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View Full Version : Bi-amp, Bi-wire and the L7



Titanium Dome
01-18-2005, 04:39 PM
The owner's manual supplement for the L7 makes a protracted case for bi-wiring the L7. It's quite specific and detailed, including bi-wiring schemes that use up to four amps for two speakers. If you're not familiar with it, then here you go:


Bi-wiring
The L7's outer connection panel and internal dividing network are designed so that separate sets of speaker cable can be attached to the woofer (LF) and midrange/treble (HF) portions of the dividing network. This configuration is called bi-wiring.

Bi-wiring can provide several sonic advantages and considerably more flexibility in power amplifier selection.

Reduction of intermodulation
The majority of current flowing between an amplifier and speaker is devoted to the reproduction of bass. In fact, 60% or more of an amp's power is destined for woofers. When current flows through a wire, it produces a magnetic field (EMF) which expands and contracts at a rate equal to that of the music's complex frequency components. If a single speaker wire must conduct the full musical frequency spectrum, this preponderance of low frequency information can interact with or modulate high frequencies. The resulting intermodulation can create audible chnages to treble even before it reaches your loudspeakers.

By using separate conductors for high and low frequencies, unwanted treble modulation is avoided. Bass flows through one, treble through another.

Frequency-optimized cables
Having the opportunity to use separate HF and LF cables allows you to employ conductors best suited to each frequency range. As previously noted, most amplifier power is destined for your L7's woofers, so upon first consideration, it would make sense to use very thick wire for LF connections and thinner wire for HF connections.

However, the very fact that treble is higher in frequency means it is actually more sensitive to the type and gauge of wire. High frequencies are prone to attenuation from a phenomenon called skin effect. High quality speaker interconnect wires minimize skin effect by employing a large number of thin conductors with very low oxygen content. Optimally, you should use audiophile interconnects for both HF and LF conductors. However, if your budget intervenes, use the best quality cables for the HF connections and plan to add better bass cables later.

Amplifier flexibility
Bi-wiring also allows you the option of using separate stereo amplifiers for left and right L7 loudspeakers or even four mono power amplifiers.

Using stereo amplifiers can not only add sonic improvements but upgrade convenience as well. From a sound standpoint, dual amplifiers reduce intermodulation between left and right channels, since a complete set of input and power supply circuits are devoted to each speaker. Dual amps also provide an easy power upgrade path: you start out with one stereo amplifier, then add a second one later to quadruple power reserves.

Three or four individual amps provide even more possibilities, since you can use different brands and types of amps for HF and LF power. Many serious listeners prefer the midrange and treble sound quality produced by tube amplifiers. However, many tube designs do not provide as "tight" a bass sound as solid state models and often produce less power. Bi-wiring with separate bass and treble amplifiers allows use of both tube and solid state designs, where each is most desirable.

Whether you are using two or four amplifiers, it is important to use the same brand and power rating to power like connections on the L7s. In fact, since the crossover point for the L7's HF/LF is 150Hz, using amplifiers of the same power for both woofer and midbass/midrange/treble is recommended. For example, if you are using a 200W Brand X amp for the left L7, use a matching 200W Brand X amp for the right L7. Or if you're powering the left L7 low frequency connection with a 150W Brand Y amp and the high frequencies with a 150W Brand Z tube amplifier, use the same types and brands of amplifiers for respective right speaker HF and LF connections.


WHEW! :blah: :blah:

JBL usually doesn't make this big a deal out of this kind of thing, does it? If not, then why do so for this particular speaker? Was there something special about the L7's crossover, wiring, ????? Or is this just a warm pile? :screwy: :nutz: or :thmbsup:

Titanium Dome
01-18-2005, 04:43 PM
Oh yeah, meant to say that the manual has a separate section on bi-amping with an external, active crossover between the preamp and amps and the speakers direct to the amp (no internal crossovers).

Zilch
01-18-2005, 04:51 PM
I smell a steamin' pile reciprocity agreement with some "premium" wire outfit....

Tom Loizeaux
01-18-2005, 06:41 PM
That little treatise on Bi-Wiring made at least one major mistake. It spoke of reduced IM distortion because the treble wires won't be carrying low frequency information...this is NOT the case in Bi-Wire hookups. Both the woofer's passive crossover componants and the high frequency crossover componants get the full signal, and burn off the unused portion it heat.
In a true Bi-Amp setup, however, only the low frequencies go to the low frequency amp, and then on to the woofer and, of course, only the high frequencies go to the high frequency amp and on to the high frequency componants.
Bi-Amping makes very good sense, while Bi-Wiring is of questionable value...in my opinion.

Tom

Alex Lancaster
01-19-2005, 02:31 AM
:) Tom: You are too polite, "Bi Wiring" is :bs: , IMO spend the same $$ on better cables.


Some People think that "trick" things will work, and will talk endlessly about the "wonders", I mean, I get sick off all the BS out there; Is there a way to DeBunk them?.

Titanium Dome
01-19-2005, 01:46 PM
Just so I understand this then, the JBL people were involved in printing patently false information in the L7's owner's manual? That begs the next question: Why?

If it's for marketing purposes, that makes no sense since only the purchaser would see it and then only after purchase. If it's due to a co-marketing agreement, then with whom and how would the new owner intuitively know which brand to buy, since none was mentioned?

To be clear, I couldn't care less whether bi-wiring works or not. People tend to get very frenetic on either side of this debate. However, I do care about the integrity of JBL's published instructions. The company went to a lengthy discourse on the topic, complete with multiple diagrams and descriptions of purported benefits. So, the question is, "Why?"

:blink:

Zilch
01-19-2005, 02:59 PM
I ain't sayin' this is what happened, but if I had just had dinner with the premium wire team at a trade show, and we were enjoying refreshing beverages in the lounge afterwards, and they suggested that they would feature my latest design just introduced there consumer speakers prominently in their next print ads and literature if I would include instructions and recommendations as to how to use premium wire to "optimally" connect them with that product, it'd be a done deal.

In the interest of "Integrity," of course, I could NOT mention a specific brand at this time. This MIGHT, however, develop into a more specific cross-marketing arrangement in the future, once the details were worked out. Who knows, I might even consider using THEIR wire in my speakers exclusively and put a little label on my product touting it as a "feature!"

Alex Lancaster
01-19-2005, 02:59 PM
:bs: the question is, "Why?"

Zilch
01-19-2005, 03:10 PM
:bs: the question is, "Why?"In MY scenario?

Because it'd boost sales of both of our products:

There's synergy here, networking, all that good stuff.

AND she had big ones.... :D

Titanium Dome
01-19-2005, 04:38 PM
Well, hey, if it's liquor AND women... :bouncy: :bouncy:

transducergeek
01-19-2005, 04:51 PM
I remember reading an ad for some speakers recently, and it touted "Monster Cable used internally to wire these speakers" or some such.. I think I smell some rodents...

Earl K
01-19-2005, 05:25 PM
Hi,

Boy there sure is a real misunderstanding about "BiWiring" and this misunderstanding seems to be caused by a lack of understanding about " how most amps work " .

First a couple of definations as reference points. ( Sorry, but I couldn't find more intuitive or self-explanatory definations ).

Capacitance Reactance :
" The capacitance reactance ( Xc ) of a capacitor is the opposition offered by the capacitor to the flow of AC."
- "Capacitance Reactance" is measured in OHMS .
- Capacitance reactance varies directly with "frequency and capacitance". If either or both are "decreased" , the reactance ( measured in OHMS ) will increase ( and vice versa ) .

Inductive Reactance :
" Inductive Reactance ( XL ) is the opposition offered by the coil to the flow of AC."
- "Inductive Reactance" is measured in OHMS .
- Inductive reactance varies directly with "frequency and inductance". If either or both are "increased ", the reactance ( measured in OHMS ) will increase ( and vice versa ) .

AN OBSERVATION
- GENERALLY SPEAKING, for most of the brands of Class A/B amplifiers that a lot (or most) of us use,,, when the "load" impedance goes up - the amplifier will simply "put out less watts" . When a "Frequency Dependant" load ( measured in OHMS varying with frequency) is presented to the output section for these amplifiers - the amplifier will generate more ( or less ) watts in certain frequency areas. These watts are all dependant on the load impedances ( Reactances ) "shown" to the driving ( source ) amplifier.

HOW DOES THIS RELATE TO BIWIRING ?

Well, if one takes the HiPass section of a passive crossover and just connects it between an amplifier and a HF device ( say a horn ) - that series capacitor ( and parallel coil ) will "tell" the amplifier to diminish its low frequency ouput ( through the wires ) .
- So, the amplifier in question never even generates the LF content / or delivers it out to the speaker load through the wires.
- Therefore, if "BiWiring" with two amplifiers ( one amp driving the HF section and the other driving the LF section ), the initial statement by JBL that articulated real benefits - can be easily supported, just as the benefits from a fully biamped system can be supported.
- I personaly don't "see" the benefit of "BiWiring" with just a single amplifier , excluding the obvious of increasing the overall gauge size of the wire and also increasing the surface area ( for HF skin-effects ). But since I biamp everything - I'll have to reserve judgement until I try it.



That little treatise on Bi-Wiring ( JBLs' ) made at least one major mistake. It spoke of reduced IM distortion because the treble wires won't be carrying low frequency information...this is NOT the case in Bi-Wire hookups. Both the woofer's passive crossover componants and the high frequency crossover componants get the full signal, and burn off the unused portion it heat.


- This statement displays the commonly held "misunderstanding" about "reactive impedances" and the controlling effects that these load impedances impose onto the source ( driving ) amplifier.

Typically : Very little low frequency content is "burned off " as heat within a "series" capacitor in the typical hipass section of a passive crossover . Those low frequencies ( most of them ) are just never generated and therefore don't leave the HF amplifier ( in a 2 amplifier / BiWire setup ).

NOW : For Those Interested & FWIW ;

- I took the time this afternoon to double-check the premises that I "just made" .

- Sure enough, if one dumps "Full-Range Pink-Noise" into an amplifiers' input ( in my case a Bryston 2BLP ) / & then puts a "Reactive Inductance or Reactive Capacitance ( ie coil or cap )" in series with the load ( a 20 watt 8 ohm resistor ) and then "observes the shape" of the resulting waveform ( done by setting up an RTA "tap" on the output of the amplifier under test ) - the "expected and predicted" approx. 6 db per octave roll-off, will manifest itself on the RTAs' screen.

For me - "Seeing is Believing" .

I imagine, most people just need to see these "passively controlled" wave-forms to understand the concept, I know that I had to see them .

<. Earl K

Titanium Dome
01-19-2005, 10:27 PM
Thanks, Earl. That's what I call going the extra mile in a response.

:applaud:

You almost convinced me to take the time to pull the L7s out of hibernation and experiment with them. Hey, it's my time, so why not, eh?

I've got several Soundcraftsmen PCR800 MOSFET amps that are around 210W/ch with nothing to do and yards of unused 12 gauge wire, plus a Citation 5.0 just resting in its box in the garage, so, :hmm: Those PCR800s are considered Class H amps as I recall. Is that a problem?

Earl K
01-20-2005, 04:27 AM
Hi Titanium Dome


Those PCR800s are considered Class H amps as I recall. Is that a problem?

- Simply, I don't know since I don't know the published specs. for those amps.

- Generally speaking, the "At A Glance" spec. that I'm looking for is the amplifiers published output wattage stated for different impedance/load conditions.

- Yeh, If I had L7(s) and a couple of amps - I'd at least BiWire them ( if I had confidence in the sonic quality of the passive components ) .

The Load ( impedance ) Controlling The ( Source ) Amps Output Functions

- As a guide, I'll use the amplifiers published specs. to give me an indication of its performance under different loads. I'm "looking/searching" for an 8 ohm rating of (X) watts and a 4 ohm rating of 2 times ( or at least 1.5 times ) those 8 ohm watts. A 2 ohm rating of 3 or 4 times those 8 ohm watts is also nice to see - but not "critical".

- If those requirements are met - then I'll surmise that the "load" ( including passive components and their impedance characteristics ) will control the source amps outputted waveforms ( - properly influence the shape ) .

- FWIW: I don't use class A amps. If I were to include them in my setups - I'd want to know that any speakers' passive components and their' reactive impedances would be able to properly "control the waveform shape" being sent out by the amplifier. I'd likely have to "test for these conditions" before concluding a purchase .

-OTOH; If a given speaker has a crossover that is designed to present a consistent and constant impedance across its full bandwidth - then this "personal requirement" for the amplifier to react to "the load (for proper waveform shaping) ", is largely a moot point . :blah:

:cheers: Earl K