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Watts up with that?

I was concerned that my Belles 30 watt Class A amp (SA-30) was not powerful enough for my Montana XP speakers (seven driver 92db at 2 watts due to 4 Ohm). Using the calculation of voltage squared divided by impedance would give you watts, I hooked up my Wavetek digital multimeter across the speaker posts to read AC volts. The meter has a “max” feature so it keeps displaying the highest voltage reading until reset. My speakers have a very flat impedance curve with a low of 3 and a max of 5 Ohms, so I feel pretty safe using the average of 4 Ohms. Upon playing some music at my average listening levels I got a max voltage reading of 2.13 volts. This calculates to just over 1 watt. I then turned up the volume to much louder than I will usually listen and got a max voltage reading of 3.28 volts after a few songs. So with the volume higher than normal, and at the loudest part on the track, I get just under 3 watts being drawn. I still have a lot of watts left! Are my calculations correct? Is this an OK way to measure power? I was thinking I needed a few hundred watts of available power, but it seems I’ve got all I need at just the 60 watts capability (4 Ohm load) of my current amp. Your thoughts please.
koestner

Showing 4 responses by koestner

koestner OP
622 posts
 
Just an FYI, the Belles SA-30 is a solid state amp.
koestner OP
622 posts
 
Would you guys think I am off by a factor of two, or possibly much larger?
koestner OP
622 posts
 
Hey guys,

I looked into getting an osciliscope. There are these USB ones that can use your laptop to save on the screen and that stuff. They look interesting and only about $100. However, I have no idea how to use one, but I guess I could figure out how to read some AC volts across the speaker terminals. This way I could get a more accurate measurment of peak voltage, I hope.

Al, your 100db calculation... was that for a pair of speakers, or just one? I hope it was just one so then I could add another 3db for the other speaker, also I listen about 9 feet from each speaker. I am going to hopefully audition the MB-200 mono amps from Belles to see if all that extra power does indeed matter or not. Thanks for all the replies so far. I am really enjoying trying to measure the watts used, as long as I can do it accurately.
koestner OP
622 posts
 
Thanks Al, you're really helping a lot. So is everyone else too. It's probably what I expected, I'm fine listening to jazz and vocals at normal to slightly louder volumes, but when I want to play heavy classical pieces to stir me up, I should be aware that this amp does not have large reserves. I still think the oscilloscope is cool and I may get one to play with.
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