The Active Advantage

[Robh3606]

We can't meaningfully conclude that "active sounds no different from passive" unless we follow it all the way through.

Hello Groucho

The way I see it just bi-amping is where you get the most bang for your buck. You don't have to do a 4 way active set-up just bi-amp for very obvious reasons.

This whole Digital Room Correction issue should not be part of this conversation. What we are comparing is an active vs a passive version of the same crossover. One uses passive components the other an active crossover. When all is said and done the drivers could care less as the actual voltage drives from either version will be identical. You could also use the room correction with either version of the speaker. As I see it this just confuses and clouds the issue at hand.

I don't understand why you think it's easier to go 4 way over 2 way. You still have 2 additional crossover points that will be just as hard to get right passive or active. You are going to have to do measurements either way to confirm you got it right. Active may be easier to implement as you don't have to build up networks but you have to get the voltage drives right either way.

There is no reason you can't match dispersion through the crossover in a 2 way design all you have to do is use a horn or waveguide as Revel does.

Rob

 

[Groucho]

Hello Rob

Well I am considering the 'active advantage' to be more than just a slightly better way of implementing the same crossovers. If we can flatten the phase of each driver (not just match phases of adjacent drivers through the crossover) without undesirable side effects, then we stand a much better chance of creating a truly transparent crossover. A three- or four-way design then actually becomes easier than a two-way, and this has all kinds of advantages.

 

[Phelonious Ponk]

Hello Rob

Well I am considering the 'active advantage' to be more than just a slightly better way of implementing the same crossovers. If we can flatten the phase of each driver (not just match phases of adjacent drivers through the crossover) without undesirable side effects, then we stand a much better chance of creating a truly transparent crossover. A three- or four-way design then actually becomes easier than a two-way, and this has all kinds of advantages.

Groucho, I don't understand how 4-way can be simpler than 2-way. Can this be explained in layman's language? Or did I just miss it in a previous post?

Tim

 

[Robh3606]

Why are you concerned about driver phase?? That is not even considered as the individual drivers phase change over the drivers useable range is not audible. I have built 2, 3 and 4 ways and in no case does it get easier adding crossover points. "Fixing" the phase won't have any effect on the level of effort required to get it right.

Rob

 

[Groucho]

Groucho, I don't understand how 4-way can be simpler than 2-way. Can this be explained in layman's language? Or did I just miss it in a previous post?

Hello Tim

The only reason we use multiple drivers is that a single driver doesn't work very well if it has to reproduce a wide range of frequencies. If we split the task up into two ways, we improve the situation. However, the drivers are still having to cover a wide range of frequencies - more than ideal. The drivers are required to be high performance units and the crossover's frequency and slope is a compromise and/or quite critical. Designing a two way that works well is quite difficult (or even impossible).

More drivers would make everything easier (including the amps' task), but the chicken-and-egg aspect is that crossovers are, in themselves, thought to be a sonic problem. Different types of crossover have different characteristics, including 'phase rotation' throughout the crossover that colours the sound. Designing a successful three-way is reputedly difficult.

I think that DSP allows us to break out of that vicious circle. Flat phase is, in itself, a good thing, but it also lets us create three or even four-way speakers without the sonic consequences of traditional crossovers. In doing so, everything becomes easier. More ways means the drivers don't have to cover as wide a range: we avoid intermodulation distortion, we don't have to get near 'break-up' frequencies, we stay away from driver beaming and so on. It really is much easier than designing a two-way.

Edit: an explanation of how and why crossovers are chosen, and the sonic consequences of phase rotation:
http://www.iar-80.com/page97.html

Edit, edit: do you not find the above article interesting? It is basically telling us that a particular passive speaker can measure perfectly in terms of its frequency response, yet it sounds to have a lean mid-range on real music ('transients') and other strange, phasey qualities. By re-arranging things we can swap these for other strange sonic artefacts without affecting the frequency response. Is this not audio 'dynamite'?

 

[Robh3606]

The unpopular third order filter, which Verity employs for the Tamino, is unpopular for a reason: it forces a very cruel choice upon the designer. A third order crossover filter goes through a sudden, steep phase rotation at the crossover frequency, going through a full 360 degrees (which is the equivalent of rotating all the way around the phase clock, within a short frequency span, and coming all the way around back to 0 degrees, which equals 360 degrees).

This is from the posted article, and its flat out wrong. 3rd order equates to 270 not 360 it's 90 degrees of phase shift per pole. 360 is 4th order and is actually quite popular these days.

Rob

 

[Groucho]

This is from the posted article, and its flat out wrong. 3rd order equates to 270 not 360 it's 90 degrees of phase shift per pole. 360 is 4th order and is actually quite popular these days.

Rob

I'm assuming he means the phase response of the electrical filter combined with the driver's phase response i.e. the overall acoustic response for this particular speaker.

 

[Ampexed]

Just stumbled upon this very old and seemingly beat-to-death thread. I'm a firm believer in going the active route. So much more flexibility and ability to match character of the power amp to the specific driver and it's frequency range. Voicing is more simple and precise in an active system - actually it's difficult if not impossible to re-voice a passive system without heavy modification. I can see why active is not very popular because of the expense and need for technical ability on some level, but hey, if we wanted a cheap hobby there are lots of other choices.