Getting a "thump" from external speakers.

[Denis Danatzko]

I have an old set of Creative Labs Inspire T3000 speakers (2 speakers, 1 subwoofer purchased brand new back in 2005, maybe). When the speakers and the computer they're attached to are powered on, I hear a "thump" from the speakers when other devices power up, e.g. when my networked Brother all-in-one laser printer wakes from sleeping.

If the remote speaker switch is powered on, and I power-up the computer they're attached to, I hear the "thump".

I hear the "thump" whenever the computer and speakers are powered up and certain events occur, regardless of what I'm doing.

I also hear it when editing in Adobe PPro CC and CS6, or Audition CS6 and the audio meter peaks into red.

When I play the finished audio on another computer, or from vimeo, it doesn't appear.

It started to happen on a custom, vendor-built machine with a Tyan MB running Windows XP Pro and Adobe CS2. (Not when it was brand new, but over time it seemed to come from nowhere).
I moved the speakers to my newest machine (also custom ordered and vendor-built) with an Asus P9X79Pro MB with Windows 7 Pro and an i7 CPU, and the problem continues.

I've searched for fixes and haven't found much, other than references to theories that some MBs cause it to happen.

Is there any hope for continued use of these speakers?
Any ideas on how I might eliminate the "thump"?
If not, what brand/model would be a decent replacement? (Real high-end, i.e. Genelec, etc. would be wasted on me due to my age and slowly fading hearing).

All ideas welcome.

[Rick Reineke]

I would guess it's a computer/soundcard issue and probably not your speaker system.
You could try shutting off all the computer sounds. "Settings> Control Panel > Sounds" to "No sounds"... While your there, verify the soundcard output jacks are assigned to the correct speakers: Front L+R.. or whatever your configuration is.
Maybe install (or re-install) the latest driver for your soundcard.
Other than that, I have no idea. Sorry.

[Brian P. Reynolds]

This might be a bit out of the square... Try to isolate the speaker feed with isolation transformers, often 'thumps' are caused from DC on the signal feed.
The transformer will not pass DC.

Something like this.
http://wallcann.com/Unbalanced-Stere...nics_1102.html

[Denis Danatzko]

Thanks for the replies.

Rick,

I also noticed the thump occurs when the computer is not powered-up but the speakers are, and I power-up a television.

Might this happen if I just have too many devices running off the same electrical circuit? Maybe between all the devices, there's simply too much of a drain on the circuit when certain items are powered-on or otherwise become active?

Brian,

I'll check out that item. Thanks.
Meanwhile, with Christmas coming, I'll add a new speaker arrangement to my list.

Thanks,
Denis

[Greg Miller]

What happens if the speakers are powered on, but their input is completely disconnected from everything, and their volume control is turned all the way down?

[Denis Danatzko]

I hadn't thought of that test, but just did it:
With speakers:
- disconnected from computer,,
- powered-up,
- volume dial on absolute minimum,
I powered-up a TV/monitor that is not connected to my network or any other computer/monitor, and is located about 4 feet from the speakers,
I still get "the thump".

It seems like you're onto something. Ideas?

THANKS.

[Greg Miller]

Then the transient is getting into the amplifier one of two ways:

A.) coupled through the power line, or

B.) airborn electromagnetic radiation.

When you switch an AC load, especially when you turn it off, you generate a transient which, in effect, generates a small pulse with harmonics that extend up into the RF range, and can be transmitted like any other RF wave. That phenomenon would explain possibility (B.) above.

Here are a few more things to try.

1.) Power the speaker from an entirely different AC circuit. This may involve some sleuthing on your part, turning breakers on and off, to determine which outlets are controlled by which breaker. Then find the nearest outlet that's on a different breaker (relative to the TV/monitor), and run an AC extension cord from that circuit to power just the speakers. (Leave the TV/monitor powered where it is now.) Then repeat the "thump test."

2.) Assuming these speakers are powered by some sort of "wall wart," substitute a different "wall wart" with the same output voltage and polarity, and at least the same current rating, as the original. Repeat the test.

3.) This is rather hard core: make up a battery pack to substitute for the "wall wart" so the speakers are completely isolated from your AC power line. Repeat the test.

---

Also a question, although of course now we're getting into the realm of descriptive language. This sound you hear... is it really just a low-frequency "thump" (which you'd hear only from the woofer), or is it more of a "pop" or even a "click" with higher-frequency components to the noise?

[Chris Soucy]

I think, from your description of the problem, that there is a far more fundamental mechanism at work here.

As the issue arises even with the sound system disconnected from the sound card/ computer, it's the speakers themselves at fault.

Your "speakers" aren't just speakers.

The sound system as a whole consists of the PC sound card, which turns the digital data into an analogue line level source, and the transducer system, which takes that line level source, amplifies it and feeds it to the relevant transducers to actually reproduce the sound(s).

The amplifier requires a power supply, which can be either internal, requiring a mains AC voltage feed, or external, which turns the mains into either a low level DC or AC feed, usually DC.

Whichever way the power supply is configured, it and the following amplifier itself, will contain electrolytic capacitors and maybe series inductive chokes to suppress unwanted spikes, harmonics and associated gremlins that whiz around all mains power systems.

Chokes are pretty well bomb proof unless over rated, in which case they become expensive fuses, game over in a flash (literally!).

Capacitors are another kettle of fish altogether. The dielectric medium in electrolytic's can (and will) change character with time, gradually reducing their ability to perform their original function.

Factors in this degradation are:

Quality control during manufacture, correctly specified voltage operating characteristics, temperature and time.

I think it fair to say that pretty well all modern electrolytic's will, in time, gradually lose the will to live and cease functioning.

It sounds very much as if this is what's going on here.

Replacing the "wall wart" external power supply for a new one MAY fix the problem if the offending capacitors are actually in the original.

However, if the failing components are inside the speaker box, the only fix is to gut the box, remove the power supply/ amplifier board(s) and replace every single electrolytic capacitor on the lot.

The good thing about this is that electrolytic's are much larger components than typical "surface mount devices" which are, without special equipment, simply not repairable.

Of course, this does require the actual capacity and voltage rating of the individual capacitors to be read off the components themselves, not possible if the plastic sleeves have seriously degraded.

If that is the case, a circuit diagram is your only hope, good luck with that one.

Assuming you're "Mr Average" and as such can't really tell one end of a soldering iron from the other, I'd write Santa a note requesting a new amplifier/ speaker system in your Christmas stocking.

Regards,


CS

PS:

Electrolytic power capacitors are always packaged in a metal canister which has an overall (factory fresh) light blue** plastic sleeve with a black stripe running from the top of the canister to the base, where the two connecting leads exit the can.

As electrolytic's are polarized, the black stripe indicates the lead to be connected to the most negative part of the circuit, the other lead going to the most positive (at least, I think its that way round!).

As the capacitor ages, for reasons known to only to a few (I'm not one of them, I don't know whether this is deliberate or simply a "it just does, OK?" thing), the blue sleeve turns an interesting shade of pink.

Pink is NOT GOOD. It doesn't always mean the package contents have shuffled off this mortal coil, but it's definitely shopping for a coffin.

** Unless, of course, it's one of the later ones which, just to make things interesting, have a black plastic sleeve with a white stripe. These don't seem to go pink. They do still drop off their perch, nevertheless.

[Greg Miller]

A good discourse on possible power supply and capacitor issues. Indeed, all electrolytic capacitors have a damp paste electrolyte, which can and will dry out over time, gradually reducing the capacitance of the component. (Capacitors come in a variety of colors, not just blue; and the electrolyte can dry out without any visible change, colorwise or otherwise. Also, not all have radial leads as described above; some have axial leads, one at each end of the metal can. All this is somewhat beside the point.)

At any rate, aged capacitors might be the problem, but IMHO it's rather early to draw conclusions for certain. At this point in time, we're not entirely sure whether the "thump" is caused by a shift in supply voltage, or whether it's noise "transmitted" by the TV/monitor, and "received" by poorly shielded electronics in the speaker's internal amplifier or "control pod" wiring.

Once Mr. Danatzko performs at least the first two tests I suggested, we hopefully will know how the noise is getting into the system. Then we'll know whether it's a matter of the amplifier's being overly susceptible to electromagnetic noise, or whether the "thump" is caused by a shift in power supply voltage.

Meanwhile, I did a little surfing, and found a bit of info about Mr. Danatzko's specific speaker system. I found an online manual which says the mains adapter is "12 VAC 2.9A"; and also found one photo of the rear panel with the power input connector is labeled "12V AC IN." If that's true, the entire power supply (except for the mains transformer) is inside the woofer enclosure... bad news if we have a problem with supply filtering... not fixable by the "average appliance operator." (And if the power supply is really 12V AC, then an external battery box is not an option, obviously.)

I also note that the system has an external "control pod" so the "control pod" connecting cable might also be susceptible to pickup of radiated electromagnetic noise.

So we await test results from Mr. Danatzko, in order to have a better informed idea of how best to proceed.

Now back to the turkey sandwiches, turkey stew, turkey soup, turkey meatloaf, turkey pizza...

[Chris Soucy]

Greg...............

I can see where you're coming from, but this:

or whether it's noise "transmitted" by the TV/monitor, and "received" by poorly shielded electronics in the speaker's internal amplifier or "control pod" wiring.

is not compatible with what the "patient" has said:

Not when it was brand new, but over time it seemed to come from nowhere

I can deduce nothing else but some sort of gradual reduction in the equipment's ability to screen out extraneous EMF.

True, solder joints go bad, cables are no longer shield grounded etc but (and a big but) hey, this kits coming up for 8 years old, the power supply is in an enclosed box, the average ambient temperatures unknown, but possibly high, and has been on, probably, 24/ 7/ 365 for most of that time (mine has, pretty much the same age).

In the event that this unit has a series pass PS and not switched (Series Pass seems most likely if it's being fed 12 AC, if it was switched I'd expect 110V in the USA), I'll have to take issue with this:

And if the power supply is really 12V AC, then an external battery box is not an option, obviously.

If the power supply is being fed by 12 AC, no one with an IQ higher than their shoe size would have specified half wave rectification, which means it will have full wave rec.

If it has full wave rec, it CAN be fed with a DC source, pick a polarity, any polarity, just get the right voltage, needs to be about 30% higher than the AC source and you're good to go.

Doesn't matter which hole you stick it up (so to speak) it's gotta turn into regulated (or maybe not!) DC, full wave rec won't allow anything else.

It does put the 2 affected diodes on a 100% duty cycle, which might well bum them out, even burn them out, so possibly only a short term test procedure if adopted, though it could work for years, just a bit of temperance with the volume control will work wonders.

(Half wave rec will still work with a battery, you just have to get the battery polarity right, it only works one way. You won't blow anything up on either version of a series pass PS using a battery instead of AC, just get the voltage and current parameters right, and don't blow the diode current and duty cycle limits).

Gone awfully quiet on the "patient" front, hope neither have dropped off their perch entirely.


CS

[Richard Crowley]

Remember also that Mr. Danatzko quite likely has more/different appliances nearby than when he first got the speakers.

Also we don't know anything about the state of his mains power wiring. While it seems quite possible the problems are due to deterioration of the power circuit inside the powered speakers, it also seems quite possible that the problem is in the power wiring.

There was a period of time several years ago when copper was very expensive and houses were wired with aluminum. But aluminum is more "brittle" and less "ductile" than copper, and the connection between the wires and the screw terminals in the circuit breakers and power outlets becomes loose over time, and require re-tightening. And there are other possible problems with the power wiring depending on age and quality of materials and installation.

[Greg Miller]

Originally Posted by Chris Soucy

I'll have to take issue with this:

If the power supply is being fed by 12 AC, no one with an IQ higher than their shoe size would have specified half wave rectification, which means it will have full wave rec.

If it has full wave rec, it CAN be fed with a DC source, pick a polarity, any polarity, just get the right voltage, needs to be about 30% higher than the AC source and you're good to go.

Doesn't matter which hole you stick it up (so to speak) it's gotta turn into regulated (or maybe not!) DC, full wave rec won't allow anything else.

Chris, I have to take issue with THAT. It's possible that it's rectifying (and perhaps regulating) the AC input to produce a bipolar DC power supply, e.g. +/- 12VDC rails. In that case, feeding DC into the AC input connector will not result in proper operation, and might do some damage.

[Denis Danatzko]

Well, a big THANK YOU to everyone who responded.

This has turned out to be one of the more detailed, educational threads I've participated in.

While I have replaced electronic components with a soldering iron in my past, experience at that, as well as knowledge and talk of rectifiers, diodes, and capacitors is pretty far in my past - and mostly "over my head" any more. Despite some cursory knowledge when I was younger, I had no idea there were parts/components of a speaker/system that could "dry out".

I tried the test that Greg Miller suggested, i.e. plugging the wall wart into an extension cord connected to an entirely different outlet on an entirely different circuit in my home. I then repeated turning on/off other devices connected to the original outlet or nearby, and "the thump" no longer occurs.

Let me reiterate my THANKS to all, and pose a few more questions that reveal more of my naivete:
Given Greg's description of "transients", it now seems obvious to me that I've too many devices plugged-in to the same electrical outlet, and am generating a noticeable magnetic field of some kind.

1) Might that magnetic field be damaging to other components or leading to their early demise?

2) Might it be causing other problems that I simply haven't noticed, stumbled upon, or otherwise been made aware of?

Thanks to your replies, I'm now inclined to think that placement of devices and the power source they use may be more important than I - and probably others - have been aware of.

In simple terms, how important is it that I move devices around and plug them into other circuits in order to lower the strength of that field?

Thanks so much to all for the help.

[Greg Miller]

Based on your results, namely that the "thump" disappears if you power the speaker from a different circuit, I think it is not an issue of electromagnetic interference that is being transmitted like a radio signal, through the air (although those could also be transmitted through a vacuum). So whatever is happening is being carried into the amplifier through the power wiring.

Still, it could be one of two things:

either (a.) an electromagnetic pulse that just "rides on" the power wiring, as if it were a sort of antenna. (But such an electromagnetic pulse isn't really problematic in any other way... it won't kill your plants or make you sterile.)

or (b.) a drastic change in the AC line voltage, which turns into a change in the amplifier's DC supply voltage, causing the "thump" from the speakers.

There are two ways we might narrow this down.

1.) Back to my earlier question about how the noise actually sounds. Is it just a low frequency "thump" which is heard only from the woofer? Or is it more of a "pop" or "click" which is heard from the mids as well?

If it's just a "thump" then I'd say we've isolated a change in line voltage as the culprit. If it's a "pop" or "click" then I'd still suspect an electromagnetic pulse, but one that's too weak to be "airborne" and which needs to travel along the power wiring to get into the amplifier.

2.) You could try to observe the actual voltage on the AC mains, and see whether there's a significant change when you turn on the TV/monitor. You could use an AC voltmeter (digital or even analog), or just plug in a 100-watt incandescent bulb, and see whether there's a noticeable change in brightness when you turn on the TV/monitor. Depending on how your building is wired, the voltage might go down, or might even go up, when a load on a different circuit is turned on.

As Mr. Soucy and I have discussed, if the filter capacitors in the amplifier are suffering from decreased capacitance, even a small change in the line voltage (which is otherwise OK) might cause a bit of a "thump" from the woofer.

I would say that you might expect a change of one volt or so, but it shouldn't be significantly more than that. If it's five volts or more, I'd say there is some serious problem with the building wiring. And, indeed, that might indicate some deteriorating/deteriorated condition that might ultimately become a safety issue.

If you're lucky, it might be something as simply as an ageing wall outlet. The contacts can become oxidized, and their spring tension (making contact between the outlet and the AC line plugs) can become weakened, all of which can result in higher contact resistance and more voltage drop with changing loads. Of course having a large load (or number of loads) plugged into one small-gauge extension cord will have the same effect.

Consider Aluminum wiring, as mentioned by Mr. Crowley. If you have Aluminum wiring, there's a potential problem, as follows. When a load is turned on, and the wire carries current, its temperature increases slightly so it wants to expand. Since it is constrained by the screw terminals on the outlets, switches, breakers, etc., it can expand only lengthwise, i.e. out from under the terminals. When the load is switched off, the aluminum cools and contracts. Now the connection is a little bit looser, which makes the contact resistance a little bit higher. The next time the load is turned on, the contact resistance (where the wire is constrained by the screw) will be higher, because it's a function of pressure; higher resistance will generate more heat; the wire will expand more. When the load is turned off, it cools and contracts again. Each time the cycle is repeated, the contact becomes progressively looser and looser. This is a very destructive cycle, and corrosion also factors into the equation. Eventually this can generate enough heat at the terminals to start a fire! Note that this is almost entirely confined to older Aluminum wiring, before proper terminals, and anti-corrosive treatments, were put into use. And if it's caught in time, the problem can be solved by having an electrician properly treat and re-tighten all the connections. But if you see a significant voltage drop when you turn on the TV/monitor, it might be worth investigating.

Then again, I have seen old buildings in Manhattan where an entire apartment was served by one 20-amp circuit. If a window air conditioner and refrigerator both cycled on at the same time, the fuse blew! No Aluminum was involved there, just wiring that was grossly inadequate for today's needs. So there are all sorts of possible scenarios.

By all means, please try the "thump"/"pop" evaluation and report back. And it wouldn't hurt to check the voltage change on that circuit, if you have an AC voltmeter handy.

[Chris Soucy]

Very comprehensive and clearly written explanation, Greg, full marks.

I read Denis's questions and started trying to list and explain all the things that could be going on, and promptly tied myself in knots. Tried a few times then consigned it to the "too hard" basket.

On the subject of wiring, in my experience pretty well any mains wiring will degrade over time, no matter what the conductor material is. Screw connectors and contact fatigue (as you mentioned) are the worst offenders, the brass screws in power outlets and switches having a tendency to simply "walk" out of their threads, probably due to thermal cycling, as you said.

The impact of this "walking" can be magnified greatly depending on the type of wire termination dictated in the regulations. Some jurisdictions mandate the incoming mains feed loop conductors (live, neutral and earth) being physically spiral wound with the outgoing loop conductors so that even if the live screw in an outlet does go walkies, the feed is maintained from the distribution board to the end of the line, and only the affected outlet gets iffy.

The down side of this spiral winding is that over generous application of the pliers can cause fatigue fractures, which are absolute sods to find.

The first place I'd start if this thump phenomena is only happening on one circuit (though that can only be confirmed by transferring every single item plugged into one circuit to another one, as if!) is to check every single connection from the distribution panel to the end of the line, it's quite surprising how often a bad connection will be found.

A problematic mains feed can be provoked to really play up by throwing a switch mode power supply into the mix (linear/ transformer based power supplies are an endangered species). Unlike transformer based power supplies where the transformer itself acts as a choke to make it more or less "slow start", a switch mode supply (unless fitted with "slow start" circuitry, becoming much more common) acts like the mains has been "crow barred", with inrush currents in the hundreds of amps range, even though the steady state current may only be 1 or 2 amps!

This inrush only lasts milliseconds, but it's enough to throw a massive negative spike up and down the mains circuit, the worse the circuit impedance integrity, the bigger the spike. Interestingly, this spike never seems to impinge on other switch mode supplies, just linear ones.

This could be a factor in the mysterious thump.

[Inrush Trivia:

Whilst contracting in the UK about 15 odd years ago, one aspect of which was supervising the IT help desks, the "deskers" suddenly started getting frantic calls from one of the companies sites to the effect that most (but not all) of their PC's wouldn't power up.

Much head scratching ensued, then I had a horrible thought. A quick call to the remote sites infrastructure manager elicited the fact that they'd had the electrical inspection team from a local electrical company on site the previous night after the site closed (commercial sites in the UK are required to have all electrical appliances confirmed "safe" on a regular basis.

I promptly dispatched one of the techs in the direction of the ailing PC's with instructions to detour via the local electrical shop/ supermarket and purchase 4 dozen 13 amp fuses.

Sure enough, the tech confirmed my suspicion. Having seen the rating plate on all the PC's stating they consumed 200 Watts (less than an amp in the UK) the "inspectors", knowing nowt about inrush current, had changed all the power plug fuses from 13 amp to 3 amp.

(Every single power plug (not outlet socket) in the UK is individually fused, with fuses available in 3, 5 and 13 amp ratings)

Kaboom.

Needless to say, I had to "educate" not only the "inspectors" but all the companies infrastructure managers as well.]


CS