Speaker question

[Mick B]

Lately I have become interested in all forms of water drop photography and today while experimenting with my latest crazy idea I think I have blown up an old stereo speaker. Not knowing much about speakers am am asking for some help. Basically what I did was remove an old 8 inch diameter speaker from the speaker box, hook it up to the old amp, sit it facing upwards on my work bench, completely cover it with glad wrap and place some red coloured water in the speaker cone and start taking photos while some music was playing through it. (It is an 8 ohm speaker) I took several test shots just to get an idea if it might work.

Then I started experimenting with different amounts of water, different sound volumes and different music looking for more bass to get the water bouncing more. I was just starting to see what worked best and the next thing you know, the volume went down, so I turned it up a bit more and then it just stopped working all together. Would this be something to do with it being an 8 ohm speaker, or the weight of the water sitting it it or what ? I only had about 1/2 a cup of water in there (which wouldn't weigh much) and the glad wrap stopped any water from getting into the speaker.

I still have another speaker left and they are just old ones that I haven't got around to throwing out yet, but I really want to try and get some nice shots without blowing up another one !

[Tjfrnds]

Hey Mick, I have no idea bout speakers, but can't wait to see some of your shots!

[jev]

Are you sure it's the speaker and not the amplifier?

[Mick B]

Hey Mick, I have no idea bout speakers, but can't wait to see some of your shots!


Yeah me too. I'll have another go soon !

[Mick B]

Are you sure it's the speaker and not the amplifier?

Definately not the amp because the other speakers work fine. I checked out the dead one today wit a multi meter and there is a real fine copper wire broken somewhere inside it, so now I have another big magnet to play with. I think the problem was that with the extra weight of the water, it had to work too hard to move it and probably used a bit too much power or something like that. Never fear ........... I still have another old speaker to try yet, but this time I won't use as much water.

[fillum]

Mick, did you play any Celine Dion?

[fillum]

OK, better post a serious answer. My memory is pretty vague on this stuff but I think you have probably blown the speaker.

I doubt the problem relates to the impedance (8 ohm) of the speaker. The speaker impedance generally needs to be matched to the amplifier - if your amp is a home stereo type then 8 ohms would be normal. Serious problems can occur when the speaker impedance is less than the required impedance of the amplifier, but the damage is usually done to the amplifier rather than the speaker. I think this is more of a problem for valve amplifiers rather than solid state.

Speakers can be damaged when an amp is pushed towards its limits - ie having the volume cranked (and having the bass turned up adds to the problem). It's not the volume itself but that the signal to the speaker becomes distorted ("clipping") so that the speaker cone is unable to move efficiently, causing the coil to overheat and burn out. You would generally hear the sound as being distorted but perhaps in your case the actual speaker volume was reduced by the water sitting in the speaker cone. It might even be (as you suspect) that the weight of the water, although not heavy, was sufficient to prevent efficient movement of the speaker cone and this caused the coil to overheat and fail. (Maybe do some googling on "speaker clipping" if you want more info...)

As jev points out it could also be a problem with the amp. You could easily test this with your other speaker.


(Not sure if I have helped much...:))


Cheers.

EDIT: Obviously hadn't seen your post above before I posted this...

[jev]

As fillum says, usually speakers die because of an amp being not strong enough (distortion due to clipping indeed is a great way to damage speakers!). If the weight of the water had been the problem, the speaker's cone would most probably have been sheared. A burned wire though I suspect points to to a large DC component in the signal generated by your amplifier. Did you remove the speaker from its box without using the electronics? There should've been a filter in there - if not I'm stumped.

If you don't care about sound quality, a simple capacitor in series to the speaker should remove the DC component.