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Odd bass localization in room.

Daverz

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I'm testing bass localization in my room with these test files from Audiocheck:


A bass sweep from 200 Hz down to 30 Hz is played in each speaker alone while a voice reads off the frequency in both channels (i.e. voice is centered). The behavior in my room is odd: perceptually, the right sweep starts out on the right, is centered by about 150 Hz or so, but then continues to migrate to the left by about 40 Hz. On the other hand, while the tone on the left spreads out, it always seems to be on the left.

The question is what this will do to the soundstage, and what can I do about it?

Speakers are Buchardt S400s, which easily get down to 40 Hz in my room. The room is very asymmetric.

room_layout.jpg


The front wall behind the left speaker is an external wall, while the right speaker is in front of a fireplace. Squares are the speakers. Oval is my listening position.

If I had to guess at the physics, there's probably a strong mode perpendicular to the left front wall that kicks up some higher localizable harmonics, even from the right speaker.

I do have a subwoofer, an SVS SB-1000 Pro, placed along the wall in front of the left speaker (where the smoothest bass is) and crossed over at 80 Hz. The tests are run with the mains run full-range and the subwoofer off.
 

ebslo

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I played with those test tones too, with a similar result. Regardless of which channel the sweep plays from, L only, R only, or sub only, anything below 40Hz sounds like it comes from the front left corner. It's just the room asymmetry and I don't think there's anything that can be done about it. With actual music that has tones <40Hz, it doesn't seem to come from anywhere in particular and all the "soundstage" and "imgaging" stuff happens at higher frequencies and is unaffected.
 
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Daverz

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I guess what throws me off is that I always thought of "non-localizable" as meaning not localizable to a single place, when what it seems to mean is not localizable to the location of the source. The low bass in my room at my listening position always seems to come from that left wall.
 

alex-z

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The problems with your full-range sweep are caused by room modes, but you have a subwoofer so use it to help mitigate them.

For such a large and oddly shaped space you are going to want a second subwoofer, for further improving the bass, and gaining headroom for EQ.
 

dasdoing

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even in my much more simatrical room I can localize the modes. that's actualy the only reason I bought a subwoofer. I placed it where the bass is suposed to emerge. right in the middle of the mains. that way the corners are not acting as direct source
I think the soundwave theory is only valid in the free field
 

Kal Rubinson

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I placed it where the bass is suposed to emerge. right in the middle of the mains.
Isn't the bass supposed to emerge where its musical source is located?
 

kyle_neuron

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As weird as it might seem, the principles of superposition should mean that you can find the ‘best’ place for your subwoofer by placing the subwoofer itself at your listening position (including height!) and placing a microphone at the places you would consider installing the subwoofer cabinet.

You could also use your ears, but it might be harder to compare things when you're crawling around the floor :)
 

Destination: Moon

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I would try flanking your speakers on each side of the door. And maybe try them along the railing adjacent to the stairs. I had a similar setup trying to keep our fireplace the focal point of the room and the speakers on each side. This put the speakers firing parallel to a big wall of glass. After reading on ASR for a while I realized the entire audio image was perceived as coming far to the right of the right side speaker. I never noticed before. I'm embarrassed to say how long we lived with it like that without realizing. I moved everything so it fires into the room from the wall of glass. The difference was nothing short of amazing!
 

Kal Rubinson

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sure, but unless we are talking about classical music recordings or other special cases, the bass is allways centered in mixing
Yeah, I mean wherever the source is located. There are many non-classical recordings with the bass not in the center. Why would you bias your system based on an expectation?
 

dasdoing

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Yeah, I mean wherever the source is located. There are many non-classical recordings with the bass not in the center. Why would you bias your system based on an expectation?

are you saying anybody with a single sub is doing it wrong?
let's just say, if there is stereo below 80Hz I prefer to "remix" than hearing my bass build up in the corners and flying from left to right. it was bugging me for years, and never has again ever since. that is what is important to me.
as with anything in audio: compromises and choices.

EDIT: forgot to point something out about the psychoacustic effect of this. if there is a dubble bass panned to the right, it still will sound form there. there is much more energy above the crossover and that will dictate where we hear it.
the only thing that wont sound panned is a synth bass. and I doubt there are mixes with panned synth bass
 
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Sancus

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Just my opinion, but get two subs and EQ them right and then stop worrying about localization IMO. With un-equalized subs playing individually, I can localize which one is playing pretty easily, because they sound different due to modes. With both playing after equalization I can't localize anything.

One sub is always going to have a tough time unless you're pretty lucky with room modes and the room is very well-treated. For us poor bastards with untreated, asymmetrical disasters, multiple subs are great.
 

kyle_neuron

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Two subs collocated with the mains is usually a recipe for a big ol’ power alley, with lots of ‘fingering’ lobes off to the sides. It’s a setup we try to avoid wherever possible in sound reproduction.

Two subs is great for a home installation, but their best placement is unlikely to be where the main speakers are if you’re interested in a low spatial or tonal variance across a listening area.
 

Kal Rubinson

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are you saying anybody with a single sub is doing it wrong?
No. You were talking about "bass" and not subwoofers, per se. Bass should be localizable based on the harmonics and transients associated with it and not constrained by the position of the sub.
EDIT: forgot to point something out about the psychoacustic effect of this. if there is a dubble bass panned to the right, it still will sound form there. there is much more energy above the crossover and that will dictate where we hear it.
Yup.
 

puppet

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The railing side might work out pretty good. I see the door flanking as a no go seeing a stair case to the left.
 
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Daverz

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The railing side might work out pretty good. I see the door flanking as a no go seeing a stair case to the left.

You can't see it in the pic, but unfortunately, that's the "dining room" part of this "great room", where the room narrows to accommodate the kitchen. So there's no reasonable arrangement of speakers and listening chair there.

I've tried all the other logical placement options in this room over the years. I like the current position because the speakers are well away from any side walls. I get great inter-channel cross-correlation (ICCC) numbers there (as measured in Acourate), and the most even soundstage and best imaging. I could try moving the speakers a foot or so further away from the front walls.

I experimented with my full 2.1 time-aligned and room-corrected setup crossed over at 80 Hz. The 40 Hz part of the sweep is clearly localizable to the subwoofer. I'll experiment more with sub placement, but I'm starting to think everything I've read about subwoofers is bullshit, so I'm not inclined to spend money on another one ($700 now for the same sub in gloss white).

I'm not a home theater guy, so I'm only interested in what this might add to the experience of listening to music. There doesn't seem to be much more than ambiance below 40 Hz or so in the music I listen to anyway.
 

ernestcarl

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I've tried the test and the point where the bass becomes localized as centered in the middle differs: left channel begins right under 120Hz and the right channel under 70Hz or so. With me at the center MLP -- I do not have an issue of the bass drifting to the opposite side. Sitting in the far corners of the couch, either way, with actual music the bass mostly sounds like it's coming from the closest main monitor.
 
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