Demagnetising

[SOOTSHE]

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?

They have only ever been used in a domestic situation & not subject to any prolonged high power usage.

Thanks in advance.
John

[magnarc]

Hi John

AFAIK if yours are ferrites(8Cs) then they should hold charge no problem.

If Alnico(8Bs), then maybe they have lost some of their charge, but since you haven't driven them hard, probably not.

Easiest way is to compare with a newly charged unit.

Anthony

[SOOTSHE]

Hi John

AFAIK if yours are ferrites(8Cs) then they should hold charge no problem.

If Alnico(8Bs), then maybe they have lost some of their charge, but since you haven't driven them hard, probably not.

Easiest way is to compare with a newly charged unit.

Anthony

Hi Anthony,
Yes, they are 8B's....so Alnico. Does driving them hard make them lose their charge?
Where do you get another new 8B to compare to??????

[magnarc]

Hi John

Alnico can exhibit decreased magnetic charge if they are pushed hard for extended periods of time.

I'd doubt yours would have been subject to high power levels, we're talking extended usage in say a cinema environment when the A7 is too small, or in PA/Rock situations at pubs.

None of my 8Bs are newly recharged, in fact they need charging, so I can't lend you one. By the sounds of things, your M19s are well and truly keeping up with the La Scala so maybe they are fine??

CPC Productions out at Ipswich - Murray Keidge, he may have one you could compare with, or may be able to measure the gauss/charge of the magnet.

Cheers
Anthony

[SOOTSHE]

Anthony,

I would say that the bottom end on the 19's, after the recap, is superior to the LS now. More tuneful & more accurate...& certainly plenty of oomph.
From this I would say that they are OK.

It's really handy to have another set of speakers to compare against.

[Altec Best]

Does driving them hard make them lose their charge?

Not in a home environment unless extremely hard for very long periods,I posed this very question to Bill at GPA a couple years back I thought my woofers were in need of re-charge 416-8B's as you are doing now.Mine were built Feb, '77 and he said my woofers in my model 19's if they were in a home environment for their entire life, they should never need re-charging.He said drivers in sound reinforcement-PA in clubs and venues were they are on tour so to speak are the drivers that typically need re-charging.I said but the woofers sound weak and he said to check the bypass cap in the X-over the 21 uF cap so that's when I rebuilt them.You know the rest

I would say that the bottom end on the 19's, after the recap, is superior to the LS now. More tuneful & more accurate...& certainly plenty of oomph.
From this I would say that they are OK.

Now this is the same exact result I had with mine. My Cornwall II's bass sounded deeper,louder,tighter after the 19 crossover rebuild not anymore "Complete Transformation" If you haven't heard a model 19 in quite sometime you got to hear one with the X-over upgrade,ground lug bypass, completely different pair of speakers performance wise. John if they have lost anything it will be minimal providing your details are accurate that they haven't been driven to extremes.Bill told me that I couldn't drive them hard enough,he said you wouldn't be able to sit in the room (Too Loud)and would turn the volume down way before they lost their magnetism.Now he could have made some money by me sending them in to recone,charge magnet etc.. :2thumbsup: But shouldn't need it. But if I insisted he would do it.

[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.