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Old 21st October 2014, 05:15 PM   #1
kr1s is offline kr1s  United Kingdom
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Default New Dallas II build question

Hi All

I'm about to start a build of the Dallas II.

I've drawn the design full size on a scrap panel and have noticed something that raises a question.

In the first bend, the cross section of the horn decreases before returning to its original size. See image attached.

A similar exercise on the second bend shows that it increases before returning to (roughly) the original value.

My question is: is this by design and best left alone, or would smoother curves (by using more pieces), maintaining a constant throat size through the turn, be better?

Many thanks for any advice

Chris
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Old 21st October 2014, 06:08 PM   #2
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If I know Ron, it's probably deliberate.
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Old 5th December 2014, 10:38 AM   #3
kr1s is offline kr1s  United Kingdom
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Hello again

I now have my wood and the drivers have arrived - FE208E Sigma + FT96H.

There's been a delay as I needed to make a sled to enable me to (hopefully) make accurate, square cross-cuts on the table saw.

I'm now getting close to the point of making the first cuts, but I have another question.
I've read several times that drivers should be recessed such that the front of their bezel/mounting flange is flush with the baffle.

On FE208E Sigma the bezel is mostly tapered with a small square step at the edge (see picture attached).

So my question is whether or not I need to make a recess equal to depth of this step or whether it is unnecessary.

I notice that the Fostex standard enclosure design has no recess but I also know that their designs are not always considered to be optimal.

As always, many thanks for any advice.

Chris
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Old 5th December 2014, 12:21 PM   #4
xrk971 is offline xrk971  United States
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That is a tiny square step that is unlikely to cause any problems with diffraction compared to the shape of the bezel. IMO, no rebate is needed. Looking forward to seeing the build.
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Old 5th December 2014, 02:23 PM   #5
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Most Fostex drivers are designed to be surface mounted -- The FE and FF series for sure. The F200A is an exception. The frame the the FE208Ʃ, so it can be rabbeted in with a router and circle jib, but the pincushion frames are simply not worth the bother.

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Old 5th December 2014, 06:22 PM   #6
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We rebate to hide the step.

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Old 5th December 2014, 06:45 PM   #7
kr1s is offline kr1s  United Kingdom
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Quote:
We rebate to hide the step
LOL - all that time I've believed it was because it affected imaging

Thanks for the replies.
Hopefully there will be some progress over the weekend.

Chris
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Old 5th December 2014, 06:56 PM   #8
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Quote:
Originally Posted by kr1s View Post
all that time I've believed it was because it affected imaging
On the sigmas, notlikely much. Particularily the large ones.

dave
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