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Why does DIRAC completely remove bass response (KEF R3 + sub + minidsp flex)

mdsimon2

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I was able to do this with REW and a MiniDSP. Basically align the timing of the subs and mains to flatten that response

Unless you are making nearfield measurements you really do not know if you are anechoically aligned as the room will have a large contribution to the measurement. Unfortunately nearfield measurements can only be done individually on the sub or speaker so some modeling is required to understand combined response (I use VituixCAD). You want more than just time alignment, you want speaker / sub phase alignment throughout the x-over to ensure the x-over sums correctly. This usually involves a mix of pure delay to account for acoustic offset between speaker / sub at the listening position and high passing your speaker with a HPF identical to your sub roll-off (in addition to whatever HPF you may add to your speaker for the speaker / sub crossover).

If it works for you, great, there is more than one way to get good results. I like understand the anechoic response as it eliminates a lot variables before involving the room.

Michael
 
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Geertidow

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Oke so I think I may have found the problem.
Whenever I apply any subwoofer volume calibration beforehand to make the volume of the sub and the speakers a bit in the same region DIRAC goes haywire. Frequencies up to 300 hz get squeezed out.

Whenever I do nothing to the sub (no negative gain or PEQ with negatieve gain, i.e. a low shelf of -3 or -6 db for example from 10 - 400 hz) the DIRAC measurements work out really well, but, unfortunately, I can't really compare the DIRAC with no dirac because then there is just too much bass in there.

That is so far the only really consistent value I've found.
The new software in the end did not make the difference. Reducing the sub output (-3 dB) resulted in that very weird no-bass dirac curve.
Mesauring with no output modification worked again.

Just to check: I ended up with 6 ms delay on my main speakers.
My sub is passive and powered by an ncore nc500MP. Is that a strange delay value?
 

mdsimon2

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Oke so I think I may have found the problem.
Whenever I apply any subwoofer volume calibration beforehand to make the volume of the sub and the speakers a bit in the same region DIRAC goes haywire. Frequencies up to 300 hz get squeezed out.

Whenever I do nothing to the sub (no negative gain or PEQ with negatieve gain, i.e. a low shelf of -3 or -6 db for example from 10 - 400 hz) the DIRAC measurements work out really well, but, unfortunately, I can't really compare the DIRAC with no dirac because then there is just too much bass in there.

That is so far the only really consistent value I've found.
The new software in the end did not make the difference. Reducing the sub output (-3 dB) resulted in that very weird no-bass dirac curve.
Mesauring with no output modification worked again.

Just to check: I ended up with 6 ms delay on my main speakers.
My sub is passive and powered by an ncore nc500MP. Is that a strange delay value?

What is your sub / speaker positioning like? 6 ms delay implies ~6 ft path length difference between your speaker and sub at the listening position.

Delay will also impact phase response and is often used as a band aid to get better phase alignment between your speaker / sub rather than address the underlying issues.

Again if you are making in room measurements to set the speaker / sub crossover you have so much room influence that it is very hard to diagnose what is going on. Fortunately all that really matters is that you like the sound.

Michael
 
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Geertidow

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Yeah, that is true. But it's hard to learn if you minidsp goes bananas every time you time to program it :).

I don't trust those 6 ms either, and measurement wise from the LP it seems to make no difference.

I mainly did a delay (based on the youtube videos above) because the devteam of minidsp asked me two times why I had no delay. But my speakers and sub have the same distance from driver to LP (give or take a few cm's). The sub is right in the middle of my speakers.

For a crossover I ended up going for a simple 85 hz crossover (LR, 24 db/oct for both speakers and sub) because it sounded good and seemd a logical choice). I will look up a good tutorial to set the xo one day...
 

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Geertidow

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Oke as a recap:

1. I used this tutorial to time allign the subwoofer to the speakers (considering the speakers to be subwoofers sweeping at 30 - 250 hz):
. I then checked it with this tutorial:
and it seemed a good idea to do 6 ms.
2. I did not volume allign the subwoofer to my mains (the subwoofer generates pink noise with speaker cal frequencies almost 10 dB louder, more so in the higher frequencies like 120-250 hz) because if I lower the subwoofer output on the minidsp (by for example - 4 dB of whatever number) the DIRAC measurements go haywire.
3. Measuring DIRAC with no subwoofer volume correction and with 6 ms delay on the main speakers results in a measured post-DIRAC response that is satisfactory, both in REW and to the ears.
Afterwards, I removed the 6 ms delay and it sounded a bit better acoustically (unblinded) so i left out the 6 ms delay. This makes sense given how the setup is positioned.
4. The crossover setting was also determined using the tutorials by the same youtube channel and found to be optimal at 85 hz. To make things more easy, I ended up using a LR 4th order (24 db/oct) on both speaker and sub.

All in all the results are really good now (finally better than manual PEQ!) I am a little dissapointed that the miniDSP does not cope well with volume alligning the sub before. using DIRAC. But I will count my blessings and enjoy the great sound so far. Apparently I am not such as bass head since I ended upw ith a flat sloped dirac target curve with curtains from 30 - 1000 Hz.
FRDIRAC.jpg
FRDIRACwaterfall.jpg
 
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Flak

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REW yes, 2.1 setup, measured at listening position through all speakers
If one measures two combined channels at the same time there will be interactions between them that boost some frequencies, and cut others
 
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Geertidow

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Of course, but that is the way I listed to music right? The OP was mostly looking for a reason DIRAC went haywire on the minidsp flex.
 
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Geertidow

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Well a small update (again) for future MiniDSP Flex buyers.
No matter what I do, some DIRAC measurements with subsequent filters result in removal of frequencies below 300 Hz (in other words horrible).
Although I really enjoy the sound of the unit (as I have said in the troll post recently @abdo123).
However, it's just too much work to get this uni (750 eur + 178 eur DIRAC license) to work properly.

The seller will request a complete refund of the product and help me find some other unit. I'm also afraid to buy a C658 (owned it before and the voltage out for the sub was way too low). So we will see what happens.

There are also more issues: freezes, having to remove power before connection to the PC (else my laptop won's see the dive), etceter etcetera etcetera.
All in all I managed to get really good sound oud of it with a working DIRAC (200 Hz correction), but the number of issues is just too great.
 
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Geertidow

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Well @abdo123 , your timing instrunctions (1 measurement with DIRAC where input 1 is sub and input 2 is left speaker etc. Does seem to work.
I end up with a 1.96 ms delay on the sub, this seems to remove the issues when measuring DIRAC. I can't explain a 2 ms delay in terms of speaker placement distance, but I'll take it anyhow. Hopefully MiniDSP allow me to take my DIRAC license to a MiniDSP HD device, which seems less prone to issues.
SoundImports has agreed to take back the device and fully refund.
And, in the end I used your (Abdo) suggestion of xo'ing at 60 hz with the 1rst suggested XO's. they work really well so far.
 
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Geertidow

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@abdo123 after extensive testing your timing method (using dirac to time allign the subwoofer) seems to be the most consistent solution for this problem. I haven't had any trouble after using your timing method and thus decided to keep the unit. Even though miniDSP allowed me to send the unit back
 
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@abdo123 after extensive testing your timing method (using dirac to time allign the subwoofer) seems to be the most consistent solution for this problem. I haven't had any trouble after using your timing method and thus decided to keep the unit. Even though miniDSP allowed me to send the unit back
That's the method I use as well. It seems logical and quite simple to do it this way. :)
 
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