Originally Posted by Alimentall
That sounds contradictory! So, you're saying that you should have only one subwoofer for all channels, right? (I can't agree with that), But then you don't want that sub in front of you because if the bass hits your ears at the same time, it comes across as mono?
To hear the mono bass effect best, use only one bass speaker, placed in front of you. Of course, no one sets up a system like this, but that's the best way to learn how to hear it.
Multiple mono subs (ie. multiple subs all playing back the same signal as opposed to decorrelated signals), if not placed correctly, will cause all sorts of frequency response problems due to interference.
Originally Posted by sfogg
I think Jim had mentioned the effect wasn't a fixed phase change but that it sort of varied the phase between the L/R bass.
My recollection is that the phase shift happens only when the program material needs it --- the bass enhance algorithm figures out if it's seeing mono bass, and effects the phase shift if necessary. I also wouldn't imagine the filter to be on/off --- there's probably some kind of smooth, IIR-like progression from 0 to 90 across the frequency range.
Originally Posted by Alimentall
What is the threshold audibility/perceptibility of bass directionality in an anechoic environment?
First things first: we're not talking about directionality, but envelopment and spaciousness. Second, I would guess perceptible since the headphone experiment described a few pages ago makes the source of the effect sound pretty obvious.
Because if you look at the idea that a 90Hz wave is about 12', well, that pretty much eliminates your ability to hear/fee/ an entire waveform before you are beginning to hear/feel the reflection. Doesn't bode well for being able to sense direction.
Not necessarily. We are talking about interaural time difference (ITD) cues here: the difference in arrival times of a soundwave between the ears. You don't need to hear the entire thing to hear this. Further, if you believe Griesinger's theories, it's fluctuations in the ITD that actually cause this effect, so it's really two steps removed from hearing the whole waveform.
This is why the goal of a small-room multichannel bass is not to reproduce the actual modal structure of a large venue --- that is physically impossible as has been pointed out by many people already. Instead, we are seeking to reproduce the perceptually relevant effects of those modes in the small room. JJ will cringe at this, but think of it like making an MP3 of the acoustic field: let's capture and reproduce those portions of the soundfield that are perceptually relevant.
Some people mentioned 5.1 and how that .1 channel represents mono bass, but remember that the other 5 (or all 8 in most discrete 7.1 systems) channels are full range! Therefore, we have had multichannel delivery systems that can work for multichannel, discrete bass for a long time already. The .1 channel is not a sub channel --- it is a bass headroom channel, though it's been severely abused as a sub channel for many things already.
I remember asking John Eargle (RIP) at one of the first or second Surround Pros years ago about his miking techniques, and how decorrelated his bass signals were. He didn't have a working theory of stereo bass, but he said that he always tried to make sure his channels were as decorrelated as possible (ie. capturing as much info about the venue) so that he had a good chance to do the right thing in the future should some new thing show up.