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  The Silverado, a small d'Appolito loudspeaker 
  Sep 28, 2005, 07:30am EDT 

Selecting drivers

By: Sander Sassen

As mentioned I now need two low/midrange drivers and a single tweeter. For the low/midrange drivers I can use two smaller ones instead of one big one, hence upping the frequency of the resonance peak, and still have a good low end. For the low/midrange driver I’ve picked the 12-cm, 4.5-inch, Seas L12RCY/W121AL (H1207) a small aluminum low/midrange driver with a very strong motor, the same motor as used in its more expensive brother the magnesium cone W12CY. It has a strong die-cast aluminum frame, vented pole piece and six screw mounting points versus the usual four.

Seas H1207 back Seas H1207 front

The Seas L12RCY/H1207 driver, featuring a large magnet, aluminum cone with phase plug and rubber surround.

The H1207 Seas low/midrange driver has all the good bits of that more expensive Excel driver, but lacks copper rings in the t-shaped pole piece (for impedance compensation), and has a plastic phase-plug rather than a copper one. Obviously aluminum is used for the cone and the best part is that all of this comes at a much friendlier price point (around $50). The cone breakup frequency is high, around 8.5kHz, which means it won’t be much of problem if I filter at a crossover frequency of about 2.5kHz. The 3D waterfall shows the driver to have excellent impulse response with very good damping, due to the light cone, strong motor and well balanced suspension.

Seas H1212 front Seas H1212 back

The Seas 27TBFC/G/H1212 driver, featuring a aluminum/magnesium alloy cone, rear chamber and ferro-fluid.

The tweeter will also be a Seas one, as their aluminum alloy tweeters have a good reputation. I’ve selected the 27TBFC/G (H1212) a 27-mm aluminum/magnesium alloy dome tweeter. The tweeter’s voice coil is immersed in ferro-fluid and has a rear chamber which results in excellent damping characteristics and a low resonance frequency. With a cone breakup resonance frequency close to 30kHz we’ll not be bothered by that either as that’s above the audible range. Again the 3D waterfall shows the driver to have excellent impulse response with very good damping, as a result of the light cone, strong motor, ferro-fluid and well balanced suspension.

1. Introduction
2. Selecting drivers
3. Bass-reflex enclosure
4. Cross-over
5. Measurements
6. Conclusion
7. References and credits

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