The sonic benefits of an active crossover. A discussion.

DonH50

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That's exactly what I did. I didn't have to rip out the old, I just disconnected the passive crossover between the midranges a tweeters and added an analog active crossover and more power amps. (In the IRS-V there was already an active crossover between the woofer and midrange) I use a PassLabs XVR1 three-way active crossover. I initially set the crossover points and slopes the same as the original passive crossover as a starting point and then made slight adjustments in the crossover points between the woofer and midrange. That took a fantastic speaker and made it fantasticker.

As Robert Frost said, "Two roads diverged in a wood and I took the one less traveled, and that has made all the difference."

Great minds, one can only hope... Exactly what I did, disconnected the internal crossovers and hooked up straight to the drivers, and started with the original crossover frequencies and slopes to get things going. "Rip out" was a bit of artistic writer's license... :)
 

microstrip

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You could certainly design a line-level crossover to provide whatever response is desired, flat or not.
Connecting the amp directly to the drivers should handle the damping and back-EMF issues nicely.
Are they becoming more complex to better comensate the response? If so, why not move to active line-level crossovers?

There are many program that simplify the task of converting a transfer function into a filter. For that matter, the analysis program I use (RplusD) will create a filter function from the measured room response or T-S parameters that can then be fed directly into several DSP units.

Connecting the amplifiers directly to the drivers will just damp the units with a very low resistance - that of the output resistance of the selected amplifier. Perhaps it is not the choice of the original designer.

I have no experience with RplusD. How accurate is its curve fitting in amplitude and phase?

Also, as far as I know, the DSP units compatible with RplusD are not accepted as having quality to handle high quality audio. Some people reported in this forum that the most known, the Behringer's were good enough for bass filtering and equalization, but not for full range.
 

FrantzM

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Connecting the amplifiers directly to the drivers will just damp the units with a very low resistance - that of the output resistance of the selected amplifier. Perhaps it is not the choice of the original designer.

I have no experience with RplusD. How accurate is its curve fitting in amplitude and phase?

Also, as far as I know, the DSP units compatible with RplusD are not accepted as having quality to handle high quality audio. Some people reported in this forum that the most known, the Behringer's were good enough for bass filtering and equalization, but not for full range.

ok
 

JackD201

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A lot of people doing mods on the Behringer units.
 

microstrip

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That's exactly what I did. I didn't have to rip out the old, I just disconnected the passive crossover between the midranges a tweeters and added an analog active crossover and more power amps. (In the IRS-V there was already an active crossover between the woofer and midrange) I use a PassLabs XVR1 three-way active crossover. I initially set the crossover points and slopes the same as the original passive crossover as a starting point and then made slight adjustments in the crossover points between the woofer and midrange. That took a fantastic speaker and made it fantasticker.

As Robert Frost said, "Two roads diverged in a wood and I took the one less traveled, and that has made all the difference."

As you say you got a fantasticker speaker we must congratulate you on the slight adjustments. How did you carry them? Using measurements or listening?

BTW I notice that you used what most people consider a really fantastic crossover - the expensive XVR1. Do you consider that if you replaced it with a DCX 2496 using the same settings you would get the same results? I only refer to the DCX2496 because I own it.
 

microstrip

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A lot of people doing mods on the Behringer units.

And to the Korg MR-2000s. Happily they are learning from the hi-end people! ;)
 

hvbias

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Very interesting thread.

An excerpt from ATC regarding active vs passive (they make both types of speaker)

The performance benefits of active over passive loudspeakers is substantial. Even a system, which incorporates the best available stand-alone power amplifier, will never achieve the performance of a similar active system. There are very good engineering reasons why this is true and the following brief will introduce some of the issues.

1. The magnitude of the frequency response of both active and passive loudspeakers can be controlled, with good design, to be within 1dB of one another. However, the phase component of the frequency response will always be better in an active system. The active filters produce better filter roll-off characteristics at crossover. Combine this with the inclusion of a variable all-pass filter at each crossover point to correct the phase response of the drive units through the crossover regions and the result is a loudspeaker with much better group delay characteristics. The benefit to the listener will be improved polar response and therefore radiated power response. Such an active loudspeaker will therefore have a large stable sound field with stable imaging and source location. Not possible with a passive loudspeaker.

2. A passive crossover will only operate correctly into the load impedance of a particular loudspeaker drive unit. However, the impedance of a loudspeaker drive unit will change with the amount of power input. This is because loudspeakers are very inefficient and most of the input power is dissipated as heat in the voice coil. As a result the temperature of the voice coil will rise and because copper has a positive temperature coefficient of resistance the impedance of the loudspeaker drive unit will rise. The result will be frequency response errors as the filters move from their designed response with increased input power. This effect does not occur in active loudspeakers where the filter response is maintained independent of input power to the loudspeaker.

3. Because the amplifiers in an active loudspeaker system are only required to operate over reduced frequency bands the intermodulation distortion products present in a passive system will be dramatically reduced, by typically 20dB, in an active system.

4. In an active system the absence of a passive crossover and long cable runs together with a known amplifier damping factor prevents the modification of the loudspeaker drive unit “Q” ensuring better controlled low frequency performance.

5. For a given amount of amplifier power an active loudspeaker can be expected to produce approximately 6dB more level than the equivalent passive system. Furthermore, powers may be more optimally specified in an active system. A tweeter for, example, requires much less power than a woofer to produce a balanced system performance.
 

microstrip

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Very interesting thread.

An excerpt from ATC regarding active vs passive (they make both types of speaker)

If you are really interested in actives look for the book "Loudspeakers: For music recording and reproduction ". Philip Newell and Keith Holland give you at less 16 or 17 reasons ((I do not have it with me) why actives should be better than passives. It is all in the chapter about crossovers.
 

hvbias

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If you are really interested in actives look for the book "Loudspeakers: For music recording and reproduction ". Philip Newell and Keith Holland give you at less 16 or 17 reasons ((I do not have it with me) why actives should be better than passives. It is all in the chapter about crossovers.

Is the book in fairly layman's terms (or not involve complex crossover math)? I'm making my way through D'Appolito's Measuring Loudspeakers now, and a lot of the math goes way over my head :)

I wouldn't say I'm really interested in actives, but I do plan on hearing some full range ones to see if they're for me. More budget studio monitors have left me a bit cold.
 

DonH50

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(1) Connecting the amplifiers directly to the drivers will just damp the units with a very low resistance - that of the output resistance of the selected amplifier. Perhaps it is not the choice of the original designer.

(2) I have no experience with RplusD. How accurate is its curve fitting in amplitude and phase?

(3) Also, as far as I know, the DSP units compatible with RplusD are not accepted as having quality to handle high quality audio. Some people reported in this forum that the most known, the Behringer's were good enough for bass filtering and equalization, but not for full range.

Perhaps we should agree to disagree instead of debating every point. I added numbers when I quoted you.

1. If you are replacing the crossover I am not sure the "choice of the original designer" really matters anymore, nor am I sure why lowering the driving impedance could hurt performance, but whatever.

2. No idea the accuracy of the curve fit, or how it converts measurements into filter coefficients. I bought the package but have not used it nor really looked closely. I had a brief exhange with Doug (SW writer) at the time but don't recall much. There are a number of such SW packages but I have not looked in over a year so don't recall names.

3. I suppose we can debate "high quality" endlessly. I am not sure what units the SW targets; IIRC there were a couple of different Behringer units but I know there were several other units and I do not remember the names. None of which may pass your criteria for quality. I do know Roger Sanders uses a Behringer-based unit, although that is also subject to endless debate. If you are convinced no active crossover is acceptable there is no more to be said.
 

Robh3606

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•I have no idea why you couldn't rip out the crossover and replace it with active. Perhaps it is better to start from ground zero but I don't see a clear reason why that would be a requirement. The tests I did so long ago started with (IIRC) Polk, B&W, and Infinity speakers; we bypassed the internal crossovers and replaced them with (analog) active crossovers and connected the amps direct to the voice coils. I did similar with my Maggies for many years, but only replaced the external box so the mid/tweeter crossover was still passive.

Hello Don

It depends upon your goal. If you want to make an active version with the same on and off-axis frequency response you need to match the voltage drives to the individual drivers. If you don't care about keeping the speaker as the designer intended than it doesn't matter. You should always check the voltage drives anyway to make sure there is no response tailoring beyond the actual crossover slopes. That way there are no surprises or fewer:D


Same thing if you want to just convert them to biamp . As soon as you take out a poles of a bandpass crossover, midrange as an example, you need to model what change is going on in the remaining active poles. Typically your are going to have to make network changes in the still active poles to keep the same response.

Rob:)
 

microstrip

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(a) Perhaps we should agree to disagree instead of debating every point. I added numbers when I quoted you.

1. If you are replacing the crossover I am not sure the "choice of the original designer" really matters anymore, nor am I sure why lowering the driving impedance could hurt performance, but whatever.

2. No idea the accuracy of the curve fit, or how it converts measurements into filter coefficients. I bought the package but have not used it nor really looked closely. I had a brief exhange with Doug (SW writer) at the time but don't recall much. There are a number of such SW packages but I have not looked in over a year so don't recall names.

3. I suppose we can debate "high quality" endlessly. I am not sure what units the SW targets; IIRC there were a couple of different Behringer units but I know there were several other units and I do not remember the names. None of which may pass your criteria for quality. I do know Roger Sanders uses a Behringer-based unit, although that is also subject to endless debate. If you are convinced no active crossover is acceptable there is no more to be said.

(a) We agree on some points and disagree on others. My apologies if I am missing any of your posts, but I went through all your answers in this thread and could not find any figure in dB or degrees. If so please just say me the post number and I will re-read it. As some people seem to believe that anyone using digital can reproduce ANY transfer function exactly with great accuracy and success I find the point relevant.

1. Wilson Audio includes some damping resistors of different values (typically one value around 25 and the other around 30 ohm) that can be assembled in parallel with drivers. As they have high value compared to the resistance of the coil, changing them has almost no effect in speaker response - I have measured it. However it changes sound quality a lot. I have read that one of the effects of the usual L network used to attenuate level in crossovers is also damping the speaker unit.

2. OK

3. AFAIK we are debating why there are no more active designs that are competitive with high-end loudspeakers in this thread. Quality of existing reasonably priced and accessible crossovers is an issue. I am sure that there are many DSP hardware platforms that are suitable for the development of active crossovers that can compete with the best passives. But the lack of expertise to use them and the total cost can be one reason of the lack of enthusiasm of the community, although we have seen high-end solutions from companies such as Meridian, Cabasse, B&O and Backes & Müller.


Although not directly related with this thread subject recently Amir presented us with ARCOS- a SOTA bass management system by Harman. Curiously the steps for amplitude of each setting were very large - I think around 6 dB. However a very clever system managed to get an excellent solution just playing with Hertz resolution, four Q factors and 7 values of delays. I found it great. I think that an innovative approach (please do not ask me which, if I knew I would not be here now!) using the unique capabilities of digital is the way to go for active digital designers if they want to be competitive - just replacing the passive elements of the crossover, and trying to reproduce or ameliorate the existing speakers is not a promising way. All IMHO.
 

microstrip

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Is the book in fairly layman's terms (or not involve complex crossover math)? I'm making my way through D'Appolito's Measuring Loudspeakers now, and a lot of the math goes way over my head :)

I wouldn't say I'm really interested in actives, but I do plan on hearing some full range ones to see if they're for me. More budget studio monitors have left me a bit cold.

The book is easy reading. Just google the tittle and you will find that you can read a good part of it. But when you get in the most interesting part you find you have to buy it to go on reading. ;)
 

Groucho

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The mystique of the passive crossover endures. Yet the design is required to result in something quite simple and 'analyzable', and indeed the designers boast of their ability to juggle multiple contradictory dimensions to achieve something close to the measured and theoretical optimum. Surely this is the sort of thing that computers excel at? So why don't they simply measure their drivers and box to the Nth degree and set a computer chomping through the numbers to find the real, actual, optimum passive crossover? - assuming they really can define what it is they want to achieve.
 

microstrip

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The mystique of the passive crossover endures. Yet the design is required to result in something quite simple and 'analyzable', and indeed the designers boast of their ability to juggle multiple contradictory dimensions to achieve something close to the measured and theoretical optimum. Surely this is the sort of thing that computers excel at? So why don't they simply measure their drivers and box to the Nth degree and set a computer chomping through the numbers to find the real, actual, optimum passive crossover? - assuming they really can define what it is they want to achieve.

Harman did it - F. Toole has a paper accessible online about a simulation tool they use to design the crossovers of their speakers.
 

Groucho

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Harman did it - F. Toole has a paper accessible online about a simulation tool they use to design the crossovers of their speakers.

If done correctly, this should be the end of the matter, then..? By definition, the computer-optimised passive crossover must be the best possible, as judged against any measurable criteria you optimise for. So why do people keep 'designing' them by hand? Why do people keep on coming up with very poor speakers?
 

Robh3606

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Harman did it - F. Toole has a paper accessible online about a simulation tool they use to design the crossovers of their speakers.

Hello Micro

I think you are referring to how they measure using 72 points spinarama. The software used anyone can get, I use it as well. They currently use LEAP Crossover shop to do the crossovers and a MLSSA measurement system. I use CLIO for my measurements.


If done correctly, this should be the end of the matter, then..? By definition, the computer-optimised passive crossover must be the best possible, as judged against any measurable criteria you optimise for. So why do people keep 'designing' them by hand? Why do people keep on coming up with very poor speakers?

Hello Groucho


Easier said than done. The key to good crossover software simulations are an accurate set of measurements. The best way to do that is in an anechoic chamber and you need a large one for good low frequency measurements. Very few manufacturers have their own chambers. Gated measurements are the next best thing but you need a very large space or go outdoors on a high stand to get good low frequency resolution. You need to keep the time till the first reflection as long as possible.

LEAP is incredibly accurate with it's simulations and it will design a crossover based on whatever target curve you choose. The problem is when you go into auto mode the crossovers can become very complex. Most of the people I know who use it as hobbyists just go from intuition and experience as the program is quite user friendly and easy to use.

Any Pro designer who might use LEAP or another program is still going to build up a crossover, or emulate it and have a listen before they call it a wrap. They may end up tweaking it by ear when all is said and done.

Rob:)
 

DonH50

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Hello Don

It depends upon your goal. If you want to make an active version with the same on and off-axis frequency response you need to match the voltage drives to the individual drivers. If you don't care about keeping the speaker as the designer intended than it doesn't matter. You should always check the voltage drives anyway to make sure there is no response tailoring beyond the actual crossover slopes. That way there are no surprises or fewer:D


Same thing if you want to just convert them to biamp . As soon as you take out a poles of a bandpass crossover, midrange as an example, you need to model what change is going on in the remaining active poles. Typically your are going to have to make network changes in the still active poles to keep the same response.

Rob:)

Agreed. As I think I have mentioned, when replacing/bypassing the internal crossovers (not starting from scratch) I always started from the original crossover's transfer function and tweaked from there.
 

DonH50

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(a) We agree on some points and disagree on others. My apologies if I am missing any of your posts, but I went through all your answers in this thread and could not find any figure in dB or degrees. If so please just say me the post number and I will re-read it. As some people seem to believe that anyone using digital can reproduce ANY transfer function exactly with great accuracy and success I find the point relevant.

1. Wilson Audio includes some damping resistors of different values (typically one value around 25 and the other around 30 ohm) that can be assembled in parallel with drivers. As they have high value compared to the resistance of the coil, changing them has almost no effect in speaker response - I have measured it. However it changes sound quality a lot. I have read that one of the effects of the usual L network used to attenuate level in crossovers is also damping the speaker unit.

2. OK

3. AFAIK we are debating why there are no more active designs that are competitive with high-end loudspeakers in this thread. Quality of existing reasonably priced and accessible crossovers is an issue. I am sure that there are many DSP hardware platforms that are suitable for the development of active crossovers that can compete with the best passives. But the lack of expertise to use them and the total cost can be one reason of the lack of enthusiasm of the community, although we have seen high-end solutions from companies such as Meridian, Cabasse, B&O and Backes & Müller.


Although not directly related with this thread subject recently Amir presented us with ARCOS- a SOTA bass management system by Harman. Curiously the steps for amplitude of each setting were very large - I think around 6 dB. However a very clever system managed to get an excellent solution just playing with Hertz resolution, four Q factors and 7 values of delays. I found it great. I think that an innovative approach (please do not ask me which, if I knew I would not be here now!) using the unique capabilities of digital is the way to go for active digital designers if they want to be competitive - just replacing the passive elements of the crossover, and trying to reproduce or ameliorate the existing speakers is not a promising way. All IMHO.

I added numbers in your post when I quoted, 1, 2, 3, to make it easier to keep track of your points. No dB, phase, or worthwhile engineering terms. Language barrier, sorry.

1. The added resistors have an impact at audio frequencies because they affect the signal going into the (inductive) voice coils. They will modify the frequency response as well as lowering the Q of the system as you said (reducing ringing).

2. You could check the website; I will take a look at what the program says if I remember but I have a very busy weekend (concert weekend).

3. I probably misunderstood the thrust of your posts and this thread; my assumption was this was just to list things rather than debate the pros and cons here since there is another thread on passive crossovers. However, the exchange is good. My apologies, long week and I am grumpy today (and have rehearsal tonight so am still many hours from going home after a 12-hour workday).

On the DSPs, I think the problem is not a lack of good DSPs but rather people who understand how to program them (as you said), and good interfaces (ADCs and DACs) on either side of them (my adddition). Plus the lack of desire to work at something like that rather than having a plug-and-play speaker. I suspect those are more the reasons than cost, but I think we generally agree on (3).

All the best - Don
 

GaryProtein

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As you say you got a fantasticker speaker we must congratulate you on the slight adjustments. How did you carry them? Using measurements or listening?

BTW I notice that you used what most people consider a really fantastic crossover - the expensive XVR1. Do you consider that if you replaced it with a DCX 2496 using the same settings you would get the same results? I only refer to the DCX2496 because I own it.

The "slight adjustment" in crossover point was between the woofer and midrange. The original spec has selectable active crossover frequencies at 60, 74, 90 and 110 Hz. I had been using the 90 Hz crossover point, but when I switched to the PassLabs, I found it was best in my room on the 106 Hz point. I really did mean it was a slight adjustment. The frequency spec on the woofers go up to 1000 Hz if they didn't have a crossover in the signal path, so the change I made really was fairly small, but it took a bit of the bass load off the midrange and I thought it sounded a little better.

I made the adjustment by listening and using an AudioControl RTA.

I suppose you could use a digital crossover, but I can't say how it would sound with yours. I had a Behringer DSP 8000 in the past, and found it was slightly noisy but I never used it with the IRS-V system. Your Behringer is a newer model so maybe they worked out the noise/hiss problem.

At the time I got the PassLabs crossover, it was recommended to me by another audiophile who owned one and was not a dealer or connected with one.

There are rare occasions when I toy with the idea of playing with the crossover points 10% either way, but I am very happy with the set-up now, so I have to weigh the time it would take to satisfy my curiosity by opening the XVR1 and changing the settings against possible gains. I would rather be listening to music than playing with the equipment. Adjustments on the XVR1 are not difficult once you know what you are doing with the unit, but they are not quickly adjustable because you have to open the case to get to the adjustments.
 
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