Crossovers for coaxials... no lobing?

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outlookrt

Member
Joined 2008
#1
Hello. I've recently received some Seas T18 coaxial drivers. I've quickly thrown them into some sealed enclosures I had which provide a qtc of between .5-.6 according to calculations. I am using them close the wall and one is near a corner in a fairly near-field apartment listening setup. With some very rough measurements and based on what I can find online I've dialed in some basic crossover options into my mindsp SHD and measured to ensure they sum to a fairly similar FR. This driver seems to allow for 1st order crossovers, Seas uses 2nd order for their Loki kit, and I noticed their minidsp active preset they provide for the Loki uses 4th order LR with some EQing to flatten FR further. So far they sound pretty good! It's my first time using coaxials and I'm enjoying the 'solidity' to the sound when moving my head. As I don't always sit in the same place on the sofa and often move around the room, I can def notice a more cohesive less phasey sound when not in the sweet spot which I'm enjoying.

What I'm trying to understand is, does using a coaxial fully removing lobbing issues associated with each crossover type? and if so is there any reason a 1st order would be recommended in this instance over a simple 2nd or passive/active 4th? I suppose it depends on if I stay active or go passive, I assume running active there's little reason to not just use steeper filters, and the only reason to not do so passively would be costs/complexity of crossover?
 
#2
Hi,
There is no lobing because the drivers are coincident in X and Y axis ( can sometimes in Z axis but not always).
Lobing is the result of drivers acoustical behavior regarding directivity, their physical location and filter interaction, not only from filters.

Choice of filter slope will depend of driver ( is it able to cope with low order without complaining?) And your goal : you may favour fr or impulse response or protecting your tweeter, taming a resonance,.... it is design dependent so will depend of your choice.
 
#3
You don't want to mix up your discussion of what is necessary/best, with what is possible. That can come later.

The unanswered question is how do these perform on all axes, as running a tweeter out of the middle of a mid is not always an easy environment. This can establish where each range performs well. Then you can investigate the overlap performance.
 
#5
yes, coaxial drivers do many things well but they are not without flaws, but i find the ragged top end of many coaxials are less audible / disturbing then phasey issues with seperates that appears around the crossover frequency
 
#6
Hi Celef,
Can't agree more with your statement. But as we don't listen to the same things ( as individuals) other quality can be prior on wishing list. It is really a preference thing.

You have some experience with this driver iirc?( or one from same family)
 
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#8
Thanks for all the helpful replies! So it sounds like with Lobbing out of the equation its' much more down to balancing design goals and compromises. Does anyone have any experience or tips with this driver? It's the latest Seas T18Rex H1353.

I'm currently testing 2 xovers based on designs I've found online that use this driver. The 2nd order from Seas Loki MKiii design. And a 1st order that has a notch filter of sorts around 1200hz (around the tweeters fs) so the tweeter roll off becomes steeper but phase remains the same (I think?)
 
#11
outlookrt said:
So it sounds like with Lobing out of the equation
Click to expand...
Hmm. I don't know if that is totally true. With the tweeter in the center, you won't get the asymmetric phase-related hot and dead lobes you would tend to with a typical tweeter-next-to-woofer design. But it doesn't automatically that the combination of tweeter down in a cone will have some kind of perfect dispersion. They sure don't! Now, does that translate into "lobing" probably depends on the specific design.

As a loudspeaker engineer I respect SEAS a lot. Their coaxes, though, all seem kind of similar. The tweeters LF boosted, probably due to the waveguide effect of the cone-that seems good, make a higher crossover and thus help power handling. But the tweeter responses always look really ragged and I always wonder why the heck IS that? Does anyone know or have reasonable hypothesis?

I don't know that I'm seeing a 1st order crossover for this...maybe it looks better in an actual simulator. But you would need to Zobel the rising woofer impedance flat, otherwise a series inductor probably gives you like a "1/2"th order crossover ha ha.
 
#12
in general, for the baffle, to mount a driver almost equal distance to top and both sides as in this seas kit is a no no, i guess this is the source of the hump at 1-2 kHz

for xo i dare not to have a guess, i will try to borrow a pair soon and do some tests, i may return then
 
#13
head_unit said:
As a loudspeaker engineer I respect SEAS a lot. Their coaxes, though, all seem kind of similar. The tweeters LF boosted, probably due to the waveguide effect of the cone-that seems good, make a higher crossover and thus help power handling. But the tweeter responses always look really ragged and I always wonder why the heck IS that? Does anyone know or have reasonable hypothesis?
Click to expand...

have you looked at the "king coax"? Test Bench: SEAS E0060-08/06 6.5” King Coax | audioXpress
 
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