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Multi-Way Conventional loudspeakers with crossovers

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Old 9th April 2013, 08:05 PM   #21
system7 is offline system7  United Kingdom
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Surprisingly, Time Alignment is not to do with aligning voicecoils.

But in my experience, you need to set the tweeter back a BIT. I was lucky enough to study digital and analog filtering under the outrageously talented Prof. Tony Constantinides at Imperial College. Along with antenna Theory and the spatial Fourier transform under Doctor Clarke, which is diffraction theory at heart.

When you do it all right, and you will understand that I won't give it all away to the hopeless duffers in this ego-driven game and forum, you can get some outrageously good results with even average components.

I mean, how good is this for a 6" woofer plus 1" tweeter two way? I don't make this up.
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File Type: png 1.TimeAlignment_TwoWay_FR.PNG (20.3 KB, 193 views)
File Type: png 1.TimeAlignment_TwoWay_Phase.PNG (20.6 KB, 188 views)
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Well, there it is! Best regards from Steve in Portsmouth, UK.
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Old 9th April 2013, 08:10 PM   #22
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Originally Posted by system7 View Post
When you do it all right, and you will understand that I won't give it all away to the hopeless duffers in this ego-driven game and forum, you can get some outrageously good results with even average components.

I mean, how good is this for a 6" woofer plus 1" tweeter two way? I don't make this up.
You can tell me Steve (I am a hopeless duffer though..).
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Old 9th April 2013, 08:36 PM   #23
system7 is offline system7  United Kingdom
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Originally Posted by fatmarley View Post
You can tell me Steve (I am a hopeless duffer though..).
Well , I'll give you a clue.

I used these and a bit of time alignment (2.5cms) and a seriously clever (IMO) but simple 9 element crossover.

W 170 S - 8 Ohm

G 20 SC - 8 Ohm

It's pure quantum mechanics at heart. Think double slit diffraction.
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Well, there it is! Best regards from Steve in Portsmouth, UK.
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Old 18th April 2013, 08:29 PM   #24
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It's pure quantum mechanics at heart. Think double slit diffraction.
Hi Steve;
1st - that crossover phase alignment and frequency response is seriously sick!
2nd - HELP! I certainly don't have your pedigree in digital signal processing and diffraction, but I took your clue and tried combining various "resonators" in the forms of either series or parallel notch filters tuned at either 1.5, 3 or 6KHz in different configurations. Mostly I tried in conventional parallel driver set ups - but I also started trying a pseudo series driver set up and it is coming closer - but no way have I been able to capture all the nice aspects or your design or even come close! (worse than a hopeless duffer, if there is such a rank)

I'll put together separate postings showing what I tried - but any more clues you'd be willing to reveal? On the plus side your puzzle forced me to download and get to use boxsim and has also forced me to expand how I think about crossover networks beyond the traditional. On the down side - lots of head scratching!

Any more clues appreciated - it would be nice to actually build that thing!
Thanks - Paul
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Old 18th April 2013, 08:38 PM   #25
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Here's one attempt - a 2nd O filter with some 3kHz notches in series -
Some hope at getting good phase alignment but the rest is pitiful:
Attached Images
File Type: jpg 2order parallel notch in series schematic.jpg (20.1 KB, 158 views)
File Type: jpg 2order parallel notch in series fr.jpg (217.1 KB, 150 views)
File Type: jpg 2order parallel notch in series phase.jpg (161.2 KB, 143 views)
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Old 18th April 2013, 08:49 PM   #26
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Here is an attempt to get the steeper rolloffs you have achieved by putting series notches in parallel - tuned at -1 octave for the tweet and + 1 octave for the woof:
(phase alignment not too bad near xover - but not over a broad freq range)
Attached Images
File Type: jpg Parallel xover schematic.jpg (13.0 KB, 30 views)
File Type: jpg Parallel fr.jpg (219.5 KB, 27 views)
File Type: jpg Parallel phase.jpg (161.7 KB, 22 views)
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Old 18th April 2013, 08:54 PM   #27
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Here is an attempt to match those double impedance bumps + and - crossover in a pseudo series driver arrangement with some - resonators. Clearly I have no idea how to do this series driver stuff
Attached Images
File Type: jpg series drivers schematic.jpg (17.2 KB, 24 views)
File Type: jpg Series drivers fr.jpg (217.8 KB, 28 views)
File Type: jpg series drivers phase.jpg (144.0 KB, 22 views)
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Old 18th April 2013, 09:01 PM   #28
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So Steve - am I remotely on the right continent with any of these approaches?
Any guidance is greatly appreciated.
This all started out trying to improve my very rudimentary understanding of crossovers by looking at what was out there and "taking them apart" to the extent I could with a SPICE simulator.
Now you have thrown out this awesome FR and Phase cure that has peaked my interest to be sure.
thx
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Old 19th April 2013, 01:26 AM   #29
system7 is offline system7  United Kingdom
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Originally Posted by Nvr2manybikes View Post
So Steve - am I remotely on the right continent with any of these approaches?
Not really, you are making it too complicated.

The discussions of serial crossovers have been a torment at this forum, and I've got quite cross with some people here. But they do something rather special that you can only approach with parallel filters. An ex radio-frequency engineer like myself spots it straightaway. Radio engineers do stuff PROPERLY!

I will tell you how filters work though. Firstly "diffraction" is in any cabinet, room and drive unit. It's even in the filter. It is a power response that looks like this:

Click the image to open in full size.

You will never get rid of it, so you must work with it. The envelope is a gaussian distribution, the wiggles and cancellations reflect the wavelength. The gaussian is, AFAIK, unique in signal processing, because it is its own inverse and that is why nature (and engineers who respect elegance in mathematics) uses it so much. When you get a gaussian response, you are doing something right.

The second diagram shows how linear phase filters and the impulse response works. Everybody in electrical engineering knows this one, but few really understand it.

Click the image to open in full size.

This is a thing of great loveliness. It is known as a SINC FUNCTION. It is also the Dirac Delta function of quantum mechanics. It tells you that if a filter is steep, it makes the signal ring for a long time. The reason people don't understand it, is that it's a bit of a theoretical thing, because real world filters are causal and assymetric in response. But the transform is straightforward enough and you have to accept that any real loudspeaker will have some group delay or time signature in its response.

FWIW, group delay is the SLOPE of the phase. It's a differential relation. So phase alignment is only part of it. You also want to keep the slope fairly flat.

Hope that helps. You might think you are doing loudspeakers, but actually it's the maths of Quantum Mechanics. Which is WAY COOL, IMO.
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Old 20th April 2013, 01:40 PM   #30
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Originally Posted by system7 View Post
Not really, you are making it too complicated.
....
Hope that helps. You might think you are doing loudspeakers, but actually it's the maths of Quantum Mechanics. Which is WAY COOL, IMO.
Hmm - we might have two definitions of complicated
You know the old adage - "give a man a fish and you feed him for a day, teach him to fish and you feed him for a lifetime".... Well - with all due respect Steve I feel like your process of teaching is to describe the fish genome, the metallurgy of hook production and the organic chemistry of silk and nylon fiber production!(all while dangling a lovely fish in front of the student)
Technically I have no doubt it is fully correct and truly meaningful on some fundamental basis - but I wonder what % of those on this forum can actually make the linkage to practical crossover design?

It sure would be nice to describe your process of getting such nice phase matching and flat slope of phase change through frequency all the while maintaining flat SPL through frequency much in the way that Allen B put together a tutorial on designing crossovers without measurements.

In the mean time I hacked away at this in a more trial and error approach - starting with some LR 3rd and 4th order HP and LP filters, mixing and matching them, putting in Zoble networks and notch filters here and there, moving the tweeter z a bit back etc etc..

Can get a bit closer but still missing that nice sharp LP filter rolloff you have and a bit lumpy (a fish - but a bit of a stinker)

Thanks for pushing me on to say the least!
Attached Images
File Type: jpg trial and error schematic.jpg (20.3 KB, 32 views)
File Type: jpg trial and error fr.jpg (216.9 KB, 33 views)
File Type: jpg trial and error phase.jpg (144.2 KB, 24 views)
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