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Multi-Way Conventional loudspeakers with crossovers

SEAS MR18 3-way
SEAS MR18 3-way
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Old 9th November 2018, 07:31 AM   #11
Juhazi is offline Juhazi  Finland
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Quote:
Originally Posted by jtgofish View Post
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.
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Old 9th November 2018, 07:35 AM   #12
Juhazi is offline Juhazi  Finland
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iperno,
You can use Loki xo as starting point. SEAS have used many different tweeters in their coaxials, and it can be changed easily. I have T18REX coaxials with aluminium tweeters workin as my home theater L/C/R. Xo is not Loki, but Finnish kit design AW-7
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Old 13th November 2018, 06:18 PM   #13
iperno is offline iperno  Italy
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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 by iperno; 13th November 2018 at 06:21 PM. Reason: mistake
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Old 13th November 2018, 06:19 PM   #14
iperno is offline iperno  Italy
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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.
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Old 13th November 2018, 06:42 PM   #15
Juhazi is offline Juhazi  Finland
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^Sorry, I don't know how to design passive crossovers! But yes, values must be different!

Perhaps someone else at this forum can help iperno?
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Old 13th November 2018, 06:58 PM   #16
denbret is offline denbret  Canada
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Hi, I made several measurements and tests with the SB29NRX75-6 woofer.

The ideal xover cut is around 200hz in 12db.

At the top of 175hz, its energy decreases a lot. But at this frequency, the SB29 is excellent. Volume of 55 liters.
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Old 18th November 2018, 07:09 PM   #17
Juhazi is offline Juhazi  Finland
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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.
Attached Images
File Type: jpg blandatube.jpg (493.0 KB, 361 views)
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Last edited by Juhazi; 18th November 2018 at 07:16 PM.
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Old 21st November 2018, 05:41 PM   #18
Juhazi is offline Juhazi  Finland
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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.

Click the image to open in full size.

Here is a link to album of this project, photos and measurements
MR18 3w Juhazi - Google Photos
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File Type: jpg MR18 Blanda WT spl 0¤ 8ms.jpg (102.1 KB, 297 views)
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Last edited by Juhazi; 21st November 2018 at 05:44 PM.
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Old 21st November 2018, 07:30 PM   #19
Juhazi is offline Juhazi  Finland
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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...

Click the image to open in full size.
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Old 22nd November 2018, 11:19 AM   #20
Juhazi is offline Juhazi  Finland
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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!"
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