This is a Coeval Series drop-in speaker system for Athearn RTR SD38/40/45 locomotives. More than just a box, the enclosure features Diapasonic Tuning™, which allows the lower frequencies to accurately develop and resonate, clears the midrange of excess resonance and tunes the upper-mid/high response. The speaker uses the factory mounting screws and no modifications are needed to replace the factory speaker.
Note that the very early-run Athearn RTR SD40-2s have a narrower internal hood of around 17mmW, the speaker mount is further back and the speaker screws are spaced closer together at 10mm. Please choose "Early Version" if you have one of these. The later/current-run RTR SD40-2s have a wider internal hood just over 18mmW with the mount closer to the motor and a screw spacing of about 13mm. Choose "Current Version" for these.
The speaker comes fully assembled and tested. Please choose 4Ω (Loksound) or 16Ω (Soundtraxx) wiring.