I have a 2005 Honda Pilot EX and I want to buy a Pioneer AVH-X5800BHS headunit for it and I heard in another StackExchange question that it had a 70W subwoofer output but I heard that my car has a 50W 2 ohm sub. I want to know if there is any way that I can limit the output wattage to 50W or if I have to keep the EQ at or below a certain level to prevent damage. Any reply would be appreciated.
First and foremost, no. There is no (simple) way to specifically limit wattage output like that, nor is there a need for it. Wattage output is anything but constant, so it's really not something you can easily cap - even at constant volume different frequencies will pull different amounts of power. Your best control is the various opportunities you have to set relative volume. You can also help protect smaller subs with a HPF at 30-35hz, which would prevent them from getting signals they can't audibly reproduce anyway.
I'm not sure what you're planning with that head unit, but I don't see anything about a discrete subwoofer output in the specs. If you're planning on hooking up an external amplifier I suggest you be extremely careful for two reasons:
- Most small amplifiers will have trouble driving a 2 ohm mono load.
- Most larger amplifiers will be capable of ripping that speaker to pieces if you turn them up too high.
With that said, it is often ideal to have more power available on tap than is recommended for a speaker (my 300W "max" towers are safely being driven by a 440Wx2 amp). This is not because it's impossible to damage the speaker, but because extra available power means clean power. You can always turn it down to prevent over-driving the speaker, but if the amp isn't powerful enough you can easily start over-driving the amplifier, which is a great way to damage speakers with distortion. There are other benefits like cone control in challenging sections, but that's way more technical than we need to be here. Just don't overdo it - if you hear distortion, turn it down - and you'll be just fine.