What makes the biggest difference in sound quality?

Cables cannot make a difference comparable to the huge transformation in the room acoustic...Like just says lemonhaze...

No one selling gear or cables want to disclose that simple truth...

Acoustic passive treatment and especially mechanical active control with Helmholtz method WOULD KILL any desire to upgrade in most people who will implement it... And changing cable is a MINOR improvement, only seems to be a major improvement when someone has never correctly adress the room or had synergy gear problem already ...

Anything else is marketting or ignorance or the two....

what is the Helmholtz method?

what is the Helmholtz method?

Maybe like the “rhythm method” but as a solo actor?

Price is a factor in all this. At lower price levels, cables make a big difference. As component prices increase, spending more on cables hits the realm of diminishing returns before expenditure on electronics, speakers and vibration control does. And a good mains installation is more cost effective than spending money on more expensive cables. Last, absolutely correct speaker placement relative to walls, correct toe in and verticality is the cheapest upgrade of all if it hasn't been done in the first instance. All of that IMHO and experience.

what is the Helmholtz method?

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One of the best ways to tune any room to anyone's personal preference. 

It is the mechanical implementation of EQing a room correctly. No mater the size or shape. It is a ground up approach. Electrical, room, vibration control, passive and active tuning materials. The Helmholtz method is the final part of the embedding process. It's very interesting and the best way in my opinion.. 

Master M. has a different approach, it's also the way anyone can change a so so system into a really good one for Peanuts..

How's that Master M.? :-)

Regards