OP
- Thread Starter
- #201
Just to make you feel worse, I am sitting in the living room, watching TV, thinking about getting a shower, while the NFS is performing an over 1000 point measurement of a tower speaker.
-
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ErinsAudioCorner
- Thread starter hardisj
- Start date
Well, I have been reading them with interest. But keep thinking that with the amount of work you have put in it, by now could have built your own anechoic chamber.
BTW, the lift I bought has been a life saver. I have lifted and taken down massive/heavy speakers with near ease.
Booooooooo
Meanwhile I just measured three speakers in one go. Probably better in the long run but I never want to hear a sine sweep again....
dc655321
Major Contributor
- Joined
- Mar 4, 2018
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OP
- Thread Starter
- #204
I reached out to the local recreational authority office. $100/hour rental fee for a basketball court is the cheapest option. I’d need a few hours for setup, test, and takedown.
And like fellowships, they aren’t even open at the moment. But I have asked around. Just no luck.
And like fellowships, they aren’t even open at the moment. But I have asked around. Just no luck.
vavan
Senior Member
so now there's a hope you're going to measure your salons?
OP
- Thread Starter
- #206
After sleeping on this I have decided that merging Low Frequency with High Frequency data (similar to NF/FF merging) is the only way I will be able to do this and provide the data to the accuracy I desire in most cases. That means I will have to measure ground plane both indoors and outdoors. (If I happen to have really nice weather conditions where the outdoors measurement results in the same HF response as indoors then I won't bother at all with splicing).
Now, there are options to merge the data: using the various software available (virtuixCAD, DIY'rs excel sheets) or I can use Klippel's script. However, this all requires me to merge one at a time. To get vertical and horizontal data, that's merging about 60 files down to about 30. That would be agonizing (and most importantly, prone to accidental error). So, I wrote a script in Matlab to do a "hard splice" in a batch. I provide it all the files, tell it where I want the splice to be and it calculates the delta and makes the low frequency graph merge to the upper frequency; same premise as NF/FF merging. I am ignoring phase for this aspect and focusing solely on the resultant FR. The plan is to measure all angles... I'll have to do it twice: in the garage for mid/upper and outdoors for lower. But once I do that, I can load the FR files as txt and my script will take care of the rest and throw them all on a plot. I have another version for a "soft splice" which will try to blend data points but for now the hard splice method works well as long as I choose a frequency where there is good consistency between trends (and I have the data resolution to support it).
Edit: It was pointed out to me that virtuixCAD will do what I want but I still think I'll rely on my own script since I can just reference a folder and call it done.
This is what the result for a single axis looks like (the script will automatically populated all measured axes as needed but I only fed it a single axis for now):
For the time being I have provided the output of my combined LF/HF merged data with that of ASR's as well as Buchardt's NFS data. My result is right in between theirs. And, therefore, IMHO, certainly acceptable. Take note that I have provided two of Buchardt's NFS results: one is "original" which was measured before they implemented a slight crossover modification and the other is the "updated" which was measured more recently with the modification in place.
I still need to resolve the turntable aspect to save me time of turning the DUT manually. Making the center of rotation at the baffle creates some challenges when you have a turntable that is built with the platform an inch or two above the ground; you get a baffle step effect from the lifted platform in addition to reflection from the platform itself. I've got a couple ideas to try. I'll post on that later. If all else fails, I'll just use a piece of cardboard and turn the DUT manually as I did earlier this week.
At any rate, I'm making forward progress. Yay!
Now, there are options to merge the data: using the various software available (virtuixCAD, DIY'rs excel sheets) or I can use Klippel's script. However, this all requires me to merge one at a time. To get vertical and horizontal data, that's merging about 60 files down to about 30. That would be agonizing (and most importantly, prone to accidental error). So, I wrote a script in Matlab to do a "hard splice" in a batch. I provide it all the files, tell it where I want the splice to be and it calculates the delta and makes the low frequency graph merge to the upper frequency; same premise as NF/FF merging. I am ignoring phase for this aspect and focusing solely on the resultant FR. The plan is to measure all angles... I'll have to do it twice: in the garage for mid/upper and outdoors for lower. But once I do that, I can load the FR files as txt and my script will take care of the rest and throw them all on a plot. I have another version for a "soft splice" which will try to blend data points but for now the hard splice method works well as long as I choose a frequency where there is good consistency between trends (and I have the data resolution to support it).
Edit: It was pointed out to me that virtuixCAD will do what I want but I still think I'll rely on my own script since I can just reference a folder and call it done.
This is what the result for a single axis looks like (the script will automatically populated all measured axes as needed but I only fed it a single axis for now):
For the time being I have provided the output of my combined LF/HF merged data with that of ASR's as well as Buchardt's NFS data. My result is right in between theirs. And, therefore, IMHO, certainly acceptable. Take note that I have provided two of Buchardt's NFS results: one is "original" which was measured before they implemented a slight crossover modification and the other is the "updated" which was measured more recently with the modification in place.
I still need to resolve the turntable aspect to save me time of turning the DUT manually. Making the center of rotation at the baffle creates some challenges when you have a turntable that is built with the platform an inch or two above the ground; you get a baffle step effect from the lifted platform in addition to reflection from the platform itself. I've got a couple ideas to try. I'll post on that later. If all else fails, I'll just use a piece of cardboard and turn the DUT manually as I did earlier this week.
At any rate, I'm making forward progress. Yay!
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OP
- Thread Starter
- #207
Okay. I used my script to run the horizontal polars. Looks pretty darn good.
I'll have to clean up the script but I am happy with how it works so far. I have it set up to where I point Matlab at the directory and it prompts me for the stitch frequency, I tell it where, then it dumps out the following plots. I'll have to add info for verticals. Then there's the impedance/phase, IMD, max SPL, and other tests. But I think I finally have decided on how I am going to test and the scripts will help me automate the presentation of the data so I can focus on the analysis aspect.
I'll have to clean up the script but I am happy with how it works so far. I have it set up to where I point Matlab at the directory and it prompts me for the stitch frequency, I tell it where, then it dumps out the following plots. I'll have to add info for verticals. Then there's the impedance/phase, IMD, max SPL, and other tests. But I think I finally have decided on how I am going to test and the scripts will help me automate the presentation of the data so I can focus on the analysis aspect.
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OP
- Thread Starter
- #208
I am going to try to recap everything I have learned thus far.
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. And it's a lot easier. So I will measure in the garage for mid/high frequency accuracy and outdoors as needed for low frequency stitching. As for rotating the speaker, I built a turntable using a NEMA-23 motor and a USB stepper motor controller but the platform height is currently of concern. I'll work through this. If all else fails I'll manually rotate the speaker. It's easier to do this than it is to wait for the perfect weather and rig up a heavy speaker high in the sky. That's the method I choose. If others choose to use the 4-pi speaker on a stand method that's fine. Again, both are fine methods.
However, it is worth noting that in my garage using the Ground Plane method I can place my DUT and mic in the center of the garage, clear items out from the sidewalls and get about 11ms free of reflection window as you can see at the bottom of this post. This is significantly better than if I were to place the speaker on a stand in my garage and measure; at which point I would get about 4ms of reflection-free time (due to the floor and ceiling in my 10 foot tall garage space). That's the difference in having a data point approximately every 90hz (11ms) vs every 250hz (4ms). And for no other reason encourages one to at least consider a proper ground plane measurement in lieu of the standard 4-pi method.
The thing to note about ground plane measurements are they need to be in an area that is obviously far, far away from the nearest boundary (wall, vehicle, etc) if you want low frequency accuracy (same as any other method). And it also needs to be in an area that has a large reflective surface. You don't need a mirror (as I have shown). But concrete is necessary and grass will not cut it (ha! no pun intended). If you are looking to perform LF response only measurements and all you have is an open field to measure in, then you can probably get away with 300hz as the maximum range (my data shows 400hz in my backyard with very low cut grass). I would not trust the data higher than that, however. Plywood is NOT a good substitution.
Any measurements performed outdoors need to be performed when there is practically no wind. A little wind is tolerable but more than a couple mph and the HF data is corrupted and considerably moreso if the wind is higher (as I have shown).
And, finally, these are all just my results. I encourage you to do your own tests if you have the desire to measure your own loudspeakers. Let my results guide you but understand that different surface areas and conditions will effect the results and you need to quantify those differences before you go willy-nilly with measurements. I have seen a lot of measurements since I started this quest that make me question the accuracy and reliability because of the knowledge I have gained from my own testing of the different methods. But, such is life. As long as you understand what you're doing and you can back it up with data then you can better provide analysis.
Hopefully some of you gained some useful information from this. I know it has been enlightening to myself for sure.
- Erin
Ground Plane Impulse Reflection-Free Window ( ~ 11ms wide; 90hz data point intervals; mic 2 meters from DUT)
Stand Mounted Impulse Reflection-Free Window ( ~ 4ms wide; 250hz data point intervals; mic 1 meter from DUT)
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. And it's a lot easier. So I will measure in the garage for mid/high frequency accuracy and outdoors as needed for low frequency stitching. As for rotating the speaker, I built a turntable using a NEMA-23 motor and a USB stepper motor controller but the platform height is currently of concern. I'll work through this. If all else fails I'll manually rotate the speaker. It's easier to do this than it is to wait for the perfect weather and rig up a heavy speaker high in the sky. That's the method I choose. If others choose to use the 4-pi speaker on a stand method that's fine. Again, both are fine methods.
However, it is worth noting that in my garage using the Ground Plane method I can place my DUT and mic in the center of the garage, clear items out from the sidewalls and get about 11ms free of reflection window as you can see at the bottom of this post. This is significantly better than if I were to place the speaker on a stand in my garage and measure; at which point I would get about 4ms of reflection-free time (due to the floor and ceiling in my 10 foot tall garage space). That's the difference in having a data point approximately every 90hz (11ms) vs every 250hz (4ms). And for no other reason encourages one to at least consider a proper ground plane measurement in lieu of the standard 4-pi method.
The thing to note about ground plane measurements are they need to be in an area that is obviously far, far away from the nearest boundary (wall, vehicle, etc) if you want low frequency accuracy (same as any other method). And it also needs to be in an area that has a large reflective surface. You don't need a mirror (as I have shown). But concrete is necessary and grass will not cut it (ha! no pun intended). If you are looking to perform LF response only measurements and all you have is an open field to measure in, then you can probably get away with 300hz as the maximum range (my data shows 400hz in my backyard with very low cut grass). I would not trust the data higher than that, however. Plywood is NOT a good substitution.
Any measurements performed outdoors need to be performed when there is practically no wind. A little wind is tolerable but more than a couple mph and the HF data is corrupted and considerably moreso if the wind is higher (as I have shown).
And, finally, these are all just my results. I encourage you to do your own tests if you have the desire to measure your own loudspeakers. Let my results guide you but understand that different surface areas and conditions will effect the results and you need to quantify those differences before you go willy-nilly with measurements. I have seen a lot of measurements since I started this quest that make me question the accuracy and reliability because of the knowledge I have gained from my own testing of the different methods. But, such is life. As long as you understand what you're doing and you can back it up with data then you can better provide analysis.
Hopefully some of you gained some useful information from this. I know it has been enlightening to myself for sure.
- Erin
Ground Plane Impulse Reflection-Free Window ( ~ 11ms wide; 90hz data point intervals; mic 2 meters from DUT)
Stand Mounted Impulse Reflection-Free Window ( ~ 4ms wide; 250hz data point intervals; mic 1 meter from DUT)
Last edited:
OP
- Thread Starter
- #209
Here's some information for those of you who may want to conduct their own measurements with the ground plane method.
I've mentioned it numerous times but in case someone didn't catch it or doesn't already know: when you measure a speaker in the ground plane you need to tilt the speaker some angle in order to line up the speaker with the microphone axis. This is covered in various places online and discussed in D'Appolito's "Testing Loudspeakers" book. It's a pretty simple tangent equation but there are calculators online to make this easy for you. Here's one: http://www.mh-audio.nl/Acoustics/Groundplane.html
You enter the mic distance from the speaker and the distance from the ground to the tweeter (or other reference axis; say, midpoint between tweeter and midrange). This site recommended using your phone in "selfie" mode to make sure the microphone shows up in the center of the image. I do this from time to time to sanity check the calculations. You can see my 4th image below displaying this method.
Now, what I've read before is it is OK if you are off a little bit. But I thought it would be helpful for me to show just how much the tilt angle matters so in this example I am using the same Buchardt S400 in my garage.
First I used a laser level to draw a line on my garage floor to make sure the microphone was on-axis with the speaker. I also used a distance finder to make sure the distance was at 2 meters.
**
Side note, if you are interested, these are the two items I use and am quite happy with them. About half the price of the hardware store versions. If you plan on doing GP measurements in your garage, these will make your life so much easier and improve accuracy of your aiming/setup. I recommend you buy them. If not these, something along these lines. The links below are made with my Amazon affiliate link so if you do purchase them I'll get 2%... hey, every little bit helps.
Laser Level
Laser distance finder (bonus: this thing has an angle detector which is perfect for determining speaker tilt angle)
**
Anyway, here's some photos:
Now, keep in mind the Buchardt S400 has a 2 degree tilt on both the baffle and the rear. Literally, it looks like a parallelogram instead of a typical box enclosure.
1) The first test was ran with the speaker bottom flat on the floor; not tilted forward. (Red)
2) I then used the site above, entering the distance as 2 meters and the tweeter height as 4.5 inches (~ 10cm). I got a suggested tilt angle of 2.90°. I thought, hey, let's overcompensate here and also add the 2° tilt from the enclosure itself, so I came to 4.90° total. Therefore, the actual angle of the baffle perpendicular to the floor was now 2.90° (4.90°-2.00°). (Blue)
3) I then remeasured at 2.90° (no factory tilt accounted for) and the actual angle of baffle perpendicular to floor was 0.90° (2.90°-2.00°). (Green)
Here is the result.
You can see there is indeed a notable difference in the 2-4kHz region between the 3 measurements (and a smaller difference from 5-8kHz). I think this can be telling of the best axis to listen on but that's for a different time. For now, the point is: the tilt angle even within 5 degrees has approximately 3.0dB difference at about 3kHz. And the 0.9° vs 2.9° difference at 3kHz is approximately 1.5dB.
What does this mean? I think it means that care should be taken to ensure the intended axis of measure (the tweeter, between tweeter/mid, etc) is used as the reference plane and the speaker tilted as necessary to make this so.
Obviously, YMMV (your mileage may vary) depending on the speaker, distance, etc. But I would urge you to take care to make sure the tilt angle is correct before you continue with the measurement process.
- Erin
I've mentioned it numerous times but in case someone didn't catch it or doesn't already know: when you measure a speaker in the ground plane you need to tilt the speaker some angle in order to line up the speaker with the microphone axis. This is covered in various places online and discussed in D'Appolito's "Testing Loudspeakers" book. It's a pretty simple tangent equation but there are calculators online to make this easy for you. Here's one: http://www.mh-audio.nl/Acoustics/Groundplane.html
You enter the mic distance from the speaker and the distance from the ground to the tweeter (or other reference axis; say, midpoint between tweeter and midrange). This site recommended using your phone in "selfie" mode to make sure the microphone shows up in the center of the image. I do this from time to time to sanity check the calculations. You can see my 4th image below displaying this method.
Now, what I've read before is it is OK if you are off a little bit. But I thought it would be helpful for me to show just how much the tilt angle matters so in this example I am using the same Buchardt S400 in my garage.
First I used a laser level to draw a line on my garage floor to make sure the microphone was on-axis with the speaker. I also used a distance finder to make sure the distance was at 2 meters.
**
Side note, if you are interested, these are the two items I use and am quite happy with them. About half the price of the hardware store versions. If you plan on doing GP measurements in your garage, these will make your life so much easier and improve accuracy of your aiming/setup. I recommend you buy them. If not these, something along these lines. The links below are made with my Amazon affiliate link so if you do purchase them I'll get 2%... hey, every little bit helps.
Laser Level
Laser distance finder (bonus: this thing has an angle detector which is perfect for determining speaker tilt angle)
**
Anyway, here's some photos:
Now, keep in mind the Buchardt S400 has a 2 degree tilt on both the baffle and the rear. Literally, it looks like a parallelogram instead of a typical box enclosure.
1) The first test was ran with the speaker bottom flat on the floor; not tilted forward. (Red)
2) I then used the site above, entering the distance as 2 meters and the tweeter height as 4.5 inches (~ 10cm). I got a suggested tilt angle of 2.90°. I thought, hey, let's overcompensate here and also add the 2° tilt from the enclosure itself, so I came to 4.90° total. Therefore, the actual angle of the baffle perpendicular to the floor was now 2.90° (4.90°-2.00°). (Blue)
3) I then remeasured at 2.90° (no factory tilt accounted for) and the actual angle of baffle perpendicular to floor was 0.90° (2.90°-2.00°). (Green)
Here is the result.
You can see there is indeed a notable difference in the 2-4kHz region between the 3 measurements (and a smaller difference from 5-8kHz). I think this can be telling of the best axis to listen on but that's for a different time. For now, the point is: the tilt angle even within 5 degrees has approximately 3.0dB difference at about 3kHz. And the 0.9° vs 2.9° difference at 3kHz is approximately 1.5dB.
What does this mean? I think it means that care should be taken to ensure the intended axis of measure (the tweeter, between tweeter/mid, etc) is used as the reference plane and the speaker tilted as necessary to make this so.
Obviously, YMMV (your mileage may vary) depending on the speaker, distance, etc. But I would urge you to take care to make sure the tilt angle is correct before you continue with the measurement process.
- Erin
Last edited:
OP
- Thread Starter
- #210
It was asked on DIYA so I am sharing it here...
Yes. But to reiterate, it makes more sense to perform an indoors ground plane measurement instead of the speaker-on-a-stand measurement for the reasons I listed previously. At least for me.
The DUT I have been using is one with a passive radiator so I cannot perform the MIB test. However, I had previously captured nearfield response of both the woofer and the PR.
FWIW, I am using the sd of these drivers (as they appear to be the same ones used in the Buchardt S400, with assumed differences in electro-mechanical properties; however the physial dimensions are almost certainly the exact same):
https://www.madisoundspeakerstore.c...acoustics-sb15sfcr39-8-5x8-paper-cone-woofer/
https://www.madisoundspeakerstore.c...-sb15nbac30-4-5-black-aluminum-cone-mid-bass/
With the above stated, the nearfield method has a maximum frequency accuracy dictated by the size (as discussed in the above audioexpress link). The 5" woofer is limited to about 980hz and the 5x8 inch passive radiator I will limit to the 8 inch dimension and therefore is invalid above about 600hz. Just spit-balling here; not using the actual effective radius. But it's close enough.
... On with the results. ...
As you may know, when capturing near-field data it's hard to get the exact same level relative to distance of mic from cone and therefore the result is usually "eyeballed" to overlay them together, by using the lowest frequencies. I have done that below. What you see below is:
And here is the summed nearfield response above vs my ground plane (at 2 meters) measurement:
Understanding, of course, I had to "eyeball" where to overlay these in frequency, you see the presumption regarding NF responses showing a bump in the low frequencies due to the fact that it effectively ignores baffle step is indeed true: the 2 meter ground plane measurement is lower in amplitude on the low end than that of the NF components & summed response. This is to be expected and you can find this quote on why why stated in the above audioexpress link:
The farfield ground plane technique is more accurate as you can see (and as was expected). The NF summing technique gives you an idea of the low end response but isn't entirely accurate to that of a far-field response AND it requires care in the measurement, assumptions and final calculation. Honestly, I prefer the ground plane measurement method simply because it's less prone to personal error. Meaning, the more ports and woofers I have to measure individually and then add together, the greater chance for a human error to occur. Whereas a ground plane measurement is just sticking the mic a few meters in front of the speaker, running a sweep and then you're done. I would only use a nearfield method if I had no other choice due to area available or terrible weather.
mbrennwa;6198828 said:
Yes. But to reiterate, it makes more sense to perform an indoors ground plane measurement instead of the speaker-on-a-stand measurement for the reasons I listed previously. At least for me.
mbrennwa;6198828 said:
The DUT I have been using is one with a passive radiator so I cannot perform the MIB test. However, I had previously captured nearfield response of both the woofer and the PR.
FWIW, I am using the sd of these drivers (as they appear to be the same ones used in the Buchardt S400, with assumed differences in electro-mechanical properties; however the physial dimensions are almost certainly the exact same):
https://www.madisoundspeakerstore.c...acoustics-sb15sfcr39-8-5x8-paper-cone-woofer/
https://www.madisoundspeakerstore.c...-sb15nbac30-4-5-black-aluminum-cone-mid-bass/
With the above stated, the nearfield method has a maximum frequency accuracy dictated by the size (as discussed in the above audioexpress link). The 5" woofer is limited to about 980hz and the 5x8 inch passive radiator I will limit to the 8 inch dimension and therefore is invalid above about 600hz. Just spit-balling here; not using the actual effective radius. But it's close enough.
... On with the results. ...
As you may know, when capturing near-field data it's hard to get the exact same level relative to distance of mic from cone and therefore the result is usually "eyeballed" to overlay them together, by using the lowest frequencies. I have done that below. What you see below is:
- Woofer Nearfield (orange)
- Passive Radiator Nearfield (green)
- Summed Nearfield Response of the Woofer + PR (blue)
And here is the summed nearfield response above vs my ground plane (at 2 meters) measurement:
Understanding, of course, I had to "eyeball" where to overlay these in frequency, you see the presumption regarding NF responses showing a bump in the low frequencies due to the fact that it effectively ignores baffle step is indeed true: the 2 meter ground plane measurement is lower in amplitude on the low end than that of the NF components & summed response. This is to be expected and you can find this quote on why why stated in the above audioexpress link:
The farfield ground plane technique is more accurate as you can see (and as was expected). The NF summing technique gives you an idea of the low end response but isn't entirely accurate to that of a far-field response AND it requires care in the measurement, assumptions and final calculation. Honestly, I prefer the ground plane measurement method simply because it's less prone to personal error. Meaning, the more ports and woofers I have to measure individually and then add together, the greater chance for a human error to occur. Whereas a ground plane measurement is just sticking the mic a few meters in front of the speaker, running a sweep and then you're done. I would only use a nearfield method if I had no other choice due to area available or terrible weather.
Last edited:
OP
- Thread Starter
- #212
hardisj said:
Ughhhh.... Ok. Curiosity got the best of me. But I swear, I AM DONE after this!....
Now, let me state: I have never used VituixCAD for this purpose but I *think* I did this correctly...
I opened the Diffraction Tool.
I loaded my NF curve in the Half space response section
I checked "full space"
I modeled the enclosure with the woofer in the appropriate place on the baffle.
I modeled the microphone about where the tweeter axis is.
I set the mic distance to 2 meters.
I saved this response.
I repeated the same process for the passive radiator (using a rectangular driver since it's an oval).
I then used VituixCAD's Calculator Tool to sum the those (2) curves. What you see below is a comparison of the original 2 meter far field in Red vs the different NF sums. In blue is the summed woofer & PR response *WITHOUT* diffraction modeled. In black is the summed woofer & PR *WITH* diffraction modeled.
As I posted previously, the simple NF sum of the woofer + passive radiator (blue) shows a boost on the low end that was expected. HOWEVER, if you apply the diffraction effect to each of the components and then sum them (black) you get a combined response that follows the 2 meter GP measurement (red) quite well. Close enough, in fact, that I would feel comfortable using this method in future tests if I don't have the ability to physically measure outdoors to get the LF extension in response I need. It isn't perfect but I think it shows the necessity for modeling the diffraction effects for those of you who are dealing with how best to accurately gather data for your reviews or your own designs.
Okay. That's it! I'm done!!! I have to quit obsessing over this topic. Thanks for joining me in this journey. But I've gotta bail. I'm out of money and I'm out of sanity!
No.so now there's a hope you're going to measure your salons?
Once you get it up there, you still have to slide the thing on the stand while making sure it doesn't topple over! And then there is the issue of getting down two flights of stairs to the lab.So you know how bad it is. I literally paid for white glove service to bring them to the house from the shop and take them up the stairs.
DDF
Addicted to Fun and Learning
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If the measurement and model are correct, the near field splice and ground plane should be the same, only differentiated by the inherent resolution of the fft windows used for each.
That ground plane differs from near field splice doesn't mean near field splice as a method is wrong, but that something was wrong with either a measurement or (more likely) something in the modeling used in this particular instance.
I dont use virtuix cad but I've been using diffraction compensated near field splice for 25 yrs, and I always obtained consistent results with anechoic or other long window methods.
That ground plane differs from near field splice doesn't mean near field splice as a method is wrong, but that something was wrong with either a measurement or (more likely) something in the modeling used in this particular instance.
I dont use virtuix cad but I've been using diffraction compensated near field splice for 25 yrs, and I always obtained consistent results with anechoic or other long window methods.
OP
- Thread Starter
- #215
I’m sure the inaccuracy is likely due to the model I created. Maybe it has to do with the PR being on the back while the woofer is on the front. Or maybe the area wasn’t exactly correct (rectangle vs oval for the PR). Either way, I’m pretty happy with the results and would be OK using the model in lieu of fully low frequency ground plane measurements.
I have read most of your posting; a great deal of it I do not understand... I do realize the truly vast amount of time and effort you have invested!
Your wife will achieve beatification, if she has not already. Thank you for all of your efforts!
Your wife will achieve beatification, if she has not already. Thank you for all of your efforts!
Ughhhh.... Ok. Curiosity got the best of me. But I swear, I AM DONE after this!....
Now, let me state: I have never used VituixCAD for this purpose but I *think* I did this correctly...
I opened the Diffraction Tool.
I loaded my NF curve in the Half space response section
I checked "full space"
I modeled the enclosure with the woofer in the appropriate place on the baffle.
I modeled the microphone about where the tweeter axis is.
I set the mic distance to 2 meters.
I saved this response.
I repeated the same process for the passive radiator (using a rectangular driver since it's an oval).
I then used VituixCAD's Calculator Tool to sum the those (2) curves. What you see below is a comparison of the original 2 meter far field in Red vs the different NF sums. In blue is the summed woofer & PR response *WITHOUT* diffraction modeled. In black is the summed woofer & PR *WITH* diffraction modeled.
View attachment 62901
As I posted previously, the simple NF sum of the woofer + passive radiator (blue) shows a boost on the low end that was expected. HOWEVER, if you apply the diffraction effect to each of the components and then sum them (black) you get a combined response that follows the 2 meter GP measurement (red) quite well. Close enough, in fact, that I would feel comfortable using this method in future tests if I don't have the ability to physically measure outdoors to get the LF extension in response I need. It isn't perfect but I think it shows the necessity for modeling the diffraction effects for those of you who are dealing with how best to accurately gather data for your reviews or your own designs.
Okay. That's it! I'm done!!! I have to quit obsessing over this topic. Thanks for joining me in this journey. But I've gotta bail. I'm out of money and I'm out of sanity!
For anyone else following along, don't know if you're aware, but another option I quite like is the Bagby (RIP) Excel Program for baffle step compensation. Just feels a little easier/faster to work with than VituixCAD for anything that doesn't have an esoteric design, especially if you're not already using VituixCAD for something else. Put in a few dimensions and go.
That was some bad news to eat
but thanks anyway.
OP
- Thread Starter
- #219
OP
- Thread Starter
- #220
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 it works as well as I think it will but I can always fall back to manually turning the DUT if not.
Hopefully I can be fully operational by next weekend and start knocking out some of these tests.
Thanks for your patience.
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 it works as well as I think it will but I can always fall back to manually turning the DUT if not.
Hopefully I can be fully operational by next weekend and start knocking out some of these tests.
Thanks for your patience.
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