Help with Bi-amping two amplifiers.

[metallo]

Hi guys, its been a while since i last visited this forum, been busy with listening to my Rotel equipment

I have just bought a new rotel, a Rotel RB-990BX, and im having it bi-amped with a Rotel RMB-1075.

My dilemma is that it sounds much more powerfull in the lows and mids then im used to. I have very difficult speakers and a RMB-1075 doesnt have a chance to make them justice (Infinity Renaissance 90).
Maybe im just not used to the new sound but i suspect that the Rotel RB-990BX plays louder then the RMB-1075.

Specifications of RMB-1075
SNR: 116 dB
Input impedance: 1 volt / 33 kOhms
Damping factor: 180

Specifications of RB-990BX
SNR: 120 dB
Input impedance: 1 volt / 33 kOhms
Damping factor: 1000

As you can see, the SNR and Damping factor isnt the same, but i dont know how those two factors affects the sound.
Please explain (shortly) these two terms?
Can these two factors make the sound level higher on the Rotel RB-990BX?

Thanks in advance.
/Daniel

[Boombox]

Rotel amps are masters at handling difficult speakers. No need to worry about the damping factors or the signal to noise ratios. They are excellent, though the RMB1075's DF seems rather low. Be that as it may, the DF simply indicates how well an amplifier can tell a speaker what to do, i.e, where to move, when to stop and how fast to complete these actions. Therefore, the higher the DF the better. However is that your speaker cable, crossovers (in the speaker) and the voice coils, will reduce the DF significantly. I know that for the RB1080 the DF is also 1000, but inserting a three meter 16 gauge speaker cable reduces this value to about 91. No need to panic because there is no audible difference between 1000 and 80, however there is a significant audible difference when the DF drops to below 10!

Concerning your problem. Bi-amping will only make good sense if you have an active cross-over between your source/pre-amp and power amp. Choosing the crossover frequency will be a nightmare, because when you choose it wrongly, either the bass is over-powering or the mids+highs are overpowering, because more power is extracted/granted from/by your speaker/amp. This is because the signal coming from the source contains the full frequency range. Splitting them into highs and lows to be amplified seperately is the way to go, but if you send the complete signal to speaker, your signal then has to rely on the cross-over network of the speaker rendering this wonderfull amplification useless (in my view at least) if the x-over frequncy is to high or low. This then leads to the bass drivers receiving for power from the amps than the mids+highs, or vice-versa. In your case the bass+mids are pulling more power from the amp. I suspect that your dilemma is as a result of the speaker's crossovers which are not "fine tuned" to make full use of the power and brilliance of bi-amping. Bi-amping will make your speakers play louder if you by-pass your speaker's internal cross-overs, but then you have no control as to which frequencies reach the tweeters/mis/bass drivers.

[metallo]

Thank you very much for your detailed answer! ;x(

But i really dont get how an active crossover will make any difference, it should be same thing as using the built-in crossover in the speakers? But anyway, i will not invest in an active crossover. i rather buy a new amplifier and single wire the speakers 8)

And one other thing, the power drawn from the amplifiers shouldnt be a problem, both highs and lows should have plenty of spare effect (i hope). I use two channels from the RMB1075 for the treble speaker connection and RB-990BX for the bass connections. Y-split from the RSP1068.
So the speakers elements cant consume effect from each other as they could if connected with the same amplifier?
And both amplifiers have the same "input impedance" så the RSP1068 should send an identical signal to them both.

is it possible to just put a volume controller on the inputs of RB-990BX? My old Denon POA-2800 had this function, and NAD also have this function.

Many questions...

Concerning your problem. Bi-amping will only make good sense if you have an active cross-over between your source/pre-amp and power amp. Choosing the crossover frequency will be a nightmare, because when you choose it wrongly, either the bass is over-powering or the mids+highs are overpowering, because more power is extracted/granted from/by your speaker/amp. This is because the signal coming from the source contains the full frequency range. Splitting them into highs and lows to be amplified seperately is the way to go, but if you send the complete signal to speaker, your signal then has to rely on the cross-over network of the speaker rendering this wonderfull amplification useless (in my view at least) if the x-over frequncy is to high or low. This then leads to the bass drivers receiving for power from the amps than the mids+highs, or vice-versa. In your case the bass+mids are pulling more power from the amp. I suspect that your dilemma is as a result of the speaker's crossovers which are not "fine tuned" to make full use of the power and brilliance of bi-amping. Bi-amping will make your speakers play louder if you by-pass your speaker's internal cross-overs, but then you have no control as to which frequencies reach the tweeters/mis/bass drivers.

[Boombox]

metallo,
You are quite right that power is not a problem. There is more than enough from the Rotels you have!!! It's the physics that #$!@&-up everything with the frequencies. The tweeters and mids don't need that much energy (power) as do the bass drivers. As a result of these frequncy "preferences", the one speaker draws more power from the amp and therefore sounds louder.

Bi-amping would have been the only way to go if the speaker manufacturers made decent cross-overs. Then obiously the price would shoot up!!

I'm sitting with almost the same problem. I want to get a second Rotel RB1070 to bi-amp my Boston Acoustic VR2 speakers. However, after doing extensive research on the matter it will cost more to bi-amp than to get a more powerful amp. In the end, I've decided to upgrade my amp to the RB1080.
Here is an interesting thread on the topic I'm trying to explain quickly:

http://www.gcaudio.com/resources/howtos/biamping.html

Hope this explains quickly the difficulty in bi-amping.

[Boombox]

However, my dealer and I are still trying to experiment on this bi-amping issue. We want to find out what will be the best (price/performance) bi-amping configuration. I'll keep you posted.

[Boombox]

Yes, sorry....

About the volume controllers.

That will work, but then you are driving a Formula1 car with a speed limiter!! Is it worth the drive..??

[Boombox]

hey metallo,

have a read.....this might work for us..!!

http://www.stevehoffman.tv/forums/archive/index.php/t-19434.html

[metallo]

Boombox,

I have just visited your link, but havent had time to read it yet.
Will do it this evening.

Thanks for sharing

hey metallo,

have a read.....this might work for us..!!

http://www.stevehoffman.tv/forums/ar...p/t-19434.html