Appreciate some advice on this one.
I use a pair of active (not powered passives), two-way speakers for listening to music. They're great in almost every respect but there is a slight hum I'd like to remove from each speaker.
The hum is just about noticeable at the listening position when environment is very quite with no music playing. Obviously, playing music masks the hum.
Hum is constant and independent both of speaker's volume settings and whether input connections have or have not been made. The hum doesn't change noticeably at different times of the day either.
The hum comes only from each bass/mid driver, not from the tweeters. This baffles me because, being an active design, the amps are directly connected to each drive unit. If the hum is mains related caused by the power supply, why can't I hear it through the tweeters too?
Hum sounds like a 100Hz type mains related hum but I'm no expert and could be wrong.
Could anyone advise on a generic fix for this sort of hum problem?
I use a pair of active (not powered passives), two-way speakers for listening to music. They're great in almost every respect but there is a slight hum I'd like to remove from each speaker.
The hum is just about noticeable at the listening position when environment is very quite with no music playing. Obviously, playing music masks the hum.
Hum is constant and independent both of speaker's volume settings and whether input connections have or have not been made. The hum doesn't change noticeably at different times of the day either.
The hum comes only from each bass/mid driver, not from the tweeters. This baffles me because, being an active design, the amps are directly connected to each drive unit. If the hum is mains related caused by the power supply, why can't I hear it through the tweeters too?
Hum sounds like a 100Hz type mains related hum but I'm no expert and could be wrong.
Could anyone advise on a generic fix for this sort of hum problem?
If the hum is identical from both units with or without input leads shorted, this means typical budget system, low level hum to my understanding. One almost has to get used to this sort of performance from extreme cost-cutting measures in the electronics.
If you paid for something up-market or purporting to be hi-fi quality, you could expect better than that but a fix will depend on what's (not) inside. A schematic is needed (unlikely to get outside the service agent's control) or good pics of the works, including top and bottom side of the PCB. Then a fair bit of work and parts will be necessary if the problem is more than just poor location of the signal leads and boards. The problem could lie also in design issues like poor PCB layout, power supply, or insufficient filtering which can be major work to fix.
Generic fix?...Not without knowing specifically what you have there and whether modifications would be an economical proposition.
As other posts have suggested, the tweeter is filtered, by the definition of an active filtered loudspeaker, to exclude bass - why ever would you expect anything but a tiny amount of high residual harmonics to be heard through them? That has little to do with the tweeter's ability to reproduce bass, as you witness stabbing a bit of DC into one.
Thanks to everyone for replying.
Hum is present and constant in volume with or without input cables connected. Hum is unaffected by speaker's volume control setting. Not tried shorting input because I wasn't sure if this would cause damage. Yes, the speakers are very cheap. These in fact:
http://www.studiospares.com/studio-monitors/studiospares-seiwin-powered-monitors-pair/invt/248030/
Trouble is, their audio quality is so good that I’d like to improve them further by removing that small amount of hum. These speakers rival my main active system in some aspects of audio quality – they’re a bit special and by far the best value purchase of hifi/audio reproduction equipment I’ve ever made.
Maybe I’m missing something here? This is the way I (currently) understand it – if the hum is caused by an imperfect power supply then this feeds both amps that connect directly to their respective drive units. The audio signal passes through the active crossover before the amps so has no bearing on this.
That makes sense to me. I guess the tweeter's frequency response curve is somewhat depressed at 100Hz.
I take all points made about possible causes of the hum. I’m willing to chance that it’s caused by ripple from the power supply. If we assume that is the case, what could cause this and is there any way of improving the supply by adding additional components or replacing something? I appreciate specific advice cannot be given but any general direction much appreciated.
Hum is present and constant in volume with or without input cables connected. Hum is unaffected by speaker's volume control setting. Not tried shorting input because I wasn't sure if this would cause damage. Yes, the speakers are very cheap. These in fact:
http://www.studiospares.com/studio-monitors/studiospares-seiwin-powered-monitors-pair/invt/248030/
Trouble is, their audio quality is so good that I’d like to improve them further by removing that small amount of hum. These speakers rival my main active system in some aspects of audio quality – they’re a bit special and by far the best value purchase of hifi/audio reproduction equipment I’ve ever made.
Maybe I’m missing something here? This is the way I (currently) understand it – if the hum is caused by an imperfect power supply then this feeds both amps that connect directly to their respective drive units. The audio signal passes through the active crossover before the amps so has no bearing on this.
That makes sense to me. I guess the tweeter's frequency response curve is somewhat depressed at 100Hz.
I take all points made about possible causes of the hum. I’m willing to chance that it’s caused by ripple from the power supply. If we assume that is the case, what could cause this and is there any way of improving the supply by adding additional components or replacing something? I appreciate specific advice cannot be given but any general direction much appreciated.
Incidentally, there is none of the switch on & off thump that I've experienced with other single ended power supply amps but maybe some switch on delay circuitry is incorporated?
Let's be clear; the active filter is just 2 filters, configured to neatly divide up the frequency spectrum between the bass and treble speakers. Effectively, it's no different to the crossover network in standard loudspeakers.
In the tweeter's section of the filter, bass is attenuated so that bass, including hum, is much reduced compared to that freely passed by the bass section, which has just the opposite effect by attenuating the treble frequencies. Add to that the effect of the physical constraints of the different driver types and the net result is that you hear no hum, other than a tiny amount of high harmonic artefacts, from the tweeter.
Hum, according to the symptoms you describe, will be the result of the amplifiers inside the box not being fed clean DC power from their associated power supply. This is actually the case with all simple amplifiers but what the expensive ones have, is provision in their electronic circuits to deal with it, filtering it out, shielding or simply spacing sensitive components, leads and PCB traces far enough apart, here and there throughout, to get a nice, quiet amplifier that has the "wow" quality to the sound.
OK, so you have the likeliest problem identified, IMO, now what can you do? Unfortunately, the best thing to do is replace the electronics with quality PCB sub-assemblies but you could make small improvements by a few "bandaid" capacitors or such being added to strategic points in the circuit, upping the size of existing filter capacitors and repositioning the internal wiring to minimise hum radiated into the amplifiers by the transformer, rectifier and wiring. Any such mods need to be targeted to the specific device. Every model, brand and design type is its own can of worms, so it's pointless to offer parrot-fashion generalities about fixing or redesigning commercial equipment in the hope that some piece of advice actually works. To do this properly, we need the precise details, otherwise it's as stupid as advising how to tune up a fuel injected motor with the advice for a carburettor system.
Again, there is no generic fix. The only generic action would be wholesale replacement of the offending assemblies and that won't be cheap or an off-the-shelf item, considering that you need to retain or duplicate the active crossover section so that the "sound" you like is maintained.
We could go on about the details and possibilities but the issue here is that unless you have a good understanding of audio electronics and can nose around supply companies that may offer suitable components, better assemblies etc, you will waste your time and money trying. This surgery is not kid stuff, safe or sure-fire unless you already have learned how to mess with electronic circuits and how they work. If you have the cash, get a second pair of the speakers (test the hum before buying) and seek the assistance of a friend with the geek knowledge, tools and a good selection of components to dive in and modify the PCB or wiring to see if you can achieve much by trial and error even.
In my area, I sometimes aid teens whose junk powered speakers have issues like hum (some deafening), blown tweeters, overheating, fires etc. Most guys (always guys) just want the loud noise part to work again but I haven't heard anything cheap that is hum-free. They all buzz away like $20 PC speakers.
In the tweeter's section of the filter, bass is attenuated so that bass, including hum, is much reduced compared to that freely passed by the bass section, which has just the opposite effect by attenuating the treble frequencies. Add to that the effect of the physical constraints of the different driver types and the net result is that you hear no hum, other than a tiny amount of high harmonic artefacts, from the tweeter.
Hum, according to the symptoms you describe, will be the result of the amplifiers inside the box not being fed clean DC power from their associated power supply. This is actually the case with all simple amplifiers but what the expensive ones have, is provision in their electronic circuits to deal with it, filtering it out, shielding or simply spacing sensitive components, leads and PCB traces far enough apart, here and there throughout, to get a nice, quiet amplifier that has the "wow" quality to the sound.
OK, so you have the likeliest problem identified, IMO, now what can you do? Unfortunately, the best thing to do is replace the electronics with quality PCB sub-assemblies but you could make small improvements by a few "bandaid" capacitors or such being added to strategic points in the circuit, upping the size of existing filter capacitors and repositioning the internal wiring to minimise hum radiated into the amplifiers by the transformer, rectifier and wiring. Any such mods need to be targeted to the specific device. Every model, brand and design type is its own can of worms, so it's pointless to offer parrot-fashion generalities about fixing or redesigning commercial equipment in the hope that some piece of advice actually works. To do this properly, we need the precise details, otherwise it's as stupid as advising how to tune up a fuel injected motor with the advice for a carburettor system.
Again, there is no generic fix. The only generic action would be wholesale replacement of the offending assemblies and that won't be cheap or an off-the-shelf item, considering that you need to retain or duplicate the active crossover section so that the "sound" you like is maintained.
We could go on about the details and possibilities but the issue here is that unless you have a good understanding of audio electronics and can nose around supply companies that may offer suitable components, better assemblies etc, you will waste your time and money trying. This surgery is not kid stuff, safe or sure-fire unless you already have learned how to mess with electronic circuits and how they work. If you have the cash, get a second pair of the speakers (test the hum before buying) and seek the assistance of a friend with the geek knowledge, tools and a good selection of components to dive in and modify the PCB or wiring to see if you can achieve much by trial and error even.
In my area, I sometimes aid teens whose junk powered speakers have issues like hum (some deafening), blown tweeters, overheating, fires etc. Most guys (always guys) just want the loud noise part to work again but I haven't heard anything cheap that is hum-free. They all buzz away like $20 PC speakers.
Hi,
The ripple is either inherent : inevitable given the amplifiers PSRR ratio,
and the regulation of the presumably cheaply built in power supply, or :
some possible mistake in the layout, given : your discounting earth
loops as a cause as the problem exists without any connections.
My money's on bad layout of some sort, poor decoupling, something
like that. Hum should be completely inaudible in modern equipment.
Power supply ripple and reducing it shouldn't be the problem.
rgds, sreten.
Tweeters are something like -35dB to -50dB down at 100Hz.
The ripple is either inherent : inevitable given the amplifiers PSRR ratio,
and the regulation of the presumably cheaply built in power supply, or :
some possible mistake in the layout, given : your discounting earth
loops as a cause as the problem exists without any connections.
My money's on bad layout of some sort, poor decoupling, something
like that. Hum should be completely inaudible in modern equipment.
Power supply ripple and reducing it shouldn't be the problem.
rgds, sreten.
Tweeters are something like -35dB to -50dB down at 100Hz.
A big thanks for your considered replies.
There appear to be aspects of frequency filters that I'm clearly never going to understand so I'll set that aside for the time being.
Taking all your points about possible and likely causes of the hum, and understanding my level of knowledge, I've decided to open up the speaker box and have a look at the way the circuit boards are wired together and their position relative to the power supply and signal input leads. If there's scope to move a few things around, I will but I'm not knowledgeable enough to work at the individual component level.
Thanks again.
There appear to be aspects of frequency filters that I'm clearly never going to understand so I'll set that aside for the time being.
Taking all your points about possible and likely causes of the hum, and understanding my level of knowledge, I've decided to open up the speaker box and have a look at the way the circuit boards are wired together and their position relative to the power supply and signal input leads. If there's scope to move a few things around, I will but I'm not knowledgeable enough to work at the individual component level.
Thanks again.
I have had some issues with hum. I would suggest first trying procedure for ground loops. if any, though most people refer to ground loop as first thing but this can as easily be a bad amplifier design or some component going bad (in case it worked fine before).
Yes the hum can be very very disturbing.
Yes the hum can be very very disturbing.
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