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Old 20th April 2013, 05:14 PM   #31
system7 is offline system7  United Kingdom
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When you finally get a grip on how nature works, you will find she always goes for the elegant solutions.

Click the image to open in full size.

For instance, here's the five platonic solids that exist in 3D space. 4D space gets more interesting as it goes. There is a 6th solution.

I am being a hard taskmaster here, but you seem talented so I'll persevere. I really don't do crossover design for bricklayers. Waste of time.

Here's where I got to before being ripped to pieces by someone who I had clearly gone over the head of:
Series Crossover

That was nearly there. It just needed Bafflestep. Then it all fits into place. You can lose the notches, just keep the Zobels.

That's all you get. You must work out the rest for yourself. But I will tell you where the natural point of crossover occurs:

Quote:
Originally Posted by Lynn Olson
When working with rigid-cone drivers, there are some hard choices to make: if you lower the crossover frequency to minimize driver coloration, tweeter IM distortion skyrockets, resulting in raspy, distorted high frequencies at mid-to-high listening levels; if you raise the crossover frequency to improve the sound of the tweeter, the rigid-driver breakup creeps in, resulting in a forward, aggressive sound at moderate listening levels, and complete breakup at high levels. (Unlike paper cones, Kevlar, metal, and carbon fibers do not go into gradual breakup.) With the drivers we have today, the best all-around compromise is a 2nd, 3rd, or 4th-order (12-24dB/Oct.) crossover with an additional notch filter tuned to remove the most significant HF resonance of the midbass driver.
Go for the geometric mean of the 1400Hz tweeter Fs and the 5kHz resonance of a 6.5" driver. Roughly.
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Old 21st April 2013, 11:31 AM   #32
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Quote:
Originally Posted by system7 View Post
When you finally get a grip on how nature works, you will find she always goes for the elegant solutions.

Click the image to open in full size.

I really don't do crossover design for bricklayers. Waste of time.
Thanks for the vote of confidence - hope it is not misplaced
I too appreciate nature's beauty in math.
I have a love for the Fibonacci sequence and fractals and as I am sure you know the Platonic solids are intimately related to the Golden Ratio and thus the Fibonacci sequence. (I am sure you have probably read it - but if not Mario Livio's book is a good read) What this all has to do with crossover networks I haven't a clue yet, but will keep at it with your insightful albeit cryptic clues. (Will be vacationing in Spain for a few weeks coming up so may be a while)
Don't be so hard on bricklayers - Brunelleschi was a bricklayer at heart (some very interesting brick designs were needed to accomplish the largest freestanding dome in the world)
Cheers
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File Type: jpg dome.jpg (11.6 KB, 138 views)
File Type: jpg bricks.jpg (10.9 KB, 137 views)
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Old 21st April 2013, 01:01 PM   #33
system7 is offline system7  United Kingdom
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Ah, yes. It is good to take a break from a problem...the brain gets a rest and you come back refreshed and looking for even more symettry.

Click the image to open in full size.

That circuit is OK as far as it goes, but I don't like the overall impedance or that damping resistor in the bass shunt arm, and it's just not quite pretty enough...

But your Phi (1.618....) is surely only a minor player in the universe. It is merely algebraic for one thing. I'm all for including it in speaker boxes and bricklaying, but that's about it.

The transcendentals are much more interesting, and it's surprising how few of them we actually use. Exponential e (2.718....) and Pi (3.14...whatever it is...LOL) are the backbone of our engineering maths. And as we have discovered, Quantum Mechanics, Information Theory and Loudspeakers use the same principles right down to the uncertainty principle relating energy to time.

Quote:
Cantor confindently asserted that the transcendentals were in a vast majority to the algebraic numbers and did so without exhibiting a single conrete example of a transcendental number. Mathematical Historian Eric Temple Bell said of it, "The algebraic numbers are spotted over the plane like the stars against a black sky; the dense blackness is the firmament of the transcendentals."
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Old 21st April 2013, 10:20 PM   #34
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I was wrong.

Last edited by strawberry; 21st April 2013 at 10:43 PM.
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Old 21st April 2013, 11:00 PM   #35
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What's wrong with the impedance? It's basically 6 ohm. The 2.2 ohm is to lift the woofer a little, I think. Or are the impedances added at the crossover frequency? With some phase, gumming up? Maybe still close to 6?

Last edited by strawberry; 21st April 2013 at 11:13 PM.
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Old 22nd April 2013, 12:29 AM   #36
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Normally the tweeter would play the loudest at very high frequencies. With the 2.2 ohm that end will be attenuated. The other resistor attenuates the shelf below the high end. The woofer is also affected by these resistors with capacitors, the way the curve of attenuation looks like. Less clean capacitance gives less lift for the woofer near the crossover point. The woofer probably has a nasty peak near the crossover point.
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Old 22nd April 2013, 02:31 AM   #37
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Default Bricklayers

I won't ask for anything from the likes of you
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Old 23rd April 2013, 10:08 PM   #38
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Damn you System 7 - I can just not get the Xover steep enough near the Xover point (and match the phase at the same time)! This is the best of several tries so far where I prioritized being down ~15dB at the 5KHz cone breakup and tried to be low on the HP filter for the tweet Fs at ~ 1400Hz. Almost buildable, though the lack of crisp filters leads to ~3dB sag in the middle. - not sure about that high frequency impedance - is that ok? Also 2 more parts than you used -
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File Type: jpg tweek 10 FR.jpg (214.4 KB, 22 views)
File Type: jpg tweek10 phase.jpg (142.7 KB, 21 views)
File Type: jpg tweek 10 schematic.jpg (22.5 KB, 29 views)
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Old 24th April 2013, 06:05 PM   #39
system7 is offline system7  United Kingdom
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@strawberry: Bit hurt by your lack of faith there, my old fruit! You had it right the first time. It IS interesting. You who likes a bit of ripple in the old Chebyscheff filter.

@phivates: Don't go all sensitive on me. Irony is misunderstood by Americans. Why is that? Beats me...

@nvr2: Very good effort. You understand the need to define source as well as load impedance just like the radio frequency folks. But surely I'd told you it was series filter, not a parallel. Different animals. They do different things. Conics in Geometry shows the relationship to my way of thinking. Parabolas versus Hyperbolas.

Anyway, here it is. A thing of great loveliness, IMO. Just like Mike Creek always used to say, every component punches its weight and does several things. The tweeter Zobel can be a 22R resistor instead. Either way is good.
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File Type: jpg Conics.JPG (21.8 KB, 23 views)
File Type: png system7_Time_Aligned _Filter.PNG (13.6 KB, 46 views)
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Old 26th April 2013, 10:00 PM   #40
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Quote:
Originally Posted by system7 View Post

@nvr2: But surely I'd told you it was series filter, not a parallel. Different animals. They do different things.

Anyway, here it is. A thing of great loveliness, IMO. Just like Mike Creek always used to say, every component punches its weight and does several things. The tweeter Zobel can be a 22R resistor instead. Either way is good.
System7 - Truly a thing of beauty - sorry for not full catching on to your clues earlier. I caught that you said series crossovers did something special - but then at the same time you pointed me to the ESP posting that said they were basically the same except for different sensitivities to woofer impedance changes or back EMF - so I misunderstood your message. At the time I tried my hand with a couple of Series arrangements but was completely baffled by how both HP and LP curves moved with each change of a component value. When I saw the email saying you responded to this post revealing the secret - I was both elated that I would get to see the magic and deflated for failing - so I did not open the response without going back again to your clues and trying my hand at the series crossover again. Here is where I got to with a redo of your clues - not the full answer but not bad for just 8 components .
When I get back from vacation I'll play around some more to hopefully get a deeper understanding - then maybe I'll make one of these for my Daughter. THANKS again for pushing me on this - it was fun!
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File Type: jpg series v1 schematic.jpg (14.7 KB, 47 views)
File Type: jpg series v1 fr.jpg (217.4 KB, 27 views)
File Type: jpg series v1 phase.jpg (146.0 KB, 19 views)
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