In case anyone wants an explanation.
This table lists the maximum detection range of an enemy sub depending on the difference in noise level (in dB) between the target and the passive sonar. It's based on the sonar equation for passive sonar - the source (enemy sub) has to be louder than you by the value in the table (+x dB) and this will give you the maximum range at which you can hear the noise in ideal conditions at sea. Depending on other factors you can hear the enemy sub at a closer distance but not at a greater distance than the one given in the table because acoustic waves won't propagate in water sufficiently for your sensor to pick them up.
View attachment 73791
This next table lists the average approximate noise levels of subs - you have to add 100dB to each value in the table (17dB for Severodvinsk is 117dB)
View attachment 73792
This means that
without accounting for sonar gain during the Cold War a Los Angeles sub generating 128dB of noise could hear a Victor II sub generating 165dB of noise at a maximum distance of around 5km. Add a very modest sonar gain of 10dB for the towed array and the distance increases to some 50km. At the same time Victor II can't hear the Los Angeles sub at all because of its own noise level. The kind of one-sided advantage that US submarines held over Soviet subs is not matched by anything during the Cold War era.
Today a Virginia sub (New SSN in the table) generating 110dB of noise will hear a Yasen sub (Severodvinsk in the table) generating 117dB of noise at a maximum distance of somewhere around 50 meters. If we add the same 10dB gain the distance increases to some 500m. With 20dB gain it is 5km. At the same time due to how towed arrays work and thanks to modern processing technology it is possible for Severodvinsk to hear Virginia as long as the sonar gain of its towed array negates that 17dB difference of base noise level. It has to be significantly more though to detect it at sufficient range.
I can't remember the formula now but I think modern towed arrays or sufficiently large conformal arrays can have a theoretical gain of 30-40dB so the maximum detection ranges increase accordingly but obviously the same is true for your opponent. The key here is to hear the enemy before it hears you. The Americans have an advantage but the advantage is no longer sufficient to provide for full comfort of operations.
The reason why it worries USN commanders is that at the end of the Cold War the USN had Los Angeles subs in service and the Improved Los Angeles (San Juan or 688i) was in the process of replacing the Sturgeons. Russian on the other hand only in the late 80s introduced the Akula class (Project 971) which was somewhat comparable to the Los Angeles subs and the first Soviet/Russian sub that was better than the old Sturgeon. Better in this context means "having lower base noise level". Improved Akulas which were better than both 688's and 688i's went into service after the dissolution of the USSR and there were only two of those subs - one Project 971U and one Project 917M.
This means that at the beginning of the 2000s while the USN had altogether 62 Los Angeles and San Juan subs and 3 Seawolfs with the Virginias already in production Russia would have only about 12 Akulas of which only two were better than all US subs except the Seawolf.
With nine Yasen-class subs in production this is going to change because seven of those ships are supposed to enter service by 2024 and then two-three more by 2027-28. That will give Russians between nine and twelve subs which are within 10dB range of the Virginias apart from the new Khabarovsk class which will carry the supertorpedo and might be used for offensive operations. Still an advantage but far from the kind that USN got used to.
The main problem is obviously China which currently is not a threat due to low number of Type 09IIIs and their noise level (see table) but the Huludao shipyard has sufficient capacity to produce at minimum 2 SSNs per year which for China means a minimum rate of net SSN force growth of 20 per decade. While US shipbuilding is currently clogged with 2 Virginias per year taking half of the shipbuilding budget. So it's not just that Russian ships are catching up but that numbers are no longer to be an advantage in early 2030s as projected Chinese and Russian fleets combined will be too close to the size of USN submarine force. Any increase in Chinese SSN production and they'll match USN by 2040.
The question obviously is what the USN is going to do about it because quieter subs are not a solution. They can be as quiet as to bump into each other like the British and French SSBNs did recently. The question is how you find them and that's a separate and complex issue that I won't get into here. But hopefully you have an understanding of the article that most likely even the article's author doesn't have. That tends to be the ironic reality of people writing for money on subjects that they know very little about.