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Old 5th October 2006, 07:27 AM   #1
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Default matching speakers with an active crossover

Can anyone here please explain in simple English (most explanations I've come across are confusing) the fundamental requirements/ideas for setting an active crossover with a pair of speakers?

I understand that every setup is diff, but aren't they all the same in the sense that you basically need to adjust the output on your active crossover to match the effiency of your speakers. Is this true?
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Old 5th October 2006, 01:54 PM   #2
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hmm...this is my opinion...you have to match the output of the crossover with power handling of the speaker, to avoid damaging them. Then the same has to be done for the frequency tuning. I use a separate equalizer before de xo and tune it differently as i change the music...hope it can help!
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Old 6th October 2006, 07:25 AM   #3
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thanks, raikkonen. more questions for you

if i understand you correctly, basically there are 2 things i need to do to integrate an active crossover with the speakers.

1) control the power output from the crossover to avoid damaging the speakers (i.e., kind of like a resistor, right?)

2) tune the frequency so that the sounds coming to the speakers do not sound separate and blend together

Can you elaborate #1 a little more? I'm unclear on how you do this.
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Old 6th October 2006, 08:15 AM   #4
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No.

Basically as each drive unit has different sensitivity (i.e. how much sound comes out for a given input voltage/power) you need to set the output levels on the active crossover (can also be done by the level control on the power amp after the crossover) to take account of this.
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Old 6th October 2006, 08:51 AM   #5
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wiat wait wait...usually we have source-->eq-->active xo-->power amp-->speakers (my system)

everything depends on what you already have, for example the speakers.
they have power handling and sensitivity, and the mix of both gives you the real music power you hear.
my suggestion is to make a calculation: if you have 100w speaker and you know tha max gain of your ampli you can tune the xo to give you the right output. Then you will have a system that can give you all the power it can give, BUT it won't be equalized.
I think will be better to have a system like this, where you can decide to have ALL the available power or less but wwell balanced power.
obviously many people wouldn't share my opinion, but we're heve to discuss.
let me know if you can make calculation or if you need a hand!
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Old 6th October 2006, 11:33 AM   #6
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To be honest that is an appaling way to set your system up, the sound will be totally out of balance. It's also utterly pointless as you will never be listening anywhere near full power.
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Old 7th October 2006, 04:22 AM   #7
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Thanks for the input so far.

Let's take a more concrete example. Here's the spec for a sample speaker:


Outside diameter 221.4mm
Cut out 186.4mm
Depth 90mm
25.4mm = 1" = 2.54cm

Nominal Impedance 8 Ohms
Recom. frequency range 30-2000 Hz
Short term max. power 300 W
Long term max. power 120 W
Sensitivity (1W/1m) 90.5 dB

Voice Coil Diameter 39 mm
Voice coil height 16 mm
Air gap height 6.0 mm
Linear coil travel (p-p) 10.0 mm
Max. coil travel (p-p) 21 mm
Magnet weight 0.64 Kg
Total weight 2.2 Kg
Voice coil resistance 6.0 Ohms
Voice coil inductance 0.5 mH
Force factor 9.0 N/A
Free air resonance 27 Hz
Moving mass 29.0 g
Suspension compliance 1.1 mm/N
Suspension mech. resistance 2.0 Ns/m
Effective piston area 220 sq. cm

Vas 75 Liters
Qms 2.6
Qes 0.39


What would be the ideal/logical way to set the active crossover to make use of the speaker above?
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Old 7th October 2006, 05:37 AM   #8
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Basically, you are asking "How do you design a speaker?"

Level setting is just one of the factors to consider. You'll need to measure and adjust levels of each driver accordingly. In a three way I've found it easiest to leave the midrange alone and adjust the woofer and tweeter levels to match.

Despite the long list of specs provided, there is hardly anything there to go on for setting up a crossover. Power handling is way down on the list of things to consider when it comes to setting up a crossover. Sure, you'll look at it for determining if the driver can go loud and low enough to meet your goal, but once you determine that it has little bearing on crossover design.

You have an 8" driver. How do you plan to use it? Is this the midrange in an open baffle system or the woofer in a semi-full range two way?

How loud and low to you want the system to play?

What does the driver's top end look like? Does it stay smooth to near 2000 or does it show breakups and energy storage at 1000? How is its distortion profile? Does it get ugly loud and low or does it stay clean? Is EQ required for flat response IN THE SYSTEM?

What are you crossing it to? Above and below. Is it going to be used with a subwoofer? Is the system sealed, ported, open baffle? Can the tweeter/midrange go low enough to keep you away from cone breakups or do you need to push it a bit?

An example using the Dayton RS225. It has a bit of energy storage/cone breakup down close to 1,000 Hz. If this is a three way system, crossing over to a 5" midrange like the RS150, you can use a low order slope at 3-400 Hz. and the nastiness will be well down below the signal.

If you're trying to make it a two way, you need a tweeter that can be crossed over very low. Say you choose the Seas Millennium. Despite its recommended 2kHz. crossover, if you go with 48 db/octave slopes you can run it down to 1,000 Hz and still hit 100 db with reasonable distortion.

This should give you some idea of the thought process for setting a crossover. It is similar whether going passive or active.
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Old 7th October 2006, 05:55 AM   #9
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You sure give me a lot to think about. Very helpful though. Thanks!!!

Basically, I was just trying to have a clear picture of where all the pieces are and what they really do.

I wanted to get this active xo

http://www.marchandelec.com/xm26.html

but I'm stuck at the next step, which is integrating the XO with any pair of speakers. I want to build my own speakers or use one of those KITs, but it's the configuration with the XO that puzzled me.
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Old 7th October 2006, 11:03 AM   #10
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For a bit more depth into the process, see www.linwitzlab.com, the grandfather of active crossovers. He also offers boards that have a bit more flexibility and functionality than the Marchand kits.

Another option is to keep an eye out in the group buy section - I have run several active XO board buys and will probably do another shortly. The group buy boards are a single channel 2 way or bandpass with a pair of notch/peak EQs, shelving low pass, a Linkwitz transform and an all pass section for phase correction. Daisy chain multiple boards for multi way crossovers.
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