Dumb musician question about amp power

[JCM800]

Hi, I play guitar and have a question about a difference I see in guitar/bass world vs. hi-fi world.

• My 100 watt guitar head is connected to a speaker cabinet with four 25 watt speakers
• My 80 watt guitar combo is connected to a 150 watt speaker
• The rule of thumb is to have your total speaker wattage higher than your amp wattage so you don't blow them out.
  • Lower wattage speakers will break up at high volumes (a good thing), but too much costs a lot of money to fix
    
• In audio, I see a lot of "You're going to want at least 100 watts to drive these speakers" Never a discussion about too much wattage, only not enough. In music gear, never a discussion about "not enough" wattage.

What's the difference? Are hi-fi speakers rated so highly that there's no chance of them blowing, so the convo turns to how much you need to drive them? Why don't guitar speakers talk about needing *this much* amp to really get them going?

 

[DVDdoug]

In audio, I see a lot of "You're going to want at least 100 watts to drive these speakers" Never a discussion about too much wattage, only not enough. In music gear, never a discussion about "not enough" wattage.

Usually nonsense!!!

There is a sensitivity spec which is something like 94dB SPL at 1W and 1 Meter. Then you get +3dB every time you double the power (so with that made-up example you'd be at 100dB with 4 Watts) or +10dB with 10 times the power.

There is also (obviously) a maximum power rating.

Hi-fi speakers, if they are rated honestly, are supposed to be "safe" with regular program material and an amplifier of the same wattage (or less) that's not clipping. When an amplifier clips it can put-out more than the rated power and clipping creates harmonics which means you can fry the tweeter.* And the tweeter can't handle as much power as the woofer (or midrange) to begin with, so it's more vulnerable.

And if you have highly-dynamic music with a few loud peaks, you can get-away with peaks occasionally exceeding the speaker's rating.

It's "statistical" because it's the average power that overheats and burns-out speakers and they are counting on peaks greater than the average and the high-frequency content being lower than the lower frequencies.

Since guitar amps are commonly overdriven for a higher average level, the speaker is usually rated for twice the amplifier power.

There is an old JBL paper about speaker power ratings: spkpwfaqw.pdf





*There is a myth that it's safer to use a higher-power amplifier than a lower power amp that's clipping. It's true that you get harmonics with clipping so if you have a 100W speaker, it's dangerous with a 100W amplifier that's clipping, and with a 200W amplifer that's almost clipping. A 50W amp that's slightly clipping is probably OK.

 

[AnalogSteph]

In a multi-way speaker as the norm in hi-fi, it is possible to destroy the tweeter with a heavily-clipping amplifier. Clipping generates a lot of high-frequency content, and a tweeter generally can't handle more than a few watts by itself (nominal power ratings often assume a crossover). You can normally hear such abuse but heavily intoxicated individuals are an exception.

Guitar speakers are wideband affairs and hard to destroy short of feeding them with substantial amounts of DC, which rarely ever happens. So an underpowered amplifier is of little concern to them, but you can blow them with too much power, of course. (Wideband speakers do not particularly lend themselves to some ways of making speakers tolerate higher power input, they're essentially constructed much like they were 40+ years ago.)

 

[ZolaIII]

It's really simple. Your instrument frequency range is from 41.2Hz to 329.63Hz and harmonics go up to 4 KHz (approximately). The HiFi guys around hire want their subs to go 20 Hz and even below in a rather linear matter of 0 dB. Regarding me it's fine to 30 Hz and nice roll off behind. In order to produce that they need much more power especially as some even want their systems to be able to reproduce that on live content/club level's (about 110 dB). Take for example calculations for Linkwitz transform for sealed enclosure sub's including excursion rates not to blow either. Forget the 2.88 V LPS ratings @ 1 KHz.

 

[JCM800]

I love this forum. Thank you all for the answers!!

 

[tomtoo]

Between a guitar speaker/amp combo and a hifi speaker/amp combo there are so much differences.

With a hifi system you want distourtion as low as possible. With a guitar speaker you can like distourtion, you can even prefer it.
Thats why you use guitar speakers that are broadband and large. A 12 inch you can abuse a lot. Thats very different to a 1 inch dome.
Never mix up the sound producing side with the sound reproducing side, thats a commen but very huge mistage.