As an audio salesman for over 45 years, I will give you my answer...given countless times to clients...a "properly calibrated" loudness contour, and speakers that do not lack for extended bass response. Start with bass shy speakers and they will shut down all the faster at low levels. This is why the "high efficiency" response is counterfactual...high efficiency is achieved at the expense of bass extension in any given cabinet size. True, with bass reflex a speaker designer can engineer a "bump" to mask the lack of extension, and that may make it more palatable at low levels, but then when played a "normal" audiophile levels, it will boom.
The "properly calibrated" loudness is rarely achieved. If you have separates, and the preamp has a loudness function, then the amp MUST have input level controls to allow the system to be calibrated to the speakers' in-room response. A "Variable Loudness" control, a staple of Yamaha products, is a fair compromise. My 1962 McIntosh C-20 preamp has an excellent variable control, but hardly anyone is doing that nowadays.
The "properly calibrated" loudness is rarely achieved. If you have separates, and the preamp has a loudness function, then the amp MUST have input level controls to allow the system to be calibrated to the speakers' in-room response. A "Variable Loudness" control, a staple of Yamaha products, is a fair compromise. My 1962 McIntosh C-20 preamp has an excellent variable control, but hardly anyone is doing that nowadays.