About the only sound barrier that will actually have a noticeable effect is mass loaded vinyl on top of an isolation layer of closed cell foam. Or lead sheets. Or anything that weighs around .5-1lb per square foot. Using only dynamat is not going to have much of an effect, because it's purpose is to stop panels from vibrating, not block sound. And using only closed cell foam is going to be nearly useless because it will only be blocking extremely high frequencies.

Using the spray-on stuff or raammat, which is another CLD like dynamat, to block sound is using the wrong tool for the wrong purpose. That's why you didn't see much of a difference. You put a tiny barrier capable of only blocking very high frequency noises (10khz+) and your primary benefit was preventing vibrations that would lead to further noise. And the spray-on stuff is not sufficient unless you're putting it on in thick layers, which is going to require quite a few cans. Here's why: you would need to cover around 2 square feet with a single can(assuming it's the 1lb can) to see much results, which would still be resulting in around .5lb/sq ft of deadening material. Considering that each wheel well liner is probably around 8-10 square feet (educated guess, will vary by vehicle), you're looking at a minimum of 4 cans to cover a single liner. And at $8-10 per can, you're looking at quite a bit of money (anywhere from $60-100 depending on surface area) to achieve .5lb/sq ft of material on only the liners.
You could always use this on the liners and the underside of the vehicle: http://www.ebay.com/itm/1-Gallon-Spr...-/181211184617

 

That is the brand I used on the wheel wells. On the front wells you can really only paint the rear half closer to the passenger compartment. I did 4 coats. This is the 3rd car I have done this on and it does reduce tire noise. I still have half a can left over. I may do my HS250h with it. You actually need far less than you estimate in your calculation due to suspension components etc. The paintable area in the wheel wells is smaller than 8-10 feet. There is more to paint in the rear wells than the front on the RX and on most cars.

I did put the Raamat foam on top of the Raamat deadener in the rear compartment. I think it needs more layers, but do not want to take it apart again.

However, I see you propose putting the foam down first, then the Raamat. Interesting because I bought a product many years ago just like that for use with inwall speakers. It has a thin foam layer about 1/4 inch, then a heavy vinyl mass layer, then a thicker foam layer, about 3/4 inch. I used spray adhesive to mount pieces inside drywall when installing the speakers. I guess I should have used the left over in the car, but it's thickness may have made it hard to put the trim back in place. I have some left over in the attic and may put some under the spare tire.

 

My estimates were based on a full liner, though the rear liners on some cars have the carpet liner that are already designed for sound absorbency. Obviously the estimates will change based on the available size that you can spray on the liner, but you should still try to achieve around .5 lb/sq ft. at a minimum. This is because you're trying to block low frequency soundwaves, which requires a thicker, denser material.

I believe you misinterpreted what I said. Raammat BXT II is a CLD, constraint layer damper, and should be applied directly onto metal surfaces. Not only that, you should also be using a wood or plastic roller to firmly press it onto the surface. It's not something that should simply be stuck on or barely pressed down, you really want it on there so that it can act as a proper constraint layer. This is really only needed on panels like the door skin, roof, trunk lid and floor, and other thin panels. You can put it on the floor if you wish, but the floor pan is usually reinforced and does not vibrate easily on newer cars. Do the knock test, if you get a fairly firm thud then it's fairly pointless to smack more CLD tiles on the surface.

The sole purpose of using CCF(closed-cell foam) in a car is to act as a decoupler. CCF is a poor sound absorber due to the closed cell design (lower porosity yields lower flow resistivity, which yields poor absorbance), open cell foam is more effective due to higher porosity, but it holds water. That's why open-cell foam is not usually used in cars, since you don't want it trapping moisture, and that's why CCF is only used for decoupling (because it is a poor absorber).

Even if CCF was a good noise absorber, because it has low flow resistivity at 1/4" it would only be absorbing frequencies of around 13.5kHz. Road noise is around 200-4000 Hz, which would require a minimum 1.5" of foam with a high flow resistivity of around 10,000 rayls/m, to achieve near 100% absorbance (7% of the wavelength at STP in air yields almost 100% frequency absorbancy, because the speed of sound slows down in porous materials and the actual wavelength within the porous material is approximately 22-25%) of peak noises around 600 Hz.

So you can see that simply throwing in greater layers of foam, especially closed cell foam, is not going to be particularly effective unless you wish to build a layer of two inch thick foam. This is why we use mass loaded vinyl (MLV) as a barrier, not an absorber, and use CCF to decouple the mass loaded vinyl and have it act as a limp mass barrier. Due to its high density, 1-2 lbs per sq ft, it is very effective for blocking lower frequency noises.

So to summarize: use CLD tiles on the bare metal, place CCF over the entire surface to decouple it, then lay MLV over the entire surface with zero gaps. Any gaps you leave are gaps where sound waves can enter.

If you wish to learn more, look up flow resitivity, porosity, the Allard-Champoux model, angular frequency, real part of the complex wave length.

 

Thanks, I learned more about sound deadening from your posts than from all the other sources I had read over the years. Did not know about the MLV as a top layer.

 

There are 3 RX350's in my neighborhood and they all have the same groaning engine, it's just how they are. I don't think anything is wrong with them, just the combination of this engine pulling around a heavy car, gearing and sound deadening. They run nice and smooth and are decently quick too. Oh well.

 

Fooling with various insulation/barriers would be a waste of time with my noise. It very nicely dissapates
with 5--8 miles / 10 minutes of driving. And it does not matter weather it's 90 degrees or 30, it's always there at start-up.

 

So for the 6 months I've had my RX I've been working through the list of small annoyances/fixes required with any used car purchase. The two that remained were the steering column rattle and the exhaust droning sound.

I finally figured out the droning exhaust sound. Through a ton of forum searching, I was convinced that the "butterfly valve" in the exhaust was getting stuck, producing a loud drone at certain speeds on the freeway. It was very noticeable at the low end of the powerband at highway cruising speed.

However, after climbing under the car, I realized the car had previously been rear ended, and the exhaust took the brunt of it. The gooseneck section behind the muffler had been pushed back and bent slightly, as a result the pipe diameter behind the muffler was smaller than it should have been. A new muffler and exhuast gasket and the car is totally silent.

One other note, the dealer - Stevens Creek Lexus - quoted me $800 for the muffler and gasket. I couldn't swallow that, so I bought online using parts.com. The exact same parts came from Lexus of Roseville (that's where the CC charge hit) for $290 including shipping.

Now if someone can find me a $290 steering column to get rid of the insane rattle I would appreciate it.

 

Have had my 2010 RX since brand new, and figured that the annoying exhaust sound was just Lexus's attempt to make the RX sound sportier, a la Infiniti FX, but to me it's always been an epic fail. LOL! But the car has been very reliable these past 5-and-a-half years, so I'm good for a few more years before I start looking for a new car. Oh, and my 2010 RX must be one of the handful of RX's with the over-firm suspension too!

 

The RX350 is our 6th Lexus...obviously we'v been pleased with our experience(s) with both Lexus and our dealership (Hendricks Charlotte). But...the RX350, in my opinion, does not meet Lexus standards, unless they have lowered their standards. The "drone" sound that many owners have experienced is absolutely annoying, making the 350 a car that I hate to drive. unfortunately, I bought it for a "retirement travel" car and now I'm stuck with it unless I want to take a big price hit (which I'm considering). The tech guys say that they are awaiting a service order from corporate as soon as they figure out the problem. I hope it occurs soon. Good customer service, bad customer experience with this SUV. Could not recommend vehicle this to anyone.

 

Steve,
What year is your RX? My 13 RX AWD drones and whines at low speed. Several neighbors and friends are almost silent. Of course the dealer says no problem. I also have a few more rattles and squeaks then my wife's ES (2002) or the Highlander I replaced. It is disappointing.

 

Joe, 2016, yesterday at dealer again...2017 has same problem.

 

nature of the beast.....

 

No drones on our 2013 RX450h EXCEPT for the usual high pitched whining sound while slowing down braking. Sounds like a big jet taking off. But this is true for all Lexus/Toyota hybrids due to the regenerative braking.

 

I posted previously that my droning noise was fixed by replacing the rotors on a car with about 60k miles on it. But my Lexus was a lemon that had to end up having a new transmission with less than 100k miles. There were several other major expensive repairs that made the decision for me to trade it in for a new Buick Enclave.

 

New (to me) 2015 RX350 bought as a CPO with 33k miles. Great car so far but the exhaust drone at lower rpm's is, frankly, surprising. I'm a lifelong Honda guy and traded a 2012 Pilot in on this car and I'm now starting to really miss the refinement of that drivetrain.

On my next service visit, I'll report the noise and ask about the two-way valve in the muffler. This thread, though, is leaving me with low expectations.