How Toyota made the 460/600 the quietest passenger car
 

Nice contribution.

Quiet and smooth.

Nothing that most other cars don't have to some degree. The LS460/600 is NOT the quietest passenger car in the world, although that distinction can be twisted with any number of criteria/assumptions (eg sound level weighting)..

I don't think that statement is really accurate.

Edmunds posts dB ratings in their tests, the LS460 they tested had a 70MPH cruise sound reading of something like 58.5 dB, and the 600hL they tested was something very similar. That is VERY quiet, and if you look up their tests of other cars that you might think may be quieter...you'll find they aren't. In fact, I did this after I first saw this post...and I could not find one car that was quieter, including Rolls Royces, and in fact ANY car reading less than 60DB is very hard to come by. Some cars were significantly louder.

If you want to easily access the articles google "LS460 db edmunds" and sway out LS460 for any car you want the readings from. A lot of it depends on methodology, road surface etc. These however are all from the same source, which makes them easier to compare. I'll send a couple:

2011 LS460:
Sound level @ idle (dB) 39.2
@ Full throttle (dB) 65.3
@ 70 mph cruise (dB) 58.2]

2008 LS600hL:
Sound level @ idle (dB) 38.3
@ Full throttle (dB) 66.6
@ 70 mph cruise (dB) 58.9

2005 Rolls Royce Phantom:
Sound level @ idle (dB) 40
@ Full throttle (dB) 67
@ 70 mph cruise (dB) 59

2014 Mercedes S550 (this is the redesign):
Sound level @ idle (dB) 37.5
@ Full throttle (dB) 67.6
@ 70 mph cruise (dB) 60.1

2011 Jaguar XJL Supercharged:
Sound level @ idle (dB) 42.4
@ Full throttle (dB) 74.1
@ 70 mph cruise (dB) 66.9

2015 Tesla Model S P85D:
Sound level @ idle (dB) 36.3
@ Full throttle (dB) 66.2
@ 70 mph cruise (dB) 64.5

2013 Bentley Continental GT:
Sound level @ idle (dB) 46.9
@ Full throttle (dB) 75.6
@ 70 mph cruise (dB) 61.6

2011 BMW 740i:
Sound level @ idle (dB) 44.3
@ Full throttle (dB) 73.1
@ 70 mph cruise (dB) 63.0

2013 Audi A8L:
Sound level @ idle (dB) 40.1
@ Full throttle (dB) 68.4
@ 70 mph cruise (dB) 61.8

So...it just might be the quietest car in the world. Thats quite something when compared to say the S550 which is so much newer.

I don't buy a lot of stuff on that site. No source, how was it recorded and where? Etc.

These numbers are really not very useful for comparing cars and without some context they are sort of misleading. The numbers seem to represent a combination of how much noise a car generates (self generated noise) and its ability to keep that noise from entering the cabin (inside/outside noise ratio). These test are usually done on a test track (a very smooth surface), in an isolated area where the background noise is very low, on a calm, dry day at very moderate temperature - conditions in which the car would not be routinely operated in. When cars are operated on windy days, or wet days, in the presence of noisy vehicles such as some motor cycles or large trucks or extremely dense noise environments such as freeways then their noise isolation characteristics become very important and the self-generated noise becomes so relatively low that it becomes irrelevant.

The "wind noise" problem that affected so many of the LS460s and LS600s was caused by a trim defect that lowered the defective car's cabin isolation from outside sounds. The self-generated noise for these cars, both noisy cars and quiet cars, was the same. This was a very serious problem for Lexus, causing them to buyback thousands of cars and have many customers who were so put off they did not consider Lexus for their future new car purchases. It was a BIG deal and a BAD deal. Many cars still have this problem and others are developing it.

The numbers above may tell you which car has the quietest ride on the test track but may be very misleading as to which is quietest in other conditions.

I find the LS460s, the ones without the trim defect, to be exceptionally quiet in a wide range of real-world conditions and probably among the quietest cars available in the mass produced luxury class.

I don't disagree, but at least all coming from the same source one has some hope that the methodology used would be at least uniform enough to give you some idea of noise isolation from car to car in that ideal circumstance.

Anyways, I doubt edmunds has a test track...

Well, let's say a car has a self-generated noise level of 65dB and a noise isolation of 20dB, then the noise as it is being measured above would be 45dB.

And, another car has a self-generated noise of 75dB and a noise isolation of 30 dB, then the noise as measured above would be 45dB.

If we put both cars on the freeway where the noise environment is 100dB then the noise in the first car would be 80dB and the noise in the second car would be 70dB. The second car would be 10dB quieter.

That's sort of a simplistic comparison but does make the point.

I again don't disagree, but if you're going to compare something, you need a similar circumstance to compare them in. my point is at least this gives you some reasonable comparison. Otherwise what you're saying is they really can never be compared.

We're splitting hairs.....

There are more than s few test papers/reports about db ratings among cars on the web. Consistently. the LS460 and especially the 600 had the lowest db ratings. I can provide some more websites, but it's easily found with a Google search.