment. So, using certain values of capacitance and inductance, we can get a desired response from our drivers!!! I am not going to get into the differnet types of capacitors and inductors, cause there are many (mylar caps, polypropyle caps, electrolytic caps, air core inductors, laminated bar core inductors, ferrite core inductors, etc,etc,etc,) they all do the same thiings, just some do a better job than others in some instances.......

    Lets starrt off with the subs! we wanted them to be x'ed over at 100Hz. so, each sub being 8 ohms, we wire them in parallel for a 2 ohm load on the amp in mono. so what we want to do is find the value of the cap and inductor for a proper response.

    Now, I am not going to go through all the values, charts and such....that info is on the net all over the place, just look up crossover frequencys and such, you wil find it!!!!!! here's one if ya want to check it out

    What I need for a 12 dB/oct. slope at 100Hz is a cap with the value of 228 mF. And I need a coil with a value of 11.02 mH. Well, guess what, you aint gunna find caps and coils with the EXACT values as stated So now what? Well fortunatley we don't have to be real picky here, as long as the values of the components are within 10% or so, it will work fine. So, for a cap I will use a 220uF and for the coil, I will use a 11 mH.......Very simple.....Another thing we need to look at is the voltage rating of the caps. They are expressed in volts. Always get at least 100 volt caps or higher. Any smaller and you run the risk of venting them. Or for a more exciting term, blowing them up!!!!! Also with coils, you want them to be able to handle the power also, so ideally go with an iron or ferrite core coil or similar. Air core coils will work ok, but not with a buttload of power, they tend to saturate. Now, for the installation of them........very simple just look at the link above!!!!!!!! takes a lot of the work out of it for me!

    Moving on to the midbass drivers. I want them to run from 200Hz on up to 3kHz. again, look at the site above, I need a 114 mF cap and a 5.5 mH coil for the high pass and a 7.6 mF cap and a .36 mH coil for the low pass. this will effedtively make a bandpass filter for the midbass.

    Tweeter, simple again but I want 18 dB/oct roll off at 3.5kHz........I need a 7.5 mF, a 22.7 mF cap and a .13 mH coil. Done!!!!!!!!!!!

    I need to make another additional note here since we are getting into the x-overs now........Anytime you use a 12 or 18, or 24 dB/oct high pass, there is one thing you must be cautious of.....DO NOT run the system without the speakers connected to the x-overs!!!!! If you do, the amp will see a DEAD SHORT!!! So if you ae rocking out all drunk one night driving down the road and you blow a tweeter, you just might blow your amp too!!!! This is because when there is no speaker load on the x-over, the coil that is in parallel will show as a dead short, the speaker needs to be in the circuit for the thing to not show a dead short!!! You have been warned!!!!

    Ok, its all wired up and the speakers are installed and the system is sounding pretty good, but It still could sound better. So where do we begin??????? that's the question, yep.....

    Well, this takes some trial and error, a little knowledge of phasing, arrival times and attenution among other things.

    Lets start off with the subs and the midbass drivers. If you did things right the subs will be wired up out of phase in conjunction with the amp so that the subs are really moving in the direstion they are supposed too! Same with the mid bass drivers!!!! so in a perfest world, they would be in phase with each other and accurate in the movements. But, remember the slight over lap in the frequencies? this can wreak havoc!!!! First thing I always do is invert the phase of the subs, that way they are OUT OF PHASE with the midbass........HA HA!!!!!! this gets fun!!!!! Does it sound better? Like in the upper bass and lower midbass region??? In my car it does for this install!!!! Heres why the slight overlap in frequencies, drivers location, and arrival times to whee you are sitting is different. So even though they were electrically in phase with one another, they were actually acoustically OUT of phase with one another.....are you confused? I am at all times so this is normal for me

    Will get back to this again in a while, need a few more beers so I can think clearer!!!!!! till next time
  8. pedro quiroga

    pedro quiroga Well-Known Member

    cant going to check on making a set up for my front my sis to fund my old school amp set bidding on a M50.will be 245watts into 2 ohms mono for the i need a 2 way for the doors and my dash.hhmmm......but the dash speakers are plate set up.the 4 and tweet are seprate and the tweet allready has a coil on i need a mid bass and a mid range set up.the tweet has its own will haveing a midrange set up on thoes 2 affect the tweet?
  9. TheViking

    TheViking Well-Known Member

    ?????????????????????? huh? in english please!:confused:
  10. pedro quiroga

    pedro quiroga Well-Known Member

    ok my sister bought me anM50 phoenix gold from im taking out the power i'll have the M44 4ch to my fornt and rear speakers.2 ohm stereo in front and 4 ohm stereo in the rear.and the M 50 bridged mono 2ohm to my L5 10 duel 4 ohm what i want is the front cannels to drive the 6.5s in my doors and the 4 inch plates in the dash.but i want the doors to play only mid bass and the dash mid range.then the tweet.....well u i need to know the values for a 2 way.the dash is croossed over @175hz they sound fine but i want even less bass going to them.they are infinity refrence 4x6 plates.does that make any cense?i want a nice sounding 3 way set up.the plates are a seperate 4 and tweet,but are wired like a coaxial set.
  11. pedro quiroga

    pedro quiroga Well-Known Member

    ok today i bought some bass blockers for the 4x6 plates.they are 200hz@4ohms. it helped now i was thinking of leaveing the 6.5s on the low pass i have them now.and controling thier output with the lp44 vol control.(remember i said the HU is set @80hz hi pass to the M44 and the rear out on the amp is set for sub out @175hz lowpass.and for some reason the doors play a nice low bass out.not subbass but not midrange either.there are no vocals at all.i like it the way it is, and think if i change it, it wont be the same.)so im thinking of an L pad for the rear6x9s.running them from the front out along with the 4x6s.i just loose the fader.i had them like that before and the rear output was too the L pads is what i want.maybe 6dbs less .can i make a vol knob for the rears for more control?i guess like a i can buy another M amp later to regain the fader.
    Last edited: Oct 4, 2006
  12. aznboi3644

    aznboi3644 Full Member

    Pedro, take a deep breath and relax. lol a little better grammer would help us not go blind while reading your posts lol. Like making some letters capitalized and such lol

    But for your situation I'm sure Viking will come to the he can run 5 channels on a 2 channel amp.
  13. TheViking

    TheViking Well-Known Member

    OK pedro, you have ALOT of speakers to get dialed in too sound right......

    If I read you right, you have the subs x"ed over at 175 Hz, and the midbass/front speakers playing from 80Hz on up......This is usually not a good thing. If you can, set the subs at 80 Hz and the highs at 175 Hz and go from there

    Now as far as your rear speakers (6x9's) , disconnect them for now, lets just concentrate on the front end right now, Aint no sense in haveing a set of rear speakers phuck with things.....

    Your 6 inchers in the doors, i would like to see rum from about 175Hz up to about 5oo Hz @ 12 dB/oct. then run the plates in the dash from about 600Hz on up @ a rate of 12 dB/oct........... Try that first and see how it souinds....again, gunna have to play with polarity sometimes to get the right sound....
  14. TheViking

    TheViking Well-Known Member

    Smart Ass!!!!!!!!!!!
  15. aznboi3644

    aznboi3644 Full Member

    That indeed...thanks for the compliment lol
  16. TheViking

    TheViking Well-Known Member

    Oh boy!!!!!!!!!!

    think your a REAL smart ass now do ya?

    I need a beer....nuf said....
  17. aznboi3644

    aznboi3644 Full Member

    *passes Viking a beer*

    *then giggles cuz I shook the hell outta it and watch as Viking gets foamed in the face*
  18. pedro quiroga

    pedro quiroga Well-Known Member

    Ok.Got.You.LOL.Sorry i did not mention my sub.Its crossed over at 100hz doors are @175hz on the low pass out of my 4 ch.BUT!my radio's crossover is on. 80hz my 4 ch.It some how changes the crossover setting to the doors.they play bass,but not sub bass.80hz hipass to the amp and the low pass is set to 175hz.If i turn off the crossover on thr HU the doors play subbass.So i leave the HU's crossover on.Would that be some sort of bandpass?Whatever it is, it sounds great.i have up front bass,and i decided to leave that the way it is.Ok so 600hz hipass to the dash.not a prob.Do they make a bass blocker of that value?Or would a proper passive be the way?As for the 6x9s .I do like the sound they put out.I think my hifonics vulcan (50x2.hidden under my rear seat)set VERY low will still let me use them, and have some fill(i like rear fill).I've read that you can wire the rear fill in mono.How does that help,if any?
  19. pedro quiroga

    pedro quiroga Well-Known Member

    I hope that still is not confuseing. I hope some time soon to get yet another M series PG amp.The M25 for the rear.25x2.Then when they are all butted up together they look like one big ass amp.
  20. pedro quiroga

    pedro quiroga Well-Known Member

    i wont be able to do anything on the truck for maybe a weekor more. my sis came back from iraq on friday and will be here till the 16th of oct.her boyfriend is also comeing to visit on sunday and will stay till the 16th also.maybe when they go to disney i can do somthing.i'll remove the amp to the 6x9s.and will look for the 600hz filter.
    Last edited: Oct 5, 2006