05-Dec-2019, 21:44
Getting back to Robert E. Greene's article:
On page 2 he starts a discussion of the effect of phase angle shifts in a speaker's bass response and research showing that this is audible. There is a very brief discussion of loudspeaker phase response in Floyd Toole's book "Sound Reproduction" which refers to the same research mentioned by Greene in the article. Floyd states "Phase equalization of the bass, they say, subjectively extends the effective bass response by the order of half an octave". I think that's interesting for 2 reasons, the first is his use of the word "subjectively" indicating that he's talking about a perception rather than an actual measurable extension. In other words, phase correction on its own isn't going to make the speaker's response extend lower than it does uncorrected but our perception will be that we're able to hear lower bass. I think that's because of the gain in bass clarity that both Greene and Toole report.
The second thing I find interesting in Toole's statement is that he refers to a subjective extension of half an octave but Devialet claim a gain in extension of more than an octave for some speakers. In the case of my Sopra 2s they claim an octave gain in extension from 30 Hz to 15 Hz. If Toole's half octave claim is correct, the octave gain in extension that Devialet claim for my speakers isn't all coming from phase correction and Devialet say that phase correction is independent of the SAM setting and that you get phase correction at a setting of 0%. That means the setting doesn't relate to phase so something else is being altered. What Jim Austin's review indicates is that what is happening is the addition of a variable amount of bass boost but I suspect that the boost has a "profile" individually tailored to the speaker's response just as the phase correction obviously has to have a "profile" tailored to the individual speaker's phase response at low frequencies.
The third thing that we know is happening when we use SAM is the speaker protection function which limits the driver excursion.
How the 3 functions (phase correction, bass boost, and driver protection) all work together and interact is what we don't know. If we were discussing a cake recipe I'd say we've been told what ingredients are required but not how much of each ingredient and what the preparation process is. Given that one of the "ingredients" is the speaker protection function, I think we can make one further assumption. Turning the volume up increases driver excursion which SAM limits when it applies protection, but turning the volume up also changes our perception of the loudness of the bass frequencies relative to the mid-range frequencies as shown by the Fletcher Munson curves. Years ago many amps used to have a "loudness" control, a bass boost which varied according to volume setting. I wonder whether the speaker protection function as at least partly delivered by a variation in the amount of bass boost provided depending on volume setting, taking into account the speaker's sensitivity specification, and that SAM functions to some degree in a manner similar to the loudness controls of the past and the "dynamic EQ" functions seen in some modern room correction software products.
On page 2 he starts a discussion of the effect of phase angle shifts in a speaker's bass response and research showing that this is audible. There is a very brief discussion of loudspeaker phase response in Floyd Toole's book "Sound Reproduction" which refers to the same research mentioned by Greene in the article. Floyd states "Phase equalization of the bass, they say, subjectively extends the effective bass response by the order of half an octave". I think that's interesting for 2 reasons, the first is his use of the word "subjectively" indicating that he's talking about a perception rather than an actual measurable extension. In other words, phase correction on its own isn't going to make the speaker's response extend lower than it does uncorrected but our perception will be that we're able to hear lower bass. I think that's because of the gain in bass clarity that both Greene and Toole report.
The second thing I find interesting in Toole's statement is that he refers to a subjective extension of half an octave but Devialet claim a gain in extension of more than an octave for some speakers. In the case of my Sopra 2s they claim an octave gain in extension from 30 Hz to 15 Hz. If Toole's half octave claim is correct, the octave gain in extension that Devialet claim for my speakers isn't all coming from phase correction and Devialet say that phase correction is independent of the SAM setting and that you get phase correction at a setting of 0%. That means the setting doesn't relate to phase so something else is being altered. What Jim Austin's review indicates is that what is happening is the addition of a variable amount of bass boost but I suspect that the boost has a "profile" individually tailored to the speaker's response just as the phase correction obviously has to have a "profile" tailored to the individual speaker's phase response at low frequencies.
The third thing that we know is happening when we use SAM is the speaker protection function which limits the driver excursion.
How the 3 functions (phase correction, bass boost, and driver protection) all work together and interact is what we don't know. If we were discussing a cake recipe I'd say we've been told what ingredients are required but not how much of each ingredient and what the preparation process is. Given that one of the "ingredients" is the speaker protection function, I think we can make one further assumption. Turning the volume up increases driver excursion which SAM limits when it applies protection, but turning the volume up also changes our perception of the loudness of the bass frequencies relative to the mid-range frequencies as shown by the Fletcher Munson curves. Years ago many amps used to have a "loudness" control, a bass boost which varied according to volume setting. I wonder whether the speaker protection function as at least partly delivered by a variation in the amount of bass boost provided depending on volume setting, taking into account the speaker's sensitivity specification, and that SAM functions to some degree in a manner similar to the loudness controls of the past and the "dynamic EQ" functions seen in some modern room correction software products.
Roon Nucleus+, Devilalet Expert 140 Pro CI, Focal Sopra 2, PS Audio P12, Keces P8 LPS, Uptone Audio EtherREGEN with optical fibre link to my router, Shunyata Alpha NR and Sigma NR power cables, Shunyata Sigma ethernet cables, Shunyata Alpha V2 speaker cables, Grand Prix Audio Monaco rack, RealTRAPS acoustic treatment.
Brisbane, Qld, Australia
