Whatcha got against phase plugs, Mark? :)

[chazdrumzalot]

Hi Mr. Fenlon, please forgive my playful thread title but I've been meaning to ask you something. A few times now I've read something from you about how your drivers are "purist single cone designs: no whizzers, no phase plugs" or something like that. Now I understand your beef with whizzers, but why, in your estimation, are phase plugs not compatible with the pursuit of a 'purist' full range driver?

I ask because--I'll admit it!--I thought that a phase plug on one of your CHP drivers would look pretty cool.

[chazdrumzalot]

Ah, here's one example:

Originally Posted by Markaudio

I've put much effort into the Alpair 12's design to deliver detail and dynamics across its range. The Alpair 12 is a single cone/cap design. For a driver of this size, it's rare (possibly current production unique) to have full range delivery with no use of whizzers, phase plugs and alike, all of which have significant design, production and performance compromises.

So I guess I'm curious to know the compromises associated with phase plug designs.

[planet10]

In Mark's designs the dust cap is a significant contributor to the HF extension.

dave

[Bill poster]

Including the new chr70?

[planet10]

The gen2/gen3 dustcap (change from truncated cone to short cylinder with a rounded top) is what allows these drivers their extension to >20kHz)

dave

[markaudio]

Hi Guys,
I should point out that there a potentially many drivers using whizzers and phase plugs that are effective and pleasing their owners. However, during my early cone design experiments, I become increasingly dissatisfied with these secondary elements having identified their operational compromises. This led me to push forward on improving cone technology to the point where it could operate effectively as a pure single point source.

Historically, Whizzers and phase plugs are devices that were designed to assist emitters that had performance limitations. Typically, cones with higher mass and/or a steeper sided profiles were made this way to maintain stability under load but as a result, suffered from poor HF and dispersion performance. As cone design and the related production technology improved, some makers continued with whizzers and plugs as a low cost method to further extend the HF range, reducing the need to invest substantial effort in cone design.

Whizzers are a second source of emittance. Their position front and centre of the main emitting surface creates a mixed patten emanating from the driver, potentially creating a phase differential. Mechanically, many Whizzers create blind areas from around the area of the cone's neck, causing deflection between the cone and rear of the whizzer. Controlling the output from a driver with a whizzer is problematic. Once the input to the driver is increased, the small emitting surface area of the whizzer is less likely cope with the input, audible distortion may result.

Phase plugs in theory, act as a cancellation device between the sections of the cone or whizzer that are angled towards each-other. However, rarely is it possible to tune the plug's contour to completely harmonise with the cone's profile and emittance pattern, the result often a peak of several dB usually occurring in the mid-upper middle region. The other problem that occurs is the air gap between the moving section of the power-train (coil and cone) and the static pole with the plug located on its forward section. Once the power-train is under load, there's no way to totally eliminate the suck-blow effect around the cone neck.

Once a designer elects to make a pure single emittance design and attempt to go "full-range", the design of the cone and the rest of the power-train becomes critical. Note that I've emphasised the word "critical". To make a single cone efficiently emit a wide range, its needs a shallow profile and low mass, neither of which are mechanically or acoustically stable, effectively a designer's worst nightmare. Hence my many hours burning the midnight oil in a lab!

Cheers
Mark.

[chazdrumzalot]

Thanks Mark for that very informative answer!

[markaudio]

Originally Posted by chazdrumzalot

Thanks Mark for that very informative answer!

Hi Chaz,
Glad to help. As said there drivers out there with whizzes and plug that are popular so I'm giving you my "engineers" thinking and approach on this issue. But like so many things in audio, its down to personal taste.

Cheers
Mark.