Speaker III – Intro

The idea behind this project was to fulfill many speaker project needs:

  • My satellite speakers in Speaker I are showing thier age. Another crossover redesign might help, but it won’t overcome the shortcomings of the midrange unit, the Peerless KO-50G. I bought the mid-ranges over 10 years ago on a college student’s budget. I’m sure their design originated many years before that.
  • I wanted to give my brother Doug a fun wedding gift. His satellite speakers are similar to mine, but without my latest x-over design. Unfortunately, I wasn’t even able to finish the first prototype cabinet in time for the wedding. On the good side, now that he knows about the project, he can give some input on the desired cabinet shape.
  • A colleage at work needs (Ok, wants) a center channel to match up to his Ariels. It is going to sit above his TV, so magnet sheilding is a must. Unfortunately, the drivers used in the Ariels are not magnetically sheilded, so a straight forward adaptation is not possible.

These needs culminate into the following initial project design requirements:

  • Vifa or better drivers. Anything less won’t match well to the Ariels.
  • All the drivers are to be sheilded. (This really limits the choices!)
  • Bass response down to at least 100 Hz, 80 Hz preferred (the standard for a THX center channel).
  • The desired system efficiency is in the range of 94-96 dB in the mid-range. This is required for my brother’s system to properly integrate with the bass units whose efficiency is 96 dB. My bass units are only 89-90 dB efficient, so I see an electronic cross-over in my future.
  • An MTM (mid-range / tweeter / mid-range) setup. This helps satisfy the need for efficiency, increases the bass capability, keeps driver diameters smaller, and helps even out vertical dispersion.

Being my third major speaker project, I want to break new ground (for me) in the design of Speaker III. Thus, I have the following additional, self-imposed design goals:

  • Time-delay on the tweeter to align the driver responses.
  • As near a constant group delay cross-over design as possible. This is in addition to the usual requirement for flat frequency response.
  • A baffle shape selected with attention to the issue of cabinet diffraction loss.
  • The Ariels are a transmission line. Although too big for a center channel, they might do for the main satellites for my brother or I.