From time to time someone looks up speaker ratings on Celestion's
website and asks us why the speakers we use are rated below 200 watts.
Are we misrepresenting the amp's true power output? What gives?
To answer this question requires looking at what causes speakers to fail and how they are rated by the manufacturer for the given applications.
Speakers have two basic failure modes. The voice coil can heat up when driven hard and break or short out. The other way speakers fail is due to physical damage to the cone, surround or coil wire from excessive movement. The risk of mechanical damage is usually dependent on the the cabinet design and porting while voice coil thermal damage is largely dependent upon long-term high power levels.
Music is highly variable with respect to how much power is produced at any given moment, so the industry standard is to derive a continuous power rating for amplifiers using a pink noise signal that is more abusive to the speaker than actual music would be. Not all amplifier manufacturers rate their products exactly the same way, but across all the major brands you will generally find fair assessments of power output.
Speaker manufacturers rate their speaker's power handling fairly conservatively so that their customers can match a speaker to a given amp with a good safety margin understanding that tube amps can put out up to twice their rated power when fully clipped. In addition, pro audio speakers are rated very different from guitar speakers which muddys things even more.
To get past all the rating variability, Quilter Labs uses a real world test regimen in our speaker selection process to ensure that the speakers we supply in our amps can take the power levels safely over a long life span. This testing establishes a thermal point that is far greater than would occur through normal use of the amp. We then continue to run the speaker at this level for a minimum of two hours. Believe me when I say that lesser speakers don't last very long at all and it's a real testament to the quality of Celestion's speakers that they can withstand an amazing amount of punishment and come out sounding as good as ever.
The closed-back design of our amplifiers and speaker cabinets helps to protect the speakers from damage due to over-excursion. This allows them to safely play louder and bigger than you would expect.
We do have one more trick up our sleeve when it comes to speaker protection and that's our unique "watchdog" circuit that monitors the thermal level of the speaker and quietly eases back the headroom of the amp when necessary. This applies to the internal speaker and any extension speakers connected to the amp.
The Quilter MicroPro 200 is capable of producing 100 watts of continuous power from each channel simultaneously. With one speaker connected, maximum gain and the watchdog active, the amp is producing a little over 100 watts of power. With an additional speaker connected, the amplifier can produce the full 200 watts of power.