Active explained?

Posted by: Bruce Woodhouse on 03 October 2001

Yesterday I tried to explain the profusion of black boxes which comprise my active system to a friend. I failed.

I know the theory of active from the manufacturers blurb but I realised I did not actually understand the idea or principle. I also failed to coherently explain bi-amping to myself too.

Here are a few things that I failed to grasp;

Why should a crossover nearer the source be better-is it just an improvement on poor speaker crossovers or a fundamental difference?

Does the effect mimic that of 'more' amplification or actually alter the way the speakers work more specifically?

Why does my crossover need power-unlike the speaker crossovers?

BTW I have just had 2 weeks holiday and returned to find posts on the forum full of rancour and bile. Can we return to sharing knowledge and enthusiasms please? Lets have some informed debate, strong opinions, myths debunked etc but less of the personal stuff. A newcomer reading back over some of the long threads would walk away shaking their heads.

Bruce

Posted on: 03 October 2001 by Naheed

Bruce...

from the Naim Site
"The crossover is connected between the pre-amplifier and power amplifiers. Each power amplifier is then connected directly to the appropriate loudspeaker drive unit, and only handles one frequency band. This allows better control of the drive unit resulting in more accurate music reproduction. As there is no passive crossover no amplifier power is wasted and information loss is minimised."

I went active years ago, with a heavy mullet system, but Active just does things so right (so Naim)...

naheed

Posted on: 03 October 2001 by Dev B

If you listen to purely electronic music or heavily synthesised pices (progressive house, trance etc). I can understand why a active mullet system on loads of stands that give the impression of speed will would sound attractive. However, for mortals without bizarre musicasl taste I still maintain that a good passive system with fine sources is the way to go (and it also sounds good with trance, jungle, ragga, and techno etc)

Posted on: 03 October 2001 by Naheed

Impression of PRat - sorry i get confused with all the analytical bollocks, i judge according to what sounds good (maybe i've got bad taste)...
I'd call Ragga, and Jungle bizarre.

Yes, the heavy front ended passive system is good - but my "active mullet system on loads of stands" as you call it, does just that at a fraction of the cost

naheed

Posted on: 03 October 2001 by Dev B

I am merely pointing out why an active mullet system will sound attractive.

I have heard systems with 2x90's / 2x140's and can hear this effect clearly. I do not find it preferable to a simpler system with a better amp.

I would say that you are deaf, and your vitriolic ramblings are symptoms of a confused mind, but, I like you, you are a man of taste, my little virtual friend.

best regards,

DB/Mullet Audio

Posted on: 03 October 2001 by PL135

Hi Bruce

Just my 2 pence worth.......

Passive Filters:
1) Passive filter design is a rather hit and miss affair, as all the parameters used for the design are dynamic. i - Voice coil resistance rises with increased input power as the coil heats up. ii - The inductance of the coil varies depending on the position of the voice coil in the gap. During large exertions this changes dramatically. iii - Not only do the characteristics change due to power etc, but change depending on frequecy!
2) Passive filter components have to endure large currents and highish voltages and so are rather crude. These passive components are also not ideal components.
3) Drive unit properties also change with time. (we run speakers in!)
A few reasons why passive filter design is very much more an average than an exact solution.

Active Filters:
1) These filters are used to `drive' circuits with very much more stable properties. i - The amplifier input characteristics are for all intents and purposes consistent regardless of temperature, frequency etc. Thus the filters can be more accurately designed and fine tuned. ii - The amplifier drives the drive units directly and handles the dynamic changes far better so the filter performes according to specification regardless of the conditions. 2) The component values used are smaller, they work over narrower voltage ranges and higher quality devices which are `more ideal' in construction can be used. 3)Drive unit properties still change and one tries to design with well `run-in' drive units. (This is obviously even more important with passive filters.)

This just touches the tip of the iceberg but one can begin to understand why active systems are generally considered better. A well designed passive system can be extremely good too and not necessarily worse than an active one but active is the ideal. Given the price of a good active setup....... most of us mere mortals follow the passive route.

Hope this is of some help.

Regards
Peter

Posted on: 03 October 2001 by Naheed

You've hurt me feelings now - apologise or i'll bombard you with gremlins !!!

I see you require some of the same 'shit' (naimmarket@topica.com)

naheed

Posted on: 03 October 2001 by Bruce Woodhouse

This is good so far, I am learning here.

Are we saying that all systems should potentially gain from active as we are always going to be improving the efficiency and effectiveness of the amplification by splitting the high and low frequencies in an active crossover...

Or are we saying that some passive crossovers are compromised designs and others are not-in the latter case best to leave alone.

Anyone else think that active vs passive has a 'class effect' on sound character which exists across a whole range of systems? I had a feeling that active made my systems (I have had active credo and SBLs in a variety of guises) more precise and 'delicate'.

Bruce

Posted on: 03 October 2001 by Paul Ranson

Linn and Naim tried to make a 'cheap' active system. Naim produced an addon internal board for the NAC42 and Linn removed the crossover from the Sara. Two NAP110s were used, one powered the preamp, the other the crossover. Both 4 pin DINs on the back of the NAC42 were wired up. Simple, relatively cheap and only one extra box.

But it didn't work very well, and ever since it has been 'conventional' Naim wisdom that you only activate when the passive limit has been reached.

I don't think it's that simple. Driving a single unit requires less from a power amp, so you don't need such a capable amp in terms of voltage and current. Especially for mids and tweeters.

Clearly a NAP500/NBL is much neater and tidier physically than 6 NAP135/NBL. I just doubt that the reason the former is reputed to sound better is because the NAP500 is so much better than a NAP135.

Paul

Posted on: 03 October 2001 by David Dever

Though an active system can be set up with smaller amplifiers to some benefit, most serious active systems start with a NAP 250 as a minimum--the regulated power supplies provide a necessary degree of driver control (though this may not be enough for some compound driver situations).

On the other hand, an active crossover does provide for independent level controls per band, which can accomodate extremely difficult room situations (heh heh, active IBLs on NAP 140s in a 25' x 40' loft--yes, it actually worked fine). As long as the crossover does not get in the way from a sound-quality perspective (SNAXO 3-6 + dual-railed SNAPS, for example), this is generally an improvement anyway. A good preamplifier, though, is a necessity as a first principle (minimum NAC 82 + 2 HICAPs, in my opinion).

It's not a cut-and-dried situation--some might opt for going active earlier on to prepare for a larger system; non-active ready speakers would, of course, encourage better amplifiers along the passive route. Active iterations were much easier in the days before the NAP 500, which has tipped the scales toward system balance.

Dave Dever, NANA

Posted on: 03 October 2001 by Andrew L. Weekes

quote:
But it didn't work very well, and ever since it has been 'conventional' Naim wisdom that you only activate when the passive limit has been reached.

Doesn't tie up with the presence of the IXO in the Naim product range though?

Having refurbished a NAC42XO + 2x110's, which I have recently sold to a friend I have to disagree with your view.

The new owner is listening to lots of music, travels home lunch times to listen, so I think it works rather well.

It has design flaws (when adding external PSU's), but works better than many passive systems for similar money.

The only reason I sold it was that it was a waste of equipment in my bedroom, but I do miss it quite a lot. Even though it was used with less than perfect sources, it could play music better than many more expensive systems I've heard. The new owner likes the punchy control going active brings, and since we'd be talking 180 or 250 to achieve similar sounds in a passive setup it's an economic choice too.

I feel it depends upon several factors, not least the quality of the passive XO in the 'speaker - some are truly atrocious.

Andy.