Car and Driver tested a 2017 Chrysler minivan against a 1984 version. How much engineering progress was made on interior sound level over the 33 years that separate these two cars? 2 dBA! The old minivan measured 71 dBA and the new one 69 dBA, both at a 70-MPH cruise. The new minivan is 1150 lbs. heavier (one reason why there was no improvement in gas mileage) but apparently there isn’t a lot of soundproofing included in that extra weight.
Related:
2 dBA corresponds to about a 20% reduction in sound pressure level – not completely trivial but nonetheless barely noticeable for most people. Noise reduction is devilishly difficult. Lightweight surface treatments mainly help for reverberant noise. Reducing noise transmission requires mass which works against gas mileage. Additionally, rigidly connected structures (numerous is a vehicle) can transmit vibrations (and thus noise) right by whatever surface treatments you do apply.
I drive one of the Lexus hybrid SUVs (bought used at a fairly reasonable price) The thing’s insanely quiet and pleasant. (if you don’t mind electric car noises) It doesn’t have minivan space, but you could probably get 2 adults, 2 kids and a dog in there. The Toyota Highlander Hybrid apparently has the same drivetrain and is slightly larger. If you’re not cost-conscious, wait 3 years and buy Toyota’s largest hybrid with whatever level of autonomy they’ve managed to cram into it. It’ll be pretty nice. (A semi-autonomous hybrid sienna would be pretty sweet)
Neal: “Reducing noise transmission requires mass which works against gas mileage.” Car and Driver says weight went up from 3400 lbs. to 4557 lbs.
The additional mass would only help if it was applied to the parts which were transmitting a significant fraction of the noise, but those are precisely the parts which I would expect to be targeted for weight reduction (at least by area) to accommodate growth in size and functionality while maintaining mpg. From the article:
“The Pacifica dwarfs the original minivan.”
My point was that reducing interior noise isn’t a matter of adding soundproofing (especially since the original vehicle probably had soundproofing). Sure the instrumentation and analysis software has improved over the decades, but significant noise reduction would still require a lot of painstaking engineering work. More likely, the noise control engineers are brought in when sound levels creep up to quickly harvest some low hanging fruit and get the sound level back to where it was.
I’m just confused by one thing: “we couldn’t take the oldster past 45 mph on a loop at Chrysler’s Chelsea, Michigan, proving grounds”. How did they get the 70MPH cruise noise level?
Look at the engines: that’s 50% more moving parts (3600cc V6 vs 2500 4 cylinders). Look at the tires: 20% more friction surface, and much more stiff tires. Finally, both tire sets are M+S: that levels the noises up and makes other noise sources far less important.
What about the asphalt, was it exactly the same? Even a tesla would be quite noisy on e.g. Belgian roads.
Regarding the 45 MPH thing, the printed test results for the Voyager are the historical results that they achieved when they tested the vehicle for the magazine back when it was brand new. For purposes of this article, Chrysler let them take photos of a museum piece Voyager that they have in their collection side by side with the new Pacifica but they wouldn’t let them drive the collectible over 45 mph. They didn’t test the 30 year old car in 2016.
I imagine at least some of that weight budget went towards entertainment systems aimed at quieting the primary source of noise in a minivan – children.
Minivan engineers and product managers are very aware of interior noise as _one_ decision-influencing factor. Given the surprising consistency between the two results, I wonder if 70dBA is just below an important inflection point in their user testing.
Here in Phoenix we have special rubberized asphalt that is put on all our freeways. It is amazing stuff. It was created by local road engineer and uses a ground up old tire recipe. It makes our freeways are so quiet and fun to drive on. It reduces the noise factor down 7-12 dB or more. See here. https://en.wikipedia.org/wiki/Rubberized_asphalt
Here in Phila, we must have the opposite. There are certain (concrete, not asphalt) highways that are just deafening. I have an older Subaru that doesn’t have much sound deadening and when you get on one of those roads you have to shout to be heard by the person sitting next to you – it’s almost like being in a small plane. Someone should tell PennDOT. I notice that most of the places that us rubberized asphalt have warm climates. I wonder whether it doesn’t go down well in cold weather or hold up to freeze/thaw?