Hi there,
Just as the title says, one driver, it’s the midrange, has a very irritating buzz about it, producing harmonics, and resonant at certain frequencies. Piano seems to really set it off. A piano can sound almost like a the distorted music box recording they used to blast out of ice cream vans. Very annoying.
I just recapped my the crossovers, but I can’t think why that would be the cause.
Did I understand correctly that low bias in the amp can cause this?
Thanks in advance, Dave
Just as the title says, one driver, it’s the midrange, has a very irritating buzz about it, producing harmonics, and resonant at certain frequencies. Piano seems to really set it off. A piano can sound almost like a the distorted music box recording they used to blast out of ice cream vans. Very annoying.
I just recapped my the crossovers, but I can’t think why that would be the cause.
Did I understand correctly that low bias in the amp can cause this?
Thanks in advance, Dave
If it is just one driver in the pair then my first thought is that you might have 'dropped' a bit of something magnetic into/onto the speaker and it has found its way to the pole piece where the coil enters the 'magnet'.
Well worth a look with a good torch. It could be a burr of metal off a screw the size of single iron filing... anything like that.
Crossover distortion has a very unique sound and would be apparent with the tweeter as well as mid.
I'm assuming it is just one speaker affected and that this didn't happen before you worked on them?
Other possibilities are you have an incorrect value part somewhere and are feeding the midrange with to much bass content. Maybe a cap or resistor value out by a factor of 10 etc.
Well worth a look with a good torch. It could be a burr of metal off a screw the size of single iron filing... anything like that.
Crossover distortion has a very unique sound and would be apparent with the tweeter as well as mid.
I'm assuming it is just one speaker affected and that this didn't happen before you worked on them?
Other possibilities are you have an incorrect value part somewhere and are feeding the midrange with to much bass content. Maybe a cap or resistor value out by a factor of 10 etc.
If it is only one driver on one "side"; swap the drivers but be careful not to drive them too hard. There is the possibility that one of the capacitors has some damage that would make it act like a short circuit or as said above; possibly a much larger value. And yes, a strong possibility of a tiny piece of metal being stuck in the gap. I have started using the "TORX" head screws (star shape drive). They don't strip or "round out" as easily as Philips and certainly straight blade screws. It would only take a tiny speck to cause this problem. You could remove the driver and hold it up to direct sunlight or use a bright light with a magnifying glass. If you do see something, be very careful trying to dig it out; use maybe a wooden toothpick, small plastic scribe or similar so as to not damage a former, VC, etc...
First eliminate amp problem by swapping left and right speaker. If problem follows speaker, its that mid. If problem follows amps channel, totaly different issue.
I used to have buzzing sounds in Lowthers, when their flaky stuff started folling off in voice coil. Irritating. You can detect it in utmost silence by gently pressing mids cone, you will feel and hear it.
It seems there are two definitions of 'crossover distortion' being used here, and they are unrelated.
Hi folks.
Thanks for all the input so far!
I’d actually already swapped the speaker cables round combing from the amp to check the amp out, and it’s still coming from the same driver. At least it seems to be. I don’t thing it’s coming from the tweeter or woofer.
The question as to it being overloaded because the crossover frequency is somehow out due to a bad cap value can’t be I don’t reckon. These speakers use 8 inch Audax hd25s for their squaker. I assumed as soon as I saw them that those drivers would be handling a good amount of mid bass too, with the kef b139s handling the low stuff just from where those started to naturally roll off from. But no. They are crossed over so that the kef b139s way higher than I would have expected, the 8 inch audaxes handling what you’d think most other speakers would use a driver at least half the size for.
All screws are always nice and tight so it can’t be that, so things are hopefully pointing towards something being in that magnet bit. Can someone please explain where exactly I’d be looking please?
Also, it’s nowhere near as bad as it was last night, and barely noticeable now most of the time, further pointing towards a rogue foreign object being the culprit I’d have thought.
Thanks for all the input so far!
I’d actually already swapped the speaker cables round combing from the amp to check the amp out, and it’s still coming from the same driver. At least it seems to be. I don’t thing it’s coming from the tweeter or woofer.
The question as to it being overloaded because the crossover frequency is somehow out due to a bad cap value can’t be I don’t reckon. These speakers use 8 inch Audax hd25s for their squaker. I assumed as soon as I saw them that those drivers would be handling a good amount of mid bass too, with the kef b139s handling the low stuff just from where those started to naturally roll off from. But no. They are crossed over so that the kef b139s way higher than I would have expected, the 8 inch audaxes handling what you’d think most other speakers would use a driver at least half the size for.
All screws are always nice and tight so it can’t be that, so things are hopefully pointing towards something being in that magnet bit. Can someone please explain where exactly I’d be looking please?
Also, it’s nowhere near as bad as it was last night, and barely noticeable now most of the time, further pointing towards a rogue foreign object being the culprit I’d have thought.
Right, I’ve given it a good look at, deployed full tape on the end of plastic object technique as you suggested, and I can’t get that ever increasingly irritating noise to subside. Argh. Otherwise these speakers would be highly enjoyable.
I can only get to where the spider meets the cone. I take it this is the area where you’re suggesting the offending foreign object could be residing?
I can only get to where the spider meets the cone. I take it this is the area where you’re suggesting the offending foreign object could be residing?
Could be a rubbing voicecoil in the magnet cap you know. Common enough in big old drivers when the suspension sags over the years.
You can usually feel it scraping when you push the cone in. Tolerances are fine, a matter of a millimetre or so.
The solution is often to rotate the driver 90 degrees.
You can usually feel it scraping when you push the cone in. Tolerances are fine, a matter of a millimetre or so.
The solution is often to rotate the driver 90 degrees.
Any foreign body that was magnetic would only get as far as the gap entrance. If you can't see anything there then you have to look at other possibilities. Something non magnetic could conceivably fall right into the gap but you will never see it or know for sure if that has happened.
I wonder if a squirt of compressed air into the gap would help... last resort tactics I suppose.
Depending on the physical size of the driver and how much movement the cone allows you could try driving just that driver alone from a low frequency sine (say 2 to 5 Hz) and see if you hear any rubbing sounds as the coil moves in and out. A few volts of drive shouldn't cause any issues for a short time.
A simple test file and amp with good LF response is all you need for that although I don't think MP3 players go that low. A burned CDR might.
Online Tone Generator - generate pure tones of any frequency
I use this all the time; it can go as low as 1 Hz! Keep the volume low though. I also thought about compressed air, etc. It could still be a sharp object even if non magnetic. Stainless steel and brass for example; are any of the mounting hardware non-magnetic metals? Another thought is a vacuum. There are attachment nozzles that have reduced diameter for working on PCs and such. Of course, the last thing you want to do is cause more damage.
I use this all the time; it can go as low as 1 Hz! Keep the volume low though. I also thought about compressed air, etc. It could still be a sharp object even if non magnetic. Stainless steel and brass for example; are any of the mounting hardware non-magnetic metals? Another thought is a vacuum. There are attachment nozzles that have reduced diameter for working on PCs and such. Of course, the last thing you want to do is cause more damage.
Hi.
As I was having a poke around last night I could only fantasise about having compressed air to blow, or vacuum attachments to suck, reckoned they would have been advantageous. But had to make do with what I had.
Thanks Steve, I had suspected sag, and hoped that a rotation might have cured it but alas no. Also it’s only certain frequencies that get it going. Not bass ones. Well it’s crossed over so it’s only putting out mids so of course bass wouldn’t be making it rub. It’s certain piano notes, also the altos in a choir really set it off on particular notes. I can listen to bass heavy electronic music and it sounds clean. Also other piano recordings sound fine. Weird.
Before I properly look into the potential for running and go down some wave test, I’ve not given up on poking around to remove that potential foreign body. I don’t reckon I’ve poked about in the right place. Below the spider? It seems that on these I can’t get anywhere past where it meets the cone. It’s glued.
Talking of the surrounds sagging being the culprit, they are shrunken, as is typical of early Audax hd20s. I’ve asked about in some forums to see if I can find someone who could replace the surrounds for me, but I’ve not had any luck so far. I’ve tried the “good hifi” guys in the Netherlands, and they eventually replied saying that the only surround they had in the size I gave was a bit thick. When I asked for more information, they didn’t respond.
Maybe this is a separate thread, but while we’re here I thought I might ask. Thanks again for chiming in and helping so far. I hope we can get to the bottom of this because the speakers are very nice in my opinion. Quite rare too. I’d be open to replace it those audaxes with something suitable too, but that’s getting ahead of myself. Hopefully I can fix and restore the original units.
As I was having a poke around last night I could only fantasise about having compressed air to blow, or vacuum attachments to suck, reckoned they would have been advantageous. But had to make do with what I had.
Thanks Steve, I had suspected sag, and hoped that a rotation might have cured it but alas no. Also it’s only certain frequencies that get it going. Not bass ones. Well it’s crossed over so it’s only putting out mids so of course bass wouldn’t be making it rub. It’s certain piano notes, also the altos in a choir really set it off on particular notes. I can listen to bass heavy electronic music and it sounds clean. Also other piano recordings sound fine. Weird.
Before I properly look into the potential for running and go down some wave test, I’ve not given up on poking around to remove that potential foreign body. I don’t reckon I’ve poked about in the right place. Below the spider? It seems that on these I can’t get anywhere past where it meets the cone. It’s glued.
Talking of the surrounds sagging being the culprit, they are shrunken, as is typical of early Audax hd20s. I’ve asked about in some forums to see if I can find someone who could replace the surrounds for me, but I’ve not had any luck so far. I’ve tried the “good hifi” guys in the Netherlands, and they eventually replied saying that the only surround they had in the size I gave was a bit thick. When I asked for more information, they didn’t respond.
Maybe this is a separate thread, but while we’re here I thought I might ask. Thanks again for chiming in and helping so far. I hope we can get to the bottom of this because the speakers are very nice in my opinion. Quite rare too. I’d be open to replace it those audaxes with something suitable too, but that’s getting ahead of myself. Hopefully I can fix and restore the original units.
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