SHEFFIELD wrote:

Question he has put to me - the speakers are capable of delivering 8200 watts, but ohms law would suggest that to deliver that kind of output a 30 amp supply would be required. If I remember right, the Lab 5s have a plug top fuse rated at 10amps for their 2500 output?

I was advised in Budapest that the speakers would in most cases be run in 'energy saving' mode to avoid the need for a dedicated mains supply capable of 30 amps plus, but it reality, anyone investing £55k won't want to run them in a restricted mode?

Hi Nick,

I'll leave it to Geoff to clarify any details specific to the BL90 (and hopefully to correct me wherever necessary) but will make some comments / observations from an electrical point of view...

Firstly, fused plugs are not commonplace worldwide - the BS1363 UK plug socket arrangement is incredibly well designed from a safety perspective (those who have accidental stood on an upturned UK plug might disagree I suppose!) and the fusing is there largely as a result of the use of 'ring final' circuits in the UK and the fact these tend to be protected by a 32 Amp circuit breaker at the consumer unit as opposed to the more common (internationally) radial circuit arrangement which tends to be fused at 16 Amps or less. The history behind the use of ring circuits in the UK is largely the result of copper shortages, but my aim here is not to give a history lesson but just to make the point that plug top fuse related issues are likely to be largely a UK concern.

Now the fuse itself - A 13A BS1362 'plug top' fuse is required to carry 1.6 times it's rated current (ie 19.8 Amps) indefinitely without rupturing, and is required to rupture within 30 minutes at 1.9 times its rated current (ie 24.7 Amps). Going further it's required to rupture within 1 to 400 seconds at 30 Amps, 0.1 to 20 seconds at 50 Amps, and 0.01 to 0.2 seconds at 100 Amps. The fuse it really there to protect against short circuit scenarios and long term overload situations, and in many cases the 32A circuit breaker in the fuse board is actually likely to trip before the 13A plug top fuse ruptures. The point here is that short transient demands of several times the 13 Amp rating can be accommodated without any issues.

You are correct that 8200 Watts, at 230 Volts, is around 36 Amps - yes I know the mains is *really* 240V in the UK, but we're all harmonised with Europe now so we're officially 230V for calculation purposes 😕 In fact given no amplifier is 100% efficient, the input current would actually be higher that this, but...

I suspect none of the drivers would survive the maximum output of their relevant amplifier for any length of time, certainly the voice coils in the tweeters would melt pretty quickly if subjected to a continuous 300 Watts as that is a lot of heat to try and dissipate. 8200 Watts is roughly equivalent to three or four electric heaters or a fairly decent electric shower. Add it's stereo partner and you'll probably not need to turn your central heating on during winter and you can forget needing to go to a sauna - just stay at home and listen to load music (perhaps whilst wearing ear defenders!).

I guess the obvious question at this stage then is why such large amplifiers? Whilst this is an area Geoff will be much more knowledgable and better qualified to explain that I am, specifying amplifiers that on paper would seem overkill compared to the maximum continuous ratings of the drivers does in fact make a lot of sense - unlike the mains power, music is not (generally) a nice pure sinewave and instead consists of many transient peaks and troughs and the amplifiers need to be rated sufficiently to not clip (cut off the tops of the waveform) during these transient peaks as this leads to distortion and large amounts of energy flowing through the voice coils with no movement of the cones.

There's a common misconception with conventional amplifier plus passive speaker setups that it makes sense to specify speakers that have a higher rating than the amplifier on the basis that it is then impossible to damage the speakers by turning the volume up too high. In reality, this is often a more risky approach than the other way around because as soon as the amplifier starts to clip, a large proportion of the energy ends up heading to the tweeter (at least with the one amplifier, multiple drivers + crossover arrangement).

The bottom line then is that whilst the total rating of all the amplifiers is 8200 Watts, that figure is unlikely to ever be reached except for very short transient spikes and even then the power required to handle these is actually much more likely to come from the capacitors within the power supply than directly from the mains.

Hope this helps,

Martin.

Hello Martin, heat generation that you describe are this even valid for ICE Power amplifier.

it is not that ICE Power has a loss of 20 percent as heat? and 80 percent clean power to your speakers. In that case they should have only 20 percent heat as a conventional amplifier having a high level of 80 percent of heat.

Best regards

Jan

www.beoshop.se

BegBeo wrote:

Hello Martin, the true development of heat that you also describe to the ICE Power amplifier. Was it not the case that ICE Power has a loss of 20 percent heat and 80 percent clean power to the speakers.

I don't know the efficiency figures for the ICE Power Amps, but I can believe a figure of 80% could well be realistic. Unfortunately though, that doesn't mean only 20% of the theoretical 8200 Watts ends up as heat, it just means the other 80% gets converted to heat elsewhere in the system - be that in the interconnecting cables, within the voice coils of the speakers, or heat generated by friction of movement - both in the speaker cones and between air molecules that are moved around by the speakers whilst creating the desired sound pressure waves.

Since energy can neither be created nor destroyed, only converted from one form to another, it's safe to assume pretty much 100% of the input energy to the speakers will ultimately end up as heat.

Martin.

Out of interest I just googled for cone speaker efficiency and the indications are that cone drivers usually have efficiencies in the 1 to 2% range so (with the caveat of not believing everything we read on the internet) 98+% of the energy not lost by inefficiencies in the PSU and amplifiers and thus sent to the drivers will end up as heat within the voice coils, with the remaining 1-2% being converted into sound energy (and later ending up as heat outside of the speaker).

Kind Regards,

Martin.

Cone efficiency of speakers is not affected by the amps and power supplies, it's a measure of the radiative efficiency of the driver operating into the air, i.e. how well it couples and translates the electro-mechanical energy to actual acoustic energy, so this is an inefficiency on top of the amps and such. The only way to get higher efficiencies with transducers is to go with horn loading, which matches the acoustic impedance at the throat of the horn and the driver to maximize efficiency, and even then it's nowhere near the efficiency of, say, a power amp.

Jeff wrote:

Cone efficiency of speakers is not affected by the amps and power supplies, it's a measure of the radiative efficiency of the driver operating into the air, i.e. how well it couples and translates the electro-mechanical energy to actual acoustic energy, so this is an inefficiency on top of the amps and such. The only way to get higher efficiencies with transducers is to go with horn loading, which matches the acoustic impedance at the throat of the horn and the driver to maximize efficiency, and even then it's nowhere near the efficiency of, say, a power amp.

Hi Jeff,

I  wasn't trying to suggest the efficiency of the drivers depended on the amps or PSU.

My caveat was about the accuracy of the driver efficiency percentage and I was elaborating on the "it just means the other 80% gets converted to heat elsewhere in the system" statement in my previous post where it was queried as to whether it was valid to state that 100% of the mains input power would be converted to heat given the use of high efficiency amplifiers.

The "98+% of the energy not lost by inefficiencies in the PSU and amplifiers" comment was referencing this same 80% of input power (ie what had not already been lost to heat within the PSU and amps) as that is what will actually reach the drivers to be converted to sound waves or to heat.

eg:

• 20% of input energy converted to heat in the PSU & Amps.
• 98%* of remaining 80% converted to heat in the voice coils.
• remaining percentage converted to heat outside of the speaker but mostly within the room (you could argue any sound that escapes the room will not contribute to heating the room, but we're talking tiny percentages of the input power here).

* Previous caveat about the efficiency figures remains - the driver efficiency will vary from driver to driver (and by frequency) and I don't know how representative the 1 to 2% figure is.

Kind Regards,

Martin.

Hiort wrote:

Thanks. Many interesting videos if you look for Beolab 90 on YouTube.

Regarding the actual power usage of the ICEPower amps. 

The beauty of the amps is that they actually consume only what they need. Compared to a "normal" amp that basically uses full power from the moment it's turned on, whatever the actual output to the speakers are. (Why they are warm) 

The Beolab 5's have 2500W of amplification, but the amps are on "idle" all the time. Even as you are playing them loud. (Reason why you can play them loud) As "Idle" amps means low distortion. Why most speakers don't come close to the sound pressure able from the BL5's is mostly down to distortion. 

I've checked the actual Wattage usage on my Beolab 5's with one of those gizmos you plug in to the wall and then the BL5's mains cable into it, and the highest I saw was around 80W per speaker, it did bump to 110W or so occasionally. This was at higher than normal listening volumes.

I don't think the Beolab 90's will draw much more than a few hundred Watts of power at normal use. 

It's self explanatory that the Amps in the Beolab 90's will never reach a 8200 Watts power use, as you'd need a 37 amp fuse at 220 Volts! Not normal for any house. You would need three phase wiring with higher voltage or a VERY thick and warm cable. :D :D :D  

The seemingly outrageous total power rating of the Beolab 90 has nothing to do with continuous ratings or fuse requirements etc.

It is to ensure that each driver has sufficient power on tap to respond to the highest foreseeable transient power requirement, i.e. the individual amplifiers are sized to respond to and reproduce the maximum instantaneous power requirement without distortion.

Puncher wrote:

The seemingly outrageous total power rating of the Beolab 90 has nothing to do with continuous ratings or fuse requirements etc.

It is to ensure that each driver has sufficient power on tap to respond to the highest foreseeable transient power requirement, i.e. the individual amplifiers are sized to respond to and reproduce the maximum instantaneous power requirement without distortion.

Thanks Puncher, you've put that very succinctly. This was exactly the point I was trying to make, albeit whilst providing additional explanation and logic to explain and justify this (undoubtedly too much detail in hindsight!) as Sheffield's potential customer seemed to be questioning the ratings at a more technical level on the basis of P = I x V

Kind Regards,

Martin.