Beyond the Ariel

[gedlee]

Originally posted by Lynn Olson


It's really weird how Dr. Geddes and I are travelling on almost-parallel tracks. Spooky.

You got me, I'm really a CIA operative working in Thialand. Ai is all a front. OOPS I'd better be carefull!

Another reason for the diplomatic passport thing for the kids is that children are an assets greatest liability. This has been used over and over. So it is critical that an undercovers kids be squicky clean.

Its been a most interesting story, but I would warn that not all "coincidences" are not "coincidences". Accidents do happen and "out-of-the-blue" situation are often just that. I would say that your fathers promotion to the bank was probably ligit. The bank would cherish his credentials and contacts, even if he were incompetent (not that he was). Seems to me that the later job that he had was probably on the up-and-up. But the OSS to Foreign service is just too typical a path to be ignored.

[Lynn Olson]

Yes, no way of knowing if he was NOC or not - and you're right, he was very well-connected with the movers and shakers in Hong Kong, since he was the go-to guy when US and HK businesses wanted to have successful dealings with each other. He was also in charge of a lengthy series of trade negotiations between HK and US textile manufacturers - sounds boring, but there was a lot of money involved.

Both of us were mystified by the Vietnam War - the US certainly didn't care if the French lost their empire, and there was no real strategic interest that justified the enormous costs of propping up the South Vietnam government. With a little effort, the US could have made Uncle Ho into the Asian version of Tito, skillfully playing the Chinese against the Russians, driving both nuts, and frustrating Chinese plans in the region.

Our best guess was the Red Scare purge of the McCarthy years had removed all of the Old China Hands from the upper levels of the Federal government, thus there was no-one left at State or other parts of the US Govt that had any experience in the region.

Probably more significant, there was all the domestic consequences left over from the "Who Lost China" propaganda campaign of the late Forties - Clare Booth Luce and all of Chiang Kai-Shek's friends in DC pushed that one along, making both Democrat and Republican Presidents afraid of looking "weak" in Asia.

[gedlee]

Originally posted by Lynn Olson
Our best guess was the Red Scare purge of the McCarthy years had removed all of the Old China Hands from the upper levels of the Federal government, thus there was no-one left at State or other parts of the US Govt that had any experience in the region.

Probably more significant, there was all the domestic consequences left over from the "Who Lost China" propaganda campaign of the late Forties - Clare Booth Luce and all of Chiang Kai-Shek's friends in DC pushed that one along, making both Democrat and Republican Presidents afraid of looking "weak" in Asia.

I've read about this period a lot and your assesment is pretty much right on.

Did you ever read about General Stillwell? He was pro Mao and very anti Chiang Kai-Shek. Roosevelt was starting to listen, but Truman would have none of it. He saw Mao as a patsy of Stalin, and, rightly so, hated Stalin. I think that Mao used Stalin for what he could get, but, as events would show, had no real respect for him.

[tade]

This thread is so comical!
Thanks!

[mige0]

Hi

I certainly grant that intel "services" are necessary, if nothing else ....

Yes, belief desire and fear is the most solid soil of "reality" ( not to speak of human zombie-stupidity ) .
Look at your statement from that perspective and put it upside down once you ( we ) want to change that current reality.

Basically oppose " utopia " against " realism " - and always keep eyes and heart open ...

... but to whom am I talkin about ...

It's my thread, I figure I can abuse it every now and then, just to keep things interesting.

Dan Brown couldn't have done better ( though its no fiction here ) !


Greetings
Michael

[Pano]

Hey John K -

I've been thinking about this part of your post for a few days.

Originally posted by john k...
Suppose that you have a circular baffle. If there are no slots then the rear wave can be though of as a ring radiator at the baffle edge. On axis this reduces to a single source at the observation point. That is, the delay from all points around the circumference of the baffle to a point on the dipole axis will be the same.

Now that's an interesting thought! Usually we are told not to make a baffle symmetrical, a circle being the worst - the resulting FR is supposed to be very bad. But as you say on axis all points around the circle would be equidistant, they would appear as one source. At least in the time domain. It should sound like a bigger version of the driver itself.

But would those secondary sources cause comb filtering? Would they interfere with each other?

I ran some simulations of a round baffle yesterday in "The Edge". An 8" driver on a 16" diameter round baffle. (Actually a 200mm driver and 400mm baffle).
Yes, there were ripples in the on axis FR, but not big nasty ones. Moving the driver toward the top of the baffle a bit smoothed those out. The mic need to be 2 or 3 meters from the baffle to integrate well.

But off axis was another matter! Move the mic off axis by a meter or 2 and all hell breaks loose. It's the same for other baffle shapes, tho.

This line of thought has got me wanting to try a "Lollipop" baffle. A round baffle above the floor with a thin support. And of course it would have BudP's funny little blocks all around the edges.

Any thoughts?

[Graham Maynard]

Hi John K,

Re your post#1514 explanation >>
Suppose that you have a circular baffle. If there are no slots then the rear wave can be though of as a ring radiator at the baffle edge. On axis this reduces to a single source at the observation point. That is, the delay from all points around the circumference of the baffle to a point on the dipole axis will be the same. <<

This ties in exactly with JohninCR's stated observations much earlier in this thread, where he warned that tilting a baffle also tilts the sound 'stage'.

This would suggest time aligning the drivers wrt the baffle, though of course rear waves would be different then also.

Seems we are always challenged when we move away from the single Fullrange concept.


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

[john k...]

Originally posted by panomaniac
Hey John K -

Now that's an interesting thought! Usually we are told not to make a baffle symmetrical, a circle being the worst - the resulting FR is supposed to be very bad. But as you say on axis all points around the circle would be equidistant, they would appear as one source. At least in the time domain. It should sound like a bigger version of the driver itself.

Except that the "ring" would be inverted polasrity.

Originally posted by panomaniac

I've been thinking about this part of your post for a few days.

But would those secondary sources cause comb filtering? Would they interfere with each other?


Any thoughts?

This is my point. Start with the circular baffle with point sources and the on axis response is exactly what you get with a true dipole (two point sources separated by some distance radiating with inverted polarity). Yes there would be serious comb filtering above the first dipole peak, but that is the characteristic of a dipole and not a consequence of baffle diffraction. Certainly the rear wave is "diffracted” around the baffle edge (just as the front wave is diffracted around the edge to the rear). But on axis this has no impact on the response (for a very thin baffle). If you consider driver directionality the severity of the comb filtering above the first peak will tend to be lessened, depending on baffle size.

Off axis, what happens depends on the baffle shape since the time delays from the baffle edge to the observation point will now vary around the baffle edge. But even then, the resulting response is just the sum of the direct radiation form the front side plus the radiation from the rear source distributed around the baffle edge as a ring radiator. This can be likened to conventional edge diffraction with the edge sources twice as strong for a dipole than for the conventional speaker, but the if you decompose the response at the edge into the incident wave (from the driver) and the diffracted wave you see that the diffracted wave contribution from the front and rear effectively cancel out for thin baffles which is exactly why the strength of the sources around the edge are twice as strong for a dipole. Collectively you can call this whole thing diffraction, but you can also note that the conventional scattering of the wave incident upon the baffle edge from the front source (as well as that from the rear) don't contribute to the response. 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. While the 90 degree off axis response will still be null (assuming symmetric front and rear amplitude), on axis the front response will become more and more independent of the rear response. That may be a good thing and is a reasonable objective, but it’s more like trying to emulate an infinite baffle than a dipole. This is the case for both conventional and OB system. But of course, the degree of success will typically decrease with frequency. This problem exacerbated with OBs by the use of large baffles where the driver is fairly omnidirectional at frequencies above the dipole peak. Large baffles seem like a good thing since they increase low frequency sensitivity. Choosing the correct baffle size and shape is a trade off between low frequency sensitivity, driver directionality and how high in the frequency range you want to retain true dipole response.


I'm discussing much this on the web page I'm working on. It's nearly complete but I'll probable need to edit it a little before posting it (or not). The delay is that I also want to discuss some of the trade offs between using large baffle for improved low frequency sensitivity vs smaller baffle for minimizing response problems above the first dipole peak, as I started to here.

The other point I want to make is that I think there need to be a clear cut distinction between dipoles and OB speakers. Most dipoles are OB but very few OB speakers are true dipoles.

[el`Ol]

What about the following combination for a high sensitivity dipole: Beyma Pro 6 series (high Qts, overlooked easily because in the car section)
http://car.beyma.com/ENGLISH/listapr...?id_familia=13
and large Mundorf AMTs (similar sensitivity, also 4 Ohm)
http://www.mundorf.com/english/speak...ransformer.pdf
?

[Pano]

Thanks John K.

Still not sure about the whole thing. Circular baffle = good. Or circular baffle = bad? I'm baffled.

Maybe it would be a good use for some of those old 16" transcription records. Nice and thin and stiff. Has a musical look to it, too.