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Old 19th November 2013, 08:50 PM   #1111
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Quote:
Originally Posted by Cal Weldon View Post
Clearance needed as the baffles are not very thick and can't be used to brace the driver.
Thanks. So is there some sort of formula? Does a 2" driver need X amount of clearance? How is the depth determined? Thanks again.
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Old 19th November 2013, 09:31 PM   #1112
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I'm going to let xrk971 do the calculating but it seems to be close to the driver size. IIRC, my 4.5" driver have a 4.5" depth and same with the 3" drivers, a 3" depth.
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Old 20th November 2013, 02:19 AM   #1113
unaHm is offline unaHm  United States
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I really need a CNC machine. I've started gluing the spirals, and it looks like a mess. I did what I could while the glue was setting, but my inaccuracy frustrates me...especially in a project where precision is so important. I'll try to get some more done to it this week, because finishing the project would be nice!
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Old 20th November 2013, 03:28 AM   #1114
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by unaHm View Post
I really need a CNC machine. I've started gluing the spirals, and it looks like a mess. I did what I could while the glue was setting, but my inaccuracy frustrates me...especially in a project where precision is so important. I'll try to get some more done to it this week, because finishing the project would be nice!
Work in short sections at a time. You should be able to hold a 3 in section steady while the hot melt glue sets. You have about 15 sec to move it around before it hardens. The accuracy at the begining of the spiral where the channel spacing is tight is more critical than the wider parts. Don't worry if it is not exact. If you are scoring the foam with lots of cuts it should not be hard to curve it and hold it at a desired curvature while glue sets in 30 seconds.
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Old 20th November 2013, 03:31 AM   #1115
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by Cal Weldon View Post
I'm going to let xrk971 do the calculating but it seems to be close to the driver size. IIRC, my 4.5" driver have a 4.5" depth and same with the 3" drivers, a 3" depth.
Cal is correct in how to approximately size the channel depth. It works out that way and if is quite forgiving. I only use 2.38 in for my 3.5 in driver and it works fine. If you give me T/S params for your driver I can run a sim and tell you what the optimal depth is.
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Old 20th November 2013, 09:12 AM   #1116
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Okay. I spent a few hours reading halfway through the posts. I feel more confused.

I thought I could simply take the original diagrams and scale to match driver. Now I read about throat sizes, etc.

I am going to build a pair of these. And I hope somebody can fill in the blanks: how deep should the cavity be? Can I just scale from the PDF found on page 3 for my drivers or do I need to adjust for my specific drivers (throat size etc)? I assume 36cm is the correct size for my drivers... or could I put these in the 50cm? My drivers will be HiWave BMR12.

PRODUCT SPECIFICATIONS
Nominal Diameter 2"
Power Handling (RMS)12 Watts
Power Handling (max)24 Watts
Impedance8 ohms
Frequency Response 150 to 16,000 Hz
Sensitivity 83 dB 1W/1m
Resonant Frequency (Fs)164 Hz
DC Resistance (Re)8.13 ohms
Voice Coil Inductance (Le)0.12 mH
Mechanical Q (Qms)2.37
Electromagnetic Q (Qes)0.89
Total Q (Qts)0.65
Compliance Equivalent Volume (Vas)0.0063 ft.
Maximum Linear Excursion (Xmax)3 mm
Overall Outside Diameter 2.56"
Baffle Cutout Diameter 2.05"
Depth 0.81"
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Old 20th November 2013, 09:34 AM   #1117
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Hey guys,
I uploaded the Autocad file that I used.
You can download it here:
https://dl.dropboxusercontent.com/u/21694574/Cornu.dwg

When CNCing the spiral, I would recommend to set the drill depth to some micras less than the total depth of the middle plate, so the drill doesn't go through the entire plate. That gives consistency and prevents the central plate from breaking, because when most of the spiral is cnc'd, the middle plate loses consistency and starts moving and it's quite a mess.
Once you have cnc'd the entire spiral, you can get easily rid of the thin layer of wood with a screwdriver or something.

Another good thing to do would be to start the drilling process from the inner part of the spiral outwards to the middle plate's edges.

Not sure if I explained what I meant in an understandable way hahaha, but hope it helps Kuroguy!!
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Old 20th November 2013, 10:38 AM   #1118
wesayso is online now wesayso  Netherlands
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Here's an idea, looking at the later Cornu with the horn at the front
Click the image to open in full size.
and X's experiment with a synergy in foam core...
Click the image to open in full size.
Why not combine the two?

X is running them open back but why not put a Cornu style back horn on there... you've got 4 mids... They need to be a little closer to the entry of the horn and the vifa's being band passed you'd probably need a tweeter at the entry of the horn.
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Old 21st November 2013, 03:19 AM   #1119
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by irishpatrick33 View Post
Okay. I spent a few hours reading halfway through the posts. I feel more confused.

I thought I could simply take the original diagrams and scale to match driver. Now I read about throat sizes, etc.

I am going to build a pair of these. And I hope somebody can fill in the blanks: how deep should the cavity be? Can I just scale from the PDF found on page 3 for my drivers or do I need to adjust for my specific drivers (throat size etc)? I assume 36cm is the correct size for my drivers... or could I put these in the 50cm? My drivers will be HiWave BMR12.

PRODUCT SPECIFICATIONS
Nominal Diameter 2"
Power Handling (RMS)12 Watts
Power Handling (max)24 Watts
Impedance8 ohms
Frequency Response 150 to 16,000 Hz
Sensitivity 83 dB 1W/1m
Resonant Frequency (Fs)164 Hz
DC Resistance (Re)8.13 ohms
Voice Coil Inductance (Le)0.12 mH
Mechanical Q (Qms)2.37
Electromagnetic Q (Qes)0.89
Total Q (Qts)0.65
Compliance Equivalent Volume (Vas)0.0063 ft.
Maximum Linear Excursion (Xmax)3 mm
Overall Outside Diameter 2.56"
Baffle Cutout Diameter 2.05"
Depth 0.81"
14 in x 2 in deep should work. Just scale drawing.
X
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Old 21st November 2013, 03:22 AM   #1120
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by wesayso View Post
Here's an idea, looking at the later Cornu with the horn at the front
Click the image to open in full size.
and X's experiment with a synergy in foam core...
Click the image to open in full size.
Why not combine the two?

X is running them open back but why not put a Cornu style back horn on there... you've got 4 mids... They need to be a little closer to the entry of the horn and the vifa's being band passed you'd probably need a tweeter at the entry of the horn.
Are you saying a 4 driver Cornu with Synergy front horn? You will need channels to route back wave to Cornu center - a common box for all 4 drivers would work. A piezo or dome tweeter in middle will help cover highs lost by bandpassing fullrange drivers. Interesting...
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