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Old 31st August 2002, 06:14 PM   #1
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Default Infinite Slope Crossover

Joseph Audio has a patent on this crossover.
http://www.josephaudio.com/essay.islope.html

I haven't done a patent search but I did find an
explantion on how it works on the madisound forum.

snip.....
---------------------------------------------------------------------------------
It works using the mutual inductance of windings inside a transformer.

Picture a transformer, with one primary winding, two secondary windings, the turns ratio being 1:1:1.

Connect the amp to the primary winding. Connect a driver one of the secondary windings. Now connect
the other secondary winding to the driver, except inverted and with a capacitor in series.

At low freqs, the cap disconnects the second coil and the output is largely unaffected.

At high freqs, the cap provides an AC short, which then opposes the formation of the mutual inductance
which would be necessary to induce current in either secondary winding. Output current drops toward zero
at high freqs because the mutual inductance between the primary and secondary drop toward zero at the
affected freqs.

The reflected impedance will begin to increase as the capacitor starts to provide the short. The amp
side sees the resulting cancellation of the mutual inductance as an open circuit on the secondary.
Also as the capacitor provides the short, the driver starts to see only the paralled DCR of the two
windings (and the cap) as the magnetic field necessary to create the inductance can't form (enough) a
round the closely coupled bifillar windings when one is inverted.
--------------------------------------------------------------------------

So... the question is.. is it possible to make an active crossover using this "patent" idea using a transfomer and capacitor and an op-amp to get a 120db/octave crossover ?

Sounds too simple to be true - lol

hmmm....
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Old 31st August 2002, 06:55 PM   #2
jwb is offline jwb  United States
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I don't know how the x-over works, but I have a pair of Joe Audio RM22si floor standing speakers, and they sound awesome. They were the most musical speaker of all the models I auditioned under $2500. I don't know how much is attributable to the crossover, but I think it must be a large part of the sound of this speaker.
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Old 5th September 2002, 02:25 AM   #3
ben goh is offline ben goh  Singapore
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Hi all,

Please go to this link.

It might be of help to you.

http://www.fortunecity.com/marina/po.../elliptic.html
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Old 5th September 2002, 03:19 AM   #4
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The active implementation is also known as a cauer filter. Don Lancaster has a section on it in his Active Filter Cookbook.

dave
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Old 7th September 2002, 06:53 PM   #5
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I just read through the explanation quickly so if I missed the point I appologised, but wouldn't you need some series resistors in there too?

At high frequencies there would be a looped current in effect through the two secondary windings which would only be limited by the output resistance of the secondaries in series?

Just a point that came into my head - if the coil resistance of the secondaries is adequate to restrict current in the "high stop" operation of the circuit ignore me, lol

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Old 7th September 2002, 07:30 PM   #6
tvi is offline tvi  Australia
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<i>US Patent 4,771,466 Inventors: Modafferi; Richard September 13, 1988
<a href="http://164.195.100.11/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1='4771466'.WKU.&OS=PN/4771466&RS=PN/4771466">Multidriver loudspeaker apparatus with improved crossover filter circuits</a>
Abstract
"A loudspeaker system includes at least two loudspeaker drivers, together with an electrical crossover network having filter circuits with at least two separate mutually exclusive frequency passbands. The filter circuits comprising the crossover network each possess brick-wall amplitude responses, i.e., passbands with very high band-edge amplitude vs. frequency response slops, on the order of 100 dB/octave in the better embodiments. The high passband band-edge slopes, which are realized by the inclusion of transmission zeros in the separate crossover filter transfer functions, takes together with further appropriate crossover filter transfer function synthesis causes the separate loudspeaker drivers comprising the loudspeaker system to function independently of one another in their contribution to total system acoustic output. It is shown that the loudspeaker system permits an accurate approximation to the ideal delay function in acoustic space, while minimizing acoustic wave interference among drivers operating in adjacent frequency band, and also reducing overall system nonlinear distortion."</i>


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Old 19th September 2002, 10:39 PM   #7
Evaas is offline Evaas  Canada
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Default good timing

I too loved these speakers when I heard them some time ago. Just today I started getting curious about this particular crossover, and a I found this thread via the search. I like how you guys are one step ahead of me

my question is how does this crossover affect the phase relationship of the signals? I do know know enough to figure it out from the schematic.
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Old 20th September 2002, 08:36 PM   #8
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I'm no expert either, but all those inductors in the signal path have to affect the phase surely?
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Old 20th September 2002, 08:54 PM   #9
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Quote:
Originally posted by annex666
I'm no expert either, but all those inductors in the signal path have to affect the phase surely?
Indeed. Phase is totally frelled at the XO point, but because the XO is so very steep this is only a problem over a VERY small part of the spectrum.

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Old 20th September 2002, 09:12 PM   #10
Evaas is offline Evaas  Canada
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Question totally frelled

One thing I did notice about the speakers was that there was an enormous "sweet spot" and the imaging was dead on thoughout.

maybe I need even more about phase relationships though... ok so I understand how you can get interference if the tweet and woof are trying to drive the same signal but out of phase over a certain wide frequency range. But we've sufficiently narrowed that frequency range so all thats left is how your ears interpret it. What I'm wondering is does the phase relationship affect the way you hear the music? I'm inclined to think yes because there are people who assert that you can hear absolute phase (although I'm very curious as to what it sounds like, and am slightly skeptical) but this seems to fall along those lines...

I think its in my nature to look for hidden drawbacks. If phase isn't a problem, then what else is? Why isn't anyone else using this type of crossover? Is it only because nobody else has figured out how to get around the patent, and nobody else thought of this circuit till now? Dave, you already pointed out that a variation is in a textbook, so how could they patent it anyhow? Although I guess that the difference in active and passive crossovers is enough to call it new technology...

Thanks,

Evan
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