How many here use passive bi-amping & what did you gain

[onplane]

I'm a big fan of passive bi-amping and use it on two different sets of three way speakers. In both cases, I dedicate an amp for the woofers and another amp for the mids + tweeters.

My goal in both cases was to get control over speaker voicing. Years ago it was common for manufactures to market speaker systems with built in controls. With passive bi-amping you effectively "move" this control back to the volume controls on the separate amps.

Today, I find that I adjust speaker voicing quite frequently. That is, every time I change source, I re-balance to my liking. Further, my moods will often dictate my preference. Early in the day, I want bright, in your face speakers, while late at night or when reading, I much prefer that East Coast, "laid back" sound.

Just wondering what experiences others have had. I know that on both of my systems, I'm never going back to a single amp.

Regards,
Jerry

 

[avguytx]

Passive is ok, I guess, but unless you're limiting electrically the frequency output of the amplifiers to their dedicated ranges, it's wasting some power. You still have passive crossovers which have insertion loss.

Now, if you're using an electronic crossover where you can electrically limit what the amp is producing, you're definitely "showing" more power to the speakers, in theory. Lots of options anymore. I just use one big good amp with good passive crossovers and call it good. Now, I may go electronic crossover and two tube amps when I get my Klipsch Belle clones done.

 

[onplane]

Passive is ok, I guess, but unless you're limiting electrically the frequency output of the amplifiers to their dedicated ranges, it's wasting some power. You still have passive crossovers which have insertion loss.

Now, if you're using an electronic crossover where you can electrically limit what the amp is producing, you're definitely "showing" more power to the speakers, in theory. Lots of options anymore. I just use one big good amp with good passive crossovers and call it good. Now, I may go electronic crossover and two tube amps when I get my Klipsch Belle clones done.

Good point on power.

On my "smallest" amp (25 wpc) which is used on mids/tweeters, I turn the bass tone control full OFF. When you look at the resulting signal on a scope, it's amazing just how much smaller the signal becomes. Now, when you cut the treble control on the woofer amp, the change in signal isn't as pronounced.

Regards,
Jerry

 

[avguytx]

Have you got access to an electronic crossover so you could tinker and bypass the passive networks? For poops and grins...

 

[HTWillie]

I turn the bass tone control full OFF. When you look at the resulting signal on a scope, it's amazing just how much smaller the signal becomes. Now, when you cut the treble control on the woofer amp, the change in signal isn't as pronounced.

A speaker designer who used to frequent these forums wrote at one time the "half-power point" for music, in his experience and estimation, was about 400Hz. That is, half the energy contained in music is 400Hz and lower, and the other half of the energy is above 400Hz.

Of course music varies greatly, and that's a suspiciously round number too. But for design purposes it's probably a good starting point when choosing drivers, their sensitivity, power allocation, etc.

 

[HTWillie]

It's been a few years since I've biamped any speakers, but I remember never being quite satisfied with my setup. I couldn't get the LF and HF to track each other well at different volumes. Initially it was cool but I grew weary of trying to get things dialed in just right each day. And it gave me a whole new appreciation for speaker design and how hard it must be to get multiple differing drivers to play 0-100dB at the same time.

 

[whoaru99]

Played with it on a couple speakers but never detected any material benefit. That said, I wasn't trying to change the voicing of the speakers by using a mix of tube and SS, nor feeding different levels to the lows and mid/high.

 

[asilker]

I have never played with bi-amping so take my opinion with a grain of salt.

The reason I have not done so is because it does not make sense to me to purchase two power amps when at $x when i could instead purchase one power amp at $2x. Or in other words you cut your budget in half when you buy two power amps. Again, without an active crossover, why go through all the trouble instead of putting the effort into a better circuit design? But then I also am becoming fonder and fonder of high efficiency designs

 

[onplane]

I have never played with bi-amping so take my opinion with a grain of salt.

The reason I have not done so is because it does not make sense to me to purchase two power amps when at $x when i could instead purchase one power amp at $2x. Or in other words you cut your budget in half when you buy two power amps. Again, without an active crossover, why go through all the trouble instead of putting the effort into a better circuit design? But then I also am becoming fonder and fonder of high efficiency designs

Yes, clearly two amps cost more than one. In my first attempt, which I rate a total success, my speakers are very inefficient due to a 12 inch acoustic suspension woofer. Consequently, I powered these speakers with a fairly large amp. At the same time, I had several mid/lower power amps collecting dust. Since the high frequency drivers consume no where near the power of woofers, I simply recycled one of these small amps and put it back into service.

The gain in voice control was well worth the effort as the speakers were way, way too bass heavy prior to bi-amping.

On my next attempt, I did not start out thinking about bi-amping. My 30 year old amp died and I wanted a new amp with warantee. That is, I did NOT want another 20 or 30 year old amp. This turned out to be more challenging than I thought, because my speakers are 4 ohm. There are very few "reasonably" priced units rated to handle 4 ohms.

By accident I stumbled upon the Sherwood RX-5502 which has 4 full range amps rated at 100 wpc at 4 ohms. With a delivered price of $160, I could not resist the chance to bi-amp.

Initially, I just hooked the speakers up to the main amp and used as a normal amp. Sound was fine and amp performed flawlessly. Subsequently, I split the load so the main amp powers the woofers and the room2 amp powers the mids/tweeters. Once again, control over speaker voicing really enhanced the listening experience.

Regards,
Jerry

 

[BigElCat]

Passive is ok, I guess, but unless you're limiting electrically the frequency output of the amplifiers to their dedicated ranges, it's wasting some power. You still have passive crossovers which have insertion loss.

Now, if you're using an electronic crossover where you can electrically limit what the amp is producing, you're definitely "showing" more power to the speakers, in theory. Lots of options anymore. I just use one big good amp with good passive crossovers and call it good. Now, I may go electronic crossover and two tube amps when I get my Klipsch Belle clones done.

I'm gearing up to try vertical, passive bi-amping using the crossovers in my ADS L1290s.

The crossover point is 500Hz. The frequency output of the hi range amplifier will be limited by the passive cross-over, because the mid/tweeter will not place a draw on the amp much below 500Hz. I don't see how it will waste this power.

Actually the mid/tweet will draw from one channel of a two channel amp. The other channel will be dedicated to the woofers. I will have a left side amp and a right side amp (two channels each...the amps are Parasound HCA-750As). According to Parasound, the limited current draw on the hi-range channel will free up the power supply to shift current to the 'woofer channel'.

I haven't tried it yet, so I don't know if I will like it.

 

[asilker]

Yes, clearly two amps cost more than one. In my first attempt, which I rate a total success, my speakers are very inefficient due to a 12 inch acoustic suspension woofer. Consequently, I powered these speakers with a fairly large amp. At the same time, I had several mid/lower power amps collecting dust. Since the high frequency drivers consume no where near the power of woofers, I simply recycled one of these small amps and put it back into service.

The gain in voice control was well worth the effort as the speakers were way, way too bass heavy prior to bi-amping.

On my next attempt, I did not start out thinking about bi-amping. My 30 year old amp died and I wanted a new amp with warantee. That is, I did NOT want another 20 or 30 year old amp. This turned out to be more challenging than I thought, because my speakers are 4 ohm. There are very few "reasonably" priced units rated to handle 4 ohms.

By accident I stumbled upon the Sherwood RX-5502 with has 4 full range amps rated at 100 wpc at 4 ohms. With a delivered price of $160, I could not resist the chance to bi-amp.

Initially, I just hooked the speakers up to the main amp and used as a normal amp. Sound was fine and amp performed flawlessly. Subsequently, I split the load so the main amp powers the woofers and the room2 amp powers the mids/tweeters. Once again, control over speaker voicing really enhanced the listening experience.

Regards,
Jerry

What are the speakers?

Adcom stuff is a little old but dirt cheap and will handle down to 2 ohms. Very very easy to service.

Personal experience: when i had magnepans mg1c, I drove them with a 35wpc tube power stage and compared that with a 300wpc MOSFET stage. The tubes handled the load with much better sound quality. I really do believe the design is more important than the power.

 

[whoaru99]

Actually the mid/tweet will draw from one channel of a two channel amp. The other channel will be dedicated to the woofers. I will have a left side amp and a right side amp (two channels each...the amps are Parasound HCA-750As). According to Parasound, the limited current draw on the hi-range channel will free up the power supply to shift current to the 'woofer channel'.

I haven't tried it yet, so I don't know if I will like it.

What Parasound says is true if it's a common power supply, but that doesn't inherent mean the amp can utilize or deliver materially more power to the woofer.

The clipping point is still determined by the rail voltage and despite somewhat less current draw, the amp still has to swing the full range signal voltage unless you have a low pass filter preceeding it.

 

[Tom Brennan]

I couldn't get the LF and HF to track each other well at different volumes. Initially it was cool but I grew weary of trying to get things dialed in just right each day. And it gave me a whole new appreciation for speaker design and how hard it must be to get multiple differing drivers to play 0-100dB at the same time.

Adding to the difficulty of balancing drivers are the effects of compression--often a tweeter gets louder at a different rate than a woofer, thus changing the tonal balance of the speaker at different volumes. When Richard Heyser tested speakers years ago in Audio magazine he tested for compression and you could see the effects of compression in the graphs; often tweeters had less compression than woofers and as the speaker got louder it became more trebly.

 

[onplane]

What Parasound says is true if it's a common power supply, but that doesn't inherent mean the amp can utilize or deliver materially more power to the woofer.

The clipping point is still determined by the rail voltage and despite somewhat less current draw, the amp still has to swing the full range signal voltage unless you have a low pass filter preceeding it.

Good point whoaru99! That is spot on! This problem with clipping is exactly why I prefer horizontal bi-amping. Think about what happens when you push the woofer (right channel) hard. This can cause the rail voltages to droop and consequently, you could experience clipping where it really hurts in the left channel which powers the high frequency drivers.

Next if like me you use integrated amps, you can cut bass full OFF in the amp powering the high frequency drivers and this minor change can yield significant head room.

Most important of all to me at least, is with integrated amps and horizontal bi-amping you can vary power between speaker halves and gain some control over voice.

Regards,
Jerry

 

[onplane]

Adding to the difficulty of balancing drivers are the effects of compression--often a tweeter gets louder at a different rate than a woofer, thus changing the tonal balance of the speaker at different volumes. When Richard Heyser tested speakers years ago in Audio magazine he tested for compression and you could see the effects of compression in the graphs; often tweeters had less compression than woofers and as the speaker got louder it became more trebly.

Tom, as always, you remind us all of how complex these things we call speakers really are! You are absolutely correct everything is in motion and nothing is static. Further, nothing is really linear and that is the reason speakers interject far more distortion than any other component.

Your observation about tonal balance changing with volume just confirms that xover networks are truly limited. Speaker designers do a good job, but there is no way they can compensate for this, nor can they compensate for room acoustics. At least with horizontal bi-amping we get some chance (admittedly not perfect) to adjust for some of these things beyond control of the designers.

Regards,
Jerry

 

[onplane]

What are the speakers?

Adcom stuff is a little old but dirt cheap and will handle down to 2 ohms. Very very easy to service.

Personal experience: when i had magnepans mg1c, I drove them with a 35wpc tube power stage and compared that with a 300wpc MOSFET stage. The tubes handled the load with much better sound quality. I really do believe the design is more important than the power.

My speakers are AR's. The first set I bi-amped was a set of AR-3a's for which I am the original owner. These speakers were bass heavy by design.

The next set I bi-amped was also a set of AR's, but 20 years newer. Now these had the opposite problem in that they were too bright for my room.

Regards,
Jerry

 

[whoaru99]

Personal experience: when i had magnepans mg1c, I drove them with a 35wpc tube power stage and compared that with a 300wpc MOSFET stage. The tubes handled the load with much better sound quality. I really do believe the design is more important than the power.

Of course it depends what the metric is.

In abstract terms of sound quality watts in and of themselves are not paramount. However, if one needs to achieve some minimum SPL then certainly watts play into achieving quality sound. If one does not have the watts necessary to achive the desired SPL then SQ unquestionably suffers.

The point here is not to challenge your observation, but simply to say it's a multi-faceted scenario in which several aspects play together into any given end result.

 

[asilker]

Of course it depends what the metric is.

In abstract terms of sound quality watts in and of themselves are not paramount. However, if one needs to achieve some minimum SPL then certainly watts play into achieving quality sound. If one does not have the watts necessary to achive the desired SPL then SQ unquestionably suffers.

The point here is not to challenge your observation, but simply to say it's a multi-faceted scenario in which several aspects play together into any given end result.

Yes, agreed. I think we're on the same page here. My point is that in some situations, one doesnt really need that much more power. In my experience, room size is related to the power needed more directly than a loudspeaker's efficiency. Again, I understand that less efficiency means we need more power to reach the desired SPL's, but really unless you're trying to reach deafening levels (literally), or your room is very large, then circuit design can have a larger affect on the SQ and interplay with the speakers.

For example, with acoustic suspension designs the real trouble is not that the woofers require more wattage, but that the amplifier is more comfortable with low ohm loads as the impedance of that design will change across the frequency spectrum. Which is why I say the low-ish but constant 5ohm load of the magnepans was an easy match with my tube power stage. Sounds like the real issue with AR acoustic suspension is the amp's ability to control the woofer behavior instead of just raise the sound pressure level.

PS 99, you are always welcome to challenge my experiences and opinions. I'm hear to learn and I'm happy to learn from you if you know something I don't cheers

 

[Superampman]

I'm gearing up to try vertical, passive bi-amping using the crossovers in my ADS L1290s.

The crossover point is 500Hz. The frequency output of the hi range amplifier will be limited by the passive cross-over, because the mid/tweeter will not place a draw on the amp much below 500Hz. I don't see how it will waste this power.

Actually the mid/tweet will draw from one channel of a two channel amp. The other channel will be dedicated to the woofers. I will have a left side amp and a right side amp (two channels each...the amps are Parasound HCA-750As). According to Parasound, the limited current draw on the hi-range channel will free up the power supply to shift current to the 'woofer channel'.

I haven't tried it yet, so I don't know if I will like it.

It's going to sound better horizontally.

 

[BigElCat]

All points duly noted.

I have a powered sub woofer with a built-in active crossover. I'll set it at 60 hz.

Regarding the rail voltage, IIRC the HCA-750A is a true dual mono. I know it has double wound toroidal transformer that splits the channels. Wouldn't it have two rails, also ?

This does contradict their statement about freeing up current for the other channel, so I'm not sure what the results will be.

Parasound won't release schematics.