While using KS-BASH-C shot clock. Incase you will like to replace the embedded horn with your own horn speaker. Here is the instruction for it.

Open the back board of the shot clock, so you will see the control board in it as shown in below image.

The following red rectangle indicates the 12V horn power supply line, which is responsible for powering the horn. The circuit board has positive and negative polarity indications.

The following red rectangle indicates the 5V horn signal control line, When the system is running, by default, the output voltage of the S1 and S2 pins is 5V. When the system need to generate the sound of game clock (The major sound), S1 is 0V and S2 is 5V. When the system need to generate the sound of shot clock (The minor sound), S1 is 5V and S2 is 0V. The circuit board has labels for S1 and S2.

To connect with your own horn, you may conenct S1 and S2 to a relay as a switch to control the horn's on and off. Since there are two conditions—S1-5V, S2-0V, and S1-0V, S2-5V—two relays will be controlled to make the horn produce different sounds. The approximate schematic diagram is as follows: