Testing & wiring up external cockpit speaker

[eebygum]

My boat came with a Shipmate external speaker which is wired through to the Nav station but is not connected to anything as I removed the old non-functioning Shipmate VHF.

Is there a quick test I can do with a multimeter (please assume I know nothing about how to use obe) to test it is working BEFORE I go to the trouble of wiring it up to my Cobra Marine MR F57 fixed mount VHF.

I can see from the Cobra manual that it has external speaker outputs… a +Positive and - Negative connection. Do I need to know which is which from the external speaker or can I connect up either way.

If the external speaker works, and I connect it correctly…. Will it always be ‘ON’ or can I toggle or add a switch to make the fixed VHF speaker the primary ?

I’m working on the boat in Bangor for the next two days so any help/suggestions appreciated as I will try them out while I’m down on the boat.

Cheers,

 

[KompetentKrew]

I believe that speakers are rated by impedance, which is measured in ohms (same as resistance).

For instance, B&G told me of their new V100 VHF, "if you dislike our external speaker only due to its appearance, you can use any 4ohm 8Watts marine speaker connected to the same connector on the processor", and linked me to some random waterproof speaker on RS Components' site that met this specification (exceeded the watts, in fact).

So I would think you need to check the impedance required by the Cobra and see if it matches the impedance of the Shipmate external speaker. This may be in their respective manuals, may be printed on the back of the speaker itself (on the metal part of it, inside the plastic enclosure); you may be able to google the answers or contact Cobra's technical support.

If the wattage of the Shipmate speaker is higher than that required by the Cobra then that'll be fine.

As for testing, you could probably use an oscilloscope to generate a wave, and connecting it to the speaker would produce a steady tone. If the impedance of the speaker matches that required by your Sony Walkman then you could always wire it to a 3.5mm jack and test with a copy of Dire Straits seminal album, Brothers in Arms. But probably the easiest thing to do is simply test it by wiring it to the radio - to save running cables through confined spaces prior to testing, either move the radio closer to the speaker, the speaker closer to the radio, or use a long pair of fly-leads to connect the two (run it through the companionway or wherever just while you test them). 50m of doorbell wire is £6 from Screwfix.

 

[andsarkit]

Speakers are usually 4 or 8 ohms. This is the impedance (AC resistance) which may measure slightly differently with a multimeter. If you don't have a multimeter just put a 1.5V battery across the speaker leads. It will make a slight click or crackle.
The manual doesn't seem to indicate the required impedance but you will not do any harm by trying it as long as you don't wind it up to 11. If it is different to the internal speaker you might find that one is much louder than the other. Speakers also vary in sensitivity which will also affect the relative loudness.
No problem to put a switch in series with the external speaker for when it is not required. The internal speaker doesn't seem to have a switch. Some of the older VHFs used to have a jack socket with a switch that turned off the internal speaker when an external was plugged in.
Polarity is unimportant and only required for stereo speakers that need to be in phase. (i'm not sure if I could tell the difference by listening)

 

[Dellquay13]

Andarskit typed faster than me...

You can test the speaker with a 9v battery by briefly with tapping the cables onto it, and you will hear a clicky sound. A multimeter only tests for dc resistance not impedance, and the battery test is just as good as a dc test.
The cobra radio will work with 4 or 8 ohm speakers, the 8 ohm being a little less loud.
On the previous mr f55 model The minijack output socket is internally switched, when you plug an external speaker in it cuts out the internal speaker, so not easy to switch between apart from simply unplugging the external speaker.

 

[eebygum]

Andarskit typed faster than me...

You can test the speaker with a 9v battery by briefly with tapping the cables onto it, and you will hear a clicky sound. A multimeter only tests for dc resistance not impedance, and the battery test is just as good as a dc test.
The cobra radio will work with 4 or 8 ohm speakers, the 8 ohm being a little less loud.
On the previous mr f55 model The minijack output socket is internally switched, when you plug an external speaker in it cuts out the internal speaker, so not easy to switch between apart from simply unplugging the external speaker.

Thanks for all the replies, that gives me enough to go to test tomorrow.

I don’t have a test scope onboard but I do have a test battery. Further reading it looks like your right hand about switching between the internal/external speaker unless anybody has an easy work around ?

 

[eebygum]

Andarskit typed faster than me...

You can test the speaker with a 9v battery by briefly with tapping the cables onto it, and you will hear a clicky sound. A multimeter only tests for dc resistance not impedance, and the battery test is just as good as a dc test.
The cobra radio will work with 4 or 8 ohm speakers, the 8 ohm being a little less loud.
On the previous mr f55 model The minijack output socket is internally switched, when you plug an external speaker in it cuts out the internal speaker, so not easy to switch between apart from simply unplugging the external speaker.

All tested and it’s knackered. So I’m thinking of buying a new external speaker simikiar to the one below…

Thompsons Ltd | Pyle PLMR41B WaterProof 4" 10cm 100w Dual Cone Marine Boat Cabin Speaker Pair

since most speakers seem to come in pairs, I thought I would put the other speaker internally (near but not next to the Nav station and compasses)

My next dumb question is … how do I connect the second internal speaker, do I just run off another set on two wires to the Cobra output/split the output wire… or is it the same difference.

 

[Dellquay13]

The radio is only mono, and doesn't have connections for two speakers. If you use 2 speakers rated at 4ohms, wire them in series (8ohms total) not parallel (only 2ohms which will overload the audio output chip).
However, 2 speakers rated 8ohms should be wired in parallel (4ohms in total).
I have a very similar single 4ohm speaker on my small yacht mounted through the cockpit bulkhead, and because it is open backed into the cabin I can hear it inside and out.
With 2 you could fit an inside/outside switch to select one or the other, but i prefer to hear the radio wherever i move around the boat without having to remember flipping a switch.

Series wiring; radio positive to speaker A positive, connect speaker A neg to speaker B pos, out of B negative back to radio negative.
Parallel wiring; radio positive to both speaker positives, radio neg to both speaker negs

 

[KompetentKrew]

https://cpc.farnell.com/c/audio-vis...ance-speakers/splashproof-waterproof-speakers