What is the actual power handling capacity of my JBL Paragon, and will it go loud enough for my Mable’s 80th Birthday Motorhead theme’d bash tomorrow?
Well, it’s all explained right here.
The idea for this article came from an audiophile friend - as indeed my best ideas generally do. His experience is that many of his clients are confused about “power handling”- the detail which generally tops the list of loudspeaker specifications. Quite simply, the thinking is that the bigger the maximum power handling figure, the louder the speaker will go. If only it were that simple, but it's not hopelessly complicated either, given all the other factors involved. The key is speaker efficiency, which is as important as power handling when thinking about sound levels. So let's pump up the volume and get on down. Oh Lord! Whatever next....
This is usually referred to as “speaker sensitivity” on the manufacturer's specification sheet, and is the volume level the speaker produces at a distance of 1 metre, when 1 watt of power is fed into it. This volume level is expressed in decibels (dB's). A typical specification may be 85dB/1 watt @ 1 metre listening position. In acoustics, the decibel is used as an absolute indicator of sound power per unit area. A decibel is one-tenth of a Bel, a seldom-used unit named after Alexander Graham Bell, inventor of the telephone. What is important to remember is that decibels are set on a logarithmic scale, so a doubling of dB's bears no relation to a doubling of perceived loudness. In fact, in reality a doubling of dB's is virtually impossible over 70dB as it would represent a phenomenal sound pressure levels (SPL). For example, 85 dB equates roughly to the volume level of city traffic inside a car. What is very surprising is the big jump in sound level that just an additional 5 dB produces. Take a look at this list.
Weakest sound heard 20 dB Whisper Quiet Library at 6' 30dB Normal conversation at 3 feet 60-65dB City Traffic (inside car) 85dB Heavy Truck Traffic 90dB Jackhammer at 50' 95dB Subway train at 200' 95dB Hand Drill 98dB Power mower at 3' 100dB Snowmobile, Motorcycle 100dB Powersaw at 3' 110dB Sandblasting, Loud Rock Concert 115dB Pneumatic riveter at 4' 125dB Jet engine at 100' 140dB
Now, this next table illustrates how speaker sensitivity (efficiency) affects volume level. All the power (watt) requirements shown are to reproduce 80 dB at 2.5 metres. See how the power required changes as the speaker becomes less efficient. By the way, speakers of 104 dB are extremely sensitive, and would almost certainly be a horn loaded design.
What affects loudspeaker efficiency?
Well, there are many factors which determine how our precious watts are eaten up:
Drive units. The obvious one is the design of the loudspeaker drivers chosen by the manufacturer. This includes the weight of the cone assembly, the voice coil material and design, and the power of the magnet assembly.
The type of enclosure. A sealed infinite baffle or sealed box is generally a less efficient design than a ported enclosure, as the speaker's cone movement is restricted by the air trapped behind it. In a ported box, the port itself produces a low frequency output, but obviously uses no power directly. This is useful as bass energy is the most power hungry of the frequency range to reproduce. Incidentally, transmission line speakers like IMF/TDL excel on the bass front by utilizing a very long large tuned port. This type of speaker is called a transmission line enclosure.
Crossover network. Don't forget about the poor old crossover network inside the speaker, the invisible Cinderella part. This filters out which frequencies are sent to each driver (speaker) in the enclosure and at what level. All the drive units must "sing" at the right volume so no single one is dominant. Speaker design usually incorporates several different drivers, so the crossover is necessarily more complex. Roughly speaking, the greater the sensitivity mismatch between the indiividual driver specifications, the more components (including resistors) that are necessary to balance up the situation, and the more likelihood of wasted power in the process. I'm generally a very big fan of keeping crossover network design simple, but that's another article or ten.
Loudspeaker power handling.
Now we've covered efficiency, it's okay to think about how power handling will relate to sound volume. A “rated power handling” suggests how many watts your speaker will cope with before giving up the ghost, probably as a result of the voice coil overheating, the cone moving too much or an electronic component failure in the crossover network. Vintage speakers typically had fairly low power ratings of say 15-75 watts, especially so when they were horn loaded. For even a high quality vintage design, if it’s very efficient, power handling could be as low as 20 watts maximum. For a modern, high-end large domestic design, power handling may be hundreds of watts. We won't even think about cinema and concert hall installations. Just add a few noughts.
But what does power handling actually mean, and what's the difference between continuous and peak power handling?
Without knowing great detail regarding a particular loudspeaker design, “power handling” by itself is very ambiguous. Fot instance, how much distortion is produced at this power level? Manufacturers invariably omit this information altogether. Very bad people, I'd say.
Continuous power, as you would expect, is sustained wattage (power) being fed to your speaker by the amp, typically by playing heavily compressed loud music from the young people’s Hit Parade, or playing a recording of an uninterrupted loud pneumatic drill (strange tastes here in Edinburgh). There is no let up in the noise made.
Another obvious example of continuous noise is the sound heard when you plug up something incorrectly in your system, and it's letting you know about it through the speaker. Continuous power is also quoted as RMS, and whilst not strictly correct, there are more pressing points to think about than getting involved with Root Mean Square. In fact, I’d have to look it up myself.
“Maximum peak power” is usually a significantly higher figure than continuous power, and certainly looks more impressive on the manufacturers specification sheet. Sometimes it’s double the continuous power figure. Maximum peak power handling, sometimes also referred to as “music power”, is the maximum power the speaker can handle in bursts of high level sound such as a brief crescendo of a symphony or a kettle drum strike. Because it's not a sustained onslaught like the road drill I’m so fond of, it gives the voice coils and other components a respite to cool slightly, so they are less likely to overheat. This lets them go on indefinitely and tolerate a higher input than “continuous” programme would allow. The trouble is, the “peak” referred to is not clearly defined in terms of duration.
Is Dame Shirley Bassey belting out “gold finnnnggggaaaaaaa” for 10 seconds, peak or continuous power? Best to keep her low, just in case.
The maximum volume a loudspeaker can produce is primarily governed by it's efficiency and power handling. A speaker with 80 dB/1 watt input @ 1 metre is regarded as insensitive, and one with 95 dB/1 watt as very sensitive. Vintage speakers often had lower power handling abilities than their modern counterparts, as current designs are built with the latest components which allow greater power handling, and a greater tolerance of high temperatures. Horn loaded speakers such as the Lowther are super-efficient, so the power handling is that much less but still make a big noise. It's also worth remembering that amplifiers a few decades ago usually had a much lower power output than the powerhouses of today, but that's not to say that watt quantity equates to watt quality. Far from it.
RMS or “continuous power” will be a lower figure than “music power”or “programme power”, so be wary of quoted figures. Don’t be too concerned if your amplifier RMS output power rating is slightly higher than the speaker’s handling power. Damage is unlikely to occur unless you are irresponsible with the volume control, which is never a good idea anyway.
In my humble opinion, these are the main factors around speaker volume. There are plenty of other considerations to do with amplifier/speaker interaction that will affect the quality of sound from your cones, or electrostatic panels. This relationship between a particular speaker and amplifier is well worth further exploration. Check out my article on “nominal impedance”- a real belter that one!
Meanwhile my own efficiency is waning somewhat, and my peak power diminishing, though you may think it wasn't too high to begin with. Anyway, please let me know if you found this article useful. Too much detail or too little? I'll adjust accordingly. Meanwhile, time for a coffee methinks.