Recharging Alnico/Ferrite magnets

[Ralph856]

Epic fail!

You just summed up my life in two words.

[MikeBrewster77]

I am not sure that I can judge the effects of a couple of dB variation in sensitivity over a particular frequency range. If someone can, I'd like to "hear" about it.

I think I can . In fact, I just posted only a few days ago about a quick and dirty tweeter swap I did and how the results were disastrous. It was apparently only a few dB variation that clearly made one combination work extremely well, and another sound completely unbalanced, bright, harsh, etc. If a few dB's of sensitivity is enough to make that much of a difference through design, I don't see any reason one wouldn't encounter similar results as a result of natural deterioration and time. Then again, maybe I'm just naive, that's not an analogous comparison, and I'm completely missing something here?

I went ahead and deleted the measurements/modeling post since it was pointless.

Disagree that it was pointless - in fact, aren't measurements taken and modeling performed to replicate and/or validate what one will actually hear? I for one find it reassuring to know there's some quantifiable science behind the manufacturer's recommendations on how to maintain my gear. But maybe that's just me...

[MikeBrewster77]

You just summed up my life in two words.

Dude - stay away from sharp objects...

[Ralph856]

You just summed up my life in two words.

Lol, only joking.

[Mr. Widget]

It's too bad.


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[Mr. Widget]

I noticed something interesting. The 2404s I had sitting on the top of the cabinet I haven't used for over a year, was magnetically sticking to everything; and the 2407 wouldn't stop sticking to it. But the old 2402 driver I'd been using with the mini wood Smith horn as a tweeter on my La Scala for a few years wouldn't stick to anything!

Simple answer really. The old 2402 is an alnico motor and the other two are ferrite. The old JBL alnico motors are inherently magnetically shielded... none of their magnetic energy is wasted, it is all focused upon the VC gap.


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[m8o]

Simple answer really. The old 2402 is an alnico motor and the other two are ferrite. The old JBL alnico motors are inherently magnetically shielded... none of their magnetic energy is wasted, it is all focused upon the VC gap.

I'm such an amateur...
Lol... Much thanx. It's very good to know there's nothing wrong with the drivers in that case.

[Beowulf57]

I think I can . In fact, I just posted only a few days ago about a quick and dirty tweeter swap I did and how the results were disastrous. It was apparently only a few dB variation that clearly made one combination work extremely well, and another sound completely unbalanced, bright, harsh, etc. If a few dB's of sensitivity is enough to make that much of a difference through design, I don't see any reason one wouldn't encounter similar results as a result of natural deterioration and time. Then again, maybe I'm just naive, that's not an analogous comparison, and I'm completely missing something here?

Thanks Mike...this is interesting. I realized that yes, I can hear small differences in the regions where the ear is most sensitive (midrange particularly). I'm curious as to why greg timbers' post seems to imply that the demagging effect is largely restricted to certain types of woofers? I can also imagine that two similar drivers could have a dB or two of difference in sensitivity without it being a demagging problem unless one matched them for this parameter.

Disagree that it was pointless - in fact, aren't measurements taken and modeling performed to replicate and/or validate what one will actually hear? I for one find it reassuring to know there's some quantifiable science behind the manufacturer's recommendations on how to maintain my gear. But maybe that's just me...

I also do not think it was pointless...and still wonder about the degree of sensitivity loss in a woofer that is audible...i.e., JND (just noticeable difference)?

[spkrman57]

It was not pointless, and I'm sure the group of us who did read and follow that post did not think it was wasted!

I kind of understand where you are coming from with regards to how some folks interpet some postings here.

But there are some of us who look forward to the info!!

Thanks,

Ron sends.......

[Mr. Widget]

...and still wonder about the degree of sensitivity loss in a woofer that is audible...i.e., JND (just noticeable difference)?

"Noticeable difference." That is a your mileage may vary situation... for some people, a speaker with a blown tweeter is acceptable, for others they can hear a significant change when swapping a cable... significant enough to drop big bucks.

I don't think anyone can answer that question for you. That said, a dB or more change over a fairly broad frequency range is quite audible. How significant that is will be determined by the listener.


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[speakerdave]

On the LSR32 there are two settings for the treble. The difference is 1 dB.

[Beowulf57]

I am asking about the audibility in the low end...but okay, if no one has experience to report: that's all folks.

[Mr. Widget]

I am asking about the audibility in the low end...but okay, if no one has experience to report: that's all folks.

To me it is extremely audible. For someone else it may be too subtle to care about... The graph that 4313B posted showed it quite clearly... thinner sounding and rather lacking of taughtness.


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[spkrman57]

I had a pair of JBL 2205B's (alnico) that were very shy in the midrange and a bit boomy in the LF band.

I bought these from a individual who ran them in a high powered PA rig, I'm sure they suffered some magnet strength loss.

I measured the drivers on woofertester (the original one that ran on DOS) and it showed the Q factors were much higher than factory spec.

Just one example......

Regards, Ron

[toddalin]

I can also imagine that two similar drivers could have a dB or two of difference in sensitivity without it being a demagging problem unless one matched them for this parameter.

Very true. I have an original unmolested 075 that that is about 2.5-3 dB louder than my recently remagnetized and thouroughly inspected 2402s. Does this mean that any of them are defective? Hardly.

Just look at the variation in dcr values to recognize that drivers are bound to have differing dB levels.

As for the experience of having AlNiCo woofers and drivers remaged, yes, I have first hand experience (with WT-2 testing data) that I could relate..., but won't.