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Old 23rd December 2012, 04:56 PM   #181
gpapag is offline gpapag  Greece
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I will be off keyboard for a week more or so, thus I wish for the coming New Year everyone to achieve (or retain) the most valuable targets in life.
May we all be able to enjoy our hobby too.

["Second Law is a bitch." - SY] ["BTY my shop's large door is 14 feet wide so I can get my ego in each morning. Some evenings it can leave via the mail slot". -Ed Simon]
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Old 23rd December 2012, 04:59 PM   #182
Pano is offline Pano  United States
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Thanks George, Merry Christmas and a Happy New year to you!
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Old 26th December 2012, 11:09 PM   #183
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Hey guys, happy holidays!

I just got the holes cut for my drivers, and the drivers are on their way. In a surprise twist, I ordered a pair of Tangband W3-926SDF:

Tang Band W3-926SDF 3" Full Range Speaker 264-912

...But I plan to experiment with some other drivers later using the same cabinets. All that's left for me to do is either print out some plans or just draw the design onto the panels before I start gluing. Hopefully I will be done by the time the TBs arrive. More to come soon!

Then again, what do I know?

Last edited by chazdrumzalot; 26th December 2012 at 11:16 PM.
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Old 27th December 2012, 12:01 AM   #184
xrk971 is offline xrk971  United States
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Good luck with getting the channels glued. What size cornu were you making? The driver you ordered looks like it should work well - looks nice too.
Happy holidays.
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Old 27th December 2012, 04:56 AM   #185
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Cal you are quite insane. That is a plus. (-:
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Old 27th December 2012, 07:09 AM   #186
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Here is an updated version of the AkAbak script I posted in the other thread some time back. It now accounts for baffle diffraction, horn outlet displacement and direction, and has a wall behind it. The main use for such a script is to determine if a given set of horn dimensions will provide correct bass reinforcement for a given driver. It'll need work to add stuffing to the back chamber and HF losses in the horns before it can be trusted above a few hundred Hertz. Note that it's still "half a Cornu" - only one set of horn paths is modeled. The other half is a mirror of the first half so is just folded onto (added to) the first half. I still have my reservations about the performance of the "split length horns" - I still think you would be better off designing an optimum back-loaded horn in Hornresp or MJK spreadsheets, then plotting it into a spiral yourself.

| Cornu style horn. 
| Model developed by printing Dave's PDF and measuring
| the path lengths and widths. The printed version was 23.3 cm wide, 
| so it is scaled up to the required width.
| For example, a 70 cm horn is 70 / 23.3 = 3 times as large,
| so the dimensions are scaled up by 3. 
| This version has the horns exiting at the sides, and is mounted on a wall. 
| Required inputs:
| ================
| Horn width and height in centimetres (square baffle)
| Horn depth (wall height) in centimetres
| Driver Thiele-Small parameters (in Def_Driver further down)
| Do not delete the semi-colons;
Horn_Width = 70;
Horn_Depth = 11.5;

| All dimensions are converted to the AkAbak default unit (metres)
| and scaled up. Horn segment areas are doubled because there are
| 2 of each horn segment. 
Scale = Horn_Width / 23.3;
Depth = Horn_Depth * 1e-2; 
Tcvol = Depth * Scale * 4.5e-2 * Scale * 4.7e-2;
SxDx2 = Scale * Depth * 2;
Width = Horn_Width * 1e-2;

H1S1  = SxDx2 * 0.75e-2;
H1L12 = Scale * 2.5e-2; 
H1S2  = SxDx2 * 1.0e-2;
H1L23 = Scale * 5.0e-2;
H1S3  = SxDx2 * 1.2e-2;
H1L34 = Scale * 12.0e-2;
H1S4  = SxDx2 * 1.5e-2;

H2S1  = SxDx2 * 0.7e-2;
H2L12 = Scale * 3.2e-2; 
H2S2  = SxDx2 * 1.0e-2;
H2L23 = Scale * 6.2e-2;
H2S3  = SxDx2 * 1.3e-2;
H2L34 = Scale * 5.0e-2;
H2S4  = SxDx2 * 2.3e-2;
H2L45 = Scale * 7.3e-2; 
H2S5  = SxDx2 * 2.5e-2;
H2L56 = Scale * 6.6e-2;
H2S6  = SxDx2 * 2.6e-2;
H2L67 = Scale * 10.8e-2;
H2S7  = SxDx2 * 6.6e-2;

H3S1  = SxDx2 * 0.8e-2;
H3L12 = Scale * 1.4e-2; 
H3S2  = SxDx2 * 1.5e-2;
H3L23 = Scale * 5.1e-2;
H3S3  = SxDx2 * 1.6e-2;
H3L34 = Scale * 3.9e-2;
H3S4  = SxDx2 * 1.8e-2;
H3L45 = Scale * 7.0e-2; 
H3S5  = SxDx2 * 2.1e-2;
H3L56 = Scale * 17.4e-2;
H3S6  = SxDx2 * 2.6e-2;
H3L67 = Scale * 11.3e-2;
H3S7  = SxDx2 * 6.6e-2;


| Specify your driver here. You can use AkAbak's Def--> Def_Driver
| tool to enter the parameters. 

Def_Driver  'FF125K'
SD=66.5cm2   |Piston

Def_Driver  'TC9FD'
SD=36.3cm2   |Piston

| The wall behind the speaker.
Def_Reflector  Wall={Depth}
  HAngle=0  VAngle=0

System 'Cornu Spiral'

| Enter the name of your defined driver. 
Driver Def='FF125K' 'Driver 1'

Radiator 'Front_Rad'  
Def='Driver 1'
x=0  y=0  z=0  
HAngle=0  VAngle=0
WEdge={Width / 2}
HEdge={Width / 2}

Enclosure 'Driver Chamber'  

Waveguide 'Horn 1 seg 1'  

Waveguide 'Horn 1 seg 2'

Waveguide 'Horn 1 seg 3'

Waveguide 'Horn 2 seg 1'

Waveguide 'Horn 2 seg 2'

Waveguide 'Horn 2 seg 3'

Waveguide 'Horn 2 seg 4'

Waveguide 'Horn 2 seg 5'

Waveguide 'Horn 2 seg 6'
| Conical

Radiator 'Horn 2 mouth'
Def='Horn 2 seg 6'
| Exits top right, pointing right. 
x={Width / 2}  y={Width / 4}  z={-Depth / 2}  
HAngle=90  VAngle=0
WEdge={Width / 4}
HEdge={Depth / 2}

Waveguide 'Horn 3 seg 1'

Waveguide 'Horn 3 seg 2'

Waveguide 'Horn 3 seg 3'

Waveguide 'Horn 3 seg 4'

Waveguide 'Horn 3 seg 5'

Waveguide 'Horn 3 seg 6'
| Conical

Radiator 'Horn 3 mouth'
Def='Horn 3 seg 6'
| Exits top left, pointing up
x={-Width / 4}  y={Width / 2}  z={-Depth / 2}  
HAngle=0  VAngle=90
WEdge={Width / 4}
HEdge={Depth / 2}

Handy hint: If you want to see what the actual dimensions are for any of the elements, do the following:
1. Put the cursor somewhere in the text of the element (for example, in a Radiator element).
2. Select Net --> Acoustic -> Radiator...
3. The element editor will open. All of the substituted values will be displayed as actual values. For the 'Horn 3 mouth' radiator above, the "y" value will be displayed as 35cm.

This is very handy for debugging when you're working with formulas.

Last edited by Don Hills; 27th December 2012 at 07:18 AM.
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Old 27th December 2012, 09:52 AM   #187
xrk971 is offline xrk971  United States
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Thank you Don. This is really good stuff. I am actually playing around Hornresp right now starting with just a single horn and I already see that it provides the TC9FD with a lower bass extension than compared with a bifurcated design.
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Old 28th December 2012, 03:06 PM   #188
xrk971 is offline xrk971  United States
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Default HornResp for 24 inch with equal length horns

Here is my first cut at a 24 inch x 4 inch deep Cornu with four equal length horns - no bifurcation. In HR I am modeling it as one horn, and in practice, the single horn would be divided into 4 equal horns and rolled up. Note that the channels are now getting very close together in spacing and the 3/16 in thick foam core channels thickness will have to be accounted for. Alternatively, the critical early parts where the dimensions are narrow can be constructed with perhaps thin model building plywood (1/16 in thick birch). The 4 horns each have their own throat starting at the driver chamber. The horns were designed by modifying the Cornu bifurcation divider channel and extending it all the way back to the chamber. Some of the passages were adjusted so that the flow in all 4 channels has the same cross sectional area (see photo of plan drawing). The horn was modeled using a linear cone from the throat to the point where the curved mouth transition is. From there it becomes and exponential horn. I am using the T/S parameters for the Dayton RS100 which has a substantial xmax. The predicted xmax at 52 Hz is still < 1.5 mm. The lower frequency peak is centered at 61 Hz, with the highly amplified mid-bass peaks at 127, 204, and 288 Hz.

The final amplitude of these peaks will have to be adjusted with stuffing placed along the throat to probably about the first third of the horn may work to soften up these peaks. This is something that would be very helpful to build with a foam core back with access "windows" cut out of the back plate for adjustment of the stuffing. The windows can be sealed temporarily with a cover of foam core and plumbers' putty. Then a measurement would be made. Once adjustment provides a good result , the windows can be permanently sealed with the foam core cutouts and hot melt glue. I will use a gram scale to weigh the stuffing and estimate how long it is stretched out so that the stuffing results can be reproduced.

This is my first HornResp attempt, any feedback as to what I can try to improve the horn output would be appreciated. I have also done a similar sim at the 28 inch size with a TB W4-1337SDF with similar, albeit lower freq and higher SPL results. One thing that is interesting is that the depth controls the cross sectional area and volume of the horn, so if you make it too deep, you may have too much bass that you cannot control. It may actually be preferable to make the horn shallower than as calculated based on Sd matching the throat considerations alone. If someone would like to attempt modeling this horn in MJK's Mathcad sheets as a collaboration that would be great - it will allow for adjustment of stuffing before actually building. The HR dimensions are in the pdf file if you are interested in trying this yourself.
Attached Images
File Type: png Cornu-HR-24x4-RS100-SPL.png (46.2 KB, 850 views)
File Type: png Cornu-HR-24x4-RS100-schematic.png (8.8 KB, 843 views)
File Type: jpg cornu-plan-24inch.jpg (121.6 KB, 804 views)
Attached Files
File Type: pdf Schematic-24x4-RS100-v01.pdf (13.0 KB, 87 views)

Last edited by xrk971; 28th December 2012 at 03:35 PM.
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Old 28th December 2012, 04:57 PM   #189
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Originally Posted by xrk971 View Post
Good luck with getting the channels glued. What size cornu were you making? The driver you ordered looks like it should work well - looks nice too.
Happy holidays.
I'm making a 24" cornu.

Yesterday I got the design printed, then I copied the pattern onto the baffle with a heavy marker. Images below. My drivers aren't coming until the 3rd so I have some time to get around to gluing. I also bought some polyfil to stuff the chamber and the first third of the horns. Since I'm planning to glue right up, I will only have one chance at horn stuffing; should I err on the side of too much than too little?
Attached Images
File Type: jpg IMG_0147.jpg (237.4 KB, 786 views)
File Type: jpg IMG_0148.jpg (271.8 KB, 773 views)
Then again, what do I know?
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Old 28th December 2012, 05:20 PM   #190
xrk971 is offline xrk971  United States
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Great that you are warming up your glue gun now! You might try gluing a string to wad of stuffing and leave string hanging out to adjust or remove. Might need to put stuffing in cheesecloth sack to pull out. Good luck!
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