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Multi-Way Conventional loudspeakers with crossovers

SEAS MR18 3-way
SEAS MR18 3-way
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Old 18th May 2018, 08:55 PM   #1
Juhazi is online now Juhazi  Finland
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Default SEAS MR18 3-way

Seas 7 inch coaxial midrange crossover?

So, now I have a pair of MR18 in my hands! My plan is to make a semiactive 3-way using it and SB29NRX woofers, floorstanding sealed box and minidsp PowerICE-125 amplifier-dsp boards.

Here are my first measurements of MR18 in a 7 liter closed box, baffle 19x28cm. We can see from nearfield measurements, that the peak at 5kHz is NOT exactly cone resonance, but more like a cavity resonance based on geometry. Look how nearfield off-axis measurement changes in normalized graph!


Looks like the tweeter shows directivity only in low treble and is exceptionally non-directive up to 10kHz. Crossing around 2,5 - 3,5kHz should be ok. Peak attenuation at 5kHz is perhaps not needed at all. Lower xo around 400Hz LR2 should be easy too.

Here some Edge simulations and a 3d sketch of the box. Top part of the baffle will be tilted and I will add diamond cuts to edges following the style of Avalon speakers. Box material will be MDF with birch veneer, tinted and waxed. These speakers will be a joint project with my older son.
Attached Images
File Type: png MR18 3way sketch.png (8.2 KB, 491 views)
File Type: jpg MR18 3way woofer edge.jpg (239.3 KB, 496 views)
File Type: jpg MR18 3way mid edge.jpg (245.6 KB, 490 views)
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Last edited by Juhazi; 18th May 2018 at 09:18 PM.
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Old 18th May 2018, 09:05 PM   #2
Juhazi is online now Juhazi  Finland
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I have a test box for the Mr18, it is rectangular closed box, sharp edges 185x290mm baffle.

First I used some leftover coils and caps to try passive xo, but with poor results. Also the 3-5 kHz peaks of the midrange require some attention. I have minidsp 2x4HD so I used it to make MT eq and xo. Here are results form evening #1, measured on stand inroom at 60cm. 1,4kH is either floor or edge interference.

Looks like LR4 at 2400Hz gives smoother response, but I can't hear a difference... requires longer listening? Distortion rises below 200Hz, easy to xo with woofer!
Attached Images
File Type: jpg MR18 MT lr4 vs lr2 020 40 60¤ 9ms 124.jpg (159.4 KB, 480 views)
File Type: jpg MR18 MT lr4 vs lr2 step.jpg (87.4 KB, 473 views)
File Type: jpg MR18 MT lr2 disto 100db.jpg (120.8 KB, 75 views)
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Last edited by Juhazi; 18th May 2018 at 09:17 PM.
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Old 18th May 2018, 10:21 PM   #3
ferret is offline ferret  South Africa
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Hi Juhazi,
This looks like a very interesting project. Somewhere along the way I read an article (can't remember when or where I saw it) that advocated trying making the box in the ratio of W=1, D=1.7, H=2.3 trying to keep the volume as close as possible to the recommended volume for the mid/bass driver.
I have always liked the SEAS drivers, and built a 2-way vented box with the old P17RCY and Scanspeak D2010 back in 1992. Best box speakers I ever had.
Best of luck!
Kevin
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Old 19th May 2018, 04:16 PM   #4
Juhazi is online now Juhazi  Finland
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Measurement session #2 accomplished!
this time distance 100cm. Some more eq and delay set to 0.08ms for the tweeter (yeasterday -0.06ms).

Here individual and summed on-axis responses. Off-axis to 90 degrees horizontally, with 1/6 smoothing. All graphs here with 9ms IR gating.

The MR has shallower cone than T18, which is obviously causing the peculiar directivity pattern (low DI 5-12kHz). The MR behaves much better around 10kHz than T18, because of better matching of tweeter to cone - thanks to cone's lower Xmax/shorter voice coil.
Attached Images
File Type: jpg MR18 vs T18.jpg (377.8 KB, 145 views)
File Type: jpg MT18 MT lr4 0¤ all indiv 9ms 124.jpg (99.1 KB, 145 views)
File Type: jpg MT18 MT lr2 0¤ all indiv 9ms 124.jpg (106.5 KB, 83 views)
File Type: jpg MR18 MT lr2 0-90 9ms 16.jpg (127.3 KB, 93 views)
File Type: jpg aw7 0-90¤ 9ms 16.jpg (112.4 KB, 86 views)
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Last edited by Juhazi; 19th May 2018 at 04:20 PM.
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Old 19th May 2018, 08:01 PM   #5
Mario Pankov is offline Mario Pankov  Europe
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SEAS MR18 3-way
What causes the peaks at 2.7Khz and 4.2Khz? Doesn`t look like a diffraction artifact. Otherwise - nice project, for compact (55l or so) sealed, you may also try the Scanspeak 26W/8534 - very nice woofer if used to around 150Hz 12db/oct.
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Old 20th May 2018, 08:59 AM   #6
Juhazi is online now Juhazi  Finland
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Those are cone resonance peaks, check the link in post #1. Lr4 xo attenuates them so much that summed response is smoother. I fail to hear them so far... Needs more listening.

Because of eq needed, this will turn to 3-way active design. Fortunately Hypex has released new plateamps the Fusion series.
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Old 3rd November 2018, 06:29 PM   #7
Juhazi is online now Juhazi  Finland
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Looks like I will be making Gradient clones again, this time 1.4. Timetable open...

Gradient 1.4 loudspeaker, Jorma Salmi | Inner Magazines
Reprosoustavy Gradient 1.4 | Novinky | HI-FI studio TYKON

Click the image to open in full size.
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Old 8th November 2018, 05:50 PM   #8
Juhazi is online now Juhazi  Finland
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I do have a pair of these for bass duties. Sealed box.
10" SB29NRX75-6 :: SB Acoustics

I guess that I'll make these active with dsp using Hypex Fusion FA123 boards, but prototype will use minidsp 2x4HD. I guess I must order amps now since price will be 10% higher soon...
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Old 8th November 2018, 08:53 PM   #9
iperno is offline iperno  Italy
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Sorry for the intrusion, but I see that on this forum you know well the seas products and you are experts, I just received as a gift a couple of beautiful seas t17rex new (the version with 4 ohm woofwer and on the net I found the specifications only version 8 ohm), with which I would like to make small speakers to pair with a subwoofer, it would be my first construction.
I found the seas loki project using t18rex (similar), I ask you: could I use the same crossover used in the loki project?
Is the volume of 8 liters in a closed box enough?
I thank those who will give me a hand to clarify the ideas (even in private), I do not know how to start with the project but given the quality of the speakers I would try to make them play better.
Thank you.
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Old 8th November 2018, 11:12 PM   #10
jtgofish is offline jtgofish
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Quote:
Originally Posted by Juhazi View Post
I do have a pair of these for bass duties. Sealed box.
10" SB29NRX75-6 :: SB Acoustics

I guess that I'll make these active with dsp using Hypex Fusion FA123 boards, but prototype will use minidsp 2x4HD. I guess I must order amps now since price will be 10% higher soon...

I would not waste my time on those woofers.They might be fine as subs but not much good above about 70hz.Moving mass is too high and BL [force factor] is too low for such a heavy cone/surround.They have very poor timing and sound soggy above that frequency range.
I have tried all sorts of loadings and boxes but the fundamental character never changed.I sold mine.
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