Is One Subwoofer Really Not Appropriate For 2-Chnl

Bifwynne - Glad my post was helpful to you. If you can manage it, it would be worth the experiment to move the sub roughly coplanar with the mains and see if it improves the system's transient response. It will be audible as better coherence and PRaT.

The fact that you sum the channels into a mono signal for the sub doesn't affect anything in the procedure I described in my last post. If your sub has a polarity switch, use it. If it doesn't, just reverse the positive and negative leads on your speaker wire for *both* of the mains. Then the mains and the sub will have opposite polarity, assuming that your sub doesn't invert polarity.

Adjusting the sub's phase can be helpful, but not nearly as helpful, IME, as time aligning the sub. As I mentioned in my last post, if the sub is behind the mains, the signal that needs to be delayed is *the mains*. Adjusting the sub's phase will do nothing for that. If you cannot digitally delay the mains, you can time align the system by placing the sub coplanar with the mains, or possibly a little in front of them (to compensate for the potential latency - i.e. delay - introduced by the sub itself).

To sum up, if you can do it, move the sub so that it's roughly coplanar with one of the mains, then follow the procedure in my last post. That should get you pretty close to time aligned. IME, the results of sub time alignment are dramatic, especially when the sub is "fast" enough to keep up with the mains.

Bryon

One can work fine. I use a 10" NHT sub with my NHT Classic 3 speakers and the sound is very detailed and smooth.

Bryon,

It's been decades since I did research in binaural processing, but I wondered why someone from a university in South Carolina would publish such an article in other than JASA. Some of the contentions about levels of neural processing of temporal information seem astonishing, so I wonder if peer review may have been a problem. I'm also skeptical about the use of non-standard equipment; it makes replication of results difficult. I'm skeptical about your arguments and your source of "scientific' support. As I said, though, I haven't followed psychoacoustic literature for decades.

04-20-11: Dbphd
I wondered why someone from a university in South Carolina would publish such an article in other than JASA. Some of the contentions about levels of neural processing of temporal information seem astonishing, so I wonder if peer review may have been a problem.

The link I provided to the paper by Milind Kunchur was published in the Journal of the European Acoustics Association, which is a peer-reviewed journal, according to this page on their website.

I'm skeptical about your arguments and your source of "scientific' support.

Whether Kunchur's science is valid, I cannot say. I am no expert on auditory perception, but even if the limit of human temporal resolution is twenty 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.

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 25µs.

Regarding the science, you are certainly entitled to your skepticism. Regarding my statements about subwoofer time alignment, I would humbly suggest that you experiment with it before concluding that they are incorrect.

Bryon

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