I'd use the higher powered amp for the bass units of course.
The relative amplitude is not a matter of Watt rating but of input sensitivity of each amp. If it's the same there's no problem.
If I understood yr questions correctly. CHeers |
...and 'the same input sensitivity' doesn't mean the same number of volts for rated output, it means the same input voltage for the SAME output. If it's specified, that's usually stated for 1 Watt of output.
Since your amps have slightly different maximum outputs, I would not use them in mono; if you do, one channel will have slightly more dynamic range than the other.
The -8 uses a low crossover, and its MR/treble panels need LOTS of power, so do indeed use the 200W. channels on the planar drivers.
You'll be using the 4 speakers in a surround system?
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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. |
In sound reinforcement set ups we always use significantly more power on the bottom end than on the tops (like around 1200 wts/side or better on the subs vrs less than half of that on the tops). The bass is what drives most of the peak power requirements contrary to Eldartford's generalization. (though that could be dependant on what you are listening to...chamber music probably doesn't hit the bottom end too hard where as anything with thump most certainly will). keeping sufficient headroom keeps the sound clean and prevents clipping...clipping can be expensive. It sounds to me that you are doing the home theater thing....big amps to the bottom end no question.
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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. |
Again i think the measurements well be dependant on what you are listening to and the concern would be with peak responce not continuous. Looking at the VTL site their power amp recommendations are based on woofer size suggesting that bass is indeed the controlling factor. Ex. their MB185 monos (230 wt/side tetrode) are suggested for up to 10 in woofers with mb 450s suggested for 12 in. There may be some marketing in there but the trend seems to be consistant. Another thing to consider beyond having sufficient power to maintain headroom is the increased. Another thing to consider is the increased dampning factor the larger amp has which helps control the speaker as it returns to neutral (i.e comes back after it generates the wave pulse) which tends to tighten up the bass. Again i think you are right on about the two amps being too similar to tell. Maybe the easiest solution to the dilema would be trying it both ways and seeing what sounds best |
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. |
First time i heard about the peak/RMS ratio for high end, interesting. Was that based on your measurements? What about overall power demand? For my home unit i just use one mono per side and for live stuff it's usually moot as well because 2 to 4 18's a side are the obvious power sucks verses a couple of 12s and 10s per side. You have my curiosity though. For smaller club set ups i wonder if putting more power to the high/mid boxes would smooth out the sound (still a room battle in a lot of cases) |
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. |
Well, guys, you're waaay more knowledgeable and technical than I am. I appreciate your insights! I thought I'd just try wiring it both ways and seeing which I prefer.
I've thought the bass was a bit strong with a single pair of LFT-8's biwired at 200wpc, so I thought that maybe I'd "lighten it up" with 165wpc and putting the power more on the mid/tweet.
As you can see, I'm not scientific about this. Hopeful is more the word. I've got an ad in for an additional Outlaw 755 to match my setup if the 750 doesn't perform as hoped. But I'm going to peek at the sensitivity ratings of the different Outlaw amps to see what I can ascertain. Very helpful 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. |
Thanks for the clarification!
I have heard of people even pairing tube amps and solid state on speakers, so I'm guessing this shouldn't be the world of difference between these two amps:
Outlaw Audio 755 (200wpc) input sens. 1.43v
Outlaw Audio 750 (165wpc) input sens. 1.2v
Again, much obliged for info! |
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. |
Eldartford, you have gone above and beyond the call on helping me learn about my amps. I appreciate it! I'll probably post on my audiogon virtual system the results. |
