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Multi-Way Conventional loudspeakers with crossovers

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Old 3rd March 2013, 07:38 PM   #81
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LR 2nd is Linkwitz Riley second order filter function.
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Old 3rd March 2013, 07:41 PM   #82
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LR
Speaker builder shorthand for Linkwitz Riley a second order short-hand for a XO where the coil / inductor value is doubled and the value of the capacitor is halved.
Use the drop down box in the Bagby program to select
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Old 4th March 2013, 07:13 PM   #83
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Found this definition on Parts Express FAQ:

What is the Difference Between Acoustic and Electric Crossover Slopes?

An electric crossover slope refers to the cutoff produced purely by the electrical components in the crossover. Electrical slopes do not take into account the behavior of the drivers themselves. The combination of both the natural characteristics of the drivers and the electrical filtering produces the acoustic slope. It is in fact this acoustic slope that should be designed around and optimized when building a complete system.

Therefore the option to select different electrical frequencies in Bagby PCD seems to be another variable that can changed to influence values of components and shape of filter curve and is NOT related at all to XO design frequencies.

I think we need a Bagby PCD thread for all Qsn Bagby....
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Old 4th March 2013, 08:44 PM   #84
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Stevenn,
I would partially disagree with the statement of only looking at the acoustical function. What you have to remember besides the slope and crossover point that is not address by only the acoustical function is the electrical phase angle and interaction of the two signals to each device. You really need to read a book like the Doug Self book on electronic crossovers and all the perturbations of crossovers and the interactions of each type. Though the title says active electronic crossover it does directly apply to and is spoken of in the passive implementations also. You would really do yourself a favor reading something that is more accurate than some of what you are reading, it will help you to truly understand all the factors that many here seem to overlook and often not understand. The slope rate is not the most important factor to look at, that is a simple concept to grasp, but it is only a single piece of the overall design. The summation at the crossover point is more important than the slope chosen. The slope can be as high as 100db per octave with a dsp device or as slow as 6db per octave with a first order crossover. Second and third order crossovers have phase relationship problems at the crossover point and that is why many jump to 4th order as that problem of phase alignment are similar to first order without having the overlap of devices in the pass band.
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Old 4th March 2013, 09:10 PM   #85
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Hi Kindhornman, I'm not sure how electrical phase is relevant (except from the point of view that to get the desired accoustic phase the electrical phase will have to be some particular value), surely it is the accoustic phase that is relevant, as it is the sound waves themselves that are adding or subtracting depending on whether they are in phase or not.

If accoustic measurements are used in the simulation (or phase is derived from a traced SPL using a hilbert transform) and attention is paid to that phase (see the example I posted earier) then the summation at the crossover should be fine. (and noted depending on the order of the crossover there will be differences in the phase tracking).

Depending on the order of the crossover the phase shift will be different. with 90deg per order being the norm. Perhaps the example I gave earlier is only relevant to 4th order. Certainly the original 2nd order crossover I had had no where near as good a phase tracking, but then I didn't spend the time optimizing it like I did the 4th order.

So maybe it is a semantics issue. Yes the the electrical order is important, in that you need to get it right to hit your correct acoustic target, but if the acoustic target is what you concentrate on, then the electrical side should sort itself out

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Old 4th March 2013, 09:55 PM   #86
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Wintermute,
You may not have realized that by using the 4th order LR filter function you took care of the phase problem fairly well at the crossover point as you would with a first order filter. But if you used a 2nd or 3rd order electrical filter you can not get there in the acoustical response, that is my point exactly. The phase shift of 180 degrees with a 2nd order requires inverting one of the devices and then you still have the time shift at crossover and the 3rd order will give you 270 degrees of shift and that is impossible to correct with any method. Yes the slope is greater so the overlap is much less and so the apparent problem appears less, but you can't fix that acoustically. The 4th order filter is 360 degrees out of phase and you know where that gets you, it is no longer a real problem. Then we have to look at all pass filters and everything else such a Bessel filters and all the rest. It is much more complicated than just looking at part of the problem, that is what I am alluding to here. I wish it was as simple as some want to make it out to be, but it just isn't the case in reality if you dig deep enough.
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Old 4th March 2013, 10:11 PM   #87
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Kindhornman all that may be true, but sometimes near enough IS good enough and most of our attempts are better than the stuff you can buy. Not all of us are after perfection, a close approximation suffices sometimes
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Old 4th March 2013, 10:40 PM   #88
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MoonDog,
I am in agreement on that. After you look at some of the extremely simple and crude crossovers using electrolytic capacitors and ferrite core inductors with 22 gauge wire at best it gives you pause doesn't it!
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Old 5th March 2013, 12:16 AM   #89
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From the man himself:

"The target transfer function is completely separate and independent from the crossover circuit. The purpose of the target is simply to provide a line on the graph you can "target" as you dial in the crossover values. It may only take a second order electrical filter to achieve a 4th order target when the driver's response is included. They do not have to be the same order.


The crossover frequency that is entered is only used if you have the program calculate textbook values, otherwise it is not used at all. By the way, textbook values are not usually very useful.


Jeff
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Old 5th March 2013, 09:37 AM   #90
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Hi Steve, yes that sums it up nicely. textbook crossovers assume a resistor for impedance (whereas a driver varies) and ruler flat frequency response.

KindHornman, I have to admit I struggled getting good phase tracking with my second order version of the crossover. I put it down to the problems I was dealing with with the midbass' response curve, but it could well be otherwise. I had a bit of a play today to try and make it better but didn't get very far.

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