Gearing it and not lugging really helps.
Those TI systems are great. Exh or catbacks arent really the power robbers everyone thinks they are unless youre pushing rediculous amounts of power.

 

OP, my complements for the Science/engineering/fabrication/product testing lesson! Thats a lot of experimentation, and I have to save this and study it! Great info!

 

Drone occurs when you hit the resonant frequency of the exhaust system. Typically it occurs in straight pipe/less muffled systems. Like a tuning fork, the exhaust will resonate when the exhaust waves within it reach a certain frequency. Exhaust pressure waves are basically sounds waves, and move like a slinky through the exhaust...there comes a point when all is in harmony, with the waves in sync and the drone occurs. You don't get drone when accelerating because the system is constantly changing (through rpm)...drone comes at a steady state rpm. Usually someone finds the drone right at cruising speed in a certain gear at a certain speed...will really be annoying...in some cases tough to talk and hear inside the car, depending on the setup and how aggressive it is.

 

LT, catless x pipe and Ti bypass is the way to go. Add in cutouts for when you want it stupid loud! That’s what I did.....Nice and tame sounding when the wife is in the car and LOUD when she isn’t!

 

You're welcome. I'm not sure how scientific this is other than effort swapping/making exhaust combos LOL. Exhaust tinkering is an odd disease I have and really enjoy playing/understanding it. I wish I had better sound recording equipment other than my iPhone app to see more details about the interior noise with different setups in different driving situations and report back. You can start to gauge how loud something is compared to another catback. The takeaway is that I use the same app on the same phone, so while it may not be very "accurate" you can still evaluate the increase or decrease of sound.

Decible readings are not linear...so 100dB is not twice as loud as 50dB. IMO keeping interior noise 80dB or lower and higher than 150Hz would be real nice. When things get loud inside the car I've seen 85-95dB

I would agree BUT, IMO drone is there when accelerating. I have experienced it overtime I had a system that had drone. It would come on at say 1500-1800 RPM then go away. Whether I was driving normal on the dress from a stop light through the gears, or cruising it would still drone around that range. Yes it is typically worse/louder at higher loads situations like cruising uphill in 6th and 1500rpm.

 

I only hear drone on acceleration.

 

I ended up getting the bypass mod done on my stock catback (Ti system in the attic). It sounds pretty decent at cold idle with a good hint of crackle with the cam I have. A LOT less interior noise than the GHL catback by far.

It does have a slight "hum" around 2000rpm when cold and 1500rpm when hot. Any more and I would consider it "drone". It's livable but the downside is that when hot, the idle has tamed down a tad and lose some of that cold crackle. So I'm glad I did this to a stock catback and not the Ti system in case I experienced this on the Ti system.

I went with a full 1.75" bypass to match the pipe size of the exit pipes. I also made full size holes the same oval/oblong shape that the bypass pipe created when spliced into the system at awkward angles. I did try to make it come tangent off the over-axle pipe as best I could without hitting the trunk floor.The bigger 1.75" bypass MAY be the culprit for this "hum" but it gives the better idle crackle I like...and I'd still like MORE crackle/volume at hot idle. Hmph.

It needs some RPM to really open up and still sounds smooth/exotic. Another quirk is the earlier style catbacks have those small black tips...so I'm at the point where I determine do I spend the extra money/time getting tips figured out?

Longterm this car may end up with a Corsa Sport or Extreme...