precisely. Time is all that is saved. The temptation in active filtration, for me, is the possibility to use class A amps for the majority of audible bandwidth leaving a class B for helper woofer. That is the route to signal purity in my book. Switching amps just arent viable in the same way. My experience of such amps is that their only advantage is efficiency, and sonically they stink. For the price of a 'good' class D/H i may aswell go analogue active with class A and live with the electricity bill.
Why the limit to 6dB/octave? It is easy to build higher order passive filters at line level . . . the inductors required are conveniently small and easy to hand wind.
The ability to use (and match) appropriate amps to individual drivers is indeed one of the many advantages of "active" crossovers.
The forumers deserve to read better arguments than that.
Andrew, have you taken notice of the SPL levels quoted?
This is not a good comparison because what we want to optimize is the system, which includes at least two drivers and one (or more) amplifiers.
Yes, I have. Compression driver horn sound, distortion and efficiency is engineering compromise accepted for easy access to hearing impairment inducing SPL.
In tracking phase, recording engineer's job is to capture clean signal, because "crap in = crap out". Monitoring at excessive SPL is not necessary for assessing microphone placement issues. It is producer/artists determination if captured recording has usable sound; to that end if they need deafening levels to make their determination, so be it.
For many types of music, mixing phase is major point at which the desired sound is created often requiring long hours, where high SPL is fatiguing, and destructive to hearing.
Sound stage performance doesn't require high SPL either.
Mastering engineer has a nice job.
Andrew
Andrew,
essentially i agree with what you said, but for relatively short period of time* true level monitoring is nescessary for assessing microphone placement and for aesthetical reason too :even if technical, choices of microphone couple or microphone themself define aesthetic results. And to be sure of choices made and behavior regarding peak distortion (dynamic), imaging, 'color' you need to listem to original instrument and compare with reproduced sound at equivalent level.
* as you work with your ears you can't be exposed too long at high pressure as sessions usually last 10 to 12 hours a day and repeated nearly each day a week... Most of professionnals are now aware and take seriously this concerns about deafning levels... but it wasn't nessecerely true 20/30 years ago, and as Fletcher and Munson stand the louder the better (the more linear our ears we should say)...so let's say 10minutes every couple of hours is usual and relatively 'safe'. Most of the time this day, when clients want to be pushed against diffusors of rear wall by spl enginneers leaves the control room...
I wasn't precise enough: for acoustic music tracking is where the sound is made. Including rock, pop, variety,... As you said mixing is an important and major phase aesthetically, but being lucky enough to had access of original tape multitracks of major artists/bands (from the 80's mainly) i can swear you only need to put faders to unity gain to have the 'sound' of the albums... without the refinements added by mixers and mastering engineers however.
We agree about SPl, and this is one of reasons nearfield monitoring took place in studios.
About listening conditions i fully agree!
By far the most impressive listening conditions i've heard was in mastering rooms (mainly the couple system/room's acoustic responsible for that). For the rest it's a job... with enjoyments and pain in the *** !
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What is the significance of the steep crossover slopes that are possible with active? Are many of the 'black arts' of passive crossover design geared towards circumventing the problems of shallow crossover slopes? (i.e. drivers working outside their range, mis-aligned phase of drivers throughout the crossover region, acoustic lobing effects of drivers combining over a broad crossover region?)
With steep crossovers many of these problems are reduced, and the only issue seems to be the ringing of the filters - which at least one report on the web suggests is not a problem until you have incredibly sharp filters, which is also how it seems to me. As Barleywater suggests, crossover design then becomes a scientific, methodical procedure involving measurements and automatic computation of the perfect filter - in fact it's more than mere crossover design, and becomes a fine correction for the deficiencies of each driver. Are we really just talking about the difference between passive and active crossovers, or also the fine tuning of the drivers individually?
My own experiments (gradually heading towards this ideal) suggest to me that the automatically corrected and crossed-over speaker, far from sounding flat, neutral (in a bad way) or 'grey' as I might have imagined, sounds magnificently colourful (in a good way) and fills the room with sound.
I'm comparing my two way activated Mission speakers (digital filters modified in response to microphone measurements) with some, on paper superior, conventional three way Tannoy speakers. If I've been playing the actives for a while and swap to the passives, the passives seem more immediate and 'raw' with music like this:
1979 Semi-Finalist by The Bad Plus on Spotify
At moderate volumes the passives don't sound compressed at all with music like this, but just the opposite: notes seem shorter and the recording seems dry, reverb-wise. Swapping to the actives, the sound is smoother and the effect of the recording room's ambience seems greater. If anything, I prefer the passives, initially at least. I'm guessing that the brighter spectrum of the attack of the notes lines up with the peaks in the response of these passives, while the spectrum of the note decays and reverb are suppressed. The Tannoys are very good at emphasising the rasp of horse hair on catgut, that sort of thing, but I think it's just an artificial effect, like EQ.
If I change to larger-scale orchestral music like this Shostakovich: Symphony No.5 in D minor, Op.47 - 4. Allegro non troppo by Shostakovich, Dmitri, Royal Philharmonic Orchestra, Vladimir Ashkenazy and Vladimir Ashkenazy on Spotify, the Tannoys fall apart, sounding like two boxes under stress, and quite tiring to listen to. Swapping to the actives (with measured, corrected frequency response and 12th order crossovers) as I have just done while writing this, the transformation is extraordinary, and the room is filled with the sound of a real orchestra in a concert hall. It's quite amazing, and you immedately know that it's 'right'. The bass percussion towards the end of the piece is stunning.
I can't say that it's passive vs. active, as such, that accounts for this difference, but getting the actives to this state of rightness didn't involve any black arts or tweaking in response to listening, nor a long apprenticeship; merely measurements and automatic software (and a ready-made box and driver selection, of course - but they were rubbish with the original passive crossovers). I think I'm almost at the stage of being perfectly happy with my system, and it cost almost nothing!
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I also have heard examples like that . . . decent driver selection, well regarded (DIY) passive crossover, dramatic improvement when switched to active. Not active that tries to mimic the passive design, but active that does what active does best.
Most of the "art" of passive crossover design seems to be endless tweeking to hide, or at least disguise, the design's inherent flaws. Downright silly stuff, like asymetric (often too shallow) slopes adopted because it's the only way to "passively" correct for driver offset. And then the inevitable assertion: "If you match that transfer function with an active crossover it will sound the same". Well maybe yes, but why would one? Why not design it right in the first place? And no, you won't be able to match that transfer function in a passive design . . .
Perhaps that's one school of passive crossover design, but there are others. The nearest of which might be to work with the driver's flaws, which they all have. Another is to find the acoustic slopes that work the best for the drivers, boxes, baffles and room and achieve those via passive means. Nothing wrong with that.
Some of that exists, but I wouldn't call it great design (unless it works
) Silly ideas and bad designs are not limited to passive or active. Both can be just as bad. With DSP we now have great, very flexible tools at our disposal. That does not mean everyone knows how to use them or how to make speakers sound good with them. The new tools may be faster to learn and implement than the old, but that doesn't necessarily make for better designs.
True, you can do it that way, but perhaps a brief apprenticeship in the black arts of crossover design would do you good. These days anyone with modest outlay of money and material can make a computer perfect crossover - and they'll sound like it. I don't exempt myself from that, I believed for years that the only way to a good crossover was active means and paper perfect slopes, points and FR. Ultimately it was a road to frustration.
Audio shows are full of computer designed crossovers, you can tell when you walk in the room. Mostly correct, but lifeless and artificial sounding. That's true for active or passive versions.
I may be a lone voice in this thread crying out against the mutual love-fest
for actives crossovers saying "Beware! There is more to learn than you think, don't close off future paths of knowledge."I like active crossovers and use them, but working with passive crossovers taught me a lot, and I'm still learning. Passive crossovers taught me much of what's important.
Just on the coppertop quote in pano's post above. When I made the new passive crossover for my MTM's There was NO listening, tweaing, listening cycle at all.
I took accurate measurements of the drivers, imported them into speakerworkshop simulated various passive networks until I had what I wanted (4th order bessel with excellent phase tracking through the crossover region, and quite a way either side).
I then ordered the caps, wound the coils and built the final crossover. After building it I measured the response and compared to the sim and they were VERY close. Any differences will have been due to the fact that the new measurement was not done in exactly the same place as the original measurements used for designing the crossover.
The only "black art" involved in this process was the careful selection of capacitor and inductor values and electrical order to obtain the desired phase matching and acoustic slope (which was done completely in software). Something that would be no different should you decide to go active if you want full control over what the drivers are doing, rather than simply pressing a button and letting the software do what IT thinks is best.
A year later and I have not altered the crossover in any way, even after moving house..
Tony.
I took accurate measurements of the drivers, imported them into speakerworkshop simulated various passive networks until I had what I wanted (4th order bessel with excellent phase tracking through the crossover region, and quite a way either side).
I then ordered the caps, wound the coils and built the final crossover. After building it I measured the response and compared to the sim and they were VERY close. Any differences will have been due to the fact that the new measurement was not done in exactly the same place as the original measurements used for designing the crossover.
The only "black art" involved in this process was the careful selection of capacitor and inductor values and electrical order to obtain the desired phase matching and acoustic slope (which was done completely in software). Something that would be no different should you decide to go active if you want full control over what the drivers are doing, rather than simply pressing a button and letting the software do what IT thinks is best.
A year later and I have not altered the crossover in any way, even after moving house..
Tony.
Measurements? Software? Simulations? Phase tracking?? Tony, really. Obviously you folks down under don't know how to properly design a passive crossover. Where was the chicken blood? The burning of sacred herbs? The full moon incantations? The guilding of ears? How can you possibly design without that?
Tony, really. Obviously you folks down under don't know how to properly design a passive crossover. Where was the chicken blood? The burning of sacred herbs? The full moon incantations? The guilding of ears? How can you possibly design without that?
Pano and Wintermute. I hear you both, ive been spin quoted enough to serve the pro actives.
When I first started DIY I textbook table designed a 2 way, 1st order. Without experience I vehemently believed that if I went 2nd order, then Id hear some malady, some ear bleedingly horrendous colouration. I soon found how wrong I was!
Im neither for or against actives. Id like to make one, but I just dont feel DSP at a price I could afford is good enough. Its just getting accessible. Id go analogue but thats just me.
Zobels do a lot for any amplifier, whether it drives a passive or active speaker. Just the same as Bi or Tri amping, often criticised, actually has a marked improvement in aspects of reproduction if done property. The question to me is whether DSP, op amp, line level passive, or high level passive. The most elegant active solution in my minds eye, is a set of class A bjt amps, each band optimised for gain, if required then input or output RC networks to dial in what remains of the slopes. More power per device in class A due to a reduced bandwidth, simplest way to integrate filtering. With modern spice software, just like with PCD Boxsim and others simulation is quite reliable and it should be quite possible. I must try it.
When I first started DIY I textbook table designed a 2 way, 1st order. Without experience I vehemently believed that if I went 2nd order, then Id hear some malady, some ear bleedingly horrendous colouration. I soon found how wrong I was!
Im neither for or against actives. Id like to make one, but I just dont feel DSP at a price I could afford is good enough. Its just getting accessible. Id go analogue but thats just me.
Zobels do a lot for any amplifier, whether it drives a passive or active speaker. Just the same as Bi or Tri amping, often criticised, actually has a marked improvement in aspects of reproduction if done property. The question to me is whether DSP, op amp, line level passive, or high level passive. The most elegant active solution in my minds eye, is a set of class A bjt amps, each band optimised for gain, if required then input or output RC networks to dial in what remains of the slopes. More power per device in class A due to a reduced bandwidth, simplest way to integrate filtering. With modern spice software, just like with PCD Boxsim and others simulation is quite reliable and it should be quite possible. I must try it.
From the top of my head and not counting models with super-tweeters I can think of the Buckingham Monitor (10"DC + 2x 12"), FSM, 215DMT (both 15"DC + 15" woofer) and the Dreadnought (15"DC + 2x15").
Rather large and fairly uncommon all of them. FSM and 215DMT can be run either 2 or 3 way.
Which software are you using for IR measurement and correction generation?
DSP may be performed with computer/laptop, multichannel sound card, and freely available software; workable crossover filters may be made using Audacity, PEQ filters easy to work with and export using Room EQ Wizard, which also has excellent swept sine measurement. Of course there is DRC and associated GUI. HOLMImpulse is also excellent measurement software.
Audacity with Aurora plugins has excellent convolution engine for testing, and Kirkeby inverse filter, also available for Audition/Cool Edit. I can do all analysis and correction generation, simulation in Cool Edit Pro 2.1 with Aurora plugins. Copies are floating around cyberspace.
I have for grins simulated two way Linkwitz-Riley 24dB/Oct crossover with LTSpice, fed sim a swept sine, used resultant IR to correct the all pass phase smear, and rerun sim with corrected sweep that returns beautiful IR. Cool Edit is much easier.
ECM8000 or EMM-6 with calibration <$100 dollars this side of pond; suitable preamp/soundcard start in same range. This is in league with big fat microphonicly plagued crossover caps.
I've got a PIII laptop with no sale value, and got my first DSP system up on it with Creative's old Extigy USB and Souceforge Convolver plugin for Windows Media player; two way stereo + sub.
Very good two channel DSP EQ/correction may be worked with any decent speaker.
Regards,
Andrew
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