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Old 20th February 2013, 01:10 PM   #1
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Default Naked driver dipole with different Seas tweeters

I’m thinking of unboxing my SEAS Excel speakers to try out naked drivers on a chain like StigErik had going for a while.
My tweeters are the CRESCENDO T29CF-002. I don’t see myself sink this amount of money in another pair of domes as I then rather try out some true dipole tweeters.

Question is. How do you think the cheaper Seas T25CF001 will perform as back tweeter in a naked driver dipole setup with the CRESCENDO? Dome size are 29 vs 25mm.
I understand I have to address the difference in sensitivity. But will it degrade the CRESCENDO to same sound quality as the T25CF001. Or could the difference in performance be “camouflaged” as reflection from my not treated back wall?

http://www.seas.no/images/stories/ex..._datasheet.pdf
http://www.seas.no/images/stories/ex..._datasheet.pdf

Last edited by DEQ+TheEnd; 20th February 2013 at 01:14 PM. Reason: Made a phoh. Dome size are different.
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Old 20th February 2013, 03:35 PM   #2
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In a 'naked' dipole the way to go for the tweeter section is either an AMT (expensive), a Neo3W (cheaper) or a pair of small neodymium domes (also cheap). It's important to minimize the source separation to avoid blooming of the polar pattern, which is impossible with dome tweeters with large magnets.
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Old 20th February 2013, 04:22 PM   #3
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Thank you!

Will you say that its better to priority polar pattern before source linearity (quality of speaker element)?
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Old 20th February 2013, 04:43 PM   #4
zmyrna is offline zmyrna  United Kingdom
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If you run a 4 or 5" dome just under the tweeter and cross high,
you may not need a second backfiring tweeter.
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Old 20th February 2013, 05:29 PM   #5
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Thank you for input.

I should maybe clarify a little. The quest is to check out if its' possible to implement a DIY dipole solution in our living room in a manner my better half can accept. I already know I will not be able to do any visible room treatment. That's what kept me inside the box until now

Budget for the prototype should be as low as possible, but I realize I'm not going to this party for free. If I can make it work I can see myself with some BG Planar in the end.

My current "parts bin" for this prototype holds the following parts:
2 pcs Seas E0040 T29CF-002 - CRESCENDO Tweeter
4 pcs Seas E0018 W18E-001 Mid/Woofer
2 pcs Peerless XXL 12" Sub

3 pair Class-D amp modules from Hypex and Coldamp. All of them different
DCX/DEC2496 combo with mic.

Come to think of it there are a couple Esotec D260 tweeters laying around here also. Maybe I can use these for the initial tests?

Last edited by DEQ+TheEnd; 20th February 2013 at 05:44 PM.
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Old 20th February 2013, 07:18 PM   #6
Rudolf is online now Rudolf  Germany
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Some things to consider:
If you have no control whatsoever of the front wall situation, it might be a good idea to show a picture (or any helpful illustration) of that wall before starting the project. Placing a dipole too near to a highly reflective wall is no good idea.

The dipole-8 is quite sensitive to SPL differencies between the front and rear source. Anything more than 3 dB difference will be critical. If you see a need to attenuate the rear driver 6 dB (half as loud as the front driver) you have lost the figure 8 almost completely.

Naked drivers are the least forgiving dipole implementation. Are you able/going to do in-room measurements?

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Old 20th February 2013, 07:36 PM   #7
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Thanks Rudolf. I'm currently reading your thread "On the directivity of dipole tweeters". Very informative although I'm not smart enough to grasp it all yet

Am not clear if the size of the figure 8 are related to the size and shape of the driver/baffle rather than frequency depended? I've always thought the later, but lost my bearing reading your thread?

Quote:
Originally Posted by Rudolf View Post
Are you able/going to do in-room measurements?
I got a mic and preamp, but missing software and knowledge so any pointer to the modern way of doing it is appreciated.

Last edited by DEQ+TheEnd; 20th February 2013 at 07:38 PM. Reason: typo
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Old 20th February 2013, 09:40 PM   #8
Rudolf is online now Rudolf  Germany
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Quote:
Originally Posted by DEQ+TheEnd View Post
I'm currently reading your thread "On the directivity of dipole tweeters". Very informative although I'm not smart enough to grasp it all yet
So we are on the same level: I wasn't smart enough to tell the story in a way that everybody can grasp it.
Quote:
Am not clear if the size of the figure 8 are related to the size and shape of the driver/baffle rather than frequency depended? I've always thought the later, but lost my bearing reading your thread?
Neither nor - or both. Depends on the way you look at it.
The "figure 8" is related to the radiation pattern of a dipole. This pattern should have maximum SPL to the front and back, and SPL "nulls" to the sides. Ideally the shape of this "8" should be the same for all frequencies. To achieve that, baffles should be small (compared to the wavelength involved). If you mount your tweeters back to back, you create quite a distance between the front dome and the rear dome of that pair. This distance is equivalent to the radius of a baffle, where you would mount a Neo3 (for instance) on, which has no distance between the front and back side of its diaphragm.
That's why you no longer see such bulky tweeters in the newer efforts of johnK or SL.
Quote:
I got a mic and preamp, but missing software and knowledge so any pointer to the modern way of doing it is appreciated.
Learning loudspeaker measurement on this project is like learning to swim in the breakers.
Not sure if this is the best way to get ones feet wet.

Rudolf
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Old 21st February 2013, 02:27 PM   #9
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Thanks Rudolf! I will not lay any fault on you sir. It's all mine doing BTW, your cook book "Open baffle dipoles - How they work" is great reading. Thank you for sharing.

One thought though. I'm wondering how a dome that fires into a disperser will perform in a dipole? It should eliminate some of the problem with dual sources? But might introduce other problems even harder to work around?
If it's worth testing I'm thinking one can tilt it in different position if needed.
Top mounting might not be the best place?
Experiment with direction. The dome might work better pointing down or to the side depending on the efficiency of the disperser?

Click the image to open in full size.

Regarding room measurement I've only used the internal DEQ sw for guidance to tweak eq. Anyone here experienced with REW? Is it worth investing time to learn this application, or can I do better with my time?
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Old 21st February 2013, 07:51 PM   #10
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A Man of Character marries one woman for life, but fools around with several different speakers :-)

YOU MIGHT:
1) Keep your current speakers and just remove the Peerless XXL 12" for dipole experiments. The Seas T29CF and W18E are not "great" candidates for a SOTA dipole like the JohnK Nano Note II or Linkwitz LX521.
2) Admit that you will never "really" be happy until you experiment with a 4-way dipole similar to NoteII or LX521.
3) Design an H-frame for your current pair of Peerless XXL 12" and cut wood for two for future stereo.
--- FIRST BUILD... one H-frame with both Peerless XXL to test if your ears love dipole bass in your room.
4) Design a "paddle" shaped baffle that can be used for (8" or 10" midbass) + (3"-4" mid) + (dual domes or BG3 planar). Cut wood for 2*3=6 baffles which you can later route for different speakers.
5) Add some European engineering flair by developing a hanging baffle design. The LX521 wastes 2" in width for the mid-tweet isolation stand-off frame.
6) Admit that you are in love ... with dipole bass ... and set a budget for midbass+mid+tweet. Admit that you are kinky enough to try a 4-way!
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