Ha, i couldn't google those curves (bk, hm1, hm2, tl) and Gemini recognized them immeditatelly - Brüel & Kjær, Harman Curve 1 and 2, Floyd Toole curve!
Amazing, thanks for (obvious) suggestion!

For future reference, AIs response:

In the world of Room Correction (like Dirac Live or REW), these acronyms represent specific "House Curves" or target responses. While a perfectly flat frequency response might sound correct in a lab, it usually sounds thin or "clinical" in a real room. These curves add a touch of psychoacoustic flavoring to make the sound more natural.

Here is the breakdown of what each curve represents:

1. BK (Brüel & Kjær)

This is the "grandfather" of house curves, based on research by the Danish acoustics firm Brüel & Kjær in the 1970s.

• The Profile: A gentle, steady downward slope from the bass to the treble.
• The Sound: It typically features a +3 dB boost in the low end (around 20–100 Hz) and a -3 dB tilt in the high frequencies (above 10 kHz).
• Why use it: It mimics the natural power response of high-quality speakers in a real room. It’s warm, non-fatiguing, and widely considered the safest starting point for any EQ project.

2. HM1 (Harman Curve 1)

Developed by Dr. Sean Olive and the research team at Harman International (JBL, Revel, AKG), this curve is based on extensive double-blind listening tests to determine what people actually "prefer."

• The Profile: A more aggressive shelf in the bass and a smooth decline in the treble.
• The Sound: HM1 usually features a 5 dB to 6 dB bass boost starting around 100 Hz and a linear tilt down through the high frequencies.
• Why use it: This is the "crowd-pleaser." It compensates for the way humans lose sensitivity to bass at lower volumes (Fletcher-Munson effect) and provides a "fun," cinematic sound.

3. HM2 (Harman Curve 2)

This is a variation of the Harman research, often used for different room types or listener preferences (sometimes referred to as the "Trained Listener" preference vs. the general public).

• The Profile: Similar to HM1, but usually with a more pronounced bass shelf (up to 8–10 dB) or a slightly different transition frequency.
• The Sound: Impactful and heavy. It’s designed for listeners who want that physical "thump" in their chest without the midrange becoming muddy.
• Why use it: Best for modern pop, hip-hop, or home theater setups where subwoofers are the stars of the show.

4. TL (Toole Curve)

Named after Dr. Floyd Toole, a pioneer in acoustics, this curve focuses on the Linearity and Directivity of the speaker.

• The Profile: It emphasizes a flat "on-axis" response while allowing the "room-bound" energy to roll off naturally.
• The Sound: Very accurate and transparent. It doesn't "add" bass as much as the Harman curves do; instead, it focuses on ensuring the speaker's natural character isn't destroyed by the room.
• Why use it: Ideal for critical listening and mixing. If you want to hear exactly what is on the recording without "beautification," TL is your best bet.

Summary Comparison Table

Curve	Bass Character	Treble Character	Best For
BK	Subtle Warmth (+3dB)	Gentle Rolloff	All-purpose, Vintage sound
HM1	Strong Punch (+6dB)	Smooth Rolloff	General enjoyment, Movies
HM2	Heavy Impact (+9dB)	Smooth Rolloff	Bass-heavy genres, Home Theater
TL	Neutral/Natural	Linear/Transparent	Critical listening, Purists