I would like to add one additional comment regarding active vs passive x-os. The second major argument that actives are superior to passives is based on the idea that voltage transfer function of the passive crossover will be affected by changes in the VC impedance due to temperature changes, and with an active crossover it will not be. This is true, providing the amplifier's output Z is small compared to the driver's Z. But again the implication is that the unchanging transfer function of the active crossover is better. Maybe, maybe not. The point is that the force accelerating the drivers radiating surface is a function of the current through the VC, F = Bl x I = Bl x Vapplied/Zdriver. Thus the actually transfer function of the radiating surface's motion is a function of Vapp/Zd, not just Vapp. Thus holding Vapp constant as the VC Z changes due to temperature does not imply that the acoustic transfer function of the filtered driver will remain constant.
There are lots of other issues but I think enough worms have gotten out of the can for now.
There are lots of other issues but I think enough worms have gotten out of the can for now.
I'm not saying its a bad thing. I'm just avoiding it in my own designs because I've no reason to believe it helps.
Nope, I don't see. Where is it in the question please?
Just cut and paste this 'assertion' that you're asserting I've made. I predict you will fail to do so because I can see none. So this is a red herring, a distraction.
Who's making the observation here? Certainly not you - you're inferring something that's in reality absent. I'm observing you doing so
The first part of your straw man is indeed correct. I am drawing attention to an effect I prefer myself to avoid, by going active. Presumably you have good reason not to avoid it, to even advocate that others don't avoid it themselves. Its this reason that I'm curious about. If it turns out to be good (by which I mean to say helpful, an improvement), when I've digested your arguments then I can introduce it into my designs without any difficulty.
<snip>
So then why are you making it out to be a 'devil', even though its a devil that you choose not to avoid?
As I said earlier, I have no preference. If you look at my speakers you will see I offer an active (analog or digital)/passive hybrid as well as fully active (active between woofer and mid is pretty much required for a dipole if you want to maintain the midrange efficiency).
Re the other comments, I was not pointing at you (which I why I said I'm not asking you to provide proof, sorry if you took it wrongly), but the argument about damping is one that active crossover proponents commonly use as an example of all that is bad about passives and it just really isn't the case. It is those proponents that imply that lack of damping is the devil. I'm personally petty neutral on active vs passive.
Exactly my view, too. To make active really any better than passive one must make full use of optimized damping. I found there is often a "best" drive impedance profile that is sort of a (graphical) inverse of driver impedance. Amp and driver must team-up in a very literal sense. "Best" is of course open to discussion, it's again preferences and compromises as usual.
"Driver impedance" in its common usage itself is a problematic terminus IMHO, because we lump in two mechanisms (somebody mentioned already), the true electrical impedance of the coil at the given DC excursion position in the gap (clamped cone) plus the microphonic voltage from the coil (gives a voltage proportional to cone velocity) which pickes up any motion no matter what caused it. Both are distorted, but when we do feed as little as possible of this sensor voltage back into the system, chances are better to get lower overall distortion, except at unstable / ill-defined points of mechanical driver resonance. Geometrical resonances (standing waves) tend to be stable and can be handled with signal pre-correction.
- Klaus
I did a series of test some years ago to look at distortion vs. amplfier output impedance. I saw no connection between output Z and LF distortion.
Of course changing drive impedance changes Lf response considerably and so changes excursion vs. frequency. To get around this and insure an apples and apples comparison I used one of the old B&K oscillators with the compressor (feedback loop) and connected to keep the output SPL flat (showing my age here). In fact the compressor was tracking the fundamental so that the non distorted "1st harmonic" component was dead level.
I achieved high and low Z with one of the old Fisher "Z Matic" tube amps. Second and third (I might have plotted to 5th) were identical as long as the compressor held the fundamental output curve flat. This was true all through resonance +- and Octave or so.
The only place where output Z made any difference to distortion was in the midrange area where there was high 2nd harmonic due to flux modulation. High Z lowered the distortion.
I don't know if that agrees with Hawksford but I still have the measurements.
David S.
A lot of what is pictured is superfluous, being that this 'case' was an experiment in swapping capacitors. The 'cap-banks' to one side of the switchboard is only applying 2 different positions to the circuit.
Later,
Wolf
You should think about your copper EI-core/toroids, aluminum amp-cases, and all the metals involved in your amplifiers.
Same difference, bud.
Later,
Wolf
Zobels in the true sense of the word are not always required. You can actually have a lower net impedance of the system using them to minimize Le of the multiple drivers in 3-ways.
You optimize the xover from the impedance/FR/phase data, so you can't just say, "it's this impedance at this frequency, so I need this value L and C for this xover Fc". The Fc (corner) is selected by the components used in reference to the impedance and the dB level of the FR at that point. The Fc is where you put it with that in mind, not "shifting" if you don't do something else.
Later,
Wolf
Sometimes the rise in impedance of a driver at high frequencies due to its inductance will be transformed by the crossover into a decrease in input impedance - in this case adding a zobel network to flatten the impedance of the driver will actually increase the input impedance of the crossover, as in the example I cited earlier with the 3rd order butterworth driving a tweeter.
Whether adding zobels increases or decreases the net input impedance presented to the amplifier is highly dependant on the topology of the rest of the crossover network, and how it interacts with the drivers impedance.
What level of improvement were you measuring in midrange distortion ? I presume the tests were done with a driver without a copper shorting ring or other means of achieving very low inductance, that would tend to offset reduction in distortion achieved through current drive ?
I was recently thinking about the possibility of a pseudo-current source network for a midrange driver, and whether there would be a worthwhile improvement in distortion.
If we assume a driver that is quite sensitive and needs more than 6dB of attenuation relative to the woofer, the idea is to provide all the attenuation only via series resistance to present as high as possible source impedance to the driver.
The usual shunt resistor of an L-Pad would be placed before the series resistor instead of after it, and the zobel (if needed) would also be placed before the series resistor and scaled the correct amount to still present a flat impedance to the output of the crossover at the high frequency end.
Of course that imposes two issues -
One would be a rise in response of the driver at higher frequencies relative to pure voltage drive, but that could be corrected for in the filter section before the series resistor, or depending on the driver a gradual rise in response may actually be desirable and beneficial if the driver already has some natural roll off. (The latter is likely with the driver I have in mind)
The second issue is controlling the fundamental resonance of the driver, which will be greatly increased in amplitude with the higher source impedance. This will almost certainly require an RLC compensator connected directly to the driver to accurately correct this, but chances are depending on the driver and midrange enclosure size an RLC compensator already would have been required to flatten the fundamental resonance anyway - all that changes is that the required values will be different.
So essentially we have the same number of components (assuming both zobel and resonance compensator were wanted in the more conventional configuration) but the question is, is it worth the trouble ? I guess it depends entirely on the individual driver, both in terms of how much attenuation it requires (and therefore how closely you can approximate current feed) and also in terms of how much L(e) modulation it has.
I'm also assuming it would be fairly pointless for any driver with a copper shorting ring.
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Is that the same debate as active crossover vs passive crossover, though? Do active speakers necessarily have active crossovers ? I don't think so but i could be wrong. An active speaker has the amp inside it but it could be built with exactly the same crossover (ie passive) as in the passive version. The active version usually has one amp per driver but that equates to bi-amping / tri-amping, not to having an active crossover.
As for the Dynaudio BM5a, they are absolute crap compared to the passive version with a good amp. They use car audio electronics and the passive version on a cheap used Bryston sounded waaaayyyy better.
I could be wrong but i think you're confusing active speakers with active crossovers.
An active speaker has separate amplifiers for each range and XO before the amplifiers -- the amps can be inside or outside. A powered speaker has the amp(s) inside and can be active or passive.
dave
Aha, i didn't know that.
For me active always meant it had an amp inside it, and passive that it didn't.
As per this, for example :
http://www.dummies.com/how-to/content/understanding-active-and-passive-speakers.html
Now, i also thought there was no difference between active & powered, as per this, for example :
Powered speakers - Wikipedia, the free encyclopedia
"Powered speakers, also known as self-powered speakers and active speakers, are loudspeakers that have built-in amplifiers."
(the article later explains what you say above, however).
So...let me get this right :
- an active speaker is not necessarily powered/amplified...because the amp can be separate.
- a powered/amplified speaker is not necessarily active.
Would I be right in thinking that a passive speaker can only ever be truly correct for the room and position at the moment it was designed/refined/optimised? If the speaker is placed in a different room, or moved closer to a wall, or the furniture is moved around it all becomes something of a lottery.
It also seems to me that with active speakers, the fine tuning involves some very subtle tweaking over, possibly, hundreds of iterations, and these tweaks can be applied from the listening position so a direct A/B comparison can be made between settings. Gradually, over a period of months, the tweaking subdsides and the owner can be content with the setup. Even then, the perfectionist owner might like to apply different setups for different moods, situations or types of music.
I can't imagine ever being satisfied with building my own passive speakers due to the overhead and delay involved in each tuning iteration. Do passive people ever make themselves mad scientist style crossover boxes with caps, resistors inductors and relays and a remote control so they, too, can compare setups quickly and easily?
Refinements open to the DSP-based active speaker builder:
Crossover frequencies
Crossover slopes
Gain setting for each driver
Baffle step compensation (maybe different slopes for separate boxes or drivers)
Driver and/or room correction
-phase
-amplitude
-delay
It could take a while to get there with a passive speaker!
It also seems to me that with active speakers, the fine tuning involves some very subtle tweaking over, possibly, hundreds of iterations, and these tweaks can be applied from the listening position so a direct A/B comparison can be made between settings. Gradually, over a period of months, the tweaking subdsides and the owner can be content with the setup. Even then, the perfectionist owner might like to apply different setups for different moods, situations or types of music.
I can't imagine ever being satisfied with building my own passive speakers due to the overhead and delay involved in each tuning iteration. Do passive people ever make themselves mad scientist style crossover boxes with caps, resistors inductors and relays and a remote control so they, too, can compare setups quickly and easily?
Refinements open to the DSP-based active speaker builder:
Crossover frequencies
Crossover slopes
Gain setting for each driver
Baffle step compensation (maybe different slopes for separate boxes or drivers)
Driver and/or room correction
-phase
-amplitude
-delay
It could take a while to get there with a passive speaker!
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I guess the end user could tweak an active or passive design ad infinitum if they really wanted to but if the active design contained a user-programmable DSP crossover then it would certainly be far more 'tweak-friendly' than a standard passive speaker. Even analogue actives often incorporate bass/mid/treble level or shelving controls.
I sometimes wonder if people constantly tweak when they're dissatified with the sound of their set-up yet can't quite identify the source of their unease. Personally, I'm not inclined to tweak my current speakers (cheap actives) although I was always trying to improve my old speakers (mid-priced passives).
I respectfully suggest that you may have 'outgrown' passives?
I sometimes wonder if people constantly tweak when they're dissatified with the sound of their set-up yet can't quite identify the source of their unease. Personally, I'm not inclined to tweak my current speakers (cheap actives) although I was always trying to improve my old speakers (mid-priced passives).
I respectfully suggest that you may have 'outgrown' passives?
I think that in this hobby, tweaking is par for the course - whether or not they like the sound of their system, everyone always wonders "what if..?", and usually ends up buying new gear to fiddle with. Marketing is designed to make everyone feel dissatisfied with their system, anyway.
Tweaking the DSP can be a lot cheaper, and is actually quite educational: you soon begin to listen for, and hear, the effects of the subtle changes you're making. If the tweaking involved substituting new cables, or de-soldering and substituting new caps, I'm not sure I could maintain the 'auditory memory' between tweaks. Understanding the effects properly could take several lifetimes it seems to me.
As Above 
. Went from Passive X overs to a Bespoke designed Active setup.
Seriously pricey build using State of the Art bits.. Lots of them ($$$)
Hey No fool like an old fool.
Subsequently; Listened.. Tweaked...Listened some more... for ~ a year.
Finally reverted to the (admittedly well tweaked) Passive crossovers previously used and Noticed NO differences.. Truly. An Epiphany of sorts.
We ..all..start believing the Brochure Babble, eventually, as it comes at us from all directions, relentlessly.
Mostly it's self serving and sadly even delusional drivel
Ugly truth is we all lose hearing range as we age.
Basic Human (male) condition.. without any pretense of a Cure.
Don't laugh! If over 30 your hearing losses are significant.
If over 60 ?? Hell.. just who are you trying to fool?
Seriously?? spend yer spare $$ on Wine, Wimmin and some songs as long as they are inexpensive ones. Cuz there's no way you can notice any differences
. Went from Passive X overs to a Bespoke designed Active setup. Seriously pricey build using State of the Art bits.. Lots of them ($$$)
Hey No fool like an old fool.
Subsequently; Listened.. Tweaked...Listened some more... for ~ a year.
Finally reverted to the (admittedly well tweaked) Passive crossovers previously used and Noticed NO differences.. Truly. An Epiphany of sorts.
We ..all..start believing the Brochure Babble, eventually, as it comes at us from all directions, relentlessly.
Mostly it's self serving and sadly even delusional drivel
Ugly truth is we all lose hearing range as we age.
Basic Human (male) condition.. without any pretense of a Cure.
Don't laugh! If over 30 your hearing losses are significant.
If over 60 ?? Hell.. just who are you trying to fool?
Seriously?? spend yer spare $$ on Wine, Wimmin and some songs as long as they are inexpensive ones. Cuz there's no way you can notice any differences
I could have told you that without even listening to the speakers
What do you think if that?
I only read the first two pages and some of what the smoking chimp wrote.
This might be a moron's analysis but here goes
One does more or less what you want and the other does kind of sort of what you, but not really, and some other crap you really would rather not have done.
Or look at it this way: passive cross-overs only exist because they came before active ones and/or before active ones became readily available and digital.
It's like a horse and wagon, it pretty much only exists because it came before automobiles were around. If autos came first or active cross-overs, you wouldn't have horse and wagons or passive crossovers.
Two major advantages passives can have are: price and simplicity.
Negating design of course. If you feel designing a passive cross-over network is complex try designing a DAC.
Actually even DAC suck.
I used kx drivers for my last speakers and needed the fancy (was it "Phat) EQ add-on to make the adjustments I wanted to make. Which I couldn't use, I forget why. The kx drivers have way more options than a DAC, never mind caveman crossovers.
I didn't have the best sound card and who knows what else got added to the signal from the computer, passives probably would have sounded better
I could have told you that without even listening to the speakers
What do you think if that?
I only read the first two pages and some of what the smoking chimp wrote.
This might be a moron's analysis but here goes
One does more or less what you want and the other does kind of sort of what you, but not really, and some other crap you really would rather not have done.
Or look at it this way: passive cross-overs only exist because they came before active ones and/or before active ones became readily available and digital.
It's like a horse and wagon, it pretty much only exists because it came before automobiles were around. If autos came first or active cross-overs, you wouldn't have horse and wagons or passive crossovers.
Two major advantages passives can have are: price and simplicity.
Negating design of course. If you feel designing a passive cross-over network is complex try designing a DAC.
Actually even DAC suck.
I used kx drivers for my last speakers and needed the fancy (was it "Phat) EQ add-on to make the adjustments I wanted to make. Which I couldn't use, I forget why. The kx drivers have way more options than a DAC, never mind caveman crossovers.
I didn't have the best sound card and who knows what else got added to the signal from the computer, passives probably would have sounded better
Yet the BM15a are way inferior to the passive version on a good amp.
I would like to post my results with passive/active crossovers that I had while trying to upgrade my studio monitors. Studio monitors are used in the studio to provide musicians with a feed of the sound or to amplify an instrument, they are usually not used for mixing or in the control room. This means they are normally a large speaker capable of competing with other instrument amps and loudspeakers so efficiency is important. Mine are a three way design with a 12" woofer, a sealed mid and a large compression horn. They were hand built from commercial sound drivers, the cabinets are thick birch plywood with braces and covered with Ozite and chrome corners with recessed handles and large rubber feet, sturdy and tough but certainly not what you want in your home.
The speakers always sounded good to me but after a session with some talent that continually produced a rather harsh feedback both my horn drivers were blown and I had to open them up. The JBL diaphragms were easily replaceable but I noticed that the tiny crossover looked barely capable of 50 watts even though I had the cabinet attached to a 450 watt Citronic/Lantek mosfet amp.
I acquired a pair of beefy McIntosh three way crossovers and started to modify and upgrade them for my use. Here is the schematic and simulation, https://www.circuitlab.com/circuit/y4d7y9/ml10c/ As a control I took two three-way active crossovers (dbx 234 and an Ashly XR70-12, substituting one for the other) and three amps and for the other channel I used the modified McIntosh crossover and a single channel amp.
Much to my dismay, after many hours of substituting and upgrading components I could never get anything that sounded as good as the tri-amp system and the flexibility of having all the control sure beat all the soldering and expensive caps and chokes I was going through. The more I added to the circuit to achieve the response I wanted the more the crossover sucked up wattage. Initially I was using a 60 watt amp for my testing but as the crossover grew so did the power requirements and the overload lamp started to light at even low volumes. Now I know why there was such a huge heat sink on the crossover, who wants to pay amp dollars just to heat a resistor?
I finally gave up on the crossovers and just built a tri-amp system. My studio monitor system now contains a Rane MA 6S 6x100 watt amp with 4 channels bridged driving the woofers and the 2 remaining channels on the mids. An Ashly SRA with 60 watts is driving the horns and believe it or not I'm using a Behringer CX3400 three-way stereo crossover. Its my first Behringer product and for the money ($79 at GC) is a screaming deal and has even more control and more modern circuits than the more traditional pro units I was testing with. I'm only one rack space taller than the old setup but overall its lighter and infinitely more flexible.
The only real drawback to me is I now have to maintain non-standard speaker cables with 6 leads in 8 pole Speakon connectors that only fit this system. This system has been a real pleasure to use, so much so that I find myself often in front of them for reviewing material and even some musicians who had no idea they were modified commented how much better they sounded.
I realize my system is a bit over the top and may not appeal to audiophiles but I've noticed that pretty much all of the control room monitors have gone bi-amp or tri-amp. Even my audiophile friend who has a rare and huge bi-amped Infinity IRS system wanted to borrow my crossover.
Cheers,
-Brian
The speakers always sounded good to me but after a session with some talent that continually produced a rather harsh feedback both my horn drivers were blown and I had to open them up. The JBL diaphragms were easily replaceable but I noticed that the tiny crossover looked barely capable of 50 watts even though I had the cabinet attached to a 450 watt Citronic/Lantek mosfet amp.
I acquired a pair of beefy McIntosh three way crossovers and started to modify and upgrade them for my use. Here is the schematic and simulation, https://www.circuitlab.com/circuit/y4d7y9/ml10c/ As a control I took two three-way active crossovers (dbx 234 and an Ashly XR70-12, substituting one for the other) and three amps and for the other channel I used the modified McIntosh crossover and a single channel amp.
Much to my dismay, after many hours of substituting and upgrading components I could never get anything that sounded as good as the tri-amp system and the flexibility of having all the control sure beat all the soldering and expensive caps and chokes I was going through. The more I added to the circuit to achieve the response I wanted the more the crossover sucked up wattage. Initially I was using a 60 watt amp for my testing but as the crossover grew so did the power requirements and the overload lamp started to light at even low volumes. Now I know why there was such a huge heat sink on the crossover, who wants to pay amp dollars just to heat a resistor?
I finally gave up on the crossovers and just built a tri-amp system. My studio monitor system now contains a Rane MA 6S 6x100 watt amp with 4 channels bridged driving the woofers and the 2 remaining channels on the mids. An Ashly SRA with 60 watts is driving the horns and believe it or not I'm using a Behringer CX3400 three-way stereo crossover. Its my first Behringer product and for the money ($79 at GC) is a screaming deal and has even more control and more modern circuits than the more traditional pro units I was testing with. I'm only one rack space taller than the old setup but overall its lighter and infinitely more flexible.
The only real drawback to me is I now have to maintain non-standard speaker cables with 6 leads in 8 pole Speakon connectors that only fit this system. This system has been a real pleasure to use, so much so that I find myself often in front of them for reviewing material and even some musicians who had no idea they were modified commented how much better they sounded.
I realize my system is a bit over the top and may not appeal to audiophiles but I've noticed that pretty much all of the control room monitors have gone bi-amp or tri-amp. Even my audiophile friend who has a rare and huge bi-amped Infinity IRS system wanted to borrow my crossover.
Cheers,
-Brian
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