VHF extension speaker

[JeremyF]

Ive seen a VHF cockpit speaker that is in a standard 110mm casing, with a switch on it. Does anyone know its make, or where to get one. Ive found a Simrad, but without a switch.

I want to mount it alongside other instruments, and Ive only got space for one more 110m device.

Jeremy Flynn

 

[bedouin]

Take care - most (all?) extension VHF speakers REPLACE the internal speaker within the radio itself - so having one that you can switch off means that you will be able to turn the radio off all together.

Just unplugging the speaker from the VHF will "turn off" the extension and re-enable the internal speaker.

What are you trying to achieve?

 

[Twister_Ken]

If you can't find a switchable one, then the Simrad/Navico can be installed very easily with a switch (£1.40 from Maplin) spliced into the speaker wire, with the switch placed just far enough inside the companionway to remain dry. Incidentally Marineforce chandlers had the Simrad speaker at half price last week.

 

[JeremyF]

Good point. I'm trying to leave the speaker on down below, and have the external one switchable. I'll check with NASA to see how their DSC behaves.

On my last boat the internal speaker stayed on when the external one was switched on, so I guessed they all behaved the same.

Jeremy Flynn

 

[bedouin]

Highly unlikely that it will work the way you want. It is difficult to design an amplifier that will work that way (all to do with the impedance of the loudspeaker load).

Any arrangement that simply involves switching one speaker on and off will either waste power or risk damaging the amplifier by overloading the output devices (but probably not a very high risk).

 

[JeremyF]

Rather than put a regular switch in the companionway, I guess I can always buy a waterproof switch from Maplins.

Thanks for the Marineforce tip.

Jeremy Flynn

 

[Robin]

The NASA set in common with most cuts out the internal speaker when the extension is plugged in. NASA suggested to me connecting two external speakers in parallel, one mounted near the setr and the other in the cockpit, impedance of both should be 8 ohms.

This is a very irritating design feature, what good is a radio you cannot hear in the cockpit, or if you can then you cannot hear it down below at the set! Our old Husun with a telephone handset worked OK since you could still hear via the handset even though the set speaker was cut off. Most new sets that are affordable have additional controls in the mike so handsets cannot be substituted.

By the way, nice little waterproof extension speakers available from French chandlers for £11 to £15, I bought one but now find I need a second one to make it usable as above.

 

[JeremyF]

Thanks for the info, Robin. Saves me a call to NASA. Seems a strange design failure, perhaps the amp can only drive one speaker, but you would have thought that it would be more expensive for NASA to implement the feature than leave it off.

BTW, Twister Ken's advice is correct - contact the Victoria branch of Marineforce and they are clearing the Simrad speakers at £9.95 rather than £35 as seen on the ybw Shopping Quay.

Jeremy Flynn

 

[bedouin]

As mentioned above, it is much harder to implement that you would think. Amplifiers are designed to drive a specific load (speaker impedance). If they have a higher impedance load they will lose power, if they have a lower impedance load you risk damaging either the output devices, or part of the power supply.

Let's assume the internal speaker on the NASA is 4 ohm - there is no way to add an external speaker to the circuit and retain the 4 ohm load. If you put another 4 ohm in series (bad idea anyway with speakers), the total load is 8 ohms - reduced power AND divided between two speakers = considerably quieter. If you put another 4 ohm in parallel, you get a load of only 2 ohms, and risk blowing something.

Hence the standard advice is to add two external speakers, each 8 ohms, wired in parallel to give a 4 ohm load, and bypass the internal speaker with that...

 

[Guest]

I've used the simrad as you wish to, with an inline switch, by connecting it internally to the VHF wires running to the internal speaker. The external cable exits the set through a hole left by removing a rubber 'foot' from the VHF base.

 

[milltech]

Have seen the little black Nasa one?
www.allgadgets.co.uk > the shop > marine instruments


John

 

[billmacfarlane]

I've got a switchable one on tne binnacle and I'm almost certain it's made by Shipmate.

 

[Joe_Cole]

Do you have a compass on your binnacle?
Any problem caused by the speaker?

Joe

 

[philip_stevens]

All this talk of impedance, amplifiers and so on.

I've had two speakers wired to my Navico for five years and nothing has gone wrong with anything so far!

I plugged the external speaker feed into the socket at the rear of the set, and ran it to two switches. One is for the cockpit speaker, and the other for the navigation area speaker. Either or both can be switched on or off at any time - and volume is plenty loud enough. The volume control on the VHF set controls both external speakers in parallel. If night sailing and quiet is required, both can be switched off and the handset speaker is still loud enough to hear with the volume control turned up.

The obvious mismatch of speaker impedance doesn't appear to have upset the VHF amplifier. One speaker was already installed in the cockpit, and I fitted another into the nav area. Both switches are at the nav area, next to the VHF set.

regards,
Philip

 

[JeremyF]

Its good to hear that the impedence and qty of speakers does not seem to matter in practice, but I am going to switch the external speaker from the instrument binnacle, as thats where you decide you want to hear something, rather than having to dive below to turn the external speaker on.

Jeremy Flynn

 

[philip_stevens]

Yes, fully agree.

I usually leave the cockpit speaker on most times, and switch the nav speaker on when I want it.

Good IP66/7 toggle switches/rubber covers are available from RS. I have one in the cockpit to operate the cockpit area light.

regards,
Philip

 

[billmacfarlane]

Not that I'm aware of. I've checked it against the handbearing and also against the autopilot and it seems OK. It's mounted about 3' from the compass.

 

[simrad]

Dear Jeremy

I am a technical salesman for Simrad UK. I believe you are looking for a VHF cockpit speaker with a built switch. Simrad produce a speaker of this description, the part number is 101.8330.001. If you wish for further information or to purchase the product either contact one of our dealers or contact myself at Simrad UK, Fareham, Hampshire. 01329 245 100. Kind regards Matt Straker

 

[EdEssery]

Wiring a VHF Extension Speaker

Finally done the research and fitted a VHF Extension Speaker and it works a treat.

I wanted a setup where I could have the cockpit speaker switched on or the one by the chart table or both

The rules are:
1. the speaker ohm load must be equal to or greater than the rated output of the amplifier
2. You must never run the amp without a speaker load on it (this means you shouldn't just put a simple on/off switch on each speaker in case they both get turned off)
3. The formula for calculating the load of two speakers wired in parallel is 1/"total load (ohms)" = 1/"Load (ohms) of Speaker A" + 1/"Load (ohms) of Speaker B" - thus two 8 ohm speakers present a load of 4 ohms when wired together in parallel.

The rated load of my VHF (from manual) is 4 to 8 ohms. It's a Swiftech M168. Plugging in an external speaker cuts out the internal speaker so I needed to find two 8 ohm speakers - one for the cockpit and one for the chart table area.

After considerable difficulty I determined the Simrad/Navico 110mm speaker is 8 ohm - it's not marked on them or in the packaging/documentation anywhere ! I had to call the manufacturer (Simrad) to find out their load. I then managed to pick two up in the City Yacht Centre for £19.99 each just before it closed.

I then had to figure out a circuit for wiring them. Unfortunately Maplin don't do an A/B/A+B switch which is what you really need. They don't even do an ON/ON/ON switch which would have done. I believe RS Components do one.

As I have a Maplin locally I decided to use their products. In the end I wired it with a Dual Pole (so I can switch both sides of the speaker cable) ON/ON switch with the VHF feeding the common terminal and one speaker wired to each of the switched connections. I then bridged the two switched terminals with a dual pole (ON/OFF) switch.

When the ON/OFF switch is OFF, the Cockpit or Chart Table is selected by the ON/ON switch. Turning the ON/OFF to ON bridges the output of the ON/ON switch and both speakers are on irrespective of the position of the ON/ON.

I wired the two toggle switches into my electical panel replacing an unused position - one replaces the existing single pole ON/OFF switch and the other replaces the fuse holder assocaited with the removed switch.

The switches I used had spade terminals and therefore all the wiring was done with blue crimp connectors with no need for soldering - a real bonus as far as I am concerned.

It all works a treat and is much louder than the internal speaker which was very muffled because the set was flush mounted.

Hope this is of use if anybody is planning a little project for the winter.

Ed

MG C27
Skybird
K8452Y

 

[kdf]

Re: Wiring a VHF Extension Speaker

Would it be possible to connect the VHF output to cockpit stereo speakers?