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One Monoblock or Two?

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When driving a speaker with a difficult load, is there a difference in driving the speaker with one large monobloc or biamping the speaker with two smaller monoblocks?

Specifically, would it make a difference in driving the speaker with one 600 watt monoblock, or to bi-amp the speaker with two 300 watt monoblocks? This is assuming that each amp doubles in power as the impedance halves.
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mitch4t
magfan
1,583 posts
 
First, what do you call a 'difficult load'? Are you just referring to impedance / sensitivity? Or, the rest of the equation. If you have to ask what that is, you need to know.

Please check out the link on bi-amping. good information for down the road.
http://sound.westhost.com/bi-amp.htm

I especially recommend section 1.4
ghostrider45
449 posts
 
If you bi-amp, you probably don't want 2 - 300 watt amps instead of one 600 watt amp. The high frequencies need much less power than the lows, so it usually makes more sense to use a fairly large brute force amp on the bass half, and a much smaller but hopefully higher quality amp on the treble half (finesse!).

The details depend on speaker specifics, but a simple down the middle split you describe will waste a lot of amplifier. The unused reserves of the large amp on the treble side are not available for peaks on the bass side. The treble amp loafs while the bass amp works hard.

A better split might be 300-400 watts on the bottom and 30-40 watts on the top. Again, the devil is in the details and this should not be taken as a recipe.

You also have to consider gain matching of the amps, unless you use an active crossover (recommended). If you use an active crossover you will also want to bypass the speaker's passive crossovers if possible. This of course opens other cans of worms....

You also need to consider the sonic signatures of the amps used on the top and the bottom. It's safer to stick with the same brand line, but you can sometimes get great results by breaking that rule. A low powered tube amp on the top combined with a large solid state amp on the bottom sometimes works well.

You will have years of audiophile nervosa ahead of you!
magfan
1,583 posts
 
Ghost, instead of saying.....how much power is needed per 'half', I'd have asked what the crossover frequency was.

The 50:50 power point is about 350hz while more power is indeed needed by the lows as crossover goes to higher frequencies.

Also, I think it is just possible that amps have different latencies...That is, the amount of time it takes for a signal to go from inputs to speaker. Even very small differences will result in phase shift near the crosover.

And as a final point, I'd agree that Active crossovers would really open up a can of worms, but if I had deep pockets, that's the way I'd head and start with as close to the 'stock' transfer function as reasonable.

Again, please look at the biamp link I provided. Good stuff:
ngjockey
1,042 posts
 
For Infinity, don't bother with an active crossover. Sure, the DIY'er in me is curious but, instead, stepped up to Genesis, which already has all that.

BTW, there's a Genesis V listed in the Chicago area (local pickup only) for $1200.
spectron
130 posts
 
"First, what do you call a 'difficult load'? "

- High values of "Equivalent Peak Dissipation Resistance" or EPDR which is, simply, the resistive load that would give rise to the same peak power device dissipation as the speaker itself. Using EPDR as a figure of merit, the speakers can be compared directly with each other.

"The high frequencies need much less power than the lows,"

It is correct assumption with some speakers and wrong with others. For example, most of electrastatic speakers high
frequencies required 7-15 times more of EPDR (see above for definition) then low frequencies.

All The Best
Simon
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