Old speakers - less distortion?

[walpurgis]

Presumably all this apply to cartridges as well?

Some of it certainly. In fact I'd say the effects of some of the break in, loosening, age effects and varying magnet characteristics must apply to all transducers seen in Hi-Fi to an extent.

[Firebottle]

Many thanks for a most detailed response Paul

[ScottL]

Just adding a few thoughts to the above -depends what you mean by 'distortion' since there are a whole range of factors there. Depending on suspension design / materials, it usually doesn't take very long to bring a driver from factory fresh to the baseline operating window, and there it will remain for quite a long period assuming no other external force is involved. Eventually it will deteriorate, when again depending on the design & materials involved. Cones vary also; in themselves it's rare for them to deteriorate significantly, although some will eventually start to break down; those intended to flex will probably let-go sooner as they're more vulnerable to stress fractures over an extended period. Rarely an issue though -they're more likely to be damaged via an external mechanical force than as a result of normal use. If you hammer them constantly to extreme excursions of course, that will accelerate the deterioration for obvious reasons. I sometimes lost the will to live on another site (which will remain nameless) when a handful clambered onto their soap-box to proclaim that 'drivers should be able to be taken to Xmax indefinitely', which is a little like saying 'I expect my car to last as long, if I flog the nuts off it, as it would if it was driven normally'. Madness. Especially when you consider that Xmax doesn't actually mean a lot since there is no industry-standard definition for what it actually is. Last I checked, there were more than half a dozen different ways of generating a figure you could call Xmax, they all give different numbers if applied to the same driver, and very few manufacturers state which they used anyway.

Be that as it may. Driver distortion in terms of normal measurements is typically referring to frequency / amplitude response deviation from what it was designed to have, and harmonic distortion, which is affected by cone / suspension resonances and the motor design. THD, although popularly noted, is generally worthless without the individual plots since without those, you've no way of knowing what order the distortion is, where it is, how much it changes with drive level etc., all of which are significant elements in the basic character. Some of these will be affected with driver age -either through the moving components moving out of spec through deterioration with age / use / other environmental effects, or the magnet losing some strength. Depends on how well it's been handled / treated, but as a rule, it's more likely than not that an AlNiCo magnet will have lost some strength over time & require re-magnetising to bring back spec. Ferrite tends to be quite stable, likewise the rare-earth types. Something to look out for with some vintage speakers (as in speakers rather than raw drive units) is damping material from the box getting into the driver basket, particles in the magnetic gap etc. It's more of an issue in the US, since it was more common there to staple thin layers of damping material across the rear of the driver in reflex boxes, adding more layers until a basic click test indicated the alignment was properly damped, without [excessive] ringing. A very sound policy on the whole, but it does mean that over the years, fiberglass strands (the most popular type of material used) had more opportunity of getting into the driver, which doesn't do it many favours.

That apart -as was noted, if electrolytic caps were used in the crossover, they're likely to have dried out & moved away from the design value; generally its better to replace like-for-like if you don't know what the original transfer functions / acoustic slopes were and want to keep it reasonably 'original' as it's quite possible that the ESR of the cap was accounted for in the filter design -it almost certainly will have been in a quality speaker. Otherwise, you either have to keep your fingers crossed, or measure the impedance, phase & frequency responses of the drivers in the cabinet & design a new filter. Cabinets, if they haven't been subjected to abuse, are usually OK & rarely have any issues other than possibly some leakage if a glue-joint has failed, which is easy enough to fix. If it is a type with a screw-on baffle, I'd be wary of making any major changes unless a gasket is obviously perished, as a small amount of leakage may have been accounted for (or even in a handful of cases intended).

[awkwardbydesign]

That's not exactly what it says here:

http://www.rare-earth-magnets.com/co...n-Handbook.pdf

That's useful, thanks.

[Barry]

I have to confess I've never understood the desirability of Alnico magnets over rare earth types. Surely a magnetic field is a magnetic field regardless of source? Can someone enlighten me - and whilst we're at it, explain why field coils are thought by some to be the best of all?

[struth]

Supposedly greater immunity to flux modulation, greater heat stability and greater suitability to shielded applications..personally i like em as they sound good.

[Barry]

Supposedly greater immunity to flux modulation, greater heat stability and greater suitability to shielded applications..personally i like em as they sound good.

Can you explain what you mean by flux modulation Grant? Surely all permanent magnets are saturated. Are you saying the flux created by the speaker coil tends to demagnetise the magnet?

[struth]

I think ferrite mags had a copper shorting ring around the pole to make them respond better. Ferrite without these doesnt fair so well flux stability wise, or so i,m told. Ferrite is crap stuff but because of all the work done on them they are pretty much as good now..also there is lots more ferrite around..think the availability of alnico magnets stopped for a while( maybe due to a African war but not sure)
If you put too much current through alnico it can demagnatise. More of a problem now although this too can be enginnered out, but its very expensive so ferrite wins... Doesnt sound so good imo though.