Combining measurement methods to get a more accurate EQ - MMM + Gated Nearfield + Klippel Measurements

[abdo123]

The original orange line in Figure 1 is the HTM-12s with no EQ, so certainly there is room to EQ the transition/modal region for sure.

yes but to boost that dip at 180Hz over 10 dB you effectively eliminated any Dynamic range your speaker and amplifier would have at that region. these sort of issues cannot and should not be solved at the digital side.

the modal region is also the region that plays the loudest during playback so it should also be the region where you have the biggest headroom.

Can you please give a before and after graph on Distortion as well?

 

[johnp98]

yes but to boost that dip at 180Hz over 10 dB you effectively eliminated any Dynamic range your speaker and amplifier would have at that region. these sort of issues cannot and should not be solved at the digital side.

the modal region is also the region that plays the loudest during playback so it should also be the region where you have the biggest headroom.

Can you please give a before and after graph on Distortion as well?

Yes I agree that as you boost you are cutting down on dynamic range so should be done with that knoledge. I guess I don't know how much of a factor that is when I typically don't listen anywhere near reference and it seems that these speakers can get way louder than anyone would listen in their right mind.

Here are the distortion graphs pre and post EQ (from a point measurement at the MLP).

No EQ:

Post EQ:

So it certainly has increased a bit, but does not look too bad to me. But I don't have lots of experience in this area. What do you think? Is it pushing this area of the system too much?

It is not letting me attached the raw REW file, so let me know if you want to see anything else from the point measurements.

 

[johnp98]

Many thanks @johnp98, one question for you:
I would be interested to see the step response (first 10ms) of your Left and Right channels to see how early reflections affect it.
My Best

Here you go!
Measured from a point measurement at the MLP

Left Pre EQ:

Left Post EQ:

Right Pre EQ:

Right Post EQ:

Unfortunately I am not too familiar with how these graphs are posted, so let me know if you want to see them another way or another scale.

The speakers themselves are ~3-4ft from the front wall yet quite close to the side walls (~1ft) but toed in quite aggressively just infront of the MLP to help with time intensity trading that some people do for waveguide speakers. I think because these speakers have a more narrow directivity I thought keeping them that close to the side wall was reasonable (although probably get some SBIR in the low end).

 

[FrantzM]

Cool stuff!

+1

 

[johnp98]

I think we need to combine additional measurements to determine what to EQ and by how much for optimal result, so if OP have time I'd suggest looking at the minimum phase plot and the spectrogram to see the in-room effect of EQ based on MMM below 1 kHz.

Unfortunately I am not too familiar with minimum phase plots, so if someone could point me in the right direction I can display them.

Here is the spectrograph and also waterfall plots pre and post (based on a point measurement at the MLP)

Pre EQ:

Post EQ

Pre EQ: I changed the vertical axis to see how long it takes to decay to near steady state.

Post EQ:

 

[Kvalsvoll]

If you use these settings on the spectrogram, it will actually show you much more readable and useful information:

 

[ernestcarl]

Can you post your before and after EQ mdat files by any chance?

 

[johnp98]

If you use these settings on the spectrogram, it will actually show you much more readable and useful information:

Never looked at it this way, will have to do some reading about it and how to interpret. But here are the graphs pre and post.

Pre EQ:

Post EQ:

 

[johnp98]

Can you post your before and after EQ mdat files by any chance?

It does not let me attach it, nor does it let me attach it when compressed and zipped.
I put it on my google drive and here is the link.
https://drive.google.com/file/d/19Y6_2W0JFh6MVkiQ2WbDNXTgZwDGnBW9/view?usp=sharing

Let me know if there is an easier / better way.

 

[bigjacko]

MMM in all 3 axis over your MLP

I have watched the MMM vedio but did not see three axis. What do you mean by three axis? Why do we need to do three axis?

 

[abdo123]

I have watched the MMM vedio but did not see three axis. What do you mean by three axis? Why do we need to do three axis?

The 3 axes are x y and z. There seems to be a language barrier

 

[ernestcarl]

It does not let me attach it, nor does it let me attach it when compressed and zipped.
I put it on my google drive and here is the link.
https://drive.google.com/file/d/19Y6_2W0JFh6MVkiQ2WbDNXTgZwDGnBW9/view?usp=sharing

Let me know if there is an easier / better way.

Looks pretty good. I prefer to apply vector averaging between L+R (when mic is not exactly centered) to see none of that phase cancellation in the HF.

Following are attachments of your measurements where I shifted the IR using 'Estimate IR' and vector averaged the L+R; as well as applied FDW 7 -- just to reduce the file size a bit.

Overall clarity looks improved with your 'combo EQ' which is good. Personally, I'd probably reduce the sub bass a little esp. around 21 Hz or so -- but if this perceptually sounds much better to you, then go ahead and keep it.

There is one small consequence of your EQ which is visible in the wavelet spectrogram at right around 200 Hz:

40dB scale, 1/6 resolution

Decay slightly extended around 200 Hz. Plus transition around 250 Hz may be a tad "rough"

Honestly, I don't know if that will pose any obvious audible issue -- although my own guess is that its probably just fine.

*T60M

My room is veeery dry (100+ ms) by comparison

 

[bigjacko]

The 3 axes are x y and z. There seems to be a language barrier

Thank you for reply. The part I don't understand is why measure different axis. Is it because bass frequency going into microphone at different angle will have different spl? For y and z axes which way should I point to? Up or down and left or right?

 

[abdo123]

Thank you for reply. The part I don't understand is why measure different axis. Is it because bass frequency going into microphone at different angle will have different spl? For y and z axes which way should I point to? Up or down and left or right?

because the response is different in every point in the room/space, so you try to 'capture' all the 'space'

keep the mic direction the same but move it in a spiral around your body.

 

[ernestcarl]

Spectrogram will confirm this. At one point I tried to replace the EQ for sbir cancellations with a bag of Rockwool insulation and the sound was a lot better for it.

I think we need to combine additional measurements to determine what to EQ and by how much for optimal result, so if OP have time I'd suggest looking at the minimum phase plot and the spectrogram to see the in-room effect of EQ based on MMM below 1 kHz.

That would be better, of course...

FDW 7 cycles

Is this the 'minimum phase plot' you wanted to see? It does look improved after EQ.

 

[Kvalsvoll]

Never looked at it this way, will have to do some reading about it and how to interpret. But here are the graphs pre and post.

Pre EQ:
View attachment 137635

Post EQ:
View attachment 137636

Now you can clearly see differences around 200Hz, and you can also see better what this type of eq can not fix.

Horizontal is frequency - as in a frequency response plot - vertical is time. Level is represented by colour. This shows when in time the sound starts, and how it decays. Resolution will always be a compromise between time or frequency - more resolution in one gives less in the other. This scaling makes it possible to view the entiry 20-20k spectrum in one picture.

As for reading - start with any book with a title like "Introduction to Signal and Systems". If you are an engineer you may already have this basic knowledge-

 

[Kvalsvoll]

I hope I did not kill this thread, that was not my intention with posting about those graphs.

EQ can be useful, and the opening post here was good. Now, I am curious about how this sounds - how did the eq change the sound, was there an improvement, how did the sound improve.

 

[johnp98]

I hope I did not kill this thread, that was not my intention with posting about those graphs.

EQ can be useful, and the opening post here was good. Now, I am curious about how this sounds - how did the eq change the sound, was there an improvement, how did the sound improve.

No I am very happy with the extra information and pushing me to learn more about various graphs.

I am not the most experienced when it comes to reliably noting changes in the frequency response so I don't want to pose as a certified Harmon listener.

But the changes certianly are notable! And it does seem like a significant improvement! It even stood up to blinded testing with my wife changing when the filters were active vs not. So that's a good sign.

The biggest difference I noted was how all parts of the soundstage seem to be on the same level / depth / plane. Before some of the highs felt more 'forward' than the rest. But now the sounds seem more consist in depth if that makes any sense.
I know from reading Dr Floyd Toole that pink noise can be the most revealing, so playing pink noise and comparing pre and post was actually very revealing!
The pink noise was a lot more even and focused in the center between the speakers withuch tighter imaging. I was actually quite impressed!

I have been thinking about toying with RePhase or another DRC that does phase correction as I have heard it can have positive effects... But correcting the frequency certainly helped imaging mush more than I expected!

 

[mitchco]

I have been thinking about toying with RePhase or another DRC that does phase correction as I have heard it can have positive effects... But correcting the frequency certainly helped imaging mush more than I expected!

You might want to give http://drc-fir.sourceforge.net/ a try. User gmad from diyAudio has written some useful scripts including a default starting place to try to make using it simpler. https://www.diyaudio.com/forums/ful...ectrical-loudspeaker-correction-networks.html There is also a GUI that goes with it if you want to use that instead: https://www.diyaudio.com/forums/full-range/242171-towers-25-driver-range-line-array-73.html

There are good explanations in the thread including how it is different than rePhase. The big deal is the addition of psychoacoustic filtering, adjustable frequency dependent window (FDW) and excess phase correction. Denis DRC documentation also does a great job of explaining this and showing what is going on. If you have the time it is worth a read as excess phase correction at low frequencies is where it is at. This allows you to clean up the step response overall but especially the low end.

Looking at your step responses in post 23 we can see a peak at around 7 to 7.5 ms that is greater in amplitude than the direct sound. This is usually due to non-minimum phase behaviour as described in John Mulcahy's explanation of minimum phase. See section, "Minimum Phase and Ivertibility." You may want to check your step response out to 100ms to see if there are any other peaks greater than the direct sound...

To my ears, the end result using this type of DRC software where you can adjust the FDW to be long a low frequencies (+500ms or greater) and just the direct sound after 4 x your room's Schroeder frequency, produces the clearest bass response I have heard.

Good luck on your journey!

 

[Newman]

10hz - 200-400hz (Below ones schroeder frequency which is room dependent):

Hi,

thanks for posting your good and very helpful thread. I have a very minor point to contribute. You have made many references to the Schroeder crossover frequency, but what you actually mean is the transition frequency (or transition region). The Schroeder crossover frequency doesn’t apply to small rooms like home hifi, and if you try to calculate it from measurements in a small room, you get low values that are too low to describe what you actually wish to convey, namely, the frequency (region) below which room modes dominate and above which reflected sounds dominate. This is referred to as the transition frequency or transition region.

cheers