SEAS MR18 3-way

http://www.diyaudio.com/forums/mult...coaxial-midrange-crossover-2.html#post5415661

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.
 

Attachments

  • MR18 3way sketch.png
    MR18 3way sketch.png
    8.2 KB · Views: 2,218
  • MR18 3way woofer edge.jpg
    MR18 3way woofer edge.jpg
    239.3 KB · Views: 2,229
  • MR18 3way mid edge.jpg
    MR18 3way mid edge.jpg
    245.6 KB · Views: 2,192
Last edited:
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!
 

Attachments

  • MR18 MT lr4 vs lr2 020 40 60¤ 9ms 124.jpg
    MR18 MT lr4 vs lr2 020 40 60¤ 9ms 124.jpg
    159.4 KB · Views: 2,063
  • MR18 MT lr4 vs lr2 step.jpg
    MR18 MT lr4 vs lr2 step.jpg
    87.4 KB · Views: 2,036
  • MR18 MT lr2 disto 100db.jpg
    MR18 MT lr2 disto 100db.jpg
    120.8 KB · Views: 354
Last edited:
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
 
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.
 

Attachments

  • aw7 0-90¤ 9ms 16.jpg
    aw7 0-90¤ 9ms 16.jpg
    112.4 KB · Views: 536
  • MR18 MT lr2 0-90 9ms 16.jpg
    MR18 MT lr2 0-90 9ms 16.jpg
    127.3 KB · Views: 427
  • MT18 MT lr2 0¤ all indiv 9ms 124.jpg
    MT18 MT lr2 0¤ all indiv 9ms 124.jpg
    106.5 KB · Views: 410
  • MT18 MT lr4 0¤ all indiv 9ms 124.jpg
    MT18 MT lr4 0¤ all indiv 9ms 124.jpg
    99.1 KB · Views: 786
  • MR18 vs T18.jpg
    MR18 vs T18.jpg
    377.8 KB · Views: 888
Last edited:
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.
 
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.
 
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.
 
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.

I got them cheap, second hand. We will see, xo will be around 2-300Hz LR2. Actually I am more concerned about the low end of MR18, must be careful with distortion.
 
Grazie, bel kit, lavora in pochi litri rispetto al loki.
La mia domanda è: i t17rex che posseggo hanno il woofer a 4 ohm, invece che 8 ohm come trovo su tutti i progetti, quali modifiche devo apportare ai crossover?
Devo cambiare i valori di condensatore e induttanza della parte passa basso per mantenere il taglio ai valori previsti?
Grazie.
 
Last edited:
Thanks, nice kit, works in a few liters compared to the loki.
My question is: the t17rex I have have the 4 ohm woofer, instead of 8 ohms as I find on all the projects, what changes do I have to make to the crossovers?
Should I change the capacitor and inductance values of the low pass part to keep the cut at the expected values?
Thank you.
 
I have made some purchases for the project - IKEA Blanda bowls (one extra for prototyping) and a casting tube from Biltema. Here you can see them in my well equipped and organized laboratory and storage rooms!

Diameter of bowls is 28cm (inner volume 7,2L) and the tube is 31cm. I will cut the tube in two pieces and slice it longitudinally, then expand it with a blank of wood cut in trapezoid shape to make it a little wider at the bottom (volume 43L). Top and bottom plates will be cut naturally from Finnish birch plywood.
 

Attachments

  • blandatube.jpg
    blandatube.jpg
    493 KB · Views: 927
Last edited:
I installed the MR18 on a cut IKEA Blanda Matt ¤30cm bowl and took some preliminary measurements. The woofer has nasty 4kHz spike that must be attenuated by cone treatment or with eq. Serial 6.8uF cap makes tweeter's response easy to eq and protects it from pops.

Bi5XZJBlKYFjfgDmoy-HH7G7xMpKjgr-pFjhF3B1q3G-kdlj3Wd2c0K5RgwHhHN1grSE10tFwjiJrPIIFhMFN1C_a0-5EBPjjrzOTQhI4AeUin4SuR2ylpfSn6LuID7dHxAxVyaBXmxlyW2MAPHJ9vuhbGczrJxt5nUZxnl66luHFK3nbIgE4xalUi36HauCMvuEXKZHSAsn9XNjnZqzrGoDxLGXOvVV6dIo5nVvaeiebrDkJ6gx4306Oj1c59S3oj7XO0z7-ZKlK9kD-hJ1yU4ZWcGkEiHxfczU0wSOUkfTtw8JH_95Vs0hcl1on4FKGc1O_51yD_W1KMiVfpdFI-99Wb_uQZqwkAyjy5BV0w08QpNT5FA7dj9PiknJzsdACVT98eoq6wmdC2QF8iGSw27FxLkEB0oQSsiYs0LfJukJ7FQXBD2UYkjMJg5AIMLg2vDB2bs5MUMthMF2WG-xCdtvMJ-UyQkOsFkY7lUW-YgciDtmHXB5nLtLE8kya8vNU6hJuwLpjb4kyzvfwn18IR7PvlzcSB6rpKwGHKKUMBqWVoGjsg2ExoFuRd1wyFYiL5YDqgySmZsmMOi3U388WTN0WPBsNLCQvM7cQaVC5Fn2j_WZpbs99e9gJwT4h4YCir2y1jKHCIaGauZqzGdC8CBa2BOHZAQFL7PJB2b5HqjpWJ47e1pJ8RRvcOi01XzNpPYMNWJMS4DUxtrWyg=w651-h867-no


Here is a link to album of this project, photos and measurements
MR18 3w Juhazi - Google Photos
 

Attachments

  • MR18 Blanda WT spl 0¤ 8ms.jpg
    MR18 Blanda WT spl 0¤ 8ms.jpg
    102.1 KB · Views: 774
Last edited:
  • Like
Reactions: 1 user
More measurement of cone issue. Nearfield at various radii and on-axis at various distance, added in the shared google-folder that I linked in previous post.

Here nearfield 10mm from cone, midline, near center, middle and edge. Pretty smooth up to 2,5kHz...

S8wSMdD0oM4Tub_EYTiKJM1aNlhKzqeWcbeyJmOhdjtyIXwOGioQ7Sgz0OMfM7NX_ksc_bR9ZlrEpLjzW6ClK0ZzGZM6ps53Rnu384I75uUAVdjPfMKvWV9s_GgIMr_b0t9yvQOU6of-0nUX7MQ1zNiM2-isDFmYO_vIf8mkbeu_6qSySnNLyYosqcJAf9fFbXyye6pabk_7QQBB8d76hOhkZGh7epRLMG3PhqZKIxbtqCLZV33uLIeBzOwEENxxd-odBcv0mK0O2lBj_mDOZMJ_dJQdxwMSR5UG6LHfAEoUT88wykFalCpSb2z9zuc378sVZ8lwDNnsEDLMmnDvTW7I7q2imebx5-9O1y1TDX68zjS1jooPGCEOH_KvsahujlnFK7Z16jWhovF3x1EHOEBBtc7brJ9Exk-ieXPgZYKGp9Lr0sHSWAdHdfCedyy-PDfalrm5igUHGk-XnhlBmyjO3H-fg-U7gGd3xc6mXsHFQGipz7FIKPOnaThgxFuiZPCuR4bcblVIwKqPnzcW60RlGzLOL72Y-PUhHCaOcQF0QVssqGDOXbkEbCjZuCfu-yHkohvZ0n77KDEA2swKHdIFSJML6sjO8Vl58_TbXLY7PTQmr0sBCUTEqa9Yv9EwSoUpy781VGJHTFbHZ0v4KA9cptkElCAwiT8BRkWWrzkxWBUv3lz_sj39okgd0CMpXynOnzjnx3wsIi9XQg=w800-h498-no
 
I cut the bottom plates today, from 30mm thich birch plywood. I will mount the woofer on the inside to leave room for legs. Outer diameter of the disc is 35cm, inner 25cm.

This will be quite a Scandinavian speaker! SEAS from Norway, SB Acoustics has Danish roots, box from Sweden and design from Finland. Then amp from Netherlands.

This reminds me of a story about Eurpean politcians flying back from United Nations meeting. In the middle of Northern Atlantic ocean the pilot tells that if three passengers don't jump off, the plane will sink in Atlantic because of too little petrol. First the Britain stands up and shouts "God save the Queen!" before jumping. Then the Frenchman shouts "Vive la Liberte!" and jumps out. After a while the Norwegian and the Finn grab the Swede and throw him out shouting "Heja Nordisk samarbete!"