What technologies or inventions made jazz more accessible to the masses or other such things.
Well, there are a few different, important contributions that electrical and acoustical engineering has made to the development of the music. Foremost among these is of course the advances that we've made in recording technology since the beginning of the twentieth century. Other important contribution to the music include, though are of course not limited to, the development of portable amplification for basses, guitars, pianos, and vocalists; the development of the instruments themselves; and the development of transportation of an economically viable nature.
For years "jazz" wasn't really written down commercially, with musicians playing off of hastily drawn "lead-sheets" when they had to read at all. For the most part, players learned their parts by ear, listening to the records of the masters who had gone before them, or in person on the bandstand. Alyn Shipton writes:
"When Oliver's band made its first discs in April 1923, it caused somethig of a sensation, and other musicians wore out their records, learning the parts note for note." ^1
In a large number of cases the earliest jazz musicians, at least the black ones, would never have been taught to read music in the first place. So since jazz was, in its first several decades an art form with a purely aural for of propagation, it required the invention of recording technology of sufficient popularity for it to spread. Initially jazz was mostly a product of New Orleans and its surrounding areas, which is where early jazz gets the name "Dixieland" from - a name most black musicians are uncomfortable with, and for good reason. Until the first commercial recordings of jazz musicians, spearheaded by the "Original Dixieland Jass Band", a lot of people in the north had never really heard the music.
As well as enabling the spread and learning of jazz music, recording technology was an impetus for composers to write longer and longer works. Small ensemble groups, where improvisation made up a great deal of the music, were rarely constrained by record times in their live performances. Larger groups, such as the Duke Ellington Orchestra, would commonly stick closer to the time limitations of recording technology of the day. This limitation allowed arrangements to be used both live and in the studio, and you can see a proportional increase in composition length and recording length capability.
The LP, or long playing record, would also allow jazz improvisers to record improvised solos in the same manner in which they would play them live. Charlie Parker, early in his career, would be forced to distill an entire improvisations worth of music into a minute or less to fit on early records.
Modern jazz playing is in some ways based around the bass player. The counterpoint between the bass player and the soloist, and the basses contribution towards the overall groove are absolutely essential to the sound of the music. Bands without bass players are notable for this fact alone. In the early days, however, the bass part was often played by tuba or bass saxophone. As well as contributing a different sound, these instruments had the practical advantage of being louder. The string bass is simply not loud enough to play a dance-hall amplified and be clearly heard. Many bands would simply include the bass anyway, and have it function more for the band than for the dancers, but with the invention of the portable amplifier we see the bass come into its own, enabling more complex and swinging music.
This is also where guitars become viable solo instruments in a jazz context!
1 - Shipton, Alyn. Pg. 88, A New History of Jazz. Continuum Publishing Group.