Repair or replacement Cessna Speaker?

I did a google on

loudspeaker with 2 coils

and found that these are basically speakers with – no kidding – 2 coils, and the idea is that you can connect them in series or parallel. If both coils are say 4 ohms then you can get 2 ohms or 8 ohms.

Funnily enough I had never seen one before

Yours are clearly wired in parallel, with the return being the eyelet terminal

which goes to the airframe (bad practice to send speaker current via the airframe but that’s a separate issue).

I can’t find any data on this P/N but if you put an ohm-meter across either blue or green, and the ground (both should yield the same resistance) that will tell you what it is.

It could be that the purpose of the 2 coils in this case is to deliver some level of redundancy. Either the blue or the green will generate the (same) sound. So if e.g. the speaker was used for either a stall warner or for a gear warner, either will work unless the respective coil is damaged.

Practically the same level of redundancy would be achieved with a single coil speaker fed from the secondary winding of a transformer, with its two (identical) primary windings connected to the two sources. Transformers (and magnetics in general) are extremely reliable especially if vacuum varnished.

No, it’s much worse than that (guess how I know). One coil is wired to the stall warning and the other to the gear warning. Whatever the original intent of the speaker design, that’s how it’s used in the 182RG.

If you want to be squeaky clean legal, you have no choice but to pay Cessna’s outrageous price (or find another source of supply, and good luck with that, and even then since it doesn’t have the Cessna p/n you wouldn’t really be legal).. Of course there are people who could argue that the chance of anyone ever dismantling the roof to determine that your speaker installation, even though it works perfectly, is not the original Cessna part, is extremely low. You may think that, but I couldn’t possibly comment.

Putting a new diaphragm in a speaker is no big deal. Many, many moons ago I was involved with things like that (very, very big ones…) and we had that done on a regular basis. Too long ago to be able to send you somewhere, but totally doable. A Google should bring up some shops in your area. Look for something like ‘professional sound equipment’ or ‘studio speaker repair’, ‘PA Systems’, etc, etc.

even then since it doesn’t have the Cessna p/n you wouldn’t really be legal

We could debate that one

For N-reg, if you look up the flow chart for Minor v. Major alteration, you find the words “basic change to the electrical system” and putting in a different brand of 2-coil speaker would not be that. It’s like changing a Gill battery for a Concorde one – another long forum debate. Everybody I know has just put them in. I would agree the transformer method might be a bit more debatable…

For EASA-reg, I don’t know. I don’t even know where to look for the regs. There are provisions under CS-STAN but only if it is not a “critical” part. Maybe @wigglyamp knows.

As for getting the cone repaired, you get into another argument which is whether the repair shop can issue an 8130-3 (for N-reg) or (for an EASA-reg) an EASA-1 form.

These forms can be issued only by 145 companies but it isn’t necessary for an N-reg because an A&P is authorised to inspect a part and declare it airworthy, but you sure get GB of forum debates

What @172driver wrote – just get the diaphragm exchanged. Worst case scenario is you end up with an owner produced part. I don’t think you need an 8130-3 for that, just a logbook entry and blessing from A&P/IA.
I know you used the magic words (CAMO) but surely there is a provision for OPP in the EASA regs too. If not, perhaps leave a plate nice cookies and some milk for your hangar elves? Very useful creatures they are.

FlyingDutchman wrote:

So you are basically saying that a regular single coil speaker in the right way connected could be a sufficient replacement as well?

They’re not necessarily just wired in parallel. There may be two separate sources. Without further investigation or a reliable schematic, you can’t jump to that conclusion.

You could put your meter across the green and blue wires (ie., the airframe side, not the speaker side) and see what you get. If they really are joined at the other end, you will get close to a short circuit.

A small speaker like that with dual voice coils is quite unusual. It’s very common (almost routine) on subwoofers.

Provide some dimensions (diagonal screw fixing distance, and depth from front to back?

Peter wrote:

For EASA-reg, I don’t know. I don’t even know where to look for the regs. There are provisions under CS-STAN but only if it is not a “critical” part. Maybe @wigglyamp knows

There’s nothing specific in EASA that would allow replacement with an alternative part number without approved modification paperwork unless the new part was a PMA’d item and the aircraft was listed on the PMA certificate.

One route would be to use a commercial part without a Form 1 per 21A.307 (c) but that requires the part to be:
2. manufactured in conformity to applicable design;
3. marked in accordance with Subpart Q;
4. identified for installation in the specific aircraft;

In the past I’ve use Quam replacement speakers but don’t recall a dual-coil version like this, so you may be stuck with using a new one from Cessna.

This, although in the FAA context, might be of help: