6) Creating the Spinorama in VituixCAD
You don't need VituixCAD to create a spinorama, but it makes it a lot easier. VituixCAD creates a spinorama automatically upon importing the relevant data, and it can simulate the off-axis bass measurements we ignored in previous sections.
(Note: this guide was written with VCAD version 2.0.65.0)
First we need to export the data out of REW with the proper formating. If you ignored my suggestions in the previous section, you'll need to label your files as +/- horizontal and vertical angles. The VCAD default suffixes are 'hor' and 'ver' but we can change that; I prefer H and V because I'm lazy.
Order doesn't matter, just that they are labeled as positive and negative. VCAD will ignore duplicate angles (such as V0 and V180), so it's up to you whether you want to keep them in there or not. I delete them so I can just choose which duplicate I want to use.
I will also remind you that all your angles should use the same gate, or else the directivity information gets screwed up without some workarounds.
We begin by going to File>Export> Export all measurements as text. These are the settings I use:
- Use range of measurement
- Use resolution of measurement
- Use custom smoothing: No smoothing (smoothing should be added at the end).
- Use REW export format (recommended)
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I recommend exporting these files into their own folder called 'Spin angles' or 'For VituixCAD' or whatever. Because this will export all the measurements in your REW session, I recommend deleting anything you do not strictly need to create the spin: the angles and the corrected nearfield bass response.
You can only export one measurement or all of them. I recommend deleting or moving these extraneous files after exporting to make your life easier, except for the corrected bass response we created earlier, which we will merge with VituixCAD.
Now we open up VituixCAD. Before we can do anything else, we'll need to go to the crossover tab, and link the amp and driver (just draw tap from one dot to the other). VituixCAD is a speaker simulation app, and we're basically asking it to imagine that all these measurements came from a single driver.
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Next we're going to set up VituixCAD to format data the way we want it.
Click on the Options menu. When the window pops up, you want make sure all the settings are kosher for a proper spin. Here's what I'm using:
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Simply pressing the "CTA-2034A" button should make it match the spin standard right away. But some things to note:
- Set "plane keywords" to whatever you are labeling your files. I just use "h" to denote horizontal and "v" to denote vertical. The default is "hor" and "ver," so you'll want to switch that if you're using a different naming scheme. The CTA button won't affect this setting.
- Make sure mirror missing angles is checked (it fills in missing horizontals on symmetrical speakers).
- Make sure "Listening Window DI" is checked, as this is more common than on-axis DI for spinoramas.
- Make sure the Power & DI section matches the above image. Although you can mess with the Angle Step setting if you'd like if you'd like -- VCAD will interpolate the results if you choose a different angle step.
- I'm using 1000 mm listening distance because that's the distance I measure at. The spin standard is 2000 mm, but it shouldn't have a big impact on your results either way.
Now return to the "Drivers" tab of VCAD. Right-click on the "Power & DI" panel and select 'Traces.' Make sure all the Spinorama curves are selected (this is just for previewing the data, we can export it later). These are the standard ones we use, although lately
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Now let's generate the spins. Although we already showed how to merge the nearfield and farfield respones in REW, we will do it again in VituixCAD to generate a complete spin.
Go to Tools> Merger, or press F4.
First, let's import the corrected bass response. Tap on the folder icon in the 'Low frequency part' section and open the bass file we just exported. On the bottom right of this section, make sure 'No baffle loss' is selected. By default it is set to spherical baffle loss, but we need to switch it as we have already corrected the bass in a more accurate way.
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Let's import the farfield data next. Select the folder icon under the 'High Frequency' part of the window. Navigate to the folder where you've exported all your measurements. Select all the spinorama angles, and double check that nothing except for the angles are selected before you import.
Next we are going to scale down the bass response to line up with the high frequency measurements. First look through the high frequency measurements and click on H0 to preview the measurement. It should be checked as 'axial,' but if not, make sure it has a checkmark.
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Then scale down the low frequency measurement until it lines up. You can simply tap on the 'Scale' text box and press your keyboard's down arrow until the two measurements line up, or enter the value manually.
Now in the 'Transition' box to the right, select where you want to merge the data. As noted earlier, somewhere between 200Hz and 800Hz, depending on how well the measurements line up. You may have to experiment with this to see what gets you the best results, as it may vary depending on your gate, but in practice, I usually select between 300 and 600 Hz.
Next to 'Blending,' select how smoothly you want to merge the measurements. I usually blend them across 1/2 an octave, though 1 octave works too.
In the "Output" segment at the bottom right, select "create merged responses" and "feed speaker". Select TXT as your file format. Then click Save on the bottom right.
Chose a place to save your merged frequency responses. I usually keep them in a subfolder for the speaker I'm measuring and call it 'V Merged'
If all goes well, VituixCAD should tell you it's done after a few seconds (it may also warn you that a duplicate direction wasn't loaded, which is fine). Return to the main window, and.... congratulations! You should now see an honest-to-goodness Spinorama in the 'Power & DI' section. You can double-click on this window to see a larger version.
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Now you should save the project file. From here it's up to you how to present the data.
If you just want to use VCAD's spin and call it a day, you can right-click on the spin and select 'export image.'
If you want to change the colors, you can right-click on the image and select 'Traces,' then pick the colors from the 'Line Color' column. If you want to smooth the data, you can do that from the right side of the window where it says 'smoothing.
Personally, I prefer to deal with data presentation in REW. It makes the measurements prettier and makes it easier to present consistently.
To do so, make sure smoothing is disabled, then simply go to File>Export> CTA-2034-A data. Find a folder to keep the spin curves; I recommend making a separate folder as there will be 16 resultant curves. Set the file name to something reasonably short, since REW has short character limits.
Under 'Save as type' select '.txt.' This will create all the traditional spinorama curves, as well as the early reflections breakdown (ceiling, floor, side, rear, and front reflections), total horizontal and total vertical reflections, as well as horizontal and vertical ERDI DI.
Now navigate to the folder where you saved the files, and drag and drop them all into REW.
Note: You will need to add an offset to the Directivity curves in order to make them visible next to your other measurements. You can use whatever value works, but I recommend a multiple of 5 (say 45 or 50 dB) so it lines up cleanly with REW's grids.
You can then of course change the colors to whatever you want them to be. If you want to make any of the curves dashed, say the predicted in room response, you can do that from the trace options menu.
Lastly, I consider consistent scaling to be extremely important. As noted earlier In REW, we can use the 'Capture' button in the All SPL window. Select 25/dB per decade as your aspect ratio to make sure your images are always at the right scaling. While VituixCAD also has the option to export an image at specific aspect ratios, for whatever reason, it doesn't seem to be consistent.
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Some notes:
- You can visualize directivity from the 'Directivity' window of VituixCAD. Right-click to see more directivity views, including polar maps and SPL plots; you can also opt to normalize the graphs or add contour 3dB lines to the polar maps
- Sometimes the off-axis bass just doesn't look right for whatever reason. In these situations, I prefer to cut off the data below 200Hz. To do this, import the spin data into a new REW window, then select 'Export all measurements as text.' This time select 'use custom range' and cut off the data below 200Hz. Then re-import these truncated curves into REW, which you can present alongside the merged on-axis.
- I like to apply 1/24 smoothing in REW.
- You might want to rename the spin curves from VituixCAD's defaults, as many of them are rather long.
- Dark mode looks cooler
And that's it! Hopefully this extremely long guide was helpful to get you on the way to creating a spinorama without having to buy a Klippel NFS or anechoic chamber. Good luck, and feel free to ask me any questions!
P.S. Apologies for any typos. I wrote a lot of words very fast.
