Is One Subwoofer Really Not Appropriate For 2-Chnl

Correction to my last post. It should have read...

...even if the limit of human temporal resolution is *two hundred* times higher than Kunchur claims, that would still place it at only 1ms, in which case placement differences of approximately a foot or more would result in potentially audible time misalignment.

AND...

What I can say is that, IME, differences in z-axis sub placement are audible down to about 4 inches. That would correspond to about *300µs*.

I was off by an order of magnitude. D'oh! I should not do math in my head at midnight.

In any case, my error actually *underestimated* the degree to which Kunchur's estimate could be off while still making time misalignments of about a foot potentially audible, leaving my argument for the importance of subwoofer time alignment unaffected.

04-20-11: Dbphd
I wondered why someone from a university in South Carolina would publish such an article in other than JASA.

It's true that Kunchur's article wasn't published in JASA, but here is a list of articles that WERE, all on the subject of human temporal resolution:

--B. Leshowitz, “Measurement of the two-click threshold”, J. Acoust. Soc. Am. 49, 462–466 (1971).

---Ronken, D. (1970). “Monaural detection of a phase difference between clicks”, J. Acoust. Soc. Am. 70, 1091–1099.

--Henning, G. B., and Gaskell, H. (1981). “Monaural phase
sensitivity with Ronken’s paradigm”, J. Acoust. Soc. Am.
70, 1669–1673.

--Plomp, R. (1964). “Rate of decay of auditory sensation”, J. Acoust. Soc. Am. 36, 277–282.

--Penner, M. J. (1977). “Detection of temporal gaps in noise as a measure of the decay of auditory sensation”, J. Acoust. Soc. Am. 61, 552–557.

--Eddins, D. A., Hall, J. W., and Grose, J. H. (1992). “Detec- tion of temporal gaps as a function of frequency region and absolute bandwidth”, J. Acoust. Soc. Am. 91, 1069–1077.

And here is Kunchur's synopsis of the conclusions of those JASA articles...

In one experiment by Leshowitz (1971), listeners were presented with a single pulse or two narrower pulses (with the same total energy) separated by an interval Δt. The click and click-pair could be distinguished down to Δt ≈ 10 μs. In this case, the two stimuli have differences in their amplitude spectra and their discernment was explained on this basis. Isospectral variants of this experiment were carried out by Ronken (1970) and later by Henning and Gaskell (1981) where one stimulus consisted of a short pulse followed by a taller one separated by an interval Δt. The second stimulus was a similar pair with the time order reversed and hence had the same amplitude spectrum. The shortest Δt for which these stimuli could be distinguished was about 200 μs. Another type of constant-amplitude-spectrum experiment involves the detection of gaps in noise (Plomp, 1964; Penner, 1977; Eddins et al., 1992). In these the threshold for gap detection was of the order of 2 ms.

As you can see, those estimates of the limits of human temporal resolution range from 2ms to 200μs all the way down to 10 μs. If we average those estimates, we get 736μs, which corresponds to differences of less than a foot.

Hence there is reason to believe that the human limits of temporal resolution may be sensitive enough to make time misalignments of a foot or less potentially audible.

Bryon



Bryon

Bryon,

I quit following the literature around 1970. I was an admirer of the Jeffries model of binaural processing, but a study I did using computer generated signals and narrow bands of noise was inconclusive about the phase relationships of the signal and noise even though the detectability of the samples differed markedly, and the models did not explain the results. I reported the results at a special JASA session devoted to Lloyd Jeffries, but never published them. After that, I lost interest in psychoacoustics.

I can believe moving a sub a foot or so can make a detectable difference, but I'm not sure I'd attribute it just to time alignment, given the potential interaction with room boundaries.

db

I make it a point not to hijack threads. But that is exactly what I've done to this one. My apologies to Ryder (the OP) and to everyone else following along.

Dbphd - Your last observation is a valid one, but I have experiences that are inconsistent with attributing the audible variations resulting from small differences in sub room placement to frequency response. You can read about my experiences on a recent thread I initiated.

I'd be happy to discuss this further, as it is a topic that interests me a lot. But, in the interest of courtesy to other folks, we should move our conversation to the thread I linked above.

Bryon

Bryon.

One of the most reliable phenomena in psychoacoustics is what Is know as the masking level difference (MLD). Present a mid-freuquncy sinusoid in correlated noise to both ears and adjust the level until it becomes inaudible; flip the phase of the sinusoid in one ear, and the signal pops up as much as 15 dB, depending on frequency. At the time, the data suggested the auditory system doesn't preserve timing as such up the neural chain, but may convey such information by the more central areas excited. Thus, the vector model of Lloyd Jeffries.

db

I couldn't afford a pair of the subs I wanted...so I went a little upline and bought a single sub.
That's OK, though. My room has enough walls to bounce the sound around and leave no 'hot spots' for bass. That would be 9 walls and a vaulted ceiling. Very asymmetric.
That nasty room and a very low crossover ensures the sub is both invisible and seamless.
Depending on how messed up your room is, that may also work for you.

The manufacturer of my sub recommends a near-field approach to sub use.