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Good Experience with Passive Bi-Amping of ET LFT-8Bs

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Posted on October 5, 2015 at 14:20:40
Dimitry
Audiophile

Posts: 457
Location: Massachusetts
Joined: January 26, 2006
I recently purchased a pair of Eminent Technologies LFT-8Bs and enjoyed their sound quite a bit with a pair of 50W Canary 339 monos.

A couple of weeks ago I added a pair of Monarchy Audio SE-100 Mk. 2s to drive the woofer sections in passive biamp mode. C C Poon had graciously modified his amps for me to match the Canary's gain at minimal cost.

The new sound is better in the low frequencies, with more solidity and weight as well as better pitch definition to the sound of the drums and bass guitar.

I think this adds to the flexibility of the ETs panels and their use in different installations. I did this with my Mag 1.6s before and liked the results as well - solid state on the bottom, tubes on top.

I also have to say that it is a pleasure to deal directly with the actual makers of the equipment - Bruce and CC. You get the best service and by far the best product knowledge then you can get from a sales person.

 

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RE: Good Experience with Passive Bi-Amping of ET LFT-8Bs, posted on October 5, 2015 at 19:26:35
andyr
Manufacturer

Posts: 12548
Location: Melbourne
Joined: September 2, 2000
Sure - IMO, the "more solidity and weight in the low frequencies, as well as better pitch definition to the sound of the drums and bass guitar" is due to having much more powerful ss amps driving the woofers.

I suggest you would get even more increase in SQ by actively bi-amping, rather than passive bi-amping. The Monarchys will be able to control the woofers better, not having series inductor(s) "in the way".


Regards,

Andy

 

RE: Good Experience with Passive Bi-Amping of ET LFT-8Bs, posted on October 6, 2015 at 12:17:17
Dimitry
Audiophile

Posts: 457
Location: Massachusetts
Joined: January 26, 2006
Well, Monarchy has a much higher damping factor than the tube Canary. However, I measured the output voltage at my normal listening volume with pink noise and I never break 10 watts.

My understanding is the damping factor is an independent design parameter in an amplifier, separate from output power.

Therefore, "high power amplifier" is not identical with a highly damped amplifier.

Active by-amping seems more than my electronic "skills" will allow. I can insert a pre-made line level low pass filter into the Monarchy's RCA inputs jacks, but I will have to disconnect the woofer's internal cross-over, which doesn't seem easy with ET's physical design.

 

Reaplacing a typical OEM speaker's passive crossover with an active crossover?! ALWAYS better? pffffft! , posted on October 6, 2015 at 20:07:37
Timbo in Oz
Audiophile

Posts: 23221
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
Why does everyone assume this is going to work well, each time?

It is not at all uncommon in even the low-pass section to smooth the response of the bass drivers around the crossover point, OR to provide Z-rise compensation. If that is built-in to the crossover - IE is not across the woofers' terminals - it will be absent when you remove the passive xover, and the sound will not be as OEM voiced!

The slope may be a compound one - with a knee. There may even be a notch filter for the woofer's break-up region, above the xover point.

Then we look at the high-pass crossover, where for domes you may have another trap for its Fs and response shaping

I wonder if a standard active crossover that matches all that is going to be particularly easy to make, or at all cheap.

And if the active crossover doesn't have those features - and MOST just don't - why do so many people convince themselves that going active bi-amping will be an improvement on passive bi-amping?

So, you will need to get a bespoke active crossover made, after your find out what the actual examples of the low-pass& high-pass in each of your speakers actually does.

Hmm take a speaker to crossover company so they can measure what it does. Better to take both, given driver production variances. The business that does this for you will need measuring gear. .... And this is going to be cheap?

For high-pass duty? It is not my experience that typical off-the-shelf active crossovers are more transparent than passive spkr-level or line-level crossovers built with high quality components like film caps, air core coils, and low-l Rs. It's the other way around.

My experience with passive bi-amping has been with spkrs with no low-pass but with Z-rise compensation across the terminals, which we kept.

The high-pass uses a 3rd order slope, an FS notch-trap t-filter - tuned to each big dome tweeter - plus response shaping.

Did I go and pay someone to replicate each channel that in an active box? No I did not. No low-pass did help in that decision, and I retained the z-rise compensation upgrade.

We tried vertical bi-amping - it wasn't much better, and we had buzz and hum issues.

What we did do was use one matching stereo amp for mid-bass but in pentode and upped its storage again*, and put the tweeter-only amp in triode mode.

Big improvement on one stereo amp in UL, and that was with both amps *rebuilt with BIG PSUs already.

There is a lot more headroom, bass is a lot better, everything's better, and no hum / buzz.

Because one stereo amp and its PSU was doing just mid-bass, the treble amp's PSU was not working hard at all, ever.

This is called horisontal bi-amping and IMO&E will be the best way to passively bi-amp with any gain-matched pair of stereo power amps.

Our OP has used two large mono-block power amps for the bass job, so the advantage - given possibly audible PSU effects in the mid-treble - from heavy bass passages - is slightly better, again.

IMO if you want to try bi-amping? ...... Unless you can - easily and certainly - match at line/active level what your existing passive crossovers do, you should still try passive horisontal bi-amping.

Yes, you will need amps with matching voltage gain or a matched pair of the same circuit.

IF the bass demands are serious a bigger amp but with matching voltage gain is a fine idea. OR a bigger PSU.

Even where we assume that active HP/LP matching 4LR slopes for sub-woofer use is going to be best we still might be wrong.

It might be simpler - and sound better - to allow the main speakers to roll off naturally. If the mains are sealed we could add a 2nd order passive line-level (PLL) input filter to that power amp's sockets -using high quality Rs and Cs. This will cascade with the 2nd order sealed roll-off giving a 4th slope acoustically. Likely to be more transparent than any active line-level HP crossover.

Then gain-match with 4lR low-pass in the active crossover. If they are Rbs then a 2nd PLL would help kill cone bounce, but you do end up with a 6th order HP acoustic slope. Killing cone bounce is audibly a good thing.
Stuffing the ports is cheaper!

So, IMO&E there are quite good reasons for trying passive bi-amping if you can get a matching-gain bass amp or two matching amps. But go 'horizontal' if the PSUs are shared across both channels.

Hi-fi systems are called systems because they are systems, so each one has its own dependencies. Eg. a complex OEM passive crossover in each speaker, possibly built for the individual drive unit's variances.



Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger


 

Good for you mate., posted on October 6, 2015 at 20:09:08
Timbo in Oz
Audiophile

Posts: 23221
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
See above?!


Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger


 

RE: Reaplacing a typical OEM speaker's passive crossover with an active crossover?! ALWAYS better? pffffft! , posted on October 6, 2015 at 20:20:41
hahax@verizon.net
Audiophile

Posts: 4279
Location: New Jersey
Joined: March 22, 2006
Agreed. The crossovers of great speakers do more than crossover; they equalize non-flat drivers(almost all of them). So an active crossover should be designed for each application. Generic designs won't get all there is out of a speaker. However I do believe that done correctly an active cross over is the ultimate way to go.

 

RE: Reaplacing a typical OEM speaker's passive crossover with an active crossover?! ALWAYS better? pffffft! , posted on October 6, 2015 at 20:33:38
All of these issues addressed and discussed many years ago on this forum. :)
Obviously a generic set of filter curves (like you might see on a typical commercial active unit) may have issues that need to be understood and/or corrected.
You can see an example of accurate matching active crossover in a post I made to the tweaks section back in 2001. :)
http://www.integracoustics.com/MUG/MUG/tweaks/davey/mg3.6xo.htm
And I'd done a few passive-to-active transfer function conversions many years before that. The concept is straightforward and not rocket science.

The key to bi-amping is not only the removable of the stock high-level components, but also the bandwidth limitation implemented by placing the crossovers before multiple power amps. This yields an objective power improvement efficiency.

Please do some further reading on this. All of this has been much discussed on various audio forums for many years.

http://sound.westhost.com/bi-amp2.htm#a50

Cheers,

Dave.

 

RE: Reaplacing a typical OEM speaker's passive crossover with an active crossover?! ALWAYS better? pffffft! , posted on October 6, 2015 at 20:34:17
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
Sounds like a job for MiniDSP.

EVERYTHING you mention can be done with one of the units on offer. The 2x8 which is 2 in for stereo and designed for 2 way, 3 way or 4 way speakers or use with sub or even potentially a 2nd zone has a 5 band PEQ on EACH input and OUTPUT.
IIr filters for shelf, hipass / lopass.

Some of the MiniDSP stuff even will handle the FIR filter which is PHASE FLAT thru the bandpass.

You can even apply time delay, in the case of the system I'm evaluating, up to 9 milliseconds from ANY output or combination thereof.

Easily done? No, not to the extreme level of detail asked for, with notch filters and all the rest.

The main advantage of an active system would appear to be as much as 3db increase in apparent amp power when you simply do not call upon an amp to deal with out of band information.
This applies Less as certian wackiness comes into play, like a 500 watt 'd' amp crossover over at 600hz to a 100 watt tube amp for the mid/high.
Too much is never enough

 

Waht if the system owner doesn't have the skills you raise? Nor wants to pay for them., posted on October 6, 2015 at 21:12:24
Timbo in Oz
Audiophile

Posts: 23221
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
Are you claiming that even IF the existing passive crossover is a simple first order HP, that there will be NO benefit from passive bi-amping?

(I would prefer a simple 1st order PLL on the treble amp and a matching reduction in sensitivity for the bass-amp - also at line-level. Cheaper and probably more transparent.)

OR that there can never be any benefit from passive bi-amping, ever?

I have been aware of the possibility of doing the kind of matching you are able to do and for a very long time. Very probably longer ago than you learnt about it.

You would think no-one here has a budget to stick to!

I was pointing out that audibly effective bi-amping is possible - in some circumstances - as the OP reported.

While you have re-iterated the alternative as if it was the only option, ever. But you have not shown that passive bi-amping is always going to be ineffective. And you can't.

It depends, okay?

LBNLeast, learn some manners.

:-)!



Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger


 

Budget? eh? what I f the sytem owner doesn't find DSP to be particularly transparent, yet at least?, posted on October 6, 2015 at 21:19:59
Timbo in Oz
Audiophile

Posts: 23221
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
IMO DSP has a long way to go. Because the back-plane it is done on isn't good enough.


Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger


 

"EVERYTHING" BUT " not to the extreme level of detail asked for, with notch filters and all the rest." , posted on October 6, 2015 at 21:25:15
Timbo in Oz
Audiophile

Posts: 23221
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
wowww!

Is audibly effective passive bi-amping possible or not?

yes or no?


Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger


 

RE: Good for you mate., posted on October 6, 2015 at 23:11:40
Dimitry
Audiophile

Posts: 457
Location: Massachusetts
Joined: January 26, 2006
I did not bargain for such a heated discussion...

I always assumed that a really high quality line level cross over made to exact values is an expensive proposition. Even a simple one would require expensive parts, jacks, presentable enclosure and some decent electronics knowledge and soldering skills.

Additionally, one would need to bypass or remove the built-in speaker cross over, which may be hard in some speakers and will probably void the warranty.

So, I always stayed with passive by-amping, and was generally quite happy with the results. My 1.6s were done with Adcom 565s monos on the bottom and single ended parallel triode amps on top. It was a really good sound, though it took a while to get the triode amps' gain to match the Adcoms. I did it by ear, listening to Aaron Neville and changing the input voltage divider over and over again. It was fun!

 

It just MIGHT work?, posted on October 6, 2015 at 23:38:01
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
I have NO idea if it sounds like a train wreck or helps to the extreme. Or perhaps, somewhere in between?

However, it is just possible that the helps provided by the DSP approach are a tradeoff in the PLUS direction VS a fully analogue approach.

Some of the DSP stuff can use FIR filters which are PHASE FLAT.

Back plane? You mean the means of implementation? We don't KNOW if it is good enough or not.
The 2x8 using the 4x10 plug in (app?) runs at 96Khz and 56 bit resolution. The potential would appear to be there.

Frankly, for the $$$, I think it's worth a try.

And finally, from our FWIW department, Josh mentioned that the folks at LINKWITZ use the miniDSP stuff. Link to 'DSP CHALLENGE'. An Electronic Death Match:
Too much is never enough

 

RE: Yes, "audibly effective passive bi-amping *is* possible" ..., posted on October 7, 2015 at 03:03:30
andyr
Manufacturer

Posts: 12548
Location: Melbourne
Joined: September 2, 2000
... in certain circumstances.

In particular, when you add a sub (or subs) to your main speakers and you want to roll off your mains rather than running them full-range (so as not to get both drivers duplicating a larger frequency range than they would, if the woofers were rolled-off).

In this situation, you need to feed the mains from the HP filter on the sub. However, generally speaking, sub HP filters are not high SQ - so the highs will suffer (on your main speakers).

Whereas, if you passively bi-amp your mains, the woofers can be fed from the sub's HP filter - and the mids/tweeters can be fed directly from the preamp (so their signal doesn't pass through the sub).


Regards,

Andy


 

RE: Waht if the system owner doesn't have the skills you raise? Nor wants to pay for them., posted on October 7, 2015 at 06:51:23
Did I claim anything about passive biamping one way or the other?
Did I claim anything about the costs of a line-level approach? (although it can be done fairly cheaply.)

These kind of knee-jerking straw-man comeback arguments remind me of JBen. :)

Passive bi-amping is an approach....certainly. But it doesn't achieve certain objectives that line-level biamping does.

As I said, please do some further reading on this topic.
If you want to have an adult conversation about this, I'm willing, but please don't waste my time with silly rhetorical nonsense and straw man arguments.

Dave.

 

RE: Waht if the system owner doesn't have the skills you raise? Nor wants to pay for them., posted on October 7, 2015 at 09:13:04
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
passive BiAmping DOES get one thing done.
I now have a PAIR of amps available and running on each speaker. That's part way TO an active system.
Now, everyone can have at the various approaches, be they active, passive or DSP based.

And NO, I do Not have 'deep pockets'. I'm not going to run down several paths only to find blockage at the end of each. I'm going to do a bunch of thinking prior to the big commit.
So Far? I'm just getting up to speed on the DSP approach. This strikes me as potentially the most cost effective AND overall 'best'. Done properly you address room issues as well as speaker issues.
Dumpingground has been down this road and I'm reading his stuff carefully:
Too much is never enough

 

RE: Waht if the system owner doesn't have the skills you raise? Nor wants to pay for them., posted on October 7, 2015 at 09:30:40
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
As Davey AndyR and pictureguy pointed out you can copy the electric behavior of the XO including all notch filters and FR shaping - Be it in analog or in a DSP unit with its flexible software. The only truly problematic issue is duplicating a series crossover in line level analog. It is less than straightforward.

There is a great benefit from passive biamping. Particularly from having the amp that does bass be separate from the one that does higher freq, even if the top end ampt is not restricted in the range it is driving it is still not seeing the bass XO.

But there are issues with passive biamping that are better addressed at the line level - first is the fact that the top freq amp is still wasting power trying to drive the high pass filter with low frequencies. Second is the low end amp having reative XO components between it and the drivers. Drivers and amp will perform better without those in the way. The second issue is the quality of parts at a given cost. Top level line level parts are 10 X cheaper than their speaker level equivalents.

 

RE: Waht if the system owner doesn't have the skills you raise? Nor wants to pay for them., posted on October 7, 2015 at 10:24:43
A series crossover is also straightforward to duplicate at line level.

I think you have numerous misunderstandings of passive bi-amping regarding power splitting and "wasting of power."
My suggestion is the same as to Tim. Do some further reading on the entire topic. The trade-offs involved in passive bi-amping are different, but also well known for many years.

Dave.

 

The post of mine you critiqued implicitly encompassed the possibility of matching the, posted on October 7, 2015 at 12:51:42
Timbo in Oz
Audiophile

Posts: 23221
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
transfer function of a passive speaker-level crossover at line level / actively. And you missed that.

I wonder why?

No, I don't need to read up on this field. I think I began reading up about it in the early 1980s. But active was already around by then

It is likely that I have been a technically aware member of this hobby for longer (>50 years) than you have been alive, so don't presume to lecture me. John Dunlavy and I had a few conversations when he was based here in Canberra, and he didn't presume.

If, as you have agreed, passive bi-amping can bring audible improvements despite the 'waste' of power, why was it necessary for you (or Andyr) to comment on Dimitri's experience, at all?

On the evidence I think you both do believe that passive bi-amping is 'fools bi-amping'.

Now, I have a question for you - about human responses to music.

How do humans identify instruments by their characteristic timbre? That is, what do we pay most attention to, with all notes, by all instruments?

Your turn.


Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger


 

RE: The post of mine you critiqued implicitly encompassed the possibility of matching the, posted on October 7, 2015 at 15:46:39
Line level active crossovers were around long before the early 1980's. And I was doing more than reading about them then....I built my first one in the early 1970's when I tore apart some KLH 6 speakers and "actified" them with some old Stereo 70's. Good fun.

Believe what you want to believe regarding the various multi-amping schemes. It's obvious that myself or Andy or anyone else is not going to change your mind.

Dave.

 

I see you have ducked the question I asked you., posted on October 7, 2015 at 16:12:50
Timbo in Oz
Audiophile

Posts: 23221
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
Super adult.


Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger


 

RE: I see you have ducked the question I asked you., posted on October 7, 2015 at 16:50:11
Your question was so far above my head I couldn't understand how it related to the topic at hand.
I'll cogitate on it and consult with some people that aren't as dumb as me and get back to you in a couple of months.

Dave.

 

In other words, you don't know! It underpins my understanding of music and audio., posted on October 7, 2015 at 18:01:01
Timbo in Oz
Audiophile

Posts: 23221
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
And, this means that you haven't done some reading that I haven't done. Now that is ironic.

Andyr actually doubts that I am right about it, which is instructive, about Andy's attachment to particular mental models.

You couldn't see how it was relevant? And that is instructive.

Not only because it is, but also that you don't want it to be.

:-)!











Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger


 

RE: In other words, you don't know! It underpins my understanding of music and audio., posted on October 7, 2015 at 18:19:07
You haven't done reading that I haven't done? Lol. Yeah, that's ironic all right. :)
You're an entertaining fellow...I'll give you that. I haven't laughed this much on this forum for a long time. :)

Dave.

 

RE: Waht if the system owner doesn't have the skills you raise? Nor wants to pay for them., posted on October 8, 2015 at 16:18:31
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
I did the comparison a few times with line level and speaker level HP for the mids set for the same freq and the little dynas had to be switched to UL when driving the cap but could handle the same large scale music in triode when the XO was at line level.

Using a Nuforce ref8b it ran hot on the speaker level HP but just warm on the line level XO.

So while power draw should be about the same it wasn't so in reality, Not that I measured power output, just spl levels for matching levels.


If you have a solution for series XO in line level, can it be done in passive line level with reasonable parts count?

 

RE: Waht if the system owner doesn't have the skills you raise? Nor wants to pay for them., posted on October 8, 2015 at 17:54:08
Power draw should NOT be the same. Where were you getting the idea it should be the same?

You can't implement an actual series XO at line-level because it's impossible with the grounding schemes of amplifiers coupling back to the source. You simply create the exact transfer function that the high-level series crossover would create and construct it as a normal parallel PLLXO or ALLXO.
I think some folks are still under the impression that series crossovers create some sort of magical blending combination that can't be created any other way. That's nonsense. :)

Dave.

 

RE: Waht if the system owner doesn't have the skills you raise? Nor wants to pay for them., posted on October 8, 2015 at 20:04:22
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
I haven't tried to duplicate a series XO at line level, I only saw Neolith try it and hit some problems and the solution seemed to be getting complex. So I asked about a simple one.

Back when I was trying these XO schemes about a decade ago I calculated the power draw and it was under 2db difference IIRC - since I was trying to figure out how come the nuforce amp melted the tennis ball damping construct I put it in. The mids are 95 db sensitive so I could not have been pushing that hard.

.

 

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