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Old 18th April 2016, 02:49 AM   #1
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Default Help breaking down the Dayton III crossover

I'm still a relatively newbie to speaker building and certainly a n00b to crossover stuff. I've unpacked a few schematics now, so I'm stepping up my complexity level a little bit now. I'm looking at the Dayton III project specifically trying to unpack exactly what everything in there does - perhaps even see a response graph of it in action if anyone has such, but I haven't found one.
Speaker Project - The D III -- 8/17/2011

Here's the crossover schematic:
Click the image to open in full size.

It's obviously a parallel HPF/LPF setup. I think I've got a good grasp on the tweeter. It's just a 2nd order at 2k with a zobel network in there, though I'm not exactly sure what the zobel network does. I know it 'neutralizes the effect of the voice coil inductance', but what does that mean to my ears? Does it make the ohm load (hence the volume) flatter across the spectrum, which makes it smoother? Does this ultimately lead to more detail and a crisper sound across the driver spectrum?

I'm still a bit fuzzy on the woofer stuff. The project description says it's a first order, so I presume that's what L2 is doing. The C3, L3, and R1 group look like a filter, but I'm not good enough yet to figure out the frequency, Q, dB, etc of it without finding a calculator for it. I think C4 and R2 are fiddling with the ohms, but if hooking 2 4-ohm drivers in parallel already gives you 2 ohms total, hooking another 8 ohm resistor in parallel won't give you 8 ohms to match the tweeter - it'll give you 1.6. Not really sure what's going on with that bit...?

Once I figure out what everything does in there, my next challenge is to modify the LPF to use the DC160 8-ohm drivers instead of the 4 ohm drivers. Yes, they are slightly different, I know, but they're pretty dang close. Close enough for some crossover practice, at least, I should think. Plus, I've got 4 laying on the floor collecting dust that could be making smooth tunes.

Pro tips and explanations are definitely appreciated!
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Old 18th April 2016, 03:19 AM   #2
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OK on the tweeter, the 4R is for attenuation, and the 2.7uF in parallel with it means that at higher frequencies it is NOT attenuated. This is probably to bring up a drooping top end.

On the woofer the LCR is a notch filter I'm not going to take a guess as to the frequency but it is probably for taming breakup.

C4 R2 is actually a zobel and will be flattening out the naturally rising impedance of the woofer.

Tony.
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Old 18th April 2016, 03:22 AM   #3
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The resistor and capacitor in the tweeter circuit are there to lift the higher frequencies somewhat. Zobel compensation refers to making an impedance consistent with frequency (resistive looking), and C4 and R2 appear to be an example of this kind of thing. In this kind of use they would only achieve this with regards to the load seen by the filters, and the speaker as the load.. in other words while Zobel compensation could be used anywhere, this is the limit of this implementation. It is used either for helping to get a certain response or for simplifying design by creating a simple load to calculate for.

The RLC combination is reducing the response at 3k7Hz, maybe to do with cone breakup? The L and C set the resonance and the resistor sets a limit for the effect.
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Old 18th April 2016, 03:49 AM   #4
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Try XSim to simulate your crossover. Parts-Express has FRD and ZMA files for all Dayton drivers which you can import to XSim.

This is a fantastic and free experimentation and learning laboratory. Play with it for a week and next year you'll be selling speakers at the Rocky Mountain audio festival.

Best,

Erik
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Old 18th April 2016, 02:46 PM   #5
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Ahh! Thanks for the input! I knew I was somewhat close, but it seems to make more sense now. Thanks all!

Thanks for the reminder on Xsim too, Erik. I had fiddled with that once upon a time, but couldn't find it on my computer the other day when I went to sim all of it out. I went back to the excel version, but I like Xsim much better. Good to have a fresh link again!
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Old 19th April 2016, 01:22 AM   #6
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Wow, that looks terrible! Where did I go wrong?

Click the image to open in full size.
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Old 19th April 2016, 04:08 AM   #7
AllenB is offline AllenB  Australia
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Try again with your image, maybe it's too large or something.
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Old 19th April 2016, 04:55 AM   #8
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Weird. I can see it just fine. Is this any better?

Capture.JPG
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Old 19th April 2016, 05:52 AM   #9
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That's much better. Remember you can use the ground symbol to reduce the wiring. Just remember to connect the amp (-) as well as the speaker (-) to it. This reduces maintenance as you move things around and cleans up the schematic. It's up to you whether you like that style or not though.

That's quite a low-treble peak there.

Without measurement it's hard to tell, but you probably need to add 1.3" or so to the woofer distances to get the phase matching correct. I'm not sure if this is mentioned in the original article. For more information, see here.

For another MTM design, since I'm close with the author, see the LM-1C here.

Best,


Erik
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Old 19th April 2016, 07:06 AM   #10
AllenB is offline AllenB  Australia
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@ kc, play with the values a bit. You might find some useful gains changing the first woofer inductor and the tweeter resistor. The lower peak might be the result of the woofer resistor across the tuned filter or the tweeter high pass components.

@ erik, any suggestions on displaying multiple traces in xsim?
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