Different approaches to managing bass

[Keith_W]

In another thread, @ernestcarl posted a video with an interview with Trinnov's Jon Herron. Most of the discussion was about Trinnov's "waveforming" technology - for me it was a fantastic video and I recommend watching the whole thing. However, this slide was of particular interest and I would like to see what ASR members thought of it.

For some reason ASR won't let me embed the video, so here is a link: Link to video (timestamped 33:49)

The traditional approach of "flooding the room" includes strategies by MSO and Harman, where multiple subwoofers are used to even out the bass response. I am not sure, but I think that Room Shaper (@mitchco review here) also uses the same approach. "Control the zone" refers to Trinnov's new DSP, and although it is not mentioned - probably also Dirac ART and VBA's (he does mention DBA's though). This approach is wasteful of subwoofer power because half the output goes into cancelling reflections. There is also bass equalization which he does not mention, where you simply lop off the peaks. And of course room treatment is the last option in my poll. My understanding is that it is intrusive and less effective.

Jon Herron says that Trinnov's approach minimizes standing waves in the room, reduces the "cacophony of reflections" that obscure bass detail, whilst also minimizing seat to seat variations in bass. Of course, he works for Trinnov and he may be biased. So I was wondering whether this was a true discussion of the pros and cons of different approaches to bass management.

I have been working on my own VBA. Although it works, it is no better than bass equalization. I have measured in multiple positions in the room, and differences are quite minor. There is no difference in the spectrogram in terms of bass decay time. Part of me wonders whether this was because my VBA was poorly designed, and whether I could get a better result by refining it. But the lazy part of me says that the result with bass equalization is already satisfactory, and I should just call it a day.

So: what approach do you use, and what are the pros and cons of each approach?

 

[ernestcarl]

Geddes mentioned the same thing where the purpose of using multiple subs is to excite as many modes in the room as possible — i.e. flooding the room with bass until it evens out. What often is left out or forgotten is the emphasis and great effort he has also put in dampening his own room so the bass does not linger. EQ is also applied so there is at least some control though…

However, Trinnov’s new method seems poised at avoiding room modes building up in the first place.

 

[dasdoing]

If I use more than one I choose "other"?

 

[ozzy9832001]

I put other.

I don't think any 1 approach will ever work all the time. A combination of different methods will give the best results. I find multiple subs to be a great and more affordable option then sticking gigantic bass trap everywhere (though cancellation/pressure management). Though, some absorption is needed across the entire spectrum, especially in a smaller room. I think after both of those are done, then adding some EQ to put the finishing touches on is a way to make good bass better.

 

[moonlight rainbow dream]

Multi-sub approach and equalization go hand-in-hand. If you do equalization alone, the bass gets even worse everywhere except your measurement position.

 

[Keith_W]

Multi-sub approach and equalization go hand-in-hand. If you do equalization alone, the bass gets even worse everywhere except your measurement position.

Yeah, I should have made the poll multi-choice. Too late to edit it now

In any case, I was hoping for more of a discussion. Nothing riles ASR members up more than to see people making controversial statements, so i'll lead off with ... "I think all of you people who don't have VBA's are dinosaurs" and "all of you who flood the room with bass are listening in echo chambers". That should do it

 

[ozzy9832001]

Geddes mentioned the same thing where the purpose of using multiple subs is to excite as many modes in the room as possible — i.e. flooding the room with bass until it evens out. What often is left out or forgotten is the emphasis and great effort he has also put in dampening his own room so the bass does not linger. EQ is also applied so there is at least some control though…

However, Trinnov’s new method seems poised at avoiding room modes building up in the first place.

See I don't get how that would work though. If the issue is standing waves, in order for them to really be problematic they need to overlap constructively, but that's not always the case. I could listen to 10 songs and only 1 of them will be enough to really excite them and it may only be 10 seconds of the song.

This is my issue with brute forcing them with EQ, for the 99% of the time they aren't problematic (or enough to really jump out at you), your just lowering the fundamental a lot for nothing. In some cases it could be enough to make it inaudible altogether.

To me, in order for these types of systems to truly work, they would need to have some sort of modal analysis configured and then have a song go through it prior to it playing.

I know Dirac was working on an active RC type thing using side/rear channels to attenuate problematic frequencies. I imagine Trinnov's would have to be something similar.

Sorry didn't mean to quote you to disagree, I'm more curious than anything else. I tried DIRAC awhile back and love the time alignment stuff it did, but hated how it handled the EQ. After the trial ended, I just couldn't justify spending the money on it.

 

[boxerfan88]

I chose "bass EQ", which is what I am using. I still think "bass EQ" is the most optimum way (for me at least)... as bass EQ reduces the signal at the room mode excitation frequencies so as to even out the bass response.


Unless the walls/ceiling/floor can move dynamically with frequency, I don't see how room modes can be "controlled". It is my opinion that any out-of-phase cancellation sound can only work for "certain spots at certain frequencies" but not everywhere at all bass frequencies. (Happy to be proven wrong)

 

[Chrispy]

Bass management and room management aren't quite the same thing.

 

[neRok]

I could listen to 10 songs and only 1 of them will be enough to really excite them and it may only be 10 seconds of the song.

You could simulate this effect by exporting your measured IR from REW, then convolving it with a problematic song in the likes of Audacity. Then bandpass the result around the frequency you are interested in seeing, and that will effectively show what you will hear in room.

This is what I've been doing in the Room equalization through inverse delayed and attenuated bass signals thread. I've showed in some posts that at various frequencies a "long tone" will increase in SPL at the listening position as the note is played longer (compared to the SPL heard from a 1 cycle tone). This is because the n'th cycle is being heard over the top of n-1 and n-2... cycle reflections that are still in the room. EQ'ing down the source will not correct this gain over time, because that is function of the decay time of the old reflections (until they lose so much energy due to moving and reflecting that they no longer have enough energy to impact the SPL at the LP). All EQ'ing these problematic frequencies does is make their 1 cycle SPL the same as other frequencies, which is an improvement, but it's not a fix.

Anyway, I'm not going to bang the same drum in this thread that I am in that one. But my latest post does show that VBA can maintain a "full power" direct wave and achieve a desired SPL equal to EQ method, but EQ method has a weaker direct wave in comparison. And whilst I didn't do the simulation in that post, based upon previous tests in the thread, VBA would have a stable SPL after 2 or 3 cycles that is roughly equal to 1 cycle SPL, whereas EQ method would gain SPL for at least 6 cycles until it settles in at the higher SPL (vs 1 cycle SPL).

"Control the zone" refers to Trinnov's new DSP

I haven't watched any videos on it, but the screenshots suggest it's just a double bass array. And maybe the "steering" is an extra level of correction on top? Say you have an array of 4 subs on the front wall, but 1 is firing in to an ottoman or something. If your system had enough channels to make adjustments to each sub independently, then that sub could have certain corrections applied to alleviate any problems caused by the ottoman.

probably also Dirac ART

Have any users started posting results yet?

 

[ernestcarl]

However, Trinnov’s new method seems poised at avoiding room modes building up in the first place.

See I don't get how that would work though.

According to @René - Acculution.com:

Many different multi-sub approaches could now be tried out but let us focus on the so-called Double Bass Array method. Here, the strategy basically is to turn the room into a tube. Tube acoustics is a little more involved than room acoustics (and a good topic if you want to really understand room acoustics better), but there is one major thing to understand: “The plane wave will always propagate”. Tube modes differ from room modes in that the former type really exist at all frequencies at once and will either propagate if excited above an associated modal frequency or die out as an evanescent wave below it. The only wave that will always propagate is the plane wave, and one way to achieve a propagating plane wave is to excite both the front wall and the rear wall in a pistonic-like fashion as shown in the animation below.

The front wall has its particular displacement, and the rear wall has a modified displacement to account for the phase shift coming from the wave travelling the room distance. You now effectively sit in an infinite tube with only a travelling wave and no reflection.

If the issue is standing waves, in order for them to really be problematic they need to overlap constructively, but that's not always the case. I could listen to 10 songs and only 1 of them will be enough to really excite them and it may only be 10 seconds of the song.

I don't really care what "problematic" means to one person. You need prior knowledge of the goals set forth for any given project/application.

"I think all of you people who don't have VBA's are dinosaurs"

So that "revolutionary" EQ approach again? People have been equalizing without "VBA" successfully for a good while now.

 

[DWPress]

Had to go with "other" - I use a combination of these techniques for my space.

 

[dasdoing]

Had to go with "other" - I use a combination of these techniques for my space.

me too. other is the only option if you combine

 

[dasdoing]

has the multi-sub aprouch actually been mathematicly proven, or is it all anecdoticly?

In a simple simulation in REW for example I fail to find benefits for 3 people on a sofa:

2 subs

1 sub

 

[ernestcarl]

has the multi-sub aprouch actually been mathematicly proven, or is it all anecdoticly?

I'm assuming Welti's modelling work on this would be sufficient? Dunno how to use Matlab, but apparently the math/physics does work:

https://www.harman.com/documents/multsubs_0.pdf

Then again, room acoustics characterization and positioning would still matter a lot here where pressure maximum very close to wall boundaries would still be a conflicting issue if also equalizing for seats that are closer to the center of the room.

 

[dasdoing]

I'm assuming Welti's modelling work on this would be sufficient? Dunno how to use Matlab, but apparently the math/physics does work:

https://www.harman.com/documents/multsubs_0.pdf

Then again, room acoustics characterization and positioning would still matter a lot here where pressure maximum very close to wall boundaries would still be a conflicting issue if also equalizing for seats that are closer to the center of the room.

ok, but this is a theatre? 4 rows x 4 people. if you have several rows you will obviously ride around the nodes of the first mode. I feel like anything that goes beyond optimizing for a single 3- or max 4- seat couch is completly diferent usecase from the general audiophile usecase

 

[NTK]

Todd Welti did provide simulation results in his paper (MSV = mean spatial variance).

https://www.semanticscholar.org/paper/Low-Frequency-Optimization-Using-Multiple-Welti-Devantier/00da51387c572cfd27c0256cb15e44e976a1a72e

 

[dasdoing]

Todd Welti did provide simulation results in his paper (MSV = mean spatial variance).

https://www.semanticscholar.org/paper/Low-Frequency-Optimization-Using-Multiple-Welti-Devantier/00da51387c572cfd27c0256cb15e44e976a1a72e

View attachment 305759

pretty similar to the other one.

 

[neRok]

Anyone got 2 normal subs and want to try something out? A few weeks ago I made a post in the thread Simulation Overview of the 'Double Bass Array' Configuration, and in my post I wondered if Inverted Stack or Cardioid arrangment would be another way to do bass arrays, albeit I wasn't sure how they would go at making the "plane wave". But I did manage to set REW Room Sim up in such a way to show an improvement at the first room length mode;

It's hard to see, but 1 sub is firing forward, the other back with a delay. There is clear improvement at 43Hz, the first room mode, but not at 86Hz, the second.

However, I have just clued on to what is actually happening in that picture. There is no "cardioid" output happening, it's just a cancellation wave. Normal DBA fires the cancellation wave when the direct wave hits the back wall, and then those 2 waves travel together summing together for 0dB, so the only thing you hear at the listening position is meant to be new direct waves. Well all that's happening in the room sim above is the 2nd sub is firing a direct wave that is summing with the backwave at the listening position. Not revolutionary at all, but apparently working. So just now I've fiddled with the orientation and delay some more and got the 86Hz mode fixed too!

Here it is in near field;


It's not the same as stacking 2 subs in phase, because those just add together;


If the listening position were further back in the room, you now start to get into a null caused by the back wall like I outline in this post (at ~60Hz in image).


When sitting close to the back wall, there is significant gain in general, but the length modes are still relatively controlled.


And to compare that with 1 sub;


Edit: In case any one asks, here's some random 2 sub arrangements. I can't see how 2 subs placed anywhere will fix room length mode issues like a cancellation wave can.

Edit2: There is some improvement in that second sim at 86Hz room mode. 343/86=4m wave length, and that sub is ~1m further forward. I'm guessing that by chance it happens to be 1/4 wave offset and is summing in a such a way to reduce amplitude. Because actually, if I reduce its volume and increase its delay on account of it being closer to the listening positions, the sim becomes worse;

 

[ozzy9832001]

You could simulate this effect by exporting your measured IR from REW, then convolving it with a problematic song in the likes of Audacity. Then bandpass the result around the frequency you are interested in seeing, and that will effectively show what you will hear in room.

This is what I've been doing in the Room equalization through inverse delayed and attenuated bass signals thread. I've showed in some posts that at various frequencies a "long tone" will increase in SPL at the listening position as the note is played longer (compared to the SPL heard from a 1 cycle tone). This is because the n'th cycle is being heard over the top of n-1 and n-2... cycle reflections that are still in the room. EQ'ing down the source will not correct this gain over time, because that is function of the decay time of the old reflections (until they lose so much energy due to moving and reflecting that they no longer have enough energy to impact the SPL at the LP). All EQ'ing these problematic frequencies does is make their 1 cycle SPL the same as other frequencies, which is an improvement, but it's not a fix.

In my case, I know the problematic frequencies, it's between 185 and 220. A lot of tangential and oblique modes in that region for me. Could be these crap speaker stands vibrating too. All I know is it's very grating and will show up on RTA analysis with pink noise, but not on a sweep because the duration is too short.