In the one case where i did it (Acoustat 2 with 2 x NAIM 160) it was decidely beneficial. This is a bit different from a typical passive bi-amp thou.
dave
Bi-amping (with a passive cross over) doesn't add any available power because both power amplifiers will handle and amplify the same voltage. This means the most difficult speaker to drive will limit the available power in the same way a single amp would. They do share the total current between the separate speakers but the minimum impedance presented by one of the speakers to one of the amps causing the maximum current is still the same and it will clip at the same level.
1. Actually, the current going through the voice-coil of the speaker will be more stable and less affected by non-linearities in the voice coil impedance connected through a series passive coil. This reduces distortion and thermal compression greatly compared to connecting the speaker directly to the amplifier terminals. It doesn't reduce the current needed to drive the speaker voice coil, it's the same, but increases the voltage needed towards higher frequencies.
Your conclusion is wrong.
The passive crossover is essentially two filters, each feeding a speaker driver.
The combined pair of filters with their drivers attached presents an average impedance that we see stated as the nominal impedance of the speaker in the audio pass band.
When the crossover is split into two separate filters each with their own driver attached, each filter + driver presents a higher impedance to the source (amplifier).
That higher impedance draws LESS current from the Source.
It makes the job of the source easier !!!!!
The two amplifiers have a better chance of performing to a higher standard BECAUSE each is driving just one half of the crossover+ drivers.
Don't make up a bit of fiction and present it as a conclusion to the scientific data.
This is actually a very common misconception from theoretical numbers to practical reality. The reason is amplifiers are essentially voltage limiting devices presented with a suitable speaker load that wont distort the sound too much and even a tough one that will. It is not the total current drawn from the amp that limits the output, it's the voltage amplified which will be the same.
The typical situation: adding a second power amplifier that alone could drive the speaker pretty well. In this case they will share the total current drawn and still amplify the voltage which will clip at the exact same level as before. They will share the delivered power between them but with zero increased total maximum deliverable power to the speaker.
The rare situation: you have an amplifier that barely can drive the speakers because of low impedance. After adding a second amplifier to the tweeter you will still have at least one amplifier that barely can drive the speakers without distorting the sound heavily. The other amplifier might see the easier part of the load and wont be driven into clipping before the original one, at best, at least saving the tweeter from the resulting square wave, but still; the bass is poorly driven by a bad amplifier spoiling the sound. In practice: zero added hifi-headroom.
The typical situation: adding a second power amplifier that alone could drive the speaker pretty well. In this case they will share the total current drawn and still amplify the voltage which will clip at the exact same level as before. They will share the delivered power between them but with zero increased total maximum deliverable power to the speaker.
The rare situation: you have an amplifier that barely can drive the speakers because of low impedance. After adding a second amplifier to the tweeter you will still have at least one amplifier that barely can drive the speakers without distorting the sound heavily. The other amplifier might see the easier part of the load and wont be driven into clipping before the original one, at best, at least saving the tweeter from the resulting square wave, but still; the bass is poorly driven by a bad amplifier spoiling the sound. In practice: zero added hifi-headroom.
You are of course entitled to any opinion you'd like, and I've been there too so I understand perfectly where you come from.
Think about what about the speaker makes the job hard for the amplifier. It is either low voltage sensitivity (voltage clipping) or too low impedance at some frequencies. Making the impedance higher outside of the region (i.e. in the treble, if the lowest impedance is in the bass) where the impedance is too low wont make the job of driving the low impedance any easier it will still be too low for the amp to drive comfortably. The voltage needed to drive the speakers to a certain level will still be limited at the same level.
Neither of these two reasons for limitations in the amplifier is helped by adding a second amp to drive the treble separately. They do share the developed power delivered to the speakers, but it is by increasing the impedance where it does not do any benefits if there is a problem to begin with.
I would never use any single amp that would add any significant amount of power by bi-amping a passive speaker. To me, that amp would be totally useless driving the speakers on its own. However if they can be bridged to double the power without overloading them or if an active crossover is present the benefits of added power is clearly there.
Think about what about the speaker makes the job hard for the amplifier. It is either low voltage sensitivity (voltage clipping) or too low impedance at some frequencies. Making the impedance higher outside of the region (i.e. in the treble, if the lowest impedance is in the bass) where the impedance is too low wont make the job of driving the low impedance any easier it will still be too low for the amp to drive comfortably. The voltage needed to drive the speakers to a certain level will still be limited at the same level.
Neither of these two reasons for limitations in the amplifier is helped by adding a second amp to drive the treble separately. They do share the developed power delivered to the speakers, but it is by increasing the impedance where it does not do any benefits if there is a problem to begin with.
I would never use any single amp that would add any significant amount of power by bi-amping a passive speaker. To me, that amp would be totally useless driving the speakers on its own. However if they can be bridged to double the power without overloading them or if an active crossover is present the benefits of added power is clearly there.
this para is where your thinking is wrong.
A higher impedance will draw LESS current from the amplifier.
Gents,
It almost seems like you're arguing over semantics here. This is a pretty simple concept and I think you both understand it, but you're just explaining it in different ways.
If splitting Speaker X into two halves and using two amplifiers (A & B) to drive it, the power load obviously splits between the amplifiers. If the xover frequency is in the 300-400Hz range the power split between A & B would be approximately 50/50.
Since there's no crossover before the amplifiers the waveform (voltages) applied to each half of the system will still be identical. (Assuming both power amps are similar/identical and operating as voltage sources.)
Thus the split in power load is directly a result of the split in current load.
Cheers,
Dave.
It almost seems like you're arguing over semantics here. This is a pretty simple concept and I think you both understand it, but you're just explaining it in different ways.
If splitting Speaker X into two halves and using two amplifiers (A & B) to drive it, the power load obviously splits between the amplifiers. If the xover frequency is in the 300-400Hz range the power split between A & B would be approximately 50/50.
Since there's no crossover before the amplifiers the waveform (voltages) applied to each half of the system will still be identical. (Assuming both power amps are similar/identical and operating as voltage sources.)
Thus the split in power load is directly a result of the split in current load.
Cheers,
Dave.
Hi,
Quite simply sell all your drivers, they go for far more
than than their intrinsic worth, loads more in reality.
They should go for about £1000+.
Then just build the Sunflowers, which which be miles
better than any hotpotch version using the old drivers.
You should have enough cash left over
for a very nice amp and CD player.
rgds, sreten.
Quite simply sell all your drivers, they go for far more
than than their intrinsic worth, loads more in reality.
They should go for about £1000+.
Then just build the Sunflowers, which which be miles
better than any hotpotch version using the old drivers.
You should have enough cash left over
for a very nice amp and CD player.
rgds, sreten.
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I've read about crossovers and bi-amping and I have a question: how to you scale the amp in an active crossover system?
Rod Elliott posted a table about how much power should be sent to each driver, but I still don't get it.
So let's say I have a woofer and a tweeter and they're both rated at 60W (ignoring the other specifications for now, it's just a general example).
I would obviously need less power to drive the tweeter than to drive the woofer. But how much? How do you calculate?
To power a 60W speaker system with passive crossovers I know that you need an amp 10-20% bigger than than the needed power.
Rod Elliott posted a table about how much power should be sent to each driver, but I still don't get it.
So let's say I have a woofer and a tweeter and they're both rated at 60W (ignoring the other specifications for now, it's just a general example).
I would obviously need less power to drive the tweeter than to drive the woofer. But how much? How do you calculate?
To power a 60W speaker system with passive crossovers I know that you need an amp 10-20% bigger than than the needed power.
If the two drivers have the same sensitivity, then the two drivers receive the same voltages from the amplifier+crossover.
The proportions of the whole bandwidth fed to each driver will be different.
Here I am nearly alone. I contend that the maximum peak transient signals sent to two equal sensitivity drivers are similar.
The average power sent to the two drivers are very different.
Those last two paragraphs give two requirements:
a.) the peak voltage capability of the amplifiers feeding the tweeter and bass/mid should be similar.
b.) the average power dissipation of the amplifiers will be very different. This requires the heatsinks of the bass/mid amplifier to be much bigger. It also requires the smoothing capacitance of the bass/mid amplifier to be much higher.
When the drivers have different sensitivities and/or have different impedances, then the amplifier capabilities need to be scaled to give the same speaker SPLs as found in the signal.
The proportions of the whole bandwidth fed to each driver will be different.
Here I am nearly alone. I contend that the maximum peak transient signals sent to two equal sensitivity drivers are similar.
The average power sent to the two drivers are very different.
Those last two paragraphs give two requirements:
a.) the peak voltage capability of the amplifiers feeding the tweeter and bass/mid should be similar.
b.) the average power dissipation of the amplifiers will be very different. This requires the heatsinks of the bass/mid amplifier to be much bigger. It also requires the smoothing capacitance of the bass/mid amplifier to be much higher.
When the drivers have different sensitivities and/or have different impedances, then the amplifier capabilities need to be scaled to give the same speaker SPLs as found in the signal.
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same output voltage requires same supply voltage.
The two amps do not need to be the same. The dissipations in the treble amplifiers are very much shorter. That allows the designer to use more of the transient temp derated SOA.
Looking at the different amp designs, one would use less smoothing, less heatsink, less output devices, but all allowing the same output voltage and allowing the same peak transient current. That does not equate to a waste of resources in my book.
The two amps do not need to be the same. The dissipations in the treble amplifiers are very much shorter. That allows the designer to use more of the transient temp derated SOA.
Looking at the different amp designs, one would use less smoothing, less heatsink, less output devices, but all allowing the same output voltage and allowing the same peak transient current. That does not equate to a waste of resources in my book.
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