# Fact or fiction - will underpowering a speaker damage the speaker?



## JLNorthGA (Dec 4, 2012)

It looks like one of the channels may be going out in our inherited amplifier. It is an old Carvin 600. This our house main. It manages to put out a reasonable amount of sound for our space.

We obtained some SM58 microphones by a donation (new in box!) - so we've now got four Shure SM58 vocal microphones. So we don't have to spend the money on that. We've got five Shure SM57 instrument microphones - so even the bluegrass bands should be happy.

We've got to spend the grant money in a timely basis. While an amplifier might not be flashy - it is a needed piece of equipment. I can always use the Carvin to power one (or more) monitor channels for those groups which want several monitor channels (as opposed to just two). I'm currently looking at the QSC GX5. The amplifier would be powering a Nady PS115 500W speaker. My other alternative would be a QSC GX3.

Realistically - we're at maybe 1/3 of the volume per channel on the Carvin. I was thinking about the QSC GX3 as it is less expensive by $100 or so. The GX5 is more sized to the speakers though.


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## Aman121 (Dec 4, 2012)

If speakers could be damaged by under powering, every time the engineer turned the volume down things would explode. No speaker will die from a lack of power alone. 

I think the rumor started because people would drive their low power amps to clipping in an attempt for more volume, this can cause all sorts of problems with the amp and speakers and if sustained can cause the amp to fail catastrophically (outputs to DC, magic blue smoke, fire, turns into plasma grenade, ect), thus converting your speakers into smoking piles of paper and melted wire. So, while indirectly, under powering speakers can cause issues if your clipping your amps, but if you simply don't need the volume no harm in getting a small amp. That being said never a bad idea to go big, ideally the amp is roughly matched to the speakers peak rating so your never clipping anything.


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## Les (Dec 4, 2012)

Aman121 is right -- you won't have problems unless you are often clipping or hitting the amp's limiter as the distorted signal causes the speaker cone to move in very non-musical ways. 

I have the GX3 and it is a great little amp. I have it matched to a set of JBL JRX 112m's, but they are fairly small monitors with about a 300w rating I believe. If you have the money, I'd spring for the GX5. You will not regret having the extra headroom. Even the GX7 wouldn't be a bad idea, but it may be out of budget.


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## museav (Dec 4, 2012)

You cannot really underpower a speaker but you can have an underpowered system.

I'm still trying to figure out what Nady's "Peak program power rating: 500W (250W RMS)" rating really means. Is it 500W Peak or 500W Program or something else entirely?


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## chausman (Dec 5, 2012)

I have nothing but praise for the GX series. I've dragged mine all around for Marching Band (not a very friendly environment for equipment) and they just keep going. They take all common inputs, and have many common outputs as well.

If the amp is going to have to be moved around, and the speakers can handle it, the GX7 is the way to go. It weighs 15 lbs, and the difference is astonishing.


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## FMEng (Dec 5, 2012)

While we are at it, let's destroy the myth that the gain controls on a power amp indicate how much power is being delivered. All they do is adjust the gain structure. Set wide open, the amp might produce full power when the console output is delivering 1 volt to the input. Turn down the gain control down to half, and the amp will need more voltage from the console, say 10 volts for example. As long as the console can deliver enough voltage, the amp can still reach full power. Of course any console, or other piece of audio equipment has a limitation on its output voltage before clipping.

The real purpose of those gain controls is to set the gain structure for the whole system, so the console and other equipment in the chain is operating in its sweet spot while speakers are producing the target sound level.


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## DuckJordan (Dec 5, 2012)

also it doesn't change the out level, it changes the input level.


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## museav (Dec 6, 2012)

DuckJordan said:


> also it doesn't change the out level, it changes the input level.


I have to get a bit picky here as the input attenuators on amps will change the output level by altering the input level, what they do not change is the potential output level. This may be an important distinction as it is common to use the amplifier input attenuators to get a desired output level from some nominal input level. Cinema system are an example where in order to recreate the same experience in multiple venues the goal is to provide a standard sound pressure level at the listeners from a standard source signal level, a result often best obtained by having proper gain structure and then adjusting the amplifier input levels.

On most audio amplifiers the input attenuators do not directly control the output level or the potential output of the amplifier. What they do is more to adjust the input level required to obtain a specific output. So basically, as you turn down the inputs (add attenuation) you decrease the output level for a given input level and increase the input level required to get any specific output, however the amp is still always capable of its full output regardless of the attenuator settings, it will simply require a different input level to get that full output. So turning down the input attenuators does not make a 1,000W amp anything other than a 1,000W amp, it just changes the input level required to generate that 1,000W output.

Along those lines, I find amplifier sensitivity to be one of the most overlooked specifications. Amplifier sensitivity is the input level (with no input attenuation) required for an amplifier to deliver full output. An input level above the amp sensitivity does not provide greater output or at least not anything desired, however there are valid reasons to have a higher signal level hitting the amp. That is why it is common for a system with proper gain structure to require some attenuation at the amplifier inputs.


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## JLNorthGA (Dec 7, 2012)

chausman said:


> I have nothing but praise for the GX series. I've dragged mine all around for Marching Band (not a very friendly environment for equipment) and they just keep going. They take all common inputs, and have many common outputs as well.
> 
> If the amp is going to have to be moved around, and the speakers can handle it, the GX7 is the way to go. It weighs 15 lbs, and the difference is astonishing.



The budget won't stretch for the GX7. Our executive board did approve buying the GX5 instead of the GX3. They also approved something I didn't ask for - a new inexpensive laptop.


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