Are these speakers worth refurbing?

[Reid Malenfant]

The speakers had one flaw that was identified in measurements at the time, and I had found mildly audible: there was a response depression in the presence region, between 2 and 3 kHz, and a prominence around 10-15 kHz. The latter would probably be welcomed at my age, whereas the former was a bit unpleasant and I had devised a couple of electrical workarounds back then (playing with capacitive loading for the cartridge, or with the Sugden's comprehensive tone controls).

Hi Kai, i think you'll find this is probably due to the crossover & drivers & it may be rather difficult to cure

It sounds as though it's around the crossover region which is why i suspect it's an interaction between the tweeter & woofer being out of phase with each other. You see while it's difficult but none the less not impossible to get the drivers in phase there is one rather massive problem to overcome. That problem is the distances that the voicecoils are from your ear...

What tends to happen near the crossover point if this isn't taken care of is that the way the two drivers interact beams the sound down towards the floor rather than straight out in front of the speaker. I reckon this is what is causing the dip in response, try it out & see if that dip disappears if you move nearer to the speaker & move your head up & down in front of it with a nice load of material that is in the region affected

[Kaiman]

Thanks, Mark, I'm still in "idea-gathering" mode anyway, so there's no rush. In due time I think I'll be able to do some gated measurements using my omnipotent Metric Halo. It seems likely to me too that the response dip is a cancellation of sorts, because it looks too sharp to be anything else. Two way speakers with an 8''er are tricky anyway. I think I should try to fit a slightly larger tweeter and use a lower XO frequency, but will a larger tweeter fit the hole? Wish I knew at this stage.

I need to find out what the crossover topology is, above anything else. Second order filters are easier to fix phasewise, as you say,; fourth order are unlikely to have been used; third order ones start with phase at quadrature, which means that they are hardly fixable: usually they either work or they don't.
If I'm not mistaken, the picture Mothman took shows six capacitors, three resistors and three coils (two of which are aligned next to each other, rather than being at right angles!). Could be second or third order filters, or both, with or without baffle step compensation, who knows?

[Reid Malenfant]

The only passive way of fixing these things tends towards adding a second bass mid driver above the tweeter, the D'appolito arrangement (MTM).

Doesn't really help you though!

You'd need to dig the crossover out & draw the circuit out to see what it's doing, as i'm sure you aware the crossover could well be second order but with extra components to tailor some midrange peaking due to the intrinsic breakup modes of the bass/mid driver..

Like you say, you need to dig deeper