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The Absolute Sound disects SAM
#11
(05-Dec-2019, 12:46)David A Wrote: I don't think the bug you mentioned is my problem. What I'm hearing depends on the SAM % setting and occurs with Bass set to zero (I  always run with Bass and Treble set to zero). It becomes more noticeable as the SAM setting is increased.

The fact that the distortions are severe and noticeable with SAM and BASS different from 0%, makes me believe that they exist also at SAM and BASS set to 0% (but they are harder to perceive - it may even manifest differently because signal processing may be different).
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#12
(05-Dec-2019, 12:46)David A Wrote: exciting a room mode and if that is the case, reducing the setting could well reduce the noticeability of the issue

That makes sense. I measure for room correction on top of SAM (90%) and this will obviously detect any resonant behavior in speaker/room. Without rc I would have to adjust SAM % down to avoid the extra energy from room modes. In a previous speaker setup I had  a very strong peak at 47Hz (+12dB) and one at 94Hz. When I moved speakers to the long wall, much of this disappeared.
Another thing is that SAM's  phase correction in the bass may make previously 'hidden' frequencies audible.
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#13
I have measured the frequency response / SPL curves for my system with REW, and plotted the differences with various SAM % settings. In broad terms, SAM boosts the SPL's for the frequencies below the point at which the speaker's bass response would otherwise theoretically "roll off" in a neutral room or anechoic chamber. I could plot the curve using REW and see the SPL's for the bass end of the curve pick up progressively for SAM 10%, SAM 20%, SAM 30% and so on.

In my case, the room provides a degree of bass reinforcement at the lower frequencies, so SAM and the room work together to "boost" bass. Hence why reducing the SAM % can be very desirable for many. As an example, you would not really want the room naturally boosting bass by +15dB at a particular frequency and then have SAM adding another +15dB on top.

Of course, SAM will behave differently for every room / speaker combination, so it easy to imagine that things might go a little wrong in some cases, with SAM boosting frequencies that happen to coincide with room modes.
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#14
I found the article to be interesting, informative and generally well-written. However, I am uncomfortable with the almost evangelical recommendation. I have used SAM with 2 different amplifiers, 2 different speakers and in 2 different listening rooms.

In each case, I found the best result was with SAM enabled (to give phase correction) but set to 0% (so, no EQ). Otherwise, things quickly got muddy. I am sure that this is due exactly to the point that the Confused one makes in the above post regarding room interactions etc.

I can imagine people reading that article, spending money on a Devialet, and then finding that it sounds best when SAM is turned off! Maybe I just need a bigger house . . .
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#15
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.
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#16
So funny, I had to actually look this up as well...and will SAM off just bypass the entire thing I assume?

onejobaudio in Southern California /
Expert 140 Pro
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#17
A friend of mine User the 400 to Drive the Manger P2. He Said he cant hear any difference when switching Sam on and off and Mangers are Samed.
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#18
(10-Jan-2020, 07:56)Duomike Wrote: A friend of mine User the 400 to Drive the Manger P2. He Said he cant hear any difference when switching Sam on and off and Mangers are Samed.

That of course does not mean there is no difference as measured objectively. I can only suggest to do the same as "Confused": buy a microphone and use software to measure your speakers and room. Then you can also see the effect of SAM. It is not that expensive either, and you can start improving your room with some accoustics panels / diffusers knowing that they will bring value to your sound (by experimenting with the REW software). In general, people observe a bit less effect of SAM in the expert pro series (e.g., a 440 with respect to a 400) and most have favoured 'lower' settigns of SAM; say in the region of 10% - 40%.
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#19
Interestingly, on my speakers, with certain recordings, SAM gives the subjective feeling of reduced bass, because in my case that was a resonance and therefore a kind of 'overshooting' of my speakers.
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