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First Order Crossovers: Pros and Cons

I wonder if some folks might share their expertise on the question of crossover design. I'm coming around to the view that this is perhaps the most significant element of speaker design yet I really know very little about it and don't really understand the basic principles. Several of the speakers I have heard in my quest for full range floorstanders are "first order" designs. I have really enjoyed their sound but do not know if this is attributable primarily to the crossover design or to a combination of other factors as well. In addition, I have heard that, for example, because of the use of this crossover configuration on the Vandersteen 5 one has to sit at least 10 feet away from the speakers in order for the drivers to properly mesh. Is this really true and if so why? Another brand also in contention is the Fried Studio 7 which also uses a first order design. Same issue? Could someone share in laymans terms the basic principles of crossover design and indicate the advantages and disadvantages of each. Also, what designers are making intelligent choices in trying to work around the problems associated with crossover design? Thanks for your input.
dodgealum
cdc
1,412 posts
 
Perhaps the single drive IS the perfect solution. They just don't want people to know. Satisfied people don't need to upgrade evry few months.
cdc
1,412 posts
 
Perhaps the single driver IS the perfect solution. They just don't want people to know. Satisfied people don't need to upgrade every few months.

What happened to the "edit my post" feature so I don't have to post twice.
skrivis
30 posts
 
I don't think I've ever seen a perfect driver, let alone a perfect full-range driver.

Given the limitations of current materials, I think that it's possible to do less damage by using multiple drivers, even though you need x-overs.

The end result seems to be better than what you get with single-driver speakers. Even the most savvy (IMO) of the single-driver designers (Ted Jordan) doesn't really recommend single-drivers. He recommends line arrays of mid-tweeters, along with subwoofers.
dodgealum OP
976 posts
 
Not sure if anyone is still paying attention here but I was just reading a review of the PMC OB1 loudspeaker in which the reviewer states that the crossover is wonderfully designed and produced a plot of phase coherence that is the best he has ever seen. According to the review, the crossover maintains the drivers in perfect phase with each other except for a small abberation at one point in the frequency spectrum. Given all that has been stated above by the first order crowd, how can this be given the use of 24db fourth order slopes? I'm sure I'm missing something here as this discussion lost me a long time ago. I'm just wondering how a steep slope design like the one in the OB1 can produce such perfect phase relationships as measured in the review.
eldartford
4,262 posts
 
Dodgealum...There is no magic! No matter who designs the crossover each section, which is worth 6 dB, causes a 90 degree phase difference between Hi and Lo. Both Hi and Lo phase vary with frequency, but the difference remains 90 degrees. Of course, as you go away from the filter break frequency (crossover frequency) the amplitude of the Hi and Lo signals diminish so that phase is not a big issue.

So, a 12dB crossover has a phase difference of 180 degrees, and if you hook the tweeter up with reversed phase the audio output will be back in phase. With the 24dB crossover that you mention the phase difference is 360 degrees, which is the same as zero, so the drivers, both connected with normal polarity, will be back in phase.

So why do people like 6dB crossovers? The audio output of the drivers may be phase shifted from the electrical signal, and, at a selected frequency, can also be adjusted by positioning of the tweeter with respect to the woofer. So, with tweeks, a 6dB crossover can avoid the 90 degree phase shift, at least at the crossover frequency which is where it matters most. FWIW, 6dB crossovers also require the minimum of crossover components.

A passive 24dB crossover is a tough nut to crack, and therefore rare, but is easily implemented in electronic crossovers, where it is very common.
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