Beyond the Ariel

[Graham Maynard]

Hi Michael again

In post#1546 you make another very valid point which Lynn has separated to fine front and coarse grained spacial behavior.

When I have used round edging to optimise reproduction on baffle/driver axis, it has led to an increase of error the moment you move off axis, like intensity concentration rings around a poorly fucussing torch beam.

I find this change more distracting than the frontal advantage gained, and thus short, thick, fine piled carpet remains my surface wave limiting preference.

Cheers .......... Graham.

[mige0]

Hi

I'll be measuring and auditioning the 18Sound 12NDA520 and 8NMB420 on a large flat baffle, like a door.

I've found that speakers with narrow-width directional artifacts have quite poor image quality and odd, hard-to-pin-down colorations. These are evident on measurement as ripples that zip up and down the spectrum as the microphone is slowly swept in an arc across the frontal listening plane.

Lynn, I am not sure if your approach " measuring and auditioning.... on a large flat baffle, like a door." will reveal what you are searching for.







The simulation shows a 220mm speaker in a baffle the size of a door – on axis to 45 deg off axis on 5 steps.

You can see that right in the most sensible region there are heavy disturbances.
Maybe if you make a CSD and window out the arrival of the edge diffraction but this most likely will be of little value to judge a speakers performance ?

Also here a smaler baffle - remember the roughly 2.5 times the speaker diameter rule of thumb - will perform better.

Greetings
Michael

[Graham Maynard]

I found some interesting reading here from links on fullrangedriver.com

http://www.spiritone.com/~rob369/audio/audio_index.htm

http://www.google.com/patents?vid=USPAT6334505

Cheers .......... Graham.

[mige0]

Hi

The reason I make this distinction is because with a conventional speaker we can apply edge treatment to attenuate the contribution from the edge scattered wave but if we do that with a dipole then we are messing with the dipole response.

JohnK, I have a feeling that I didn't get this " messing with the dipole response " completely.
By " edge treatment " do you refer to a lossy ( mesh ) edge or to the thickness of the baffle at the edge or to an unsymmetrical edge shape ?



-----------------------

The midrange was handled by two eight inch Vifa polycone drivers on each side (very smooth response) that were hanging from crosspieces by their magnets (and possibly screwed to the side panels) - no baffle board at all , and in between them was a Scanspeak one inch dome tweeter.

Graham, this is exciting.
Sadly I didn't find anything else about Alfred Duppke's design when I ran Google.

Greetings
Michael



Greetings
Michael

[mige0]

Hi




To overcome the restrictions with the wired FR of large baffles one way might be to provoke diffraction close to the speaker by abrupt truncation of a ( rectangular ?) wave guide for example and retaining the low frequency sensitivity by the several times overall dimension of the baffle.

(I ask Earl's forgiveness for the abuse of his patent's picture- and yes, I know I need some more classes from Bob Ross )





Any thoughts on this?



Greetings
Michael

[john k...]

Originally posted by mige0
Hi





JohnK, I have a feeling that I didn't get this " messing with the dipole response " completely.
By " edge treatment " do you refer to a lossy ( mesh ) edge or to the thickness of the baffle at the edge or to an unsymmetrical edge shape ?




Greetings
Michael

What I am referring to is a lossy mesh type of arrangement. In a conventional speaker the artifacts in the on axis response due to diffraction are those associates with the acoustic wave propagation outward along the baffle surface and the diffraction of that wave at the edge. We are dealing with only the front radiation. With the dipole those edge effects cancel with the corresponding edge effect form the rear wave (for a moderately thin baffle) and what we are left with is the full strength of the rear wave coming around the baffle edge (which will be stronger than the diffraction of a conventional speaker). Now if you are in a frequency range where the driver is fairly directional, then what is coming around from the rear may already fairly well attenuated relative to the front direct radiation. In such a case the lossey edge would be beneficial since this is really very similar to conventions baffle diffraction only with different strength edge wave. But with a larger baffle, where the driver is still pretty omnidirectional at and some what above the dipole peak, the rear wave will be nearly as strong as the front. I don't believe a lossey mesh will have much success in attenuating the surface waves at these lower frequencies, just above the dipole peak, where on axis dips and peaks would be most severe. Remember the first dipole null occurs at a frequency where the wave length is equal to the radius of a circular baffle. It would be pretty hard to attenuate a frequency of that wave length significantly with edge treatment. What is required is an irregularly shaped baffle (like a rectangle) which basically scatters the rear wave in time due to the different path length around the baffle edge.

The problem is that the problem is very complex and depends on the driver's directional characteristics, baffle shape and size, yada, yada, yada... This is why I think this discussion keep going and going and going. Because may of the ideas presented may work, or seem to work well for a specific case. But they may not apply to another design because the parameters are different. That's also why I think there has to be a line between OB and dipole.

This is why I am changing the web page I was preparing. I want to try and address these issues, at least as they are important to me, to sort of put all the duck in a row.

Anyway, I'll be away for a while, working on the web page.

[Pano]

Originally posted by chrismercurio
That sounds like...the Kenobi.
http://www.hempacoustics.com/kits.php

Yep.
How did you know I've been talking to Perry at Hemp? Will be doing something a little different, but the basics are the same. Seems like a good idea. We shall see.

[Salas]

Back wave of the Kenobi looks like its going to be developing away from Lynn's principles.

[Lynn Olson]

Hi all, lots happening here, thus the absence. Baby birdies coming out of their nest (under the rafters of our roof) and learning to fly. Baby birds #1 and 2 fell off the roof, opened their wings in shock, glided and landed under the shaded porch, peeped mournfully to their mother, who flew into the porch and fed them again, and then they flew to a nearby fence.

Birds #1 and #2 are flying (somewhat unsteadily and frequently missing their target) and are starting to find bugs on their own. Baby birds #3 and 4 cling to the edge of the roof and watch what's going on - their chance to fall off, then fly, is coming soon. Of course, this whole learning-to-fly thing has a deep resonance for me, since I myself have only just started walking unassisted (no cane, no walker) in the last few days, and can now get up and down the stairs with a cane and using the railing.

Aside from the charm of the nearby flight school for the little ones that have grown up under the eaves of our house, I've been meditating a bit about that last posting.

Rather than thinking of radiation patterns from the viewpoint of the loudspeaker (certainly easier to analyze), I think a listener-centered approach is better systems design. We know the direct-arrival sound is treated differently by the ear/brain/mind than the first room reflections, including first reflection from the floor (which arrives 3~3.5 mSec after the direct sound).

I don't see the currently popular quasi-anechoic approach as desirable. By this I mean the listening room should at least have decent enough acoustics that a live instrument - say, a violin or a singer - sounds musically pleasing. I strongly feel if the listening room is so bad that live music is unpleasant, than any serious attempt at hifi is doomed from the start. You can tell this just by speaking out loud - if the room is murky and dead-sounding, or shrill and harsh, then playing games with the radiation pattern from the loudspeaker is not going to be successful.

It may sound a little simple-minded, but I almost see it as a problem in lighting. A certain amount of direct illumination is desired, along with smoothly-distributed ambient light. If the room is so live it's nothing more than a series of mirrors, it's not going to sound good. Similarly, if the room is so dead it's like a black cave, it's not going to sound good either - in fact, it'll look and sound like a dungeon lit by flashlights, a scene out of the X-Files.

The room and the speakers themselves should have a reasonably smooth distribution of direct and ambient energy, as in the illumination metaphor above. The hundreds of room reflections falling in the 3~25 mSec window don't need to completely attenuated - in fact, in their absence, the spatial impression will be quite deficient on most recordings - nor do they need to be precise and exact replicas of the direct sound. What's important is the sum of these reflections needs to have a spectral similarity to the direct-arrival, most importantly, without peaks that are not present in the direct-arrival.

With this model, the exact radiation pattern of the loudspeaker isn't that important, since what matters is the total power into a sphere - the energy fed into those hundreds of room reflections in the 3~25 mSec window. Since the total room power is processed independently of the direct-arrival, the direct-arrival integrity is still important, since it is responsible for overall tonal color and localization (but not spatial impression).

This is why I mentioned in the previous post fine and coarse-grained radiation patterns. If it's in the direct-arrival path going straight to a listener, then time, spectral, and spatial performance are extremely important, in order to provide realistic tone colors, stable and non-fatiguing image quality, and low "speaker" coloration. It's not hard to tell where the listeners are going to be - they'll be sitting in front of the speakers with their ears about 38" to 42" above the floor.

For all the other directions, the radiation from the speaker is going in the direction of one or (many) more room reflections. These fall into a different processing slot, one used to evaluate spatial impression. If these reflections are greatly diminished relative to a real, physical sound source in the room - which of course is still in memory, since the room wasn't silent when the listener first walked in - there will a conflict between the dry sound of the hifi and the characteristics of the room itself.

If the sum of the room reflections have a significantly different spectral characteristic than the direct-arrival sound, that too will draw attention to itself as a sort of spatial coloration that will be very likely be highly recording-dependent.

One of the goals I will aim for, like those birds learning to fly - is a smooth spectral characteristic (radiating into a sphere) that has a reasonably good correlation with the direct sound.

[Lynn Olson]

Moving out of the meta-discussion, BudP is reporting very good results from the EnABL'ed Lowther PM6A's. Having heard hints of greatness from Oris front horns and the Big Fun back-horn, I'm curious to measure and audition the treated Lowthers. I've also heard there are versions of Lowthers that don't have the whizzer-cone and its difficult mechanical crossover, making them candidates for the RAAL ribbon tweeter (with a crossover around 7~8 kHz). BudP surprised me when he said the 16-ohm versions have 3mm of linear travel compared to the 1mm of the 8-ohm version, something I wouldn't expect at all. This relaxes the crossover requirement quite a bit.

Also am hearing very good things about the Fertin 20EX field-coil driver, although I don't have the courage to buy a pair and EnABL the cones - that would be a very costly mistake if the cones get ruined by the treatment. Still, I am very very curious about them, and hope they make an appearance at the RMAF.

Also a terrific contribution by Kuei Yang Wang over at the Legendary Loudspeakers thread:

Originally posted by Kuei Yang Wang
Konnichiwa,

Complete Speaker Systems:
====================

Hartley Concert Master
Gradient Revolution
Audio Artistry - all models

Those are nominated for being the only commercial speakers to offer operating principles that maximise their performance in moderatly small rooms.

Quad ESL-63

Full rage ESL, still great and has it's fans.

Tannoy GRF Autograph

THE other speaker to hanker after.

Drive Units:
========

Eckmiller Koaxial from Germany

Probably the best possible coax driver EVER.

Tannoy, Altec and Parmeko Coaxials

Excellent large format Coax Drivers

Lowther (Voigt), 1940's to 1960's German Radio Fullrange Drivers (Saba, Koerting etc), old Supravox Drivers, most models in the Goodmans Axiom series but especially Axiom 80, Coral Beta 8 and Beta 10 Drivers, Hartley Fullrange Drivers

in modern times Phy Hp and Supravox make excellent drivers, Lowther seem to make/have made too many hanges to the originals, their latest drivers sound pleasant enough but nothing sounds like early PM2's in front horns.... Also noteworthy in modern times are AER, Fertin (if you can get them) and REPS.

All of the above correctly applied are excellent fullrange systems.

Other Drivers to mention, because of their sheer audacity are the Electrovoice 30" Woofer, the Hartley 24" and the Fostex 32" (80cm) Woofers.

Sayonara

I've heard about a third of these, and I would concur. The WWII-era Eckmiller Koaxial created a sensation at one of the last European Triode Festivals, according to John Atwood, who heard it and was astonished by the sound. I keep being intellectually attracted by the big pro coaxials, and keep being unnerved by the hair-raising freq resp curves of the woofer elements, which are typically even wilder than a Lowther.