Batboard

I am interested to find out how many external speakers you can connect to a cdm1550 radio. Currently we have 3 hooked up. Do you lose quality after a certain number? How can you determine the maximum number of speakers you can use, and can it damage the radio if you use too many? Also, can you set the radio to still operate the internal speaker with external speakers attached.

The internal speaker will always work regardless if there's an external speaker plugged in or not. The only way to disable it is to unplug it from the board.

I believe the maximum wattage of the CDM audio PA is 13-watts. The maximum number of speakers is going to depend on each speaker's resistance (4 16-ohm speakers puts the equivalent load of a single 2-ohm speaker on the PA), so we'd need to know that. But yes, each speaker you put on will cause the overall audio level in each to drop.

Todd

Hey Todd,

If you have 4 16ohm speakers connected in parallel wouldn't the resistance be equal to that of 1 4ohm speaker?


1/R = 1/r1 + 1/r2 + 1/r3 + 1/r4

where r1, r2, r3, and r4 equal 16ohms.

Jamie

I have found that when I add an external speaker to the CDM series that the internal speaker operates at a much lower volume than the external speaker. If the external speaker is in the rear crew cab and the volume in the front is set to allow the guys by the control head to hear, the guys in the rear cab get blasted out.

Checking this out I found the internal speaker is 22 ohms and the CDM external speaker is 8 ohm. This makes the external speaker much louder. Best bet when adding 1 external speaker is to also add 1 at the control head location.

As to how many you can add I would not go over 3 directly connected, to connect 4 I would pair them up in a series paralel arangment as 2 in series would equal 16 ohms and the 2 16 ohm pairs paralled would be an 8 ohm load to the CDM.

Also NEVER NEVER NEVER let any of the speaker leads contact ground or you will wipe out the audio amp in the CDM as it needs to float as it is a push/pull type amp.

The other complaint I run into with the CDM is if you have a handset and an external speaker the speaker is so loud that it sounds like the handset earpiece has no audio. To resolve this issue I modify the flex jumper to connect the handset earpiece to 1 of the speaker leads.

Vercomm wrote:Hey Todd,

If you have 4 16ohm speakers connected in parallel wouldn't the resistance be equal to that of 1 4ohm speaker?


1/R = 1/r1 + 1/r2 + 1/r3 + 1/r4

where r1, r2, r3, and r4 equal 16ohms.

Jamie

Yep, my hurried math was incorrect...I meant to say 4 8-ohm speakers...oh well.

Todd

I don't have an explanation for this yet. I thought it was normal until people hear said it isn't. When I plug an external speaker into my CDM, the internal speaker shuts off. If I unplug the accessory connector or otherwise disconnect the external speaker, the internal speaker comes back on. I seem to be the only person with this magical radio.

Since the CDMs internal speaker is around 22 ohms impedance, if your external speaker's impedance is much lower, i.e. 2 ohms, the internal speaker will appear to shut off when the external is connected although it won't actually completely shut down due to the very unequal audio power division between the two. If you have a higher impedance external speaker, say, 12 or 16 ohms, I would suggest trying that. Then you will probably find that although the internal speaker volume drops when the external is connected the difference will be less.