One other person has alerted me to a source that now says the miniDSP Flex has significant modulation distortion through the analog inputs only (the same testing source that initially said that the Flex tested great with no problems). The version of the Flex used in the trial was the balanced (XLR) inputs version. It had Dirac installed, but this firmware had to be uninstalled after:
1) it was determined that Dirac didn't do a very good job "automatically" adjusting the EQ, and
2) It was also found that Dirac took all of the Flex's input PEQs, so to have any access to the unit's input channel PEQs, Dirac had to be uninstalled.
This is the first time that I've seen a DSP crossover that didn't have input channel PEQs available as configured (with Dirac from the vendor). It probably would have been nice to save the $200 USD that Dirac cost (as an option) if it was widely known that having Dirac would erase access to the input channel PEQs.
Based on all of the above, I would be leery of acquiring any miniDSP crossover for high performance horn-loaded loudspeaker work. While I didn't run into problems with the 2x4 HD box for Belle/AMT-1 work, there are now identified issues with the Flex and the earlier "2x4" (without the HD) that would preclude me from recommending for higher performance duty, such as Jubilees or K-402-MEH applications.
It's okay to look for the least expensive option, but I think in this case that the Flex is too big of a risk to use if it cannot be returned for full refund. It seems that its low price point is in fact a little too low for Jubilee use. I'd recommend something with better design quality for this kind of demanding application.
Furthermore, it was difficult to use the Flex in a remote system emailing (dialing in the setup) mode. I was helping another person via iterative--round robin--emailed configuration files for the Flex based on emailed REW measurement files, since the 2x4 HD software which I own is not compatible with the Flex, and you apparently have to buy a Flex to get access to the Flex PC software application. This is something that Xilica makes freely available to all so that remote dial-ins are a breeze by comparison. This was a significant hindrance in this trial that caused many hours of delay before it was discovered that the export files from REW were not compatible with the Flex.
Chris
1) it was determined that Dirac didn't do a very good job "automatically" adjusting the EQ, and
2) It was also found that Dirac took all of the Flex's input PEQs, so to have any access to the unit's input channel PEQs, Dirac had to be uninstalled.
This is the first time that I've seen a DSP crossover that didn't have input channel PEQs available as configured (with Dirac from the vendor). It probably would have been nice to save the $200 USD that Dirac cost (as an option) if it was widely known that having Dirac would erase access to the input channel PEQs.
Based on all of the above, I would be leery of acquiring any miniDSP crossover for high performance horn-loaded loudspeaker work. While I didn't run into problems with the 2x4 HD box for Belle/AMT-1 work, there are now identified issues with the Flex and the earlier "2x4" (without the HD) that would preclude me from recommending for higher performance duty, such as Jubilees or K-402-MEH applications.
It's okay to look for the least expensive option, but I think in this case that the Flex is too big of a risk to use if it cannot be returned for full refund. It seems that its low price point is in fact a little too low for Jubilee use. I'd recommend something with better design quality for this kind of demanding application.
Furthermore, it was difficult to use the Flex in a remote system emailing (dialing in the setup) mode. I was helping another person via iterative--round robin--emailed configuration files for the Flex based on emailed REW measurement files, since the 2x4 HD software which I own is not compatible with the Flex, and you apparently have to buy a Flex to get access to the Flex PC software application. This is something that Xilica makes freely available to all so that remote dial-ins are a breeze by comparison. This was a significant hindrance in this trial that caused many hours of delay before it was discovered that the export files from REW were not compatible with the Flex.
Chris
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Dear Chris, I tried to contact you on the other forum but i did not know you were no longer active there. I just stumbled across this topic. I would love to send you some measurements of my jubilees since Craig dialed them in last year. I bet there still is something to tweak and perfect.
but i do love them very much!
i just made an account here so i was not able to send you a private message...
hope to hear from you soon.
but i do love them very much!
i just made an account here so i was not able to send you a private message...
hope to hear from you soon.
Hi Chris,
I have been following your journey with the Xilica DSP. I must agree with you this is a wonderful sounding piece of gear.
I am using one XD-4080 per channel (using its AES input) in a special arrangement to secure sync between channels. I never used the analogue inputs.
My system is not horn based it is instead a 5 way dipole and the Xilica does it all perfect. I listen only vinyl and I do not hear any degradation in the signal.
However (at least in my units) the XD-4080 used the RC-4080 IC as post DAC I/V converter and this is a NOT an optimal operational amplifier, far from it.
We changed all sixteen RC-4080 by the new OPA-1656 and the improvement was huge. No BS. We verified OPA-1656 through an AP and they were fully stable, no issues.
Regards,
C.A.
I have been following your journey with the Xilica DSP. I must agree with you this is a wonderful sounding piece of gear.
I am using one XD-4080 per channel (using its AES input) in a special arrangement to secure sync between channels. I never used the analogue inputs.
My system is not horn based it is instead a 5 way dipole and the Xilica does it all perfect. I listen only vinyl and I do not hear any degradation in the signal.
However (at least in my units) the XD-4080 used the RC-4080 IC as post DAC I/V converter and this is a NOT an optimal operational amplifier, far from it.
We changed all sixteen RC-4080 by the new OPA-1656 and the improvement was huge. No BS. We verified OPA-1656 through an AP and they were fully stable, no issues.
Regards,
C.A.
Thanks for the update/news on the Xilica, C.A. I do remember reading that the XP series is related to the XD series in that the XP's internal components used are more "cost effective" as compared to the XD. I guess you found out just what that means--and substituted the relevant parts.
I guess that I could open mine up and replace the op amps--like you did. I assume they are soldered in instead of socketed(?).
One idea that came to mind was to look for a replacement for my Xilica, but perhaps go a DIY route. Probably the most knowledgeable DSP (algorithms) guys that is around, Greg Berchin, who posts on this forum from time to time has said that he uses a PC ASIO SDK with Steinberg UR824 audio interface, and uses his own real time code to program it to do the DSP crossover role. Perhaps he will chime in here (or in a new thread) to detail his thoughts on how to do this as if he started from scratch nowadays. He's not a GUI-type of guy (as he quickly points out) but his algorithms are apparently second to none. This is what Greg does for a living (albeit he's recently retired from full-time duties). Perhaps we can entice him to post here on the subject.
Chris
I guess that I could open mine up and replace the op amps--like you did. I assume they are soldered in instead of socketed(?).
One idea that came to mind was to look for a replacement for my Xilica, but perhaps go a DIY route. Probably the most knowledgeable DSP (algorithms) guys that is around, Greg Berchin, who posts on this forum from time to time has said that he uses a PC ASIO SDK with Steinberg UR824 audio interface, and uses his own real time code to program it to do the DSP crossover role. Perhaps he will chime in here (or in a new thread) to detail his thoughts on how to do this as if he started from scratch nowadays. He's not a GUI-type of guy (as he quickly points out) but his algorithms are apparently second to none. This is what Greg does for a living (albeit he's recently retired from full-time duties). Perhaps we can entice him to post here on the subject.
Chris
I just looked up the referenced OPA 1656ID op amps from Mouser (about a 15 minute drive down Texas Highway 287 from me 
). The price for 16 of them, before taxes and shipping, is $37.60 USD. Here is the URL:
https://www.mouser.com/ProductDetai...GAEpiMZZMutXGli8Ay4kHIHQt2scfHzywgI%2BTBd3BA=
and the product description page:
https://www.mouser.com/new/texas-instruments/ti-opa1656-op-amps/
Chris
). The price for 16 of them, before taxes and shipping, is $37.60 USD. Here is the URL:https://www.mouser.com/ProductDetai...GAEpiMZZMutXGli8Ay4kHIHQt2scfHzywgI%2BTBd3BA=
and the product description page:
https://www.mouser.com/new/texas-instruments/ti-opa1656-op-amps/
Chris
The OPA-1656 are terrific sounding IC. I learnt from them here :
https://www.diyaudio.com/community/threads/opa1656-high-performance-cmos-audio-op-amp.335416/
They are indeed pcb soldered, the 4580 package is a tad smaller than the SOIC but can be replaced without problems. And it worth. I took a risk changing the IC because you never know if the new ones will oscillate so we checked this out and they were fully stable. I considered no more upgrades than this for my Xilica's.
I am also evaluating a custom (PC based) DSP using Acourate, Audiolense or rePhase with higher performance DAC's but this will take some time. The idea is to have powerful FIR to linearize, the XD-4080 has FIR filters but they are limited both in taps and frequency.
Regards,
C.A.
https://www.diyaudio.com/community/threads/opa1656-high-performance-cmos-audio-op-amp.335416/
They are indeed pcb soldered, the 4580 package is a tad smaller than the SOIC but can be replaced without problems. And it worth. I took a risk changing the IC because you never know if the new ones will oscillate so we checked this out and they were fully stable. I considered no more upgrades than this for my Xilica's.
I am also evaluating a custom (PC based) DSP using Acourate, Audiolense or rePhase with higher performance DAC's but this will take some time. The idea is to have powerful FIR to linearize, the XD-4080 has FIR filters but they are limited both in taps and frequency.
Regards,
C.A.
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Well, Chris, as you can see it didn't take a lot of arm-twisting.
To be clear, my education and experience are with DSP algorithms and mathematics; I had to learn how to program in order to implement them. I am by no means a Computer Scientist or professional Programmer (my degrees are in Electrical Engineering), but I manage to get things to work. My current system uses a plain-Jane Windows 10 computer connected by USB to the UR824. The UR824 handles ADC and DAC duties, ASIO handles the data transfers, and the Windows computer handles the computations. Everything is written in C++ (though it's very "C-like" C++ for those who undestand the difference).
I've been considering perhaps starting a thread on using ASIO for DIY DSP, but frankly I don't know where to start and I don't know how deep a ditch I might be digging for myself. I'd welcome any comments, particularly to compare notes with anyone else who has programmed for ASIO.
Greg Berchin
Have you seen this thread?
https://www.diyaudio.com/community/threads/how-to-write-an-asio-driver.400104/
https://www.diyaudio.com/community/threads/how-to-write-an-asio-driver.400104/
No, I hadn't seen that thread before now. It doesn't appear to offer any insight into the actual process of getting an ASIO system to work.
BTW (and this is getting a little ahead of myself), Asio4All has some significant clock-source limitations that are not shared by a true ASIO driver.
I need to add some clarifying information on this. The miniDSP used was the Flex (2-in, 4-out) with balanced connections (1/4" microphone connectors) and Dirac Live, using the input analog balanced connections instead of the S/PDIF digital inputs. The Flex apparently runs at 48 kHz when Dirac is loaded (and apparently even when Dirac is uninstalled). Both of these choices turn out to be issues using the Flex with Jubilees.
1) the analog inputs apparently experience significant modulation distortion. (The fix for this is apparently to use only its digital S/PDIF input.)
2) the use of Dirac causes the Flex to run at 48 kHz (apparently even when Dirac is uninstalled), which causes the export files from REW to need to be output using the "48 kHz" option under REW's selection for miniDSP crossovers. The problem, of course, is that once you select 48 kHz within REW's EQ facility for the miniDSP crossovers, you are only allocated 6 PEQs (biquads). Since the Flex actually has 10 PEQ available, you have to be creative with REW to find another option that exports 48 kHz PEQs for a total of 10 positions.
I hope that this clears up any uncertainties of using a miniDSP Flex. Both of these pieces of information (analog input distortion and 48 kHz operation--requiring another REW export biquad format) were discovered after I first reported on the problems encountered, above.
It's still unknown whether the Flex can do the job well enough for Heritage Jubilees, but it is clear that there are known pitfalls that must be avoided in using this device (the miniDSP Flex), namely that you must use the digital S/PDIF input and that you probably should be prepared to hand-transfer the PEQs from REW's EQ facility if you also elect to have Dirac installed. I would, therefore, proceed with caution if you intend to use the Flex for this most demanding DSP applications--such as this loudspeaker.
Chris
Chris I'm in the process of purchasing a pair of of XI 2050 drivers for my mid horns Presently running JBl 2482. I have a 3d printer and solid works. I would prefer just to buy phase plug extensions. Will Klipsch sell these parts separately?
Is there anyone that has these available or a sketch /drawing so i can make a pair
Is there anyone that has these available or a sketch /drawing so i can make a pair
Hello to the Klipsch Jubilee fan community Greetings from Germany,
My Name is Boris Müller I was encouraged to build a Klipsch Jubilee myself exactly one year ago by a post on the Australian stereonet forum from Member Ohms and the Input from Cask05. Thank you very much and big respect to Chris Askew.
I start to build the K-402 horn, which is almost impossible to get here in Europe.
And use them with the Celestion AXI 2050.
I would like to encourage newcomers here not to completely exclude the Mini DSP Flex. I am using the device and am very satisfied with the result. I run it at 32 bit/96 kHz without Dirac. I was able to transfer all the calculated filters from the REW manually, which takes 5 minutes. But later I ended up with the Xilica DSP settings published here. These stettings simply sound better.
I use the Mini DSP flex toslink to the TV. SPDIF for the CD player and analog for the Technics record player. All noise-free and with a convincing result. I published my designed Lens for the AXI 2050 on Thingiverse for 3D printing. Keyword „Jubilee“
I'm currently thinking about a streaming device, an Eversolo DMP A8 streamer, which is supposed to have a DSP with filter on board!
Has anyone had any experience with this or thought about it?
The device is supposed to have a very good digital to analog conversion due to its DSD oversampling.
Greetings from Germany
Boris
Foto shows only the K402 DIY Horn. Bassbin ist the next step in this project. At the moment i use the bass from a klipsch Cornwall 3.
My Name is Boris Müller I was encouraged to build a Klipsch Jubilee myself exactly one year ago by a post on the Australian stereonet forum from Member Ohms and the Input from Cask05. Thank you very much and big respect to Chris Askew.
I start to build the K-402 horn, which is almost impossible to get here in Europe.
And use them with the Celestion AXI 2050.
I would like to encourage newcomers here not to completely exclude the Mini DSP Flex. I am using the device and am very satisfied with the result. I run it at 32 bit/96 kHz without Dirac. I was able to transfer all the calculated filters from the REW manually, which takes 5 minutes. But later I ended up with the Xilica DSP settings published here. These stettings simply sound better.
I use the Mini DSP flex toslink to the TV. SPDIF for the CD player and analog for the Technics record player. All noise-free and with a convincing result. I published my designed Lens for the AXI 2050 on Thingiverse for 3D printing. Keyword „Jubilee“
I'm currently thinking about a streaming device, an Eversolo DMP A8 streamer, which is supposed to have a DSP with filter on board!
Has anyone had any experience with this or thought about it?
The device is supposed to have a very good digital to analog conversion due to its DSD oversampling.
Greetings from Germany
Boris
Foto shows only the K402 DIY Horn. Bassbin ist the next step in this project. At the moment i use the bass from a klipsch Cornwall 3.
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Wow...that's quite a gratifying story for the pdf file(s) posted at the beginning of this thread. It's really nice to know that someone could use that information to build their own.
Congratulations!
![post-22082-1381930465871[1].gif](https://www.diyaudio.com/community/attachments/post-22082-1381930465871-1-gif.1272420/ "post-22082-1381930465871[1].gif")
I think the problem occurs at the last 180 degree fold of the horn before you reach the mouth. I would lay out the volume expansion curve of the bass bin first to check to see perhaps where the disruption might be occurring--assuming it's due to a squeezing//non-smooth volume expansion profile).
If the problem is due to internal reflection along the folded horn path, then the volume expansion layout won't help very much in locating the issue. Note that I tried to help two guys remotely dial-in their clone bass bins that were designed based the above layout, and I couldn't get anything below ~55-65 Hz, even with lots of boosting EQ--which says to me it's an internal reflection issue (it should have strong response in a room corner down to 31 Hz. If I can find the REW measurement that shows the problem, I'll check the excess group delay to see if it takes off in this region--which would indicate a severe internal reflection(s).
Here is another approach or two on the folded bass bin design.
Chris
Congratulations!
Be careful of using the cross-sectional bass bin layout on the K-forum for a KPT-KHJ-LF bass bin build (i.e., the first-gen bass bin) that strongly affects the bottom octave of the bass bin (i.e., 30-60 Hz when the bin is in a room corner). There is a severe low-frequency cutoff problem using that layout--the one shown below:
I think the problem occurs at the last 180 degree fold of the horn before you reach the mouth. I would lay out the volume expansion curve of the bass bin first to check to see perhaps where the disruption might be occurring--assuming it's due to a squeezing//non-smooth volume expansion profile).
If the problem is due to internal reflection along the folded horn path, then the volume expansion layout won't help very much in locating the issue. Note that I tried to help two guys remotely dial-in their clone bass bins that were designed based the above layout, and I couldn't get anything below ~55-65 Hz, even with lots of boosting EQ--which says to me it's an internal reflection issue (it should have strong response in a room corner down to 31 Hz. If I can find the REW measurement that shows the problem, I'll check the excess group delay to see if it takes off in this region--which would indicate a severe internal reflection(s).
Here is another approach or two on the folded bass bin design.
Chris
Dear Chris
Thank you very much for your advice and for sharing your experience.
The link will certainly help me with the construction. Maybe I was a bit naive. I always thought I would take the published animations and pictures from Klipsch comercial jubilee and try to build the folded horn with the help of the dimensions from the data sheet. Regards Boris
Thank you very much for your advice and for sharing your experience.
The link will certainly help me with the construction. Maybe I was a bit naive. I always thought I would take the published animations and pictures from Klipsch comercial jubilee and try to build the folded horn with the help of the dimensions from the data sheet. Regards Boris
Attachments
Yes, that's the internally ported 2nd-gen bass bin, which is completely different from the 1st-gen bass bin (the KPT-KHJ-LF bass bin).
Two things:
1) that bass bin was initially prototyped using good birch plywood, and it reportedly didn't hold its tolerances during or perhaps after assembly (I would guess that the ply pieces warped after CNC router table cutting before they could be assembled into a finished assembly). If you intend to use plywood, I would recommend assembly on the same day as cutting the pieces to avoid this issue.
So the bass bins that Klipsch now makes are made out of MDF, instead. That leads to the second issue...
2) These bass bins made out of MDF are extremely heavy, as I pointed out in the pdf file, above. I guessimate that there is a 70 kg (157 lb.) increase in weight per bin over the 1st-gen bass bins. That's a lot. The increase in weight is almost exactly the same weight of the TH-SPUD bass bins--but in the case of the SPUDs and 1st-Gen bass bins, those are in approximately two equal weight assemblies, so moving them around is much easier than the 2nd-Gen bass bins, all in one assembly. You'll need some handling gear to be able to move the 2nd-Gen bass bins around, probably the same type of gear that piano movers use. Just FYI.
As far as the performance of the bass bins, 1st-Gen vs. 2nd-Gen: there is an increase in phase lag below about 100 Hz in the 2nd-Gen bass bins that I would guess is caused from the internal bass reflex ports inside the enclosure at the throat of the horn. While this increase in phase response isn't what I'd call dramatic, it's still there due to the bass reflex nature of the design. A good portion of the phase growth shown below for the 2nd-Gen loudspeaker is due to its 4th-order IIR crossover filters used (center frequency at ~320 Hz) vs. the "zeroth order" crossover filters that I use on the 1st-Gen loudspeakers in my listening room. But below ~100 Hz, most of that phase growth between the two bass bins is traceable to the internal bass reflex ports in the 2nd-Gen bass bin--which cannot effectively be EQed out:
Just FYI...
Chris
Two things:
1) that bass bin was initially prototyped using good birch plywood, and it reportedly didn't hold its tolerances during or perhaps after assembly (I would guess that the ply pieces warped after CNC router table cutting before they could be assembled into a finished assembly). If you intend to use plywood, I would recommend assembly on the same day as cutting the pieces to avoid this issue.
So the bass bins that Klipsch now makes are made out of MDF, instead. That leads to the second issue...
2) These bass bins made out of MDF are extremely heavy, as I pointed out in the pdf file, above. I guessimate that there is a 70 kg (157 lb.) increase in weight per bin over the 1st-gen bass bins. That's a lot. The increase in weight is almost exactly the same weight of the TH-SPUD bass bins--but in the case of the SPUDs and 1st-Gen bass bins, those are in approximately two equal weight assemblies, so moving them around is much easier than the 2nd-Gen bass bins, all in one assembly. You'll need some handling gear to be able to move the 2nd-Gen bass bins around, probably the same type of gear that piano movers use. Just FYI.
As far as the performance of the bass bins, 1st-Gen vs. 2nd-Gen: there is an increase in phase lag below about 100 Hz in the 2nd-Gen bass bins that I would guess is caused from the internal bass reflex ports inside the enclosure at the throat of the horn. While this increase in phase response isn't what I'd call dramatic, it's still there due to the bass reflex nature of the design. A good portion of the phase growth shown below for the 2nd-Gen loudspeaker is due to its 4th-order IIR crossover filters used (center frequency at ~320 Hz) vs. the "zeroth order" crossover filters that I use on the 1st-Gen loudspeakers in my listening room. But below ~100 Hz, most of that phase growth between the two bass bins is traceable to the internal bass reflex ports in the 2nd-Gen bass bin--which cannot effectively be EQed out:
Just FYI...
Chris
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Chris,
Nice work on the upgrade papers!
The 2nd-Gen bass horn's 30+ms excess group delay ringing ~200Hz also seems to correspond to a -25dB deep response cancellation.
After recently reviewing the port response of my 2-way bass reflex MEH (post #1226)
https://www.diyaudio.com/community/...rtual-single-point-source-horn.264485/page-62
found two large port resonant peaks (pipe resonance) at 335Hz and 634 Hz, out of phase with the woofer output causing response cancellations.
Similarly, I also suspect the 2nd-Gen bass horn may be amplifying out-of phase pipe resonances from the three port tubes in the throat resulting in the nulls around 80 and 200Hz.
Do you think that is the case, or are the excessively long group delay tails at 200/275Hz a result of the horn geometry?
The orange trace of the first-gen dialed-in Celestion Axi2050 driver using the Xilica XP DSP shows a -8dB null in the 350Hz crossover range, what is the cause of that?
Thanks,
Art
Hi Art.
I did see the higher Q disturbances in the bass bin amplitude and phase response (acoustic) as well as apparent higher Q boosts and notches in the transfer function output from the Klipsch-provided DSP crossover (with about a 320 Hz crossover frequency, shown below), which I would not expect to see in other Klipsch-designed horn loaded bass bin corrections (i.e., La Scala, Belle, K-horn, KPT-KHJ-LF, and MWM):
Note the higher Q corrections at 62, 115, 175, 215, and 260 Hz that are (I assume) there to correct perceived min-phase amplitude issues. There is no special DSP correction at 80 Hz, saying to me that this is much more likely a room mode (i.e., the owner's room) instead of a bass bin design issue. (I don't have anechoic measurements of this loudspeaker.)
Here is the 10-400 Hz acoustic transfer function plot of the "Heritage Jubilee" taken in-room (no smoothing):
When evaluating loudspeakers that someone owns, I believe that in-room measurements are appropriate, since that's where they listen to them. The 1m measurements are a compromise to minimize nearfield boundary reflections (floor, ceiling, walls) for apps like REW to yield better phase response plots.
Chris
Interesting. I'll add that to my list of reasons why I don't use reflex bass bin designs. My basic view is that reflex ports are really a relic of using passive crossovers without corrective EQ (as DSP crossovers can and do provide). PA loudspeaker design for those that are buying the loudspeakers tend to like monoamping for convenience (i.e., not hi-fi). I understand that, but I don't deal with that market or subject here or in my personal needs.
I did see the higher Q disturbances in the bass bin amplitude and phase response (acoustic) as well as apparent higher Q boosts and notches in the transfer function output from the Klipsch-provided DSP crossover (with about a 320 Hz crossover frequency, shown below), which I would not expect to see in other Klipsch-designed horn loaded bass bin corrections (i.e., La Scala, Belle, K-horn, KPT-KHJ-LF, and MWM):
Note the higher Q corrections at 62, 115, 175, 215, and 260 Hz that are (I assume) there to correct perceived min-phase amplitude issues. There is no special DSP correction at 80 Hz, saying to me that this is much more likely a room mode (i.e., the owner's room) instead of a bass bin design issue. (I don't have anechoic measurements of this loudspeaker.)
Here is the 10-400 Hz acoustic transfer function plot of the "Heritage Jubilee" taken in-room (no smoothing):
I think that's a quarter wave floor bounce cancellation of the microphone placement. When you move the microphone up or down, that notch frequency moves with it. Remember that all these measurements are taken in-room, not outside.
When evaluating loudspeakers that someone owns, I believe that in-room measurements are appropriate, since that's where they listen to them. The 1m measurements are a compromise to minimize nearfield boundary reflections (floor, ceiling, walls) for apps like REW to yield better phase response plots.
I think it's the result of fourth order crossover filters used between two horns that are separated by a fair distance (K-402 on top of bass bin), with the microphone placed on-axis with the K-402 at 1m. There are sensitivities of this to microphone placement in this frequency region. I've included a plot of the group delays for another 1m measurement in-room (microphone on-axis to the K-402.) below:
Probably microphone placement. Here's another measurement at 1/48 octave smoothing of the same loudspeaker on-axis with the Axi2050:
Chris
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