What difference does the "order" make with x-overs

Hi all,
I notice that some speaker cross-overs (passive) are "1st order", "7th order", etc. What does this mean and is one better than the other? Why? Any suggested readings/sites for getting information about this or cross-over/designs in general?
Thanks and happy listening!
A hundred people are all probably responding at this one. The order refers to the rate of rolloff in db above or below the xover freq. (i.e. high-pass, low-pass filters, all-pass (a combination of the first two)), since a speaker w/ a 3000hz xover the drivers just don't stop like a brick wall and change hands above or below that frequency. There's a portion of sound shared by the drivers and each "fades" into the next. 1st order rolls of at 6db an octave beyond the xover point; 2nd order=12db an octave rolloff; 3rd order=18db etc. Most don't go beyond 4th order. The highest I've seen is Joseph Audio's 120db octave: that's a 20th order. Obviously the 1st order is one in which the driver's will share the largest region of overlap. These have a cult like following (Thiel and Vienna acoustics do them). Only problem is the driver has to be able to play well beyond the crossover freq. w/ these types and so alot of drivers aren't suited for 1st order. Beyond the rate of rolloff (6db for each step up in order) is the phase relationships. Some orders change phase relationships between the drivers. I'll bail here because I'll probably mess it up. I've read several books, but none that I thought explained it very well. But no one xover type is really superior to another, in large part it depends on the driver's being used and the system itself. In a three way with a midrange in a sealed enclosure there's a mechanical rolloff only half that off a bass reflex design. So the designer would take that into account in his crossover choice to achieve a specified total rolloff into the LF driver. The sum of the mechanical rolloff and electrical rolloff is often referred to as the system alignment. 7th order would correspond to 54db an octave rolloff (a bit obscure). Which basically mean an octave above the crossover freq. the drivers output would be down 54db, fairly steep. An octave is just a doubling of the frequency. So at 3,000hz-an octave above would be 6000hz.
In very simple terms the lower the order the more the drivers share content. There are other by-products such as phase, time, signal reflection, energy storage and impedance that may be effected by cross-overs. Please keep in mind that besides "order" there are passive, mechanical(co-axial drivers), active and digital as well the absence of cross-overs in speaker designs (although all speakers have cross-over like "symptoms?") . As far as better, there are many different opinions (sometimes pasionate). I think most would agree that in an ideal world there would be no need for them (and some actual designs exist). Most (but not all) speaker designers who put an emphasis on time and phase use low order cross-overs despite the extra burden placed on adjacent (and further) drivers. Others believe that this is not a consideration and prefer to let different drivers work in there optimum range. Although cross-overs are an important design element, they are only part of the equation. For what ever it's worth while appreciating other designs ( Maggies, Martin Logan, Acustats, Aieral, Wilson) I am consistantly attracted to low coss-over designs even though they might have a very different sonic signature ( Thiel, Vandersteen, Dunlavy ). I am very much looking forward to listening to other designs (Walsh drivers, Tact digital crossovers, etc.) I hope this helped you.
This is very hard (impossible I think)to explain in a short reply at a forum. For a decent short explanation (12-13 pages) try True Audio. www.trueaudio.com/st_mr1.htm. There are two parts to this article. the second substitutes "mr2" for mr1 in the original site.

Another short one is AudioControl at www.audiocontrol.com/techpapers/techpaper102.pdf

If you want more buy Vance Dickason's book Loudspeaker Design Cookbook.

You might also do a search at www.madisound.com (one of the better diy speaker building forums)under various words such as 2nd order, 3rd order. Some of the most common filters are given names Linkwitz-Riley, Butterworth, Bessel. Use those names too. There is a wealth of info at the Madisound forum on this topic and the proper use and effects of each type of filter.

Good Luck.

I remain,
One short addition to Ezmaralda11's fine explanation. An Octave is a doubling or halving of frequency. 20hz to 40hz is an octave. 40 to 80, 80 to 160 are also octaves. 3200hz to 1600hz is an Octave going down.

If a crossover is 2nd order it is going down 12db per octave. If the crossover is 2nd order and set for 3200hz it is going to roll off 12db by the time it reaches 1600hz. This is actually a bit of a simplification but it gives you the general idea. Read the articles I mentioned in the other post for a little more info.

Your question has been pretty well answered above, so I won't elaborate except to add one point. As noted, the higher the "order" of the crossover, the more severe the roll-off. What was NOT mentioned is that as the "order" of the crossover goes up (say, from first order to second order), there is also a phase shift. The higher the "order", the greater the shift in phase. This can present a real problem to properly integrating the drivers. Thiel and Vandersteen both use first-order crossovers because their speakers are designed to be time and phase correct -- so, using a first-order crossover results in fewer complications with phase shift.
As is always the case, Sdcampbell's opinion is the kind of offering that proves he is a real world guru in this hobby.

One thing that I would like to add to his wisdom is that in addition to the issue of integrating the drivers into a "system", as the order of crossover goes up, so does the difficulty in driving the loudspeaker. I cannot deny that a more complicated crossover looks impressive, on paper.

However, in reality, each component in a crossover network acts as a "spring" to an amplifier's power output. If you will, a speed bump. Requiring more and more current to overcome the crossover, to get the drivers moving. Often, brute force solid state is the only way to go. A large number of this type of amp can sound etched, shrill, slow, ponderous, overripe, bloated, hashy, or electronic.

In my opinion, the more simple a crossover topology, the closer one is to the amplifier itself. The closer one is to the music itself. Not always a good thing. Especially, if the upstream components are not musical, natural, or grainless. But, for those of us with an appreciation for tubes, it is EXACTLY where we WANT to be.