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In Reply to: Speaker Project posted by Brad Silverman on September 7, 2002 at 16:59:25:
Brad,It's time for a basic lesson in electric power calculations. I fear that your speaker project will prove unsatisfactory because you will not be able to get enough power into the speakers from any amp built to drive lower impedance speakers.
Power = Voltage squared and divided by Resistance.
60 watts into eight ohms requires 21.9 volts RMS. RMS stands for Root-Mean-Square, a mathematical function applied to alternating voltage that allows this formula, which also applies to DC, to be used. For sine wave AC, the RMS is one-half the square root of two (0.7071...) times the peak voltage. The peak voltage of a sine wave that delivers 60 watts into eight ohms is thus 1/0.707 times the RMS voltage, or 31 volts.
This means the amp has to swing from +31 to -31 volts to generate a sine wave output that will dissipate 60 watts in an eight ohm load. The amplifier output stage has to have enough voltage 'headroom' to accomodate this plus enough more to keep the output devices from clipping or going grossly nonlinear.
Now apply this thinking to a 200 ohm load (your 400 ohm drivers connected in parallel as suggested below).
Power = 60 watts = RMS voltage squared over 200.
In this case, the RMS voltage is 109.5 and the peak of a sine wave with this RMS value is 155 volts.
You will need a power amp able to swing +155 to -155 volts to get 60 watts.
It is not difficult to build such a device. The Beveridge Model 2 uses an OTL power amplifier that swings within +3200 to -3200 volt power supply rails. However, the rails on most power amps are much lower and limit the voltage swing obtainable into even the easiest load.
The amp that could give 60 watts into eight ohms could only supply 2.4 watts into 200 ohms at the same voltage. While it is true that Atma-Sphere amps deliver more power into higher load impedances, the circlotron supplies (at about 130 volts) limit what they can do into extremely high loads like your exotic speakers.
-Al
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Follow Ups
- Re: Speaker Project - Al Sekela 12:52:46 09/10/02 (2)
- Re: Speaker Project - Paul Speltz 08:26:28 09/11/02 (1)
- Re: Speaker Project - Brad 18:22:22 09/11/02 (0)
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