Here is an inexpensive external speaker for use with a RD / Scanner. It's a Radio Shack Model: 21-549. It's about $20 but there is an old version with a different case that is often times on sale for $10 to $15.
There is only 1 problem with the speaker. It has an "auto power down / standby" mode. This thread will show you how to disable the Auto Power down / Standby" function because it takes 1-2 seconds for the powered speaker to come out of standby and start amplifying the audio from the RD / Scanner.
The main IC used in the amplifier is a KIA6248K 7.3Watt Dual Audio Power IC. Pin 9 of this IC controls the Standby function. So we want to alter this circuit so the speaker doesn't go into Standby.
Pin 9 work like this:
Standby on = 0v-2v
Standby off = 3v - Vcc (Vcc = 6v-18v)
We will be disconnecting the timed Resistor+Capacitor power circuit and supplying Vcc to pin 9 to keep the speaker in a constant on state so we get our amplified RD / Scanner audio immediately.
Start by desoldering R15 & R16 and lifting them off the board. This will disconnect them from the Pin 9 PCB trace. Cover the desoldered legs in heatshrink. You could also cut the resistor leads and remove the resistors. I just chose to leave mine in place incase I need to undo my MOD.
Now you want to flip the board over and solder a wire from the Vcc buss to the pin 9 trace. I just used one of the througholes for the R15 resistor that I desoldered. You can see that I used a length of insulated wire. Even though the PCB traces are covered with a green insulating material, I didn't want to risk the green insulation material wearing off due to vibration.
The Power LED will still turn off after about 15-30 seconds of no audio input but this is of no importance. The audio amplifier circuit will stay powered up and allow you to hear your RD or scanner instantly. Instead of waiting for the KIA6248K to come out of Standby mode. That additional 1-2 seconds could mean the difference between a ticket or no ticket when your RD starts blasting Alerts.
This modification will work on any powered external speaker that uses the KIA6248 series IC's. Just disconnect the pin 9 supplied voltage and connect Vcc to pin 9.
I had to figure this out because I bought the powered speaker thinking that it would stay powered on as long as I had the mono headphone jack plugged in and the RD turned on. NOT TRUE. You have to have a constant source of audio coming in through the Mono jack for the speaker to stay powered on. But for $10 and 15 minutes of reading over the KIA6248 spec sheet, it was worth it to have a 5W powered speaker that really makes the RD's alerts loud.