Active vrs passive

[john k...]

Originally Posted by Boscoe

Passive XOs are fine the way people are describing them here, as perfect components. But they are not inductors have series resistance and this is one of the key points. I have read through this thread and it seems no one understands what the effect of damping has on a speaker.

When a speaker is moving it's generating a back emf, ths emf needs to be absorbed for the driver to follow the signal front he amplifier. It is absorbed through electromagnetic braking as the amplifier will effectively short the loudspeaker to the back emf but when you start putting lossy inductors in series with it this effect stops and the driver is poorly controlled.

Boscoe, I don't want to sound arrogant, but I think it is you who don't fully understand the roll of damping in speaker design, particular at low frequency for woofers, which is pretty much the only place it matters. Certainly I agree with your explanation of electromotive damping, but there is a lot more to the story. As I said before, the damping force applied to the driver cone, both mechanical and electrical, plays a significant roll only near the resonant frequency. To each side of resonance the magnitude of the damping force drops off at 6dB/octave. Don't take my word for it, write the system differential equations and figure it out for yourself. You can do that, correct? The damping is characterized by the parameter Q in the system response. Q is made of two parts, Qe and Qm, the electrical and the mechanical components of damping. They combine as 1/Q = 1/Qe + 1/Qm. It makes no difference how each contribute to the system Q. What ever Q comes out describes the system damping. Qes is given as Qm = (1/Rm) sqrt (Mm/Cm). Qe is given as (Re/(BL)^2) sqrt(Mm/Cm). If a series resistor, Rs, is added between the amp and driver, then the system consisting of the resistor and driver (not the driver alone) will have the same Qm but Qe will change since now we must substitute (Re + Rs) for Re. This yields a new system Q, Q'; 1/Q' = 1/Qe' + 1/Qm. So yes, the system Q is higher. But this is no different that placing the driver in a sealed box. When a driver is placed in a sealed box the compliance, Cm, appearing in the relationships for both Qe and Qm changes to be the suspension compliance in parallel with the compliance of the air in the box, Cab. So we now have a new compliance, Cm'; 1/Cm' = 1/Cm + 1/Cab. Thus, due to placing the driver in the box, Cm' will be less than Cm along and Qe and Qm will both increase, yielding an increase in Q which means lower damping, both electrically and mechanically, compared to the driver in free air.

The point here is that any lost electrical damping due to the series resistance between an amplifier and the driver, from the DC R of a typical inductor, can usually be compensated for by adjusting the box alignment. It must be realized that when the woofer system of a speaker is designed to be used with a passive crossover it is not a matter of designing the enclosure and then designing the crossover. The enclosure, driver and crossover compose a system and the task at hand is to design the system as a whole. Additionally, this system should include the amplifier, or at least consider the range of amplifier output impedances for which the system is appropriate. If an active crossover is used it does not preclude the need to consider the effect of the amplifier's output impedance on the system response. The amplifier's output resistance is just another series resistance in the loop.

So, in summary, the series resistance associated with passive crossover can and will affect Qes of a woofer system. However, that does not mean that the system can not be designed to have the correct, desired damping, what ever that may be. The question of what the proper system Q should be is an entirely different topic.

[Boscoe]

What happens if I use a ported design?

[tinitus]

in a few years, and it may not be so far away, any ordinary sound systems will have a voice controlled computer
and you just ask it to play any kind of music, in any way you like, slower, faster, brighter, anything
it will even do that with absolute 100% perfection, no errors, nada
but if we are still around we will probably sit back and remember the days when there was more fun in life

[CopperTop]

Originally Posted by john k...

The enclosure, driver and crossover compose a system and the task at hand is to design the system as a whole.

john, it all sounds very scientific. As a non-passive crossover designer myself, but a bit of a software person, it sounds as though, given appropriate measurements, I should be able to set a computer the task of finding the optimum crossover network within a set of possible topologies and real world components that I specify. Part of the mystique of the guild of crossover designers, however, is a suggestion that while they home in on some sort of optimum crossover, including taking into account series resistance, temperature changes, humidity, tidal activity etc. like a computer could, they also 'play' the design like a violin and imbue the speaker with 'magic'. If it wasn't for that mysterious magic, it would appear that all they are doing is replicating what a computer could do, but not quite as well..? And then it would follow that a digital active setup could get much closer to the real 'optimum' than a handful of old coils, caps and resistors.

Can you give an example where you have deviated from the on-paper 'optimum' passive crossover, and imbued the system with some magic that only a passive crossover can deliver?

[tinitus]

ahh, funny again I guess

Originally Posted by CopperTop

john, it all sounds very scientific.

copper top, with all respect, can I please ask you, how old are you ?

[john k...]

Originally Posted by Boscoe

What happens if I use a ported design?

You compensate in the alignment. Again, it is a matter of system design. In simple terms, instead of designing the enclosure based on the driver's short circuit TS parameters you need to design it based on the real TS parameters which include the impedance load the driver sees at resonance. That includes contributions from the crossover and the amplifiers output impedance. It's not that hard to visualize. It is a system approach.

You don't build a house without first considering the foundation, nor do you build a foundation without consider the structure which will sit upon it. That is what engineering is about, designing the complete system, not just the components.

[chris661]

WinISD Pro has a neat feature where you can add series resistance and watch the effect on box alignment - its worth (when using passive XOs, or long speaker cables), adding the resistance of the added components in, so the cabinet alignment can be altered accordingly.

[gedlee]

Originally Posted by CopperTop

Can you give an example where you have deviated from the on-paper 'optimum' passive crossover, and imbued the system with some magic that only a passive crossover can deliver?

I have never and would never do that. It makes no sense. Either it is Hi-Fi or it is not. You can "deviate" and optimized design to add some "magic" and call it Hi-Fi. Its called "coloring the sound to suite your taste".

The DCR of a "good" inductor need not be so high as to be problematic to a woofer damping. A typical value of .25 ohms DCR in my designs does not yield an even noticable difference in the response.

And what about the tube amps that are so popular and claimed to sound so good? They can have very high series resistance (I've seen 4->5 ohms) - to the point of actually detuning a passive crossover (1-2 dB changes across the bandwidth). To me, this is the maor reason that they "sound different" (that often being perceived as "better.) Taking the inductors DCR into account in a crossover is certainly doable. I have often used a smaller inductor to increase the DCR to get what I am looking for.

[system7]

John Kreskovsky, you're on FIRE! Loving it. Always a pleasure to listen to someone who knows his stuff.

The issue in this thread is whether an active system rather than passive will get better tighter deep bass. Yes?

People fret about half an ohm of resistance in a bass coil ruining "Damping". As john_k and gedlee are saying, damping is a system consideration, more to do with enclosure, placement and, yes tinitus, room acoustic. Here's what Joachim Gerhard says about his fine Anima speaker:

So, taking room response into account is one reason for the astounding bass the Anima is capable of from its modestly sized enclosure. It’s the result of a particular, deliberately designed combination of driver parameters, enclosure volume and port design that leaves no room for guessing.

What's hard to understand about Morgan Jones' diagram of speaker Q here?



Resistance and Inductance is built into the speaker and optimised for different applications. In the below 10" midbass examples, SEAS let you add inductance externally (which opens up more options for filtering) or run it crossoverless to be flat. You choose. I could work with either.

[lduarte1973]

Originally Posted by tinitus

in a few years, and it may not be so far away, any ordinary sound systems will have a voice controlled computer
and you just ask it to play any kind of music, in any way you like, slower, faster, brighter, anything
it will even do that with absolute 100% perfection, no errors, nada
but if we are still around we will probably sit back and remember the days when there was more fun in life

when ? i would like that , sitting in the couch saying " brighter , more bass , less mids "