SAM Measurements

[daniel.avasilichioaei]

For a long time, I have had the intention of making measurements that would show me more exactly what SAM does and what influence it has on the audio signal. I wanted to do this for these reasons:

• I really like the idea and concept behind SAM.
  
• In theory, SAM 100% should produce the perfect bass for the respective speaker. However, I heard SAM in several combinations of speakers and Expert PRO amplifiers and it seemed to me that SAM 100% boosts the bass much more than a simple necessary correction.
  
• I noticed that SAM behaves very chaotically and abnormally, at least for pure sine curves in the low bass area (lower than ~35Hz, probably the value depends on the speaker model).
  
• Although SAM is not supposed to impact high frequencies, I have seen user reports claiming the opposite. Some claim that they hear changes in the high frequencies. There were a few cases (very few) that claim that SAM burned their speaker tweeters (information from the speaker service, not just their personal opinion).
  
• I watched the video posted on the internet by Devialet, which shows the process used to generate the SAM profile. I detected several areas in the process that can generate unwanted results and that got me thinking.
  

Finally, today I managed to make measurements for the SAM analysis and I share them with you in this post.


Information about the measurements made and how I made them

• I measured and compared the following SAM settings: OFF, ON 0%, ON 50% and ON 100%.
  
• I used 2 Expert Pro 220 amplifiers and 2 Expert Pro 140 amplifiers, all in mono mode and connected in a Devialet chain.
  
• Each amplifier has one speaker connected, but there are 2 different models of speakers (2 pieces of each model). Obviously, for each speaker I used its SAM profile. Note: For one of the speakers I did not use the profile from the Devialet configurator: this profile is much too "aggressive", so Devialet provided me with a "softer" profile. This is an important note for some of the conclusions of the measurements.
  
• All 4 speakers are located frontally, one next to the other (two by two).
  
• I used REW software for measurements and generating test audio file (48kHz, 2M sweep, 0-24,000 Hz, -12 dBFS, 32 bit-float WAV). Note: I intentionally used a measurement band wider than 20-20,000 Hz. This is an important note for some of the conclusions of the measurements.
  
• I used Roon software for playback the test audio file (bit-perfect mode).
  
• I used the miniDSP UMIK-1 microphone for the measurements.
  
• All measurements were made in absolutely identical conditions, the only variable being the SAM setting.
  

General notes
These measurements reflect the SAM effect in my audio system and in my room. I think it is not correct for someone to consider that SAM effects are the same in other audio systems or in other rooms.
However, I believe that some of the SAM behavioral patterns resulting from these measurements are universally valid (but I'm not sure, obviously).
The general appearance of the curves is not relevant to the SAM effect: it is the result of my room's response. For the SAM effect, only the differences that appear between the curves when the SAM is activated are important.


The result of the measurements

Color legend

• SAM OFF - black color
  
• SAM ON 0% - green color
  
• SAM ON 50% - yellow color
  
• SAM ON 100% - red color
  
• Harman target curve - blue
  

   


Bass (9-500 Hz)
   

My observations:

1. SAM 0% behaves well and according to the information I received from Devialet: starting from 30 Hz down it starts to reduce the bass, and below 20 Hz it reduces it massively. This is good.
   
2. SAM 1-100% amplify the bass like this:
   

• 50-300 Hz: Small amplification. This is good.
  
• 20-50 Hz: Stronger amplification that increases as the frequency decreases. This is intentional and partly good, but I don't know if everything is good. The amplification in the 20-30 Hz range is very high (10-15 dB) and I think that this is not beneficial / natural for music.
  
• 10-20 Hz: Very strong amplification (stronger than at 20 Hz): 15-25 dB or even more. Although SAM 0% makes a massive reduction in this range (and this is very good), when SAM % increases above zero, the bass in this area is amplified back, at to much higher values than those at SAM 0% or SAM OFF. This is bad, very bad... I'm sure this is a bug and/or a design mistake. Such amplification generates great stress in the amplifier and in the speakers, and this for frequencies that humans cannot hear.
  

Treble (5,000-24,000 Hz)
   

My observations:

1. Although the SAM should not affect the treble, it seems that it does.
   
2. Starting from ~7,000 Hz, trebles are slightly amplified. The amplification level increases with the frequency, reaching ~2 dB at the frequency of 20,000 Hz. This is not good. I guess it's a side effect or a bug.
   
3. Unexpectedly, the amplification level is maximum at SAM 0% and decreases as SAM % approaches 100%. But, it never reaches the same level as SAM 0% or SAM OFF.
   
4. At the same time, this amplification continues at frequencies higher than 20,000 Hz. Again, such amplification generates great stress in the amplifier and in the speakers, and this for frequencies that humans cannot hear.
   

I'm not an expert in interpreting measurements made with REW (in fact, I'm a beginner), so I'm curious what more advanced REW users can deduce from these graphs.

Moreover, I would be very interested if someone could help me with a more elevated interpretation. I am referring in particular to the fact that I do not know how to interpret the REW graphs for phase and impulse.
Also, I can provide the original files of the measurements.

There are two things that I've been wanting to check for a long time, but haven't been able to:

1. The phase correction that SAM 0% makes.
   
2. Synchronization between speaker output for mono configurations (dual-mono or Devialet chains with more than 2 amplifiers).
   

Any help in this regard is welcome.