Sloped baffle

07-06-14: Bifwynne
......The tweeter uses an ultra low mass.....
......Similarly, the mid driver uses an extremely light and strong cobolt/aluminum cone.....

Bifwynne, do you see what's happening here in the Paradigm drivers?? they are being made light-weight, rigid. Which other driver by the very physics of is light-weight? An electro-static panel driver. You make it rigid by putting a stator around it (like Martin Logan & SoundLab). You'll find that the ESL drivers are linear (flat freq response) over a very wide freq range & that really helps make ESL time-coherent speakers. Not all of them but many of them. The cone drivers are all aspiring to become like ESL drivers - light-weight, rigid.
The hope is that the drivers are out of the pix when the signal gets crossed-over.

@Bombaywalla -- got a Q. Do most drivers remain linear through their selected pass-band with respect to time delay. In other words, when pulse testing a speaker, is it just the X-over that causes the tweeter to respond first, followed by the midrange, and then the woofer?

Bifwynne, the x-over is electrical & the drivers are mechanical (the spring & weight analog that was in one of Roy Johnson's papers that Almarg pointed all of us to in a post w-a-y earlier). So, there is some phase delay thru the electrical x-over as the signal gets low-passed, band-passed & high-passed but there are delays thru the drivers themselves as well. The fastest to respond is the tweeter. More delay thru the mid & the most delay thru the woofer driver. Every driver is flat over a certain freq range before it rolls off. How wide that freq range is depends on the driver was made by the manufacturer.

is there anyway to compensate for the time delay phase distortion through the pass-bands of the drivers? Or is that analogous to unscrambling an egg. That is the damage is done ... no fixing it with more passives.

no, I believe that there is no way to fix this - once the transducer has converted the electrical signal to sound pressure it has already imparted its signature onto the sound pressure wave. The damage is done - I cant grab the air in the room & push it back onto the driver to give it one more go-around nor can I take that air in the room & convert back to an electrical signal & push it back into the amplifier for another go-around. Impossible to do. Your analogy of unscrambling an egg is a good one.

Not sure if this hit the point, but I own a self powered Paradigm subwoofer. The sub permits adjustments for loudness and frequency cut-off. But of relevance here, the sub permits phase alignment adjustments and I assure you ... it makes a big difference. Suck-out or no suck-out at the X-over point (35 Hz).

Bingo!! So, you have experienced some effects of phase alignment & seen the dramatic effect of it. You've been holding out on us, Bifwynne! LOL!! :-) OK, so you now know just how important phase is to the bass response. Imagine doing this over the entire audio band? You are now trending towards a time-coherent speaker....
You see something like this in speaker time-domain response measurements in Stereophile & SoundStage where the woofer is in phase or out-of-phase with the tweeter. you can see the suck-out in the impedance & phase curves.

For individual drivers, cone woofers have voice coils and are inductive. So, yes, they do have phase shift as frequencies increase. Some are more inductive than others. Even dome tweeters have some degree of phase shift.

A first order, parallel low pass is an inductor coil with phase shift, typically 90 degrees in the pass band and more beyond. They're cumulative and that's called acoustic slope. In a 2-way, there's also baffle step compensation, which inolves a bigger inductor well into the pass band, causing even more phase shift, maybe another 90 degrees more or less. And that's just first order. Add another 90 degrees for every order over that. Basics 101.

In the next class, we'll discuss capacitors, high pass filters, zobels, notch and contour filters, all involving various degrees of phase shift. Then, on to impedance phase and reactance. Your homework is expected and there will be a test.

@Ngjockey ... let me try to unpack what you just wrote. Let's assume we have a single dynamic cone speaker with a pass band of 35Hz to 20K Hz. Let's forget about high frequency beaming and cone breakup. Just assume this hypothetical speaker has a flat frequency response within its pass band, as measure on axis. Obviously no X-over needed here.

Now ... like all dynamic drivers, we have a voice coil, a spider, magnets, and so forth. Let's focus on your comment about the voice coil being inherently inductive. Makes sense. After all, we have a wire coil moving in a magnetic field, producing voltage and its own magnetic field. The faster it moves, presumably, the more voltage and back inductive reactance to the input signal.

Now, if a complex signal was fed into the speaker, would there be phase shifting with respect to the higher frequencies as compared to the low order fundamentals? To be more specific, say the signal was composed of a 100 Hz fundamental, plus "n" number of harmonics into the high treble. I assume this complex signal could be visually reproduced on an oscilloscope.

If the driver's output was compared to the input signal, would there be some sort of harmonic difference between input and output signals? Would the speaker's lack of inherent phase coherence be the cause of this distortion? Would this phase nonlinearity be caused by the inductance resulting from the voice coil moving in the speaker motor's magnetic field??

Let's assume the answers to my questions are -- yes?? Is there a frequency range where a speaker is phase coherent, or does phase nonlinearity increase as a function of frequency ... period??

If the answers to all of these questions are -- yes, then it seems to me using 1st order X-overs and sloped baffles is at best a rough justice engineering response to a problem that is inherent with dynamic speakers that use voice coils.

So ... where do we go from here?? Magneplaners, ESLs??

Cheers.

P.S. Bombaywalla and Al, feel free to chime in. I think I'm getting tangled up in my shoe-laces.

Bifwynne,
I would very much like Roy J to jump in here & answer your question.....
Meanwhile, have you read Roy's white paper on "Time & Phase Coherence" on his website?
http://greenmountainaudio.com/time-and-phase-coherence/
when you read this paper, skip the initial part & read this section titled "Time Coherent Speakers". You'll see the response of the individual driver & how they add up in a time coherent speaker.
Then scroll past the rest of the material & read the section titled "Where a speaker goes wrong". I *think* you might get many answers (maybe not all) to your questions. Thanks.

Thanks Bombaywalla. I read Roy's White Paper, but will re-read the sections you suggested.

Meanwhile, I just checked Stereophile's bench test report of the Maggie 3.5R and see that it is not time coherent. In fact, JA speculated that the midrange was connected in reverse polarity to the tweeter and woofer. I assume similar characteristics for the 3.7i.