Dodgy driver, couple of years gigging fortnightly.
And we haven't done a bloody thing all day...
Hmmm, is this indicative of finding the issue or is it just a matter of damping something else?
"Nice and tight" isn't necessarily the way.. but firm and evenly torqued. In addition the baffle surface should not be warped. Front panel vibrations might be a concern there, and that does go both ways. Sometimes a soft mount is preferrable.
My earlier thoughts were toward an overheated coil with crispy insulation. Might be tricky to measure with just an ohmmeter.
Can you (gently)(eg using index fingers and thumbs) manage to run the excursion without scraping, which would signify that the issue is location, rather than swelling/physical distortion..
You never know what the problem is in Engineering.
But at a certain point you just give up! Sometimes things are broken and unfixable.
If I have understood this thread your 8" midrange is broken.
I'd buy a new one:
Monacor SPM-205/8 Size 200x200mm
Probably works. For £35 including tax, I'd give it a go. I know. It is painful to put your hand in your wallet.
But at a certain point you just give up! Sometimes things are broken and unfixable.
If I have understood this thread your 8" midrange is broken.
I'd buy a new one:
Monacor SPM-205/8 Size 200x200mm
Probably works. For £35 including tax, I'd give it a go. I know. It is painful to put your hand in your wallet.
OK, I got off track; sorry. What is the frequency band these mids operate in? There are some full range drivers in that size that might do very nicely if you can't get them rebuilt. There are people that do "re-coning" but it isn't the cone obviously. BUT, some of these guys are very skilled at disassembly and reassembly. Maybe someone could replace the VC and former and keep the original surround and spider??? Might be a stretch but ask around anyway; it would be a shame to have to give up an original classic unless there were no other options.
if the OP is hell bent on keeping it original then repair of the voice coil via a good reconing service is the way to go.
i'd be on checking the x-over for a fault if i was certain the driver never was driven hard enough to reach thermal limits, as past experience tells me that's the only condition that can soften the glue to develop that sort of problem, to wit just the other day i pulled an old pair of Heathkit AS27's that i have where one of the woofers suffered from a loose voice coil it was a tedious job disassembling and reassembling/reglueing that driver but in the end i was successful and saved 250 CND + shipping!
i'd be on checking the x-over for a fault if i was certain the driver never was driven hard enough to reach thermal limits, as past experience tells me that's the only condition that can soften the glue to develop that sort of problem, to wit just the other day i pulled an old pair of Heathkit AS27's that i have where one of the woofers suffered from a loose voice coil it was a tedious job disassembling and reassembling/reglueing that driver but in the end i was successful and saved 250 CND + shipping!
Okay, so the bloody thing does it unvaryingly no matter what I do with screw tightnesses, and when not even mounted to the baffle, so I don’t reckon there’s any warping issues at play here.
I’m keen to keep these things original as they are rare and fine examples of mid seventies English speaker design. It would be the ideal scenario to have the drivers resorted but I, unsure of who could do this. Wembley loudspeakers were suggested but they don’t answer their phone or their emails it seems.
Failing that, those Monacor look fairly similar and would be a cost effective solution provided they’d work. Thanks Steve. I’ve posted on audiokarma looking for replacement suggestions for these in the recent past but to no avail. I see they only go up to 5khz. I’m wondering if that’s high enough to cross over nicely to the tweeters. I actually just ran a sign wave generator and listened and it does sound like mine are set to crossover around that point. So would these potentially just drop in a straight replacements for what I think are Audax hd20 25b H ? Have you had experience of these replacing drivers of the type I have here?
Also, checking the crossover, there is that 30uf cap that made contact with my solder iron long enough for it to be melted on the outside. I forgot about that. Perhaps it’s knackered right enough and so I’m going to swap drivers to see if the noise follows the driver or stays on that speaker. Should have tried that already really. Think one of you already suggested that.
Will report back. Even if it’s the crossover, and I can eliminate this buzz with a new cap, the drivers still have shrunken surrounds, which although there’s nothing glaringly obviously wrong with the sound, surely must be getting hindered in efficiency and dynamics and detail etc by the surrounds being less flexible than original. Would be really nice to have them replaced, but if it’s not going to be possible, new drivers could be great if there’s something suitable.
I’m keen to keep these things original as they are rare and fine examples of mid seventies English speaker design. It would be the ideal scenario to have the drivers resorted but I, unsure of who could do this. Wembley loudspeakers were suggested but they don’t answer their phone or their emails it seems.
Failing that, those Monacor look fairly similar and would be a cost effective solution provided they’d work. Thanks Steve. I’ve posted on audiokarma looking for replacement suggestions for these in the recent past but to no avail. I see they only go up to 5khz. I’m wondering if that’s high enough to cross over nicely to the tweeters. I actually just ran a sign wave generator and listened and it does sound like mine are set to crossover around that point. So would these potentially just drop in a straight replacements for what I think are Audax hd20 25b H ? Have you had experience of these replacing drivers of the type I have here?
Also, checking the crossover, there is that 30uf cap that made contact with my solder iron long enough for it to be melted on the outside. I forgot about that. Perhaps it’s knackered right enough and so I’m going to swap drivers to see if the noise follows the driver or stays on that speaker. Should have tried that already really. Think one of you already suggested that.
Will report back. Even if it’s the crossover, and I can eliminate this buzz with a new cap, the drivers still have shrunken surrounds, which although there’s nothing glaringly obviously wrong with the sound, surely must be getting hindered in efficiency and dynamics and detail etc by the surrounds being less flexible than original. Would be really nice to have them replaced, but if it’s not going to be possible, new drivers could be great if there’s something suitable.
Put the meter on Ohms. Is it auto-ranging or do you select the ranges manually? A "normal" capacitor will "charge" under the influence of the Ohm meter battery. It might start showing very low resistance or maybe even a short circuit at the very beginning but then the resistance should rapidly rise; almost to infinity. Use the highest range setting for Ohms if you set it manually; if it is a auto-range type; you will see it go through many ranges, low to high, as the capacitor charges. If it stays at a lower resistance reading (and does not charge) then you have a problem for sure.
https://www.hunker.com/13414457/how-to-test-a-capacitor-with-an-ohm-meter
This explains it. It is for a motor start capacitor but the idea is the same.
https://www.hunker.com/13414457/how-to-test-a-capacitor-with-an-ohm-meter
This explains it. It is for a motor start capacitor but the idea is the same.
It as oldspkrguy details...
Select a 'low' ohms range. That means one that accurately measures resistors of say 100 ohm and lower. A short will show as 0.00 on the display (or very very low). It is the reading you get when you short the leads together.
A 'high' ohms range can be used to test for leakage. This is the range you might measure a 1Meg resistor with.
See what you get...
Right. So I’ve swapped them around, and the sound followed the driver, so the crossover isn’t to blame, although I’d still like to know how to test that cap all the same for peace of mind.
So send away to be restored, or replace.
What does anyone reckon on these Monacors as replacements for Audax HD20 25b H?MONACOR: SPM-205/8
And/or does anyone have a decent recommendation for a good place to send these to be restored?
So send away to be restored, or replace.
What does anyone reckon on these Monacors as replacements for Audax HD20 25b H?MONACOR: SPM-205/8
And/or does anyone have a decent recommendation for a good place to send these to be restored?
I know a guy in North Carolina but that would way too costly! Sometimes the musical instrument stores have speaker re-coning guys for blown guitar amps. They would NOT likely however have parts for your home HiFi drivers BUT, they may know people that do.
Yes, I forgot about low Ohms range for leakage and dead shorts.
Yes, I forgot about low Ohms range for leakage and dead shorts.
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