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Multi-Way Conventional loudspeakers with crossovers

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Old 9th November 2012, 10:56 PM   #1
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Default NEWBIE Need help with a two way design ...

Hi everybody

I m trying to learn how to design a loudspeaker so if you see some dumb newbie questions I m sorry for that .
I picked 2 drivers to begin with :

Woofer : Scanspeak P17WJ-00-008
Tweeter : Scanspeak D2905/930000

then I ran Speaker Builder pro to calculate internal volume for woofer and I ended up with a vented box with volume of 22.8 liter and one 9cm long and 5cm diameter port for fb of 45hz . (I didn't go for a custom volume ,just went with suggested volume for maximum flatness)
then I desiged a 3rd order butterworth crossover at 2500hz as suggested and lPad for woofer and series notch filter for tweeter @ 650hz as it is the fs of tweeter
(I attached crossover circuit)
but when I ran simulation in Boxsim I have a big spark around 4000 hz (Image attached) so I changed the series notch filter to 4000hz and the spark is gone (crossover circuit attached) but I have a another small spark around 2500hz now(Image attached) .

so where did I go wrong ? or is it as good as it gets ? can I add BSC to solve it or it s not because of that because as I change the placment of drivers it doesn't change that much ,...

thanks in advance
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Old 10th November 2012, 12:44 AM   #2
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Without the raw driver responses on that graph, it would be hard to give advice. Did you measure the speakers or trace the published graphs, or what? Are the real driver impedance plots loaded? Anyway, I can say a couple things:
1. watch your impedance, you're hitting ~2Ω on that first plot
2. The hump at 2500Hz is just the drivers summing. Start the rolloff sooner on one or the other, and it will go away, although if phase isn't being included correctly, the sim won't be accurate there anyway.
3. You seem to have a rising response to about +6dB in the treble - do you want that?
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Old 10th November 2012, 01:42 AM   #3
system7 is offline system7  United Kingdom
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Ahmad, my friend, you are going seriously wrong in applying that 650Hz LCR Fs impedance correction filter to the tweeter. You simply don't need it here. Changing it to 4kHz is just making it worse. Lose it altogether. You are getting out of your depth.

Very nice Vifa P17WJ-00-08 Polycone Woofer. And the Scanspeak Classic D2905/9300 Tweeter looks OK too.

I would try this simple Visaton 3kHz Filter for a bookshelf. Add a 10W wirewound resistor around 2.2R or 3.3R to the tweeter input filter if the treble is too bright.

Naturally we could do better. Read Lynn Olson for deeper thoughts. But bear in mind Lynn is using an effectively 4 ohm bass setup.
Attached Images
File Type: jpg Visaton_3000Hz_Generic_Crossover.JPG (35.1 KB, 124 views)
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Old 10th November 2012, 12:16 PM   #4
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thanks dumptruck and steve . I didn't import anything (raw driver responses ,real driver impedance plots , ...) I know it s hard and almost impossible to have a accurate answer without them but it doesn't matter because i don want to build this speaker ,i m just trying to learn and understand crossovers and how speakers behave . and another thing is I donno how to import driver's raw graphs and plots into boxsim yet :P, I could easily go with a already added visaton driver but I wanted to learn how to work with other drivers as well .
anyway thanks again for your tips , I changed L2 from 0.75 to 2.3 mh and L3 from 0.25 to 30 mh and I got rid of mid low 3db boost and added 2.2ohm before the tweeter crossover and I got a almost flat respond from it (the 2500hz spark still exist but it s smaller) then I removed snf as steve said but I got a very big spark arond 3.5k to 4k , so I reattached it again , so am I good now ???

Quote:
you are going seriously wrong in applying that 650Hz LCR Fs impedance correction filter to the tweeter. You simply don't need it here. Changing it to 4kHz is just making it worse. Lose it altogether.
why is it wrong ? as you see i removed it and i have that peak around 3.5k-4k , maybe I can get rid of that without snf and with changing the rolloff poit ?

what EASY to use () software for simulating drivers and box and crossovers you guys suggest ?
Attached Images
File Type: jpg with snf.jpg (260.7 KB, 24 views)
File Type: jpg without snf.jpg (275.4 KB, 14 views)
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Old 10th November 2012, 12:42 PM   #5
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I don't understand..... If you didn't import any responses what are the curves for woofer and tweeter in the graph? A 12 db hump in the tweeter response at 4K seems very odd.

Tony.
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Old 10th November 2012, 12:48 PM   #6
ersa191 is offline ersa191  Equatorial Guinea
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Quote:
Originally Posted by Ahmad_tbp View Post
thanks dumptruck and steve . I didn't import anything (raw driver responses ,real driver impedance plots , ...) I know it s hard and almost impossible to have a accurate answer without them but it doesn't matter because i don want to build this speaker ,i m just trying to learn and understand crossovers and how speakers behave . and another thing is I donno how to import driver's raw graphs and plots into boxsim yet :
You can use SPL copy for FRD/ZMA files
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Old 10th November 2012, 03:24 PM   #7
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Unless there's something wrong with the response you're using, that peak is something you are causing, not something to get rid off. That's why you don't need the LCR. You're probably ending up with too high of Q. Go to the last tab "frequency response electrical". Does the HF curve look crazy? You can figure this out yourself. Start changing the values of the HF components (just a basic topology, no LCR) and watching what happens.
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Old 10th November 2012, 05:10 PM   #8
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thanks as I said i didn't import any raw driver responses ,real driver impedance plots , ... and it seems that boxsim assume it as flat , I don want it to give me accurate results i just want to learn crossover and speaker behavior ... i will start to change values and maybe drivers and I ll let you know
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Old 10th November 2012, 05:18 PM   #9
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this raw driver frequency respond i got from box sim
Attached Images
File Type: jpg Drivers Respond without any crossover.jpg (260.3 KB, 21 views)
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Old 10th November 2012, 06:02 PM   #10
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Oh, well if that's what you're doing, it's really nothing like what happens with the real driver measurements. I mean really, not even close. As a learning experience, you would be better off loading some of the included drivers, as you mentioned.
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