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Crossovers?


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bogey 
Copper - Posts: 68
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Posted: February 10, 2006 at 11:00 AM / IP Logged  

I have been considering going to a 3-way active crossover system with a separate amp for sub/mid/hi. My first question is what to do about the mid frequencies? Most crossovers I've seen only give you options to send the mid say frequencies >80. How do you cut out the high frequencies? (I believe this is called bandpassing?) Do you have to place a cap to cut those frequencies? If so, what should I look for that will accomplish my goal and not degrade signal.

Also, I've read on here that active is the better way to go, over passive crossovers, but there are some cautions that one must be aware of. Are there any online tutorials?

stevdart 
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Posted: February 10, 2006 at 6:23 PM / IP Logged  

Read what "Mr. Active" says here:  http://sound.westhost.com/bi-amp.htm

The unit that you eventually decide to use will provide bandpass capability for the mids.  Before you go this route of using active through the entire range of freqs, ask yourself what it is about the mids-to-tweeter transition, using the provided passive, that you want to improve on.  The passive has an impedance correction and certain tonal characteristics that you will miss using an active filter.  That might be one of the things you heard that you should be cautious of.

...and that's about all I know about active filters.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
DYohn 
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Location: Arizona, United States
Posted: February 11, 2006 at 10:20 AM / IP Logged  
If you are going to bi-amp or tri-amp you can certainly use passive crossovers, but unless you are very skilled and experienced with passive network design I highly recommend using a good 3-way or 4-way active crossover instead.  This will give you the ability to fine-tune the system to match the driver's capabilities rather than guessing, building fixed passive networks and being stuck with whatever results you get.  You will also need to know the fs of each driver to choose your crossover points, and an RTA really helps getting the system response curve tweaked and the amplifiers gain matched to the drivers sensitivities (although a good SPL meter can be used for that if you know what you're doing.)  You may end up needing a good EQ to tame some harshness depending on a number of factors including driver location.  Setting up a good bi or tri amped system is a challenge but can result in some incredible SQ when done correctly.
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bogey 
Copper - Posts: 68
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Joined: October 23, 2003
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Posted: February 11, 2006 at 9:02 PM / IP Logged  
Thanks for the article. I understood a fair amount of it, but some of it was a little over my head. May be you can clarify a few things. He mentioned using a 20uF capacitor to prevent DC from reaching the tweeter voice coil (section 3.2 of article). So if I'm using a 3way Active Xover do I still have to worry about this?
He also talked about "padding" to help equalize each speaker's sensitivity (i.e. Low 90dB / W @ 1m, Mid 93dB / W @ 1m, High 92dB / W @ 1m from section 1.10). Pad the mid's 93dB by 3dB to equal the low. Is this something I have to worry about with an active crossover? I wouldn't think so, but I want to make sure.
Is there any electrical components that I'll need (i.e. capacitors, resistors, et cetera)? I wouldn't think so. I would think it would just be a matter of tweaking the crossover and amp gains.
Next question is choosing the appropriate amps for proper output to each range (low, mid, high). I had a basic understanding of the equations he gave (although I couldn't figure out where the button is on my TI-83+ to calculate the "antilog" for P2 = antilog (dB / 10) * P1 from section 4.2). Anyway, I have a Butler Tube amp (4x75 @ 4 ohm) and soon, hopefully, I'll be getting the Seas/Lotus Ref. tweets(89.5 dB, 6ohm) & 6.5 woofers(90 dB, 4ohm). I'm not sure of what sub and sub amp I want to run. Perhaps Dayton Titanic 10 or an Adire Shiva or Koda and not sure about the amp (I want solid sq in the lows, but don't want to break the bank). If I send two channels to the tweets @6ohm (56w?) and two to the mids @4ohm (75w) will they provide roughly equal output? If this is good, what kind of output should I look for from my sub amp? According to the article's formula it would call for 118w to the sub(for the Dayton with an approx. 88dB Sens.), but that seems a little light. Although, the article did say tri-amping was the eqivalent of doubling your amp output.
DYon said: "You will also need to know the fs of each driver to choose your crossover points..." Is "fs" the equivalent of "Free Air Resonance"? How do I use the fs to determine crossover frequency?
Please forgive the length. I do appreciate your help.

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