Here's mine. I put my phone on top of the speaker in the middle and pull up a compass app and just rotate the speaker while REW does repeated measurements. It's a pretty annoying setup to use but it did generate some off axis data that was useful for filter development. I want to make a better system but I also just want to buy some ascilab and call it a day lol.
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mikewxyz
Member
Here are the measurements using my DIY turntable. I think the non-uniform spacing between the two middle angles (30* & 45*) and the rest is a function of the turntable base being more exposed to reflections at these positions. Taking accurate measurements is difficult but the results seem OK to me.
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Curvature
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You can try developing a compensation filter for those angles using a known source. For example, a flat-measuring speaker reviewed by Amir or Erin.
mikewxyz
Member
Thanks for the suggestion Curvature. I didn't intend to do anything with the data - more just a curiosity. $8 and some wasted time is about the level of investment I'm comfortable with. I would not spend the money to buy known measured speakers to use as a "measurement standard" for a gauge study.
terryforsythe
Major Contributor
Here is my turntable setup I just finished building and testing. I still need to cut down the platform and mount it to my ladder, but it seems to be working well.
It uses an Adafruit controller and stepper driver expansion board, connected to a Nema 17 stepper motor. It uses a 6mm belt to spin the table using a 4:1 gear ratio.
I created a Python GUI to run it. The GUI runs both on my Linux computer and my Windows laptop.
It uses an Adafruit controller and stepper driver expansion board, connected to a Nema 17 stepper motor. It uses a 6mm belt to spin the table using a 4:1 gear ratio.
I created a Python GUI to run it. The GUI runs both on my Linux computer and my Windows laptop.
terryforsythe
Major Contributor
I have the GUI working with REW to automate the measurement and rotation process. I explain it in this post:
www.audiosciencereview.com
Modifications to Elac Uni-Fi Reference UBR62 Bookshelf Speakers
What do you call that connector? It is a circular connector with push-pull locking. The manufacturer is Weipu. It is in the WEIPU IP67 - Large SA28 series. There are different pin configurations available - see the section "Solder Spec". https://www.weipuconnector.com/products/sa28/ They...
www.audiosciencereview.com
I just built a new measurement turntable that is basically a knock-off of MTG's turntable as seen here (post #3)
I did add one feature to help with getting large, heavy speakers up on a stand this high. I found this block and tackle pully system used for hoisting game for cleaning. I attached it to the outer and inner columns and this allows me to put the speaker up on the stand while its lower, then pull the rope to extend the column up to measurement height. Once its extended, the tower is locked in place with some steel pins. I still have to climb up a ladder with the speaker, but at least not as high.
The speaker pictured is at least 40-50lbs.
Just like MTG's design, the table spins on these MDF "wheels". I did not have a large Lazy Susan bearing, so I just made up something that works. The pivot point is just a steel pipe mounted to the lower wheel. The upper wheel is supported by a number of these "roller balls" which are basically casters with spheres instead of wheels. Cheap and worked well. Probably not as smooth as a real Lazy Susan, but it wasn't hard to turn with the speaker on there and I can upgrade later if I feel the need.
I did add one feature to help with getting large, heavy speakers up on a stand this high. I found this block and tackle pully system used for hoisting game for cleaning. I attached it to the outer and inner columns and this allows me to put the speaker up on the stand while its lower, then pull the rope to extend the column up to measurement height. Once its extended, the tower is locked in place with some steel pins. I still have to climb up a ladder with the speaker, but at least not as high.
The speaker pictured is at least 40-50lbs.
Just like MTG's design, the table spins on these MDF "wheels". I did not have a large Lazy Susan bearing, so I just made up something that works. The pivot point is just a steel pipe mounted to the lower wheel. The upper wheel is supported by a number of these "roller balls" which are basically casters with spheres instead of wheels. Cheap and worked well. Probably not as smooth as a real Lazy Susan, but it wasn't hard to turn with the speaker on there and I can upgrade later if I feel the need.
terryforsythe
Major Contributor
If you are using REW to take the measurements and want to automate the process, I have posted the computer code to google docs. I am using an Adafruit Itsy Bitsy M0 Express controller, an Adafruit TMC2209 Stepper Driver, and a stepper motor. It requires use of the Pro upgrade for REW.
Here is a link to the prototype in action:
c++ code for the Adafruit ItsyBitsy controller:
https://docs.google.com/document/d/10wD4b7UR8v50WHPFHFuK0yz3xInsSkIPP4k2B9Npf-0/edit?usp=sharing
Python code for the User Interface:
https://docs.google.com/document/d/1oOfAn9XkeB79seE6KC5B5qNTPhNGkp3o4Nadbv5lvgk/edit?usp=sharing
The user interface runs on Linux and Windows using Python. It also may work on a Mac, but I have not tested it.
Here is a link to notes for using it:
https://docs.google.com/document/d/1qE0cRJhmeEhFoTQvvIdHkSx0EpI7wzNtZMJEaeFMAA8/edit?usp=sharing
It's not that I dislike the solutions presented here. In fact, I've been considering similar approaches. I simply want to point out that rotating the speaker isn't strictly necessary. If you're in an open space, you can move the measuring microphone within a certain radius instead of the speaker. This, of course, reduces the load to be moved to a ridiculously small fraction. Aside from the reduced risk to the object and the operator, the measurement results are absolutely comparable. Maybe this may give some here new ideas for the same problem.
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As much as a single mm of relative difference in terms of distance between the microphone and the rotation point will show up in the phase response. as time-of-flight will be affected. Your suggestion leaves way too much room for error, unfortunately.
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It depends on what you want. For a DIYS developer this is a viable solution.
You only need a low weight arm to fix the microfone on. You need some stand for it anyway. The arms other end is fixed near the DUT and you get a perfect circle that way. As far as I know Klippel does something compareable. The larger distance makes it even simpler to get a correct angle, if that counts.
It is close to a philosophical question how much use one can make of his measurements in a DIYS case.
If you want to brag in a forum and compete with Klippel measurements you may need something different compared to a solid base for developing actual multi-way speakers. A ladder in a garden can get very close to a measurement in a million Dollar anechoic chamber if the resulting speakers sound quality is important.
I know a developer that uses very basic measuring stuff and goes to an expensive lab only for final verification. He is fully aware of the shortcomings of his measurement environment and integrates them into his decisions. It would be much to expensive to do the whole process in such a place. It is not the gear you use that does the work, without the human calling the shots it is quite useless.
You only need a low weight arm to fix the microfone on. You need some stand for it anyway. The arms other end is fixed near the DUT and you get a perfect circle that way. As far as I know Klippel does something compareable. The larger distance makes it even simpler to get a correct angle, if that counts.
It is close to a philosophical question how much use one can make of his measurements in a DIYS case.
If you want to brag in a forum and compete with Klippel measurements you may need something different compared to a solid base for developing actual multi-way speakers. A ladder in a garden can get very close to a measurement in a million Dollar anechoic chamber if the resulting speakers sound quality is important.
I know a developer that uses very basic measuring stuff and goes to an expensive lab only for final verification. He is fully aware of the shortcomings of his measurement environment and integrates them into his decisions. It would be much to expensive to do the whole process in such a place. It is not the gear you use that does the work, without the human calling the shots it is quite useless.
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That's all fine man, you do you. But this thread is about DIY turntables and not a place for discussion.
So once again:
So once again:
somebodyelse
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Am I right in thinking you need the rotation axis to be in line with the tweeter axis, so can't just stick the tower on its side on the same turntable unless you add some sort of outrigger to support the other end of the tower? Presuming it's not so tall that the tweeter is in the middle.
At the extreme we have the other thread where there seems to be good progress on DIY soundfield separation.
At the extreme we have the other thread where there seems to be good progress on DIY soundfield separation.
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For a 2-way speaker it's often sufficient to measure halfway between the drivers (half CTC) as a single axis. But yes it needs to be the same in both planes, so for a tower that means one side indeed sticking way out. I'm talking about "normal" towers. I won't be measuring a 300lbs behemoth in any case. I have a good idea of how to do it but just curious what everyone else came up with.
I'm keeping an eye on the DIY NFS, looks amazing - amazing effort.
I haven't seen the terms being mentioned yet. The industrial versions of these "lazy Susan" plate are "slewing bearing" or "slewing drive". Unfortunately, being industrial grade products they are usually high precision devices and have high load capacities, and aren't within the budget of most DIY projects.
https://www.google.com/search?tbm=isch&q=slewing bearing
https://www.google.com/search?tbm=isch&q=slewing drive
https://www.google.com/search?tbm=isch&q=slewing bearing
https://www.google.com/search?tbm=isch&q=slewing drive
a4eaudio
Addicted to Fun and Learning
I am still a month or two away from finalizing my turntable - just a DIY manual thing. But the objective is to be able to measure small bookshelves as well as tower speakers up to 250 lbs. At this point, that is an engineering target, as I couldn't get a 250 lb speaker up on it anyways, but my son and I HAVE measured a 50" tall, 155 lb speaker horizontal and vertical.
The base jig is built on a pillow bearing that can hold I think 1000 lbs, something like $15 off amazon, and heavy duty casters with 300 lb limits. (Pictures are too dark, but there are two casters on the back. The platforms are double layers of Birch plywood.) It is adjustable in height and has various "top plates" to fit various size speakers and reduce reflections. It has a vertical platform that can attach on top of the largest top-plate and extends to the side. (Vertical platform is at 48" and not adjustable.) The pictures below are illustrative, taken for another forum. It is a little wobbly with a BIG speaker, so I am expanding the size and weight of the base. To finalize the vertical platform I still need to roundover any sharp edges and cover most surfaces of the entire jig with open cell foam.
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Looking good! Planning something similar but with an adjustable stand on wheels. It won't hold as much weight as your contraption, but I'm a bit tight on storage space.
somebodyelse
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