Question:
How can you have a 100 watt head power like four speakers and then have it power 8 and be louder? Wouldn't it be less wattage going through each speaker? And how can you have a 30 watt vox head power two 12 in speakers and still be loud? I am just wondering how it all works. Thanks
Answer:
Originally Posted by spyrotheleo How can you have a 100 watt head power like four speakers and then have it power 8 and be louder? Wouldn't it be less wattage going through each speaker? And how can you have a 30 watt vox head power two 12 in speakers and still be loud? I am just wondering how it all works. Thanks there are lots of things to consider...let's start with the first question:
100W-->4 speakers vs. 100W-->8 speakers (both amps being identical)
There's some different things to consider:
1) ohm rating: given that one of these setups matches the impedance of the amp better, the better match is going to have a higher wattage output.
2) speaker efficiency: 2 top of the line speakers will be louder than 8 poor, inefficient speakers. With alot of 1x12" combo amps, a simple speaker swap take the amp from almost sucking to majorly rocking.
3) volume dispersion: I have a 40W combo with a 1x12" speaker. I have run this through a 4x12", and it's MUCH louder...speaker differences aside, a major reason for this is dispersion...4 speakers are going to move more air than 1 speaker, creating more air movement in the long run and generally getting a higher perceived volume in front of it.
4) other intangibles...
now...the second question
30W-->2x12" vs. 100W-->2x12"
1) all other things being equal, it takes 10 times the amount of power to double the overall volume of an amp. thus, 100W does 3.4X as much work than a 30W amp, but it isn't 3.4X louder. If you have a 30W amp, you'd have to be running at 300W to double the volume (given that everything else is ideal)
2) the particular Vox you're likely thinking about (the AC30) is biased to run very hot (so hot that many people believe it's a Class A amplifier, but from what i've read, this isn't actually the case). When you bias an amp hotter, it'll push the tubes harder which leads to a higher output and a shorter tube live.
3) comparing tube vs. solid state (transistor) or digital wattage ratings: alot of times people buy amplifiers based on wattage alone. In my experience, a 40W tube amp will keep up with 120+ SS watts with ease. Part of this is because tubes introduce harmonics into the signal path that add to the apparently volume. SS circuits don't do this as much. other reasons exist because companies rate wattages using different methods (clean wattage vs. overall wattage...peak vs. RMS...etc.)
Answer:
And about why running more speakers might no reduce amp wattage output...
Now, speakers wired together by chaining them, either in series or parallel. The current going through the speakers creates the sound. After the current runs through one speaker it just runs through the next, and the next, and the next. That's how an amp can power many, many speakers at once. Now, there is loss of voltage between speakers, and that's measured by the speaker's resistance. So the ohm-rating of a speaker chain always goes up as you add more speakers. Add a speaker, and more signal is lost going through the chain.
Now, many tube amps have impedance switches. That determines how much power the amp will produce to drive the speakers. So, say you have a 30 watt amp. On the 4 ohm setting of the 30 watt amp, the amp will produce enough power to drive 30 watts through 4 ohms of speakers. On the 16 ohm setting, likewise, the amp will produce enough power to drive 30 watts through 16 ohms of speaker resistance.
So whether you're running a 8 ohm 4x12 cab or a 16 ohm 8x12 setup, the amp should be set to produce enough power to drive all the speakers at 30 watts, provided you match impedances.
REMEMBER- DO NOT RUN AN AMP FOR A HIGHER IMPEDANCE RATING THAN YOUR SPEAKERS. As your amp tries to produce too much power, and it is being resisted by the speakers, the effects are almost always disasterous for tube amps. As is running tube amps without speakers (BAD!).