Isobarik, biamp, active?

Being a three way speaker, there are very compelling reasons for going active with isobariks.....a 3 way passive crossover cannot achieve a "seamless" join at both crossover points simultaneously (the main reason why, in a passive setup I would always sacrifice the extra bass and power handling of a three-way for the coherence of a two way)

Active operation does bring benefits to two-way speakers of course...the benefits with 3 ways are much more obvious

In my experience, multi-amping(passively) with naim gives the worst of all worlds....most the expense of an active setup,without most of the benefits. If you are going for passive operation, my personal advice, based on having heard the alternatives, would be to use a single amp, higher up in the range,eg a single pair of 135s will outperform a pair of passive 250s etc

Laurie S

[This message was edited by Laurie Saunders on THURSDAY 11 December 2003 at 15:09.]

James

quote

"how on earth did I arrive at that conclusion"

I read the textbooks. I suggest you do the same

Ask any speaker designer who knows anything about LCR filter theory.

It is factually impossible to achieve , simultaneously, seamless crossovers between bass and mid and treble and mid which do not introduce severe phase distortion. This situation is made much worse by the use of a port.

It also explains why a large number of speaker manufacturers choose the two-and-a-half way option as a compromise



The fact that there are so many three ways out there shows that manufacturers/designers are quite adept at disguising this problem. They usually opt for worst distortion at the mid-bass join where it is less obvious.

You may well think that there is nothing obviously wrong with passive three-ways...until you hear what you are missing by going active, or using a two way.

In the same way , speaker designers are quite good at disguising the problems inherent in ported speakers and you may not realise how poor most of them are until you hear a really good sealed box bass..sadly, there are not too many of these around now, as sealed box bass brings its own set of problems which are usually more expensive to solve

Laurie S

james

qoute

"I`ve read most of the ones that matter. Have you?"

Yes I have

"I`ve also applied the knowledge I have learnt and built a few pairs of loudspekers. Have you?"

Yes...more than a few pairs

"I am a speaker designer"


Can you identify some of your designs?

I`d be interested to examine your circuit diagrams


So James, you can achieve "good" phase tracking within the crossover frequencies using a passive 3 way crossover.


How good? Good "enough"?
(for you perhaps)


I`d be interested to know how can substantiate your claim to achieving perfect amplitude summation "in space".....perhaps directly on axis

What about, off axis by, say 20-30 degrees?

Unless you listen to your speakers in an anechoic chamber or in a field, I would suggest that the overall summation is rather less than the perfection you claim

Laurie S

[This message was edited by Laurie Saunders on SATURDAY 13 December 2003 at 12:43.]

I'm with James on the 3-way/2-way passive crossover thing.

But to answer the question...

In general bi-amping is futile (IMO) but Isobariks are uniquely amenable to it. If you have a version with two crossovers then driving each crossover with an amplifier is a win. This way each amp sees a complete 8 Ohm loudspeaker.

But since you have a NAP180 your best bet would be to move up to a NAP250 rather than add a NAP180. A pair of NAP135 would sort you for passive use, a NAP250 gets you on the low road to active, which is a wholly good thing. When you get the second NAP250 you can biamp, then move to full on proper stuff.

Paul

James......why not let me have one of your crossover circuit diagrams, along with the driver parameters, and other details, that it was designed for. You could easily e-mail it to me, or publish details on this Forum

Using CAD design is nothing out of the ordinary....I believe Hi-Fi World magazine will sell you a package for under £100.

(I mistakenly thought that you were some sort professional speaker designer)

Telling me that you have supplied one of your designs to Mr Tibbs really does`t help me, or anyone else. I am sure he will be delighted with it as a competent 3-way passive speaker


My understanding is that you DID claim perfect amplitude summation, and GOOD phase transition.

I am keen to determine how you define good. This is the essence of my point(good enough?.....as in...say... CDs 20kHz cutoff is good enough etc)

I have no doubt that your own "designs" are more than competent,as are a large number of other, commercial 3-way designs, though you have not yet explained to me how you can achieve two seamless crossover transitions passively



I contend that all passive 3-way speakers remain compromised, in areas of driver coherence, compared to a properly designed 2-way


Paul......I agree with your analysis on biamping......I understand the term to imply driving different "channels" of the same crossover board (of the same speaker) with seperate (full range) amplification. Aside from power advantages, as you suggest, biamping is not really worthwhile. So, as you suggest, a pair of 135s would not fall under this definition

Laurie S

Laurie,

in some respects, even a 2-way is a compromise. having lived with a single-driver speaker for some time, I now find most 2-ways unacceptable.

A single-driver speaker is also a cheap way of getting into active operation. You don't even need an active crossover.

While you may be right about the phase problems of a 3-way crossover, they can be minimized to an extent where they are unobtrusive.

Going 3-way allows the speaker designer to have a dedicated midrange driver. I find that having a midrange driver which doesn't have to handle large bass transients can be very beneficial.

Marcus ...I agree that even a two way is a compromise.
Having tried a single "full range" driver, the extra coherence and the lack of crossover go a long way towards compensating for the restricted frequency range.

My contention is that with a two way, there is only one "join" whereas with a three way, there are two "joins"...twice as bad.

Getting back tyo isobarics, which are fine speakers, even driven passively, the extra transparency and seamlessness becomes immediately obvious when switching to active drive

Laurie s

I heard a demo of Bingoed Isobariks [just before the launch of the Bingo, I think] and I was amazed at how this active system made the speakers "disappear", which I would until then have thought most uncharacteristic of Isobariks.

On the strength of this I imagine Naimed active Isobariks would sound fantastic - especially with amps from the new range.

Jeremy....exactly....active operation really does make a three way speaker sound much more seamless and transparent...as you say...the speakers "disappear". This simple experiment- (I have compared passive isobarics(3xNAP 250) to the same speakers in active mode-) alone would strongly suggest that passive three way speakers are much less than perfect when it comes to driver integration..although the ear is quite good at "papering over the cracks" - there may not appear to be anything obviously wrong in passive mode-until you hear the same speaker in active mode-it is a revelation

Having performed a similar comparison with SBLs, active operation is clearly superior, though the improvements in transparency here are not as large (starting from a "higher" base)

Of course thre are other benefits from active operation...more efficient use of power from the amps, better control, dynamics, transient response etc

Laurie S

[This message was edited by Laurie Saunders on MONDAY 15 December 2003 at 11:36.]

James......I can find the text required, if I dig it out of my loft....I will endeavour to find it for you at the earliest opportunity...that`s a promise. I am quite certain, however, regarding what it stated.....it is not possible to perfectly integrate three drivers passively.....thus the imperative for active operation I alluded to,which you so gracefully described as "bollocks" (an engineering term I am not totally at ease with)

And your contention that you have succeeded has also not been answered...why not publish all your details, including driver parameters etc so that they can be scrutinised.(I will refrain from using your terminology....promise!)


Laurie S

James

quote

"so you want all my FRD & ZMA files as well. What is this going to prove?"

Well James, I`m interested in how you arrive at your conclusion that you have achieved perfect integration, as you claim.

If these files do not prove it, then how on earth do you substantiate YOUR claim? What are the empirical measurements you mention?

I am not doubting that your 3 way designs sound good, as do many commercial 3 ways - I come back to my earlier point.....when does "good" equal "perfection"

I too have "designed" and built 3 way speakers that have sounded very good and mightily impressed critical listeners.....to the point of offering large sums of cash for purchase, ie I also have very satisfied "customers"


Now...... perfection (of driver integration)well even in my most immodest moments, I would never claim that

It comes down to a point I made above....given that ANY "join" between drivers is going to carry with it discontinuities, then by definition, the more joins there are the worse this problem becomes,,,hence my original assertion that on these grounds,a passive three way suffers more in this respect than a two way

Laurie S

It is hard to accept because no commecial 3 way passive loudspaker, to my knowledge, has yet been able to achieve this.

If what you say is true then you have made some kind of breakthrough.

Couple this to your apparent reticence in providing details, and my scepticism seems entirely reasonable

Laurie S

James

"I honestly cannot be bothered to convert all my files to HTML just to prove my point"

interesting contrast:

this is what you said earlier

"I`d humbly (your words) suggest this (what I am saying) is complete bollocks"


I am still awaiting your evidence to support your assertion, that what I have said is complete bollocks



Laurie S

Hi all. I've got a pr. of Neat Vitos. Neat recommends biamping these. From what I gather from your 'discussion' isobariks benefit from this more than most designs. Why is this? What will the benefits be, sound like? I am currently running a single 250 mkII. Would biamping a pr of 250's still be preferable to say going to a single 300?

Thanx for any input.

Regis

Regis....perhaps your question is best addressed to Neat.


My understanding of Naim`s power amp design philosophy (comments from Naim please?) has always been to avoid the use of parallel output devices, ie one transistor per "side" (phase) per channel. I believe this still holds true with the NAP 500. I believe that much of what is so good about the "Naim Sound" stems from this principle. Biamping does mean that the output characteristics of each device must be very closely matched....there is a risk of compromising the "single output device" character- my own experience with multi-amping (passively) has always been to prefer "single amping" with the next model up in the (power amp) range.....so INSTINCTIVELY I would guess that a single 300 would be preferable to a pair of 250s......as I said above, there may be particular reasons why Neat have made the suggestion. The best way forward, of course, is for you to compare the alternatives and then make your own judgement

Laurie S

Regis,

The Isobarik contains 6 drive units a side, and many models have two identical crossovers. These are usually connected in parallel, so with a single amp each channel of the amp is effectively driving two paralleled speakers. This works pretty well. But there's an opportunity to use two amp channels per side, each driving what is effectively a complete speaker. This makes life easier for the amp, rather than a 4 Ohm paralleled combination it sees a single 8 Ohm speaker. The effect is reported to be beneficial. If you're collecting NAP250s or NAP135s to go active then you can use 2 or 4 in a halfway house arrangement.

With a conventional speaker I think you will almost always do better to upgrade your amp rather than double the quantity of amps. Unless you have an opportunity to go active, which is a rather more interesting concept.

Paul

James

your frequency response plots do indeed show you have done a good job at sustaining a smooth amplitude response....my point concerns the issue of phase distortion...you hold that this will automatically "fall into line" provided the amplitude response is sorted. This is where I part company with you. I agree that it is likely that any phase anomolies would appear as a suckout....or a "spike"....but due to different directivities at the crossover, these anomolies would only likely appear off- axis, even if the on-axis response appears smooth.i.e you may well still achieve a "perfect" on-axis response...as you clearly seem to have achieved

PS Presumably your plot was recorded on axis....how do you accommodate the step change in directivity at each crossover, and their effects on off-axis response?

A room-averaged response plot, in my view, closer to the "listening experience" would probably show these

Now if your off axis response curves were as smooth as the ones you have supplied, I WOULD be impressed

PS I will obtain the data you require after the weekend

regards
Laurie S

[This message was edited by Laurie Saunders on THURSDAY 18 December 2003 at 11:11.]

[This message was edited by Laurie Saunders on THURSDAY 18 December 2003 at 11:15.]

[This message was edited by Laurie Saunders on THURSDAY 18 December 2003 at 11:18.]

James..I won`t disagree with your physics which appears perfectly sound, however the step change in directionality which I referred to is the result, mainl of the different size radiating sources at the bass/mid crossover. Most(all?) bass drivers are designed to operate in "pure pistonic" mode within their operating passband, and thus at the mid/bass crossover there is a step change in radiating source diameter, which can be "flattened" by the crossover for one paricular direction (usually on axis) but not for others, simultaneously.

This problem also arises at the mid/treble crossover of course, though in most(all?) cases the mid driver cone profile is designed so that a decreasing diameter of the cone is effectively radiating as frequency rises, so it is much easier to match the directivities of the mid/treble at crossover.....edge diffraction can be addressed as you suggest by baffle edge treatment.
So my point is, as before..how do you obtain a smooth transition from mid/bass in more than one direction?

Laurie S

Laurie wrote

..although the ear is quite good at "papering over the cracks" - there may not appear to be anything obviously wrong in passive mode-until you hear the same speaker in active mode-it is a revelation


I found this to be true when I first went active with the Isobariks,and have not been able to go back to passive again.
I have since tried activating Neat MF9s which is a 2 1/2 way design with good results,Naim modified the Snaxo to figures provided by Bob
from Neat.I feel there may be more improvements to be had, if the speakers were made available to the Active electronics designer.(not sure as I am neither electronics or speaker designer)

What are your thoughts Laurie and James.

(Interesting Topic)

James
Thanks for you speedy response,I now have another question.

I have spoken with Bob,and he suggested may be I should try out,Tri-amping.
As far as I know Naim dont approve it,I am using Six Nap 135s,how would one go about triamping,will probably need custom cables made up.The original passive crossovers are now in a seperate Boxes.

James....now that the indulgencies of Christmas are beginning to subside.....the text/paper I was seeking was by Bullock "paasivethree way crossover networks" c 1985 which you likely have. He refers in that paper (from memory)to the phase difficulties of combining three way (passive) speaker systems.

Your observations above on biamping are interesting....you mention that you prefer the extra grunt and control overthe loss of coherence. Curiously I tried passive biamping a pair of two way speakers(ie using 4 passive 135s rather than a single pair)
I clearly heard the gains in grip, power, dynamics(grunt) which on reflection I found surprising since relieving the mid bass/mid amps of driving the tweeters(a very light load?)migh not have been expected to make a significant difference.

I also immedistely noticed the loss of coherence you experienced.....my preference was/is for the "single-amped" (ie 1 pair of 135s).....It would appear you seemed to favour the advantages to be had in multi - amped mode. Perhaps this partly explains our disparity of preference for two/3 way passive loudspeakers

Laurie S

James

Quote

"if you had read what I said then you would realise that I preferred the coherence and swing of a single amp system"

...you are quite right James....I did (accidentally) misread your text here(must get those new specs!)...thus it would appear that we at least agree on this one

Perhaps you might be able to shed some light on an issue that has troubled me for some time now, viz why are there so few sealed box speakers out there...I can understand the "budget" sector preferring the advantages of ported speakers, but at the higher price levels the steps needed to make sealed boxes work properly are not such an issue

Laurie S

James, the problems with ports are well understood, and as you say, if there is even a small amount of driver/box/port misalignment, transient response goes out of the window.I can understand why the "budget sector" resort to ports, as you suggest, most have to buy off-the - shelf drivers, and their are "free lunches" on offer (efficiency etc)- I had in mind companies like B&W etc who spend vast amounts on R&D and manufacture their own drivers. It would be just as easy for them to go down the sealed box route, yet they clearly choose not to


Laurie S

My understanding of sealed box bass is that it provides a less steep roll-off, and thus less propensity to "ring", and that the ultimate bass extension is lower. It is also usually easier for the amp to drive(smaller phase angles) However, there are more stringent requirements on the cabinet construction, due to the pressure, and the overall "efficiency" is lower. Am I thinking on the right lines?

regarding your comments on ported bass "selling"...to my ears, sealed box bass sounds more "natural" and "integrated".... to my ears anyway.......I can usually detect a ported bass a mile away...they all seem to have that characteristic "bloated", "loose" sound

Interestingly, B&W, who do not produce any sealed box full range speakers (to my knowledge) have made some v expensive active subs, and these use sealed box loading.......and have revieved rave reviews.
I guess the inclusion of a power amp removes the efficiency disadvantage from the purchasers point of view, ie it will not compromise his/her existing amplification

I believe that the (original) Nautilus system uses what is effectively a transmission line loading (I stand to be corrected here)

(M&K and REL also make sealed box active subs and these have been praised as being easier to integrate with satellites used for music, rather than provide the amorphous splodge of ported low frequency boom that often passes for bass in many A/V systems)

Laurie S

My MAIN concern with ported speakers is as follows:

The box volume/dimensions and port parameters must be precisely matched/aligned to the driver parameters. Even a small misalignment will have a disproportionately large effect on bass "misbehaviour".

Sealed box speakers do not suffer this problem, where the box size/dimensions are much less critical.

Manufacturers of ported speakers acknowledge this and will claim that with careful design, most of the problems (mentioned above) can be avoided.

However, the parameters of drivers change with time as the suspension (spider and surround) age.

Thus a ported speaker may well perform well when new, but with time the drivers will become misaligned with the box/port and bass distortion will increase drastically.

Because of the far less critical nature of alignment for a sealed box, this problem is largely avoided, thus a sealed box will likely carry on performing well for far longer

Laurie S