Help: Speakers 'thump'ing?

Subject: Speakers 'thump'ing?
From: Mrrzy
Date: 27 Jul 00 - 11:02 PM

My [computer] speakers sound for all the world like they are connected to a turntable, the old kind where the needle didn't lift automatically and at the end it would go thump, thump, thump. Anybody know what it is and can I exorcise it? Do I have to sacrifice anything to it? I'd really like it to go away...

Subject: RE: Help: Speakers 'thump'ing?
From: GUEST,an actual guest
Date: 27 Jul 00 - 11:21 PM

sounds like the amp is oscillating -- to exorcise it, throw them away and buy new ones. Try them with something else first (walkman, another computer, whatever) to make sure -- if they still thump, throw them away.

Subject: RE: Help: Speakers 'thump'ing?
From: Grab
Date: 28 Jul 00 - 08:39 AM

They'll maybe thump on startup - that's a feature of the design of the filters in the amp. Some amps get round this by not switching the speakers on until a second or two after the rest of the amp, then the filters have settled down and they don't thump. You can make your own with a relay and a little bit of electronics, if you're interested and don't mind hacking your amp a bit. If it's a computer speaker, the amp is usually pretty cheap and nasty, so a click on startup is fairly normal.

If it's continual, there's something wrong with the amp. If it just does it after a particularly loud section, then it may be an active filter that's been driven too hard and started doing strange things (a 'limit cycle', for those in the know). Otherwise it could just be a connection somewhere has gone bad. If the amp circuit-board uses normal through-hole components, you could try remaking each solder joint - don't bother trying this with surface-mount stuff, or you'll definitely kill it!

Is it definitely a feature of the speakers (active, I presume)? Have you checked that the soundcard is OK by plugging in a pair of headphones - it may be that the soundcard is the problem?

Or do you have Doom or Quake running in the background? In that case, a rhythmic "badabadabada" is entirely normal - usually accompanied by the odd "Arrghhh"... :-)

How fast is this 'thump, thump'?

Grab.

Subject: RE: Help: Speakers 'thump'ing?
From: GUEST,Mrr
Date: 28 Jul 00 - 09:35 AM

The thumping is really at the pace of what old records sounded like - thump (hippopotamus) thump (hippopotamus) thump. It's there all the time, not just on startup. I don't own headphones, but I'll try to borrow some. I don't solder, sorry! Must be my pacifist background...

Subject: RE: Help: Speakers 'thump'ing?
From: John J
Date: 28 Jul 00 - 12:55 PM

If the thump is regular, and your speakers are 'active' ie they have an integral amplifier, it sound like low frequency instability, probably on the power supply line. Speakers with a power supply, eg a plug in mains adaptor, will be active. No power supply means passive speakers. From you friendly neighbourhood electronic components shop (there's a v good one in Sale, Cheshire) buy your self two 470uf 35volt electrolytic capacitors and wire them across the power supply rail of the amplifiers. Note that these are polarity conscious so + MUST go to + and - MUST go to -. Do this on each amplified speaker. Switch on. Hope this helps. If you're still stuck: [e-mail]. Cheers, John

Subject: RE: Help: Speakers 'thump'ing?
From: Mbo
Date: 28 Jul 00 - 04:08 PM

Quake & Doom rule!

Subject: RE: Help: Speakers 'thump'ing?
From: GUEST,an actual guest
Date: 28 Jul 00 - 04:19 PM

I don't mean to imply that the other suggestions here are incorrect (otoh there's no guarantee that adding capacitors across the supply rail will fix this, it might but likely won't).

But given that the original poster had to ask the question (anyone who knows how to fix this wouldn't need to ask the question), and that instability in amp circuits can be tough to track down even when you know this stuff, and that computer speakers are typically $20 -$30 -- I really think the best thing to do is just toss them, if basic troubleshooting confirms that the speakers are indeed the problem.

my 2 cents...