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Old 14th January 2008, 06:05 PM   #131
John L is offline John L  United States
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Dan, I really need to scan some of my drawings into the computer and post them here, because nobody has any detailed idea as to what I am planning.

And you are right, the tweeter is going to be mounted on a phase plug, with both firing upward into the diffuser. The top is going to be rounded for asthetic purposes and will need to be rounder than with the Venus. Having it more pointed is useless because the tweeter is not going to be placed there.

Unfortunately, a completely rounded top is more difficult to turn on the lathe. Naturally straight lines and concave cuttings are easier. With straight lines you only need to set up the tool rest to follow the straight line, set your hand properly, and then glide across the rest as you cut the turning. With the Concave cut, you do not need to move your hand as much, but rather turn your wrist to round the cutting.

With a convex shape, the movement of your hand is much more complex, requiring you to not only move your wrists, but your entire hand, and pivoting your body is less important. It is probably four to ten times more difficult to make a convex cut. So, the less of it I am forced to do, the easier it is for me to get a nice looking diffuser.

If you go back to your pdf, and look at the top piece, the upper sides are not rounded, but more straight. In fact they are sligltly concave, and that would have to be changed. but the top is going to have to be convex, and the less this area, the easier to turn the upper section.

Before I took that day class Saturday, I had no idea just how difficult it is to use the different tools, round corners, and actually cut into the work, rather than scraping it off. There is a big difference, and a sharp cutting tool, will produce a finish that requires less sanding the better the cut.

I really need to say something about my class, but I forgot to carry along my camera. I promise you that I will carry it the next time I go. And I will take many pictures too.

Incidentially, do you have pictures of your project where you use the diffuser? Do you have any pictures of your cabinets?
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Old 14th January 2008, 06:47 PM   #132
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Default woodturning

John,
You may already know this: ask your instructor to demonstrate shear-scraping. It is great to improve the surface and decrease sanding.
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Old 14th January 2008, 07:46 PM   #133
John L is offline John L  United States
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Default Re: woodturning

Quote:
Originally posted by Ed LaFontaine
John,
You may already know this: ask your instructor to demonstrate shear-scraping. It is great to improve the surface and decrease sanding.
Ok. Thanks Ed.
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Old 15th January 2008, 01:53 PM   #134
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Quote:
Originally posted by John L
Incidentially, do you have pictures of your project where you use the diffuser? Do you have any pictures of your cabinets?
Hi John,

This was for the waveguide omni that I posted a link to. The lower diffuser was cut down in diameter to about 8.5" from the design in the pdf I posted. By way of explanation, it has an up firing 2" dome mid into the lower diffuser, which houses a 3/4" dome tweeter, which fires up into a second diffuser. Both the dome mid and the tweeter are mounted in waveguides, creating a true horn effect. Here are a couple of photos:
Click the image to open in full size.
Click the image to open in full size.
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Old 15th January 2008, 02:05 PM   #135
John L is offline John L  United States
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Dan, is this the project in which you had less than stellar results?
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Old 15th January 2008, 05:51 PM   #136
John L is offline John L  United States
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Here is what I have in mind for the diffuser horn. Since I am not knowledgable with drawing programs, I had to hand draw, scan, and upload it to my pic site.

Click the image to open in full size.

The drawing at the top is pretty much like how I will make this first setup for the project. Since I am creating a coaxial, in which the tweeter is set up on the end of a phase plug, and both the driver and tweeter situated at the top of the cabinets, firing upward, there is no need to do anything but round off the top.

And this may be too rounded, and needing to be flattened a little bit more.

The bottom drawing is what I have in mind for the next project, in which a high compression horn/tweeter can be fit into a cavity drilled out of the bottom portion of the horn assembly, and fired upward into another diffuser, that conformes to the general shape.

Anyway, if anyone has more suggestions, please feel free.

Each of the two diffusers will be turned from two seperate blanks, with the two turned and then glued together to form one single diffuser.

With the bottom one, the top portion will have a horn effect lathed into it so a lense horn can be screwed to the diffuser and be a one piece assembly. By the time I finally get around to this example, I will probably have modified it make it more efficient. For instance the little top diffuser may well be wider and set up higher, out of the plane of the curve in order to gain a wider dispersion
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Old 15th January 2008, 10:26 PM   #137
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Quote:
Originally posted by John L
Dan, is this the project in which you had less than stellar results?
Yes, it never went beyond the prototype you see, because it simply was not as good as the other hybrid omni designs in side by side listening tests.

Based on my expereince, having a direct firing driver in the upper frequencies, tends to give you better imaging and might have less room reflection issues.
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Old 15th January 2008, 10:38 PM   #138
John L is offline John L  United States
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Quote:
Originally posted by dlneubec


Yes, it never went beyond the prototype you see, because it simply was not as good as the other hybrid omni designs in side by side listening tests.

Based on my expereince, having a direct firing driver in the upper frequencies, tends to give you better imaging and might have less room reflection issues.
There are probably some ways to get around this. First, the diffuser will have to be large, and curved enough to allow the high frequencies to be dispersed around the room at a lower level, more where the person is sitting.

And second a more efficient compression horn will tend to work better than just a high efficiency tweeter. If you look at all three models Duevel use, they are all high compression horns. HC horns are almost always far more efficient than other tweeters, and should be far better at taking up the slack.

That's just my guess, of course.


Incidentially, that must be the reason why you have that PE tweet facing front and center in your new project.
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Old 15th January 2008, 10:47 PM   #139
Illusus is offline Illusus  Canada
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Dan, I noticed only two posts holding things up... even if it feels sturdy it'll be bad on a smaller scale, vibrations will smear the driver's output. It takes three points to create a plane. keep it in mind for future reference.
Looks neat; even if it didn't work out for you, I bet it was fun to make. We learn more from failures anyway. Your subsequent stuff looks great.
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Old 16th January 2008, 12:26 AM   #140
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Hi Bartek,

I agree with you, especially where a driver is physically attached. In this case the lower diffuser is held up on 3 posts, the third being directly behind in the middle and out of site. This diffuser also holds the tweeter. The top diffuser is held up with only two posts, but serves as a diffuser only and for frequecnies above about 3.5khz. Still, it might have been better with posts. The tweeter, however, sounded pretty good.

I think the main problem with the design was mostly due to the metal mid dome, combined with the plastic waveguide and firing into a diffuser. I lined the waveguide with plumbers putty in order to kill any resonances, but it never sounded right in the midrange, though it measured quite flat. I suspect that the mid dome would have probably sounded better with more room to breath. The design may have been better with a cone midrange or with fuller range midwoofer. I took the prototype to a DIY meet in Indiana and a lot of guys actually thought it was great, but I was never happy with it.
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