Bi-amp in a mono mode bridged

[Art]

I have been reading about bi-wire and bi-amp but I am not sure I understand it all to answer question I have. Most bi-amp info is about running each amp in a stereo mode. If I have two identical power amps AudioSource 102, both have A/B speaker eight posts on each amp and the amp is bridgeable. Could I run them in the mono bridged mode, and have hi/low frequency posts on my speakers (Paradigm 60v2)? Would I ran channel A cables to to HF posts and channel B to LF posts. Would I then connect left input to one amp and right input to the second amp. And another part about the power itself. 2 Channel amp with A/B input selector rated at RMS 50w per channel at 8ohm and RMS 150w bridged. Is that rating for each A and B or combined? Not sure if I haven't read enough or maybe too much as I am lost in here.

 

[DonH56]

I would not bi-amp personally unless using a crossover before the power amps but that's just me. There are theoretical advantages of bi-amping without a crossover but in practice the difference is negligible in all but pathological cases (prepare to hear some, I am sure).

Bi-wiring simply moves the shorting connection on your speaker to the amplifier. The speaker wires can thus act like a filter, assuming the amplifier has low output impedance (high damping factor), again for a pathological case were the speaker load is very low impedance and speaker wires are high enough in resistance (impedance) to provide isolation. If that is the case, you need larger speaker wires, unless you really want your speaker wires acting like filters...

Chances are all that was too technical but I'll muddle ahead about bridging. Given two amplifier channels, normally they operate independently, say one left and one right channel, with voltage gain G, both referenced to ground (0 V):

Vout(L) = G * Vin(L) = G * [Vin(L) - 0]
Vout(R) = G * Vin(R) = G * [Vin(R) - 0]

You connect your speaker from the Vout(L/R) positive (+) terminals to ground (0). The gain simply means you've increased (multiplied) the input voltage by some amount (G) to produce a higher output voltage -- that's what amplifiers do.

Now bridging takes a single input and applies it to both amplifiers, inverting one amplifier to double the voltage swing (multiply by -1):

Vout(L) = G * Vin
Vout(R) = G * Vin * (-1) = G * (-Vin)

I left off the 0 V reference. Now, instead of taking each output with respect to ground, you take the output across the two (+) output terminals. The inversion means you are subtracting a negative number and so you get a positive result:

Vout(L-R) = G * [Vin - (-Vin)] = G * [Vin + Vin] = G * 2Vin.

OK, so bridging ideally doubles the voltage swing. You can think of it like putting the two amplifiers (voltage sources) in series (not really right but hopefully you get the idea).

Now, power goes as voltage squared:

Power (watts) = Voltage (V) * Voltage / R where R is the impedance of your speakers in ohms.

Since bridging doubles the voltage, and the square of 2 is 4 (2*2 = 4), ideally it quadruples the power output. A 50 W/channel amplifier should ideally produce 200 W when bridged. In practice there are other limitations (power supply capacity, thermal/heat dissipation, and so forth) so bridged amplifiers are usually specified at around 2x to 3x instead of all the way to 4x the non-bridged power output. Still get reasonable power increase.

There are catches, of course, like typically higher noise and distortion, and greater load sensitivity. The latter means that, in bridged mode, an amplifier is typically at twice the load impedance. An amp rated to drive 4 ohms/ch will probably be rated to drive 8 ohms minimum when bridged. Twice the voltage also means twice the current, and amps are not usually rated for that much current without overheating and such. (That is partly why the bridged power rating is usually not fully 4x the normal rating.)

HTH - Don

 

[bigguyca]

I would not bi-amp personally unless using a crossover before the power amps but that's just me. There are theoretical advantages of bi-amping without a crossover but in practice the difference is negligible in all but pathological cases (prepare to hear some, I am sure).

Bi-wiring simply moves the shorting connection on your speaker to the amplifier. The speaker wires can thus act like a filter, assuming the amplifier has low output impedance (high damping factor), again for a pathological case were the speaker load is very low impedance and speaker wires are high enough in resistance (impedance) to provide isolation. If that is the case, you need larger speaker wires, unless you really want your speaker wires acting like filters...

Chances are all that was too technical but I'll muddle ahead about bridging. Given two amplifier channels, normally they operate independently, say one left and one right channel, with voltage gain G, both referenced to ground (0 V):

Vout(L) = G * Vin(L) = G * [Vin(L) - 0]
Vout(R) = G * Vin(R) = G * [Vin(R) - 0]

You connect your speaker from the Vout(L/R) positive (+) terminals to ground (0). The gain simply means you've increased (multiplied) the input voltage by some amount (G) to produce a higher output voltage -- that's what amplifiers do.

Now bridging takes a single input and applies it to both amplifiers, inverting one amplifier to double the voltage swing (multiply by -1):

Vout(L) = G * Vin
Vout(R) = G * Vin * (-1) = G * (-Vin)

I left off the 0 V reference. Now, instead of taking each output with respect to ground, you take the output across the two (+) output terminals. The inversion means you are subtracting a negative number and so you get a positive result:

Vout(L-R) = G * [Vin - (-Vin)] = G * [Vin + Vin] = G * 2Vin.

OK, so bridging ideally doubles the voltage swing. You can think of it like putting the two amplifiers (voltage sources) in series (not really right but hopefully you get the idea).

Now, power goes as voltage squared:

Power (watts) = Voltage (V) * Voltage / R where R is the impedance of your speakers in ohms.

Since bridging doubles the voltage, and the square of 2 is 4 (2*2 = 4), ideally it quadruples the power output. A 50 W/channel amplifier should ideally produce 200 W when bridged. In practice there are other limitations (power supply capacity, thermal/heat dissipation, and so forth) so bridged amplifiers are usually specified at around 2x to 3x instead of all the way to 4x the non-bridged power output. Still get reasonable power increase.

There are catches, of course, like typically higher noise and distortion, and greater load sensitivity. The latter means that, in bridged mode, an amplifier is typically at twice the load impedance. An amp rated to drive 4 ohms/ch will probably be rated to drive 8 ohms minimum when bridged. Twice the voltage also means twice the current, and amps are not usually rated for that much current without overheating and such. (That is partly why the bridged power rating is usually not fully 4x the normal rating.)

HTH - Don

Selected effects of power amplifier bridging

It would seem that two non-correlated noise sources when combined would produce +3dB noise. The voltage goes up by +6dB, so there would be as much as a 3dB reduction in noise.

Even order distortion is asymmetrical. If two voltages are combined with one of the voltages inverted as in bridged mode, then there should be some cancellation of the even order distortion. The cancellation won't be prefect of course, but the even order distortion will be reduced. Current requirements at higher outputs into lower impedances will likely overwhelm this effect as some output level.

Likely not required within a typical power amplifier's required bandwidth, but likely slew rate would ideally double.

There a many secondary plus and minus effects.

 

[Art]

With the speakers I have I heard they work best if supplied with higher power amplification 100 to 200 watts. What would be best configuration to drive speakers I have with the 2 amps I have. Or should I toss the amps out?

Paradigm Reference Studio 60 v2 specifications
Design
3 driver, 2-1/2-way Tower / Floorstander
Crossover
3rd order electro/acoustic at 1.5kHz, 2nd order electro/acoustic at 400Hz
Frequency Response On-Axis
±2dB from 42 Hz - 22 kHz
Frequency Response 30° Off-Axis
±2dB from 42 Hz - 20 kHz
High Frequency Driver
25mm (1 in) PAL™ pure-aluminum dome, diecast heatsink chassis, ferro-fluid cooled
Mid/Bass Frequency Driver
170mm (6-3/4 in), MLP™ mica-polymer cone, AVS™ diecast heatsink chassis, 38mm voice-coil
Low Frequency Driver
170mm (6-3/4 in), filled polypropylene cone, AVS™ diecast heatsink chassis, 38mm voice-coil
Low Frequency Extension
30Hz (DIN)
Sensitivity Room / Anechoic
90 dB / 87 dB
Impedance
Compatible with 8 ohms
Suitable Amplifier Power Range
15 - 200 watts
Maximum Input Power
150 watts


Amp specs
2 Channels rated at 55 watts into 8 ohms

• 75 watts RMS per channel @ 4 ohms
• Bridge Output: 160 Watts @ 8 ohms
• Input Sensitivity: Variable, .7 Vrms for rated power at 8 ohms
• Frequence response: 10Hz to 30kHz
• Channel Crosstalk: 70 dB
• Less than 0.2% THD into 8 ohms at rated power
• S/N Ratio: 100 dB A-weighted

 

[Art]

Sorry wrong specs for the amp, here are correct ones
AMP102 SPECIFICATIONS
Stereo (8 ohm): 50W RMS per channel at 8 ohms,
20Hz - 20kHz, <0.1% THD+N
Stereo (4 ohm): 75W per channel at 4 ohms,
20Hz-20kHz, <1% THD+N
Bridged Mono (8 ohm):
150W RMS at 8 ohms,
20Hz - 20kHz, <0.2% THD+N
Frequency Response:
10Hz - 50kHz, +0dB, -3dB
Signal to Noise Ratio:
100dB A-weighted, referred to rated
power at 4 ohms
Channel Separation:
65dB @ 1kHz, referred to rated power
at 8 ohms
Sensitivity: Variable, 350mV to 2.8V for rated
power at 8 ohms
AC Power Consumption:
500W maximum

 

[Art]

I would not bi-amp personally unless using a crossover before the power amps but that's just me. There are theoretical advantages of bi-amping without a crossover but in practice the difference is negligible in all but pathological cases (prepare to hear some, I am sure).

Bi-wiring simply moves the shorting connection on your speaker to the amplifier. The speaker wires can thus act like a filter, assuming the amplifier has low output impedance (high damping factor), again for a pathological case were the speaker load is very low impedance and speaker wires are high enough in resistance (impedance) to provide isolation. If that is the case, you need larger speaker wires, unless you really want your speaker wires acting like filters...

Chances are all that was too technical but I'll muddle ahead about bridging. Given two amplifier channels, normally they operate independently, say one left and one right channel, with voltage gain G, both referenced to ground (0 V):

Vout(L) = G * Vin(L) = G * [Vin(L) - 0]
Vout(R) = G * Vin(R) = G * [Vin(R) - 0]

You connect your speaker from the Vout(L/R) positive (+) terminals to ground (0). The gain simply means you've increased (multiplied) the input voltage by some amount (G) to produce a higher output voltage -- that's what amplifiers do.

Now bridging takes a single input and applies it to both amplifiers, inverting one amplifier to double the voltage swing (multiply by -1):

Vout(L) = G * Vin
Vout(R) = G * Vin * (-1) = G * (-Vin)

I left off the 0 V reference. Now, instead of taking each output with respect to ground, you take the output across the two (+) output terminals. The inversion means you are subtracting a negative number and so you get a positive result:

Vout(L-R) = G * [Vin - (-Vin)] = G * [Vin + Vin] = G * 2Vin.

OK, so bridging ideally doubles the voltage swing. You can think of it like putting the two amplifiers (voltage sources) in series (not really right but hopefully you get the idea).

Now, power goes as voltage squared:

Power (watts) = Voltage (V) * Voltage / R where R is the impedance of your speakers in ohms.

Since bridging doubles the voltage, and the square of 2 is 4 (2*2 = 4), ideally it quadruples the power output. A 50 W/channel amplifier should ideally produce 200 W when bridged. In practice there are other limitations (power supply capacity, thermal/heat dissipation, and so forth) so bridged amplifiers are usually specified at around 2x to 3x instead of all the way to 4x the non-bridged power output. Still get reasonable power increase.

There are catches, of course, like typically higher noise and distortion, and greater load sensitivity. The latter means that, in bridged mode, an amplifier is typically at twice the load impedance. An amp rated to drive 4 ohms/ch will probably be rated to drive 8 ohms minimum when bridged. Twice the voltage also means twice the current, and amps are not usually rated for that much current without overheating and such. (That is partly why the bridged power rating is usually not fully 4x the normal rating.)

HTH - Don

Thank you for all of the info. Could I use each of the amps bridged as a mono block each driving one channel. Would that provide me the power I need to effectively drive my speakers?

 

[DonH56]

Selected effects of power amplifier bridging

It would seem that two non-correlated noise sources when combined would produce +3dB noise. The voltage goes up by +6dB, so there would be as much as a 3dB reduction in noise.

Even order distortion is asymmetrical. If two voltages are combined with one of the voltages inverted as in bridged mode, then there should be some cancellation of the even order distortion. The cancellation won't be prefect of course, but the even order distortion will be reduced. Current requirements at higher outputs into lower impedances will likely overwhelm this effect as some output level.

Likely not required within a typical power amplifier's required bandwidth, but likely slew rate would ideally double.

There a many secondary plus and minus effects.

All true. In practice, you rarely get 6 dB voltage gain, and some other noise sources do not cancel, so specs vary though ideally you should get +3 dB in SNR.

Ditto even-order distortion; ideally you should improve, but in practice it depends upon how well the channels are matched and all that jazz. Sometimes it's reduced a good bit, in other amps barely at all. Crossover distortion can get gnarly, and power noise may or may not cancel depending upon the implementation (sometimes it adds at the output even though the signal is inverted, blah). And the higher slew rate (actually slew limiting, since circuit bandwidth does not increase with bridging) and effectively lower load impedance tends to counter some of the noise and distortion advantages so often it's a wash.

But not something I follow, at least for audio amps, and a spot search shows specs all over the map. Nor have I designed an audio amplifier in the past 20-30 years so my experience may be totally irrelevant.

 

[DonH56]

Thank you for all of the info. Could I use each of the amps bridged as a mono block each driving one channel. Would that provide me the power I need to effectively drive my speakers?

Sure, assuming the speakers are compatible with the amplifier's load specifications (even if they fall a little low you'll probably be OK). That's what I would do; bridge and use them as a pair of mono amps instead of bi-amping if you need more power. Bi-amping does not intrinsically provide more power, especially the "passive" bi-amping most AVRs do. If you take two 100 W amplifiers and each drives a different signal band, it is not the same as using a single 200 W amplifier. Neither driver can "see" 200 W when driven by a 100 W amp.