2. tech-talk
  3. 1112012259

Biamping; Amps w. Different power ratings?

If a person uses two amps of differing power levels, will there be a noticeable difference in volume? I've got an Outlaw Audio 755 which is 200wpc. I'm thinking of adding an Outlaw 750, which is 165wpc also. I would use the lower power amp for the bass, and the higher for the treble.
I will have a speaker system comprising four Eminent Technology LFT-8's (biwired and biamped configuration for each of them) and will use 8 channels of amplification. The four bass drivers would be from the lower power Outlaw amp (165) and the highs from the 200wpc amp.

Or, would I be better served to make one speaker completely driven by the 165wpc, and the other by the 200wpc?

I will be sending signal to all 8 amp inputs through the same preamp - a Rogue Audio Magnum 66 (which has a selectable second main out; the signal from each pair of outs will be split and delivered to the 8 amp inputs.

So, would the difference in power cause volume discrepancies between either the bass and treble, or between entire speakers (depending on how I hooked them up).

Comments, suggestions welcome!
douglas_schroeder

Showing 6 responses by eldartford

eldartford
4,262 posts
 
Until recently I would have agreed with Gregm about using the higher power amp for the low frequency. However, in my system, where, for each channel, a stereo amp drives high and low frequency drivers, the power required for the low frequency is much less than the high. In my case this is because the low frequency drivers are more sensitive than the Magneplanars (high frequency drivers), but, in general I don't think we can assume that, in any system, low frequency takes more power.

I would suggest that you take some simple voltage measurements while music is playing and see which amp (high or Low) is working harder. Truth to tell, the difference between 165 and 200 watts is almost too small to worry about.
eldartford
4,262 posts
 
Piezo...I am sure you do "use significantly more power on the bottom end than on the tops" and for your live pop concert application I am easy to convince that this is right. My point is that your situation does not translate directly to the home audio system situation. To get the real right answer, make some measurements. I was surprised when I did that.
eldartford
4,262 posts
 
Piezo...If Peak is your concern, the High frequency amp is more critical, because the peak/rms ratio is higher.

I know that "everyone knows" that the LF amp needs the most power. And that includes VTL. It used to include me until I actually measured what was going on in my system.
Of course, other systems and other music might be different, but I bet a lot of people would be surprised.
eldartford
4,262 posts
 
Piezo...
1. With regard to the peak/rms (voltage) ratio, this would be 1.414 for a pure sine wave. High frequency waveforms are more jagged than low frequency, and the "spikes" will go much higher relative to the rms. Suggestion...look at some waveforms with a scope if you have one.

2. In general, I suggest that you measure what your high and low amps are delivering in your real world situation. If you are using high frequency horn drivers with very high sensitivities your HF amp may indeed be loafing.
eldartford
4,262 posts
 
Douglas_schroeder...Loudness is determined by the GAIN of the amplifier, not by its power rating. (GAIN is volts-out per volts-in). A 20 watt amp may play louder than a 200 watt amp, up to the point where the output reaches 20 watts (very loud).

Note that GAIN is often stated as "Sensitivity"... usually as input voltage for rated power out. For example 1.23 volts. In this case, if the sensitivity is the same for two amps, the one with the higher power rating will play louder, not because it is more powerful, but because its gain is higher.
eldartford
4,262 posts
 
Douglas_schroeder...I'm sure this is more than you need to know...but:

200 watts means 40 volts into 8 ohms
The gain is 40/1.43 = 27.972 volts/volt
This is 28.93 dB

165 watts means 36.33 volts into 8 ohms
The gain is 36.33/1.2 = 30.275 volts/volt
This is 29.62 dB

In practice I bet that the two amps use the same driver circuit, and actually have the same gain.
More to discover