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ErinsAudioCorner

QMuse

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Just an update...

I have been in talks with Klippel about my test method results. They have a module called ISC (In-Situ Compensation) and the long story made short is that I can use this module to get anechoic results in my garage based off a single outdoors measurement (per DUT). Some early tests proved incredibly useful. We have traded emails back and forth about proper use and implementation of the module. They are working on an intermittent schedule due to COVID-19 so replies from them are days apart and I am waiting on final confirmation before moving ahead.

I have also ordered a few parts to build a computer controlled turntable so I can rotate the DUT at any angle I desire. My proof of concept proved quite useful.

Hopefully I can be fully operational by next weekend and start knocking out some of these tests.

Thanks for your patience. :)

Thank you for doing this and sharing ther results. :)
 
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hardisj

hardisj

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Heard back from Klippel. All signs point to "GO". So now I have one last task to complete... the automated turntable. Thanks to a couple suggestions here I built the prototype today. I figure I’d share a little of the progress. The attached videos show this thing in action. I will need to tweak the design a tad but overall it’s a success. It supports at least 185 pounds and as you can see, it has no problem spinning my kid around. :)


Once I complete it I'll do a little video in case anyone else wants to copy the design.




 

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That was quick. Good work.
 

RayDunzl

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As we know by now, there are many ways to measure a speaker's response. All with their own pros and cons. My efforts reveal that a 2-pi ground plane measurement can give the same accuracy as a 4-pi "speaker in the sky" measurement.


What happens when you raise your bookshelf so the tweeter is 36" or so off the ground plane, as would usually be the case with a floorstander?
 
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hardisj

hardisj

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That was quick. Good work.

Thanks.

I went through some more troubles but finally got it working pretty well. I wound up building the support legs underneath and affixed to a board at the bottom of the whole assembly. Those replaced the support legs attached to the top platform, which you can see rotating. The reason for this change was the support legs would roll over the cables and cause the motor to sometimes snag and get off in step a bit. However, when I switched to a bottom support I found the top platform (made of plywood) was soft and would get divets in it from the weight of the DUT and that would also cause the motor to get hung up occasionally. So, I needed to replace the wood with something much harder like HDPE or even a sheet of steel. Material that large is costly so I instead ordered some very thin wiring and was going to go back to my original plan with the supports attached to the top platform.

I had all of this working quite well. Unfortunately, when I was adding a support leg I put my weight on the unsupported platform and twisted the stepper motor shaft. :mad: It still works but tends to bind up so I'm going to have to order a new one if I want to continue down this path. A replacement motor with the torque and specs I need is $50+ and one thing I learned is I want a stronger motor which would be in the $100 range. So, I'm scrapping this project for now. I've spent too much time and money on it. I'll go with the manual turntable until I get caught up and have some spare time and money to fix this automated one.
 
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hardisj

hardisj

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hardisj

hardisj

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All of this said, I have changed gears after talking to Klippel about their ISC module. I'll create a video discussing my measurement methods which will briefly touch on all of this other stuff I have tried and what methods I will be using going forward.
 

NTK

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... I had all of this working quite well. Unfortunately, when I was adding a support leg I put my weight on the unsupported platform and twisted the stepper motor shaft. :mad: It still works but tends to bind up so I'm going to have to order a new one if I want to continue down this path. ...
If you decide to continue/resume working on your automated turntable, you may want to add a flexible shaft coupling to the motor shaft connection to take off-axis loads off the motor.
https://www.mcmaster.com/flexible-shaft-couplings
 
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hardisj

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If you decide to continue/resume working on your automated turntable, you may want to add a flexible shaft coupling to the motor shaft connection to take off-axis loads off the motor.
https://www.mcmaster.com/flexible-shaft-couplings

Neat. I'm using a large coupling to attach the platform but hadn't seen the flexible ones.

That said, I don't think that would have stopped it from getting bent when all my body weight hit the corner 18 inches away. That's a heck of a moment arm for a 1/4" shaft. :(
 
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617

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Neat. I'm using a large coupling to attach the platform but hadn't seen the flexible ones.

That said, I don't think that would have stopped it from getting bent when all my body weight hit the corner 18 inches away. That's a heck of a moment arm for a 1/4" shaft. :(

When I was designing mine I was driving the platform off-center using a stiff notched belt. Driving from the center does simplify things. What are the specs on the stepper you were using? And how are you controlling it?
 
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hardisj

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When I was designing mine I was driving the platform off-center using a stiff notched belt. Driving from the center does simplify things. What are the specs on the stepper you were using? And how are you controlling it?

I don't recall the exact model motor I used.

This is the controller I am using: https://www.pololu.com/product/3140
Really easy to use and great interface with their Tic software.

Ok. I pulled up my order information and this is the stuff I used for the final version (ignoring the other parts I used that didn't work):
1 x #1478 Stepper Motor: Bipolar, 200 Steps/Rev, 57×76mm, 3.2V, 2.8 A/Phase = 49.95
1 x #3140 Tic 36v4 USB Multi-Interface High-Power Stepper Motor Controller (Connectors Soldered) = 51.95
1 x #2258 Steel L-Bracket for NEMA 23 Stepper Motors = 4.95

I also purchased this hub which is what I used to attach the platform to the shaft:
https://www.servocity.com/steel-1-4-d-bore-barrel-hub-for-worm-gear

You'll want some ball transfer bearings as well. For the price, this is kind of hard to beat.
https://amzn.to/3d7MrZN

You have to make sure you match up the USB controller with the right motor based on voltage/current limitations. You can 'throttle' back the current in the Tic software if you have a power supply that feeds more than the voltage required. Speaking of which, also make sure you have a power supply with enough voltage and current to support your motor. I use this power supply (had it for years for bench testing):
https://amzn.to/36ye5N0


Also, keep in mind most of these motors have rotations in 1.8° increments, so achieving a measurement every 10° isn't feasible. You'll have to adjust accordingly.



All of that said, when I pick this project back up and replace my messed up stepper motor I'll likely purchase a high torque NEMA-34 motor to get more torque, assuming I find one that works within the limits of the USB controller's spec.
 
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hardisj

hardisj

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I got started yesterday on actually completing the review of the Buchardt S400. For now, I am using my "manual" turntable to get measurements indoors until I have time/money to finish the motorized platform. The stand height is about 42 inches off the ground with the ceiling at 10 feet. With Klippel's ISC module you can use an anechoic "reference" measurement with an indoors measurement and subtract the room out of the result. You can read about it here: http://www.klippel.de/products/rd-system/modules/isc-in-situ-compensation.html

I will be using the outdoors ground plane measurement as my "reference" and getting anechoic data for the DUT. It's really impressive. The reason why I chose to go this route instead of using the ground plane measurement for all is due to a few things:
1) Accuracy in aiming. I showed in an earlier result that the difference in just a couple degrees can equate to relatively significant "errors" in the measurement. For instance, if the tilt of the speaker isn't lined up perfectly with the microphone the Buchardt S400 measurement was off as much as 3dB within a 5 degree tilt window. This issue is more trivial but it's something to keep in mind. Measuring on a stand in my garage allows me to laser-align the mic position relative to the location I want to measure (i.e., tweeter axis, between waveguide/mid, etc).
2) Noise. Ground plane measurements are subject to wind in high frequency. Aligning my available time with no wind and perfect weather isn't really feasible. So, using the GP method for lower frequency response helps alleviate this issue.
3) Temperature. High frequency drift is common in extreme temperatures. My garage is insulated and I also have a 220v heater that warms the garage quickly in the winter months. So as long as the doors are closed the garage stays within about 10-20 degrees of the house temperature which is enough to keep drift from occurring.
4) Comfort. With the ISC module I can create a room compensation curve and conduct additional tests such as distortion measurements indoors. No need to stand outdoors and conduct additional measurements and sweat/freeze.

Without Klippel's ISC module I would likely conduct my tests outdoors in the ground plane method only. But with the ISC module I am afforded some additional flexibility without loss in accuracy (actually, potentially better accuracy) which makes my life a bit easier.



Here's some shots I took of the measurement rig with the Buchardt S400 being tested. And, yes, there is a rear leg on the stand; it's just blocked in this angle. ;)

IMG_9777.jpg


IMG_9778.jpg


IMG_9779.jpg
 

617

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Hah, we were working on the exact same project. One of the reasons I was trying to drive the platform from the edge, besides the fact that I didn't think of driving it from the center, was that I could use gearing to break down the 1/100 or 1/200 rotational increment into something which could rotate 1 degree at a time, or at least a clean 5 degrees at a time. I think 1:9 gearing will do that. Using the arduino also allows you to add sensors for homing and limiting if you like, or even a hall effect sensor to sense magnets radially spaced out on your platform.

I used the same bearings too; I split the forces up so I had one set of bearings taking on the weight of the platform, and another set to take on the sideways pull from the pulley. You're avoiding that.

I was designing mine for use with a platform; I had one which was around 4 feet and one which was around 6 for use outdoors. Ground plane measurements always seemed like voodoo to me so I am following with great interest.
 

dc655321

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Also, keep in mind most of these motors have rotations in 1.8° increments, so achieving a measurement every 10° isn't feasible. You'll have to adjust accordingly.

Took a quick glance at the specs for your stepper controller, and it looks like it does micro-stepping up to 256 times.
If so, you could get an angular resolution up to 1.8/256 deg (assuming direct drive).
 
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hardisj

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Question for you guys...

Given the CEA-2034 standard for Early Reflections & Sound Power (and consequently DI) spinorama data requires axis data from the front and rear hemisphere, are any of you other folks out there ignoring the rear half of the speaker contribution or are you measuring a full 360 degrees front and back?

Right now I can provide listening window because I have measured in the front hemisphere of my DUT. The Early Reflections calls for 180 degrees and I could obtain that pretty quickly. But, I don't know how much trouble it is worth to measure 70 spaces (front and back total) in order to obtain sound power. That's a LOT of time and a LOT of data to cull through... I'm not sure I am up to that task going forward and simply may forgo providing that additional bit of information (and unfortunately wouldn't have a "full" spin set). One step forward, three steps back...


In the meantime, here's some pretty graphics of what I've managed to complete thus far...

Buchardt S400 Horizontal FR.png
Buchardt S400 Horizontal FR Normalized.png
Buchardt S400 Horizontal Spectrogram.png
Buchardt S400 Vertical FR.png
Buchardt S400 Vertical FR Normalized.png
Buchardt S400 Vertical Spectrogram.png
Buchardt S400 Spinorama.png
 

617

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If I'm designing a speaker I typically go 360, although I may reduce angular resolution at the back. Still, it's interesting to see if any gremlins appear there.

If you're careful when you collect the data you can do pretty accurate simulation afterwards. My vice is ignoring the vertical.

If you're designing a speaker with any potential for rear radiation (port, dipole, mid tunnel) 360 degrees is a must.
 

napilopez

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Question for you guys...

Given the CEA-2034 standard for Early Reflections & Sound Power (and consequently DI) spinorama data requires axis data from the front and rear hemisphere, are any of you other folks out there ignoring the rear half of the speaker contribution or are you measuring a full 360 degrees front and back?

Right now I can provide listening window because I have measured in the front hemisphere of my DUT. The Early Reflections calls for 180 degrees and I could obtain that pretty quickly. But, I don't know how much trouble it is worth to measure 70 spaces (front and back total) in order to obtain sound power. That's a LOT of time and a LOT of data to cull through... I'm not sure I am up to that task going forward and simply may forgo providing that additional bit of information (and unfortunately wouldn't have a "full" spin set). One step forward, three steps back...


In the meantime, here's some pretty graphics of what I've managed to complete thus far...

View attachment 65983View attachment 65984View attachment 65985View attachment 65986View attachment 65987View attachment 65988View attachment 65989

I measure all the way around in 10 degree intervals but I skip most of the the mirrored horizontal side on symmetrical speakers. For these I will just do the full left and right listening window, mainly to double check I properly centered the setup. Unfortunately can't do the same for verticals so those get the full 360.

All that being said, after much experimentation I found the spinoramas were nearly identical using only front hemisphere data on typical monopole speakers so long as I performed a single 180-degree measurement and allowed VituixCAD to interpolate the rest. The rear data is simply low enough in level to contribute little to such substantial averages. Edit: To be clear, substantial port noise might show up on the he sound power, but very little in the early reflections and predicted in-room.

I tested this because I had initially thought the early reflections curve only included three angles (+/-90, 180) due to to the ambiguity of CTA-2034A. After I'd clarified it included all 19 rear angles, I checked how the measurements changed if I 'deleted' those extra 16 angles and the graphs were essentially the same, which allowed me to produce some spins for my older measurements. I can give an example when I'm at my computer.

The only caveat is I cut off most of my spin curves at 200Hz so maybe there'd be a bigger difference lower where there's more port output, but I doubt it'd be much.

This obviously does not apply to more esoteric radiation patterns.

Edit: all that being said, I find most of my time measuring speakers goes into the setup. Especially If you mirror the horizontals, doing the rear should only take you a couple more minutes, no?
 
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617

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Edit: all that being said, I find most of my time measuring speakers goes into the setup. Especially If you mirror the horizontals, doing the rear should only take you a couple more minutes, no?

That's my feeling as well. Mirroring a speaker is fine, being one or two degrees off 0 is not going to change things that significantly - maybe top octave stuff but you generally don't touch that when you're designing a crossover, and adjust it to taste after.
 
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hardisj

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Sure, mirroring the horizontal axis is fine. But vertical can't be halved.

Also, remember, though, I am doing 2 sets of measurements for each axis - one ground plane and one free-space - to get anechoic-like data with full resolution down to 10hz. My window is > 100ms in most cases. I am not fond of using only gated measurements because of the extreme loss in resolution/accuracy. Most of the reviews I see have the window with resolution only down to 200hz or 300hz. That means a data point every 200 or 300hz step; that's not even 1-octave resolution. The bad thing about this is the low resolution hides high-Q anamolies in the midrange as well, for example, in the S400's response at around 500hz. The CEA 2034 spec discusses this issue as well:
"The requirement for 1/20-octave resolution cannot be achieved with windowed measurements except in the geometric center of very large, auditorium-sized, rooms. The lack of such resolution means that the nature of the low-frequency roll-off in loudspeakers is not accurately revealed and the audibility of medium- and high-Q resonances cannot be accurately estimated at lower frequencies in the amplitude response data."

So... trade-offs. To get high resolution I have to do an outdoors GP measurement and use that with Klippel's ISC module and an indoors measurement in order to get a room corrected, non-windowed response with high resolution. That's currently the best way to get the accuracy needed to provide meaningful results above 1kHz. Or, I can cut measurement time in half but also anything less than a couple octaves above the windowed frequency is not very useful. I know nearly everyone measures this way. Audioholics, nearly every DIY'r I know (myself included sometimes), and countless others. I'm not knocking it. I'm just pointing out that it's extremely limited in usefulness even a couple octaves above the gated frequency. There's no easy way to do this unless I purchase an anechoic chamber or the Near Field Scanner. :/


Anyway... just pointing out that I have to make twice as many measurements to get full resolution in a single axis. Doing that for 70 mic points means 140 measurements. I'll revisit some ideas and may mix and match methods as I see fit (for example, maybe not providing full spin data for items Amir has already tested and focus on other aspects like THD, fault finding analysis, max SPL, etc).
 
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