Beyond the Ariel

[JohnL]

Hello Lynn, I just wanted to mention something regarding the DCX. It's a nifty tool for prototyping and whatnot, but the garbage becomes VERY noticable on a high efficiency system. I'm not one of those people who can hear the third chair violinist scratching his nose on recordings, but the hiss that the DCX adds to my HE system really takes the enjoyment out of listening to it. Now I don't have a modified one, that may take care of everything, but those modifications would have to bring that hiss down a LOT.

[FlorianO]

Originally posted by Lynn Olson

How much headroom? With a 2.5 kHz 2nd-order LR highpass filter, and powered by a 120-watt amp run into heavy clipping for an hour, no damage or specification change to the diaphragm. With a 200-watt amp run into less severe clipping, the driver delivers 121 dB at one metre, again, with only a 2nd-order filter at 2.5 kHz. THAT's the kind of spec I've been looking for.

Lynn,

Are you still thinking CD below or a mid-ranger (wide-ranger ?) that can make it to 2.5 kHz "properly" (any candidate?).

[apassgear]

Lynn,

I have been following this thread with great interest and apreciate all the input and the way you have presented it, excellent work and I may even learn something... just not in this legue tho.

FWIW you may want to read what Thorsten Loech had to say about the Beringer op amps on post 6 on this thread

http://www.diyaudio.com/forums/showt...?postid=205180

[mige0]

Hi

The good thing for test baffles is that you can run tests.
Sometimes the speaker is your device under test sometimes you are the DUT – me myself and I



I have to apologise for my csd – plot in post 797.


What is shows up as a stepped decay there is simply due to low frequency cone excursion out of its linear range.

To make something useful out of my fault for this thread, I run a couple of additional measurements focusing on the limitations in SPL with respect to XO frequency. XO I have chosen to be of the Linkwitz-Riley type at 24 dB.
All measurements were done at zero distance with no EQ applied. Speaker is the same modified Dynaudio 21W54 as before.
To give a taste of real SPL I adjusted the MLS signal to 100 dB A-weighted (300Hz LR-24dB cut).

The measurements compare the test baffle to a heavily damped closed box with 30 liter volume and almost the same front size.

First the 21W54 in the closed box no XO, no EQ smoothed and unsmoothed. The dip at 750Hz is considerably lower than in the OB like predictable from EDGE simulation:






Now the closed box with XO at 100 Hz, 150 Hz and 300 Hz:






It can be seen that the closed box decay of the resonance at 750 Hz smoothes from stepped to linear at around 150 Hz





Now the open baffle at 200 Hz 300 Hz and 400 Hz:





It can be seen that with the open baffle the decay of the resonance at 750 Hz smoothes from stepped to linear at around 300 Hz.



Sure, I could have simulated this with any speaker software as well but its always interesting to have something to visualise.




And living in the Alps I got sort of addicted to that kind of pictures.




Well, it's clouded today and we had fresh snow halfway down last week






Greetings
Michael

[mige0]

Hi

imagine the rudder of a Swissair 747 - although kind of smaller, maybe 1.2 meters high. The top of the rudder is 600 mm across, and the bottom is 850 mm. The top overhangs the bottom by 150 to 200 mm.

Visualize the front of the aircraft facing to the right. Now forget the airplane, just think of its rudder, with the leading edge on the right, and the trailing edge and overhanging portion to the lower left. Remember I am also simulating the floor reflection, so there is a virtual rudder underneath the real one - it now looks like the swept wings of an aircraft, pointing towards the right.

The widerange driver is on the upper right, close to the top surface and right (leading) edge of the baffle. The midbass and bass drivers are mounted more or less in a vertical line below the widerange driver, although I run the Edge simulation looking at the WR driver by itself (1 driver) and also with all 6 drivers running at once. When I look at the single WR driver by itself, I'm not interested in the floor reflection, but am interested in all of the baffle diffraction, including the mirror-image baffle beneath the floor.

If I understood right this is what you described:
Mic position at centre of WR and halfway the baffle height

How much headroom? With a 2.5 kHz 2nd-order LR highpass filter, and powered by a 120-watt amp run into heavy clipping for an hour, no damage or specification change to the diaphragm. With a 200-watt amp run into less severe clipping, the driver delivers 121 dB at one metre, again, with only a 2nd-order filter at 2.5 kHz. THAT's the kind of spec I've been looking for.

Yep, that's really great news!

the garbage becomes VERY noticable on a high efficiency system

It should not be related to the EFFICINECY of your system unless the levels are not set properly??

but the hiss that the DCX adds to my HE system really takes the enjoyment out of listening to it

Sad to hear that!

I imagine by "biasing" you mean the old trick of a pull-down resistor (or current source) to bias the op-amp into Class A.

No, just plain and simple power supply biasing.

At the minimum, they offer a really fast way to tune up a system, and with dipoles being such a freaky challenge to measure, this is very useful to all dipole-fans.

agree 100%

Greetings
Michael

[Lynn Olson]

Originally posted by FlorianO
Lynn,

Are you still thinking CD below or a mid-ranger (wide-ranger ?) that can make it to 2.5 kHz "properly" (any candidate?).

No, I see the addition of a new driver as levelling the playing field between compression drivers and the new class of prosound ribbons. There's the Stage Accompany, and now the RAAL joins the field with what looks to me like a higher level of performance. Plus, we have contributors to this thread who have actually auditioned the SA vs the 1-high version of the RAAL, and preferred the RAAL.

I had quite an interesting conversation with Aleksandar of RAAL, and we compared our subjective impressions of horn, ribbon, and cone driver sound. We were comparing our impressions of the dynamic character of each technology - ordinary 87~92 dB direct-radiators start to noticeably compress around 90~95 dB, sound pretty flattened-out at 100 dB, and at levels below 60~70 dB, multiway systems become murky and confused-sounding.

Aleksandar mentioned that audiophile dome tweeters, as a group, have quite different impulse and CSD responses -60 dB below the usual test levels. The rise times slow down, and drivers parameters change. This failure of the drivers in a multiway system to track dynamically - over a wide range - is why complex audiophile systems sound disjointed and muffled at low levels (background music).

I mentioned that horns, in my experience, exaggerate dynamics, sometimes just a little bit, and sometimes very obviously, when they get into a high-order distortion regime with a compression driver approaches its limits. Aleksandar mentioned that the same thing happens at low levels - there's a dynamic-expansion effect that makes quiet sounds even quieter - and this is quite a different effect than the parameter change and "murk" of auidiophile-efficiency direct-radiators at low (microwatt) levels.

The big issue with ribbons, of course, is limited linear travel in the magnetic gap, along with the possibility of ribbon destruction - or stretching - due to over-excursion from excess power. Much of Aleksandar's work has been focussed on addressing high SPL's without the usual compromise of constraining the motion of the aluminum ribbon by gluing it to stretched plastic film, which substantially degrades impulse response and distortion. The issue with all of these technologies - horn, direct-radiator, ribbons, etc. - is retaining dynamically consistent performance at microwatt and 100+ dB levels.

[MBK]

Very interesting observations re: dynamics. I have heard the argument before wrt high efficiency drivers (exaggerated dynamics) but can't quite imagine a mechanism that would lead to that.

Driver parameters most certainly change with drive levels but that should be happening to any kind of mechanical construction.

[Lynn Olson]

Originally posted by MBK
Very interesting observations re: dynamics. I have heard the argument before wrt high efficiency drivers (exaggerated dynamics) but can't quite imagine a mechanism that would lead to that.

Driver parameters most certainly change with drive levels but that should be happening to any kind of mechanical construction.

Beats me too, but that's what I hear, and I've heard plenty of live acoustic music. I've noticed that phase-plug geometry has an effect on this, so I'm surmising that turbulence effects are involved - no other form of audio reproducer has such extremely small internal acoustic surfaces and transmission paths.

Another interesting topic that arose from the discussion is that horn theory relies on a true plane wave entering the horn, but in practice, the wavefront from a cone driver, or the exit from a CD phase plug, isn't very close to a plane wave. The horn doesn't magically "straighten out" the wavefront - if anything, it gets more disordered, not less, as it makes its way through the horn expansion.

I have heard a horn that was driven with a nearly perfect plane wave. The horn was a large circular Tractrix with a 3" throat, driven by a single JansZen electrostatic element. It basically sounded like you'd expect, a REALLY BIG electrostat with lots of headroom and midbass presence. In tonal terms, no horn coloration at all, but it also had some of the physically forward, in-the-room spatial perspective of large-format horns - quite different than the faraway perspective of a typical large electrostatic panel.

Aleksandar at RAAL had similar experiences with his experimental horn-loaded ribbons - the horns sounded really good, but not the same as the open ribbons, with the most of the difference being a different sense of perspective on the music. That was my take on the electrostat-horn as well - the difference between transported to the musicians, versus the musicians being in the room. Much of this is due to polar-pattern differences illuminating the local environment, but I also suspect the ear is directly sensitive to the shape of the wavefront itself. I suspect a highly curved spherical wavefront is interpreted as coming from a location nearby the listener, and as the listener moves further off-axis, the smooth curvature becomes more disrupted.

In a later conversation with John Atwood, I was mentioning how the large-format Tractrix and Le Cleac'h horns have 90-degree dispersion in the technical sense - they sound good, FR response seems all there, etc. - but the real 3D quality and hyper-vivid tonality extends to about one seat-width. So in effect, the horns have 90 degrees of high-quality sound, but only 10 degrees of super-quality sound. If you're sitting where you can see the entire surface of the driver without obstruction, that's the super-quality zone. (In my experience, at least.) In a really dialled-in top-quality horn system, the best sound is either directly on-axis - looking right smack into the drivers - or just ever so slightly off-axis, depending on how the system was set up. When you sit far enough off-axis so the drivers are no longer visible and disappear behind the curve of the horn, there's a loss of focus and precision, compared to the on-axis (or close to on-axis) listening experience.

JA and I were wondering whether this is an artifact of the rough wavefront entering the horn - it emerges reasonably intact in a narrow beam (where the horn isn't doing much), but gets more disordered further off-axis, resulting in time dispersion and small-scale irregularities in the polar pattern. Cone drivers seem to be the reverse of this - they commonly have highly directional colorations that fall in a narrow 5~10-degree window, and sound smoother, more natural, and less "megaphone-like" slightly off-axis. It's part of the reason I'm considering a 5 to 10-degree slope on the open baffle, with a separate aiming assembly for the tweeter.

It would take an interesting measurement protocol showing impulse response vs off-axis, a sort of 3D waterfall. I think JVC once did this in an early 1980's AES paper, making some interesting graphs that looked like waves breaking on a beachfront. The ribbon/horn had much nicer looking off-axis impulse response than the usual CD/horn, with the mundane dome tweeter looking best, as expected.

P.S. About the Edge simulations - you're getting close, just use a greater rake angle, maybe 200 to 250 mm of overhang, larger drivers (315 mm), even spacing between the 6 drivers, and measure at 3 and 12 meters.

[jirka]

"the difference between transported to the musicians, versus the musicians being in the room" Exactly.

[jirka]

How to make the second but for more listening seats? That is the question.