First Order Crossovers: Pros and Cons

Me too; I'll bring the barbeque! I would take issue with there not being mechanical crossovers within the cone. We are not talking about roll offs at the edges of the cones bandwidth, but different parts of the cone producing different frequencies. Probably, this is semantics, as I would also say that a driver with a whizzer cone has a mechanical crossover within the driver itself, as well. I think that we are describing the same thing in different language.

I drove my Fs with a then-new Threshold 400A, so you can figure out how far ago that was. At the time, I preferred my Dayton-Wright XG-8 MK3, series 3 speakers, which could soak up the power pretty well too. I remember thinking that, if I could afford an 8000A, all my power problems with both sets of speakers would magically dissapear. My comments are limited to the stock product, of course; clearly, you have gone a long way to modding yours. Thanks so much for the insight. So do you prefer the pulled pork or beef ribs?
Marty

Drubin: One set of my F's are "smoked" and awaiting a "full tilt" driver rebuild as per Bill at Millersound's suggestions. The other set is packed up. I am currently down to using what was primarily my HT system for both music and movies now. After relocating, i hope to have everything up and running, but i'll have to install a new AC system. My latest purchase ( 450 lb iso transformer / voltage regulation / surge suppression system ) should be here next week or so for that house. Only problem is, i don't know where i'm moving to as of yet. I may end up becoming a Hoosier and moving out of the "Land of Lincoln" if things keep going the way they are here. Illinois is becoming more and more of a "police state" as each day goes by.

Viridian: I hear what you are saying about each individual "layer" of material within the F and / or A, but this is completely different than how a whizzer cone works. The whizzer cone has a completely separate level of output / radiation pattern / frequency response than the main cone. On the other hand, the segmented Walsh design uses multiple types of material that pass signal from one into the other. If any one of the segments didn't pass signal into the other in a relatively uniform manner, you would end up with a loss of surface area. When you lose surface area, you end up with the associated reduction in low frequency extension. As anyone that has ever had a decent running pair of F's or A's know, weighty bass is definitely not their problem.

As to the Threshold 400A that you had, i looked up my notes on this amp. As most of you know, i'm a pretty vocal supporter of Nelson Pass designs, so what i have to say about this amp may come as somewhat of a shock.

First of all, the 400A is definitely not a stable amp. That is, it changes frequency response / transient response / distortion characteristics as impedance varies does so to a pretty noticeable degree. Sonically, the bass is solid so long as the amp isn't pushed. Once you start to throttle the amp, the bass gets soggier. This has to do with the lack of power supply reserve ( not enough filter capacitance ). While the warmth region and lower midrange are pretty decent, as frequency climbs, the upper mids and treble regions were noticeably forward and bright. This tends to highlight any type of lean recordings, exacerbating the problem. With most SS preamps, this amp would tend to introduce a very noticeable sibilance and glare problem.

Once into the top octave, the treble response fell off sharply. This was not as noticeable as one would think though due to the high frequency emphasis just below this point. A definite lack of brass shimmer to cymbals with more of a pronounced "raw & steely" sound.

Due to the increased upper midrange / treble output, transients seemed to be "in your face". The harmonic structure seemed slightly disjointed because of the lack of balance between the lows and highs.

Much of this could have been DRASTICALLY improved by working on and improving the power supply. After all, everything that the amp is capable of ( or doesn't do well ) starts in the power supply. This is why so many aftermarket modifications center around cleaning up / stiffening ( increased reserve ) / improving speed in the power supply of gear. If you've read any of the overly long AC based threads that i've posted, i've commented time and time again about how important the proper design of the power supply is.

As a side note, Nelson Pass has an article about how important the power supply is on his website. As to the Dayton-Wright's, Nelson also used these speakers to test various loudspeaker cabling on. He mentions these speakers in another article on his website, as they used to send some amps into convulsions. Using such a reactive / high demand speaker provided an excellent test bed to see how an amplifier would respond to changes in the load that it saw via altering the speaker cables & their electrical characteristics. As mentioned in that article, some cables allowed the amp to drive these speakers with no problems whereas other cables caused the amp to shut down. As such, there's an obvious audible and measurable difference there i.e. sound from the speakers with some cables and no sound with other cables : )

As far as ribs go, i'm trying to cut down on eating meat. When it comes to good barbecue though, i don't know how i could turn down either beef or pork. That is, until i get serious about my health and dining habits. My midsection is starting to protrude and as hot as it gets in the summer, i'll only be miserable if i don't lose some weight. Either that or convert some of that "mid section speed bump" into muscle on other parts of my body. Can anyone else relate??? : ) Sean
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One of the major advantages of the first-order crossover, which isn't mentioned often enough, is the fundamental simplicity of the network. Every increase in crossover order is accompanied by a proportional increase in the number of network elements, and the audibility of this problem is severe. Even a single high-quality inductor or capacitor in the signal path is audibly degrading when compared to none at all, which is why so many people decide to live with the severe compromises present in single-driver speakers. It's hard to describe this effect until you play around with it-- my best description is that it "sucks the life out of the music". And the higher the slope, the worse this problem gets. Not very scientific, I agree, but the degree to which this is true is stunning when you hear it.

Also, I would take issue with the research quoted by Joseph. One of the basic facts about second-order crossovers is that they require at least one of the drivers to operate in inverted electrical phase, to avoid a null in frequency response at the crossover frequency. This inversion alone is enough to utterly destroy the integrity of the musical signal, and any comparisons to fourth-order crossovers at that point are completely meaningless. Since no one in their right mind would use second-order networks in the first place, it doesn't say much that fourth-order sounds better than second-order. This paper, like a lot of quoted research, might be true in its own limited environment, but it doesn't even begin to tell the whole story in the real world.

The main drawback to first-order networks, as stated above, is the need for very wide bandwidth and very high quality drivers, with no severe "breakup modes". Thankfully, these are available at a price from Scan Speak and Audio Technology, among others.

Disclaimer: I am the manufacturer of the Ultimate Monitor, a two-way speaker using first-order series crossovers and Scan Speak Revelator drivers.

Best,
Karl

Nice to see you here again, Karl. (Maybe you've been around and I just missed it.)

Hey Sean: this is my first posting ever, but I couldn't resist. If you're watching the midsection then stay away from the Italian beefs--they'll give you a first-order speed bump in no time flat.
Say hi to Chicago for me,
Charlie