Demagnetising

[Earl K]

Do all bass speakers need to be demagnetised after a certain time period?
My 19's were built in 1978 & I can't really hear any decrease in bottom end performance....or have I just got used to the sound?

- ( FWIW ), the proper term here is "re-magnetizing" .
- Demagnetise ( or demagnetize ) , means ; to "lose magnetic charge" .


- Anyways, to answer your question, one first notices a loss of efficiency in the mid-band which actually has the effect of making the bass frequencies a bit more pronounced ( by comparison ) . FWIW, a lot of people may like this change of bass to mid re-balance .

- Additionally, I'd be somewhat cautious about having your alnico woofers remagged . Panos 416-8A dilemma should serve as a cautionary tale about what goes wrong when a tech re-mags alnico if the machine is set to the wrong polarity .

- As a "due-diligence" self check, I'd recommend that one should first verify ( with a 9 volt battery ) the polarity of ones' woofers before handing them over for re-magnetising . If they come back with the polarity switched then ( at least ) you have a good negotiating start point ( to remedy the situation, as was Panos case ) .

<> cheers

[Cal Weldon]

- ( FWIW )
- As a "due-diligence" self check, I'd recommend that one should first verify ( with a 9 volt battery )

I always used a AA or other 1.5V. Too scared to use a 9V, is that unfounded?

[Panomaniac]

9V is OK, and a lot easier to see! I don't use it on tweeters.

[Cal Weldon]

I don't use any battery on tweeters, I'm just too chicken and on woofers, the things seem to jump out of the basket with a 1.5V hence my fear of a 9V. I was just wondering in case I'm somewhere and have this incredible urge to zap my drivers with a battery. Earl does it but I am just being cautious, that's all.

Curious minds want to know.

[Earl K]

- I only use the battery method for cone drivers ( woofers ) / never on compression drivers.

- For compression drivers I use something like the following ;



- My checker is actually an older version of LA Audios' PC90 ;



<> cheers

[Altec19]

Lets say we're going to apply 1 Watt of power to a speaker with a DC resistance of 8 Ohms.

According to a variation of the power formula:

V = square root (PR)

where

V is Voltage
P is power in Watts
R is DC resistance in Ohms

we have

V = square root (1 x 8)
V = 2.8 Volts

As another check let's say we apply a 9 Volt battery to an 8 Ohm speaker where:

P = V^2 / R

we have

P = 9^2 / 8
P = 10.125 Watts

Is 10 Watts too much? Personally, I wouldn't do it to a tweeter but I'm fine testing a woofer like that.

I would also make just a momentary connection, only enough to verify cone movement and then quickly disconnect.

[Cal Weldon]

I would also make just a momentary connection, only enough to verify cone movement and then quickly disconnect.

I think that's the key. Remember you are running DC to it so you're not getting any back and forth to assist in the cooling. Also I think you have to take into account the available current available from the battery no?

[SOOTSHE]

- ( FWIW ), the proper term here is "re-magnetizing" .
- Demagnetise ( or demagnetize ) , means ; to "lose magnetic charge" .


- Anyways, to answer your question, one first notices a loss of efficiency in the mid-band which actually has the effect of making the bass frequencies a bit more pronounced ( by comparison ) . FWIW, a lot of people may like this change of bass to mid re-balance .

- Additionally, I'd be somewhat cautious about having your alnico woofers remagged . Panos 416-8A dilemma should serve as a cautionary tale about what goes wrong when a tech re-mags alnico if the machine is set to the wrong polarity .

- As a "due-diligence" self check, I'd recommend that one should first verify ( with a 9 volt battery ) the polarity of ones' woofers before handing them over for re-magnetising . If they come back with the polarity switched then ( at least ) you have a good negotiating start point ( to remedy the situation, as was Panos case ) .

<> cheers

Thanks