Anyone here an audio buff? Working on active crossovers..

[fastline]

I would like to just pop the question first, I run a fairly high performance audio system in my home and would like to switch over from passive crossovers to actives BUT I was curious if the networks could be created in a fashion that they mount in the speaker and operate at speaker level voltages rather than line level that is typically done? I realize they typically operate before the amps but I would like to avoid getting another amp just to get digital adjustment of my networks.

I also know that most people prefer nothing impeding the signal between amp and speaker so this would be a bit of a trade off. Actual power levels even at the speaker are relatively low so just thought I might ask...

 

[#12]

I think this needs some more defining.
To have active crossovers and not have another amp are contradictory statements.
An active crossover is an amplifier, and when you do it at "high performance" bass speaker levels, it is a seriously powerful amplifier.
Could you elaborate?

 

[fastline]

I think you somewhat answered my question. In thinking about it a bit, just conditioning the power signal "would" be passive by definition. I guess I did not think about the fact that the signal TO the actives would be only a function of the output of an op amp.


I might want to scratch harder I guess. I do not think my thought was really thought through when I posted it...lol

 

[4pyros]

An active crossover is an amplifier

No its a pre amp.
You could not do it in a conventional sense. You could maybe change cross over points by using relays and a computer.

a fairly high performance audio system

With out a seperate amp?

would like to avoid getting another amp just to get digital adjustment of my networks.

Just what are you after?
Andy

 

[fastline]

I run 3 Rotel RB1090s. They are not cheap and I would rather not buy 3 more I guess..... I run Klipsch RF-83s, 2 Velodyne HGS18s, and related gear. Just wanting to use active xovers but realizing now that true biamping will probably be the right way to do it anyway... I have to wonder though i there is a better way to do the current passive networks that have been used for 75 yrs...

 

[4pyros]

Bi and tri amping no xovers needed. Andy

 

[fastline]

Scratching head rather hard..... Did I drink one too many tonight or did you really say Xovers are not needed?

 

[Nigel Goodwin]

Scratching head rather hard..... Did I drink one too many tonight or did you really say Xovers are not needed?

Presumably he meant no PASSIVE crossovers needed - you obviously need active crossovers instead.

 

[4pyros]

Yes no passive crossovers are needed in the speakers with bi or tri amping the active crossover before the amps takes care of that. Andy

 

[audioguru]

A woofer with "tweet" in it sounds awful.
A tweeter with "woof" in it goes POP then doesn't work anymore.

 

[fastline]

Yes, I guess this was the whole point of my question trying to get rid of my passives. I realize what it takes to operate different drivers at their ideal frequencies. I was NOT implying to use actives AND the passives in the speakers. I want do get rid of my passives in the speakers but I was also just asking about the construction and and overall operating design of active crossovers to see if they could be made to operate at speaker output levels or on the output side of the amp and simply replace the passives.

The real problem with passives is there is signal conditioning between the amp and speaker induced by the inductors and capacitors to roll off frequencies. I was just more or less curious if there was a way to trim these unwanted frequencies without really affecting the signal.

Obviously, one of the main reasons for actives IS to reduce the range of frequencies each amp reproduces to reduce harmonic distortion. There is usually some interaction when an amp is outputting 30hz and 15khz at the same time so my thought would certainly be a trade off for simplicity. I have never tried to measure the current to my speakers but I am sure there is probably more there than can easily be handled by common semiconductors.

Just more or less thinking out loud I guess...

 

[audioguru]

You are talking about "intermodulation distortion" that occurred on very old amplifiers but is not audible on good modern amplifiers.

A passive crossover has the resistance of a coil in series with the woofer. Then the woofer is not well-damped by the extremely low output impedance of a modern amplifier which causes it to sound boomy at its resonant frequencies. An active crossover system has the crossover circuit feeding the input of the bass amplifier so that the output directly connects to the woofer for very tight control of it.

A passive crossover has very high value capacitors so that it can feed the very low impedance of speakers. High value capacitors are frequently electrolytic type that have an inaccurate tolerance of 20% or worse. Active crossovers use small inexpensive accurate 5% tolerance capacitors.

An 8 ohm speaker is 8 ohms only at one frequency. Near the crossover frequency its impedance varies a lot which messes up a passive crossover.

 

[fastline]

Exactly. I would like to realize the full damping of my amplifiers but not sure if there is really any way to do this without using passives in the speaker. Can an active be made to function between the speaker and amp?

 

[Nigel Goodwin]

Exactly. I would like to realize the full damping of my amplifiers but not sure if there is really any way to do this without using passives in the speaker. Can an active be made to function between the speaker and amp?

As has already been explained, you can't put an active between speaker and amp - at least not to serve any purpose.

You 'could' attenuate the speaker level signal to line level, feed it through an active crossover, then use extra amplifiers to feed the speakers - but it would really be a complete waste of time.

I don't know what you're on about with damping factors? - passive crossovers REDUCE the damping factor, an active crossover system connects the output of the amp directly to the voice coil, providing the absolute maximum damping possible.

You really seem a little confused about what active crossovers are? - you do realise you need an individual power amplifier for every drive unit?.

 

[audioguru]

Can an active be made to function between the speaker and amp?

Yes.
But adding a second power amplifier will make the original power amplifier redundant.
An active filter feeds the input of the power amplifier. Then the output of the power amplifier can directly feed the speaker with its extremely low output impedance.

 

[fastline]

I understand perfectly how actives are typically used and I have used them in many different apps for bi and tri amping speakers. By my answer above, I think that came out wrong and sounds like I am implying that passives IMPROVE damping. I realize the best or full damping of the amp can only be achieved with the amp connected directly to the speaker.

I guess I was wondering if there was a ""digital"" way of creating a crossover that was able to filter certain frequencies without touching the rest between the speaker and amp? then I could create a 2 or 3 way filter system with one common channel of the amp. I am just not sure if this is even doable and certainly would NOT be of the same construction of a typical line level active.

 

[Nigel Goodwin]

I guess I was wondering if there was a ""digital"" way of creating a crossover that was able to filter certain frequencies without touching the rest? then I could create a 2 or 3 way filter system with one common channel of the amp. I am just not sure if this is even doable and certainly would NOT be of the same construction of a typical line level active.

I'm sorry, but I've no idea what you're on about?.

 

[audioguru]

One power amplifier drives the sub-woofer, another power amplifier drives the woofer, another power amplifier drives the midrange, another power amplifier drives the tweeter and another power amplifier drives the super-tweeter.
Then an active crossover circiuit (digital or analog) drives all the power amplifiers.

 

[crutschow]

I guess I was wondering if there was a ""digital"" way of creating a crossover that was able to filter certain frequencies without touching the rest between the speaker and amp? then.

The short answer is no.

All practical forms of active analog or digital filtering work with low power, line level signals. Only passives can operate between the power amp output and the speakers.