GPA 604 ferrite vs alnico?

[squirrel2782]

Hi everyone I'm a newbie here who is getting ready to hopefully build a nice set of 604s. I plan on buying a set of GPA drivers, and I'm wondering if anyone can comment on the differences in sound qualities between their normal Ferrite and the Alnico version?

I have a set of Omega 6.5" alnico full range speakers, but basically I want to make sure the alnico versions are worth the almost $1000 difference.

[rogerh113]

I would be interested in hearing opinions on this as well. If anyone knows the 'theoretical' answer, that would be interesting as well.

regards -- Roger

[squirrel2782]

Agreed, opinions of the 604E Alnico from GPA seem to be quite lacking in general.

[GM]

Depends a lot on the signal chain's damping factor [DF], but the core difference is ferrite is an insulator and AlNiCo a heat sink, so obviously the former can cause rapid VC heat rise = thermal power distortion even on 'fast' transients [dynamic headroom] whereas the latter a much slower one.

This is most noticeable as a 'stretching out' of the effected BW such as an organ pipe, piano, bass string, etc., sustain and can be REALLY obvious when driven with a high output impedance amp, which is often described as from 'lush' to 'syrupy'.

Technically, heat rise lowers the driver's effective motor strength/efficiency [Qes-Qts > Qes'-Qts'] due to increasing resistance, so once all added series resistance from wiring, XO components is accounted for sets the driver's damping, which in the extreme will create a [very] audible 'smiley face' curve and why the pioneers created severely over-damped speaker systems to compensate.

As technology advanced to ever increasingly higher power, DF amps, 'bean counters' increasingly dictated speaker design, so motors were weakened [higher Qts], cheapened, hence the 'wholesale' shift to ferrite for all but the best high power, SQ systems demanded by cinema, large PA, broadcasting, etc., apps.

That said, without a complete set of comparative pink noise measurements, can't comment on any audible differences between GPA's models other than since they're apparently close enough to use many decades old cab alignments, odds are that short of using a ~matching impedance or full class A amp the differences will be subtle at best unless driven hard enough to heat the VCs up to audible distortion levels, which is unlikely in most HIFI apps.

In short, IME it's well worth the $$$ regardless of the desired degree of 'tone'/signal reproduction accuracy governed by the signal chain's DF, but then I was weaned on AlNiCo, so just a FWIW/YMMV.

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[Qts']: [Qts] + any added series resistance [Rs]: http://www.mh-audio.nl/Calculators/newqts.html

[Rs] = 0.5 ohm minimum for wiring, so may be higher if a super small gauge is used as a series resistor and/or there's other series resistance.

[Old Guy]

Part of the difference is how much does the $1000 mean to you? If you have to suffer because you spend it, it may not be worth it. My opinion is the Alnico will sound a bit better. But it won'ty be huge - more like 97% vs 100%. Sometimes 97% is "good enough".

[rogerh113]

Difficulty for many/most would be the nagging question of 'what did I miss'? I know I would. Generally I always try to do the best I can on a project, and avoid shortcuts, as I want to avoid second-guessing a decision (or a bunch of them).

I understand the cost savings issue, but the other side of the question is how much more are the Alnico worth used (when you decide to sell them)? I have been running a pair of vintage 8G for a couple of years now, and continue to be highly impressed with them. No experience with the ferrite 604 variants - to do a true comparison, I would have to pull the current alnico and put in the ferrite, since speaker cabinets and crossover variances are likely to also contribute differences in the sound (as well as the entire rest of the system).

Complex problem, but a nice one to have .......