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Multi-Way Conventional loudspeakers with crossovers

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Old 25th January 2006, 11:46 PM   #1
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Default question that i cant seem to find the answer to:

many of you have probably seen my other hi-vi b3s crossover question thread, a few ppl helped with it and for that i am thankful...

there is still one technical aspect of this project that i do not seem to understand...it deals with the use of an active subwoofer crossover vs. the use of a plate amp...

it says very specifically in the project details NOT to use a plate amps speaker level outputs as the high pass crossover for the b3s because it has some sort of impedence conflict that results in a peak...for this reason, an impedence flattening circuit must be added to protect the b3s...this is costly and therefore not recommended

however, it does say to use an active subwoofer crossover....maybe i am unfamiliar as to what this is, but i assume it to mean an active low pass crossover to keep the highs away from a subwoofer....now my question is, how does using an active subwoofer crossover work in this case? the two hivi b3s need some sort of high pass to protect them from overexcursion....do active subwoofer crossovers ALSO have high pass speaker outs? how do these high pass speaker outputs differ from a typical plate amps high pass speaker outs? how do these outs avoid creating an impedence conflict with these drivers?

sorry i am being a pest with this issue i just cant figure it out and im trying real hard to understand....thanks to all replies

EDIT: this is all in reference to this project: http://www.zaphaudio.com/audio-speaker18.html
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Old 26th January 2006, 03:09 AM   #2
Stocker is offline Stocker  United States
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I can tell you what there is on *my* plate amp. for the high-pass crossover:

A single capacitor per channel. That's it. If you didn't build the amp or change the caps, you probably don't even know what value they are, nevermind the quality... This is a "passive" crossover... no transistors, no op-amps.

An active filter will have whatever input and output cutoff frequencies you design into it. An active filter will have an input impedance way, way, way higher than this sort of thing and will likely not mess with the signal anything like as much.

HTH

-David
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Old 26th January 2006, 03:20 AM   #3
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so active crossovers have a higher input impedence, which means it wont conflict with the drivers....

passive crossovers, such as a simple capacitor, do not have high input impedences and therefore need an impedence flattening circuit to prevent any bad things from harming the drivers...

is that it?

EDIT: does HTH mean happy to help, cuz if it does, then thank you for helping, and if it doesnt....well....thanks for helping
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Old 26th January 2006, 06:06 AM   #4
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I don't know if you are powering these 3 inchers from a receiver or from a separate pre amp/power amp combo. If you have access to the signal line BEFORE it hits the main amp section- a preamp/power amp combo has easy access, a receiver will have to be opened up and traced down-you can use the Passive Line Level Xovers at our own Planet 10's site.

Although the word "passive" is used in the title, the fact is that if you put a passive filter BEFORE the final amplifying device-whether it is tube or transistor-you now have an active filter.

That is what this section shows you how to do.

It is probably a good idea to use these with a solid state device, be it receiver or separate amp, than a tube amp, since solid state amps usually have higher input impedance than tubes.

You can check back with us to make sure the math is correct. I have not used one, but I have not heard anything bad about them, either.
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Old 26th January 2006, 09:33 AM   #5
chrish is offline chrish  Australia
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What is meant by use an active subwoofer crossover is that you should split the signal into high and low before it is amplified (at "line level" using active (transistorised) components). If you have a surround sound processor you will be able to do this with the unit, the "sub-out" rca jack on the back of the unit will be a line level signal that will be just the low frequencies and the signal to your main speakers will be just the higher frequencies. The main speaker out connections on the back of the receiver will have all the appropriate signal processing done and all you have to do is connect your new speakers up using speaker wire. For the sub you would take an rca interconnect cable and connect that to the amplifier you are using to power the subwoofer. That amp will be the plate amp un the sub if it is powered, or a separate power amp if your sub is not powered. If you do not have a processor (or home cinema receiver) you will have to build a line level crossover that will split the signal into a sub 150hz line lever (non amplified) signal to go to a separate amplifier to power your woofer. This unit will also provide a line level stereo output of the >150hz signal for you to feed into your amplifier before going to your speakers. You will have to purchase or build an an electronic crossover to do this. If you are having difficulty trying to work out what is meant by active crossovers and how to integrate a sub using one, then perhaps it would be better to buy a crossover rather than build one yourself. In any case, I think you will probably get better help if you can tell us what your existing stereo components are so we can try to help you sort out what you will need to buy and how to set it up.

Good luck!

chrish
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Old 26th January 2006, 02:50 PM   #6
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wow! that link, and both posts, are really pointing me in the right direction....

my situation is as follows: these speakers are for use with my computer....i have a soundcard with rear speaker outputs and front speaker outputs....it also has a channel with center/sub out written on it, but i cant get that one to work so i assume its busted or i am an idiot....either way, i have more than one output, and it would be possible for me to use a passive line level crossover on either or even both...

the sub is part of an existing logitech computer speaker system...not the best, but it will do seeing as i need only a little low end extension from these drivers...i can hook it up to the rear speaker outs

the hi-vi b3s will be run by an aiwa minisystem with about 30 watts per channel....the minisystem will be recieving the signal via RCA cable coming from the front speaker out on the soundcard....

so...according to what u tell me, it IS possible to bypass using an extensive impedence flattening circuit if i put a crossover on the RCA cables? the circuits on the link given previously seem pretty simple and wouldnt be that expensive to build, so i am definately interested

all i need to figure out now is:

-exactly where i want to cross them over (what freq)?
-exactly HOW i would go about hooking up a resistor and capacitor to RCA cables?

i am thinking first order at either 200-250 Hz
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Old 26th January 2006, 02:53 PM   #7
Stocker is offline Stocker  United States
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The subwoofer channel, is it not working with a subwoofer driver's voice coil hooked straight up to it, or is it not working as the input to a sub amplifier? Is there a software setting to turn on the output from that connector? It would not be surprising to have a software switch setting for straight stereo or "2.1" output, with the sub out disabled in stereo.
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Old 26th January 2006, 02:59 PM   #8
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Which sound card are you using?
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Old 26th January 2006, 03:00 PM   #9
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the 2.1 logitech system i have right now is all run thru the same 1/8" jack....i tried finding some way to switch it on, while having that 1/8" plug plugged into the center/sub out jack...and it didnt work....maybe if i had an independent subwoofer without the 2 satellites, it could work then...

i found another problem as well...those calculations assume i know the input impedence of the amplifier, but i do not know what that is....

the specs of the amp are found here...page 22 on this PDF file shows different specs....

http://www.eu.aiwa.com/no/pdf/former...s/ZL100EZE.PDF

how the heck am i gonna figure out what the input impedence is? cuz i cant calculate high pass crossovers without it

EDIT: the soundcard is soundblaster live! 5.1 digital
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Old 26th January 2006, 03:09 PM   #10
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Look into http://kxproject.lugosoft.com/index.php?skip=1. Those are drivers for creative sound cards that are supposed to let you set up any crossovers that you might want.

I have a dell 5.1 SB, and I never got the drivers to work with that, so I can't really say how well it works. If it's an original creative card, then the drivers should work. Anybody that knows more about this, please help out.
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