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MultiWay Conventional loudspeakers with crossovers 

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11th March 2012, 11:43 PM  #471  
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Join Date: Aug 2008
Location: Portsmouth UK

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I'm hoping there is a flat impedance third order series lurking at some set of values at 1000Hz. Just not getting it... @speakerdave. I am using an 8 ohm source resistor as a convenience to easily measure the overall impedance, which is usually flat for paired butterworth filters. This is nice because such a load won't be affected by the type of amp you have. You can see the impedance is flat 8 ohms here for 2nd order butterworth series filter. Usual 12dB per octave and 3dB crosover points. 

12th March 2012, 12:44 AM  #472 
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Location: The Mountain, Framingham

So the 8 ohms in front is for modeling but wouldn't be used in a built up network. (also explains the 6dB drop)
Which is the impedance curve? The phase curves are of network voltage? 180 degrees apart means the tweeter polarity should be flipped? And are R1 and R2 real added resistors or are they the simulated drivers? David Last edited by speaker dave; 12th March 2012 at 12:46 AM. 
12th March 2012, 12:55 AM  #473  
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In fact the thirdorder parallel Butterworth is also flat impedance, and IIRC, flat amplitude. I'm just hoping AllenB can do better than me at some component values for the series 3rd order. My 0.5, 4/3 and 1.5 ratio really didn't hack it. Last edited by system7; 12th March 2012 at 01:04 AM. 

12th March 2012, 07:44 AM  #474 
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System 7,the ratios that suit a third order constant resistance series circuit are 0.67R, 1.33R and 2R. The second order case in theory has a 3dB rise,but with real world speakers, where we measure the parameters and design the xover accordingly; the problem is nonexistant.Labouring the point a little further,to achieve the 3dB gain would require the drivers to be coincidently mounted and have identical amplitude velocity characteristics in the xover region .Peaks an dips occur by virtue of spacing and phase effects even with perfectly flat(freq response) drivers.Text book explanations are not helpful in the real world and the current fad concerning baffle step compensation is yet another example of "heading off madly in all directions."

12th March 2012, 11:13 AM  #475  
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System7. I notice that onaxis the drivers are in quadrature, does this count? Quote:


12th March 2012, 11:33 AM  #476  
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Location: Brighton UK

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Neither am I and like assymetric 1st order parallel I don't think a series version of the solen split (6dB x/o point instead of 3dB) is possible. It seems to me the purpose of the solen split is where your crossing over two drivers at a point where they both begin to rolloff, the mid above that point and the tweeter below. If your lucky the solen split values will end up approximating 2nd order L/R acoustic, if your unlucky the standard butterworth arrangement might give a better acoustic result. I can't find any information describing what the the problem is that the Solen Split is supposed to fix and how it does it. rgds, sreten. BTW your filters will behave differently with a 8 ohm source impedance and with zero source impedance, the two cases are not the same. (TinaTi has an impedance meter function, replaces the voltage source.)
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There is nothing so practical as a really good theory  Ludwig Boltzmann When your only tool is a hammer, every problem looks like a nail  Abraham Maslow Last edited by sreten; 12th March 2012 at 11:43 AM. 

12th March 2012, 11:46 AM  #477  
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In my oppinion, aiming for constant resistance input Z will be at odds with achieving flat response. As such it is a very poor design choice. David 

12th March 2012, 10:44 PM  #478 
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I overlooked a query from system 7(#473) in which he sought confirmation of the // third order Butterworth xover constants.My old sources say ,that they are 1.5R, 0.75R and 0.5R.

12th March 2012, 10:48 PM  #479  
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Location: Portsmouth UK

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I did actually finally find a good link for the 3rd. order series crossover values @ 3kHz which were published by Jeff Bagby years back: Passive Crossover Design Calculator The inductor ratios were as you said 3:2:1, the capacitor ratios were a bit more subtle, eh? 3:3/2:1, and the L/C ratios and Q altogether deeper which is why my measly brain got confused... Very nice work, AllenB. We are there now on the constant resistance networks, which have a certain elegance. Anybody got any idea what the 4th. order series values are? 

12th March 2012, 11:41 PM  #480  
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It seems to come down to the usual flat power/symmetrical lobing issue, of which the second option is normally preferred, so why not allow the impedance to peak? You could always conjugate it. Quote:
Quote:
By pulling the crossover points apart, the 6dB points can be matched easily enough. The phase, which is already 90 degrees separated will separate further. Reversing one of the drivers will bring them closer than before. However the phase responses will still not meet up and so there will still be some lobing. The drivers will not sum entirely onaxis and there will be a droop of a couple of dB. The full response will come in above or below. I have typically been of the notion that a 4.5dB compromise split makes sense. 

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