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Measuring safe operating limits and the difficultys

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Jun 7, 2011
First i want to say this is really a difficult topic and it could probably fill a whole book, but i just want to make aware and take the chance to increase my own knowledge. My knowledge is pretty much at the lowest stage and it can be a issue when seeking for the "true stuff" and taking care at good HIFI for not damaging it.

I write this stuff, so people can 1. Confirm it is correct, 2. Working out whats specs are considered safe to use because manufacturers are hidding many important stuff, for example the exact operating limit information regarding the Neodymium magnets. I will add the issue at the end of the topic, first i want to show my maths.

So, the general issue to all electronics is the heat tolerance, thats clear and its the main issue all the Overclockers are facing but not only overclockers, it can safely by taken over to all electronics, especially high powered HIFI electronics. Liquid cooled speakers or even Amps making sense? Most people may laugh at me... but it may sound fun but it makes strong sense. The same rule will apply to any electronic, as cooler it runs the higher the lifetime and as lower the risk of damage. To some extend mechanical stuff such as HDDs should not be below zero else the mechanics may become alignment issues (because not build with those temperatures in mind), so i may not recommend below zero but this is almost the only exception and the only reason is because there is mechanics involved, not electronics only.

When it comes to speakers, i noticed that the magnets which is a main part of the drivers and extremely critical, every speaker works using a magnet, can have very low tolerance to heat. This is a serious issue because most speakers are very inefficient. A 87dB@1W speaker is wasting around 99% of energy into heat*. It will result into a lot of heat affecting the drivers, i made a short example for how much heat the drivers will have to handle in term of my setup. 99% of the energy used in the specs below is wasted as heat (efficiency already taken into account), it will directly heat up the drivers and magnets in general. The higher the heat as lower the efficiency of the speakers, so the values listed below are in fact inaccurate and rated at 24 room temp, but it could be a good amount less effective especially when even more heat added to the speaker.

*Note: Heat isnt necessarely a waste in economical terms as long as someone can heat their room using it (currently i can use it as a room heater because to cold without heater). The main issue is the damage it can cause...

Continuous handling: The capacity able to handle at permannent use (24 C room temp).

3 speaker at 100 dB @1m range. This value is safe to use in short term (probably less than 3h).
KEF Q300: ~7W (~87 efficiency)
Klipsch RB61II: ~2.25W (~92 average efficiency, tweeter 93, cone 90)
Wharfedale 10 CS: 5W (~88.5 efficiency)
KEF R400b: ~40W (~81 efficiency, actually a good value for a subwoofer). Note: It only counts as 2 speaker.

3 speaker at 100 dB @3m range.This value is safe to use in short term (probably less than 3h). (effective dB@1m = 110)
KEF Q300: ~65W (~87 efficiency)
Klipsch RB61II: ~20W (~92 average efficiency, tweeter 93, cone 90)
Wharfedale 10 CS: ~45W (~88.5 efficiency)
KEF R400b: ~350W (~81 efficiency, actually a good value for a subwoofer). Note: It only counts as 2 speaker.

3 speaker at 85 dB @3m range. This value is safe to use in very long term (probably 12h a day). (effective dB @1m = 95)
KEF Q300: ~3W (~87 efficiency)
Klipsch RB61II: ~1W (~92 average efficiency, tweeter 93, cone 90 )
Wharfedale 10 CS: ~2W (~85.5 efficiency)
KEF R400b: ~12W (~81 efficiency, actually a good value for a subwoofer). Note: It only counts as 2 speaker.

3 speaker: Maximum continous dB @1m range. This value is safe to use in very short term (probably less than 5 min) but at a critical spot. The maximum value should be avoided at a range of 1m.
KEF Q300: max rating surpassed at ~112.5 dB crossing 120 W line (it would be exactly 111 dB @2 speaker)
Klipsch RB61II : max rating surpassed at ~116.75 dB crossing 100 W line
Wharfedale 10 CS: max rating surpassed at ~115 dB crossing 150W line
KEF R400b: max rating surpassed at ~111 dB crossing 500 W line Note: It only counts as 2 speaker.

3 speaker: Maximum continous dB @3m range. This value is safe to use in pretty short term (probably less than 2h).
KEF Q300: max rating surpassed at ~103 dB crossing 120 W line (dB+4-6*)
Klipsch RB61II : max rating surpassed at ~107.25 dB (average value of cone/tweeter) crossing 100 W line
Wharfedale 10 CS: max rating surpassed at ~105.5 dB crossing 150W line (dB+2.5-4.5*)
KEF R400b: max rating surpassed at ~101.5 crossing 500 W line (dB+4* + external 12 clock). Note: It only counts as 2 speaker.
*Adjustment to catch up to the Klipsch cone and tweeter.

Theoretical power capacity required in order to drive speakers at max rating: 1240 W
Practically sustainable capacity related to Amp specs: ~1000 W (sufficient for ~101-102 dB@3m range).
Concert peak loudness =110 dB possible at a range between 1.5 m and 2 m, Amp is sufficient

Rule of the thumb:
+1 speaker = +1.5 dB
+2 speaker= +3 dB
Because different mode use different speakers, average value is used (+1).

Calculator used: http://www.sengpielaudio.com/Rechner-wirkungsgrad.htm

Peak handling: This term is of low use because the dB should never exceed 110 , because it is considered unsafe to the ears, even in short duration. Although not a single (consumer grade) speaker can realisticaly handle above 110 dB @3m without having a clirr factor (above -+ 6 dB) that is easely hearable and in that term "not favorable". It got no meaning for real use and is not more than simply showing off muscles. Above 110 dB (110 dB = concert peak loudness, which is the max a audiophile may ever wish for), even short duration, should always be avoided. The question is what will last longer, the ear or the speaker... so the peak values of speaker is foolish but i would take the one from the ear instead.

Lets say someone want just have highest noise possible... it may simply require the most huge tweeter, Amp and a very big horn in order to guide the sonic waves in a direct front lined condition... this kind of technique is partially used by Klipsch so they use a trick in order to raise efficiency, but it is not necessarely due to the quality of other parts but simply a tech feature that got pros and cons at the same time. A tweeter of big size may not necessarely sound better, usualy even worse because the sonic dispersion when it comes to the angle will be rerduced (the same issue a horn is facing), so a 25 mm tweeter could be a sweet spot and size related to tweeter isnt necessarely a cost factor. In term of Klipsch, they seems to use the efficiency of the horn "loaded" tweeter and the tweeter is going all the way down to the 1500 Hz line, so it will cover so much frequency that the bass driver is kinda a minor component but with lacking efficiency it seems. So thats the reason i have to add +2 dB to the horn "loaded" frequency in order to become harmonic in sound balance. So the truth is a bit more brittle then the stuff Klipsch seems to claim. But in overall it is a nice and affordable almost audiophile grade speaker with some tricks added, that may be in favor or disfavor, dependable on hearer. Although i was using my own "by hearing" rating and not the official one because i noticed it is not able to keep up the claimed efficiency when i was comparing it with other speakers and trying to adjust the balance. Generally the Klipsch are outstanding when the Amp is weak, perhaps some audiophile Amp with low power but high sound quality and generally for very large room that may require some more dB pushing.

Now the main cause why im writing this:
I was investigating the safe operation limits of Neodymium magnets, known as Nd2Fe14B, the currently strongest magnets on earth and usually used on high end tweeters. The raw Neodymium material from Nd2Fe14B magnets is vulnerable to heat above 80 C and at that point the magnet can suffer permanent damage, but it will still continue to work in a "reduced efficiency state", so as soon as the magnet is heated up above 80 C it will already suffer efficiency and may have decreased sound quality. The Curie point, the the point where a magnet will suffer critical damage, to the point of a total loss of any magnetic power and when that line has been passed the speaker will be destroyed... because the magnet will completely stop to work and unable to be recovered. The Curie point for Nd2Fe14B is 310 C, this is not the "safe operation limit" but the point of "badaboom". However, there is more heat tolerant versions of Neodymium magnets available with additional rare earth materials. In some term the manufacturers use certain solutions, they may actively air-vent the tweeters (probably used by KEF) or even use liquid cooling, but i dont know if sufficient or not and under what conditions.

2 questions will appear now:
1. Whats the exact material used (manufacturers rarely hand out informations)
2. How hot will it become in usual, is there any real risk involved.

Question 1 is difficult because there is many versions of Neodymium magnets possbible, some got other rare earths added in order to raise the operation limits. In most terms such a "raise" is not needed because the magnets wont heat up a lot. But for HIFI it can truly become a issue, because able to heat up a lot, even above the usual safe operation limits. The logical result is that HIFI is not only in need of powerful magnets but heat resistant magnets too... which can be considered the most expensive magnets on the market, in term they are used. It truly is a matter of quality... and simply hard to be cheap on that matter, else the risk of damage can be high.

Question 2 is difficult too because way to many factors and actually almost no one know good numbers...
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Yes... Speaker efficiency/db ratings /1W.

Assuming I understand your point (which is a huge question...) There is more to it than just the magnets. Not to mention, I just use the rms rating on the box. K.I.S.S!

Edit: how about you reply to your rambling diatribe about consoles you put in the forum feedback section too....
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No need to worry the other parts... either they will burn or melt down or they will stay functional, but a slow depletion in the way a magnet is doing, is not really possible. Of course the cap of a frequency switch will have the lifetime reduced by countless times but it usualy will stay functional until the end of life.

There is mechanical parts that can become weared out or damaged, but it would usually need a insane load that will produce crazy clirr. Most hearers will never reach such a point, unless they are totaly crazy or using it in a way that is not intended (small speaker in a huge concert hall or whatever). The problematic spot is usualy magnets and amps, i would say. Those parts simply tend to overheat and can suffer permanent damage. Additionally, not every room is 24C, my room may heat up over 30 C at some point, but rather rarely. Many manufacturers wont give more than 3 year warranty to an Amp, usually not even more than 2 years, and in term law isnt forcing it they may just hand out 1 year. Because they know exactly that the failure rate is simply to high in order to be affordable. In such terms... i would be careful... a good sign of a low quality amp in term manufacturer is not willing to give at least 5 year warranty. Luckily most people rarely use their HIFI, they are working most of the times in order to get cash (so they can buy stuff that is not used nor needed and constantly thrown away) and so the Amp is rarely ever activated and it may easely surpass 5 year... but those using it 24h a day... thats another scale and most mainstream Amps tend to break above 2 years under such conditions. I guess its hard to see the truth but thats why i bring up so many stuff...

Forum feedback? I now need to go to prepare my food because im almost starving, didnt eat whole day because so busy with countless issues... so i have to hand out prioritys to critical matters.
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Apparently rambling on about speakers magnets has a priority over your other thread everyone is confused over.. :)

Eat up... You have two threads now to clarify their points!
The magnets are composed of approximately 70% iron, 5% boron and 25% neodymium. Manufacturers don't state the case because it's a standard composition to produce such a magnet.

Pretty obvious its mostly iron content as most magnets are composed with high iron content in order to magnetise them.

It's basic school level science.... Did you ever make magnets from a nail? Firstly by stroking a magnet along the nail... Then again by placing a nail within a coiled charged wire. :)

As for the rest... You gets what you pay for. I've thrashed neodymium with no notable performance drop off. there's no maximum wattage on some high end speakers. My Lynn simply have "the spider" a device at the back of the cone to catch it should you put too much energy into them.
It's a tiny enclosure and cooling is provided by the port and cone drawing air back into the speaker enclosure.

As regards power... I'll take a clean 20-40 watts as apposed to the room abandoning figures you've pulled out.

And a lot of high end amps involve designs that run hot... Sooner or later your electrolytics will dry up. Just nature of the beast.

You seem to have over thought the situation... If you needed damaging energy to get to the back of your favourite recordings then somethings drastically wrong with your component choice.

And now I run away... Not a big fan of talking guff about audio... Folk debating over what neither can hear first hand is a futile pass time :salute: :burn:
Made wrong maths but it is corrected now, should be accurate yet.

According to my specs you can easely go 85 dB using your "clean" 20-40W, but there is no reason to ever go above 100 dB, and actually in a range of 3m it wont go much above that value (now that my maths are corrected im pretty sure). So i would'nt consider it "room abandoning", i think it is very suitable for any demand.

Thanks for the magnet infos but unfortunately it doesnt say much about safe operating range and dunno how hot it may become. A standart Neodymium magnet, such as the one you are showing with same composition, will be damaged at 80 C+. How big the risk... i cant say and thats one of the main reasons i created this topic. There is non standart Neodymium magnets available with higher tolerance but i guess it is not used.

Besides, i never said i needed "damaging energy", in fact i dont even know how much could be damaging. Your comment is not really that useful but thanks anyway.
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Excess heat... First in line would be voice coil failure (fused wire loosing a few hundred winds) followed by mechanical failure.

Any theory's of magnet failure... Well I'd try and consolidate pedantic ramblings to some kind of concise question and put it to engineers involved in speaker design (if you catch them on topic they'll spill all about there passions)

What we do here is aid end users a knowledge base to overcome issues and get the best from their products.

Philosophical and vague broad spectrum questions maybe best under general discussion where we can speculate our Internet assembled opinions and shoot theories in the hopes someone in the know can settle debate. :)