2. amps-preamps
  3. 166419-141390

Passive bi-amp question

I understand this might have been discussed in the past, but wanted to get some better insight as to doing it correctly. I am looking to biamp (passive only, not crazy about active biamp) my speakers. I have MA PL500II, and after discussing with monitor audio, they strongly recommend passive biamping. Trust me, these speakers are already amazing with just stereo amp driving them now. I am trying to push the envelope to see if I can get best out of it. 
I am looking to use different amp brands for biamp. I know, ideal will be to use same amp or at least same company amp, but wanted to see if anybody have done passive biamp with different brand and what was their experience, pros, cons and how did you guys made decision while selecting different amps.
What are the amp specs that needs to be matched (or closely matched). Is it gain, input sensitivity, input impedance, watts per channel. Or in other words will results be still good if the amps have different gain, impedance, sensitivity and wattage. Anything else should I be looking for. Any valuable thoughts will be appreciated. I will be using same power cords and speaker cables in both (including the lengths). 
Currently I have thrax dionysos preamp with audia flight strumento no.4 mk2. 
romney80
erik_squires
16,057 posts
 
The thing to keep in mind, with amps, is that the gain specification measurement is just not that important to makers.

That is, maybe they will specify 29 dB but maybe it’s 28.5 and maybe it’s 29.7.  It's rarely 29.00 dB

Since 99.9999 of their customers will use 1 stereo amp, accuracy here is just not that important. I’m sure it is consistent among the same model but across different models or makers probably not.

So, good to have some way of measuring the relative gain and adjusting if wrong.
romney80 OP
150 posts
 
@erik_squires 
let’s say if it is few decibels apart, how much of the impact will this have. In other words, if they are apart, how will the sound quality be affected. Will it be like one amp sounds more than other one ? Or will it affect the coherency in the music ?
auxinput
2,920 posts
 
A few decibels is actually a LOT!  The difference between 29 db and 32 db means that you would have either too much bass or very weak bass depending on what amp you put on the bottom.

If Erik is correct that gain is not always 100% perfect specification, then the variance might be small.  A .7 decibel variance is not that much, but I wouldn't say it's that bad.  Speakers are never perfect anyway and actually will vary up to 3-5 decibels through the entire frequency range.

If you put a amp on the woofer that is .7 db higher gain, you might have a "slightly thicker" bass midbass.  It's almost like a very slight EQ. 

I would ignore those "1.24V" sensitivity numbers.  It is just a representation of how much input volts are required to have the amp output a certain amount.  The "gain" is the only thing you need to look at.
romney80 OP
150 posts
 
Sounds good. Thanks for those technical inputs. I am assuming, even if the companies mention 29 db gain, they may vary at best few decimal of decibels. I am OK with that. 
Just one question though. It may be silly. Does it matter even if the amp have different watts of power (like 250 vs 150 at 8 ohms) even if gain is same. 
erik_squires
16,057 posts
 
A few decibels is completely noticeable!! :) You would be changing the sound of the speaker completely. Dude, if you are OK with that, then go with active bi-amping instead. You’ll get more control, more dynamic range and can fix your level mismatches.

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