Not many people know...

Super synergy: single driver horns love transconductance amplifiers

Back in the earliest days of audio, valves were the only amplifying devices available, so amplifiers developed which exploited their greatest strength. They were, and still are, the best VOLTAGE amplifier.

Loudspeakers, however, use the magnetic field created by a CURRENT flowing through the voice coil to make their sounds, and it soon became apparent that when the voltage from the amplifier went up the current through the speaker didn't always follow it exactly. At both high and low frequencies the speaker simply didn't let enough current through to produce equal levels at high, middle and low frequencies. This led to the development of separate woofers and tweeters.

Even with this added complication, if the speaker has been driven hard the voice coil heats up and once again restricts the current flow. This is sometimes called "Dynamic Compression" .

Single driver horns
A few people always felt that the sonic benefits of a single drive unit outweighed their disadvantages and horn loudspeakers have generally retained one wide range speaker unit.
It is possible to design an amplifier which "forces" current through the load in exact proportion to its input; these are TRANSCONDUCTANCE (TC) amplifiers, or more simply current amplifiers.

Not many designers have bothered to apply these techniques to audio, until recently.

More bass
Of course there are drawbacks to using them. Their lack of damping at bass frequencies causes ordinary loudspeakers - particularly reflex types - to flap around, producing particularly monotonous sounds, but a well designed horn enclosure suppresses the main bass resonance quite effectively and so what one hears is a more extended/louder bass.

More treble, too
At the treble end, though, the advantages are immediately obvious, with much greater detail in the upper registers. Furthermore, even after very loud passages the amplifier forces the correct current through the speaker so, no more compression! At last the speaker is being allowed to operate optimally.

It is important to understand that these are not tone controls; we are not manipulating the signal to cover up deficiencies in the drive unit. The frequency response into a resistive load is as flat as any ordinary amplifier's.

We are simply creating the same conditions for the speaker at the frequency extremes as it has in the mid-range: effectively extending its frequency response.

David Wright, Pure Music