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Old 18th September 2010, 01:36 AM   #121
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My position remains, that if there is more than one filter poll in the signal path, the network it is not 1st. order; it is higher, irrespective of whether it is phase coherent or not.
This is the wrong position to take. My topic is about electric crossover order. This can be 1st,2nd 3rd etc The problems you get with phase deviation at the extreme ends of the response are different from that of combining 2 drive units together.

Why do you criticise 1st order crossovers for inadequate protection when even 4th order has problems? Any speaker has a specific polar pattern which is fixed. How can a fixed polar response mimic what we hear in real life? It cannot!
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Old 20th September 2010, 12:35 AM   #122
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Default Not Fixed!

All filter networks have "problems" particularly when they are interposed in the low but variable impedance circuit that connects the power amplifier to loudspeaker driver(s). A HP filter with 24 db/oct slope will adequately protect most MR and HF drivers. The reasons for doing this have already been outlined in several earlier posts, so there is no need to repeat them here. However, it should be noted, that it is not clear, that the phase coherence in the drive signal, gained by use of a single poll, 1st. order filter, is worth the trade of increased IM distortion and reduced driver protection, particularly when the drivers themselves do not exhibit a 1st. order response as well. In fact to get phase coherence at the acoustical output may require a high order filter network that has a phase incoherence that offsets that of the drivers.

Driver polar pattern narrows as signal frequency increases. The onset of this narrowing is determined firstly by driver diaphragm size. If the baffle in which it is mounted in is not flat (including horn), this pattern will be altered but will still exhibit narrowing with frequency increase. There will always be some degree of pattern mismatch because of differing diaphragm sizes between LF, MF and HF drivers, particularly when they are operated in the crossover region where driver outputs overlap. Here LF/MF or MF/HF driver pairs, when operated in these regions, will have opposed (narrow vs. wide) polar responses. An acoustic lenses and/or CD horns may be used to mitigate this problem. I see this mismatch as a much bigger problem than pattern anomalies that may be generated between drivers by the crossover alone.

Regards,

WHG
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Old 20th September 2010, 01:27 AM   #123
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Default Mayday

Quote:
Originally Posted by dlr View Post
My understanding of this forum is that anyone may discuss any aspect of any multi-way loudspeaker system at whatever level one wishes to include debate on previous work. The only limitation is appropriately "Conventional loudspeakers with crossovers".


The operative word is "may". Many problems may arise. The key is designing to minimize such for the goal desired. Things that may arise do not preclude a design that minimizes them, to include out-of-band signal issues. Even first order if done right. Then the question becomes is it audible during the intended usage. All systems reach a level at which they will distort.

Critique is quite common. Besides, you have already indirectly, though significantly, critiqued the basis of the works of others such as Dunlavy without reservation.

Dave
Hi Dave,

The use of the word "may" is appropriate here, because consequences are dependent on the signal content of the program being reproduced, and the setting of the level (volume) control in the system used.

My intent is to critsize no one. I will take issue with misnomers and try to provide useful information concerning audio systems design, irrespective of thread or technology ownership. When appropriate, references to the work of others, that I am aware of, will be given to guide those pursueing audio perfection.

Regards,

Bill
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Old 20th September 2010, 01:29 AM   #124
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Originally Posted by whgeiger View Post
However, it should be noted, that it is not clear, that the phase coherence in the drive signal, gained by use of a single poll, 1st. order filter, is worth the trade of increased IM distortion and reduced driver protection, particularly when the drivers themselves do not exhibit a 1st. order response as well.
Not clear, no. That may not be the goal. Yours obviously is different than many others. The issues you raise can be mitigated with good driver selection and design. It does take more care and the drivers certainly are taxed more. But that's a design decision.

There is another benefit to Butterworth, first or third, that I mentioned to which you failed to respond. If one's goal is a passive system, there is a distinct difference that may make the Butterworth better than any other passive system. That is the power response. This can have an easily measured difference on the order of 3db in the crossover region. As such, since even a first order system that varies in the stop band is still essentially first order in and around the crossover area, the power response is essentially that of a true first order system. You may not think this to be a benefit. Others just may find it better, despite other "possibly audible" issues.

For reference let me point to the article by John K on power response. For a passive system, there is no system with a better power response than an Butterworth if the drivers are not coaxial/coincident. Note that in every case, the higher order L-R has a worse power response than does the Butterworth one order below. It may be that the better power response of the first order Butterworth is more audible than the other issues of concern, so it's not clear that any crossover type is better or worse than others, since it depends on the goals of the designer.

From John's page:

Quote:
Second, the power response for the odd order Butterworth crossovers is constant in all cases. Third, the power response for the inkwitz/Riley crossovers shows a notch at the crossover point. Fourth, the characteristics of this notch are dependent on the order of the rossover and the separation of the drivers (not shown) and the depth of the notch can actually be greater than 3dB.
Dave

Last edited by dlr; 20th September 2010 at 01:31 AM.
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Old 20th September 2010, 03:11 AM   #125
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Default What's Audible? vs. What's Inaudible?

If a claim is to be clear and certain, then it requires quantified comparative evidence to support it. Anecdotal testimonies won't dispel doubt. There is not even industry consensus that phase incoherence in a typical higher order crossover is audible.

What are the criteria being used for driver selection? There are tradeoffs being made here as well to support the shallow high pass slopes used, particularly bandwidth vs. efficiency that intern effect rise times, overshoot, ringing and transient response of the drivers selected.

As the polar response of all drivers narrows with frequency, matching polar response between drivers in the crossover region is not possible unless a acoustic horn or lens is used; and even then, the results may be of marginal benefit.

In the case of uniform power response, out of necessity, on axis intensity (SPL) will rise with frequency due to the resulting frequency dependant concentration of constant power across a diminishing wave front. I suspect the acoustics of the listening space will determin if this is benificial.

If you pose a question to me, and I read it, I will probably answer it. However, you can forget the suggestion that I am avoiding an issue you raise and that somehow that omission diminishes credibility. I answer several post here most every day and I suspect from time to time I will miss a few. In those cases, a kind reminder will suffice.
Regards,
WHG
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Old 20th September 2010, 12:57 PM   #126
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My point is that from the beginning your responses in regard to the benefits of first order vs. others, the origin of the thread, seemed to be not much more than to dismiss first order without indicating that there may be benefits, with comments such as
Quote:
high pass filters with slopes of 6 db/oct do not afford the required protection
Quote:
the pursuit of "1st. order loudspeaker systems" is like Ponce de Leůn seeking the Fountain of Youth
Is any of this obvious? I would say no and I'm sure were Dunlavy still around he would have quite a bit to say in disagreement as well. First order has limitations as do all systems. One needs to know them and take them into account and I suspect that sort of input may be what the OP was seeking.

With regard to tradeoffs, of course they are being made. That was an early point of mine, but done in a way to indicate that they do not preclude a good system of what is considered to be a first order system. Your approach as I read it is to maximize response from the selected drivers and do so in the digital domain. Fine. Do you think that this is the input being sought by the OP? Possibly, but I suspect not.

Now I may be wrong, but it appeared to me that your input had the result of being dismissive of first order due to your preferences, whatever that may be, rather than simply stating the benefits or demerits in an informative way to allow the OP to make a decision based on the input. Your comments quoted above are an indication. That seemed to be your focus and to me is not being helpful to someone who may be interested in a first order system as even most in the industry use as a term of reference to those systems.

I certainly agree with many of your statements, but I don't agree with the dismissive approach.

Dave
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Old 21st September 2010, 12:04 AM   #127
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There are some practical issues I think you guys should consider in all this.

First order networks sum to flat only when there is 90 degree phase shift between sections. This guarantees asymmetry of polar response. Response will sum higher than flat in one direction and fall into a hole in the other direction (of the vertical polars). If the choice is between asymmetry near the listening axis vs. a power response hole, then I would choose the symmetry of Linkwitz Riley approaches every time.

Low slope means high overlap or more octaves before a driver has faded enough to not cause off axis response ripple. There was an interesting paper by (I think) Glynn Adams formerly of B&W where he tried extremely high slope digital crossovers with imperfect summing. They had deep holes at the crossover frequency but when the holes got narrow enough they became inaudible.

When considering first order filters we have to be referring to the combined acoustical response of driver and network. Since most of our drivers will be falling off at a second order or higher rate at some frequency, then we canít maintain a first order roll off much below resonance. If response is low enough at that point then the system response might not be impacted, then again, it might. If natural rolloffs are near the crossover point you will need to boost response. Good luck doing this with a passive network.

A first order rolloff isnít as simple as putting a capacitor in series with a tweeter. A low order crossover will have large interaction with the driver impedance. Conjugating the driver impedance at resonance would be a minimum requirement. Higher order passive networks give more degrees of freedom and a better control of response.

Regarding Dunlavyís comment, he was obviously talking is simple terms to a journalist. He was also disregarding the distinction between electrical filtering and acoustical response filtering, although Iím sure he understood the distinction. With conventional networks, first order is the only solution, but more complex solutions are out there, subtractive networks (with perfect drivers) would one example. The one that Dennis H. offers seems to be another good example. The fact that response is only 1st order through the crossover region is immaterial. The underlying goal isnít strictly to be first order, but to achieve the phase linearity that a first order network can offer.

David S.
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Old 21st September 2010, 01:32 AM   #128
dlr is offline dlr  United States
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Quote:
Originally Posted by speaker dave View Post
There are some practical issues I think you guys should consider in all this.

First order networks sum to flat only when there is 90 degree phase shift between sections. This guarantees asymmetry of polar response. Response will sum higher than flat in one direction and fall into a hole in the other direction (of the vertical polars). If the choice is between asymmetry near the listening axis vs. a power response hole, then I would choose the symmetry of Linkwitz Riley approaches every time.

Low slope means high overlap or more octaves before a driver has faded enough to not cause off axis response ripple. There was an interesting paper by (I think) Glynn Adams formerly of B&W where he tried extremely high slope digital crossovers with imperfect summing. They had deep holes at the crossover frequency but when the holes got narrow enough they became inaudible.

When considering first order filters we have to be referring to the combined acoustical response of driver and network. Since most of our drivers will be falling off at a second order or higher rate at some frequency, then we canít maintain a first order roll off much below resonance. If response is low enough at that point then the system response might not be impacted, then again, it might. If natural rolloffs are near the crossover point you will need to boost response. Good luck doing this with a passive network.

A first order rolloff isnít as simple as putting a capacitor in series with a tweeter. A low order crossover will have large interaction with the driver impedance. Conjugating the driver impedance at resonance would be a minimum requirement. Higher order passive networks give more degrees of freedom and a better control of response.

Regarding Dunlavyís comment, he was obviously talking is simple terms to a journalist. He was also disregarding the distinction between electrical filtering and acoustical response filtering, although Iím sure he understood the distinction. With conventional networks, first order is the only solution, but more complex solutions are out there, subtractive networks (with perfect drivers) would one example. The one that Dennis H. offers seems to be another good example. The fact that response is only 1st order through the crossover region is immaterial. The underlying goal isnít strictly to be first order, but to achieve the phase linearity that a first order network can offer.

David S.
All very good points, a number of which have been covered. Regarding passive systems, this is certainly more than most DIYers would do, but consider this Dunlavy system:

Quote:
Frequency response: 25Hz-20kHz, Ī0.5dB (approx. -3dB at 20Hz). Acoustic phase response: less than +1 degrees, -2 degrees, 100Hz-10kHz. Sensitivity: 91dB/W/m (2.83V RMS). Nominal impedance: 5 ohms. Minimum impedance: 3 ohms. Maximum impedance: 7.5 ohms (including bass resonance). Radiation pattern: symmetrical in both vertical and horizontal planes. Low-frequency damping: Q = 0.6 (with initial rolloff of 6-8dB/octave). Crossover design: minimum-phase type (6dB/octave) compensated for driver response anomalies and resonance/phase variations. Harmonic distortion: less than 0.3% for an spl of 90dB at 1m for all frequencies above 40Hz. Power handling: approximately 250W peak for 10ms.
Extreme, admittedly, but a real system backed up by measurements.

Step response on tweeter axis:
Click the image to open in full size.

Just one example. Extreme, yes, but proof that it's not just academic? Also yes.

Dave
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Old 21st September 2010, 04:30 AM   #129
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Default Its Magic

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Originally Posted by dlr View Post
My point is that from the beginning your responses in regard to the benefits of first order vs. others, the origin of the thread, seemed to be not much more than to dismiss first order without indicating that there may be benefits, with comments such as

Is any of this obvious? I would say no and I'm sure were Dunlavy still around he would have quite a bit to say in disagreement as well. First order has limitations as do all systems. One needs to know them and take them into account and I suspect that sort of input may be what the OP was seeking.

With regard to tradeoffs, of course they are being made. That was an early point of mine, but done in a way to indicate that they do not preclude a good system of what is considered to be a first order system. Your approach as I read it is to maximize response from the selected drivers and do so in the digital domain. Fine. Do you think that this is the input being sought by the OP? Possibly, but I suspect not.

Now I may be wrong, but it appeared to me that your input had the result of being dismissive of first order due to your preferences, whatever that may be, rather than simply stating the benefits or demerits in an informative way to allow the OP to make a decision based on the input. Your comments quoted above are an indication. That seemed to be your focus and to me is not being helpful to someone who may be interested in a first order system as even most in the industry use as a term of reference to those systems.

I certainly agree with many of your statements, but I don't agree with the dismissive approach.

Dave
I will stick to the attribution of systems, and not those that design and build them. From microphone to media and then on to a loudspeaker, the system that delivers the music to us is not 1st. order, nor are the instruments that produce it, and the ears that hear it. But, how amazing it is, that the facsimile can be so real, despite our efforts to improve it.
Regards,

WHG
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Old 21st September 2010, 06:08 AM   #130
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Quote:
Originally Posted by whgeiger View Post
I will stick to the attribution of systems, and not those that design and build them. From microphone to media and then on to a loudspeaker, the system that delivers the music to us is not 1st. order, nor are the instruments that produce it, and the ears that hear it. But, how amazing it is, that the facsimile can be so real, despite our efforts to improve it.
Regards,

WHG
I can not for the life of me see any sense in what you wrote! They are also not 2nd, 3rd or 4th nor are they digital! So what has 1st order got to do with your statement. Maybe I missed something.

Terry
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