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Multi-Way Conventional loudspeakers with crossovers

Seas Idunn revisited-project
Seas Idunn revisited-project
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Old 21st December 2012, 10:52 PM   #1
faija is offline faija  Finland
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Default Seas Idunn revisited-project

Hi all,
I am a new member, about to retire though.
I have built several loudspeakers published in a Finnish Hifi-magazine. Some of them have become classic, especially the 85/3 which still sound excellent after 25 years in a 450 m3 loghouse driven by a 2x25W amp.

Now back to business: I have spent plenty of hous searching for suitable loudspeakers for my 19m2 livingroom having concrete walls. Seas Thor was one of the candidates but having read several sites it was rejected. Not only because of contradicting opinions but also because they were oversized for my needs.

Finally I ended up with a Murray Zeligman design, the Idunn, which seems to satisfy my needs. Not least because of the sound quality but also because of the box redesingn of a Finnish HiFi company.

The boxes were built by a young friend in the vocational school. He did an excellent job! I also changed the boxes for two tubes in order to be able to adjust them for the room acoustics.

My main worry is that the baffle widht is less than in the original plans. The woofer is also placed on the top of the box which also is different from the original. Now I am wondering how these changes are affecting the sound quality and what changes should be eventually done to the crossover.

I am going to cover the inner sidewalls with adhesive bitumen sheets and add 250g polyester wool into the two upper compartments to start with. The backplate is fastened with M4 bolts to enable easy changes and experiments.

I'll finish now wondering if I can add some pictures. Typical newbie problem
Well, it seems that I am in trouble now! Maybe next time.

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Old 22nd December 2012, 05:27 AM   #2
system7 is offline system7  United Kingdom
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Hi jouko, welcome aboard!


Very interesting speaker. Advanced U18RNX/P polycone H1571-08 U18RNX/P and DXT tweeter H1499-06 27TBCD/GB-DXT.

Will follow this with interest. TBH, wouldn't think small baffle width changes or turning the drivers upside down would make a huge difference, but you are in best position to judge the sound. The DXT tweeter is an odd thing though. I do always wonder if some more regular tweeter would make more sense as in the SEAS CURV design.
Best Regards from Steve in Portsmouth, UK.
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Old 22nd December 2012, 04:50 PM   #3
faija is offline faija  Finland
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Hello ,
and many thanks for your comments.
You made an interesting question concerning the tweeter choice. 0 Having read the article in the Audio Beat written by Allen Edelstein I became ever more convinced about the skills of Murray Zeligmann. The Audio Beat - SEAS Idunn Loudspeaker Kit. If I understood him right the W ad T have about the same dispersion at the crossover frequency which helps to hide the transmission. The T also has a wide dispersion at higher frequencies which widens the off-axis response at higher frequensies. I am pretty much for this type of tweeter design, not least because my old speakers (HiFi 12/2 designed by a Finnish "guru" Pekka Tuomela) are using Dynaudio D-28 tweeters and I really never felt like sensing the crossover transfer. D-28 has a clean convex while the 27TBCD/GB-DXT has a proportional reflector just like the well known Vifa D25TG-55-06.I will hopefully have the starting version ready in two weeks time, the burn-in will be at least a 100 hrs. I'll be back then at the latest.

Maybe you can help me out of the problem attaching photos. I understand that I need to open (an) internet page(s) and link them as in many sites. Copying from my computer did'nt work.

In the meantime I wish you a peaceful xmas time. We have here temperature of -12C plus wind factor and there is 35cm snow on the ground. The organic ham will soon enter the owen for a 8-12 hrs sauna session at 80C.

Best regards,

Jouko, Helsinki Finland
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Old 22nd December 2012, 05:14 PM   #4
sreten is offline sreten  United Kingdom
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The x/o is designed for a listening axis on axis with the tweeter. This means
vertical dispersion will not be symmetrical and worse with the drivers inverted.

The BSC of a driver mounted in about the middle of a tall box will change
somewhat if its mounted at either extreme (open stands for the bottom).

Baffle width will make a minor difference, it cant be much smaller.

rgds, sreten.

Nothing wrong with the principles of the DXT tweeter, the
distortion (which is better) or controlled dispersion wise.

Last edited by sreten; 22nd December 2012 at 05:19 PM.
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Old 22nd December 2012, 05:31 PM   #5
jmsent is offline jmsent  United States
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The Idunn is not a Murray Zeligman project. It was designed by the R & D lab at SEAS.
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Old 22nd December 2012, 06:18 PM   #6
faija is offline faija  Finland
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Hello jmsent,

what you stated would mean that the article in Audio Beat (the link is in my previous message) is a fairy tail or pure advertisement. I cannot understand why. I don't know the publication at all but you may wiser as a native.


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Old 22nd December 2012, 06:29 PM   #7
jmsent is offline jmsent  United States
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I think if you reread the article closely, nowhere does it say that Murray actually designed the Idunn. Only that he built a pair himself. He did do some earlier designs for SEAS, and perhaps that's where the confusion comes in.

Last edited by jmsent; 22nd December 2012 at 06:32 PM.
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Old 22nd December 2012, 06:41 PM   #8
faija is offline faija  Finland
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Hello streten and thanks for your comments.

I am sorry but I cannot understand what you mean. If the loudspeakers are placed inversely they are still on the same vertical axis from the x/o point of wiev. I don't believe that gravity would play any role here.

Best regards,

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Old 22nd December 2012, 07:48 PM   #9
Juhazi is offline Juhazi  Finland
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Hei Jouko,
sreten is trying to explain the concept of "design axis" which is practically never 90¤ to the front plane. Usually this axis is at tweeter level measured 1 or 2m from the speaker. If you increase distance, the optimal listening/measuring level is higher and vice versa (supposing the tweeter is above the woofer). How and how easily the effect of this is heard depends on many factors.

One issue of Idunn is the booming of 2 kHz area despite of the claims of not happening. Check the attached graphs of Idunn and MarkK's ER18DXT, which is better (different scale). ER has 2nd order xo instead of 4th of Idunn - thus the tweeter plays earlier in frequencies.

The graphs are copied from these original pages
The Seas ER18DXT ported two way

You can attach files from your computer by pressing "Go Advanced" - first Select files then press Upload

Hyvää Joulua!
Attached Images
File Type: png ER18DXT%20FR%20081709.png (15.7 KB, 437 views)
File Type: png ER18DXT%20horizontal%20off%20axis.png (21.9 KB, 433 views)
File Type: jpg idunn_spl-imp.jpg (96.8 KB, 436 views)
File Type: jpg idunn_offaxis.jpg (82.7 KB, 431 views)
AINOgradient speaker project

Last edited by Juhazi; 22nd December 2012 at 08:02 PM.
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Old 22nd December 2012, 08:16 PM   #10
tvrgeek is offline tvrgeek  United States
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With all the comments above, most very astute, you will find out there is one overriding parameter that is the most important to all others in speaker design: "It depends"

In other words, you don't know until you measure. Welcom to our little bit of self inflicted hell.
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