AR (Acoustic Reality) series xo... some theory please

[rabbitz]

I've noticed a lot of builders such as Andy G, Ken P, Tony G who use series crossovers are now using the AR series or a variation.

Having played with them recently, the results are extremely good and better than I achieved with the classic series crossover, but does raise a lot of questions such as:
* Is there a set of formulae for starting points?
* How is the crossover point calculated?
* I'm trying to understand the function of the C1 cap in the scheme of things and what is happens as you go lower or higher. My tweaking came up with different conclusions as going up helped the mids on one occasion and the same happened with going down in value on another??

They are so easy to work with by adjusting the R1 resistor and L2 inductor, but I'm trying to get some theory behind them or pointed to somewhere that has more info than what's on the AR site.

http://www.acoustic-reality.com/ar-sxo2.htm

[sreten]

Originally posted by rabbitz

* I'm trying to understand the function of the C1 cap in the scheme of things and what is happens as you go lower or higher.

Hi,

You can look at it as a kind of Zobel which flattens the impedance
changes as you go up in frequency. Omitting it is like omitting the
capacitor on a normal drivers Zobel network, wastes loads of
power, unnecessarily lowers impedance and the resistor power
rating must be increased drastically.

Like a parallel networks Zobel capacitor and resistor, fine tuning
is possible my moving away from the "ideal" Zobel values. Typically
for example the resistor value for the Zobel is double "ideal".
It still limits the impedance rise due to inductance but wastes
less power and gives higher impedance at high frequencies.

edit : unlike a parallel network though C1 effectively becomes
a series capacitor for the tweeter and R1 become the attenuator
resistor for the tweeter, hence the comments on removing C1.

Series c/o's are tricky things to get your head round, IMO they
can work well in certain circumstances but have no "magic".
Try downloading the circuit sim TinaTI and play around with them.


/sreten.

[soongsc]

Having played around iwth series XO I would say the results are very pleasing. I would not use any other topology unless specifically requiring biamping.

I would not think the design process is as simple as mentioned at the site because almost anything I change will change a lot. Basically half of the power goes though the drivers and half goes though the other componenets. What you are doing is to tune the current flow and how it runs though the drivers. Increasing impedance on one path effects the whole current flow. C1 does it's magic by redirecting the low frequency current though the wooffer, in combination with L2 effectively creates a baffle step function. If your XO point is around the baffle step rising point, you may not need L2, but L1 will be large. It's very complicated to explain the theory because all your time is spent on tuning how the current flows. I think if you using s SPICE program to to some simulation you will get a better feel for what's going on.

With parallel XO designs you change the high frequency path with little effect on the low frequency path and vice versa. This is not so in series XO. The results are rewarding.

There are actually some US patents that address this called the capacitorless XO, which in reality is not possible. Another company I think it's called Diaural claims to license the technology, but I have not seen any design that actually is capacitorless unless you try to leave the impedance response as it is.

Never assume that Zobel networks are going to react the way you think, adding such circuit changed many things in a way unexpected when I first tried it.

[footstony]

Hi rabitz

I have been playing around with series xovers.

I like to tune by ear.

I have been experimenting with the capacitorless and AR series crossovers with a widerange and helper woofer.

I like the capacitorless series xover, I can't believe it's patented!
For the uninitiated this consists of a coil across the high frequency driver and that's it! good if your woofer is well behaved at higher frequencies. At high frequencies both drivers are in series so the woofer response is shelved slightly, at low frequencies the tweeter is shorted.

I also like the AR series xover without the cap. works well when the high frequency driver is more sensitive than the woofer so the resistor is a higher value say around 20ohms which wastes less power. If the resistor value is closer to the value of the woofer I would use a cap so that the resistor is out of circuit at low frequencies.

p.s. greetings from sunny Melbourne!

Regards Philip

[Irwin AR]

From the ARXO page it seems that there's one important link that's already dead (study done by John Krevs).And that link has everything you need to know of what's going on as you change
every component values including the big cap.

I remember having it somewhere (made into pdf) but really hafta
dig in me old unused HD

But honestly, what's really getting me going with this topology
earlier was the aid provided by Jeff B (SeriesCrossoverDesigner simulator in the FRD group).There's a project file for this topology
that lets you work around with it and also change your own
drivers (own measured).From there you'll be able to see what's
really going on....

Seriously i can't thank him enough on this one

[Geenius]

L1 acts as the high-pass function for the tweeter! It must have a very low Rdc otherwise some low-frequency energy will go through the tweeter (especially if you use a low Re tweeter like the Vifa XT's).

L2 is to compensate the baffle-step. A Zobel can be added across the woofer terminals to make it more effective at higher frequencies.

If you leave out C1, you need R1 otherwise you will have a short-circuit across the teminals. Effectivly R1 flattens the system impedance. Being across the terminals it also eats power and therefore you loose some system efficiency. R1 must therefore be able to take some power (use at least a 20watt resistor) if you want to play loud. R1 also tames the output level of the tweeter.

I also don't understand why it is patended, if you make C1 smaller (like 10uF) and L1 larger (like 0,33mH) for example, you have a standard 1st order series crossover with baffle step compensation. When is it an Acoustic Reality crossover and when is it a standard series crossover?

The Souns Faber Extrema is an example of a capacitorless parallel crossover.

[rabbitz]

Many thanks for all the information as it's always nice to have some insight into anything different that one tries.

I played around in Jeff Bagby's spreadsheet last night and it illustrated what was happening with each component change.... much clearer now and a better understanding.

Yeah, I tried that link on the study and it's a shame it's dead.

Philip.... greetings from wet Newcastle (which is usually sunny).

[soongsc]

Originally posted by Geenius


..
I also don't understand why it is patended, if you make C1 smaller (like 10uF) and L1 larger (like 0,33mH) for example, you have a standard 1st order series crossover with baffle step compensation. When is it an Acoustic Reality crossover and when is it a standard series crossover?

...

When something is patented, it just means it's gone through the process. It does not mean that it will withstand legal contesting. The Government wins whichever way any disputes result.

[Snickers-is]

How can they claim to have invented anything new?

It reminds me of the patent application section in the Voice Coil magazine. Some guys filed a patent application on a parallell capacitor over one of two serially connected woofers.

I wonder how they are going to defend such a patent

[Doc.Doom]

Have great results with this type also, but ran into some problems too. The L3, I take is the combined inductance of the woofer and L2 which procede it, correct? It seems to be so, I have 4 identical woofer wired in parallel pairs then in series with final 8-Ohms. I am effectively using the three way example from the site and am rolling off the two woofers after L3 as a bass-woofer. With this I was wondering how the L2 effects the total Le at the end of circuit? I may wire the entire system as a two way and disregard the 3way. but I was hoping to gain some seperation in frequency to better control mid bass responce.
The 4 woofers are F6 HI-VI Research mid-bass drivers. that display some breakup modes at 14kHz I placed a trap filter at 11kHz to 2130Hz where I believe it to be safely crossed over, allowing smooth transition out to tweeter. All drivers share some box volume and are wired as three drivers in a three way. It sounds good but there seems to be something missing or too much happening someplace. Still listening