Anyone built a Loudspeaker Measurement turntable? - AVS Forum
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post #1 of 11 Old 05-20-2014, 08:16 AM - Thread Starter
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I am just getting my measurement software/hardware setup and looking to get started on doing some measurements of various horns/drivers I have (a bunch). One thing I thought of making is a turntable to do directivity and polar measurements which is key to modern designs. It seems to be a relatively simple concept but was wondering if anyone rolled their own and has a nice design?

My measurement setup thus far:

1) Omnimic V1 (updated the software)
2) Bought a little amp with volume control for measurements as most of my equipment is tube based and thus complicates pure measurements.
Dayton Audio DTA-120 Class T Digital Mini Amplifier 60 WPC
3) Have Soundeasy

Recently decided to invest in the "full monty" setup since I have so much vested in speakers/drivers/projects.
3) Earthworks M30
4) Focusrite Scarlett 6i6 (was on ARTA's tested list)
5) ARTA
6) MiniDSP 4x10 (intended to prototype the crossover)
7) ATI 1504 (for use with above, but already had it)

Also downloaded HOLM, REW for good measure (pun). Will look at PCD too. Once I get all the measurements I'll need something to design the crossovers in.


Some challenges to good measurements include my room, which is rather small (think 12 x 20 but 12' ceilings) and cluttered. I do have a lot of RealTraps on stands that I can move around to block first reflections in measurements.

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post #2 of 11 Old 05-20-2014, 08:22 AM
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I made one years ago, the design was published in Speaker Builder. Just get a large lazy Susan ball bearing turntable from a hardware store, put it between two pieces of plywood. It can't be really small, though. The speaker has to sit atop it with the baffle on the center of the platter, so the platter diameter must be twice the depth of the largest speaker that you'll measure.
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post #3 of 11 Old 05-20-2014, 08:25 AM
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NICE measurement gear man! I've wanted soundeasy for some time. Everytime I have a little play money I spend it on drivers or tools instead of the program rolleyes.gif And that mic! Dang dude.

You have 12' ceilings, that's better than 99% of rooms out there for measurements. You can get the driver 6' from any and all reflection points. It's amazing how much clutter doesn't matter IME. I think this setup will give incredible results.

As for a turntable. Ya, I've made them, but nothing notable. Most people get a lazy suzan bearing from Home Depot and make a base out of plywood. Then make markings every 15 degrees or what ever increment you want. I'd start with a lazy suzan bearing and see what you can come up with. For your setup, I'd make it 4' tall so that your DUT is about 6' off the ground. Use blocks to raise it up if needed, but hard to shorten the stand after the fact. So error on the side of short rather than tall.
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post #4 of 11 Old 05-20-2014, 08:29 AM - Thread Starter
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I was thinking the base of a miter saw (broken one off craigslist or something) might make a good one if the platform was modified a bit. At least it has a nice control over the angles and stops.

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post #5 of 11 Old 05-20-2014, 08:40 AM
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Quote:
Originally Posted by AudioJosh View Post

I was thinking the base of a miter saw (broken one off craigslist or something) might make a good one if the platform was modified a bit. At least it has a nice control over the angles and stops.
As long as it's not a tiny speaker, stops shouldn't be an issue.

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post #6 of 11 Old 05-20-2014, 10:43 AM
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I did the lazy Susan bearing thing between 2 scrap pieces of MDF. I put some of those plastic furniture slider deals meant for carpet on bottom of the top piece of mdf to act as outriggers for it to slide on. Bigger speakers made it tippy when the baffle was centered on the rotation point. IIRC Geddes said that he used 2 pieces of mdf with melamine laminate, a hole through the middle, a dowel and some grease.

Thanks for the reminder I need to build a better one!
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post #7 of 11 Old 05-20-2014, 11:51 AM
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Originally Posted by AudioJosh View Post

At least it has a nice control over the angles and stops.
All you need for that is to drill a 9/32 inch hole through the top piece on the axis. Rotate it by as many degrees as you want for your resolution, drill through that hole through the bottom piece, repeat until you have a hole in the bottom piece at each rotation point. Lock the top plate where desired by dropping a 1/4 inch bolt through both holes.

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post #8 of 11 Old 05-20-2014, 12:47 PM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post

All you need for that is to drill a 9/32 inch hole through the top piece on the axis. Rotate it by as many degrees as you want for your resolution, drill through that hole through the bottom piece, repeat until you have a hole in the bottom piece at each rotation point. Lock the top plate where desired by dropping a 1/4 inch bolt through both holes.

Good idea, why didn't I think of that? lol

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post #9 of 11 Old 05-20-2014, 03:10 PM
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Here is mine. 10 degrees graduations. The lower section slides up and down in the base section, you can see the holes spaced every 1" where I stick a bolt to hold everything at the height I want it.

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post #10 of 11 Old 05-20-2014, 06:24 PM - Thread Starter
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Here is mine. 10 degrees graduations. The lower section slides up and down in the base section, you can see the holes spaced every 1" where I stick a bolt to hold everything at the height I want it.

Awesome, exactly what I was thinking of doing. Just wanted to get the juices flowing. There is always someone that has some clever ideas that you didn't think of.

I am going to do 7.5º gradation, cause that is what the good Dr. Geddes (pay homage) uses as resolution. That is where I got the idea, that is what I'll use.

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post #11 of 11 Old 05-20-2014, 06:29 PM - Thread Starter
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btw, does anyone know what the Dr. G uses as weighting for the polars? I haven't done vector math in some time, but something tells me this is such.

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