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To start off, my system is a dirt-cheap system built off of many used components given to me. So, I apologize that my system may be impractical but humor me please...
I'm planning on running two old Rockford 8-inch subwoofers (8-ohm) and two 6x9's on the same Rockford Prime 150 watt amp. First things first, is this possible (3-channel operation)? Will this cause severe distortion in the full range speakers? Will this severely tax the amp?
For this odd setup I need crossovers and an active one is out of budget and will be troublesome to wire in the car. So, I want to build some simple, old-fashioned passive pieces but I'm unsure of how exactly to go about this...
What are some common components used to make these connections? I realize that capacitors and inductors do the filtering but how exactly could I wire these into the speaker wires most effectively? I figured on using a first-order bandpass on the woofers and second-order high pass on the full range speakers. I didn't figure that I could just cut the speaker wire and solder them in since the leads would most likely be tiny and this connection may be unreliable. Are there small circuit boards that are commonly used? Could I have a small set of connections that don't require soldering that I could wire directly from the amp?
Also, is "Zobel" circuitry really necessary for this type of setup? I know that impedance constantly varies, but is it really necessary for this type of crossover?
I would also appreciate some clarification about the phase changes created by a second-order crossover. If I had a second-order crossover on each speaker of a 2-channel stereo amp would I need to wire on of the speakers backwards in terms of polarity?
A crossover is much more than some resistors, capacitors and protection circuits. They are usually designed with the specific speakers in mind with the intent for them to do specific things. In your case you have a few options.
First: Use something premade. Phoenix Gold is the first and only that pops into my mind that will do close to what you want. It's a XVR12 or XVR14, a three way passive crossover for a two channel amp. The biggest problem is finding them since they were introduced in 95 or 98, if I remember correctly.
Second: You could make your own. Which is good that you have done some diggin into what you would need to complete this, though you have seen that they can be very complicated and usually have some particular components involved. For a manufacturer, they will use all of the speakers specs to make the most suitable set of crossovers for the given speakers. Since you don't have all the equipment you can make some educated guesses as to what you would need along with one of the many crossover design programs. This is doable, even for someone that is a novice.
The thrid option is to use a simple cap type crossover after the 8" sub with the amp set in full range. This way is the most comporimise since nothing works with its intended range only, but you will get the general sound that you need. Since the 8 will have a full rnage going to it, it will try to play higher frequencies, which isn't terrible but it may sound odd. The 6x9's will get some of the lower frequencies knocked down from an inline but they will also be similar in that they will only be operating in a general set of frequencies that they are deisgned to work within.
Zobel networks are great, since every driver changes impedance with frequency, and it makes sure that everything is in check as the driver cycles through it's movement. A properly designed crossver will have a zobel protection circut, as well as some other pieces to protect the individual drivers.
Phase changes are within the drivers movement along their given range. Orders in crossovers are indicating many things, first off is the slope of how the driver is attenuated past the crossover point, like first is 6db, second is 12db, third is 18db, fourth is 24db, etc... There is also a phase change that usually coincides like first of 90, second of 180, third of 270 and fourth of 360, but that's about where the simplicity ends.
Basically lets back up and start with a list of what you want, what you've got and where you want to go. Some of what you have may work, some may need to be rearranged, and some pieces may need to be replaced. I applaud you for trying to get into some areas that are left up to us old guys, but let slow down and start much simpler!!!
Thank you for taking the time to deal with my situation, I know it is complicated and I really appreciate your response.
I really would like to build the crossovers myself since I am highly interested in this topic. I realize that passive crossovers are less than ideal in comparison to digital active pieces but my entire system is less than ideal but that doesn't mean I can't have some fun tinkering with it...
I currently have the four factory-location component speakers (low front doors, rear deck), two 12-inch subwoofers, and two amps in the car. I plan on adding the 8-inch subwoofers, two high-mounted tweeters, and two amps. Three of the amps are small and I have one adequate-sized Rockford Punch 500.2 (old class A/B amp) to power two Blaupunkt 12-inch subs in two 1.25 ft^3 boxes. The small amps are a Coustic 20x2 (tweeters), Coustic 45x2 (front 5.25-inch speakers), and a Rockford Prime 150 (8-inch subs bridged and 6x9 rears). Two of these amps were given to me, one I picked up for $10 and one I picked up for a $100. All of the speakers were giveaways/cheap finds other than the subs which were still cheap at about a $100. So that's why I'm doing something this ridiculous - since four channel amps and fancy new speakers are expensive and are hard to find.
The coustic amps will only run in full-range and the two rockford amps have onboard crossovers (adjustable low-pass, nonadjustable high pass at 80Hz).
I will be happy to add Zobel circuitry but I need a little guidance as what to use as a board for all these components and to some extent on how to wire them.
I would take a step back, and possibly make some plans and possibly start simple first. In my personal opinion using both the 8's and the 12's as subs will be cumbersome and not beneficial. Usually when you have multiple size speakers playing the same frequencies you can make things sound odd. I would start with one or the other. If you ditch the 8's and just use the prime 150 for the 6x9's you make things much easier and sound better. Once you do this, making the crossovers will be much easier since you will only be making each one for a specific set of speakers and frequencies.
When it comes to making the crossovers I would look to parts express and use google to find some other sites. I'll see if I can't find something that will guide you when it comes to physically making the crossovers themselves.
I never did consider that. I was thinking of using the 8's to crutch the bass by having a 45-60 crossover point, and have a 80-100 for the 6x9's since they are in the rear deck. I didn't think I could cross the front 5.25" speakers below 80 Hz so there would be little low bass from them.
Agreed that If I put a single set of 6x9's on the Prime 150 amp it would simplify things. In that scenario I would probably be satisfied with the built-in 80hz high-pass filter. Then depending on what I decide I would just build some 2nd order high-pass crossovers for the front 5.25's and the tweeters.
You can get crazy with crossover points once you go easy with the volume. In my setup, I have the subs from LP-50Hz, the 7" midbass from BP-50 to 500Hz, 3" domes BP from 600Hz to 4.1kHz, and the tweets from 5kHz and up. Granted like you said this requires a digital processor but it could be done with simple crossovers built into the amps.
I've had customers in the past that have tried to do what you want but once they were finished you could unhook the 8's and not notice them at all.
Like I said you could play with the crossovers and stay with low volumes to make sure you don't "hurt" anything. I would even go so far to use one track and check each set of speakers on their own.
The PC boards on parts-express.com don't really specify whether or not they could handle zobel circuitry, but I assume that they can.
Do you know of any places to find some cases for boards such as these? A case may be necessary for me since I have some of the amps under seats and there are grounds not a long ways away.
When is Zobel circuitry absolutely necessary? Or should I say, is it really that beneficial to a tweeter? There isn't any large variance in impedance in a tweeter along its movement, is there?
I surely can drop the idea of using the 8's. They will take up a lot of space in the car anyway. So then I only need to worry about making crossovers for the tweeters and the front 5.25" - since they will be on ancient amps that have no built-in crossovers. I will get specs on these speakers on Friday afternoon.
I suppose that my 8's wouldn't function well as mid bass speakers since they are dedicated subwoofers, am I on the right track here?
I would appreciate some guidance on the values of the components to use. I of course have looked at several tables and some calculator and it doesn't seem like rocket science but what is rocket science is getting the entire system to work well together with the aid of the crossovers/protection circuitry. I am really a novice to the acoustics in a vehicle (or acoustics anywhere for that matter).
I notice your setup has no overlap whatsoever in the frequency ranges. Does this have anything to do with the slopes of your crossover(s)? What about your "hole" from 4100 Hz to 5000 Hz?
Another site that I couldn't think of the other day is madisound.com. They also can help you out when it comes to making the crossovers. I would look into one of the programs that will allow you to keep things simpler and allow someone else to do the "dirty" work. Another option could be to look into any premade two way crossover since they can be a little more generic to see just where you lie in terms of sound before you put alot of time into design and building the crossover. The specs of the speakers will determine what crossover frequencies that are recommended. It will be more beneficial for you in the start to keep things simple so that you don't overwhelm yourself.
The 8's will function well as midbass, but they might not be ideal. They also may require you to get creative or destructive to install them correctly. Like I've said before, lets keep it simple on the start and move that way in the future.
I don't have any overlap, as well as holes due to speakers themselves as well the ever important acoustics of the car. I've competed with the same car for nearly 8 years and have had plenty of time to tweak and tune with many setups over the years to get where I am today. One of my closer competitors has the same model car with different equipment and completely different settings.
I like your enthusiasm, and don't stop trying to learn everything you can, but always remember that there isn't always a book, paper or even another person that can tell you one way or another how something will turn out. Keep coming with the questions and keep your mind open. Just take my advice and take your time to try things out, since no one will tell you how it will sound or if you will like how it sounds.
Coming to the realization that passive pieces for all of this is not practical I went ahead and bought an active crossover network. I have a Coustic XM-4 on the way, along with a Rockford OEQ2. I really thought that these components would work well for my setup.
What may have also changed is that I did get a set of Rockford Punch 5.25" coaxials and 3.5" JL coaxials in each of the front doors. I also hooked up the Series1 8-inch subwoofers in an isobaric "clamshell" configuration in a tiny box behind the center console of the car. I'm current working on getting a port functioning for this enclosure as I believe that these speakers will really respond to it. I'm not really sure if this will really improve the mid bass of the car or if I'm completely defeating my purpose but I'm having fun experimenting with all of this...
My questions deal with the preferred frequencies for rear-fill and the tuning capability that I will soon have with the RF OEQ2.
Now that I have a bandpass crossover for the rear 6x9's I was wondering where I should start in tuning the rear fill of the car. I figured for imaging that there shouldn't be the entire vocal spectrum in the rear, and the extreme-highs should be cut as well. What about the rear mid bass? Should the rear fill have mid bass or should it be cut?
Now, about my equalizer. What are the advantages of tuning the left differently from the right channel? At the moment I'm really viewing this as just added confusion to almost an infinite amount of available tuning - which I'm excited about to a certain extent but I'm unsure of how tuning the channels individually will help. Is there some secrets to imaging that I don't comprehend that can be improved by adjusting the channels independently?
I'm glad you started with active, I was afraid you were going to make things rough for your self!!!
The rears can be set close to the fronts LP part of the BP, and the upper end somewhere near the 2-4kHz region. I've got a set of old Quart 6.5" midbass drivers in my rear deck that aren't even hooked up right now!! I would recommend on using the drivers up front to get things started and add the rear fill once you get the front locked down.
You are right that you've opened up a can of worms but as long as you keep it simple you can learn while you tune. To start set everything in the middle (no boost or cut) and play some tracks that you know what the frequencies are, like some of the IASCA set up and tune discs or the autosound 2000 discs to find where the drivers break up when driven. The independant L/R is awesome because it allows you to move the image. The best way I can describe it is when you have pink noise playing, you can use either channel EQ for a given frequency and listen to the sound move as you adjust the EQ. Because of reflection differences, unless you are driving a McLaren F1, it helps to adjust the L or R because of glass, consoles, fabric, feet, or legs to get a stable center image.
Should I even mess with the frequency "warp" controls unless I have a RTA?
I'm a little worried that I won't know really what to listen when setting this EQ, but I guess I will start learning once I get it in the car.
This crossover is center-channel capable but is that worth doing? Would it depend on how well I can set the EQ? I would need to add another amp to have rear channels, and I have considered another Coustic 102 amp to do it too but that would make five!
Whoa Bob!!! Lets start simple. Don't worry with the center and the frequency warp since they would probably make things sound wierd and may cause you to chase your tail, so to speak.
I would like to ask your opinion on subwoofer enclosures, or at least for my situation.
Now that I've had my new 12's in the car for several weeks I'm wondering If I can improve them.
The subwoofers are matching Blaupunkt GT-series 12-inchers in two separate 1.25 cubic feet sealed boxes. They are powered by a Rockford 500S.2
The problem lies in the wiring, since they are 4-ohm SVC woofers I cannot get them wired in any configuration below 4-ohms per 'side' of the amp. The speakers are also extremely heavy-duty. They have a heavy suspension and a huge surround. I've read on the web that they may be intended for free-air applications, but Blaupunkt doesn't specify this.
I was wondering If you would recommend porting these boxes. I can surely do this for sake of maybe getting a little more power efficiency, but is it really going to improve my bass significantly over a sealed enclosure? I do have the enclosures packed with polyester-fill, about 1.5 lbs/cubic ft at the moment, but even this doesn't seem to improve them much.
What I was wondering about is the location of the port. Isn't it true that a large part of the output from a vented enclosure comes from the vent? If that is the case, will that detract from the bass acoustics in the trunk? I cannot put the porting on the front face of the box, the box isn't large enough. So, I would have to put the vent probably on one of the side-faces of the box, likely pointing towards the lid of the trunk, is this a usable scenario?
I've noticed with some jazz-fusion music in my car that the bass sometimes will really ring and sound distorted, but with some heavy metal music it is barely audible. I know this is highly speculative, but is the source entirely to blame or am I really hitting a resonance frequency of the car? If this is the case, do you think that the OEQ2 may be beneficial to fixing this problem?
When it comes to porting, it should be a completely different enclosure, and the luck that just adding a port to your box and it sounding the way you want is a chance, and may ruin a good box. The port can be placed anywhere within the enclosure, not just on one side, or specific area. In most cases the ported enclosure will be twice the size of the sealed, and due to port size may be more than that over the sealed box. Besides efficiency you could loose some power handling, or because of design cause other problems with response that may not be tuned with the OEQ.
When it comes to daily listening versus competition, I have my subs turned down, as well as the whole lower region of sound it cut because of how my setup will add significantly at around 30Hz with your head at certain locations. Before I went through and ported your box, I would play with placement and firing directions to see if you can gain some output. You will never find a woofer/enclosure that sounds great with every track or type of music since it could be the way that the engineer, artist, label or acoustics will let it sound. Take the newest Metallica CD, it was recorded hot, and sounds like crap in any car with some decent equipment. Their older stuff sounds great, but with the new mix it has clipped levels and it pretty obvious. I would try some new material and placement to see if the bass you crave comes back. You could also try bridging the amp to one driver.
I did try bridging a single subwoofer on the amp and I was unimpressed. I thought that it just ran the amp hotter and the bass suffered.
I've experimented with the placement of the woofers a lot, without any major changes. Seems to me that the best location is midway through the trunk facing the rear seats. Facing them towards the rear of the car especially makes them seem dull.
I am also reluctant to punching holes in these new boxes. These speakers probably won't respond to porting the way I want them in to in such a small box. Blaupunkt recommends a 3.5 cubic ft. box for one of these subwoofers in a vented enclosure.
I had a thought regarding the use of passive crossovers on my subwoofers...
How exactly do 2-way passive crossovers with two 4-ohm speakers attached present a 4-ohm load to the amplifier? I know this usually happens with tweeters and midrange speakers but could a 2-way passive crossover have the same effect on two subwoofers?
I'm currently facing a dilemma with a 2-channel subwoofer amp (Rockford S500.2) and two SVC 4-ohm subwoofers. I can only achieve a 4-ohm stereo load and I was wondering if I face a small penalty with a passive crossover that I may be able to get a steeper attenuation slope and bridge the amp onto both speakers as a 4-ohm load. The most ideal situation would be getting a 25-Hz high-pass filter for the subwoofers since I would like to have a subsonic filter but my amp or Coustic crossover does not have one built-in, but I could also deal with a low-pass variety to stack on top of the standard 2nd order one built-in to the Rockford amp.
Discussion Forum
Passive Crossover Advice Needed...
Posted - 10/05/2009 : 6:37:41 PM
