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Never Put Subwoofers In Corners... Even with DSP and Multi-Sub Setups?

Hipper

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I'm seeing a little bit of evidence below 80 Hz in your first measurement, but nothing that's outside of what I see from measurement variation. Your second measurement though shows a big difference. You definitely tapped into some issues with the additional corners.

Do you have a post-EQ graph?

RE: decay times, those are mostly down due to the reduction in amplitude, and will see a similar result from multi-sub + EQ. Do bass traps reduce decay even if amplitude isn't affected? That I don't know. Bass traps work to make the room appear larger, like adding stuffing inside a speaker. A room acoustician would have to answer that.

I have (currently) four GIK Tri-traps, and went with them because after measuring my space, I couldn't fit the soffit traps. I didn't see any changes below 80 Hz with those.

Post EQ:

No EQ-EQ 9.18.jpg

This was done by applying filters created by REW to the ten Parametric EQ of a Behringer DEQ2496.

And the spectogram of the EQ'd signal (again, 40Hz is mostly traffic noise):

EQ Spectogram 9.18.jpg


This is the various stages of adding bass traps:

F Adding Bass Traps.jpg
 

Hipper

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Multiple subs (plus a bit of EQ) is the only practical way to get smooth (and even in different positions around the room) low frequency response in domestic sized rooms.

See here for 1 to 4 subs and 4 subs plus EQ

https://www.audiosciencereview.com/...subwoofer-selection-criteria.7080/post-163945

https://www.audiosciencereview.com/...subwoofer-selection-criteria.7080/post-163949

Single subs will never work well even with EQ. Corner placement with multiple subs works fine, as you can see in the example above. You benefit from room boundary gain, however mid wall may be a bit smoother.

I'm impressed with the measurements in your links, particularly the waterfall plots.

Assuming using four subs plus DSP with standard three way box speakers as mains:

1. What is the ideal crossover point for subs to mains in these circumstances? Is it room dependent? Or main speaker dependent (say electrostats)?

2. Is the use of bass traps still required or useful, both below and above the crossover?
 

March Audio

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I'm impressed with the measurements in your links, particularly the waterfall plots.

Assuming using four subs plus DSP with standard three way box speakers as mains:

1. What is the ideal crossover point for subs to mains in these circumstances? Is it room dependent? Or main speaker dependent (say electrostats)?

2. Is the use of bass traps still required or useful, both below and above the crossover?
This is all circumstance dependant, you can't really give specifics. However I would generally crossover between 60 to 80Hz.

The room those plots were taken in did have Vicoustic traps, absorption and diffusion. I don't like overly live rooms and this, was needed to bring the RT(x) time down.
 

Chromatischism

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I agree that it's system and room dependent. Between 60-80 Hz for me as well. Higher and vocals start coming from the subs, lower and you don't get enough benefit from the subs.
 

ernestcarl

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If you're talking about arrival time differences, 20 milliseconds of relative delay corresponds to a path length difference of about 22 feet, which is imo a much greater path length difference than we're likely to have in a home audio listening room.

You're right, in a small room one really should not have such big differences in arrival time between multiple subs. I was imagining multiple subs being placed so, so far apart from each other that the closest sub's peak is arriving many ms earlier than the one at the complete opposite end. Of course, in small rooms this should not be an issue...
 

ernestcarl

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I don't remember. I looked into group delays of vented box systems years ago and concluded that the calculated group delay of my system was perceptually benign, but don't remember the specifics of where the perceptual thresholds are. And I'm not aware of how that would be any different for multiple subs versus a single sub.

Some years ago in a different house, I had my sub about 80 ms late behind my mains (xo probably at 80Hz* -- actually that probably was lower at 50 or 60Hz as I was using the speaker's natural roll-off then). I really did not notice this causing gross audible issues in sound quality until I discovered it months later after re-measuring. Maybe if I were more of a critical listener, I may have noticed it earlier -- but I don't think I am. Over 100ms around the xo point, though, that is something that I can definitely immediately tell even without measuring. I was somewhat a little baffled how awful my perception of time delay was in the lower bass, while some 'audio-zines' proclaim that the total delay should never be allowed to exceed 20ms max for all sub bass frequencies. Probably these strict guidlines makes total sense in recording /mastering rooms and reference systems. I still suspect, many people aren't nearly as sensitive to this delay in the sense of it causing music to sound "bad" automatically, perceptually.
 
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patate91

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A little bit out of subject but how do you guys manage cables (typical room dimension, how long is the longest cable), electrical outlet for multisubs optimal placement? I fiddle a little bit with REW's simulation and optimal placement is not always ideal for every day use.
 

Duke

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A little bit out of subject but how do you guys manage cables (typical room dimension, how long is the longest cable), electrical outlet for multisubs optimal placement?

The system I peddle consists of four passive subwoofers which normally are connected in series-parallel and driven by an amp which goes on the shelf or equipment rack. So the only wires which wrap partway around the room are speaker wires. There is one set of speaker wires running from the amp to the first sub on each side of the room, and a second set of speaker wires running from that first sub to the second one. The "first" subs each have two sets of terminals because they will be connected to two sets of speaker wires, while the "second" subs only have one set of speaker terminals.

In case anybody wants to DIY something like this, the amp I use is available from Parts Express.
 

Willem

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And with active subs you can explore the wireless option. For many potential locations in the room that is what I would have to do if I get round to buying a second sub.
 

FeddyLost

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This is very interesting topic: passive bass traps vs. multisub.
I have very dry room from around 100 Hz up, but below is a mess, of course. Now i try to use it as some kind of Harman curve and have no problems with excessive pressure and RT because i'm not a mastering engineer, but often i return to question "how to tame bass below 100" and there's no easy and straight solution.
Passive bass traps require more power lost useless and a lot of more or less heavy tuned tools (and expensive with almost no resale value contrary to subs), but
active multisub intuitively (for me) looks nice only for seismic effects when you have earthquake "everywhere", i.e. low frequency noises decorrelated with higher frequencies, like 40 Hz and less (below any instrument's main tone), because in perfect setup and record we have to simulate "source" and "coming wave". Like, maybe, big bass kick drum in front of listener. It can be tuned very low, maybe at 50-60 Hz, and what will experience listener if "kick simulation" virtually located few meters in front, but multisub setup is pumping pressure of main tone in synchrony from all sides? I don't even ask about voice freqs, delays and all that stuff that will arise when we'll try to tune system further or cross it higher. All this is not very simple, when I think about "correct stereo".
Also, it's very interesting situation with dual kick drum, when they "fire to different sides", L-R-L-R very fast, so listener must somehow feel ..er.. "dynamic asymmetry". All this duty will consequentially be done by higher frequencies, am I correct?
And this might be applied not only to heavy genres, if I remember correctly, double basses in orchestra also not evenly distributed, so they could produce same "pressure zone" with expanding front.
Sincerely, I don't know how often these effects was considered serious in mix/production, but anyway we may "alter the planned illusion" or all these frequencies are too low and we are choosing "much lesser evil"?
 

Duke

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active multisub intuitively (for me) looks nice only for seismic effects when you have earthquake "everywhere"

Done right, there is no sense of the location of the individual subwoofers. And in this context, ime "done right" includes running any subs located away from the mains no higher than 80 Hz, and rolling off their top end rapidly (4th order lowpass is what I use). This prevents subs placed to the sides or rear from passing upper bass/lower midrange energy loud enough to betray their locations.

If you are not averse to reading a review of a distributed multisub system, and not offended by the maker of that system being the one who posts the link, click here.
 
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Chromatischism

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Like, maybe, big bass kick drum in front of listener. It can be tuned very low, maybe at 50-60 Hz, and what will experience listener if "kick simulation" virtually located few meters in front, but multisub setup is pumping pressure of main tone in synchrony from all sides?
This is not a problem because the kick drum fundamental is below the point of localization. You can't pinpoint a bass frequency played in a room under about 100 Hz. And, depending on the mix, that drum is usually accompanied by other tones coming from your main speakers, which provides the directional cue. The end result should be the same either way, except the subs will provide more power and a smoother response.
 

FeddyLost

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And subs must have distortions low enough, but we suppose "ideal subwoofer entities" for simplicity.
Done right, this must work right in case of X.1 record. By X.1 I mean not exact standard with separate LFE channel, but any record with bass decorrelated spatially with all other frequencies. Like kick centered, bass panned between left and right and no special effects.
But let's assume that someone want to capture "shootout" of two drummers in free field (or two bassists with huge stacks and basses tuned low enough to have lot of information below 80 Hz) . One is 45 degrees to left from recording point, another is 45 degrees to right. Both are more or less far away and we capture one kick in L channel and another in R channel. Both kicks are low, tuned to 60 Hz main tone, and our drummers work together like jazz jam, fast but intermittent.
In such case we have real stereo below 80 Hz with "decorrelated events" in channels and in case of correct stereo reproduction we'll be able to feel pressure waves according to their original location and understand musical idea (if present).
But in case of our "pressure downmix" we'll have wrong impression and maybe some of composer's intent will be lost.
It's rare and very "synthetic" example, but I'm not sure that dual-mic recordings of big orchestra in open-air (where bass-rich wavelets don't reverb in closed volume, but just fly away) will be correctly reproduced with "uniform pressure LFE channel" system. Listener might be "inside of pulsating chamber", even with flat resulting FR in LP.
So, I mean that uniform pressure field is not always good substitute for "free field" or its impression/simulation and multisub solution is not equal to insane bass trapping and resulting low RT/decay time even if achieved FR will look alike...
Of course, in real life anyone will prefer compromise better suited to his needs/tastes/abilities, but i'd like to say that these methods are not the same while possibly having equal measured results.
But maybe our perception will find no difference, i don't know.

PS If i remember right, Yello uses stereobass, and it's kind of .. impressive with closed eyes. Like bending/waving room around.
 
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Chromatischism

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In such case we have real stereo below 80 Hz with "decorrelated events" in channels and in case of correct stereo reproduction we'll be able to feel pressure waves according to their original location and understand musical idea (if present).
Is this true, though? The bass pressure sensation comes from SPL, which is, in a room, equally all around you (more or less).
 

Duke

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In such case we have real stereo below 80 Hz with "decorrelated events" in channels and in case of correct stereo reproduction we'll be able to feel pressure waves according to their original location and understand musical idea (if present)...

It's rare and very "synthetic" example...

Given how long it takes for the ear to begin to detect the presence of bass energy (at least one wavelength), and how long it takes for the ear to detect the pitch of a pure bass tone (multiple wavelengths), I suspect that for all practical purposes the localization cues will come from the mains anyway.

As far as feeling pressure waves goes, I looked into that once and didn't find any directly applicable information. What I did find was studies about synchronizing tactile sensors with sound delivered through headphones, like for a high-end gaming system where you have shakers in the chair. What I remember is that for optimum synchronization the shakers had to be activated slightly before the sound occurred to allow for the time it takes for physical sensation to travel to the brain, versus the time for the auditory signal to travel the (much shorter distance) to the brain.

If someone believes the low bass energy should originate only from the direction of the sound images and wants to optimize a distributed multi-sub system for recordings like you describe, it's easy to do: Use stereo, and limit the distribution of the subs to the angles you want.

Imo there is an argument for having two channels (presumably but not necessarily stereo) in the subwoofer region, but it has to do with a sense of envelopment rather than image localization.
 
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Chromatischism

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But then we get into the topic of "stereo bass", which runs into big problems with SBIR and phase cancellations because the locations aren't optimized for bass.
 

Duke

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But then we get into the topic of "stereo bass", which runs into big problems with SBIR and phase cancellations because the locations aren't optimized for bass.

I'm must be missing something obvious. How does "stereo bass" change the speaker boundary interference situation? (Imo "stereo" is of limited utility in the subwoofer region at best, but I'm still interested in understanding what you're referring to.)
 

FeddyLost

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The bass pressure sensation comes from SPL, which is, in a room, equally all around you (more or less).
If so, it must be something else.
But if we pan LF generators fully left and right and will turn them on and off one by one with rhythm, shouldn't we notice "moving of pressure source"?

Use stereo, and limit the distribution of the subs to the angles you want.
Like sub array L and sub array R?


stereo bass", which runs into big problems with SBIR and phase cancellations because the locations aren't optimized for bass.
Unless it's soffit mounted which is also impossible for home users.
Will these problems persist even if we separate LFL and LFR from mains?
Like mains 80 and up, optimized for scene and localization and LFL, LFR symmetrical arrays optimized for perfect FR below 80.
But it will be kind of overkill and not cheap at all.
And anyway will require significant bass trapping because even 80 is very low and powerful.
 

Duke

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If we pan LF generators fully left and right and will turn them on and off one by one with rhythm, shouldn't we notice "moving of pressure source"?

My guess is that in the absence of any signal north of the subwoofer region, yes we'd hear the source moving. But with normal low-frequency music notes which include harmonics at frequencies where our directional hearing is much more acute, I believe we'll localize the sound source by those harmonics.

Like sub array L and sub array R?

Yes, something like that.

... LFL, LFR symmetrical arrays optimized for perfect FR below 80.

True acoustic symmetry at low frequencies may be a lot more rare than physical symmetry. "Soft" spots in the room boundaries, like doors and windows, change the modal behavior and hence the effective room dimensions at low frequencies. In other words, what looks like symmetry may actually not be, at least with subwoofers. Personally I prefer to embrace and even exploit asymmetry.

"Perfect frequency response below 80 Hz" is pretty rare, and is certainly not a claim my underpaid marketing department would make.

But it will be kind of overkill and not cheap at all.

More expensive for a given SPL or in-room bass extension, yes. But as the number of subs goes up, the size of each individual sub can go down, for a given SPL/extension target.

And anyway will require significant bass trapping because even 80 is very low and powerful.

Imo bass trapping is less likely to be "required" with a distributed multisub system.
 

Chromatischism

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I'm must be missing something obvious. How does "stereo bass" change the speaker boundary interference situation? (Imo "stereo" is of limited utility in the subwoofer region at best, but I'm still interested in understanding what you're referring to.)
Because most people don't put their speakers against the walls, and to do "stereo bass" they put their subs right next to their speakers. The distance to the walls causes SBIR which is normally avoided with proper sub placement.

In addition, the subs are generally not aligned as a mono source, which causes them to work against each other and potentially the main speakers, too. That is what mono subs and bass management solves.
 
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