Linesource,
Does the paper you have have a solution to the forth order function as a single filter? I have used cascaded 2nd order filters in this way in the past, in comercial designs but this only works if you can impedance scale the filters so that the values are an order of magnitude apart. As previously mentioned this places restrictions on what you can actually do as it very easy to end up with current drive problems at one end and Johnson thermal noise problems at the other.
In the circuit I was working on the cascased filters were not part of the same filter. One was a low pass for the crossover and the other was a mild peaking high pass for base extension and excursion control this helps in the seperation of the impedance so makes this more viable.
However this was all done a long time ago when the cost of opamps was still significant. Surely these days its better to simply use another part and avoid all the complication along with the very high sensitivity to part variation that a circuit like this is likely to have.
Regards,
Andrew
Does the paper you have have a solution to the forth order function as a single filter? I have used cascaded 2nd order filters in this way in the past, in comercial designs but this only works if you can impedance scale the filters so that the values are an order of magnitude apart. As previously mentioned this places restrictions on what you can actually do as it very easy to end up with current drive problems at one end and Johnson thermal noise problems at the other.
In the circuit I was working on the cascased filters were not part of the same filter. One was a low pass for the crossover and the other was a mild peaking high pass for base extension and excursion control this helps in the seperation of the impedance so makes this more viable.
However this was all done a long time ago when the cost of opamps was still significant. Surely these days its better to simply use another part and avoid all the complication along with the very high sensitivity to part variation that a circuit like this is likely to have.
Regards,
Andrew
Time for a revival !
IMHO this is the "heart and soul" of a realistic sounding music playback system, so I brought this back to life !
IMHO this is the "heart and soul" of a realistic sounding music playback system, so I brought this back to life !
Direct from the original Linkwitz article:
SB1980-3way
only used the sub low-pass and mid high-pass. Substituted tl074 op amps (what was available in 1989)
When you build analog, you are at the mercy of what parts are available. If, say you need a 12,75k resistor, you're not likely to find one. I was lucky, I had access to 1% resistors then. 10% caps were what I could get, and I had no meter to measure it. Crossover was certainly not exactly what I had calculated, but was "close".
New system all done in an old PC running Linux. MPD, Ecasound and Richard's filters. It does exactly what I want, was free, and sounds great.
Digital Crossover/EQ with Open-Source Software: HOWTO | Richard's Stuff
SB1980-3way
only used the sub low-pass and mid high-pass. Substituted tl074 op amps (what was available in 1989)
When you build analog, you are at the mercy of what parts are available. If, say you need a 12,75k resistor, you're not likely to find one. I was lucky, I had access to 1% resistors then. 10% caps were what I could get, and I had no meter to measure it. Crossover was certainly not exactly what I had calculated, but was "close".
New system all done in an old PC running Linux. MPD, Ecasound and Richard's filters. It does exactly what I want, was free, and sounds great.
Digital Crossover/EQ with Open-Source Software: HOWTO | Richard's Stuff
Of more importance than how one cross’s over is that the crossover is optimal for the upper and lower driver’s behavior and measurements.
If the upper and lower sources are so close together that they add coherently into one new source (less than ¼ wavelength apart) then there is often only one best solution and if passive, will hardly ever be one from a text book as you must include the magnitude and phase of the upper and lower drivers in the calculations AND it’s impedance curve magnitude and phase if passive.
A good path is measurements taken outdoors entered into a program like LSPcad and going active and tweaked using a digital loudspeaker controller and more measurements. When all is happy, measuring the xover transfer functions and then (except for time delays etc) making a dedicated circuit is the way to go.
If the upper and lower sources are so close together that they add coherently into one new source (less than ¼ wavelength apart) then there is often only one best solution and if passive, will hardly ever be one from a text book as you must include the magnitude and phase of the upper and lower drivers in the calculations AND it’s impedance curve magnitude and phase if passive.
A good path is measurements taken outdoors entered into a program like LSPcad and going active and tweaked using a digital loudspeaker controller and more measurements. When all is happy, measuring the xover transfer functions and then (except for time delays etc) making a dedicated circuit is the way to go.
1/4 ?
What if, because of actual physical constraints, this "keeping it within 1/4
wavelength" can never be met ?
How about keeping the 2 drivers within one wavelength ?
And, what if, at the crossover point each driver is already operating in a linear phase and amplitude mode (?) Will then an 18db/oct butterworth filter be acceptable ?
For me, an active smokes the passive, every time it's been tried.
What if, because of actual physical constraints, this "keeping it within 1/4
wavelength" can never be met ?
How about keeping the 2 drivers within one wavelength ?
And, what if, at the crossover point each driver is already operating in a linear phase and amplitude mode (?) Will then an 18db/oct butterworth filter be acceptable ?
For me, an active smokes the passive, every time it's been tried.
Thanks
What is the possibility and success rate of adding active crossover only for woofer in a 3-way (so XO point is relatively very low ala subwoofer)? The midwoofer could be in sealed box to get the 2nd order roll-off, but it wouldn't be electronically equalized to 4th order (ala Linkwitz). So at worst it will be like Harsch's transient perfect alignment.
What was the XO frequency? The passive mid-tweeter should determine the SPL limit. May be a passive line-level for the HPF...
I see, thanks, I have just read some of the pdf reference you posted, might try it though I found Linkwitz's circuits are too complicated.
Actually, the circuit is pretty simple. Remember that you are looking at a 3-way crossover with muting. You can eliminate more than half of it for a 2-way. To get a 4th order low-pass takes two op-amp stages, so that's minimum. Linkwitz likes an input buffer, and a 2nd order high-pass takes another op-amp. Makes a total of 6 op amp stages for a mono- subwoofer and two high-pass. The amps I used, tl074 are quad op-amp in a package, so there are only two packages in my old crossover.
I doubt you'll find much of anything that's "simpler" to build.
I doubt you'll find much of anything that's "simpler" to build.
I meant not from how it work, but one opamp is already complicated
That's why I was asking about the possibility of using LPF without HPF.I think there is
I cannot see the circuit right now, but I think what makes it complex is its modularity/transportability. I prefer to treat active XO as passive XO, no off-the-shelf crossover.A speaker crossover needs two filters.
The high pass one could be the natural roll off of the speaker. The easiest to achieve is the 2pole roll off of a sealed box, when the box volume is selected to give the Butterworth Q of 0.7071.
But you still need the other low pass filter. An electrical 2pole based on S&K single opamp works OK.
I don't think you get any simpler.
It is my view that a Cap as a high pass and an Inductor as a low pass to form the two filters is more complicated and gives poorer results, especially when used for Bass to Mid/Treble crossing at around 80Hz to 150Hz.
The high pass one could be the natural roll off of the speaker. The easiest to achieve is the 2pole roll off of a sealed box, when the box volume is selected to give the Butterworth Q of 0.7071.
But you still need the other low pass filter. An electrical 2pole based on S&K single opamp works OK.
I don't think you get any simpler.
It is my view that a Cap as a high pass and an Inductor as a low pass to form the two filters is more complicated and gives poorer results, especially when used for Bass to Mid/Treble crossing at around 80Hz to 150Hz.
Do you mean a 2nd order Butterworth filters, with only enclosure filter for HPF and a single opamp for LPF?
I think for an active LPF, 2nd order or 4th order doesn't really matter for me. I can accept more opamp for the LPF but not HPF.
The problem then, will be the subjectively too low crossover point. Not high enough to release the midwoofer from bass duty. An extra single big capacitor has been tried but it affected treble quality negatively.
this leaves you with no active solution. You are rejecting opamp for high pass and stating insufficient attenuation of out of band signal
Then you reject additional passive filtering.
Do you consider all filtering to be wrong leaving just a wideband driver as the only remaining topology?
Hehehe. Of course I have built many active solutions, using many kinds of opamps. It is just that I still expect someone came up with a solution never tried before (such as using the Harsch crossover). And I wont give up trying to find a solution which is better than the rest. Can be from the Opamp being used, the shunt power supply, the slope, the filter type, etc...
From the beginning it is already clear that some "hard core players" do not like the idea of this analog active amplification, especially when opamp is included. That's probably the reason why the thread died before resurrected by Scott, which in several threads mentioned that he thought analog active XO has something to deliver. Naturally, I wanted to see how Scott did his such that he seems to be very satisfied with it.
But based on your suggestion I can try the 2nd order Butterworth S&K with single opamp for HPF. This opamp will be in TO-3 package with slew rate from 1000-2000 V/us. Who knows it will make a different.
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