[Alfalfa]

I was wondering what benefits other PMC users have noticed by biwiring their speakers, or even triwiring when connections allow. I am wondering if this can bring any sonic benefits. Is it usefull or are the extra binding post only usefull for bi- or triamping? Could bi- or triwinring still make a difference when speaker leads are extremely short (in my case 20 cm)?


Any comments and above all experiences are welcomed!!

Lets make this forum THE BIBLE for Bryston/PMC stuff!

Greetings,

Alfalfa

[Levi]

It would really be special if you bi or tri-amp.  That's 4 to 6 Bryston amplifiers for a 2ch setup!   You simply get higher SPL, best imaging and clarity if done correctly.  You may not hear the difference between 20cm or 60cm, just make sure they are equal in length.  It would be subtle.  Tri-amp are not subtle change for both your wallet and  sound.

One example of you have PMC lB1 speaker.  A 6B SST 3-ch amp or Three mono-block 7B SST amps = 600Watts per driver!

bi/tri-amp is beneficial if you carefully match components for each driver.  They are not beneficial if you don't know what you are doing.  System matching and carefull listening is a task.  You can hit it the first time have synergy or ruin the sound altogether.

How loud do you listen to music?  How much bass do you need? What type of music you listen to?  Questions may help you tune the speaker.  

To answer your question:I have a triamp setup in may car and loved the SPL and clarity.  I will not do triamp setup in my home for practical reason.

Enjoy,
Levi

[nicolasb]

Biwiring is a con-trick invited by speaker cable manufacturers to sell more speaker cable. It can occasionally produce sonic improvements because it effectively halves the resistance of the cables, but you'll only hear a difference if the wires you're using have too high a resistance to begin with (i.e. they are too long or too thin). Using a single length of thicker wire should sound just as good.

Bi-amping on the other hand can have significant advantages, though personally I think the benefits are sometimes exaggerated. It's not that it doesn't sound better, it definitely does, it's just that using a single amplifier with output power of 2n Watts is likely to sound better than using two amplifiers with an output of n Watts each. (How these two options compare in price terms is a whole other question, of course!)

[Mike Pickett]

Just a note from my personal experience.

I tried passively bi-amping my IB1's with a 3BSST on the mid/highs, and a pair of 7BSST's on the woofers.  I found that the 3B would clip before the 7B's and at a lower SPL than with just using the 7B's.  My feeling is that a 4B might have done a better job, but since the inputs see the same input signal, the amps should be as close in power as possible.  In an actively biamped system, this wouldn't be the case, of course.

How did it sound, you ask?  Great, but not so much better that I could justify having amps all over the floor.  Some day, if I'm really bored, I'll try it with four (or maybe six) 7B's.

Also, after this experiment, I tried bi-wiring, just connecting the two sets of cables I'd used for bi-amping to my 7B's.  I did this because it was less work than reaching behind the speakers to disconnect the cables and replace the jumpers.  It didn't sound worse, so I left it that way.

[Alfalfa]

Dear Levi (and others)

My listering levels are moderate to reasonably high levels. I'm quite satisfied with the bass quantity of the IB2's connected to &B ST's in my 15 x 17x12 half of 2 connected rooms and my music is large film scores, heavy metal and sometimes acoustic music. I llike the idea of improved clarity and imaging but don't need extra SPL's!

Thanks for sharing your experiences!

[Alfalfa]

Nicolas,

Would you consider matching an Bryston amp with any PMC driver to be good matching, or do you mean that each unit could have its own specifically voices amp?

[Levi]

Get 6x 7B SST mono-block amps.  You will get 99.999% excellent Dynamics, Imaging, Clarity, Depth and slighly lighter bank account.   Your wife may beat you up but when the bruises are healed, you still have the amps!  

Great sound!

[Skyhawk]

Other high end manufacturers like Krell only put one set of binding posts on their speakers because they think there is no benefit at all to bi amping unless you are using active crossovers.

More power into the same passive crossover network would just reach saturation quicker is my guess.  But again, I am one of those wierdos that bought expensive bi-wires ...LOL

[KCLam]

Hi, the PMC MB2/XBD in my system and recently triamped. The difference is not subtle. Played at low volumes, the mids and highs have much clarity from a biamp setup. Depths and soundstage is greatly improved, it extends beyond the speakers.
In a nutshell, larger drivers requires the power for sheer musical pleasure, and it will do the speaker a disservice by underpowering it.

[guest2521]

The benefits of triamping my mb2s were pronounced. I am using two 4bst and and a pair of 7bst. I also tried 3b-st. The benefits come from independent control of each driver not the increase in power - so going from an amp of n to 2n (for bryston) makes no difference, while going from n to n*2 makes a huge difference. I don't know if all speakers will respond this positively - I would guess not. There can be some marginal earthing benefit to biwiring in some instances. However the difference is very small. Effects of cable are largely exaggerated. I use cheap custom cable at a few £/m and to me it sounded better if anything than top of the range nordost or argento silver cables etc. Other than the LCR characteristics and good quality connectors and construction I don't think there is anything more to it than these factors - certainly nothing mystical and certainly of very small magnitude. I note that cables are where shops make a lot of their profits .

Using a 7bst for the tweeter is bit excessive. a 3bst is fine.

[Yogus]

Are you guys with the MB2s using active crossovers?? (i.e. active biamping).

[guest2521]

no - i bought the mb2s x-dem and the amps 2nd hand, for £10K. A new active system with those amps would have cost £25K. However I plan to convert and use an external crossover eventually. The only difference in the speakers is that the active mb2 has a tweeter with better power handling and slightly better performance, and PMC modified the bryston amps and crossover to get even more out of the system. I plan to replace the bryston kit with custom diy amps and crossover.

[nicolasb]

The benefits come from independent control of each driver not the increase in power - so going from an amp of n to 2n (for bryston) makes no difference, while going from n to n*2 makes a huge difference.

That's an oversimplification. It depends very much what it is you're trying to achieve.

Bi- (or tri-) amping is most likely to improve your mid-range and treble performance, but is unlikely to do anything for the bass. Using an amplifier with twice the power is likely to improve the bass response, and may also help treble and midrange as well.

In either case it pretty much comes down to power consumption. If the output from the amp is not enough to drive the full speaker, then this introduces distortion. By using an amp to drive only the much-less-hungry midrange and treble, thus ensuring that they have all the power they need, you make them sound better - but without helping the bass much.

To take some example numbers, imagine we've established that a single 200W amp is inadequate, and we have a choice between a pair of 200W amps and a single 400W amp. With the single 200W amp the bass is probably siphoning off 150W or more, leaving 50W or less for the treble and midrange.  If we bi-amp we've now got 200W for the bass (only 50% more) but a full 200W for the midrange and treble (150% more, big improvement). If we single-amp with 400W then we might end up splitting it 300/100, so both sections of the speaker end up with double what they had. But of course 400W might still not be enough to feed the whole speaker as much current as it needs, so the bass driver might still be sucking away current that the midrange and treble needs to use.

So if you're looking to tighten up the bass, you need a more powerful amp, and bi-amping won't help. If the bass already sounds good but you want to try and improve the treble and midrange, then bi-amping may be a better option.

The ideal, I guess, is to bi- or tri-amp with different types of amps for the different drivers. A tri-amped speaker, for example, probably won't even need 50W to drive the tweeter in isolation, but might need 300W or more to drive the bass driver.

[guest2521]

deleted repeated post

[guest2521]

Hi,

Sorry but I should have made it clearer - my comments are not made in generality, they apply specifically to bryston amps with the pmc mb2. Therefore they are not a simplification at all - they are just very specific. Apologies if that wasn't clear from my post.

If you go from 7bst monos in isolation to adding a 4b either channel then you get big improvements accross the board - I found these were greatest in the bass. Also going from 7bst to 3*3BST was an improvement accross the board including the bass. I spent a lot of time trying different combinations of 3/4/7bst . I settled on 2*4bst and 2&7bst as they were available - the former were used to drive a von neuman cutting lathe at a studio and were consecutively numbered, and the latter were sold with the speakers and came used from a studio, also consecutively numbered. A 4b and a pair of 3b would have sounded pretty much the same, though i think the topology of the 7bst adds something above and beyond the 4bst's ability. I think the benefits are due to the tighter coupling between driver and individual amp and also the reduction in intermod distortion and interaction accross the crossover. I don't think power is an issue for any of the bryston (did you really mean current and not power limiting?). Also, I do not think the crossover works in the way you are suggesting. The biggest benefit (95%) comes from triamping the mb2 - regardless of power configuration.

These comments might very well not hold true for other equipment - in fact I would expect it not to be the case.

Nick.

[PEB]

From my post at AA a while back:

Bi-wiring does not bypass any crossover components.
Each driver has its own dividing network section. Each section has +/- inputs (at the binding posts), and +/- outputs (that go to the driver terminals). With single wire, all the + input leads are connected to the + post, and same for the - input leads.

With bi-wiring, a second set of posts is added, and then the network sections' input leads go to each dedicated pair of posts. Electrically, both configurations are basically the same. Bi-wiring requires two sets of speaker cables, of course. So what's the big deal?

The theory goes like this. The midbass woofer cone motion generates a back EMF, which can jump over into the tweeter network input and slightly modulate the tweeter. Of course, the tweeter network by definition filters out the lower frequencies, and rejects most of this corrupting signal. However, right around the crossover region, a small amount of intermod remains.

With bi-wiring, the back EMF would have to "travel backward" to the amp on the woofer speaker cable, and then jump over onto the dedicated tweeter cable before it could modulate the tweeter. So that's several feet more of wire. Won't the signal still affect the tweeter? Not really, because don't forget the very low output impedance of the amplifier is across the +/- legs of both speaker cable inputs. IOW, the amp effectively "shorts out" the back EMF signal, and prevents it from going down the tweeter cable.

Sonically, you hear a very small improvement in the crossover region. To me, it sounds like an increased "purity" and definition. The effect is subtle. I don't recommend it except for reference grade systems, where subtle improvements are more audible.   However, I put it in the same class of tweaks such as cables, spikes, etc.  Given enough tweaks (scientific ones that is), the tiny differences finally add up to become a *small* difference!  And if not overly expensive, small differences are worth pursuing.

HTH.

[guest2521]

I agree - biwiring is a tweak level improvement which may or may not make an audible difference. Tri-amping, even passively, is much more worthwhile. I found it was akin to significantly upgrading a turntable front end.

[PEB]

Agreed.

If you have a setup which demostrates a good image, bloom, and stage depth, then you should be able to detect a little better focus a little further back in the stage.  Program material dependent, of course.

With bi-amping (whether with active crossovers or passive networks) it is of paramount importance to either use amps with identical gain for the mids and tweets, or else attenuate the higher gain amp until they match.

Fully active is a shot-in-the-arm, since then the dynamics improve from "rigid" coupling of the amp to the driver, as well as no veiling from nonlinear passive components.

[guest2521]

Yup - so I am waiting for my warranty to expire before I pull out the internal xover and put together an active external crossover

[PEB]

How do you plan to match the passive alignment with the active filters?