Soundlab speakers with sub woofers?

In my feeble mind I imagine a relatively fixed voltage across the speaker terminals. As the impedance changes with frequency so will the current drawn from the amp and so will the power supplied by the amp. When the impedance rises in the bass, the current drawn from the amp will decrease as will the power supplied by the amp. Likewise when the impedance decreases in the midrange and treble, the current drawn from the amp will increase as will the power supplied by the amp. I think that's based on Ohm's law.

Hi Bob- your statement here is correct. So the impedance curve of the Sound Lab goes up to just over 30 ohms in the bass, and is about 1.5-3 ohms at 20KHz depending on the setting of the Brilliance control.

So let's do the math. We will assume a constant voltage, and for fun a 600 watt transistor amplifier driving 8 ohms.

Power = Current (I) x Resistance squared. So we need to solve for current.

600 = I x 64, 600/64= 9.375 is the current of 600 watts into 8 ohms. Using Ohms law: 8 Ohms =V/9.375 Amps, we see that the voltage is 75 volts.

Now we change the Resistance to 30 ohms, keeping the voltage constant. So: 30=75/I, solving for I we get 2.5 Amps.

Power is Voltage x Current, in this case the 600 watts is now 187 watts.

At the other end of the frequency range, the amp can put out over 1200 watts, as there is a 10:1 difference in impedance.

Basically what the math shows is that a 600 watt amp can't make that kind of power- and so a 150 watt tube amp can easily keep up with it, as the difference between 150 and 187 watts is not even 1db. If you have a 200-watt tube amp, you would need a transistor amp with about 800 watts in order to keep up.

The math also shows that there is a good chance that the transistor amplifier will be bright on the Sound Lab.

Now the application of negative feedback will cause the amplifier to reign in its power somewhat at higher frequencies. But since the feedback voltage is really not correct on this load, there will be an error that causes the amp to make too much power at the higher frequencies. Its is easily audible.

Now the speaker curve is not based on a driver in a box as we all know. Its based on a capacitor. Its efficiency is thus not a function of its impedance- its about the same at high frequencies as it is at low frequencies. You can see that a constant voltage characteristic in the amplifier is not really all that desirable. You can read more about this phenomena at this link:

http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

I thought I was pretty clear with my point, but maybe not. Here it is, referring to the math I posted earlier:

1) many solid state amps will not get flat frequency response- if so they will be bass shy and too bright.

Some people with transistor amps have the speaker placed closer to the rear wall than is ideal; in this way they get some bas reinforcement, but its usually a 'one note' sort of bass as the reinforcement from the wall only happens at one frequency. The speaker should be 5-6 feet from the wall for best results.

2) A solid state amp will manifest approximately 1/4 of its rated 8 ohm power specification.

Its not voltage that drives a Sound Lab. Its power. That is why I provided the link at the end of my last post.

Keithmundy,

That is exactly how I have them running. I'm using Transparent Audio super interconnects balanced signal from the pre to the subs crossed over at 40HZ. You can only sense they are on if the music has definite bottom end. It's amazing on well recorded pieces.