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if this topic is active elsewhere please advise and i will join that thread

new kef q700 bi wire posts
new q200 centre bi wire posts
older denon avr 3801 7.1 channel amp
older nad c 320bee not connected

interested in bi amping capability of the KEF's. I am assuming the kef engineers know a little bit about audio and provided that capability for a good reason.

have not read good reviews regarding bi wiring from one amp. not even sure my unused channels on the denon can be used ? nothing in owners manual about assigning unused channels.

So in order to use my NAD i will need an active crossover....any recommendations here? how would volume control work with two amps? also...the Denon is more powerful so i assume best config would be denon ==> low range and NAD ==> mid/ high range

thank you for taking a few moments to look at these question?
 

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There are endless threads talking about this. I would guess Marketing, not Engineering, added those posts. Engineering knows how to design a good crossover, built it into the speaker, understand that to increase power to the speaker you need to use an amplifier with more power, and to properly implement bi-amping you need to bypass (remove) the internal crossovers. Not really worth the effort and I would not bother.

If you want to try anyway most decent active crossovers include level controls, e.g. this dbx unit: https://www.sweetwater.com/store/de...MIs66ZwPf_2AIVzCSBCh2XaAscEAAYASAAEgKjHvD_BwE You'd have to get some sort of measuring system to properly set the crossover frequency and levels.
 

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I would also add that bypassing passive crossovers in decent speakers is not a good idea. To spite the minor issues with passive crossovers, making a good active bi-amped systems is no small task to align it properly.

KEF makes good speakers. You are best off with just using them as-is with a single cable for each speaker. Bi-wiring is essentially a waste of money and effort. Any benefit is strictly math on paper and will not be audible at all.
 

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Marchland XM9 Electronic Crossover

if this topic is active elsewhere please advise and i will join that thread

new kef q700 bi wire posts
new q200 centre bi wire posts
older denon avr 3801 7.1 channel amp
older nad c 320bee not connected

interested in bi amping capability of the KEF's. I am assuming the kef engineers know a little bit about audio and provided that capability for a good reason.

have not read good reviews regarding bi wiring from one amp. not even sure my unused channels on the denon can be used ? nothing in owners manual about assigning unused channels.

So in order to use my NAD i will need an active crossover....any recommendations here? how would volume control work with two amps? also...the Denon is more powerful so i assume best config would be denon ==> low range and NAD ==> mid/ high range

thank you for taking a few moments to look at these question?

Hello Paul,
I have a Marchland XM9 Electronic Stereo Crossover I'm selling. I was using it with a pair of Focal Aria 5s and a 15" sub.
if you google Marchland XM9 you will find all the details about the unit.
My model is configured as a three way with 80 and 200 hz. These frequencies can be reconfigured by changing the filter Resistor modules.
 

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Pretty sure you meant "Marchand". They make some really great stuff, albeit much more expensive than the pro dbx unit. They are one of my "step-up" recommendations.

http://www.marchandelec.com/xm9.html
 

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I've owned, used, and professionally sold active bi-amped systems. In a nutshell they are, in this day and age, an overly complex way to add:
- a modicum of driver protection,
- a modicum of higher output, and
- extremely limited EQ capabilities.

There are much, much better ways to achieve these three goals in 2018 and not only are they superior, they are also (often) less expensive.

The notion that the original designer that made one's speaker's passive network did it incompetently and that a consumer's selection of crossover points, Q, phase, and level will be better is unlikely.

On top of their added expense and complexity keep in mind:
- you'll be voiding your speaker's warranty [because to be done properly you must truly bypass (remove) your speakers' passive crossover*]
- a not inconsequential investment in measurement gear is required as well as the education as to how to use it.

Active bi-amping for consumer hobbyists was a good way to go in say 1980, but not today. Now it is best left for the pro sound reinforcement industry.


*Don't be fooled into thinking that removing the speaker's rear panel jumper straps accomplishes that; it doesn't.
 

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Hmmm... Generally agree with @m. zillch, with a few caveats:

- Going active may actually reduce driver protection in the event of amp failure (nothing betwixt amp and driver).

- Going active does not really increase power except for the loss in the crossover (which may be significant in some cases). It does allow "right-sizing" the amplifier for the frequency band. Some people (no, not you m. zillch) continue to think that going from a 100 W full-range amplifier to two 100 W amplifiers (one for highs, one for lows) is equivalent to using a 200 W amplifier. Not so, no driver sees more than 100 W, just in different frequency bands. There is some theoretical benefit but in practice it's usually moot. Additional power is not one of the reasons for bi-amping, active or passive.

- There are very sophisticated DSP-based crossovers these days, some including room correction, for not a lot of money (miniDSP) up to a whole bunch (DEQx).

Everyone wants to think they can do better than the speaker designers. DSP solutions have made it a lot easier to try, assuming you actually put in the time and effort (including completely bypassing the internal crossover, which as m. zillch said is more than removing the straps), but most consumers who bi-amp hear improvements with their eyes and wallets, not ears.
 

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Hmmm... Generally agree with @m. zillch, with a few caveats:

- Going active may actually reduce driver protection in the event of amp failure (nothing betwixt amp and driver).

- Going active does not really increase power except for the loss in the crossover (which may be significant in some cases). It does allow "right-sizing" the amplifier for the frequency band. Some people (no, not you m. zillch) continue to think that going from a 100 W full-range amplifier to two 100 W amplifiers (one for highs, one for lows) is equivalent to using a 200 W amplifier. Not so, no driver sees more than 100 W, just in different frequency bands. There is some theoretical benefit but in practice it's usually moot. Additional power is not one of the reasons for bi-amping, active or passive.

- There are very sophisticated DSP-based crossovers these days, some including room correction, for not a lot of money (miniDSP) up to a whole bunch (DEQx).

Everyone wants to think they can do better than the speaker designers. DSP solutions have made it a lot easier to try, assuming you actually put in the time and effort (including completely bypassing the internal crossover, which as m. zillch said is more than removing the straps), but most consumers who bi-amp hear improvements with their eyes and wallets, not ears.

It's also necessary to characterize the drivers used in the loudspeaker if the existing crossover is removed, since the loudspeaker with a new crossover is essentially a new loudspeaker design. The drivers used in the loudspeaker have native frequency responses, they also have resonances and a phase response. A well done passive or active crossover accounts for these variables. For example, most drivers have at least one resonance outside of their passband in the crossover that is ameliorated with a notch filter. Remove the passive crossover and this filter is also removed. Typically the phase response of a driver is considered in designing a crossover. The nice curves produced by a new crossover in isolation may not be so nice if the phase response of the driver interferes with the phase response of the crossover. The original designer like knew all of these variables and also the typical production variations in the drivers so that, depending on budget, the crossover could deliver the best response from the finished product.
 

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- Going active may actually reduce driver protection in the event of amp failure (nothing betwixt amp and driver).
This assumes systems which utilize active bi-amping have nothing but a set of wires from the binding posts going straight to the raw driver. Yikes, that's risky considering the pops and thumps sometimes made, for instance when powering an amp on or off, [hence why better ones usually have muting circuits, speaker output relays, triggered during this dangerous period]. This "nothing but bare wire" approach is usually not true in better pro setups though, especially with the delicate (more likely to fry) tweeter. There usually is at least some modest degree of protection and/or gentle filtration (including sometimes some signal level padding) at least protecting the tweeter. Here's, for example, that very circuit used on the actively bi-amped (only) JBL M2:


When I wrote that there can sometimes be a modicum of protection what I meant is that in a bi-amped setup where say you have a 50w amp for the tweeter and another 50w amp for the woofer (instead of a single 50w amp for the whole speaker wired passively), there is a ~99% likelihood that as you gradually increase the master volume the first amp to start clipping will be the woofer amp, not the tweeter amp. If you stay in this borderline, but potentially dangerous, over-driven clipping state the tweeter won't care nor be harmed because its amp is still doing fine and is providing a clean, un-distorted signal [hence why some people chose to economize by buying a weaker amp for the tweeter since it rarely needs as much power].

If you happen to be one of these people who insists "Clipping amps being harmful to the tweeter is just a myth: all that matters are the mechanical excursion limits of the driver and the overall power that reaches it" [I'm unconvinced: a squarish looking wave from a clipped amp is more dangerous thermally, IMHO, but please start a new thread if you want to go there.], OK, then fine. When I stated, to parphrase "It offers a modicum (albeit usually trivial) amount of protection" you can take that to mean "Protection from hearing any audible distress as you approach this borderline, red-line amp output level because the ear is more sensitive to distortion in the highs than the lows and in an equal power [say 50w woofer + 50w tweeter] active bi-amped setup the LF amp is ~99% more likely to be the first to clip. No distortion in the tweeter amp = no distortion in the high frequeny range it is solely responsible for.

Does this really matter in real world use? IMHO no, but a con man trying to push active bi-amping sales could artificially dial in the incredibly precise point where one amp (the woofer's) is starting to clip yet the tweeter's amp isn't, just yet, and find some very specific material where people might hear it.
 

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Those of us with the JBL cinema speakers have a much easier path to active nervana. Many of their speakers are paired with an amp that has the tunings preconfigured in the DSP. I use a Crown DSi 1000 with each of my 4622's. I do think the overall improvement vs. passive is well worth it.
 

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This assumes systems which utilize active bi-amping have nothing but a set of wires from the binding posts going straight to the raw driver.
Yes, that is true for most of the live sound reinforcement systems I set up. Mid/HF drivers were more likely to have a series cap "just in case". Woofers usually had nothing. The M2 is a monitor and does include both a series cap and attenuator to the HF driver. And yes you counted on your pro amp not doing anything stupid, and the sound man or power sequencer (may be one and the same) to turn things on and off in the right order.

When I wrote that there can sometimes be a modicum of protection what I meant is that in a bi-amped setup where say you have a 50w amp for the tweeter and another 50w amp for the woofer (instead of a single 50w amp for the whole speaker wired passively), there is a ~99% likelihood that as you gradually increase the master volume the first amp to start clipping will be the woofer amp, not the tweeter amp. If you stay in this borderline, but potentially dangerous, over-driven clipping state the tweeter won't care nor be harmed because its amp is still doing fine and is providing a clean, un-distorted signal [hence why some people chose to economize by buying a weaker amp for the tweeter since it rarely needs as much power].
OK, got it. I did not read that into your original post, sorry. Given loudness curves show we need 20 - 30 dB (100x to 1000x the power) to hear deep bass as loudly as midrange sounds that is a typical argument for (active) bi-amping. For pro setups, a smaller (lower-power) treble amp costs less, takes up less space, draws less power, and throws off less heat (less a concern these days when class D is so common). It also makes it more likely you'll not blow breakers in a live venue if you can keep the wall power draw down some. Not usually an issue for concert halls and stadiums, but a PITA in a nightclub or bar scene when there are one or two outlets on stage, often on the same circuit. Blah.

Probably worth the reminder (again) that "passive" bi-amping implemented by most AVRs does not provide any meaningful advantages since both amps have the exact same signal applied to their inputs and the passive speaker crossovers must stay in place. The treble amp will dissipate less power but still clips at roughly the same point as the bass amp since voltage is the same, and the overall power (and thermal load) is greater because there is standing bias current in both amps and neither are 100% efficient so the overall power requirement is higher.

In the real world, losses can be high in certain crossovers, but perhaps the greatest benefit of going active is that you can implement high-order filters and get all the drivers time (phase) aligned using DSP so the overall sound is cleaner (lower in distortion).
 

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Here's, for example, that very circuit used on the actively bi-amped (only) JBL M2:

Why, you may ask, would there be padding on the uber-expensive M2 when it is part of an active system with level controls?

It appears that JBL (more accurately, JBL Marketing) decided to forego design and development of an appropriately-sized (read: smaller) dedicated HF amplifier/DSP that could have been integrated entirely into the enclosure (think Genelec) in favor of a quick, turnkey solution (off-the-shelf Crown, Levinson and BSS gear): an external, kilowatt amplifier channel cabled to a 50-watt compression driver.

Those resistors aren't there to burn off all that excess power. They are there to attenuate all of the noise resulting from the excess gain intrinsic to the excessively large amplifier channel.
 

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Why, you may ask, would there be padding on the uber-expensive M2 when it is part of an active system with level controls?


Yes, its a down and dirty quick way to suppress high gain amp hiss. We aren't nearly as sensitive to noise in the bass so its the tweeter where we need to worry about it.
 

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Combination of higher sensitivity compression driver and desire to use matching amplifiers, so the attenuator solves both issues (level mismatch and hiss).
 
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