What is the Altec 604 sound?

What is special about the Altec 604 - The 15 inch driver plays a very wide frequency range up to 1500Hz. The mid bass driver moving mass is very light (compared to JBL and modern Tannoy) to afford to play midrange. Driver quality is on a higher level similar to JBL and better than EV drivers used in Klipsch. Lightweight 15 inch Altec 604 and 515 drivers have better low midrange and upper bass texture compared to JBL drivers, even legendary JBL LE15. JBL drivers have deeper and puncher bass.

The main drawback of 604 is that the 15 inch driver can’t play equally good bass and midrange. The old series: 604, 604b, 604C have a better midrange texture on trade off of bass depth and weight. More modern series have a better puncher bass on price of midrange texture. Old 604 have sectoral--stile horns. More modern models from H, have improved Mantaray horn and phase plug that makes upper mid and high frequencies sound smoother and extended.

https://www.technicalaudio.com/pdf/Duplex_Speakers_related_to_Altec_604/DUPLEX.html

And the 605B?

Altec 605 was a cost reduction version of 604. I has a little bit smaller magnet and sensitivity. But the sensitivity is still very high and weaker magnets give a little more bass (Qts is higher).

Altec 605 monitors were The Beatles monitors in Abby Road studio.

605s lack the high end of the 604 due to the reduced magnet on the horn.  My brother had a single 605 in a utility cabinet and it was sort of dead sounding even though the horn seemed to work fine.