Would you guys think I am off by a factor of two, or possibly much larger?
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.
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When ever I had an amplifier with meters I was always amazed at how little watts is being used. Although, not all amplifiers are created equal. I have owned 60 watt amplifiers that sounded more powerful than 200 watt amplifiers. When I owned Dunlavy SCIVs I had incredibly good sound with 60 watt tube monos. The best way to find out if an amplifier is powerful enough is to listen. |
Not to change that subject too much, but this sounds very similar to the argument you will get when it comes to those who believe Tube S.E.T. Amps are the best. These low powered Tube S.E.T. Amps only put out 2 to 8 watts but will still player loud and proud with the proper efficient speakers. Also similar with Pure class A amps, for the most part when people listen to music at a reasonable level they are only pulling a few watts anyway. It's only after you really crank up the music or play movie soundtrack with lots of full range of sound going on will you start eating up watts. Or if you have some really inefficient speakers that can be hard to drive due to their design. I could be all wrong about thus, so please feel free to correct me if needed. |
09-28-12: KoestnerI have no idea. IMO, though, Ron (Rrog) correctly stated the bottom line: "The best way to find out if an amplifier is powerful enough is to listen." Some additional points: I found measurements of your amp here. They indicate that it can provide 76 watts into 4 ohms at 1% distortion. However, it is indicated that while the amp operates Class A up to the clipping point into an 8 ohm load, with a 4 ohm load it transitions to Class AB at some unspecified level that apparently is significantly below the clipping point. Conceivably that could have some effect on sound quality at power levels you would be using. Another way to look at it: Let's call it a 60W amplifier into 4 ohms. Assuming that the 92 db/2W/1m/4 ohm numbers for the speakers are accurate, it can be calculated that at listening distances of say 10 to 12 feet, 60W will result in a sound pressure level of approximately 100 db, neglecting room effects. Provided that the sound quality of the amplifier is still holding up at that level, 100 db will certainly be loud enough for most listeners with most recordings. It will also certainly not be loud enough for some listeners with some recordings, particularly (as I mentioned earlier) recordings having very wide dynamic range. For instance, I have many classical recordings on labels such as Telarc, Sheffield, Reference Recordings, etc. that at my listening position reach peaks that I've measured at around 105 db, although the average level during those recordings is perhaps in the low 70's. Keep in mind that a 30 db difference between peak volume and average volume means that 1000 times as much power is required for those peaks, compared to the average level of the recording. Hope that helps. Regards, -- Al |
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