[Steve Kendall]

Paul, I think Peter is talking about something different. As I understand it, a dual voice coil loudspeaker allows you to connect two amplifier outputs, usually only the bass frequency parts (sub woofer out puts), to a single speaker. Why do that? Well you might only have space for one speaker, such as under the parcel shelf of a DS, but have a stereo radio/amp. And as bass frequencies are not directional, it won’t mess with the stereo effect as that can still be provided by two speakers for the higher frequencies, say at the front of the car. Which is possibly what Jonnas did.

So it’s not relevant for a mono radio.

Apologies if you already knew this stuff.

[Steve Kendall]

Hi Paul, I’ll answer as best I can.
It is the speaker impedance that affects how much current is drawn from the radio, not it’s wattage rating. So a 40watt 4ohm speaker will draw the same current as a 6watt 4ohm speaker.
The 40watt speaker won’t necessarily be any louder either – the 40watts is how much input it COULD handle, if it was provided with it (if you installed a 40watt amplifier for instance). But a modern speaker might have a neodymium magnet and they are much more powerful than the old type and so they do get the cone moving further ie. louder sound.
The speaker you saw at Chromelondon doesn’t say if it has a neodymium magnet. They also seem to imply that it will magic 40watts for you from somewhere!
The price seems very steep to me. I bought one, admittedly in 2016, for £30 from Autosound in Bradford. Company still going, but that speaker isn’t on their current website.
As to whether your radio will handle a 4 ohm speaker, I’m afraid I don’t know. I’d expect it would either be ok, or start to complain by distorting at high volume. And if you have the fader set to the middle position, with two 4 ohm speakers, you’ve effectively got an 8 ohm load anyway. Not true if you switch to either end of the range though.
Lastly, in case anybody cares, I discovered much to my surprise that 7-way switches are plentiful on eBay, so I may go down that route.

[Steve Kendall]

I meant also to say that the values of resistor on your switch would be related to the impedance of the speaker, not the power of the radio. That is the 0.5 ohm etc. Their power rating would be related to the power of the radio or amp, but again, 4 watts or 6 ain’t going to make much difference.
The impedance of the speaker can be checked with a digital meter if you have access to one. An 8 ohm speaker will measure about 6 ohms and a 4 ohm one, about 3 ohms.
But again, I’d expect your switch to work pretty well with either.

[Steve Kendall]

Thanks again Paul, you’ve given me all the info needed thanks.
Wattage of 4 or 6 isn’t really going to make much difference to the pot requirement. Nor in fact to the loudness level of the output – 6 watts is only 3dB louder than 4, and 3dB is just slightly louder. Both would struggle against the engine and wind noise of my car at 70mph! But a good modern speaker with a neodymium magnet could make a big difference.

Re siting of the control, I’ve already mounted my phone holder on the front of the ashtray so that location is already taken. Next to the HRW switch will be good though.

[Steve Kendall]

Aha! It all makes perfect sense now! I’d been thinking about this for ages and getting nowhere (I wanted to say I’d been thinking about it all night, then it dawned on me. But that would be untrue 😉 )

Thanks for the resistor values. With that info, I stopped thinking about it as two separate speaker circuits, with what would have given an obviously unacceptable volume drop in the centre setting, and considered it as a whole. In that centre position, both speakers are in series and the pot, or switch with resistors, isn’t making that much difference. No volume drop! And I’d thought that speakers always have one side earthed, don’t they? I must have forgotten that this is a Citroen. Why do everything like everyone else?

Those cleverly chosen resistor values almost certainly mean that the fade from from front to rear is smoother than with the pot where I expect most the adjustment is in a few degrees of rotation.

And I have that space on my switch panel in my DSuper, so I may use that either for the pot or for the switch and resistors. Just need to find a 7-way switch. They’ll be with the Unicorns…

[Steve Kendall]

I was put off that one by the splined shaft – but having a custom 3D printed wheel, it might actually be better.
There’s also this 5watt big boy from the same supplier

https://cricklewoodelectronics.com/wirewound-5-watt-potentiometer-100-ohms.html?gad_source=4&gad_campaignid=483462886&gclid=CjwKCAiAzrbIBhA3EiwAUBaUdT4VGG8JYNiKKfqLLY8O5ERLySGvugQdUmAE7Kj6774h9qbfksvxDRoCxw8QAvD_BwE

There’ll be a setting of the pot where it gets the highest power dissipation. I think calculating that position might be beyond my capabilities, so I’ll just go with ‘5watts is better than 1’ !

I can see what your Edison switch is doing by the way, traced the circuit out, it’s just mimicking a pot with 7 positions. But the wiring of it to the speakers is the crucial bit of info.

[Steve Kendall]

PS Paul, if possible, it would be very helpful if you are able to say where each of the six wires goes on your set up (Green, pink, grey, black, red, blue). Then all should be made clear! Thanks 🙂

[Steve Kendall]

Many thanks for the great reply Paul
As I’m allergic to spending money, I may have a go at DIY with a pot like this £8 one:

https://uk.rs-online.com/web/p/potentiometers/8427071?cm_mmc=UK-PLA-DS3A-_-google-_-CSS_UK_EN_PMAX_RS+PRO-_–_-8427071&matchtype=&&gclsrc=aw.ds&gad_source=4&gad_campaignid=20690300296&gbraid=0AAAAADkeWNMs7LFWNTNwCY-w5HxSTRT6M&gclid=EAIaIQobChMIo5utyuHfkAMVzo5QBh24XBUxEAQYASABEgIByPD_BwE

And a 3-D printed thumb wheel.

But whether doing that or purchasing one of those on line, I’m still confused about the wiring. I’ve studied the wording of the text description that you sent but it does not seem like it would work without wasting loads of radio power and/or being very quiet. I cant see how to upload pictures here (you obviously can) otherwise I’d show diagrams of what I mean.

The pic of your Continental Edison switch is interesting. Looks like lots of wires but I see that the green and pink, and the red and blue, are connected together. So in effect there are only three connections, just like the pot way of doing it.

Without wishing to sound X-Files, the solution is out there…

[Steve Kendall]

Thanks Paul,
Well it certainly is single gang. Mono radio output goes to the centre (wiper) tag, front speaker to one end tag, rear to t’other.
Bit crude, but if it works…
The centre position of the control will be equal volume front and rear, but I’d expect it to be overall a lot quieter in that position. I’ll have to experiment!
And yes please to the links of ones for sale, my searches have so far yielded nothing.

[Steve Kendall]

Thanks Paul,
That’s all very helpful. I’d never noticed that the mounting bracket is already there! So the physical mounting arrangements for pot and thumb wheel are all very straightforward. I doubt that thumb wheels that size are readily available but I might be able to get my wife to 3-D print one on her new toy!
But as far as the actual circuit is concerned, I can definitely see how the fader or pan as you call it would work if it were a two-gang pot, but much less clear how it would work as a single gang. Would be great to get a side view of the pot and its connections if possible. Ideally it would be two-gang log/antilog, but at those low resistances/high power they might be wirewound type, which would be linear (and still work ok, just not such a smooth change). Used to be an electronics injneer, I did. Long ago. Thanks for your help so far. And do please send those links.

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