Bi-Amping Question (RF-83s Driven by Denon AVR-2807)

[severoon]

Hi all,

I have a pair of RF-83s driven by a Denon AVR-2807 receiver (110Wpc, 7.1). I currently do not use the surround back (SB) channels and this receiver allows the SB power amp to be assigned to bi-amp the front left and right. I am a well-educated neophyte when it comes to high-end audio--lots of book reading but not a lot of practical personal experience (besides growing up listening to my Dad's La Scalas, which has given me a strong preference for the clarity and effortlessness that Klipsch brings to audio). Eying the dual set of posts coming out the back of my RF-83s got me to thinking--I definitely want to put my unused SB amp to use, but I want to do it in the most effective way possible.

I understand there are multiple ways to bi-amp, but it seems my options are limited to vertical stereo bi-amping (letting one amp drive one speaker, both highs and lows) and horizontal stereo bi-amping (one amp drives the lows of both speakers, one amp drives the highs of both speakers). At the moment, I have the low end being driven by the front amp on my receiver, and the high end being driven by my SB amp. To my knowledge, there's no electronic crossover capability in my receiver, in bi-amp mode it simply replicates the signal on the Front amp to the SB amp, so each amp is amplifying a full-range signal and the internal passive crossover in the speakers is filtering out the highs and lows, respectively.

Question 1: if the SB amp is driving only the high end of both speakers as a result of the speakers' internal passive crossover, is it under the same load as the Front amp, which is driving the more power-hungry lows? To put it differently: is the SB amp doing less work because only the highs are making it through the internal crossover, or is it under the same load as the Front amp because it's amplifying a full-range signal, regardless of what happens to it down the line?

I'm assuming for the remaining questions that the SB amp is under less load, only driving the highs.

Question 2: if my assumption is right, then my current setup is a horizontal stereo bi-amp configuration. Should I leave well enough alone, or is it better to arrange it in a vertical stereo bi-amp configuration by switching the Front left for the SB left connections?

My gut on this one says that I should go for vertical stereo bi-amping and let each amp power one speaker. Otherwise, I'm limiting the power that drives the power-hungry low frequencies by dumping the load all on the same amp while leaving the potential of the SB amp driving the highs mostly untapped. Are there advantages to horizontal stereo bi-amping I'm not aware of?

Thanks!

[DrWho]

Each channel in your receiver is its own independant amplifier. Since they all draw from the same power supply, the difference between vertical and horizontal doesn't make any difference.

Often times, the main LR outputs have more power assigned to them than the other channels (especially the surrounds), so I would recommend putting the LR main woofers on the LR main outs...and then driving the highs with the LR surround outs.

Also, you want to maintain stereo symmetry - so if there's any difference between amps in the receiver, then you're going to want the different to be the same on both sides - again pointing towards using the LR main outs for the woofer sections.

For the record, I wouldn't recommend going through all the hassle. I think your time and money would be better spent finding a dedicated 2-channel amplifier to drive off the preouts of your Denon.

[ben.]

OK, I have a question. Does it sound different the way you have it set up at the moment compared to the traditional way? What's better/worse?

[Guest " "]

"Each channel in your receiver is its own independant amplifier. Since they all draw from the same power supply, the difference between vertical and horizontal doesn't make any difference."

I would qualify this statement based on how much capacitance is in the power supply.

  A reciever with 133,000uf of capacitance would have less of an issue than one that only had 40,000uf.  

 SInce the later is the most common senerio the vertical (HF and LF on one amp) vs the horizontal (LF and LF on one amp with HF and HF on the other) would provide a greater amount of capcitance to the systems LF sections. 

 The LF sections benifet greatly by more capacitance. 

 In a vertical senerio each LF section would have 40,000uf capacitance in our example for a total of 80,000uf of system LF capacitance. 

 In a horizontal senerio, you would only have 40,000 of capacitance available to the systems LF sections, since they are sharing our sample 40,000uf

[DrWho]

The value of the power supply cap doesn't magically change when you connect the drivers differently....I dunno what you're talking about.

[severoon]

Each channel in your receiver is its own independant amplifier. Since they all draw from the same power supply, the difference between vertical and horizontal doesn't make any difference.

Often times, the main LR outputs have more power assigned to them than the other channels (especially the surrounds), so I would recommend putting the LR main woofers on the LR main outs...and then driving the highs with the LR surround outs.

Also, you want to maintain stereo symmetry - so if there's any difference between amps in the receiver, then you're going to want the different to be the same on both sides - again pointing towards using the LR main outs for the woofer sections.

For the record, I wouldn't recommend going through all the hassle. I think your time and money would be better spent finding a dedicated 2-channel amplifier to drive off the preouts of your Denon.

In my case, far as I know, my receiver puts out 110Wpc through 4 separate internal amps. Sure, they're all driven by the same power supply, but I'm thinking that does *not* equate to a situation where I could expect 770W (110Wpc x 7 channels) if I only use it to play my fronts in a stereo configuration. (Am I possibly wrong on this?) As far as I know, the amps driving the fronts are no different than the other amps, except the one driving the center channel--that one only has one output, the other three have two. (http://usa.denon.com/AVR-2807LitFinal.pdf)

Currently, I have the configuration set up the way you suggest, with the LR main outs driving the LF on both speakers. More than trying to change things around, however, I'm primarily interested in understanding exactly what's going on. In my previous reading, I'd come to understand that a passive internal crossover in a speaker had the job of separating frequencies and directing those frequencies to the appropriate part of the speaker. In my case, it seems that I don't have a "crossover" per se, but rather two independent filters...a low-pass filter connected to the low posts and a high-pass filter on the high posts that have nothing to do with each other. (My impression of a crossover is a circuit that would pick up the highs from the low posts and add them to the highs from the high posts and vice versa--apparently the high posts and low posts have nothing to do with each other.)

Also, I'm interested to know if these filters have any effect on the load on the amp. In other words, if I have an amp pushing a full-range signal into a set of posts, does it matter if its the HF posts or the LF posts? Either way, the amp is amplifying a full-range signal. Does it consume the same amount of power regardless of whether some of the signal is being filtered down the line?

I'm confused by your last comment. As far as I can tell, I already have three 2-channel amps in my Denon (and one 1-channel, for the center). How will adding an external amp to the mix help me? (Incidentally, I'm more or less done spending money--the only reason I even started messing around with bi-amping is because I had more speaker wire than I needed and an idle amp.)

[severoon]

Each channel in your receiver is its own independant amplifier. Since they all draw from the same power supply, the difference between vertical and horizontal doesn't make any difference.

Oh yea, one last thing. Is this right? Each channel is its own amp? It seems from Denon's product sheet that there are four amps to drive the 7 channels: front (2 outs), center (1 out), surround (2 outs), and surround back (2 outs).

http://usa.denon.com/AVR-2807LitFinal.pdf

Am I reading this wrong?

[severoon]

OK, I have a question. Does it sound different the way you have it set up at the moment compared to the traditional way? What's better/worse?

Ah, the pragmatist!

It's impossible for me to say for certain, as it takes a minute to pop one set of connections and install the conducting straps to connect the two sets of posts together. It would be much easier to see if there's a sonic difference if I could do the A/B/A test, alas it's not to be. The other thing to keep in mind is that my listening room is not ideal right now...because of space constraints, my sound stage is not nearly as expansive as it could be (or as expansive as it was in the listening room) and I am currently working on treating the room to address other issues such as flutter echo (bad), direct echo (bad--makes everyone seem like they're singing a duet with themselves), and wall-stud resonance (minor). (Now that I think about it, I'll make another post to get info about sonic room treatments after this!)

Having said that, I trust my ears. When I had the speakers wired normally, during loud passages including a wide range of frequencies, imaging on the high freqencies would dissolve, cymbals were first to go. All instruments maintain their timbre and the cymbals still had the beautiful brassy sheen and shimmer that only horn-loaded treble can deliver, but the ability to pinpoint where on the stage they're coming from would just go out the window when there's was a lot of midrange and low frequencies present. I noticed this immediately upon setting up my new system a couple of weeks ago and initially thought it was my untrained ear simply losing track of imaging in the louder passages, as I've been listening to a substandard system until now. However, after noodling around with bi-amping, I noticed--or rather, didn't notice--any problem at all when hitting these same passages whereas before they stuck out a bit.

Also, I've noticed one other weird thing, and I'm not sure if this is an improvement or not. When listening to music with kick drums or lows that push the speakers toward the bottom end, before I was getting fairly consistent impact regardless of where I stood in the room--more sound than impact. Now, after bi-amping, when I move to the back of the room away from the speakers or at the exact half-way point between the speakers and the opposite wall, I get a thump in the chest with each beat. My impression is to say that this is more sonically accurate, as I remember a similar feeling in high school when listening to a good buddy of mine practice on his drum set...back then listening to him practice was more of a whole body experience than just hearing. I did not move the speakers at all between the single wire setup and bi-amping either (or change anything else about the room that would affect the bass).

[LoudnClear]

Wow, difference on the high and low end, and not maybe, sounds pretty noticable.

I thought about trying the bi amping with my RF-63s, but after reading some threads on here, it sounded futile without doing crossover before the amplificdation stages so the full watts per channel could be applied to the upper and lower posts. Feeding full range signal to the upper and lower posts both was said to be a zero sum gain effort cuz the non passed frequencies (out of band, ie lows on the high posts, and highs on the low posts) would be lost and not make it to the actual drivers. That makes logical sense to me.

I was also concerned about running 140 watts across the tweeter horn by itself, all I could see was smoke when I thought about actually bi amping.

But you're doing it and it sounds like you're getting tangilble gains, so I think I'll do some testing too.

[ben.]

Cool. Now bypass the passive networks and see what you hear.

[colterphoto1]

I agree with Doc, the power supply is really the limiting factor in modern receivers. You might be getting a teensy bit cleaner signal, but even with truly double the wattage, it would only be 3 db gain and with the biamp configuration the high amp is not putting out nearly as much as the main amps. Headroom is increased a petite amount.

Neat experiment and good of some receivers to allow this, but you'll derive much more from using the pre outs if you can have them assigned to the active crossover and drive a second amp. Get a big one and use it for the mains, the onboard for your highs. Now you've given the power supply some breathing room for the other channels as well.

Does the biamp option give you controls such as selecting the crossover point, slope, and balance/volume for the lo/hi sections?

I wonder if my new Yammie 2600 has this feature, I'll experiment. I'm using a Crown DC300AII for my mains now, with the proper settings I could biamp my LS now!

M

[severoon]

I talked to a technical rep from Denon today and asked several questions about this bi-amp configuration. He had some very interesting information for me and I just wanted to run it past you folks to verify it and pass along all the info.

1. He said that the current drawn through a particular amp is determined by what is actually played by the loudspeaker. If I have a channel connected to a the high posts, the presence of the high-pass filter means that the speaker is going to draw only enough current to play the highs that pass the filter. So, no worries about "overdriving" the tweeter--since the lows are filtered, even though the amp is amplifying a full-range signal, the low part of the signal will never make it to the tweeter and affect the wattage output in the least.

2. My assumption that high frequency component is always less power-hungry than the low frequency component of the signal is not always correct. Generally speaking, it's right, but because the voice coil of the tweeter must move very rapidly and for long, continuous stretches (as opposed to bass, which is typically a short-lived thump), it can draw the same or more RMS wattage as the lows depending on the music. Even though this is so, the variations in wattage will not be as great as with the lows, so he agreed with me that it's not optimal to do horizontal stereo bi-amping--it's just not nearly wasting as much headroom as I'd thought.

3. So, vertical stereo bi-amping is a better way to go. If a single amp is driving the lows on both sides, it's going to have to deal with massive impedance drops whenever bass kicks in. This is not a problem with my setup (because the RF-83 are so sensitive), but it does mean that if each amp drives a high and a low, then the impedance drops caused by the variable wattage draws due to the lows is distributed over both, which is a better allocation of available headroom.

4. It makes no difference that all the amps are driven by the same power supply. Any single amp (of which my 2807 has 4) is designed to continously put out 110W RMS of power into an 8 ohm impedance, period. The power supply can run way more power through any given amp, and will do so if I pump the volume too high--but the circuitry of the amp is only designed to handle that 110W RMS. (Having said that, they're designed way over specifications because they don't drive an ideal load, and the FCC regulations requires that they advertise amps at a continuous wattage level far below what they can actually comfortably handle...and you don't even want to know about peaks.)

5. So, then, what is the disadvantage of amplifying a full-range signal (as opposed to using an active crossover and amplifying only the HF component into the high posts and the LF component into the low posts)? When a full-range signal is amplified, the high component rides on top of the low...think of a big, long wavelength with a tiny wavelength superimposed on it. The HF component will be delivered to the tweeter always slightly Doppler shifted when it's riding on top of a LF component. So, after the full-range signal goes through the high-pass filter, the high frequency part doesn't come out totally undistorted--it contains Doppler shift remnants of the LF signal that was filtered out. When the high component is split out before being amplified, it still contains these Doppler shift remnants, but only remnants contributed from the *unamplified* LF component, meaning it has far less of an overall impact.

6. More important than the last point, another reason to use an acive crossover is because of the skin effect. It turns out that the skin effect, according to this guy, operates differently for different frequencies (effectively, an isolated low frequency signal penetrates much closer to the center axis of the cable than the highs do). If a full-range signal is carried, however, the skin effect across all frequencies is the same as the highest frequency present. In other words, if there is a high component, the lows suffer the same skin effect. By separating the components with an active crossover, the lows are free to move through much more of the cable because the skin effect is less of an issue in that band. The most important point here is that lows cause the biggest instantaneous wattage demands because of significant impedance drops, meaning that mitigating the skin effect for lows will make bass tighter and more responsive. (Though the skin effect is much more limiting with the highs, since highs aren't so variable they don't cause these impedance drops, so they're mostly unaffected even though the skin effect is more prevalent with HF.)

He told me that this last point is why he thinks bi-wiring works. If you simply get a thicker gauge cable, when you put a full-range signal into it the skin effect means that the extra thickness doesn't amount to much. Doubling the gauge of the cable does not double the volume of cable along which the signal is transmitted--it's far less than that. But, when you add an entire extra cable, you're effectively doubling the volume of cable that can carry the signal. That's why, he said, it's better to bi-wire with 16 gauge than single wire with 10 gauge. (Best of all, of course, is to bi-wire with the thicker wire.)

So, the ideal solution would seem to be active crossover coupled with bi-amping. However, he said that this is not all it's cracked up to be, and that he's seen more systems that are worse off than better off when configured this way. The reason is that the speaker designers choose the internal passive crossover very carefully to have characteristics that support the particular needs of that loudspeaker. If you replace that with an external active crossover with different characteristics, you might start emphasizing the worst aspects of your speakers. He said this solution is not for very dedicated audiophiles only, and most often these people will compensate for the mismatch by using different amps for the highs and lows. (He said for the true audiophile, monoblocks tend to drive the lows while tube amps tend to drive the highs, sometimes single-ended triode, or SET, tube amps.) He said this is a large investment of time and money and most people end up ultimately degrading the sound for all their efforts, so vertical stereo bi-amp amplifying the full-range signal into the internal passive crossover is the probably the best solution for me.

Finally, he mentioned that it's very smart to match amp wattage to the max power requirements of the speaker. For instance, my RF-83s have a max of 250W RMS. With a vertical stereo bi-amp arrangement, I'm now driving each speaker with about 220W RMS. That's pretty close, and that's good because it means that the available headroom is matched to what the speaker can handle. This provides a maximum of dynamic range while keeping the floor on black noise as low as possible. With a single-amp approach, I'm driving speakers than can handle 250W RMS with an amp that can only put in 110W RMS, meaning that dynamic range is limited. On the other hand, if I was driving these speakers with 2 1000W monoblock amps, the dynamic range would be unreal, but the black noise floor would be higher than it needs to be. (Apparently, with the monster amps, the black noise floor is lower only with respect to maximum RMS output, but overall, it's higher.)

Anyone care to correct anything he said (or that I may have misunderstood)? Thanks!

[severoon]

Wow, difference on the high and low end, and not maybe, sounds pretty noticable.

I thought about trying the bi amping with my RF-63s, but after reading some threads on here, it sounded futile without doing crossover before the amplificdation stages so the full watts per channel could be applied to the upper and lower posts. Feeding full range signal to the upper and lower posts both was said to be a zero sum gain effort cuz the non passed frequencies (out of band, ie lows on the high posts, and highs on the low posts) would be lost and not make it to the actual drivers. That makes logical sense to me.

I was also concerned about running 140 watts across the tweeter horn by itself, all I could see was smoke when I thought about actually bi amping.

But you're doing it and it sounds like you're getting tangilble gains, so I think I'll do some testing too.

According to what I understand, you could put a 1000W monoblock amp driving just your tweeter and it won't overdrive it unless you pump the volume up beyond what the speaker can handle. Even if you're amplifying a full-range signal, the current that goes through the tweeter voice coil is determined only by the part of the signal that makes it through the high-pass filter in front of that voice coil, so the draw on your amp is still going to be the same as if you were playing at the same volume level with a single amp configuration.

If you think about this, it makes perfect sense when applied to the speaker as a whole. I could take a speaker with a 50W RMS max wattage limit and drive it with a 2000W monoblock amp. That speaker will never see clipping because the woofer cones will be ejected from the enclosure and the tweeter voice coil will melt before clipping could ever occur, but neither of these things will happen provided you don't crank the volume up and dump more than 50W into the speaker.

According to what I know, it's *far* more dangerous to underdrive speakers. So, if I hook up my RF-83s to an SET amp that can only put out 1W, it will start clipping the peaks at fairly low volume levels. Speakers don't like square waves and all sorts of horrible things will start happening even though the wattage going into the speaker is far below its max rating.

[jimmy4300]

severoon, thanks so much for your description and explanation.  The only problem I have is that you said your 2807 has 4 amplifiers, I believe you ment 7.  BTW, I also have a Denon, but only a 1907, and only 85 watts per channel.  I'm driving RF-82s with a RC-62 center.  Right now they are powered by single 12 guage monster cables with the jumpers still in place.  It was always my intention to bi-amp the 82s since the Denon allows this, and I have more 12 guage cable and banana plugs on order to accomplish this.  Your discussion with Denon has reconfirmed my decision.

Thanks

Lou

[DrWho]

2. My assumption that high frequency component is always less power-hungry than the low frequency component of the signal is not always correct. Generally speaking, it's right, but because the voice coil of the tweeter must move very rapidly and for long, continuous stretches (as opposed to bass, which is typically a short-lived thump), it can draw the same or more RMS wattage as the lows depending on the music. Even though this is so, the variations in wattage will not be as great as with the lows, so he agreed with me that it's not optimal to do horizontal stereo bi-amping--it's just not nearly wasting as much headroom as I'd thought.

3. So, vertical stereo bi-amping is a better way to go. If a single amp is driving the lows on both sides, it's going to have to deal with massive impedance drops whenever bass kicks in. This is not a problem with my setup (because the RF-83 are so sensitive), but it does mean that if each amp drives a high and a low, then the impedance drops caused by the variable wattage draws due to the lows is distributed over both, which is a better allocation of available headroom.

That can only be true when you have multiple power supplies.

4. It makes no difference that all the amps are driven by the same power supply. Any single amp (of which my 2807 has 4) is designed to continously put out 110W RMS of power into an 8 ohm impedance, period. The power supply can run way more power through any given amp, and will do so if I pump the volume too high--but the circuitry of the amp is only designed to handle that 110W RMS. (Having said that, they're designed way over specifications because they don't drive an ideal load, and the FCC regulations requires that they advertise amps at a continuous wattage level far below what they can actually comfortably handle...and you don't even want to know about peaks.)

But it does matter that they all share the same power supply...

There is simply no way you can reduce the power draw on the supply for the same SPL by splitting the signal up to multiple amps. In other words, conservation of power.

6. More important than the last point, another reason to use an acive crossover is because of the skin effect. It turns out that the skin effect, according to this guy, operates differently for different frequencies (effectively, an isolated low frequency signal penetrates much closer to the center axis of the cable than the highs do). If a full-range signal is carried, however, the skin effect across all frequencies is the same as the highest frequency present. In other words, if there is a high component, the lows suffer the same skin effect. By separating the components with an active crossover, the lows are free to move through much more of the cable because the skin effect is less of an issue in that band. The most important point here is that lows cause the biggest instantaneous wattage demands because of significant impedance drops, meaning that mitigating the skin effect for lows will make bass tighter and more responsive. (Though the skin effect is much more limiting with the highs, since highs aren't so variable they don't cause these impedance drops, so they're mostly unaffected even though the skin effect is more prevalent with HF.)

Ok, now that is extremely misleading. Yes, the skin-effect exists, but not at the frequencies our music is playing at. Also, the behavior of one frequency range isn't going to affect the behavior of another frequency range - specifically, any skin-effect that might happen with the highs has absolutely nothing to do with the lower frequencies. In fact, if that were possible, then the entire world of electrical models and analysis would be completely invalid [] Were you talking with an engineer or tech support? There is an entire field of study for "transmission lines" and I think you'd be hardpressed to make the math show these connclusions.

He told me that this last point is why he thinks bi-wiring works. If you simply get a thicker gauge cable, when you put a full-range signal into it the skin effect means that the extra thickness doesn't amount to much. Doubling the gauge of the cable does not double the volume of cable along which the signal is transmitted--it's far less than that. But, when you add an entire extra cable, you're effectively doubling the volume of cable that can carry the signal. That's why, he said, it's better to bi-wire with 16 gauge than single wire with 10 gauge. (Best of all, of course, is to bi-wire with the thicker wire.)

"Better"? Sure, but let's not ignore diminishing returns. If insanely larger guages were indeed necessary, then the engineers designing the amplifiers and speakers would have done one of two things:

1) Chose a different electrical interface to allow smaller wires

2) Not sell smaller wire, and build the equipment to naturally accept much larger guages

The fact of the matter is that the engineers already chose an interface that allows smaller wires and they build the equipment to accept large enough cable. I won't argue the "audibility of better wire", but I'll argue that it's completely pointless in light of a million other variables. What does +-0.01dB matter inside a system of +-20dB?

So, the ideal solution would seem to be active crossover coupled with bi-amping. However, he said that this is not all it's cracked up to be, and that he's seen more systems that are worse off than better off when configured this way.

I agree, but it's not fair to consider the worst case active crossover scenario versus the best case anything else. Active crossovers do indeed take a little extra work to be done correctly, but when done correctly are absolutely the best approach. I bet if you were seriously considering it, you might be able to find a Klipsch engineer willing to provide you with all of the numbers you'll need to drop into your active crossover. Otherwise, you're going to need to use measuring equipment.

Finally, he mentioned that it's very smart to match amp wattage to the max power requirements of the speaker. For instance, my RF-83s have a max of 250W RMS. With a vertical stereo bi-amp arrangement, I'm now driving each speaker with about 220W RMS. That's pretty close, and that's good because it means that the available headroom is matched to what the speaker can handle. This provides a maximum of dynamic range while keeping the floor on black noise as low as possible. With a single-amp approach, I'm driving speakers than can handle 250W RMS with an amp that can only put in 110W RMS, meaning that dynamic range is limited. On the other hand, if I was driving these speakers with 2 1000W monoblock amps, the dynamic range would be unreal, but the black noise floor would be higher than it needs to be. (Apparently, with the monster amps, the black noise floor is lower only with respect to maximum RMS output, but overall, it's higher.)

I'm not sure what you mean here. I believe in the approach of starting with speakers that can play as loud as you want them to and then making sure you have an amp that can drive them to those levels within its linear operation. Generally, it's safer to overdrive your speakers than to overdrive the amp (since a clipping amp wreaks havoc on tweeters).

Anyways - that's just my take on it all. There's no shortage of different opinions out there.

[mas]

4. It makes no difference that all the amps are driven by the same

power supply. Any single amp (of which my 2807 has 4) is designed to

continously put out 110W RMS of power into an 8 ohm impedance, period. The

power supply can run way more power through any given amp, and will do so if I

pump the volume too high--but the circuitry of the amp is only designed to

handle that 110W RMS. (Having said that, they're designed way over

specifications because they don't drive an ideal load, and the FCC regulations

requires that they advertise amps at a continuous wattage level far below what

they can actually comfortably handle...and you don't even want to know about

peaks.)

But it does matter that they all share the same power supply...

There is simply no way you can reduce the power draw on the supply for the same

SPL by splitting the signal up to multiple amps. In other words, conservation

of power.

I am going to run like heck from the skin effect comment whoever you talked

to made!

But Doc is right. As Colter also mentioned earlier, the shared PS is a

potentially major bottleneck that can contribute to many system

issues. One might even make the point that a major advantage of Bi-Amping is

precisely to avail the amplifier stages to a separate independent power supply!

I think that Bi-amping, and the confusion that seems to surround it (which

frankly has caught me a bit by surprise) is starting to crowd the ol' Interconnect/speaker cable

issue as the topic that won't die and that gets reopened each week. Who woulda

thunk it?

[][]

[DrWho]

I think that Bi-amping, and the confusion that seems to surround it (which

frankly has caught me a bit by surprise) is starting to crowd the ol' Interconnect/speaker cable

issue as the topic that won't die and that gets reopened each week. Who woulda

thunk it?

hmmmm.....maybe give it another 20 years and it'll get replaced by something new? Perhaps the limitations of 192kHz sampling rates? []

[severoon]

severoon, thanks so much for your description and explanation. The only problem I have is that you said your 2807 has 4 amplifiers, I believe you ment 7. BTW, I also have a Denon, but only a 1907, and only 85 watts per channel. I'm driving RF-82s with a RC-62 center. Right now they are powered by single 12 guage monster cables with the jumpers still in place. It was always my intention to bi-amp the 82s since the Denon allows this, and I have more 12 guage cable and banana plugs on order to accomplish this. Your discussion with Denon has reconfirmed my decision.

Thanks

Lou

Hmm...well, the 4 v. 7 amps is a point I didn't quite get clear. I asked him about the number of amps and he said something that I didn't understand completely. My impression is that each channel is not separately amped, but instead both fronts are driven by one stereo amp, same story for the surrounds and the surround-backs. This seems to be supported on the data sheet for my receiver (http://usa.denon.com/AVR-2807LitFinal.pdf), which says that the front amp is "110W + 110W". (Actually, the datasheet can also be read in such a way that it implies there's a single 7-channel amp...I guess it all depends on what you mean by "amp".) I'll admit I'm a little out of my depth on this point.

A tip on bi-amping (or bi-wiring)...make sure that all the cables are the same length and that you use the same banana clips for all connections. If you use different length cable or a different clip, the signal that reaches one set of posts could be slightly behind the other. Since the internal passive crossover isn't digital, there is some frequency overlap between the tweeter and woofers--a tiny delay could throw that frequency out of phase and you'll end up getting cancellation effects wherever there is frequency overlap. (The Denon rep told me he's seen lots of people do all kinds of stuff to ostensibly improve their system, but they don't do it right and end up degrading the sound.)

You say "only" a 1907 with 85Wpc, but I think that receiver is perfectly matched to your speakers according to what the rep told me if you bi-amp. The max wattage your RF-82s take is 150W RMS, and with a bi-amp setup you'll be driving each with 170W, which is just about perfect. If you had the 2807 bi-amped with those speakers, you'd be putting 220W into each and raising the black noise floor with no increase in dynamic range (all of the extra headroom is beyond the speaker's capability anyway). From what I learned on this phone call, matching components is far more important than having "the best" of one thing and shorting your system in other areas.

Also, you can take some solace in the fact that both Klipsch and Denon rate the max wattages well below what the components are capable of in the real world, so on both counts you're probably closer to 250W bi-amp driving 250W speakers.

[severoon]

But it does matter that they all share the same power supply...

There is simply no way you can reduce the power draw on the supply for the same SPL by splitting the signal up to multiple amps. In other words, conservation of power.

Agreed--you can't reduce the power draw on the supply simply by splitting to multiple amps. I think his point was that the power supply in this receiver can dump ungodly amounts of power into the amps, but it's the amps that are the limiting factor. In other words, let's say that you're playing only through the amp driving the fronts and the rest aren't connected. Does this mean that my front amp can take up all the power that's available to the other amps? (110Wpc x 7 channels = 770W, 770W / 2 channels = 335Wpc...by unplugging all the other outs does my receiver suddenly become a 335Wpc stereo receiver?) No...according to what he said if I'm getting him correctly, the circuitry comprising the amp is rated to continuously handle 110Wpc. Even though the power supply can provide it far more, it will overheat and start degrading performance.

But it sounds like you know what you're talking about, so I'm interested to hear what you think. I'm not necessarily inclined to believe this guy simply because he worked for Denon--lord knows the first level customer support rep I spoke to didn't know much. :-)

Ok, now that is extremely misleading. Yes, the skin-effect exists, but not at the frequencies our music is playing at. Also, the behavior of one frequency range isn't going to affect the behavior of another frequency range - specifically, any skin-effect that might happen with the highs has absolutely nothing to do with the lower frequencies. In fact, if that were possible, then the entire world of electrical models and analysis would be completely invalid [] Were you talking with an engineer or tech support? There is an entire field of study for "transmission lines" and I think you'd be hardpressed to make the math show these connclusions.

So this is a definite point of disagreement. This was an engineer I was talking to who works in the lab, not a customer support rep. He said that the skin effect is a function of two variables: cable gauge and frequency. Signals traveling through thicker cable use flow along a higher cross-sectional area than the same signals traveling through lower gauge cable. Also, lower frequencies penetrate more deeply to the center of the cable than highs, and when highs are present the low frequencies are constrained to the cross-sectional area of the cable occupied by the highs.

I was inclined to believe him simply because he seemed knowledgable about other areas, but if there's one thing I've learned since starting my foray into high-end audio it's that the skin effect is one of the least understood aspects. Since I'm not in a lab doing my own research with an understanding of the fundamentals, my mind is totally open. You seem to be saying that in the 20Hz-20kHz range the skin effect is negligible altogether, which I will now file under "definite possibility" next to the info the Denon engineer told me. :-)

"Better"? Sure, but let's not ignore diminishing returns. If insanely larger guages were indeed necessary, then the engineers designing the amplifiers and speakers would have done one of two things:
1) Chose a different electrical interface to allow smaller wires
2) Not sell smaller wire, and build the equipment to naturally accept much larger guages

The fact of the matter is that the engineers already chose an interface that allows smaller wires and they build the equipment to accept large enough cable. I won't argue the "audibility of better wire", but I'll argue that it's completely pointless in light of a million other variables. What does +-0.01dB matter inside a system of +-20dB?

I'm in total agreement with you here--I was simply reporting this part of the conversation. My own personal belief on wire is that thicker is better, but cheap is king. I'd be running my RF-83s off of 16 gauge zip cord if I hadn't found 30' of 8 gauge Monster cable at Fry's for $40. I know a guy that's got his system wired up with firehose on cable elevators, and it cost him probably $1k to do it. Can I hear the difference between that and 16 gauge? Nope. Can I hear the difference between my $40 bi-amp'd solution over the single-wire, single-amp 16 gauge solution I had before? Yes, but only in imaging on the high frequency components during complex, loud orchestral passages. I may have gotten the same effect simply by bi-wiring or upgrading to the 8 gauge cable in a single-wire configuration...I didn't try it so I don't know.

The main reason I'm even bothering with bi-amping is simply to protect my speakers. Like you say, avoiding clipping is more important than anything else, and that's all I'm aiming to do.

I agree, but it's not fair to consider the worst case active crossover scenario versus the best case anything else. Active crossovers do indeed take a little extra work to be done correctly, but when done correctly are absolutely the best approach. I bet if you were seriously considering it, you might be able to find a Klipsch engineer willing to provide you with all of the numbers you'll need to drop into your active crossover. Otherwise, you're going to need to use measuring equipment.

Yes, this is essentially what he told me--the best case active crossover will be an improvement. I think he gathered from earlier in our conversation that I don't have the commitment (in terms of time and money) to achieve that, though, so by doing a half-wit job of it, I'd simply spend money and end up with worse sound. In this respect, he was a wise, wise man. :-)

I'm not sure what you mean here. I believe in the approach of starting with speakers that can play as loud as you want them to and then making sure you have an amp that can drive them to those levels within its linear operation. Generally, it's safer to overdrive your speakers than to overdrive the amp (since a clipping amp wreaks havoc on tweeters).

Anyways - that's just my take on it all. There's no shortage of different opinions out there.

Yes, I think we're in agreement on this last point as well. It's *safe* to vastly overdrive speakers (provided you don't crank the volume beyond the limits of the speaker), whereas underdriving speakers means clipping, which means speaker death. However, I think his only point was that leaving excess circuitry out of the equation will result in a cleaner signal. Why put all the extra circuitry in the pathway that can amplify to thousands of watts when your speakers can't handle thousands of watts? The extra circuitry in this case can never provide a benefit, but you're still making sonic trade-offs for the capability which will never be tapped. This makes sense to me at a gut level--doesn't it somehow seem inelegant to have vastly untapped potential at any stage in a system? That attitude feels right to me (which is why I question my friend, who has a $2k receiver capable of dumping huge amounts of power into Bose lifestyle speakers that are tiny and don't consume that much power...the system sounds good, don't get me wrong, but it probably would sound every bit as good had he saved a grand or so on that receiver, no?).

[colterphoto1]

I've got to run, but #2 is pretty much universally untrue unless you're listening to blisteringly loud violin solos. Much of the muscial energy is in the lower registers. Witness any PA system for any touring act (AC/DC through Pavarotti) and you'll find racks of power amps and speakers, most of which are used for the bass frequencies. Even a small band with a bi or tri amped PA might have a few thousand watts for the bass, a few hundred for the mids and maybe 100-200 for the highs.

I generally have to take Docs' word on things. Not to poo-poo experiementing the Bi-amping, Heck my new yammie 2600 will allow it, I'm wondering if I can use the onboard electronic crossover to use the onboards to drive my mid/hi horns on my LS and then route the pr outs to my Crown and the bass section just for kicks.

And YES the power supply is a limiting factor. Just look at how most major manufacturers rate their RMS wattage. Is it with ALL SEVEN CHANNELS driven? Usually not. They get that 110 watt or 170 or whatever by maxing out only one channel. That is why realists know that most modern HT receivers, when taxed with loads on 5 or 7 channels, will probably only put out about 80% of the rated wattage. There is just no way a home HT receiver is gonna pump out 1000 watts of clean power, aint' going to happen.