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Old 25th March 2011, 10:25 PM   #11
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I need to advertise it, but with driver purchase the plan-set comes as a freebie.

I'll send an email, just packing up the 2nd last pair of FE127eN and headed down to the post.

dave
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Old 27th March 2011, 03:28 AM   #12
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Waiting for the speakers to arrive, today I bought some veneer and 18 mm birch plywood and played a bit with Google SketchUp. I plan to make the fonken cabinet evolve into something like that. I will keep all the inner dimensions the same so I hope sound will not be hurt. I also think of using birch for the front panel only and solid foam for all the rest. I will build one first and try it and then decide if I need to switch back to 100% birch.

I noticed in the fonken plans that the driver seats into a recessed hole. Is this the mandatory way to go? What are the pros and cons of seating it on top of a hole with no recess?
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File Type: jpg Cabinet model 1.jpg (63.9 KB, 266 views)
File Type: jpg Cabinet model 2.jpg (49.7 KB, 257 views)
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Old 27th March 2011, 04:30 AM   #13
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The rebate sets the driver flush with the baffle to reduce diffraction effects. Ideally the driver should "see" a box that has edges that fall away backwards. Anything that protrudes* from the baffle will degrade the diffraction signature and make it harder, if at all, to disappear. Diffraction off edges, is like someone sticking up their hand and sayng shoot me, shoot me...

*(what is and is not a protrusion depends on the frequency of interest)

The render you show will probably have a high diffraction signature. It does look like a mini-CurvyChang, but that loudspeaker uses an 8" unit with much narrower dispersion , such that the protrusions small enuff at the frequencies where they would be seen that it gets away with it. Still it probably has more issues disappearing then just a normal chang.

With your design, you would also need to take care to maintain the length of the ports, not forgetting the effect of horn loading the vents with the protrusions.

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Old 27th March 2011, 08:44 PM   #14
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Dave, I think I have a problem with drivers mounted flush with the baffle. I read that a rounded edge of the driver flange helps fight against diffraction. Since the Alpair is square, how about adding a ring? I find it more pleasing. I could make the ring wider if needed.
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Old 27th March 2011, 11:41 PM   #15
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by Michael Speaker View Post
Dave, I think I have a problem with drivers mounted flush with the baffle. I read that a rounded edge of the driver flange helps fight against diffraction. Since the Alpair is square, how about adding a ring? I find it more pleasing. I could make the ring wider if needed.

Rebate the driver so the mounting bezel is flush. In the case of the generously thick flanges of the Alpair7, this does mean either thicker material for the front baffle (25mm would be great) or a square of 6-9mm thick material on the backside of driver cut-out would provide more core for the mounting screws. Whichever material is used, remember to bevel or round-over the rear side of cutout - before assembly. Yes, I've been in automaton mode more than once and forgotten that

The large chamfers and narrow effective baffle are specifically purposeful
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Last edited by chrisb; 27th March 2011 at 11:48 PM.
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Old 28th March 2011, 02:03 AM   #16
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Note: In the picture Chris posted, he has a not quite finished A7eN installed (2 singles for centre channel use) -- ie yours will look a bit different with an EnABL ring on the bezel and gloss over that.

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Old 28th March 2011, 02:25 AM   #17
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Quote:
Originally Posted by Michael Speaker View Post
I read that a rounded edge of the driver flange helps fight against diffraction.
For a rounded edge to be effective against diffraction it needs to be large... much larger than possible on a driver bezel. So in practice the driver still needs to be flush mounted in the sub-baffle and that subbaffle have significant rounding. Then you need to consider that round is good for wave launch, but not so good for diffraction -- with a circle the edge is equal distance all round the driver so all diffraction happens at the same frequency. An elipse is a good compromise. But, from Olsen, it turns out that a champhered box is not that far behind. Having the 2 edges on the Fonken-style boxes gets you most of the way there, adding material top and bottom and adding champers there improves things a bit.

dave

The attachment is an FE166eN^2 in a C&C SuperAbby (one of their budget models) which has a decreasing radius supraBaffle that starts falling away at the edge of the driver bezel. It is not as thick as larger models which are closer to what would be optimal.

Here is Olsen's landmark page 23 which gives a broad guide for the diffraction signature of basic shapes:

Click the image to open in full size.

And a Fonken with additional top & bottom layers to allow for champhers there:

Click the image to open in full size.
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File Type: jpg FE166en^2-superAbby-sB.jpg (52.5 KB, 32 views)
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Old 29th March 2011, 05:14 AM   #18
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OK, will mount it flush then.
Now how about the chamfer? Can I do round edge instead?
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Old 29th March 2011, 05:40 AM   #19
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A round edge is fine, you just have to ensure that you maintain the vent length. Getting this right is complicated by the end of the inner side being part of the vent (i can help with that).

You want the round over to be as large as possible,

dave
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File Type: gif Mar-Ken-vent.gif (3.9 KB, 46 views)
File Type: jpg Scott-fonken.jpg (61.8 KB, 66 views)
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Old 29th March 2011, 03:27 PM   #20
chrisb is offline chrisb  Canada
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Originally Posted by planet10 View Post
A round edge is fine, you just have to ensure that you maintain the vent length. Getting this right is complicated by the end of the inner side being part of the vent (i can help with that).

You want the round over to be as large as possible,

dave


The issue with round-overs is expense of larger router bits ( 1/ 1/2" R = $149 ) and the machine in which to safely spin it - something like the PC 3 1/2 HP production is $400, and you wouldn't want to be hand-holding this one - a very sturdy router table bolted to the floor is essential..
Bits this size, the power / weight of the average home DIYer's tooling , and hand held use is a recipe for You-tube disaster footage.


The other option would be a shaper, but again expense of tooling and access to this type of machine is far less common I'd imagine than the table saw required to cut the chamfers. This is one cut on the box where using a coarser tooth ripping blade and clean up with a sanding block can make things faster, that 72T ATB or negative angle melamine blade will very likely bind, overheat the blade and burn the plywood.
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Last edited by chrisb; 29th March 2011 at 03:30 PM.
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