They are not tuned to your room, but "focused" to your listening position via moving the mid and tweeter in the C-2 and new C-3. You are setting what we call the "Soundfield Convergence" for time coherency at your seating spot. This is done with a tape measure and takes a few minutes max.
The phase response of the C-2/C-3 will thus be- by definition- compromised everywhere else. But by many HUNDREDS of degrees less than speakers with higher-order crossovers.
We do note that with a first-order crossover, off-axis comb filtering does not seem to be an issue except on test tones and pink noise.
Moving completely up and out of the main listening plane (where off-center listening was still fine), we hear the depth of field decreasing, as the time domain becomes progressively "warped" from bass to treble. But at least there are no sudden "jumps" in the relative acoustic phase from driver to driver as there are with high-order crossovers, no "twitchiness".
Standing up, the time delay warp across the spectrum is still far less than with high-order-crossover speakers. We do not hear the soundfield degenerate into "a wall of sound"- plenty of ambience remains.
High-order designers are getting better at smoothing out the abrupt jumps in phase- for less "separate tweeter-separate woofer" effect.
They are also getting better at damping the ringing present in the highest-order crossovers, but the result is a hard load on the amplifier.
What you hear from the smoothing and damping is less image depth, less dynamic impact, and less rhythmic definition (finesse) anywhere around those crossover points. Which is why, quite often, the approved "audiophile recordings" used to demonstrate them are so bland performance-wise. Not much there to challenge the speakers. Something aggressive won't be pleasant- no Zappa allowed...
I noted in some postings above, references to the possible lack of phase shifts in minimal-driver speakers- single panel electrostats, Jordan module, Lowther, etc.
In a single driver, phase shift won't be caused by an electrical crossover- there isn't one!. The signal remains free of crossover parts distortions/haze too.
However, any driver has mass, suspension, and damping (by the suspension's resistive losses and the amplifier). Thus it is a "damped harmonic oscillator"- in a Physics 101 book.
A harmonic oscillator has a 1/4 wave's worth of time-delay down at its low-frequecy resonance, compared to the midrange tones. For a sealed woofer with -3dB at 40Hz (close-mic'd measured), that means 1/4 of 1/40th of a second, or 1/160th of a second=6.25 milliseconds. That doesn't sound like much time delay, but it is ~7 feet of distance, at the speed of sound.
Put two microphones on a piano- one for the left hand, one for the right; both equally close to the strings/soundboard. Now, impose 6.25 milliseconds delay between those two mics- that is, between the lowest notes and the mid-scale notes.
Imagine what the piano would sound like if the right hand tones got to the microphone seven feet sooner than the left hand's lowest notes, because that's what's happening as you slide down the scale for ANY loudspeaker- and it's a gradual change in phase, which is why we don't complain too much. Any driver does this- headphones, Walsh, electrostats, Lowthers...
A damped, harmonic oscillator also has a high-frequency limit, imposed by its moving mass- which equals phase shift in the highs, or time delay.
It has phase shift in the low frequencies, because it has mass bouncing on a suspension (it's a mass/spring system), as described above.
And since it cannot be an infinitely-rigid cone, it has cone breakup too, which imposes a ragged phase error across the roll-off region, a raggedness that changes with loudness too.
If it has a whizzer cone for the highs, like a Lowther, then there is a time-delay (phase shift) between cone and whizzer, seen as a wiggle in the driver's impedance curve. At that mechanical crossover frequency, the idea is that the cone stops moving as the whizzer starts moving.
Yet the amount of time delay between those two parts is far more than some electrical crossovers would've imposed. Even as the whizzer moves, the cone is also breaking up- parts of it "rattle on" in non-pistonic motion, so the phase change is not smooth with frequency.
Finally, since the forward edge of the whizzer is un-terminated (not damped or otherwise constrained), it has its own breakup modes. Which makes complex, loud, high tones sound hazy, fizzy, fuzzy or dirty (depending on the whizzer's breakup modes).
Any mechanical transistion also changes its characteristics with loudness, humidity (possibly) and aging of the materials. You are asking a piece of paper, plastic or glue joint to flex, predictably, for billions of cycles (per week), and flex in a completely linear, proportional manner on the very softest sound and the very largest- often simultaneously.
A mechanical transition is also happening at the leading and trailing edges of the ripple moving down a Walsh driver, or spreading out across the face of a Manger diaphragm. It is hard to find driver materials that do not change very much in flexiblity with age, or humdity, or loudness- which means the designers of those two drivers were truly ingenious to get as far along as they did. What those drivers offer is minimal phase shift in their mid-bands- which is good. But neither one can handle low bass, nor is very sensitive.
To check the transistion to whizzer (happens in the high-voice range), see if something abrasive such as Janis Joplin, can be tolerated in that tone range. Then listen to her on a good headphone (has no phase shift in that tone range). The whizzer transistion could be apparent on massed, loud strings- as wiry, steely, or strident- it all depends on where that mechanical crossover point is in the tonal scale, and how much you aggravate it.
No single driver can cover the whole audible range including low bass, unless it is a large single-panel driver, for which you have to sit exactly in the middle- exactly.
The Lowther drivers and Jordan 5" drivers do have some bass, but not enough to balance out the voice-range when listening > 10 feet away, and they have loudness restrictions: Their high efficiency comes from low moving mass, due to a short voice coil = minimal stroke available for midbass and lower tones. Look up the x-max specs on the drivers- you'll be surprised.
If a design has a mid cone with no electric crossover, yet the tweeter does, then at the acoustic crossover point, you have:
the electrical phase shift of that tweeter's circuit,
plus the phase shift caused by the tweeter's having its own low-end resonance,
plus the phase shift and ringing at the mid cone's breakup modes(indicated by wrinkles in the impedance curve of that mid driver),
plus the emf sent back into the amplifier from those extra cone oscillations, which gets into the negative feedback loop.
If you have ANY kind of frequency-response roll-off, then you have phase shift (time delay) that gradually comes on as you approach those roll-off points, no matter what object in your stereo, or in the recording studio you examine- amp, mic, mixer, A/D & D/A converters, analog tape recorders, disc-cutting lathes.
But all those devices have very little phase shift in the main part of the audible range. What they do impose comes on gradually, octave by octave, as you approach the devices' -3dB points, with the exception of certain microphones, like a Shure SM-57/58, that have a ragged phase shift in the sibilance range- lending a hard edge to the voice, often intentionally employed by the recording engineer.
It is the speaker's phase error vs. frequency that is much higher than anything else in the recording/reproduction chain. It is caused by high-order electrical or mechanical crossovers that "twist" or warp the phase in the mid-bass or low treble- wherever those crossover points are. It is caused by cones breaking up (or going soft, ala KEF and B&W) in the middle of their range, before they even get close to crossing over to the next driver. It is also caused by the drivers not being the same acoustic distance from the ear.
To find out what effect any crossover (mechanical or electrical, or combination thereof), has on music, listen to simple sounds that move through those frequency ranges- there you lose depth, clarity and dynamic expression. Also listen to a lot of musical instruments in person, up close, perhaps at a music store on a slow afternoon. Talk with the store's percussionist- let him show you why musicians pick certain cymbals, bell-trees, drum kits, sticks, mallets. Have the guitar person play you some differences in his gear.
Any speaker designer worth his salt needs to know, quite intimately, what goes on in the studio, in the musician's hands. After all, that's what needs to be heard on the other end.
Roy Johnson
Green Mtn. Audio
