BI-AMPING

[cjgeraci]

Actually, the QSC PLX 1202 that I've been using recently for the bass bins comes with its own output levels. It is an added benefit to be able to increase or decrease the volume of the Khorns bass bins in relation to the upper end (in total). I've been using separate amps for awhile now, and also have variable options to adjust squawker levels and tweeter levels in the form of adjustable taps and tweeter attentuators. BTW, I initially tried this "fool's biamping" with my Belles before I moved them to the rear (and Khorns to the front). I found that my Belles reallly benefited because even though Belles (and LaScalas) are somewhat bass shy (due mainly to the balance of the speaker), you can increase the bass bin volume by using a QSC. This tended to work in addition to tweeter and squawker attentuation to further balance out the speaker by bringing the bass volume level up. Attentuating the squawker and tweeter and bringing up the bass bins, the Belles sounded like different speakers. And I could have lived with them - period - had I not stumbled across Maron's bass bins (with historical benefits on top of them).

Again, for me, ultimately I may end up going to a fully active three-way setup. But, in the meantime, this gets me tubes on the top end, and SS (with adjustable volume levels) on the bass bins.

Carl.

[pauln]

Does it help to mention that PWK experimented with bi-amping and measured greater distortion? He didn't recommend it (DFH 15-4).

[DrWho]

The marketing logic in that article referencing crappy electronics of the 70's is hardly accurate on today's standards.

The writer also conveniently chose to ignore distortions from the passive crossovers in the speakers. Removing the crossovers also improves the interaction between the amplifier and the speaker, thus also reducing even more distortion in the speaker. The key point is that there is no comparison of distortion levels between two complete systems.

In fact, PWK became a fan of signal alignment later on in his career and the only way to achieve that is through Bi-Amping with an active crossover...

[thoppa]

Hi,

Can I jump into this conversation and ask if you have tried class-t (hybrid digital) amps with bi-amping ?

I am using class-t amps from DIYparadise 'cos they have very low distortion and sound sooo sweet - rich and detailed. They are what has prompted to upgrade my whole system. However their max output is around 20 watts as a bridge-tied load so bi-amping, fool's or passive, is the way I am inclined to go for just a bit more headroom and complaints from the neighbours. I'd rather not add components so a fool's bi-amp set up really intrigues me because I don't think the power would be lost in heat. As far as I know, they don't suffer the heat problems of linear or tube amps and have very good damping (they are very efficient so they don't even need a heatsink at full output - incredible but true).

Is it still fool's bi-amping if it works ?

Also I'm planning to buy either RF-52s or RB-61s - both can be
bi-wired/bi-amped I believe ? Do the RF-52s really go as low as 34Hz ?
They're 5.25" after all. Is it weak output in the bass ? If anyone has listened to these in a decent room and has an opinion please let me know what your experience was.

Finally, now completely off the thread (sorry) but can anyone recommend a modestly priced (a few hundred US$) DAC for 24bit 44.1khz signals ?

Thanks to all,

Tom

[Guest " "]

If I am reading your question correctly, you said you are using a bridge tied load.  This means for stereo, you are using 4 channels.  In a bridge tied load, the music signal gets inverted and sent to one channel, the normal non-inverted siganl gets sent to the other channel.  Speakers are connected across the + positive terminals only.  This results in power equal to what the amps load predictions would be for a reduced load.  Example.  If you have 10 watt amps that deliver 10 watts at 8 ohms, and 20 watts at 4 ohms, in a bridged tied load senerio, assuming you were using 8 ohm speakers, your bridged amp would produce 20watts since each amp only sees half the speakers actual load.   

This is not bi-amping, fools bi-amping, passive bi-amping, active bi-amping.  In bi-amp senerios, amplifiers or transformers drive dedicated drivers shuch as tweeters, tweeters and mid drivers, and woofers, seperaterly.  Commonly indicated as HF and LF on speakers that support Bi-amping.  This requires 2 pairs of speaker wires per speaker cabinet.

It is simply bridging your amps.

[thoppa]

hello speakerfritz - thank you for the post !

I don't think I was very clear - sorry - I have eight class-t amps - they work in pairs as btl amps - so I have four btl amps, 20 watts each. 80w total. So this would be 20w for the HF speaker input and 20w for the LF speaker input for each of a pair of speakers. Obviously it is a tad weedy on paper but in reality, 20 watts into an efficient speaker is quite tasty, especially a distortion-free 20 watts. Plus there's the argument about high-power amps heating coils etc etc. I digress.

Because the crossovers are low(ish) at 1.8Khz on the speakers I'm lusting after, I reckon fool's bi-amping would mean about 20% or more power available for the LF stage and an HF stage that never ever gets near distortion output levels. I have no argument with the comments above about this power turning into heat because of very high impedance in the crossover reacting with the output stage of some amps, nor that fool's bi-amping is not suitable for tube amps. But I wonder if this applies to BTL amps ? and how about class-t amps with high damping factors and awesome thermal efficiency ? and, of course, BTL class-t amps ! Class-t stuff is quite new and quite different from the norm so I wonder if the rules are different for this kind of setup. So will this extra 20% add a dB or two to the headroom or just keep me cosy on a cold night ? Is it even worth trying ?

I noted above that it was said Klipsch Techies were saying bi-amping was the way to go until someone from MacIntosh said no thank you. Does anyone know where I can find this discussion ? It doesn't seem to be in this loverly forum.

Incidentally; I read in another thread that a $10,000 music setup blew people away with RF-52s so I'm definitely leaning that way now too. Quite excited in fact....sad eh ?

Thanks for reading,

Cheers !

[DrWho]

Biamping is not going to increase the power output of your speakers. The efficiency of your woofers is the limiting factor, so no matter how you look at it, 20W into the woofers = the same volume. It's easier to visualize if you think of the amp as a voltage source...the voltage across the woofer terminals on your 20W amp is going to be the same regardless of the voltage you're sending to your tweeters. Assuming a 4 ohm load, your 20W amp is putting a little under 13V across the terminals.

The rails in digital amps tend to be set rather low...probably around 18V in your situation. The only way to get more output from your RF's is to upgrade the amp driving them.

[Guest " "]

Klipsch was pro fools bi-amping until we got into discussions of differences in architecture, then their position was check with the manufacture of your amp.  Which is a good position to take.

The Mcintosh info was not at hand at that time.

The goals as to why folks bi-amp vary from individual to individual.

In my case, I was able to avoid the whole fools bi-amp, active vs passive bi-amp issues simply by using the different taps of my amps output transformers and run them via a dedicated speaker cable, to bi-amp terminals of my Klipsch crossovers.   I added a second xover, and moved my mid driver to it, resulting in a tri-wired senerio with  each section of a passive xover powered by a deicated portion of the output transformers windings.

This combination married Mcintoshs recomendations of using the transformer taps to control output levels with Klipsch's recomendations of using their crossover circuts to protect their drivers.  

So the answers to the  specific's to your question rest with the manufacture of your amps.  Lets us know what you find out.

[Guest " "]

'Biamping is not going to increase the power output of your speakers."

Let's not confuse speakers with speaker drivers.  An example of a speaker is a LaScala.  It has a HF section and a LF section.  In the LaScala HF section, there is a tweeter, and a mid driver.  In the LF section, there is a woofer.

I think folks expect, and probally are correct in thinking, that if they bi-amp a set of speakers like the LaScala, via the speakers LF and HF section using dedicated amps and speaker wires to each driver set, that the output of the  speaker system will increase.  

Simply put.

Amp 1=20 watts, assign to LF section, consists of a woofer

AMp 2 =10 watts, assign to HF seciton, consists of a mid driver and a woofer.

The expectation, and reasonable to expect, is that this combination would bring speaker output levels simular to what a 30 watt amp not using bi-amping would provide.

Driver output levels are limited to the amp that powers it capability's.

 

[thoppa]

Thanks for the replies !

I think the thing to do is buy the speakers, run them in, get used to them and then try a fool's bi-amp and see if my ears can hear any difference. I'll be sure to let you know if the amp designer or Tripath know a technical answer in the meantime.

Still, now I have an excuse to buy a new pair of speakers and spend hours on the sofa......!

Cheers,

[DrWho]

Is it still fool's bi-amping if it works ?

Yes

Also I'm planning to buy either RF-52s or RB-61s - both can be
bi-wired/bi-amped I believe ? Do the RF-52s really go as low as 34Hz ?
They're 5.25" after all. Is it weak output in the bass ? If anyone has listened to these in a decent room and has an opinion please let me know what your experience was.

34Hz will effectively be the -6dB point of the speakers crammed into the corner. I wouldn't expect much authority in that region - more like clean solid output down to 45-50Hz.

Finally, now completely off the thread (sorry) but can anyone recommend a modestly priced (a few hundred US$) DAC for 24bit 44.1khz signals ?

I think you will get the most bang for your buck by going with a quality receiver. The Denon AVR's actually have great preamps - just find one with analog preouts on the back and you're good to go.

[DrWho]

This combination married Mcintoshs recomendations of using the transformer taps to control output levels with Klipsch's recomendations of using their crossover circuts to protect their drivers.

Why not just use the volume controls on the amplifiers and reduce the number of parts in your signal path?

[Guest " "]

This combination married Mcintoshs recomendations of using the transformer taps to control output levels with Klipsch's recomendations of using their crossover circuts to protect their drivers.

Why not just use the volume controls on the amplifiers and reduce the number of parts in your signal path?

The only parts in the signal path is a lenth of wire.   One lenth for each section of the crossover, which attaches to the drivers.

To get +3db with the LF, 0db change with the MF, and -3db with the HF.

My implementation was to tri-wire using the 8ohm tap to the LF, 4ohm tap to the MF, and 2ohm tap to the HF.

The 8ohm tap has twice the turns of the 4ohm tap, twice the voltage, +3db.

The 2 ohm tap has half the turns of the 4 ohm tap, valf the voltage, -3db

The amp is rated at 135 watts per channel.

McIntosh Autoformer Training Page.pdf

[thoppa]

Is it still fool's bi-amping if it works ?

Yes

Well I'm gonna be a fool and try anyway. I'm too much of a 'purist' to add components when I reckon the amps will be quite happy. Actually, there's plenty of punch and drive with just one amp but what the hey....I'll have fun trying.

Also I'm planning to buy either RF-52s or RB-61s - both can be bi-wired/bi-amped I believe ? Do the RF-52s really go as low as 34Hz ? They're 5.25" after all. Is it weak output in the bass ? If anyone has listened to these in a decent room and has an opinion please let me know what your experience was.

34Hz will effectively be the -6dB point of the speakers crammed into the corner. I wouldn't expect much authority in that region - more like clean solid output down to 45-50Hz.

I bought a pair of RF-52s (HK$4200 = US$540 incl some cables) and have spent the whole weekend discovering previously unheard details ! Awesome ! I did an SPL test (very approx) and they produce bass all the way down to 20Hz but it only really kicks in at 40Hz. 70Hz and 150 Hz are both a dB or two up. So I suspect the driver's free air resonance is around the 70Hz area and the cabinet helps extend this almost an octave. Pretty good design work if you ask me. I also found out I can't hear over 15Khz. I'm only 37. Too many discos...

Finally, now completely off the thread (sorry) but can anyone recommend a modestly priced (a few hundred US$) DAC for 24bit 44.1khz signals ?

I think you will get the most bang for your buck by going with a quality receiver. The Denon AVR's actually have great preamps - just find one with analog preouts on the back and you're good to go.

Can't justify the moula on a power stage I'll never use - gonna demo some Chinese DACs and a Musical Fidelity and see what takes my fancy.

[thoppa]

Biamping is not going to increase the power output of your speakers. The efficiency of your woofers is the limiting factor, so no matter how you look at it, 20W into the woofers = the same volume. It's easier to visualize if you think of the amp as a voltage source...the voltage across the woofer terminals on your 20W amp is going to be the same regardless of the voltage you're sending to your tweeters. Assuming a 4 ohm load, your 20W amp is putting a little under 13V across the terminals.

The rails in digital amps tend to be set rather low...probably around 18V in your situation. The only way to get more output from your RF's is to upgrade the amp driving them.

Hmmm....not sure I agree. I tend to think of these things in terms of energy; voltage and current together make power = energy. If I disconnect one driver I'm releasing energy for the other (because less current will be used for the same voltage so the power use goes down) hence more power available for the remaining driver (assuming it doesn't just turn into heat). What often happens in power supplies is the voltage dips a little with high current drains and pulses. So in theory the extra energy available should add a little volume (very little probably - I expect only 1 dB) but it will allow more headroom for dynamics, which is actually what I'm after - a system that can really punch. It's why I like the idea of 5.25" drivers. Anyway, just MO. The proof of the pudding...

[DrWho]

Biamping is not going to increase the power output of your speakers. The efficiency of your woofers is the limiting factor, so no matter how you look at it, 20W into the woofers = the same volume. It's easier to visualize if you think of the amp as a voltage source...the voltage across the woofer terminals on your 20W amp is going to be the same regardless of the voltage you're sending to your tweeters. Assuming a 4 ohm load, your 20W amp is putting a little under 13V across the terminals.

The rails in digital amps tend to be set rather low...probably around 18V in your situation. The only way to get more output from your RF's is to upgrade the amp driving them.

Hmmm....not sure I agree. I tend to think of these things in terms of energy; voltage and current together make power = energy. If I disconnect one driver I'm releasing energy for the other (because less current will be used for the same voltage so the power use goes down) hence more power available for the remaining driver (assuming it doesn't just turn into heat). What often happens in power supplies is the voltage dips a little with high current drains and pulses. So in theory the extra energy available should add a little volume (very little probably - I expect only 1 dB) but it will allow more headroom for dynamics, which is actually what I'm after - a system that can really punch. It's why I like the idea of 5.25" drivers. Anyway, just MO. The proof of the pudding...

You don't have to agree with the physics, but that doesn't change how the world works. []

Take a simple two way speaker with an 8 ohm purely resistive tweeter and an 8 ohm purely resistive woofer. Put an infinitely steep crossover point between the speakers at 1kHz.

Feed your single amplifier with two frequencies: 500Hz at 1V and 2kHz at 1V. If your amplifier has a voltage gain ratio of 1:16, then it will output 500Hz at 16V and 2kHz at 16V. This will then be fed into your speaker and will draw only 32W total from the amplifier (16V x 16V / 8 Ohm = 32 Watts).

Now take two of the same amplifier, one feeding the low end and one feeding the top end, still using the passive crossover components (low pass to the woofer and high pass to the tweeter). Feed the same signal at 1V into both amplifiers with the same voltage gain ratio. The HF amp is going to output 16V at 2kHz (and 16V at 500Hz) and the LF amp is going to output 16V at 500Hz (and 16V at 2kHz). Because of the crossover, the tweeter is only going to see 16V at 2kHz and the woofer is only going to see 16V at 500Hz. In both situations, the amplifier is going to output the same voltage and the power draw on each amplifier is still going to be 32W.

In real life, there are many nonlinear factors, but that fact remains that the voltage output is going to be the same. If you're operating the amplifier into nonlinear regions (like clipping), then you have much larger issues to consider. I personally prefer to operate my amps within their linear range of operation where the distortion is low - and in such situations, doubling up on amps for fool's biamping makes absolutely no difference.

[thoppa]

the amplifier is going to output the same voltage and the power draw on each amplifier is still going to be 32W.

In real life, there are many nonlinear factors, but that fact remains that the voltage output is going to be the same.

Thanks for the ongoing debate ! []

I'll try to explain myself another way. Dynaudio (can I mention them here ?) pulse test their drives at 1KW for a millisecond or something and they like to tout that their drive does not distort with transients like this that are far above the rated power; they rate them at 150W or so; a continuous load. Amplifiers are also capable of transients far above their continuous rating. How would this be possible if output voltage is going to be the same ? What do you mean by this ? I think it is never the same but always varying, unless I'm listening to white noise (otherwise known as thrash metal. ...[])

Music (not thrash trash - but a full orchestra or something) is about dynamics - I think fool's bi-amping allows better dynamics because the amp is not working so hard; it's sharing part of the load with another amp. The frequencies determine the amount of energy needed to push the driver and because the drivers are pushing different volumes of air, more energy is needed for an LF driver than a HF one; about 80/20 of the total output power for a 2Khz crossover. Would you dispute this ?

I think the greatest benefit of bi-amping will be found in HF because that will become very lightly loaded and have tons of headroom for transients. The LF, by contrast, will only get maybe 20% more energy to play with so the increase in transient response will only be a few dBs; but just 3dBs is a doubling of the pressure level and that means twice the volume on a transient. If I get that I will be so happy - it'll be a huge difference for just US$110.

I completely agree that it is a very complicated matter because amplifier output impedance, damping factors, heat, and slew rates also have to be considered. It is why I am curious about using class-T for bi-amping. I can't find anyone posting on this topic. They are much more efficient amps so I can almost ignore heat losses I hope. However, I have no real data about their ouput stage because it is quite different from tubes and linear amps - it's via hand-wound air-core coils and they are bridge-tied load too.

So what I'm saying is, if you still don't see what I'm saying, then no worries, my class-T bi-amping 'research' will continue !

Enjoy your tunes !

Cheers,

Tom

[thoppa]

OOps, just realised I said white noise. I meant the pink kind....although purple is more my colour....matches my ...er.....

[mas]

Biamping is not going to increase the power output of your speakers. The efficiency of your woofers is the limiting factor, so no matter how you look at it, 20W into the woofers = the same volume. It's easier to visualize if you think of the amp as a voltage source...the voltage across the woofer terminals on your 20W amp is going to be the same regardless of the voltage you're sending to your tweeters. Assuming a 4 ohm load, your 20W amp is putting a little under 13V across the terminals.

The rails in digital amps tend to be set rather low...probably around 18V in your situation. The only way to get more output from your RF's is to upgrade the amp driving them.

Hmmm....not sure I agree. I tend to think of these things in terms of energy; voltage and current together make power = energy. If I disconnect one driver I'm releasing energy for the other (because less current will be used for the same voltage so the power use goes down) hence more power available for the remaining driver (assuming it doesn't just turn into heat). What often happens in power supplies is the voltage dips a little with high current drains and pulses. So in theory the extra energy available should add a little volume (very little probably - I expect only 1 dB) but it will allow more headroom for dynamics, which is actually what I'm after - a system that can really punch. It's why I like the idea of 5.25" drivers. Anyway, just MO. The proof of the pudding...

Doc, I think I finally get the drift here....

If you have several drivers and you disconnect one, more 'energy' is available for the other remaining drivers, thus increasing their, ah, 'energy'. Now, if I follow this logic further, the more drivers we disconnect, the more 'energy' is available for the remaining drivers until we disconnect all of the drivers and there is an infinite amount of 'energy ' available for the...oh wait...now I am confused again. ...But I think we have even solved the issues inherent in the time domain as well!

Having a few extra minutes I tried to follow this thread until...OK, I give... []

Let's just summarize and say that in far too many years I have never seen fool's bi-amping utilized in any arena except a few individual's systems who persist in rationalizing their experience - and that is of course fine if they want to do it and they can muster the rationalization for such. ...Not meaning to denigrate anyone, but there is a good reason for such a configuration earning its name! But we see what we want to see and believe what we want to believe.

But again, in environments where bi & tri-amping (and I tend to generalize and use slang to refer to all multi-way 'amping' as 'bi-' amping) have been the norm for over 30 years, the only configuration that has consistently proven itself is to use an active crossover which then feeds individual amps for each passband. And the Doc is correct, this is not done to increase output SPL! But it offers many advantages ranging from increased linearity in a particular passband to the advantages of introducing delay to individual active components that are now the norm in high-powered SR environments. It might also be instructive to take the journey back and to discover why such practices came into being and subsequently into widespread use; and to also gain a better understanding of the practical limitations for which this approach ('real' bi-tri-amping) provided a solution. And it was not simply for concerns about esoteric 'energy' and other more subtle fringe nuances.

There is MUCH more to the model then simply voltage and current and this exotic commodity called 'energy'. Your investigation seems more akin to an investigation of the power factor correction of the amp and load... May I suggest a deeper investigation into complex impedance and reactance, and to the how a system stores and releases energy, thus its relationship to potential and kinetic energy. There's that word again! And if you are heading that way, you will want to look into the Nyquist and Heyser spirals that actually measure and display these very complex frequency and time variant relationships as well as their mappings into the various associated domains.

But have fun, and try to be careful and avoid 'burning up' anything. []

Oh, and noticing the latest observation....the greatest benefit in bi-amping is in the LF!

Its all yours Doc![]

[thoppa]

Yo,

Energy = power x time. No mystery. Why patronise ?

Transient = power x very short time = energy

An amp is only any good if it can deliver transients while also delivering a continuous load. So it needs energy of two kinds - continuous load and transients. Bi-amp for transient response. You won't know it works it unless you do some serious testing. I don't plan to, so I hoped to find someone who has/will. It's just for fun for me. What did Klipsch engineers say ?

Actually came to this forum to find out if anyone knew about class-T....heck.

Cheers,

Tom