1. Fletcher Munson, infrequent and temporary need.
Separate from basic match to your room. (Stupidly named ’Loudness’, it was for ’Lowness’ the opposite of loudness).
Fletcher Munson is a separate eq curve needed ONLY for very low listening, best if implemented automatically with volume reduction. If not automatic, then when listening at very low volume, manually raise the bass tone control, or engage the ’loudness’ circuit in your unit.
2. EQ to Match the Speakers to the Room. YES! Implemented HOW?
"In the Old Days":
1st a mono Radio, mono speaker with a mono amp; next, Stereo, add a second speaker with it’s own mono amp (thus dual mono). next add a preamp for moving magnet cartridges, Phono needs ’automatically engaged’ RIAA EQ and ’automatically engaged’ tape EQ if just a tape deck.
FM was Mono, then Armstrong solved Stereo FM. MPX EQ had to be added for FM Stereo, beginning with external mpx units, later MPX circuits added to preamp’s FM inputs.
Almost ALL that era’s speakers came with LEVEL controls,
i.e. 3 way had two level controls: ’Presence’ and ’Brilliance’.
You adjusted your SPEAKERS to both your space AND your ’taste’. Move them, re-adjust the LEVEL controls.
3. Next, Speakers no longer came with Level Controls,
thus Pre-amps were used to ’adjust the SIGNALS’ sent to the amps thus sent to the Speakers to adjust the sound for the space and/or your taste.
Basic signal adjustments included: balance; bass; treble controls.
Fully equipped preamps or receivers added:
Filters: Rumble; Phase (normal or reversed); automatic FM Muting between stations; Low Frequency Filter (acoustic feedback or noisy records); High Frequency (scratch or tape hiss); Some units included a ’Loudness’ (Fletcher Munson EQ) circuit, (mostly manual, automatically engaged Loudness came later).
Some units let you pre-match the separate component’s signals levels so the main volume would be the same when changing input devices.
Some units included MODE switches for: Stereo; Stereo Reverse; MONO; L+R to L; L+R to R; L to L+R; R to L+R
Later, more tone controls were added to some units, i.e. Treble. Mids, Bass. Or, more bands, like mini-equalizers in the preamp.
Next, separate Equalizers, with more bands to adjust individually, units had various # of bands, of various ranges of their assigned frequency.
Equalizers: Popular, then unpopular, then ’straight wire with gain’, which leaves you with zero adjustments in the space or your taste: (no controls in the speakers themselves, or to the signals sent to the amp/speakers).
Note: some modern hi-end speakers included EQ modules, located near but outside the speakers, to adjust the speakers to the space.
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Well, let’s add room treatments!