Decay / ringing issue

[thexder]

Hello,

I've been dealing with bass issues for quite some time now. I just can't get it right.
I'm not particularly experienced so I started by focusing on the FR.
Turned out I can get a decent one but the sound is still not what I was hoping for.
I then looked at waterfall and decay plots. And no matter what I do, there are awful results at 40-55 Hz. No way I can get it to -20 dB within the 160 ms.
The room has some treatment, most of the surfaces are covered with 8" absorption. Ceiling too.

One time I was able to get it to 16 dB but the sound was still not good. I could feel the vibrations in the seat so something clearly wasn't right.

My question is if this can be "fixed" by placing the speakers/subs on optimal locations and fine tuning the gear?

 

[Bpape]

a few questions.

Can you post a waterfall with 5db gradations along the left side and 300 ms depth please.

Room size, seat location, sub location?

Are you cutting off your mains or overlapping them with the sub?

 

[thexder]

Sure thing. I'm attaching the mdat file as well.
Two subs next to front speakers (equidistant)
One sub behind MLP (approx at. center lenght - I tried to move the mic forward anc backwards but the critical decay was even worse)
One sub at left sidewall.
Mains not crossed over but I closed the ports.
I can provide separate plots of mains.

 

[DanDan]

You appear to have a lot of 'rumble' going on below 30Hz. Is any of that useful to you? You might try blocking the ports if your subs have such. If your speakers are big enough you could try running them full range with the subs augmenting.
DD

 

[jtalden]

DanDan,
Try removing the "normalize to peak at each frequency" option. I think you may be looking at the noise floor that is being pulled up below 20Hz due to the frequency response rolloff. I don't really see any big problems. There is late arriving 47Hz probably due to significant EQ there used to pull up an otherwise sagging response there. I don't think that should be any issue either. It all looks pretty good to me. I don't know why it would not sound good.

 

[DanDan]

I think that facility is only on the Spectrogram. I am using the Waterfall.

 

[jtalden]

Yes, I assumed you were looking at the spectrogram as 65 dB at 20 Hz will never be heard or felt. It might rattle some windows or doors though.

 

[DanDan]

I believe it is not necessary to establish actual tones in order to stimulate such resonances. I reckon Kick drums would get this rumble going nicely.

 

[thexder]

There is late arriving 47Hz probably due to significant EQ there used to pull up an otherwise sagging response there. I don't think that should be any issue either. It all looks pretty good to me. I don't know why it would not sound good.

No EQ is present here yet. Just mains + 4 subs. I was going to ask you for time align check but I will try some other positions first.
Why it does not sound good? That's what I'm trying to figure it out. You think 500-600 ms decays are not a problem? And less than 10 dB drop at 160 ms? And no matter what I do, the decay at 47 Hz is always louder. That's why I was asking if gear placement or tuning (crossovers/HP/LF/delay etc) could improve this.

This, attached mdat, sounds better. Speakers moved further from front wall and two subs only, placed slightly different than before and with reversed polarities.

Note: i'm talking about stereo listening, so probably tones below 30 Hz are less usable in this case. But still - if I'm getting vibrations in my back while leaning on a seat, something is happening, right?

 

[DanDan]

It is all relative. This is broadly speaking a much better than usual result. EBU Critical Listening specifications require around 200mS Broadband but allow a rise to around 400mS at LF. Indeed a room without such decay would be very different from normal human experience. Very Anechoic and bass light. The vibrations in your back confirm that the infrasonic mountain is moving! I would block the reflex ports in the subs, and/or use High Pass Filtering. By all means play sine waves at the ringing peaks and search the room for places to apply treatment. The 45 Hz region is sticking out a little bit, so by all means treat those modes more aggressively. Such Low problems are very amenable to EQ. Dirac Live with Sub Management extension perhaps. Don't forget that Listening position has powerful variations.

 

[jtalden]

I have no real experience with such heavily treated rooms and rapid decay targets. DanDan is a much better resource.

You think 500-600 ms decays are not a problem? And less than 10 dB drop at 160 ms? And no matter what I do, the decay at 47 Hz is always louder.

Scaled to see a 40 dB drop range, we can see your room has decayed that far within 120 ms @200 Hz - 220 ms @10 Hz on average with a couple of frequencies that hang on. Most all rooms will be difficult to remove the impact of all modes.

That's why I was asking if gear placement or tuning (crossovers/HP/LF/delay etc) could improve this.

Moving setup locations will change the result, but likely just expose other resonances. EQ any peak resonances flat helps, but does not remove the issue. The others have no impact. Only specialized room treatments will be effective and I suspect they have limits also.

Note: i'm talking about stereo listening, so probably tones below 30 Hz are less usable in this case. But still - if I'm getting vibrations in my back while leaning on a seat, something is happening, right?

A chair vibration is likely to be very low frequency issue so that it is not surprising. A suspended floor or ceiling can also cause a low frequency resonance.

 

[thexder]

It is all relative. This is broadly speaking a much better than usual result. EBU Critical Listening specifications require around 200mS Broadband but allow a rise to around 400mS at LF. Indeed a room without such decay would be very different from normal human experience. Very Anechoic and bass light. The vibrations in your back confirm that the infrasonic mountain is moving! I would block the reflex ports in the subs, and/or use High Pass Filtering. By all means play sine waves at the ringing peaks and search the room for places to apply treatment. The 45 Hz region is sticking out a little bit, so by all means treat those modes more aggressively. Such Low problems are very amenable to EQ. Dirac Live with Sub Management extension perhaps. Don't forget that Listening position has powerful variations.

Playing the 45 Hz seemed a good idea to me as well. I did that, of course, corners have been targeted. Treatment didn't help. By the way, subs are not ported.
Dirac Live Sub Management is currently just a theory. AFAIK you can't buy it in a commercial AVR at this moment. They said january 2020 but before that they said October 2019.
Altough, in my opinion, room correction systems can't really solve room issues. They can improve much but they can't do magic.
But than again, based on my experiece, of course, stereo never sounded good with room correction.

 

[thexder]

I have no real experience with such heavily treated rooms and rapid decay targets. DanDan is a much better resource.

Oh, thank you for flattering words but I don't see my room as heavily treated. Like you see, my understanding of acoustic is below average, I assume the same goes for treatment.

Scaled to see a 40 dB drop range, we can see your room has decayed that far within 120 ms @200 Hz - 220 ms @10 Hz on average with a couple of frequencies that hang on. Most all rooms will be difficult to remove the impact of all modes.

Is it safe to assume that hanging frequencies affect the whole picture?

Moving setup locations will change the result, but likely just expose other resonances. EQ any peak resonances flat helps, but does not remove the issue. The others have no impact. Only specialized room treatments will be effective and I suspect they have limits also.

Here's some plots that made me think settings/placement could help.
Here we have main speakers waterfall. We see longer decay at 40-50 Hz area. Then one sub is added which improved the situation. In other words, more bass, less ringing. Situation at critical area is still better with two subs added. Finally, reversing the polarity on second sub improved the whole thing sonically. Music now sound decent and not ugly. There are still two subs left to integrate.

A chair vibration is likely to be very low frequency issue so that it is not surprising. A suspended floor or ceiling can also cause a low frequency resonance.

This is actually interesting. The vibrations are almost gone If I raise my back so it doesn't lean on the chair. Which made me think it might be caused by a chair. Replacing it is one more test I'll have to make.

 

[DanDan]

"But than again, based on my experiece, of course, stereo never sounded good with room correction."
All of the products I have seen introduce a small delay and gain off set between L and R. I have never managed to get the mic so perfectly central as to achieve a zero time delay. Certainly in critical listening rooms, this has a horrible effect.
That plus the fact that we sometimes implement as a plug in and then listen in mono.......

 

[Bpape]

One other thing to check.... Do just the left, then just the right, then both together. Any differences between the singles and the pair is an interaction between the 2 where spacing may help. Or introduce a null that coincides with the peak to help smooth things out. I agree with DD that room correction should be the LAST thing you do. ANY time you EQ, you are introducing phase anomalies.

 

[thexder]

Thank you all for participating.

I did some more gear movements and I'm really surprised how moving a sub just a couple of inches away can change the sound. Not to mention turning on its own axis. I was sure it couldn't make a difference but man, was I wrong.

I was able to get rid of the ringing as well. It's still there as this is clearly a room mode but it has been vastly eliminated. I removed some treatment that proved to be ineffective and the rest was done with placement and extensive (and time consuming) sub settings (phase, polarity, HP and LP filters, slopes, gain and contour*).
* This seem very helpful setting for changing volume at only one frequency. Manual says this act as an extra EQ for manipulating the frequency contour.

The FR looks pretty decent (and so does the sound, finally), except for the 87 Hz peak and 105 Hz dip (if I focus at the area below Schroeder).
I will try to solve this with absorber. If this would fail I can try with PEQ.

Now I'd like to focus on the spectrogram. The way I see it the sound should die faster, right? But than again, I had better spectrograms with poorer sound experience. Probably the decay and waterfall graphs were less good as they are now.

 

[thexder]

One other thing to check.... Do just the left, then just the right, then both together. Any differences between the singles and the pair is an interaction between the 2 where spacing may help. Or introduce a null that coincides with the peak to help smooth things out. I agree with DD that room correction should be the LAST thing you do. ANY time you EQ, you are introducing phase anomalies.

What spacing are we talking about? Distance between speakers or from front wall? I pretty much exhausted all the options. Any other locations would block the screen or create more ringing.
When looking at left, right and both together it is clearly they point at a 45 Hz mode/null, correct?
Some people use EQ below 150 Hz. I always assumed it's less critical there?