Dynaudio speakers going bananas again...

[molecular]

There is a set of Dynaudio BM6A MkII here. They work fine in general but when first powered on they make the most terrific thumping and the main woofer is driven repeatedly over and over again (maybe twice per second?) it's full travel distance.

Quite scary and no doubt incredibly bad for the speaker.

I've got around this by basically not switching them off unless I absolutely have to, and when I do switch them on if I go ON OFF ON OFF ON OFF a few times it minimises the number of thumps and eventually it subsides and I can carry on.

Does anyone have any thoughts on the cause of this?

To be clear - this is not an incoming signal issue, it happens when no input cable is present.

I do have a gory video of it on my phone, will try and upload later if it would help...

Another dying power supply in my life?

[Sam Spoons]

My bass player mate has a Phil Jones Briefcase combo that does much the same thing.

[Hugh Robjohns]

Yes, it's probably a power supply issue. But it's clearly not as it should be, so some TalC from a competent tech would be advised.

H

[James Perrett]

Yes, it sounds like a power supply cutting in and out - possibly due to something else taking too much current at switch on. I would strongly suggest getting it repaired before something major (like a bass driver or output stage) gets damaged.

[molecular]

Sound advice, thanks - and agreed this is not one for and my screwdriver.... I did forget an important note which is that this started at the same time on both, although they are independent powered monitors.

It would make sense for both to fail, being identical and the same, but it did make me wonder if there might be something else at play in terms of the power supply upstream or something I might have done to both....?

Anyway, yes will arrange for them to go to a tech at the soonest opportunity!

[James Perrett]

It would make sense for both to fail, being identical and the same, but it did make me wonder if there might be something else at play in terms of the power supply upstream or something I might have done to both....?

If both started doing it at the same time then there must have been some common factor to cause them to break. It is very unlikely that they would both fail from ageing components in the same way at the same time. Did you change any wiring or anything feeding the monitors at that time? Have you ruled out an issue with the mains power supply (I'm wondering if a high resistance mains connection could case this)? It may be worth plugging one of them directly into a wall socket with nothing else connected to them to check that it isn't a wiring issue.

[molecular]

Thanks James - something to try there. I can't remember the exact setup but they are on a 4-way and also the room is an old academic computer room so the wall sockets are on a spur with it's own fused switch at one end and so there's definitely unknowns. I hadn't thought of just plugging them into a socket elsewhere in the building but will try it!

H