Installed TS catback, have drone, anything I can do?
 

Hello all. I installed the Top Speed Pro 1 cat back exhaust. All my stock cats are still in place.

I have a loud drone between 2,500 and 3,100 rpm. Car is a '01S.

Anything I can do about it? Any hints to improve the drone? Everything else sounds good but the drone is quite loud and annoying, if I can get rid of it all is good.

I wonder - I used some steel about 1.5" long to lower the mounting bracket as it seemed high to me. I did not want to tilt it down with spacers. Wonder if the slightly less support from bracket contributes to drone?

Thanks!

If the muffler is a 2-can design, there's not much you can do. My car came with a Brullen catback muffler (no longer in business) installed by the PO. Made me nuts for a while. I love the sound and the volume and have adjusted my driving style to stay over 3k as much as possible.
You'll learn to love the drone, or keep the revs out of the drone zone. I did, however, find a factory muffler (free)and all the incidentals (pipes & clamps for $30) to install it if I decide to break down and go back to stock.

I've heard tails that using these EasySeal Exhaust Clamps will take away the drone.

EasySeal Exhaust Clamps: Torca EasySeal Clamps in Stainless Steel for Lap Joint Connections

Kram is dead on with the clamps. Guys that are using those clamps have eliminated the drone problem. Stay out of the drone zone. Not good for the car anyway. Just my opinion.

Not gonna work... Clamps don't fix resonance. ;)

[The exhaust pipes in automobile exhaust systems are designed as acoustic resonators that work with the muffler to reduce noise, by making sound waves "cancel each other out"[1]. The "exhaust note" is an important feature for many vehicle owners, so both the original manufacturers and the after-market suppliers use the resonator to enhance the sound. In 'tuned exhaust' systems designed for performance, the resonance of the exhaust pipes can also be used to 'suck' the combustion products out of the combustion chamber at a particular engine speed or range of speeds.]

http://en.wikipedia.org/wiki/Resonator

I also installed the top speed cat back mufflers on my 01 S and got the drone.

The solution was to get the 2nd cat delete pipes from Top Speed and no more drone and awesome sound.

You will very happy if you do this and its an easier job than the mufflers.

Thanks everyone.

I replaced my muffler because stock had something loose inside that rattled. Getting better sound was a benefit I looked forward to, however this drone is excessive.

Appears as though the 2 can setup is prone to drone (rhyme every time) but can be minimized.

I am going to recheck my set-up for possible leaks, put on the recommended clamps, and if that does not work will consider installing test pipes.

Concern I have with test pipes will be that the exhaust will become loud. Any input here is appreciated as well - how much louder without the secondary cats? And does the 2nd cat delete eliminate all the drone, or just make it better?

I would put the stock exhaust back on but the rattle is annoying.

Thanks!

Gary

I put on my GHL exhaust a few weeks ago and thought the drone was obnoxious. BUT - now that I ahve had it a few weeks, first off I dont notice it too much but it is very easy to feather the throttle when need be to lessen drone. I am now in love with the sound and drive the car just to hear it. It can rattle my brain all it wants, I cant get enough.

I got the TS. Same resonance at those rpms. Helps remind me to keep the revs up when cruising around. I like a loud sports car, so it's fine.

Someone who installed the test pipes recently mentioned basically the opposite, that it was too noisy at higher rpms, but they didn't seem to complain of the brain-shaking resonance at low rpms, so I was confused. I guess you need the test pipes, as others mentioned.

I had fitment issues with mine that caused minor drone. After getting a welder to tighten everything and fix the exhaust leaks for $50, there were less vibrations and no drone. The car and exhaust feel very solid and well put together now. The car is quiet when I am cruising and only gets loud when I accelerate.

My tips were high hitting the rear bumper. Once I put spacers(50 washers) in and longer bolts from Home Depot, the tips lowered and now they look great.
One thing to mention. I installed Test pipes a month before the cat-back exhaust.

It looks like this now.
http://farm4.staticflickr.com/3736/9...49df954f39.jpg

I installed the Cat delete pipes at the same time that I installed the exhaust. At first, I thought what have I done? The drone was unbearable. Once I put the clamps on, sealing a major leak, and then fiddling with the u-pipes to make sure they weren't leaking, the drone was eliminated. The key seems to be eliminating any leaks and making sure everything is solid. Once you get it sorted, the sound is great! Good luck:cheers:

Topless - wonder what would happen if a pipe is welded between the 2 cans, connecting them? Would resonance go away?

Just had a muffler shop look at it, said there are no leaks and all looks well assembled.

I am going to next step, trying out the clamps. Is 2" the right size?

By the way, the car does feel more responsive...

Yes, 2" is the right size.

Lets all be clear on this. You never want any exhaust leaks in the system. Make sure it is absolutely tight. The sound from an exhaust leak is different from 2-3k acoustic resonance drone caused by exhaust tuning. Apples and oranges. The goal is a tight exhaust AND no 2-3k acoustic resonance.

To solve the resonance problem you need wave cancellation in the 2-3K drone zone. Sort of the same technology as the Bose headphones that cancel outside noise. A perfectly placed connector pipe that is the right length and right diameter might work. It will require math or a lot of trial and error. A noticeable drone or nasty exhaust note is an indication that resonance and acoustic standing waves are interfering with the free flow of exhaust gases. I have not yet seen a drone-free 2-can exhaust but it is possible with precise acoustic tuning.

Essentially Porsche engineers carefully tune the stock exhaust to cancel frequencies in the 2-3K drone range, reduce overall loudness from 110db to about 90db, and let the sweetness of the motor come through under full throttle. They spend a ton of R&D time and money to get the sound right because it is a big part of Porsche DNA. The stock exhaust is big and heavy but it works well. The best solution I have seen is to do the Pedro sport exhaust mod which retains the 2-3k wave cancellation while letting more sound out.

I hope this helps.

Topless, excellent post, thanks! Fascinating stuff.

I am going to give the clamps a shot because it is easy and simple, if that does not work I will rethink what to do - TS or return to stock?

from another thread:
You could try this, though the fabrication may not be cheap:
http://www.planet-9.com/987-cayman-boxster-modifications/50861-exhaust-drone-resonator-fix-design-construction.html

Stephen,

Interesting read. People say deleting 2nd cats takes away the drone, which seems counterintuitive to me as it increases flow, and I would think also increases noise.

However after reading the Planet-9 thread my conclusion is that taking away the cats changes length of exhaust path, which changes shape of sound wave, and in this case apparently reducing resonance.

Still scratching my head - test pipes, or go back to stock with Pedro mod.

Gary

This guy definitely understands the problem. The devil is in the details and it looks like he did a lot of R&D to get the results he wanted. Good link! :cheers:

I would still consider the cat delete pipes. They aren't needed, reduces weight, less restrictive air flow, and probably helps with the drone. The clamps will help as well.