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MultiWay Conventional loudspeakers with crossovers 

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7th March 2008, 10:34 AM  #1 
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Join Date: Jan 2005
Location: Brighton

Formulae for calculating crossover magnitude and phase based on component values
I'm looking to build a spreadsheet into which I can enter speaker SPL and phase and then inductor and capacitor values for given crossover networks and get a summed output. To do this I need the formulae for the effects of inductors and capacitors on signals but I can't seem to find this basic stuff. Could anyone point me in the right direction?
Am just looking to do 2nd order 2way crossovers initially but presumably once you know the sums then one can extrapolate from there. Thanks! Alex 
7th March 2008, 09:45 PM  #2 
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Join Date: Jun 2002
Location: USA, MN

Look for Jeff Bagby's Passive Crossover Designer. It does what you want without needing to know the formulas.
Someone could give you the formulas, but they would have to type it all out.... and then not know if you even know how to use them. In my mind, if you knew how to use them, you could derive them yourself.
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8th March 2008, 09:29 AM  #3  
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Quote:
Alex 

8th March 2008, 03:06 PM  #4  
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Location: Cape Town

Re: Formulae for calculating crossover magnitude and phase based on component values
Quote:
Plot the magnitude of that function versus f for the magnitude response, and the phase versus f for the phase response. This approach is accurate and easy  if you aren't afraid of complex numbers. 

8th March 2008, 06:20 PM  #5 
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Location: Indiana

If you're going to draw a schematic, you might as well draw it in LTspice (free from linear.com) and have the entire magnitude and phase response plotted automatically.
You will probably want to remember to include the parasitic series resistances of inductors and capacitors.
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19th March 2008, 07:35 PM  #6 
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Have been messing with LTspice and also working on an excel spreadsheet. Suffice to say that my brain is melting...
Whilst I get my head round all that I've designed a simple 2nd order Butterworth crossover @ 750Hz (as this bass cab will rarely be onaxis I felt the flatter power response was more important than onaxis response). Have used the actual impedance at that point, not nominal impedance for the component calculation. Hopefully as the impedance stays +50%/20% an octave either side of the crossover point, the filter response won't be too far from theoretical? Alex 
19th March 2008, 11:08 PM  #7 
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Here is how to do a 2nd order lowpass to get you started
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20th March 2008, 08:17 AM  #8 
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Thanks!
Can I just clarify a couple of things on there? U0/U1 is the transfer function. R is the resistance of the inductor. U0/U1 is the magnitude of the transfer function. To calculate how the woofer and midrange combine acoustically, I presume I also need the argument (phase) of the transfer function? Alex 
20th March 2008, 04:08 PM  #9  
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However, it messes things up if you start to split the equation into magnitude and phase and try to add them afterwards. It is better to just add the two complex transfer functions. Are you familiar with complex numbers and the jwmetod? 

20th March 2008, 06:40 PM  #10 
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Join Date: Nov 2003
Location: Brighton UK

Hi,
Why are you doing this ? It may save time making a set of purely theoretical calculations. The reality is real crossovers done properly bear little resemble to any simplistic approach, which this is. You can go on line to easily find the simplistic (and wrong) values. http://www.mhsoft.nl/CrossoverNetwor...udspeakers.asp /sreten. 
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