Adjust SAM Level?

[David A]

I just did new tests on SAM% impact, using ear perception and monitoring the membrane movement of the speakers. I used pure frequencies between 10 Hz and 300 Hz.
The results were some expected, as well as some unexpected.

The expected result: the impact of SAM% decreases with increasing frequency. I think it was expected to be so, as the value of the correction needed and introduced by SAM decreases with frequency.

Unexpected results:

• SAM% impact is major in the range 10 Hz - 30 Hz and very small outside this range (30 Hz - 300 Hz).
  
• Even if SAM% is set to "0", an audible bass boost is made. As stated by Devialet, this setting should only effect phase correction and speaker protection, and not bass boost.
  

Following this test, I decided to use SAM% set to "0". Now I will see what is the effect of this change in real life (music audition)...

There is research which suggests that simply correcting the phase at low frequencies, which is what SAM does at a setting of 0%, can extend bass response by up to half an octave. Devialet claim up to an octave or slightly more extension from SAM with some speakers and we have to assume that claim is based on what can be achieved at the maximum, 100%, setting.

It's not surprising that you're seeing the greatest effect at the lowest frequencies, in the 10-30 Hz range. Once we go beyond the extension noticed with phase correction there has to be progressively greater boost given as frequency drops in order for the bass to be audible simply because of the ear's drastically decreasing sensitivity at low frequencies. There's no point in trying to counter the driver's natural roll off unless your results are going to be audible and at the lowest frequencies it requires significant boost to produce an audible result because one has to counter both the speaker's roll off and the ear's decreasing sensitivity. For every dB of rolloff correction achieved, the audible result will be less than one dB, that's if the result is audible, so it's necessary to boost bass frequencies  by more than 1 dB in order to obtain the perception of a 1 dB increase.

What you also need to be aware of is that boosting the speaker response at those frequencies is also going to increase room problems if you have any room modes in that range and, since bass frequencies have overtones at higher frequencies which will also increase in level, you can increase the severity of modal problems at higher frequencies as well. Jim Austin of Stereophile reports experiencing what sounds like this problem in his recent review of the 140.

I use a setting of 0% with SAM. largely because I notice issues in the lower voice range once I start to increase the setting above 5-10%.

So some of the clicks or noises you're reporting may not be the result of a problem in SAM. They could be sounds from the room or objects in it as a result of increased room modal behaviour.

In my view Devialet have definitely made one mistake with SAM, that is making the default level setting 100%. In my view the default should actually be 0% and the basic advice should be to increase the level slowly and carefully until you start to notice problems and then to back off slightly to a lower level. The fact that most people seem to use it at a much lower level than 100% indicates that 100% is most definitely not a good default setting.