Monopole and dipole lineaums- differences/how do they work?

[thedelihaus]

Spent a bit of time at an acquaintances's house, who had a pair of 2-way Radio Shack monopole tweeter speakers mounted in the wall. Filled the room and kitchen nicely- though when sitting in the living room, on the couch, the speakers, he and I both agreed, were placed too high.

Nonetheless, I liked the sound. They were assisted by a well-placed subwoofer.

My question is-

what are the differences between the monopole and dipole (besides singular/plural) and how do dipoles work? They look like electrostatic ribbon tweeters in a small way.

And besides Radio Shack/Lineaum, who else used a similiar design? Is this what the tweeter basically is on some of the Polk 12s, and HPMs, and wild Technics speakers?

Thanks,

Paul

 

[Texas42]

I had a pair of Pro LX-8 towers once and they had the dipole type Lineaum tweeters. Thought about modding it (the cabinet and woofers which were crap) because the tweeter is so sweet but never got around to it. I currently have a pair of RCA speakers with the monopole Lineaum in it and some pretty nice kevlar bass drivers that I use in a surround system for rears due to their wide dispersion characteristics. The dipoles project in a much wider area of course as it is firing both front and back.

Currently the Gallo Reference speakers use a CDT tweeter, while not the same as a Lineaum has similar projection patterns. Both tweeters sound great although the Gallo is a high end design and is really a great full range speaker. Just my two cents...

 

[Texas42]

Oh, here is a pic of the RCA with Lineaum tweeter....

 

[Charivari]

What are the differences between the monopole and dipole (besides singular/plural) and how do dipoles work? They look like electrostatic ribbon tweeters in a small way.

Linaeums are just heavily modified conventional dynamic drivers. Here's a Stereophile review on the Linaeum that describes how the principle works. (Kind of funny that they have the slang "Rat Shack" in the URL.)

What's so special about the Linaeum tweeter? In a conventional tweeter, a coil of wire suspended between the circular poles of a ring-shaped magnet moves backward and forward according to the dictates of the electrical signal, driving a dome or cone diaphragm to excite the air. In the Linaeum tweeter, there's still a voice-coil, but this time it's flattened into a vertical shape and suspended between opposed rectangular magnet poles. It still moves backward and forward, but instead of driving a diaphragm, it pushes and pulls the vertical joining point of two semi-cylindrical 3"-long sheets of stiff plastic film, each of which is fixed at its other end. Imagine two (empty) beer cans side by side: the point where they touch is where the voice-coil is attached. Under the influence of the electrical signal, the two semi-cylinders rotate back and forth, the resultant traveling waves producing sound.

Hmm, in theory the principle could be adapted to a large full-range design provided a sufficiently stiff material is used for the semi-cylindrical sheets.

And besides Radio Shack/Lineaum, who else used a similiar design? Is this what the tweeter basically is on some of the Polk 12s, and HPMs, and wild Technics speakers?

Well, the HPM supertweeters work on a principle similar to the piezo electric effect. Basically, when the amp's output voltage is applied to the specially formulated polymer, the material expands and contracts slightly in response moving the immediately adjacent air and thus producing sound. For the others, I've no clue.

- JP

 

[thedelihaus]

JP,

Thank you.

Paul