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Old 20th November 2012, 01:22 AM   #1
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Default 3 way crossover help

Hello, am new here but have been registered for a long time. I've been stuck on designing a new crossover for a pair of homemade 3way speakers i aquired from my friend. here is some of what i have came up with.
speaker drivers are

model/frequency range/imped/sensitivity/fs /watts

tweeter-focal tc120td5/1,650-22,000Hz/6ohm/93.5dB /812.7Hz/150 max
midbass-focal 8v413 /30-3,500Hz /6ohm/89.5dB /29.8Hz /120 max
woofer - NHT 1259 /19-1,000Hz /6ohm/90dB /19Hz /300 max

The below attachment schematic picture i drew is a rough draft of combining the low pass,high pass, and L-pad schem that i also attached below.
I'm not sure if it'll work so please if anyone has any constructive and or professional advice, before i cause my speakers irreparable damage, i thank you in advance!
i also attached a 2nd order reverse polarity 3-way schem as a plan B if anyone thinks that's be better or not.
Attached Images
File Type: jpg high pass 2nd order.jpg (53.4 KB, 237 views)
File Type: jpg low pass 1st order 200hz.jpg (44.3 KB, 232 views)
File Type: jpg L-pad attenuation circuit.jpg (45.0 KB, 227 views)
File Type: jpg 3way speaker pic.jpg (93.2 KB, 229 views)
File Type: gif 3way schematic drawing.gif (48.9 KB, 267 views)
File Type: jpg 2nd order reverse polarity crossover schem.jpg (97.5 KB, 87 views)
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Old 20th November 2012, 01:28 AM   #2
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Hi, I've moved your post to the multiway forum, as this is a passive crossover rather than a line level active one

and welcome!!

Tony.
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Old 20th November 2012, 03:29 AM   #3
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your rough draft schematic won't cause any damage to your speakers, but, a couple of questions - where did you get the impedance values from? - these should come from an impedance plot of the driver, at the chosen crossover frequency.
Why did you choose those particular crossover points and slopes? (links to the driver specs & plots might help)
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 20th November 2012, 03:31 AM   #4
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Hello,
Click the image to open in full size.
The topology of this schematics is good but i see some improvements
1. Reverse the polarity of the tweeter
2. On the mid increase L2 to 1mH and add 10 ohms in series with C2

Have fun.

Last edited by jerome69; 20th November 2012 at 03:36 AM.
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Old 20th November 2012, 04:01 AM   #5
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The trouble with passive crossover networks is that you have to level match, and you have to calculate the reactive elements based on what they will see looking out in the rest of the circuit. The "nominal" or rated impedance of a given driver is rarely what you'll have at the frequency you want to do the crossover at. On an 8 ohm driver, it's often more like 15 ohms at 2kHZ, for example. My personal experience trusting published impedance curves has not been very good, but may be better than using the nominal rating. You can measure them, or if you don't have the equipment to do that properly, a good way to get it right is to use a calibrated mic and a pinknoise signal source to see the response of each driver independently. Start with calculated values, and tweak to get it where you want it. This is much easier to do this with a simple one pole (6dB/oct.) circuit. The more complex the circuit (2 pole, etc.), the harder it is to calibrate it. This is why many (including myself) have gone to active crossover circuits with separate poweramps for each driver. With the active approach, it's easy to make it VERY accurate, and with 4 pole cutoff rates. If you had the woofer in a closed box, you could also add low end active EQ, to make the woofer acoustically flat to 20 or 30 HZ (which I do and I love it!). Using active EQ on a ported woofer is not recommended.

My latest speaker is a 3 way, with a 4 pole active crossover at 150HZ, and a one pole passive crossover at 7kHZ. If you're above about 6kHZ, the damage done by a passive crossover is less noticeable.

One other point; if you set the crossover point near where the driver naturally rolls off, this natural rolloff will introduce phase shift, which will add to the phase shift in the crossover electronics. In the end, you might get a flatter frequency response when you reverse the phase of one or more drivers, relative to the driver that is adjacent to it in frequency. Hope this helps.

Last edited by Bob Richards; 20th November 2012 at 04:05 AM.
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Old 20th November 2012, 08:21 PM   #6
system7 is offline system7  United Kingdom
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No point in reinventing the wheel. It would do you no harm to study some existing designs. This three way by Visaton called the Stralet is much the same as what you are trying to do.

Sim it in Boxsim and adjust your acoustic centre depth (point of sound origin) to get the drivers aligned as in your cabinet. I'd look up some Visaton drivers of similar dimension and voice-coil inductance to get an idea of how it will all work and possible changes. The optimise button usually does a good job.

FWIW, the bigger midrange capacitor usually goes at the INPUT to the filter. Keeps the load tidier.
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Old 20th November 2012, 08:37 PM   #7
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Hi,

If you can't measure, model and stay well away
from x/o calculators. See the FRD tools guide.

rgds, sreten.

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Last edited by sreten; 20th November 2012 at 08:39 PM.
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Old 20th November 2012, 09:20 PM   #8
system7 is offline system7  United Kingdom
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Oh, one other thing. Visaton do some standard crossovers for well-behaved drivers in typical boxes. A choice of crossover frequencies and doubtless you would need some wirewound resistors for attenuation to get the levels right. But not a bad start for your simming.

Crossovers

For all that, some drivers play together nicely, and some are stinkers...
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Old 20th November 2012, 09:59 PM   #9
xjr100 is offline xjr100  Europe
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Quote:
Originally Posted by elves1111 View Post
... designing a new crossover for a pair of homemade 3way speakers....
You cannot build good speakers without measurements.
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Old 20th November 2012, 10:23 PM   #10
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Quote:
Originally Posted by xjr100 View Post
You cannot build good speakers without measurements.
and maybe not even with that
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