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Old 22nd October 2003, 05:03 PM   #1
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Default New Open Baffle Dipole Pics

Well, I think this project is finally coming to a close. It took about 6 months, and about 6 pairs or drivers to finally make me happy. The final driver selection is the Seas Millennium tweeter, and the Vifa XT18 Wood Pulp woofer. If you have been following this whole project, you definitely noticed that the tweeter is now on top. After all of this time, I have come to the conclusion that a short speaker really should not have the tweeter on the bottom. It definitely changed the sound by moving it to the top. The reasons for moving it to the top werenít purely aesthetic, or a shot from the hip. The phase response is actually smoother on the design axis when the tweeter is on top, giving me a much deeper reverse null. The crossover is at 2200Hz, just like the original shorties, I had considered changing it, but everything worked out here. My ears and measurements would tell me that the XT18 could actually play a bit higher than 2200. We all know that the Millennium tweeter can play much lower as well, as low as 1400 in the Linkwitz Orion.


I really enjoy listening to this speaker, it gives me exactly what I want. Albeit I have by no means heard everything there is to hear, it is my current realization of "ultimate". The sound is very lightweight, extremely textured, and to me sounds very accurate. It really feels like you hear every last detail of the music. It is in no way harsh, and is very easy to listen to. The character is a bit sweet and warm, but from many people's opinions, the Millennium tweeter has this character. It is far and away different from the ribbons in this class. I donít know how exactly to describe the differences, but I am not a fan of the single ribbon I have heard. It is just my preference. The highs are extremely dynamic, the Millennium definitely can bring out the best in many recordings (also the worst) the leading edge of sharp and transient sounds have a whole new feel. Cymbals and snares have the best attack and decay that I have ever heard. The midrange sounds very pure to me. It has a feel to it like I have heard with the Fostex Speaker at DIY Milwaukee, but without the "breathy" forwardness. It has that incredible crispness and presence that the Fostex Full-Range/Super Tweeter had, but it lacks all of the things I did not like about that speaker.


Many of you will notice that I did not round over any of the edges. I did this for several reasons. First, I did work out an optimal location, using the 1.6x1x.6 "golden" ration to locate the tweeter on the baffle. This places it optimally-unequal distances from each edge, to reduce baffle edge diffraction. The main reason that I did not do any roundovers is because the Seas Millennium really doesnít have the best far-off-axis response. Since the 90 degrees off-axis response is what will result in edge diffraction, I measured it. To put it lightly, it is so far below the on-axis response that it is not going to make much of a difference.


In the picture of the rear, you will notice that there are 4 bolts on the lower rear. Those hold a panel on, behind which you can place a bag of sand, to further anchor the speaker. I may also re-route the wires, so that I actually have connectors, and don't have to lug around big cables every time I want to move them. This also allowed me to put in a horizontal brace about half-way up the speaker to damp baffle vibrations. The baffle is made of .5" MDF


For the base, I wanted to do a hovering look. First, on the bottom is a 9" x 12" .75" thick slab of MDF, on top is a 7" x 10" x .5" piece. The speaker is mounted to this, via three t-nuts in the base. The bolts screw through the speaker, into the base, securing it.


The veneer is Fiddleback Anegre, and I used Boiled Linseed Oil to finish them. I will do a few more coats after this one soaks in and hardens a bit. The base is brushed on gloss black paint. I would highly recommend this finish. It is not nearly as labor intensive as a gloss-black, but gives a good irregular look.
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Old 22nd October 2003, 05:05 PM   #2
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Old 22nd October 2003, 05:06 PM   #3
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And one more:
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Old 22nd October 2003, 05:22 PM   #4
Erik is offline Erik  United States
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These baffles are drop dead gorgeous. The "hovering look" and the choice of veneer really do the job.

You should be very proud. Happy listening.
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Old 23rd October 2003, 08:51 AM   #5
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Great job! What kind of a highpass are you using on the XT18?

What is rub-on glossy paint? Some wax-based stuff that you rub on with a cloth?
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Old 23rd October 2003, 05:12 PM   #6
Nuuk is offline Nuuk  United Kingdom
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Nice job Paul! When the linseed oil has fully dried after a few weeks, I would suggest building up coats of Danish oil (five or six).

Rub down with the finest grade wire wool after each coat except the last.

And instead of MDF for the panel brace, granite will be much better. Of course, you could add it as well as the MDF brace.
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Old 24th October 2003, 02:19 PM   #7
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Great job! What kind of a highpass are you using on the XT18?

3rd order electronic XO. The Dipole roll-off adds an aditional 6dB per octave, making it a 4th order acuoistic crossover. The frequency is at 95 Hz. It keeps the cone movement down at most listening levels. It is an awsome woofer period.

What is rub-on glossy paint? Some wax-based stuff that you rub on with a cloth?

It is actually just a standard brush-on acrylic black gloss paint. I was going to sand it down to a perfectly flat finish and do a clear coat on top, but this turned out to look really nice anyways.

Nice job Paul! When the linseed oil has fully dried after a few weeks, I would suggest building up coats of Danish oil (five or six).

Rub down with the finest grade wire wool after each coat except the last.


I will take that into consideration, thanks.

And instead of MDF for the panel brace, granite will be much better. Of course, you could add it as well as the MDF brace.

Um... overkill. I dont really ever fell the cabinet move at all. The moving mass of that vifa driver is a mere 10 grams, lighter than almost any 18cm driver available.

-Paul
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Old 24th October 2003, 02:35 PM   #8
Nuuk is offline Nuuk  United Kingdom
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Um... overkill. I dont really ever fell the cabinet move at all. The moving mass of that vifa driver is a mere 10 grams, lighter than almost any 18cm driver available.
Yes, your baffles are constructed better than my temporary chipboard versions and I am using much bigger (12 inch drivers) where the panel damping/bracing is more of an issue.

I have just added a lump of marble to my temporary baffles and it has improved the bass considerably.
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Old 24th October 2003, 02:47 PM   #9
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Very sweet. Are they efficient? How do you think they would mate to a 20-watt push-pull EL84-based tube amp? How bout to a GainClone?

Oh, and if you want to sacrifice your speakers' uniqueness in favor of the undying gratitude of future DIY'ers, you could post a detailed drawing, with measurements, full component list and hints/tips for posterity...


GnD

p.s. 'Course, then you'd have to think of a catchy name for us to remember them by...
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Old 24th October 2003, 04:44 PM   #10
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They use an active crossover.

Overall they are pretty efficent. I drive the midrange and tweeters with a gainclone. It works fine, and sounds very good. I am betting that you could safely drive the tweeter with a 3.5W SET amplifier. It really does not use that much power at all since there is no padding between the amplifier and the speaker.

I would say to use an gainclone on the midrange and a SET amplifier on the tweeter. Or any Class A amplifier.
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