Hey guys, I recently fixed my exhaust leak but I ran into the same issue I had a couple months ago, my horrible drone. I was wondering if anyone knew what size and length piping I needed for my 2008 Lexus IS 250 AWD to make a Helmholtz resonator or cavity resonator. I have a set of custom resonator/exhaust tail pipes that work great for my liking but the drone is just unbearable to me from the 1900 RPM until 2400 RPM with 2200 being the most notable and loud. Or are there any other ways to remove drone, besides buying a whole new cat back or axle back exhaust? Thanks

 

There are lots of online definitions of "drone".

In the C3 corvette world, you typically hear it in the context of someone running sidepipes without isolators between the pipes and the body, thus negating any isolating the engine mounts are doing and vibrating the birdcage directly, causing a drone.

In the Cummins world, drone is sometimes from using a straight-through aftermarket exhaust that just so happens to be the correct length to behave like a brass instrument, and it resonates for it's entire length at certain RPMs--usually around 60-70mph locked-up in overdrive, depending on gears/tires--and "shouts" out the tailpipe, sometimes resonating the bed quarterpanel (US/Canada drivers have all heard this, guaranteed). Other times, it's from the material the aftermarket exhaust was made from being more acoustically lossy than the OEM provisions (it's skin vibrates, which bounces off the ground and reverberates in the cabin), and so it isn't uncommon to see a number of feet of angle stock welded to the bottom length of pipe between the downpipe and axle (more common on MegaCabs and QCLBs), to change it's resonant frequency, and disrupt the sound waves going from the pipe to the ground and back. Doing so then almost always gives you the first Cummins drone I mentioned.

What I'm saying is that you have to figure out what's causing the sound you don't like, and change it's acoustic properties. The traditional way of doing so is with fiberglass wrap, and as long as you're not wrapping cast iron (would be pointless, anyway) or galvanized steel (I don't think any aftermarket kit for 2IS is that cheap), then the only caveat is how much/how many layers it'll take to bring you to where you want to be. On our platform, I'ma say it's the y-pipe 90% of the time, especially since we've seen the OEM Y-pipe fail at the junction somewhat consistently...there's a whole awful lot of dynamic thermal and acoustic stresses going on there