This is purely a subjective opinion.
We have a couple of products in which if you flip the polarity of the HF driver, the response does not change much (just the "wiggles" are a little different) but the phase goes through a 180° shift. The response is a "little" bit flatter with the phase shift-but not much.
I have set up tests on this in which I simply hook up a DPDT switch so that the polarity can easily/quickly be changed.
I got a group of "ears" together and would play a number of different tracks, and all they knew was that one "sound" was A and the other was B.
They had no idea what I was doing by flipping the switch.
They all picked the position in which the phase as flat through crossover.
I know it was not real "scientific", but when given the choice-the "picky guys" chose the flatter phase response vs amplitude.
Hi Ivan, all
The thing is, listening with headphones to an all pass filter or addition of a simple high pass and low pass filter electronically which acts like an all pass filter, these produce a change in the time or Z domain and nothing else. In the hifi world, this test was used to argue you can’t really hear crossover phase shift or more correctly, it is only detectable / audible under some conditions, with some kinds of music.
Loudspeaker drivers on the other hand radiate in 3 dimensions X, Y and Z and so most often two drivers rarely add coherently like two electrical signals do when added through resistors etc. More often two drivers radiate (if more than about ¼ to 1/3 wavelength apart) as two independent sources. This can be seen if one does a polar plot of the two, where they interact, they usually produce an interference pattern recognized by a series of lobes and nulls (one might think of this as comb filtering in 3d).
In that case, what you measure so far as phase depends on the filters but also the individual path lengths to each source and the latter part makes what you get depend on location. As a result of radiating in 3 dimensions. The phase response may or may not be a good predictor of what you hear, two system which measure identically may sound quite different if they spatial radiation is different for each.
On the other hand, with Ivan's switch test, you ARE dealing with the relationship between individual sources and so it is more complicated than the coherent addition case using headphones and now how these sources also radiate as a sum in X and Y can be altered by that switch change or not altered if they add coherently (less than ¼ wl apart).
Also, one can use FIR filters to electronically alter the Z relationship however the sources still interact in the X and Y domains as well so when there are problems (incoherent addition) in X and Y, the DSP correction only works for the range on axis or where the data was taken to derive the correction and not globally.
The loudspeaker generation loss testing we did starting 11 years or so ago was a good reality check and did several things.
First, it separates you from your automatic hearing process which seeks information and discards problems without your awareness. It more easily lets you hear a loudspeakers warts, even just listening to a loudspeaker with a good measurement mic and headphones will usually let you hear flaws which you would have a harder time hearing straight up. Second, it’s a good indicator of how faithful the speaker is in reproducing the music your using, obviously the more generations you can go, the more faithful it is. Third it is humbling reality check so far as showing how bad loudspeakers are compared to every other part of the signal chain. Make a speaker that sounds good on the third pass and it will sound unusually good listening directly. Also, often when you hear a speaker that sounds bad through a measurement mic, once you become attune to the flaws, you will also be able to hear them much more clearly without the headphones.
Intelligibility; There is an article on the fort page at PSW written by Pat Brown. It mentioned a seminar he conducted which was an eye opener and like every Synaudcon seminar I have attended, I learned something(s)..
Inteligibility unlike musical quality is measureable and thanks to the STIpa measurement, there is a window to what hurts intelligibility. STIpa is measured using a speech bandwidth version of the optical MTF or modulation transfer function where the signal is rapidly gated on and off and the corruption of the off periods is what reduces intelligibility.
The optical version is here;
http://www.edmundoptics.com/technical-resources-center/optics/modulation-transfer-function/https://en.wikipedia.org/wiki/Optical_transfer_functionOne can picture that preservation of time (related to phase) is key to this but also in a room, the directivity is equally important as reflected sound also corrupts the “off” periods. This is partly set by how the multiple sources interact, where the lobes and nulls go and go on to produce delayed arrivals. Interestingly, intelligibility is not always important for music reproduction, for example a choir in a large church there is hardly any information which is time sensitive and a large reverberant room sounds good.
On the other hand, if the music has transient information or a lot of detail, then it matters a lot as that stuff can be lost and is usually lost in large array based sound systems due to the scattering of time information and reflected sound.
Ivan gets to go to large stadium installations pretty often (we have speakers in about half of the 100,000+ stadiums so far) but I don’t get to go that much so for me, it has been a lot of fun hearing the difference preserving time / phase can make vs the live sound style array systems they replaced.
I have made a few recordings with a cheapo canon vixia camcorder which might be fun if you have headphones on your computer. These demonstrate both effect of the coherent driver addition, phase and directivity so far as its impact on intelligibility and musical articulation.
Like any system though, especially one that is signal faithful, stinky sonic garbage in equals stinky sonic garbage out.
Try these with headphones, the loudspeaker are all in the scoreboards
https://www.dropbox.com/s/0u58zsinsz1gd4j/20140805114837.mts?dl=0https://www.dropbox.com/s/gwlxss1uxioi4mq/20140805115158.mts?dl=0https://www.dropbox.com/s/tnsw5mb4v5vdlwq/20120726122124.mts?dl=0https://www.dropbox.com/s/2cl3l4blx6r9r11/20120726114539.mts?dl=0https://www.dropbox.com/s/va4mihvefqyxk24/20130723140018.mts?dl=0https://www.dropbox.com/s/oyosfc3adc6j1du/20130723135350.mts?dl=0Best Regards
Tom
