Yes exactly and prefer 6 db whenever possible if one can get away with it as in most of the Apogee line
Absolutely the crossovers must be first-order to preserve phase and amplitude response. I’ve read recommendations for second and third order crossovers for Apogees before in various forums. Play with that all you want but the result will not give the coherent naturalness that Apogees are capable of with first order filters.
Yeah, but most all of the Apogee models are not first-order crossovers. Stage, Caliper, Duetta, Diva, all are at least second-order crossovers.
Regardless, even the first-order crossover models do not achieve any sort of (acoustic) phase coherence. The transducers and their layout are just way too big. "Phase coherence" is pretty much a marketing term.
Dave.
Stronger magnets will change the Q of the fundamental resonance. It will lower the Q and reduce the low bass compared to the original magnets and tuning of the diaphragm.
Dave, The story on Apogee crossover slopes is actually more involved than we're discussing here.
For starters here's what the 1986, 1989, and 1990 brochures said about crossovers for the various models made in those years (these are cut-and-paste quotes):
Full Range:
“Dedicated active crossover with seamless
6 dB per octave slope”
Scintilla:
“Seamless 6 dB per octave slope, internal
passive crossover. A dedicated active
crossover is optional”
Diva:
“Step-adjustable seamless 6 dB per octave
slope, external passive crossover. A dedicated
active crossover is optional:”
Duetta Series II and Signature:
“seamless 6 dB per octave slope, internal
passive crossover. A dedicated active
crossover is optional”
Caliper:
“Seamless 6 d8 per octave slope, internal
passive crossover”
Stage:
6 dB per octave, gradually increasing to 12 dB per octave”
DAX Active Crossover:
“6 dB per octave, gradually increasing to 12 dB per octave”
Marketing hyperbole? Maybe, but they are consistent year-to-year, model-to-model.
I too have seen the additional reactive components in the passive non-bi/tri-amplified speakers. Some of these cases were frequency shaping that was not directly involved for the crossover function. Other times, such as in the Diva's woofer low-pass filter, Spiegel may have been compensating for the beaming that the woofer would exhibit a few octaves above the crossover, by introducing a second pole to compensate for the zero added by the beaming. The combined electromechanical effect might have thus been very approximately first-order at crossover.
The DAX active crossover (which I used with my Divas, modified) definitely was first-order, but it "gradually increased to 12 dB per octave" (second order) several octaves on either side of the crossover, so as to not have much impact on amplitude and phase at crossover. This would be to protect the drivers from excessive out-of-range amplitudes and comb filter effects with other drivers. The degree of toe-in plays into the crossover behavior, too. It does get complicated.
My Full Ranges use the original Apogee passive line-level crossover that is definitely textbook first-order. By the way, I added input and output buffers to that crossover to very good effect. I think you (if I have the right Davey) did that too years ago, right?
My main issue is when people willy-nilly suggest 18 dB per octave or 24 dB octave crossover filters for these Apogees without considering the effect on waveform integrity.
These efforts from Apogee shows the art combined with solid engineering that Bloom and Spiegel were capable of.
I agree that "phase coherence" is mostly a marketing term, and real speakers in real rooms greatly depart from the ideal. But most multi-cone speakers are so bad at phase response that they shred any semblance of pulses and square waves. The proper rasp of brass or the reedy tone of woodwinds is damaged. When a speaker approximates phase coherence, as the Apogees do, our ears recognize and welcome the transparency and natural timbre, even if it's not perfect
By the way, a true line source that spans from floor to ceiling actually makes use of the floor and ceiling reflections in an advantageous way, by extending the line source as though it were starting at an infinite distance below the floor and going up to an infinite distance above the ceiling, like a house of mirrors. This case resolves any reflection problems to an ideal. A true line source eliminates the floor and ceiling from the equation. My 80" tall speakers are in a 12 foot high room, so I have a gap in that ideal, but the approximation is there. Also, since dipoles do not radiate energy to the sides, any reflections to the sides are less problematic. The combined line source and dipole effects actually make it more possible to enjoy something like coherence because the speaker's radiating pattern is closer to ideal compared to point-source cone speakers. The distance to the wall behind the speakers must be large so that the reflected sound from the back wall is delayed enough to be perceived as reverberation rather than mucking up the direct sounds.
Fun stuff...
Yeah, I'm aware of all that. I've looked at the networks of all these speaker models (even the active network in the big Grand's) and understand how they work.
The "seamless 6db increasing....." is just marketing-speak for a second-order network with low Q. I don't have anything against marketing, except that audiophiles make a lot of incorrect assumptions based on marketing.
BTW, there are numerous editions of the DAX crossover. Not all of those are first-order slope. (I've repaired a number of them for Apogee users.)
Floor to ceiling line-sources are still not phase-coherent. You are most likely listening in the near-field with any speaker like that, such that the distance from your ear to the center of the line is different than the distance to the top (or bottom) of the line. That's an inherent comb-filtering effect and definitely not phase coherent.
If waveform integrity is an objective, Apogee's have numerous problems......just like most any other speaker.
Dave.
The "seamless 6db increasing....." is just marketing-speak for a second-order network with low Q. I don't have anything against marketing, except that audiophiles make a lot of incorrect assumptions based on marketing.
BTW, there are numerous editions of the DAX crossover. Not all of those are first-order slope. (I've repaired a number of them for Apogee users.)
Floor to ceiling line-sources are still not phase-coherent. You are most likely listening in the near-field with any speaker like that, such that the distance from your ear to the center of the line is different than the distance to the top (or bottom) of the line. That's an inherent comb-filtering effect and definitely not phase coherent.
If waveform integrity is an objective, Apogee's have numerous problems......just like most any other speaker.
Dave.
@Brian Beck; Brian when you had the Divas did you ever measure the impedance and sensitivity of the TW ribbon ?
I think the difference here is between coherence (in the objective sense) and "coherence" (in the subjective sense.) I can't argue with on the latter, but I could certainly make an argument on the former.
All other things being equal, I would agree better waveform fidelity is advantageous. But, all other things are never equal.
If waveform fidelity is 'really' high-priority, it's probably time to switch to headphones.
Dave.
PS: I would like to comment on something you said that is factually incorrect and is not well understood by most audiophiles: “the distance from your ear to the center of the line is different than the distance to the top (or bottom) of the line. That's an inherent comb-filtering effect.”
No, a comb filtering effect is a periodic series of dips and peaks in the amplitude response as a result of fixed delay(s) in the time domain. A line source is a smooth and continuous emitter and generates no fixed delays nor any comb filter effect. A line array with numerous stacked drivers, like so many high-end speakers use, can generate a comb effect, but not a continuous ribbon.
Furthermore I think you’re misunderstanding the vector math that takes place with a long line source. This is especially true when you sit close because that better approximates the infinite ideal relative to the listener. Any arbitrary point on the ribbon, say 2 feet above your ears, produces a vector of sound in the direction of your ears. But there is a corresponding point which is the same 2 foot distance below your ear that also produces a vector in the direction of your ear. Both individual vectors have components in the X, Y and Z axes. But these two vectors add to produce a vector that exists only in the X/Y plane (horizontally), cancelling out the Z axis. Every point above your ears on the line source is matched by a corresponding point below. There are an infinite number of vector pairs that cancel out the Z direction, and leave only emission in the X/Y plane. So what results? An expanding cylinder of sound that is capable of perfect impulse response in the ideal case, not the mish-mash of various times of arrival that concerned you. The line source is one of the examples of the beauty of symmetry.
No, a comb filtering effect is a periodic series of dips and peaks in the amplitude response as a result of fixed delay(s) in the time domain. A line source is a smooth and continuous emitter and generates no fixed delays nor any comb filter effect. A line array with numerous stacked drivers, like so many high-end speakers use, can generate a comb effect, but not a continuous ribbon.
Furthermore I think you’re misunderstanding the vector math that takes place with a long line source. This is especially true when you sit close because that better approximates the infinite ideal relative to the listener. Any arbitrary point on the ribbon, say 2 feet above your ears, produces a vector of sound in the direction of your ears. But there is a corresponding point which is the same 2 foot distance below your ear that also produces a vector in the direction of your ear. Both individual vectors have components in the X, Y and Z axes. But these two vectors add to produce a vector that exists only in the X/Y plane (horizontally), cancelling out the Z axis. Every point above your ears on the line source is matched by a corresponding point below. There are an infinite number of vector pairs that cancel out the Z direction, and leave only emission in the X/Y plane. So what results? An expanding cylinder of sound that is capable of perfect impulse response in the ideal case, not the mish-mash of various times of arrival that concerned you. The line source is one of the examples of the beauty of symmetry.
I did measure the impedance of the tweeter, but not its sensitivity which requires calibrated microphones that I don’t have and elimination of room effects. I will look to see if I have a plot of the impedance versus frequency somewhere that I can share here.
Brian,
I suggest to consider a test case where a longish line-source is measured free-field in an anechoic environment.......with the microphone in the near field.
Clearly the differing distances from center/microphone to end/microphone will manifest into the measurement as interference dips in the response. This is not the classic example of signal-processing comb filtering, but in the speaker design world many times it is referred to as such.
If my label of it as that causes your academic hair to stand on end, I apologize. I won't use that designation any further.
Dave.
I suggest to consider a test case where a longish line-source is measured free-field in an anechoic environment.......with the microphone in the near field.
Clearly the differing distances from center/microphone to end/microphone will manifest into the measurement as interference dips in the response. This is not the classic example of signal-processing comb filtering, but in the speaker design world many times it is referred to as such.
If my label of it as that causes your academic hair to stand on end, I apologize. I won't use that designation any further.
Dave.
The Diva tweeter is around 1.1 ohms. And, as you might expect, resistive.
The stock Diva crossover has a 3 ohm resistor in series, so its impedance portion in the design isn't too bad. A 3 ohm resistor for a 1.1 ohm driver is a considerable pad, so you can make an estimate of its sensitivity relative to the other drivers.
I built a few Poor Man's DAX Diva crossovers many years ago. Ishfaq (Gallant-Diva) refers to it here (down at the bottom):
https://forum.audiogon.com/discussions/help-with-apogee-diva-crossover
I think he moved onto something else......audiophiles being as fickle as they are.
Anyways, way off the thread topic.
Dave.
The stock Diva crossover has a 3 ohm resistor in series, so its impedance portion in the design isn't too bad. A 3 ohm resistor for a 1.1 ohm driver is a considerable pad, so you can make an estimate of its sensitivity relative to the other drivers.
I built a few Poor Man's DAX Diva crossovers many years ago. Ishfaq (Gallant-Diva) refers to it here (down at the bottom):
https://forum.audiogon.com/discussions/help-with-apogee-diva-crossover
I think he moved onto something else......audiophiles being as fickle as they are.
Anyways, way off the thread topic.
Dave.
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Yes, Dave, I think you’re referring to the boundary condition at the very ends of the line source interfering with the shortest direct radiation. In other words “missing vectors”. Yes this is part of the non-ideal reality of lines sources. This can be mitigated by two things. One is sitting closer to the line source as you suggest (which is the same conceptually as increasing the length of the line). When the “direct” path is close relative to the line length, the higher received amplitude from the direct path of the line can swamp the effect of the farther-away discontinuity. The second mitigation is your ceiling and floor virtually extending the line to infinity, reducing the gap. If the floor is pretty close to the bottom of the ribbon, as it is with the models discussed, there is only a small gap before the reflected image starts. Ideally a lower ceiling that just brushes the top of the speakers is ideal. This may seem counter-intuitive but it’s how the line sources can be made virtually infinite and closer to the ideal. Closer than any point source can be. Acoustat, Beveridge, Soundlab and Infinity used to make floor-to-ceiling speakers to take advantage of this effect. In practice the ear can still take advantage of a non-ideal line source to create magic. I argue more so than with a point source with its many destructive reflections.
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Here is a pretty decent non-technical explanation of line sources:
https://counterstrikess.com/line-source-speaker-advantages/
https://counterstrikess.com/line-source-speaker-advantages/
Sorry, I don't need a non-technical explanation. I'm well aware of how they work and the advantages/disadvantages.
Take a look at Roger Russell's IDS-25 system. THAT's a line-source system for domestic use. Apogee's are a long way from that.
Cheers,
Dave.