I am affraid you are wrong on a couple of points.
Indeed, but this is in contradiction with what you say later on in your same post.
Twice the power gives 3dB gain in SPL, not 6
At 1 KHZ, you are still in the area where the ear is sensitive to ITD, better keep your cross over frequencies away from that, psychoacoustically speaking. The only reason to use 1KHz is to prevent excessive beaming from a large mid driver.
So what you propose is to put a load of coils and caps in a passive xover, which is pretty cost ineffective to begin with, and then do electronic corrections before the speaker, which is an additional expense. The nice thing about electronic xovers is that you can easily incorporate any correction you need. And there are typically a number to be made. Mid drivers tend to slope upwards, so you might wish to have a low shelf filter on that one, and the acoustic centres typically don't align perfectly, so an all pass on the high is usually mandated. The all pass network can´t be realized ahead of a speaker with an passive xover.
I know you like to solve this with asymmetrical filters, but that is just patchwork imo.
I am not that aware of much of Elliot's writings, but I can tell you this: of course, when designing LR filters, you take into account any possible acoustic roll off so that the total acoustic response will conform the desired curve. Only bloody amateurs would think otherwise, and I am sure Elliot doesn't qualify as such.
As stated before, it is 3 dB, but beware. The power actually drawn from the amps is identical between active and passive. There is no such thing as a free doubling of power. It is just that you need less headroom in the amps driving the different drivers. And because you need less headroom, you can have lower voltage power rails, leading to less dissipation. In other words, total power delivered to the speakers is identical, but total power dissipated is lower in an active setup. What you spend on extra amplification, you save on lower power supply demands and heat sinking. It is the green solution.
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To me it is a very big advantage and one of the (many) reasons you don't NEED to go active with a brace of big amps and the upstream complexity is justified by that. Sadly some view active as 'LR4 at 3KHz, spot of BSC jobs a goodun'. We all know its a lot harder than that, but with the tools available anyone who can think and has patience can do it.
I specify EXACTLY what I mean as follows. "ie it sounds like a 100W amp rather than 2x25W."
But thanks for the Arithmetic lesson
It is for precisely this reason that I like 1kHz xovers .. quite apart from the advantages when Bi-amping.
You may like to consult "Loudspeakers & the Stereo Image" - G Millward for details. I persuaded Gareth to do the work on this.
For more underlying theory on ITD & ILD and the psychoacoustics, there is General Metatheory of Auditory Localisation - M. Gerzon and its references
Some things are easier & better to do passively, others using active filters & still others easier using DSP. I've done speakers using all 3, sometimes in combination ... including non-linear stuff.
The availability of cheap DSP power has changed some rules but not all.
This Millenium, I use mainly DSP in probably the best mike of the 21st century. Last Millenium, I used active EQ for the best mike of the 20th century.
For a domestic speaker, I presently think a combination of all 3 approaches is best .. depending on the product brief of course. I wouldn't use as much DSP on a speaker as I would in a mike cos readily available media players that allow arbitrary IIRs are not yet available.
This may change overnight.
Good speaker designers have been using 'asymmetrical' passive filters for decades to do shelfs and avoid evil all pass networks bla bla. My thinking on this is in Is Linear Phase Worthwhile? I'm rather surprised that there's not a lot I would change after 34 yrs.
And you can do the active stuff you (vac) like without going to full electronic xovers.
I've sorta indicated where each approach is appropriate but this is a HUGE subject.
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All this wanking just obscures my main admonition for Bill to try test-how-much-voltage-power-do-your-speakers-need-103.html
[*] Actually it can (though you would be stupid to put it into a production speaker). Alex Garner of Tannoy (& ex Wharfedale) did it and so did Graham Bank of Celestion (also ex Wharfedale surprise surprise). One of them may have published ... but its all 30+ yrs ago.
Was is das BSC?
Please enlighten a beach bum who has been out of circulation for nearly 2 decades.
And what speakers are these?
NO, two different effects caused by different things requiring different remedies.
Mike
Thanks Vac .. & Bill & Soong.
I wrote an internal Engineering Memo describing the effects circa 1978 though the main aim of the work was another topic entirely.
But all the speaker designers I know, from the major manufacturers, would laugh if you told them they needed extra bits in their EVIL passive xovers to compensate ... let alone a fancy name for it
I think you underestimate how flexible a passive xover can be .. done by someone versed in the art.
For an automated version, see Design of Optimized Loudspeaker Crossover Networks Using a Personal Computer - Peter Schuck.
BTW, 'Correction to .. ' & 'Further Corrections ..' published in JAES were cos Julian Wright of Celestion.
Modulus-86: Composite amplifier achieving <0.0004 % THD+N.
I think there is no doubt that passive crossovers are flexible, and you always might need some passive components even with active crossover. To tell you the truth, I have never tried to specifically identify the sound difference using various compensation by the book. But very early in my audiophile experience, when I read about baffle diffraction, I did to some experiments to effect the diffraction, there was a detectable difference, but not so critical. To date, I see a measured difference, but still have not tried to determine how much audible difference is.
BSC is different issue, I would do the compensation if the response is not what I am expecting, and depending on where you plan to locate the speakers, you may want to play around a bit.
I would go as much active as possible for a few reasons:
1. There are some things you can do digitally that is not possible in analog.
2. Playing with crossover digitally allows faster turn around between configurations.
3. Passive components need to take consideration component current response data of which is not always readily available. Unless you have measured specific brands and models, sound will vary quite significantly.
I think there is no doubt that passive crossovers are flexible, and you always might need some passive components even with active crossover. To tell you the truth, I have never tried to specifically identify the sound difference using various compensation by the book. But very early in my audiophile experience, when I read about baffle diffraction, I did to some experiments to effect the diffraction, there was a detectable difference, but not so critical. To date, I see a measured difference, but still have not tried to determine how much audible difference is.
BSC is different issue, I would do the compensation if the response is not what I am expecting, and depending on where you plan to locate the speakers, you may want to play around a bit.
I would go as much active as possible for a few reasons:
1. There are some things you can do digitally that is not possible in analog.
2. Playing with crossover digitally allows faster turn around between configurations.
3. Passive components need to take consideration component current response data of which is not always readily available. Unless you have measured specific brands and models, sound will vary quite significantly.
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Not at all. I love seeing a well optimised crossover. Some of the ones Zaph did are superb, but does require the right way of thinking about it and they DO throw away lots of power (LS3/5a is grand example).
But the fundamental point that Mod-86 is small and cheap enough to allow you go to active for less remains true. No excuse not to at least try it!
As it so happens, I've done exactly that.
Circa 1990, the BBC asked us to make an active speaker based on the Active Diamond to replicate the sound of the LS3/5a. This was easy as the box & units were about the same size. I used bridged TDA2040s with passive xover for various reasons. It had a strange requirement to run, if required, from the 24V emergency supply in Outside Broadcast Vans.
We were so successful, they asked us to replicate the sound of LS5/9 instead, their favourite 'Control & Monitoring' ie Sound Quality speaker as opposed to the LS3/5a which was only 'Content' ie just check for rude words.
As this was MUCH larger with a built in QUAD 405, it took a lot of dirty tricks (besides easy stuff like matching directivity
) for something with only 20W to make them happy. I learnt a lot about active speakers and how to squeeze every dB of dynamic range from every item ... some of which I've mentioned on this thread.Alas, though the project was very successful technically, both from the BBC as well as our point of view, it coincided with a directive that henceforth, Beeb would only buy commercial stuff and not specify specials. So these 2 unicorns exist only with a number of ex-BBC & Wharfedale employees.
Horny handed engineers who twiddle knobs for BBC radio & telly often disagreed with the ivory towers of BBC Research .. eg their preference for LS5/9 instead of more exotic offerings from Kingswood Warren.
Also impressive was how the BBC assess & accept each speaker they buy which included Listening Tests for individual speakers in an anechoic after the usual measurements.
And LS3/5as differ too. The 'reference' LS3/5a they lent us was MUCH better than several pairs from various makers we'd looked at in the past. There are makers whose LS3/5as the BBC wouldn't touch with a barge pole.
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Looking back at this, if I was doing it again ..
Yes, I would use the same approach with one big amp (perhaps bridged LM3886 or MOD86), electronic EQ and a simple but funky passive xover.
Doing it with electronic xover would not give anywhere near the performance for the same price and/or size constraints.
This Millenium, I've used and tested a 'pro' (??) bi-amplified active speaker with active xover, larger than the original Active Diamond which is nowhere as refined as its BBC project(s) sisters
I'm confident even the 25+ yr cheapo Active Diamond will easily beat the newcomer in a DBLT.
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