Changing a passive crossover to active

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Re: Re: Re: Changing a passive crossover to active

sreten said:



Active 2-ways are a waste of exspense driving the tweeters
unless you have suitably lower power amplifiers for them.

:)/sreten.

This is unless you want the system to play loud without lots of distortion and smoked tweeters.

When playing loud, passive crossovers are the #1 cause of tweeter death, particularly 6dB/oct and 12dB/oct ones and the ones that achieve the most ideal acoustic response, because they are also the ones allowing huge amounts of low frequency energy to reach the tweeter. Also, when coils and voice coils get hot their Rdc can increase by 30% or more thus detuning the system.

Only active crossovers allow you to use all-pass filters (and delays) to compensate for driver/enclosure phase shifts and get phase matching and optimum summing without requiring ideal acoustic responses.

Given the same sensitivity, peak power requirements for tweeters are actually equal or higher than for woofers, particularly with recordings involving real instruments and little compression. It's the average HF power what is much less than average LF power, but the crest factor is also much lower for lows, so a smaller amplifier is a huge mistake unless the tweeter has a much greater sensitivity. This is something that you easily learn when setting up the limiters in active filters, because it gives you the chance to analyse actual signal levels after frequency division.
 
Re: Re: Re: Re: Re: Changing a passive crossover to active

Eva said:


Given the same sensitivity, peak power requirements for tweeters are actually equal or higher than for woofers, particularly with recordings involving real instruments and little compression. It's the average HF power what is much less than average LF power, but the crest factor is also much lower for lows, so a smaller amplifier is a huge mistake unless the tweeter has a much greater sensitivity. This is something that you easily learn when setting up the limiters in active filters, because it gives you the chance to analyse actual signal levels after frequency division.


AndrewT said:
agreed, but no one else wants to believe us.

Hi,

This one has been done to death.

The simple fact is for active bi-amping a good c/o point for 2
identical amplifiers is around 350Hz, i.e. a 3-way with active
bass/mid and passive mid/ treble.
Move this up to 3.5kHz and you are simply dead wrong.

The argument implies active amplification is a complete waste
of time, i.e. a 200W amplifier will always be better than 2x100W.
However the active 2x100W can swing the equivalent of 400W ....

:)/sreten.
 
Robert GS said:
why is a 200Watt amplifier always better than 2x100W.

Then a 20000Watt ampilfier will be unbeatable unless someone comes up with a 20001Watt :eek: :confused:
it depends very much on the spread of frequencies in the music signal.

A single tone played through a 200W amp to a speaker is capable of playing louder than the same single tone played through a 100W amplifier to the same speaker. The other 100W amp is sitting idle waiting for it's frequency range to be utilised.

Now apply a two tone signal. If each tone is in the passband of the respective 100W amps and speakers then you can get xSPL from the pair.
Play the same two tone signal through the 200W amp and the maximum SPL is similar to the 100W+100W amps.

But when the frequencies are widely distributed and playing through multiple amp/speaker combinations, the multiple speaker arrangement is capable of playing louder than the single amp/speaker with the same TOTAL power.
Pink and/or white noise would be the logical extension to this SPL contest. 5 active channels each with 100W available into 90dB sensitivity speakers, will play louder than a single channel 500W amplifier playing into a 90dB speaker operating in wideband mode.

Most commentators forget to tell you the conditions for which their statement applies.
 
Hi sreten

The 350Hz "equal power distribution" point is only valid when average spectral power content is considered. However, when peak power requirements are considered (the true criteria for amplifier size selection), the middle point may be around 1Khz. Have you ever seen the waveform from a trumpet on oscilloscope? It has big killer >5Khz peaks repeating at the fundamental frequency. This requires big tweeter amplifiers for proper playback.

Active systems can produce 6dB higher output than initially expected in the crossover overlap region. Bessel filters (with global EQ to lift the wide 1dB hole that results) may be employed to make that region intentionally wider (like one octave for LR24) without resorting to lower crossover slopes. 250Hz is a great place for this (lots of kick without clipping).

Not to mention that several amplifiers clipping each one its own frequency range sound much better than a single one clipping all frequencies together.
 
Robert GS said:
I doubt that this thread started out to be a quest for higher SPL, but a gain of better sound quality. In both cases I would simply say active rules, but there is a financial aspect - which often prevents the obvious choice :)


Hi,

The answers to the original post are : No it won't. No it isn't.

There is nothing wrong with active done properly.
For a compact domestic 2-way IMO it is not cost effective.

:)/sreten.
 
AndrewT said:


Now apply a two tone signal. If each tone is in the passband of the respective
100W amps and speakers then you can get xSPL from the pair.
Play the same two tone signal through the 200W amp and
the maximum SPL is similar to the 100W+100W amps.

Hi,

There is the rub (or one of them). Its not. With equal gain
the 200W amplifier will clip as it cannot provide the same
total voltage swing as for 2 superimposed 100W signals.
The 200W maximum SPL is 3dB lower.
Conversely for a single frequency its 3dB higher,
i.e. 2x100W can swing the equivalent of 400W.

For 300W versus 3x100W optimally split :
For single frequencies the 300w is 4.5dB higher.
For triple frequencies, 1 in each band it is 4.5db lower.
i.e. 3x100W can swing the equivalent of 900W.

:)/sreten.
 
My experience is that an optimized passive xover using the minimum component count & good quality parts will be more 'transparent' sounding than virtually any commercial active xover.

Of course this consideration will probably not override that of correcting driver arrangements that have significant time domain problems.

Also for pro sound systems that require the absolute maximum SPL from an available driver complement and power budget, the active approach is often preferred.

I have used with good success a resonant network that flattens woofer in system impedance peaks and also provides significant response extension with proper system tuning. With this circuit, the voltage at the resonant frequency at the woofer VC may be as much as double (or even more) that at the amp terminals, approximating an amplifier with up to four times the available power rating near that frequency. Try to do *that* with an active xover.
 
sreten said:
There is the rub (or one of them). Its not. ....................
the 200W amplifier will clip as it cannot provide the same
total voltage swing as for 2 superimposed 100W signals.
The 200W maximum SPL is 3dB lower.
Conversely for a single frequency its 3dB higher,
i.e. 2x100W can swing the equivalent of 400W.
but I can see you are agreeing that it depends very much on the signal that is being reproduced.
Mono tones suit mono amps. Multi-tones suit multi amps (active) if you require maximum overhead or maximum SPL for any particular signal type.
If you're reproducing normal music with mixed tones over a wide bandwidth then multi amps driving multi speakers in active format do have a significant advantage.

BTW,
3dB by my somewhat loose definition is similar.
 
There is also an 'in-between' approach that with using a speakers' internal xover network, configured to be bi or tri-ampable, simple passive LP/BP/HP RC first order networks before the power amplifiers can save you the money of a dedicated active xover that may not be satisfactorily tuneable in any case.
 
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sreten said:
For a compact domestic 2-way IMO it is not cost effective.

That does hit the nail on the head. At least in my experience.

And then there is the Behringer unit itself. Maybe not the most transparent of circuits, balanced in and outs to deal with, etc.

But it could be made to work, if one wanted to. But cost effective? No.....
 
Cost Effective?

Worth the time?

Are we having fun?

Maybe point three is what we should
consider. There are DIYers that will
spend $400 USD on a single full range
driver! Cost is not always considered
with some of us. . .others it is. . .I had
a blast converting my old JBLs to three
way electronic crossover setup. . .it never
sounded better. . .I killed the woofers in
the first hour. . .but I had fun. . .and it
sounded big, open and louder than I
could have ever imagined. There are
many companies that pair electronic x-overs
to two way speakers and call them "studio monitors."

Without the desire and willingness to move forward
we will never gain knowledge or experience triumph.

Wow, I almost got philosophical. . . like I said before:

Make those passive speakers into electronically crossed-over
monsters and then deal with killing or fixing the monster
later. . .Doctor Victor Frankenstein did. . .remember, the
monster wasn't bad, the doctor just didn't show it the
respect that a human soul deserves. . .

Well I'm off on vacation and going to my 20 year high school
reunion. . . maybe I'll get to see the stereo system that I set
up for the school. . . a pair of La Scalas and a big amp . . .those
were the days. . .
 
gni said:

Cost Effective?

Worth the time?

Are we having fun?

Make those passive speakers into electronically crossed-over
monsters and then deal with killing or fixing the monster later. . .

Hi,

The point is you will not create "monsters", they will be simply wrong.
Fixing it after the predictable fact is simply not very sensible.
If it does not work, do not do it. Choose something else.

:)/sreten.
 
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