Speaker ageing (not burning-in)

[A.S.]

Even I, cautious as a I am, sometime have rosy memories about speakers that caught my eye or ear 20+ years ago. And from time to time, if the price is tolerable, out of curiosity I'll buy them. There are always disappointments, and long-term ageing of their mechanical parts seems to be very common. It is worth commenting that Harbeth-brand speakers - even old ones going back to the Mk1 from 1977 - age well. That is, the performance whilst (perhaps) not completely to the original specification is acceptable and most important, they don't seem to exhibit nasty colourations as time passes.

This good news situation with elderly Harbeths is not the universal situation throughout the speaker industry. If you ask speaker designers to comment on the long-term ageing of designs they've been involved with, I'd guess that most would admit to a problem model. It's not that they deliberately designed-in a latent problem, it's that materials in the consumer's operating environment are not completely predictable, not perfectly stable. What happens in the hot, humid home may be quite different to the long-term behaviour in a temperature controlled lab. Our wider experience in manufacturing drive units for our friendly competitor's service needs has opened our eyes to this whole issue. In my observation, the problems of long-term ageing always related to the soft moving parts of the system - this includes all glue joints (which can be very critical to performance and sonic quality), the surround, the dope applied to the cone, the suspension and the dust cap. Should any one of these gradually slip out of spec. and they may (rubbers and plastics are never completely stable over the long term as they have to be flexible, and this flexibility opens the door to molecular change with time) - you can expect the system performance to change. You may or may not notice the effect on sound quality, but this is over the very long term life of the speaker - perhaps 15 years after manufacture.

The magnet, if metal/ceramic (as all Harbeths are) has a very stable energy (flux) with time. The previous generation of Alnico magnets had a marked flux leakage with time which meant that the bass unit becomes quieter relative to the tweeter and also that the bass response became flabby as there isn't enough restoring force from the magnet. Harbeth have never used Alnico magnets for that reason so I wouldn't expect the bass response of a Harbeth to change with time.

Perhaps the single most problematic part of any speaker system is the bass/mid unit's edge surround, analogous to a cars shock absorber. It looks so deceptively simple but it is super-critical. It has to be flexible to allow the cone to move backwards and forwards but this flexibility carries with it an arthritis-like vulnerability. PVC and PVC-like surrounds as used on BBC-style monitors in the 1960's and 70's have notorious problems in that they have polymer memory and like to return to the flat state over time, hence, weak over-damped bass. The original user simply wouldn't be aware of the gradual change and will describe his speakers in the most glowing heart felt terms new listener's see and hear them for what they really are: in their twilight years. Very sad. What is the operating life of a high quality speaker system? Impossible to say with certainty outside the lab.

General across-the-industry Rule of Thumb then:

Operated regularly (keeps the moving parts flexible), used in 21-24 degrees air conditioned and air filtered environment with low ozone level ... A1* performance (say) about 10 years. Under these ideal conditions the speaker could be perfectly operational at B+ grade at 10-20 years. Replacing the tired bass units at the 12-15 year point (if available) may well extend the life upwards to 25+ years.

Note: none of these degradations will necessarily effect sound quality; to the best of our knowledge Harbeth HL series and Monitor series speakers do not significantly degrade with time if they are treated with respect..

[Myron]

This question is for you Alan. I know i am out of topic, but is there a possibility to tell me when is the next shipment to Greece? I can't wait any more (i want my SHL5's - a month and a half without music - i am going crazy).

[A.S.]

This thread is for technical matters and your question is about Sales. Please try and put your question in the most appropriate section since now it is here it is not possible for me to move it. This is a limitation of this Forum software.

Hello - and sorry to hear your situation. Actually, I am not sure about deliveries. What I can say is that some of our Distributors have placed orders out to 2008 - that's 8+ months. Of course, that doesn't mean that the end of the queue is 8 months away but it does mean that a wait of a month and a half is really a very short wait! The average lead time from order in (to our UK office) to goods out has been 12 weeks and that is unlikely to change.

What I can say is that the wait will be worth it.

[Thanos]

My -perhaps childish questions- don't only concern "ageing" of speakers, but also other equipment. I fully agree with Alan's wholistic point of view which rather explains the difference between real -music devoted- listeners and technology freaks (or, if you wish, digital era machine maniacs). So:

1. How really better is new digital equipment compared with those old Leaks, Quads, Bozaks, Rogers, Garrards, etc.,etc.,etc......? Does it SERVE musical emotion in some better way?

2. Because our speakers "age", do we have to change (?) them every few years? This applies also to our other equipment...

3. Why marketing promotes always new models with a devastating rate compared to yesteryear? ( not to mention also car companies, you know what I mean...)

4. What's wrong with serving and keeping in fine working order our beloved oldies?

5. Does all this have to do something with profit, the latter being the centre of gravity or the only religion in this new world?

6. Why do they call me a fool anachronist when I express these ideas with passion, but with enough experience of life, which -by the way -now counts half a century?

Then, when Shaw really respects longevity and tradition, and the man is not a profit freak at the heart of his motives and honestly balanced offer to us, I also have to respect the axiom that "ageing" is not loosing value... Old time cars lasted 30-40-50 years, even more, unless spare parts became obsolete or even "caput". New ones are programmed to die within a decade (at max.).

I don't mean that something or someone will last forever... But I do mean that marketing, profit making and artificial needs shorten the life of goods and alienate many important values.
HARBETH really incorporates such values, even inspires new ones, I believe. So, ageing is not such a big matter or problem, not even by technical standards... It is more a challenge, I would say...

And, a last little question: Why Amatis, Guarnerisand Stradivaris cost a fortune and play so divine? Aren't they "ageing" and loosing their properties? Might sound idiot, but is it really so?

Thanks for your time and hospitality!

Cheers from Athens,
Thanos

[A.S.]

More wisdom from Athens, seat of western culture!

I think that whether we like it or not, to enjoy the high standard of living we do enjoy in the west requires that the 'economic machine' spins round faster and faster .... and that big manufacturing companies have to keep their shareholders content. This means newer products more often, loaded with features - but with the inevitable consequence that the product life cycle is shortened. But who cares? If the consumer must have the latest features then that same consumer will move on to something new and even more feature-laden just before it fails - obviating the need for any spare part!

Of course, we here object to the reckless consumption of resources in society. But we also recognise that to keep millions of people in work there is no other economic system that can generate enough 'tax take' for an advanced western government.

'Green economics' - a wonderful and appealing concept but I just don't see it funding the society we enjoy, and hence quasi-Green manufacturers like Harbeth will remain in a very small niche. Once a manufacturer severs his connection with tradition he is a hamster in a wheel chasing economic success along with all the others hamsters! I'm confident that we'll remain respectful of our heritage and traditions.

[DSRANCE]

I readily agree that worst case ageing can be in ten to fifteen years (I remember a friends favourite speakers with an 8" French made bass/mid unit starting to come apart after around 15 years or so - right around the cone/coil joint if my memory serves - and it would have been difficult to almost impossible to fix without a complete re-build. He now still uses HL5's as I remember for his monitoring...

Electronics also have finite lives before servicing is required. I could be wrong, but much "decent" valve equipment seems to last for years with only the valves needing replacement every so often on the best, underrated designs. Capacitors seeming to last decades before going severely out of specification. Solid state equipment seems to get through supply capacitors after ten years or so like nobody's business - even Quad 405's had physically leaking supply caps after eleven years. Twenty years on, I wonder how the replacement components are doing...

I want a cheap slim used integrated amp for headphone use (and a standby power amp if needed). it seems that anything bought that is UK made and over twenty years old is going to be risky. Anything from the seventies (especially UK built integrated amps) is almost a no-no as designs have moved on quite a bit since then and this, coupled with component ageing makes them almost worthless in real terms.................

[A.S.]

...Electronics also have finite lives before servicing is required.

Electronics do indeed age. It seems to be the capacitors that suffer the most in solid state amplifiers and the capacitors and tubes in tube (valve) amplifiers. Here is an example what happens when an amplifier spontaneously goes "DC" and dumps it's power supply reservoir across the loudspeakers. The only way to save the speakers is to leap out of your chair and unplug them, taking care not to short the speaker cables and then to turn off the amplifier. That assumes that you can hear that the amp has failed - by that time it may be too late.

For that reason, never leave your hifi playing unattended for long periods, and don't leave the house with it still running. Certainly don't leave the house with amp running performing some sort of "burning in" ritual or there is a chance you'll burn it and the speakers out.

[Shutterbox]

Electronics do indeed age. It seems to be the capacitors that suffer the most in solid state amplifiers and the capacitors and tubes in tube (valve) amplifiers. Here is an example what happens when an amplifier spontaneously goes "DC" and dumps it's power supply reservoir across the loudspeakers. The only way to save the speakers is to leap out of your chair and unplug them, taking care not to short the speaker cables and then to turn off the amplifier. That assumes that you can hear that the amp has failed - by that time it may be too late.

For that reason, never leave your hifi playing unattended for long periods, and don't leave the house with it still running. Certainly don't leave the house with amp running performing some sort of "burning in" ritual or there is a chance you'll burn it and the speakers out.

For the matter, what would one hear(or see) when the loudspeakers does not sound right, either due to its drivers/part failing catastrophically, or amps going DC?

Is the latter the only way that will cause irreversible damage to loudspeakers?

[A.S.]

To answer as best I can based on very limited personal experience ....

We read occasionally of the erroneous belief that "huge amplifiers are needed to make good music at home". This misconception ignores the certainty that the weakest parts of the entire audio chain, are of course, the electromechanical parts at both ends; namely the microphone or pick-up cartridge and the speakers. Inside the speaker the motor action that produces sound is the result of the movement of a voice coil cylinder of very thin, hair-like copper wire* inside a narrow gap in the magnetic circuit. Thin copper wire is malleable (a good thing to aid forming and winding it neatly) but it is also has resistance (a bad thing) and that resistance reveals itself as heat when current is passing through the wire. Also, copper expands when it becomes hot.

Now we can see the potential scenario: if the thin copper of the voice coil has dumped on it a heavy current it will (a) become hot (b) expand (c) vaporise the insulating varnish on the copper wire (d) partially short-circuit (e) draw more current from the amp (f) become even hotter (g) expand more (h) become so bloated that it actually jams inside the magnetic gap and cone motion ceases. In these conditions it is very difficult to even cut the unit apart - the coil and the magnet metalwork will have literally fused together.

Luckily this is very rare; I have seen it only a few times over the years and I suspect that the unfortunate user was caught completely unaware as stages (a) to (h) would take less than a minute. Sound of a sort may be audible during (a) to (f) accompanied by the smell of hot varnish. But in a sealed box this smell would be trapped inside; in a vented system it would probably waft towards the user.

A more likely failure mode than the amp going "DC" is overdrive due to playing too loud, probably for too long. Again, if the power amp is excessively powerful then there is more potential energy available to do damage, and to do that damage more quickly and more destructively. We'll dissect an over-driven woofer as soon as we have one available for inspection. Yes, I suggest that the attentive listener would indeed hear that the woofer was under overload stress and could salvage the situation by simply lowering the replay volume. But I guess that overdrive happens because the listener is not in fact near the speakers - probably not even in the same room - and fails to hear the tell-tale distortion of a distressed drive-unit and take quick action. Extreme, continuous overdrive is unmistakeable as it is evidenced by a dramatic increase in distortion and degradation in sound quality.

* I've shown the copper wire in this clip and what happens to it when it 'cooks'. In this case it is probably due to an amplifier fault. Even with a normal functioning amplifier, after very heavy continuous drive at the extreme of the woofer's capability (but avoiding total destruction) there is usually physical evidence of that torture deep inside the drive unit, revealed by dissection. Heat usually leaves a clue to its presence. So why use an amplifier that is needlessly more powerful than the fine copper wire voice coil can properly dissipate as heat?

[David Schalkwyk]

I can unhappily attest to the fact that I have been the victim of an amp "going DC". As Alan says, it takes about a minute, and by the time one realises what is happening it's too late. First, there was a slight harshness, then a moment of bad distortion, silence, and, finally, a whisp of smoke coming from the cone when I'd got my wits together, unplugged everything and taken the cover off the speaker. The volume on this occasion was quite low. What a sinking feeling as I touched the dust cap and it collapsed like an old ice-cream cone...

David

[DSRANCE]

I must once again recall the day that a brand new demonstration amp developed a fault in its "phono" circuit when left for no more than an hour and the direct coupled design amplified the DC into the much loved Epos speakers we were using, causing the voice coil of one to heat up like an electric fire and melt its way through the plastic cone. The fact that this coil was hanging out of the front of the speaker and still conducting spoke volumes for this models durability, but nothing for the amp, which retains a grim reputation to this day (for its mediocre performance).

There's a load of nonsense talked about leaving equipment on all the time, started in this era by one UK manufacturer which uses a particular circuit which exhibits wildly changing bias/offset voltages during the first hour of use and a pre-amp circuit which never fully "forms" the feedback capacitors apparently due to the very low voltages in this particular circuit. We had a few problems with this maker during a low point in the late eighties, as amps would "go DC" for no reason and fry speaker units during the day when the client was out at work... Of course, this blip is long forgotten and people worship used items from this brand just like their forebears did twenty - thirty years ago when these products were new...

As for me, I soon learned just how good Quad amps are if the load they're presented with is benign and I cherish a re-built valve set of "II" power amps to this day.

[eelekim]

There's a load of nonsense talked about leaving equipment on all the time

Bryston is one of the biggest amp manufacturers telling people that an amp should be kept on all the time with appropriate ventilation for more reliable and durable performance. I've once been a Bryston user. I followed their suggestion. Then I found some liquid on the top of one of the big caps. I'm not sure whether it's the result from the 24/7 power on practice.