A Question For Audio People

[Jonj1611]

Right this is driving me around the twist, my car door speaker has been sounding like a tweeter so I removed it to take a look, these speakers are known to rust between the magnet and whatever that attaches to. The cone does not move, not one bit so I ordered a second hand replacement from eBay and that has arrived in poor condition and is exactly the same.

Now my understanding is the cone needs to be able to move as I am guessing that's how a speaker works, you should be able to move it if you push against the cone, even just a bit, mine and the replacement is rock solid.

But the eBay seller is having none of it saying that's how they are but I don't think thats the case.

Yes I could take another speaker out to have a look but just as quick to ask the question, the speaker has to move doesn't it?

[g8ina]

Can you take a small video of you pushing the cone and up it to Dropbox or similar ?? Yes, the cone *is* supposed to move, but only if its a mid range or woofer, it is v unlikely you would see any movement in an actual tweeter

[Jonj1611]

Hi g8ina, I probably didn't explain myself very well, it sounds like a tweeter, its actually an 6" car door mid range speaker. I can do a video but its completely solid, its off a Land Rover and they are known for rust in the magnet gap.

Just trying to tell this person on eBay that the cone is supposed to move is a nightmare. I expect he has a load of rusty ones which is why none of them move.

[g8ina]

ahhh OK, then yes, push it..... Complain till yer blue in t'face etc .... good luck.

[Jonj1611]

Just wanted to make sure I wasn't going insane and there was some type of speaker where the cone doesn't move

[matts-uk]

Hi g8ina, I probably didn't explain myself very well, it sounds like a tweeter, its actually an 6" car door mid range speaker. I can do a video but its completely solid, its off a Land Rover and they are known for rust in the magnet gap.

Are they known for rust in the magnetic gap or are they known for rusty magnets? I am asking because rusty magnets are really common but rust in the magnetic gap is an unusual failure. Typically the magnetic gap is made by pressing a non ferrous former into the magnet.

A quick and dirty speaker test is to measure the DC resistance of the voice coil, using a multi-meter to probe the speaker tags. The resistance should be a little under (<1 Ohm) the rated impedance (usually stamped on the speaker). A 4 Ohm impedance speaker should read about 3.7 Ohms and 8 Ohms impedance about 7.4 Ohms. Much less or much more than those figures, the voice coil is toast.

The definitive test is to hook the speaker to an amp you know works and play a low frequency signal, say 50Hz, at low to medium volume. Don't assume the amp in your car is working on both channels. Running a speaker with a jammed or shorted voice coil for too long can blow the output transistors in the amp.

Just trying to tell this person on eBay that the cone is supposed to move is a nightmare. I expect he has a load of rusty ones which is why none of them move.

Rusty speakers that work perfectly fine are very, very common.

On a typical paper cone dynamic speaker pushing on the cone in the wrong place has a good chance of breaking the cone before you feel the voice coil move. There is usually a domed dust cap over the voice coil. Put your fingers either side of the dust cap and you may be able to feel the edge of the voice coil. Anyhow, press at the edge of the dust cap where it mates with the cone, gently but firmly. I would expect to feel the voice coil move 1/2 to 1mm without doing any damage.

[Jonj1611]

Thanks for the comprehensive reply, I will take a look at the resistance.

Seriously this thing does not move at all, I mean not even a mm

[matts-uk]

Thanks for the comprehensive reply, I will take a look at the resistance.

Keep in mind an Ohm test is a guide - Most (not all) voice coil damage involves a short or open circuit.

Seriously this thing does not move at all, I mean not even a mm

If there is no movement at all you need a new speaker.

It is possible for rust to sieze up the voice coil when a speaker is left standing in a damp environment for a long time - It just isn't as common as people think. More often voice coils fail due to overheating. The insulation breaks down or the glue used to build the coil melts and sets solid when the power is turned off. Whichever way the coil is destroyed the remains can end up jammed in the magnetic gap.

OEM automotive speakers are often made from cheap(er) materials, over-amped and prone to overheating. Playing 'loud and low' rave music will age a cheap car speaker much faster than listening to The Archers.

[Jonj1611]

As I had two speakers I took one apart, like completely, it all looks amazing clean strangely enough. Under the "dome" bit of the cone I wasn't sure what to expect but turns out its just an empty hole going to down to the magnet, looked like new in there so I proceeded to remove the magnet from the bottom of the speaker, was easier than I thought, just pulled off, wasn't even stuck down or anything. With the magnet removed the speaker was free to move up and down as I expected it to.

Actually last night I took off the other door card and that speaker moves freely in and out when gently pushing on it and thats the speaker that works, anyway put the magnet back on and its frozen solid again.

Now i'm just confused.

Computers I can do most things with, speakers seem a black art now lol

[Zak33]

Thanks for the comprehensive reply, I will take a look at the resistance.

Seriously this thing does not move at all, I mean not even a mm

take out the one that DOES work and compare it

try each speaker on the door wiring that DOES work...

[Jonj1611]

Yes did that, the one that does work the only difference is the cone is free to move, the working speaker works in the non working side so speaker for sure.

[Zak33]

and can you get something "new" from a speaker brand to fit it instead? Because nearly every speaker is a default size.

[Zak33]

Get it photographed and post it up here. Nice clear photos from above, the side etc. Hold a ruler up for measurents visuals.

It'll likely just be a 6" speaker than you're better off buying brand new and will likely out shine the old ones

https://www.amazon.co.uk/JVC-CS-J620...s%2C122&sr=8-3

that sort of thing £15

[Jonj1611]

I will get some pics done. They are Harman Kardon speakers, you can get alternatives but means drilling new holes etc

[matts-uk]

As I had two speakers I took one apart, like completely, it all looks amazing clean strangely enough.

Not strange...Normal

Under the "dome" bit of the cone I wasn't sure what to expect but turns out its just an empty hole going to down to the magnet, looked like new in there

The empty hole is the centre of the voice coil former. So far, so normal.

so I proceeded to remove the magnet from the bottom of the speaker, was easier than I thought, just pulled off, wasn't even stuck down or anything.

Not normal. I would expect the magnet assembly to be securely attached to the basket. Press fitted or riveted, usually.

Now i'm just confused.

There are only 6 or 7 components in a speaker but it is surprising how many different ways manufacturers can find to put them together. It will be interesting to see how your speakers are assembled. Logik 7s by any chance?

Computers I can do most things with, speakers seem a black art now lol

It sounds like you have a mechanical fault displacing the voice coil. When the speaker is jammed, is the speaker cone extended?

I was made to do electro-mechanical before they let me near digital. Speakers are easy. Radio (RF) is the black magic

[Jonj1611]

Thanks for the reply, always great to have people who know there thing, I am going to get some pics done today and hopefully will put words into pictures.

When the speaker is jammed the speaker cone is fully out it would seem as when I remove the magnet it will move in and out freely.