Do I need a two place or four place intercom?

[training wheels]

Hope this is the right place to be asking this question. Since I gather the use of portable intercoms would be more prevalent for PPLs, someone here may be able to offer some advice.

The aircraft in question (C172) has the normal input plugs for headsets for the two control seats, but there are no plugs for the back seat passengers. So to enable one back seat passenger to listen in on ATC and speak to the pilot and passenger upfront, would a two place intercom be sufficient (I'm assuming I only need to use the headphone jacks from the right hand seat and plug the two place intercom in to this). Or, would I need a 4 place intercom and all three people plug their headsets in to this?

[BackPacker]

I would say you need a different aircraft.

Just think about what this will look like to a passenger who has no experience in flying light aircraft. It won't be confidence-inspiring if the first thing on entering the cockpit is a tangle of wires.

[training wheels]

I would say you need a different aircraft.

Just think about what this will look like to a passenger who has no experience in flying light aircraft. It won't be confidence-inspiring if the first thing on entering the cockpit is a tangle of wires.

How it looks is of little concern as the aircraft is not for hire and not used for private flying.

Can anyone else answer the question? Perhaps I should post this in one of the technical forums...

[jxk]

You need a 4 place unit. You can hide most of the wires under the carpets and in the side pockets. The unit I've used turns itself off automatically if nothing plugged in. If I remember correctly it needs a 9 volt battery. It just needs to be plugged into one set of sockets (1 mic - 1 tel). It worked very well! The normal PTT operates it although there separate PTT switches on the unit.

[Zulu Alpha]

At present I suspect you don't have an intercom. The radio is probably wired so that each of the headsets are in parallel and you can hear each other because of the foldback.
Therefore to add any more headsets you need to add an intercom. If you plug a 2 place one into the passenger sockets then you will effectively add an extra place, however this can be fraught with difficulties as the intercom and the pilots headset may not match so the volumes and micrrophone levels could be all over the place. However, you might be lucky and it may work OK.

If you get a 4 place intercom and plug it into the pilots sockets and then plug all the headsets into the intercom sockets then you will have a good chance that all will be OK. However, beware, cheap intercoms don't cope well with different headsets. So if you want to use 3 or 4 different make headsets then you should really try the intercom with them all first.

The reason for the problems with different headsets is because cheaper intercoms do not use a separate input and output amplifier for each headset and mic. This is to save money. Thus if you put headsets with different impedances or output levels together then one may be much louder than the other.

So, the bottom line is that there isn't a simple answer and the best is to try the intercom with the headsets you want to use.

[tmmorris]

Thus if you put headsets with different impedances or output levels together then one may be much louder than the other.

though better headsets have a volume control which may mitigate this (e.g. you can turn up to the level where the quietest headset is OK and then turn the control on the louder ones down a bit).

Tim