Seas coaxials

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#2
SEAS of Norway has recently introduced two new coaxial midrange-tweeter transducers, the Excel series C18 and her grey sister MR18 in Prestige series.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.


The layout is improved from H1333, because the cone is flatter and surround is reversed and narrow. The sacrifice is is the bass department, these must be 3-ways or use stereo subwoofers with crossover around 200-300Hz.

Troels Gravesen has done some tests with C18 and is planning a new speaker around it. Seas has already published KingROY. Unfortunately the price of the unit is more thatn 500$/€ which makes many diy-people to think over. The pricing of MR hopefully will be reasonable and it's reed cone has smoother behaviour too, making passive xo design easier.

My personal preference would be a hybrid active 3-way like KingROY, but with MR18 and a stylish narrow floorstanding cabinet. Perhaps something artistic...
 
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#3
It will probably cost 150-200 Euros, far more reasonable, but still expensive. SEAS also appear to have omitted the shorting rings and pole shape. This really gets my goat, this is an expensive driver, add bloody shorting rings, they are pretty standard these days in 50-100 euro drivers. Argh >.<

Inductance is as low as the excel version though, which is odd. The reed cone is anything but smooth however.
 
#4
Perhaps lack of dust cap makes the reed cone behave worse than ER18. With LR4 at 2kHz this 6kHz peaking should not a big problem. C18 cone resonance is at 8kHz.

Perhaps copper rings were left out because of using this as mid? I'd love to see distortion measurements...
 
#5
It's the midrange performance that the copper affects the most. The C18 has them.

Distortion sweeps would be very nice to see how the 4k stuff affects things further down. The resonance in the C18 is at 6kHz and that shows up as peaks in the third order at 2kHz. If the reed cone has issues of a similar nature then it really will make it less useful, with the C18 you can cross the tweeter over just low enough to push the HD3 spikes off the radar. 4k spikes would be impossible to get rid of.

I wondered if the lack of dustcap was responsible for this too but it could also be related to the surround or cone profile.
 
#6
I remembered the resonaces wrong. Like 5th element said MR woofer peaks at 4kHz. It must be handled but I don't think that this is a problem, I have seen worse - we must remember that SEAS does not use "makeup" for it's graphics! When that peak is attenuated in xo, 3rd harmonic distortion is not a problem either. Tweeter response has typical on-axis dip at 9kHz, something to not be afraid of.
An externally hosted image should be here but it was not working when we last tested it.
 
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#8
The third harmonic distortion occurs at 1/3 the frequency of the resonance, it doesn't matter how steep your xover is, at say 2kHz, the third order peak still shows up.

What's happening is you deliver a 1.33kHz tone to the driver, the driver inherently produces a certain level of 3rd harmonic at 4kHz, but if the cone rings at 4kHz then it will amplify the level of this 3rd harmonic. This is why metal cone drivers display peaks in their HD plots significantly below where the resonance occurs.

As the excitation for this occurs when you deliver a 1.33kHz signal, no amount of signal attenuation at 4kHz helps.

Metals cones almost always display these peaks. Lots of the stiffer alternative materials do too, but some do not. If the MR18 has significant peaking in the third harmonic at 1.33kHz then there's not a lot you can do about it.
 
#10
The T18 has one very good property, that being it doesn't need much stuff in the crossover. Actually, it is one of those rare drivers that can make do with just the bare essentials: a coil and a cap. I used the T18 in a 3-way dipole configuration, and I think I had a 2,7µF cap on the tweet and something like 0,82 mH on the midrange low pass.
 
#11
rutcho said:
Here are my measurements and first listening impressions.
Click to expand...

Thanks for posting these! The cone breakup of the woofer doesn't seem to translate into HD peaks at 1.33 khz etc., so it seems to be more usable than expected – cf. 5th element's post:

5th element said:
If the reed cone has issues of a similar nature then it really will make it less useful, with the C18 you can cross the tweeter over just low enough to push the HD3 spikes off the radar. 4k spikes would be impossible to get rid of.
Click to expand...
 
#12
Adolf Corkscrew said:
The T18 has one very good property, that being it doesn't need much stuff in the crossover.
Click to expand...
T18RE/XFCTV2 is one of my favorite drivers too.
For my opinion the drivers with polypropylene cone are sometimes undeservedly ignored by audiophiles. This is true that sound expression of a good paper cone has no competition, but it often needs too complex crossover that can reduce their advantages.
wowo101 said:
Thanks for posting these! The cone breakup of the woofer doesn't seem to translate into HD peaks at 1.33 khz etc., so it seems to be more usable than expected – cf. 5th element's post:
Click to expand...
I tried first MR18REX/XF with second order crossover and a notch filter tuned at 4kHz. This is not the final crossover, I will re-work it when I mount the driver in the dedicated box...
 
#13
Adolf Corkscrew said:
The T18 has one very good property, that being it doesn't need much stuff in the crossover. Actually, it is one of those rare drivers that can make do with just the bare essentials: a coil and a cap. I used the T18 in a 3-way dipole configuration, and I think I had a 2,7µF cap on the tweet and something like 0,82 mH on the midrange low pass.
Click to expand...

To be precise the not shielded T18REX/XACG (sold at least here: Seas T18REX/XACG - Hifitalo) is the one that needs basically only coil for woofer and cap for tweeter. The magnetically shielded version T18RE/XFCTV2 needs more parts.

I haven't tried the ...XACG in normal stand mount enclosure, but here's a article of on-wall loudspeaker with this coaxial. Basically 1,0mH for woofer and 2,2uF for tweeter is all that is needed to make perfect crossing. In hard acoustics I'd add a 1-1,5ohm resistor in series with the tweeter:

Kaiutinrakennusohje - Purismi - neljän sähköisen osan kaiutin 6,5-tuumaisella koaksiaalilla | AudioVideo.fi

I'm sorry the text is in gibberish, but at least the pics are in universal 🙂
 
#18
Adolf Corkscrew said:
The T18 has one very good property, that being it doesn't need much stuff in the crossover. Actually, it is one of those rare drivers that can make do with just the bare essentials: a coil and a cap. I used the T18 in a 3-way dipole configuration, and I think I had a 2,7µF cap on the tweet and something like 0,82 mH on the midrange low pass.
Click to expand...

I know this is a long shot but have you reversed the polarity of the tweeter like the one shown here:

Kaiutinrakennusohje - Purismi - neljan sahkoisen osan kaiutin 6,5-tuumaisella koaksiaalilla | AudioVideo.fi

?
 
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