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Automated polar measurements using ARTA

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With the advances in free speaker simulation software (VituixCAD), DIY morons like myself can now design speakers of extremely high quality; we can now adjust passive and active filters and see the resulting acoustic summation in whatever form we please; directivity graphs, spinorama, listening windows.

However, the accuracy of these simulations is dependent on the data you feed them. In the case of VituixCAD, you're going to want horizontal and vertical polar measurements of each driver. For an asymmetrical 3 way speaker, using 10 degree increments, you need to make...something like 210 measurements.

If you're getting up to walk to your turntable, and it takes you 20 seconds to get set up for the next measurement, this is still going to take over an hour, and it will not be a fun hour. Lack of fun creates the risk for lack of focus, which can then result in mistakes.

Inspired in part by the ASR Community Speaker Project, I have been refining my measurement platform, building something which has a robust enough motor to rotate a large speaker on a tall platform, and also working on software which allows ARTA, my measurement software of choice, to automatically control the turntable - rotating it a set number of degrees, capturing a test signal, rotating again, etc.

Since this is where most of my efforts are going right now, I've decided to share information about this platform here rather than in the speaker thread.
 
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The most exciting news is that I have got the software working:

This program is a windows .exe compiled from python. It takes two command line arguments from ARTA - one which tells the motor to go to the home position, and one which tells it to go to a set number of degrees.

If the supplied argument calls for homing, the program does a homing routine which is controlled by an optical limit switch. If the argument is a number, the program calculates the steps needed to move to this position, taking into account some variables supplied by a configuration file. This configuration file allows the user to describe their setup - microstepping mode, stepper motor degrees per step (normally 1.8) and any gear ratio which is involved. The program then calls the motor controller and tells it to do the right thing.

The motor controller used is a 'tic' which is made by Pololu. These motor controllers come in a variety of configurations, distinguished mainly in how much current they can supply a motor. The tic I am using can run a 1.5A stepper.
 
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The mechanical side of things is in some ways more difficult. The platform I am building is 36" square (~915mm) and constructed of MDF, plywood and 2x6 lumber.

My current plan is to have the stepper motor control the platform using a belt and a 3d printed gear attached to the underside of the platform. By selecting the right gears, I can both increase the mechanical advantage of the motor, and also allow the turntable to rotate an integer number of degrees.

Another alternative is to use a high torque stepper motor with planetary gearing, and to attach this directly to the platform. The reason why I don't favor this approach is that I cannot find a suitable way of attaching a motor shaft (6-8mm) to a plywood base, given the potentially large torque generated by such a set-up. By using a 3d gear, I can attach it to the platform using as many screws as I want, as far away from the center of rotation as needed.
 

headshake

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With the advances in free speaker simulation software (VituixCAD), DIY morons like myself can now design speakers of extremely high quality; we can now adjust passive and active filters and see the resulting acoustic summation in whatever form we please; directivity graphs, spinorama, listening windows.
I too just started messing with VirtuixCAD. Tracing some SPL's and trying out crossovers has been an education. I used to think "how hard can it be blending two sources?" I did not think of what happens to the directivity. :p It has been nice "breaking" things in a simulation and taking things to the limit just to see what happens.

Another alternative is to use a high torque stepper motor with planetary gearing, and to attach this directly to the platform. The reason why I don't favor this approach is that I cannot find a suitable way of attaching a motor shaft (6-8mm) to a plywood base, given the potentially large torque generated by such a set-up. By using a 3d gear, I can attach it to the platform using as many screws as I want, as far away from the center of rotation as needed.
Why not laser cut mdf/hardboard with gears built into the shape? You could even have the degree lines burned in. Just spitballing.

I've read of folks using laminated mdf and greasing the 2 inner facing laminated sides so that the plates can spin heavy speakers(Dr. Earl Geddes I think).

Looks like you are mostly there! Good luck!
 

Arash

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Why don't you use REW instead of ARTA for automatic polar measurement? It's much nicer than ARTA and has no demo restriction, is far more user-friendly and has more graphical capabilities and a handful of other tools like Trace Arithmetic, Alignment tools, etcetera which ARTA doesn't offer.
 

Arash

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Why don't you use REW instead of ARTA for automatic polar measurement? It's much nicer than ARTA and has no demo restriction, is far more user-friendly and has more graphical capabilities and a handful of other tools like Trace Arithmetic, Alignment tools, etcetera which ARTA doesn't offer.

It's piece a cake! You only need an automatically controlled turntable with a stepper motor and an Arduino controller. You set the setting and click "Start" and voila! In a couple of minutes, your polar measurements are ready. You can set the increments in whatever degrees desired for 90, 180 or 360 degrees. I did this by 10 degrees increments for a 180degrees measurement.
We usually use this turntable using Clio FW02, but I was wondering why would anyone even bother to use ARTA while REW is much more comfortable.

Footnote: measurements are done with an empty turntable. Graphs are laptop speakers out and laptop mic in, don't take them serious.
120.gif
 

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kimmosto

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but I was wondering why would anyone even bother to use ARTA while REW is much more comfortable.
ARTA is better, easier and faster option if data processing and XO simulation is done with VituixCAD. ARTA just measures and saves files, and VCAD takes care of the rest.
The same story with CLIO because VituixCAD supports also mls and crp files of Audiomatica.
 

Arash

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ARTA is better, easier and faster option if data processing and XO simulation is done with VituixCAD. ARTA just measures and saves files, and VCAD takes care of the rest.
The same story with CLIO because VituixCAD supports also mls and crp files of Audiomatica.

I've used ARTA for many years with a Behringer ECM8000. Maybe for seven years. Afterwards, I've been working with Clio and rarely used ARTA. But I've used REW for comparing graphs, exporting capabilities and merging responses and making filters now and then. When I started using ARTA/LIMP I struggled for months to get used to it, but REW was much easier to get going. Perhaps is personal preference of software logic and platform. Both are great, both have their own pros and cons.
About VituixCAD I can't agree more. It's been years we have ceased using LspCAD and Crossover Shop of LinearX both of which costed thousands to be acquired but VituixCAD is far more comprehensive and saves a huge amount of time. The only crossover software I want to try out is Fine X-Over.
 
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617

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I've used ARTA for many years with a Behringer ECM8000. Maybe for seven years. Afterwards, I've been working with Clio and rarely used ARTA. But I've used REW for comparing graphs, exporting capabilities and merging responses and making filters now and then. When I started using ARTA/LIMP I struggled for months to get used to it, but REW was much easier to get going. Perhaps is personal preference of software logic and platform. Both are great, both have their own pros and cons.
About VituixCAD I can't agree more. It's been years we have ceased using LspCAD and Crossover Shop of LinearX both of which costed thousands to be acquired but VituixCAD is far more comprehensive and saves a huge amount of time. The only crossover software I want to try out is Fine X-Over.

I checked out fine xover and from what I can tell, vituixcad is superior. This is 2021. If you aren't designing your speakers with some kind of directivity graph you cannot achieve even hobbyist levels of performance.

Vituixcad optimizer works pretty well, but honestly if you know what you're doing an optimizer is not that useful.
 
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