REW ECM53 RFC (Request For Comment)

[boxerfan88]

Got a little restless because I haven't tweaked my system for several months, I decided to start a new tweaking project.

I am testing out the theory that if I move the crossover point from 80Hz to 100Hz, the bass will be "stronger" because more of the low range is handled by the subwoofer, and hopefully the upper range distortion will be lower because the mains need for LF excursion would be lower. My subwoofer is located at the center (between LR), and I'm okay with mono bass.

After re-doing the FIR filters (room correction + 100Hz crossover), below is the resulting REW measurement.

I'm also liking what I hear -- slightly different -- a little more bass -- a little more clarity in the upper bass/lower mids (might be confirmation bias, who knows).

I'm hoping to hear your comments about the resulting measurement.

A little more low end (<100Hz), less messy 100-300Hz area.
Please ignore the wide bump at the 3-10kHz area, that's the microphone bump (no mic cal file).

System wide distortion is really low (<1%) throughout most of the audio band (40Hz-10kHz).
Starts to climb above 1% starting 40Hz ... and only reaches 5% at 20Hz.

In-room sound decay is nicely <300ms throughout the audio band, except for the room mode peaks at the low end.

The mdat file is also attached.

Thank you in advance.
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[boxerfan88]

For interested parties ... a sample recording with mic at MLP (mono, in-room, Superlux mic, Topping E2x2 OTG, Audacity) ...

I listen to the recording on headphones, and found two things that stood out:

• the bass in the recording seems to be more boomy vs. what I hear inside the room
• the slight "cave like" reverb in the recording, I don't hear in the room.

The microphone captures everything as it is.
I guess the Brain is clever enough to "tune out" the room reverb to some extent.

 

[ppataki]

Your FR and distortion graphs look great, KUDOS!

I was just checking the Step response graph

Is this room related or sub integration related?


Also the Wavelet diagram shows a bit of a delay in the bass region
Do you have a ported subwoofer?

 

[boxerfan88]

Your FR and distortion graphs look great, KUDOS!

Thank you

I was just checking the Step response graph

View attachment 441552

Is this room related or sub integration related?

I think it is subwoofer related. The 2ch mains only sweep shows the tweeter spike, followed by midrange hit 100% <3ms, then the woofer reach 100% around 25ms.
Only after I integrate in the subwoofer, the 100% mark moves out to that 40ms+ area.

(Old 2-channel mdat attached.)

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[boxerfan88]

Also the Wavelet diagram shows a bit of a delay in the bass region
Do you have a ported subwoofer?
View attachment 441553

Sorry I am not familiar with wavelet charts.
Is there any anomaly you see in the chart?
(Where/How do I learn how to interpret the wavelet chart?)

My subwoofer is a sealed unit, 2 drivers in a push-pull configuration.
Ref: https://www.orisun-acoustics.com/os-dd12/

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[ppataki]

(Where/How do I learn how to interpret the wavelet chart?)

I just learned using this chart here from one of the members from Germany (sorry but I don't remember his username)

Basically I set it up like this:

And it shows a few things, let me take my system in my home office as an example:

The left arrow shows the pre-ringing (if any) - in my case there is some, since I am using linear phase crossover to cross my sealed DIY sub to my front DIY speakers

The right arrow (and basically everything right from the 0ms point) shows the post-ringing and the dashed line represents the peak energy delay - like how much bass is 'lagging' behind the rest of the frequency range (8.58ms in my case)

With a sealed sub, you should ideally not have more than 20ms (max). Ported subs can go up to 40ms or even much higher than that
But also if this value goes higher it may mean that there is still some tweaking possible with the crossover or alternatively it is just the room
I have a sealed sub in both my systems and I never get more than 10-15ms delay max.

The corresponding step response curve looks like this:

And the FR curve:

 

[boxerfan88]

@ppataki Thank you so much for the tutorial ... let me dive into it over the weekend. Very interesting new area for me to learn. Much appreciated!!

 

[ernestcarl]

Reflection-decay characteristic in the bass region of your room is a bit messy/smeary -- clarity drops below 250 Hz.

It's just a room acoustics thing... and not something you can fix with DSP.

 

[boxerfan88]

Folks, quick check, should I consider A as the subwoofer impulse peak, and ignore B ?

I am guessing that B is room related, since it comes after such a long time (40ms).

X is the mains (L&R) impulse peak.

encl: mdat
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[ppataki]

Folks, quick check, should I consider A as the subwoofer impulse peak, and ignore B ?

I am guessing that B is room related, since it comes after such a long time (40ms).

X is the mains (L&R) impulse peak.


View attachment 442421


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I would use A

 

[boxerfan88]

I would use A

Thank you

 

[ernestcarl]

I would also think about where the ‘impulse start’ is which is very close to A anyway. Maximum phase in the room would be B — blame your room acoustics — and it has an even bigger peak, but the shape of it could still be reduced with EQ.

 

[boxerfan88]

Tried a slightly different approach ... did independent sweep of L,R,Sub between 75Hz to 150Hz.

Analyzed the impulse response first peak difference ... it's 5.99ms.

Next, analyzed the phase difference between the mains & sub at the 100Hz crossover point ... it's 216 degrees., which also translates to 6ms @ 100Hz.
How interesting...

Redid the roomEQ with the 6ms delay added to the main channels.

Probably it's confirmation bias ... the bass seem to be punchier ...

And strangely, with the new time alignment, the room mode decay is faster ... that's unexpected (good outcome) ...
For example, the 55Hz tail dropped from around 750ms down to 500ms.

I'm speculating when the mains & sub are time aligned, when signal stop, all drivers stop at the same time.
Contrast to situation when not time aligned, mains stopped but sub still adding energy into the room.
Is my speculation on the right track ... or am I talking rubbish

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[ernestcarl]

This time it looks better:

I'm speculating when the mains & sub are time aligned, when signal stop, all drivers stop at the same time.
Contrast to situation when not time aligned, mains stopped but sub still adding energy into the room.
Is my speculation on the right track ... or am I talking rubbish

Combined IRs from all the different drivers sum together relatively closer in time (also a more compact IR) as they reach the microphone position. Although, for obvious reasons, I can't hear the "improvement" you might have heard for yourself.