The Sedan Exhaust Thread
Well, not exactly. At the risk of thread-jacking, it depends on whether you're talking about the root-power ratio or field-power (amplitude) ratio. In the case of the power ratio, increasing power by a factor of 10 increases the sound level by 10db. When talking about amplitude, the same increase raises the sound level by 20db. In audio systems it's a generally accepted math shortcut that doubling the amplifier power raises the output level by 3db, all else being equal. That's the root power ratio measurement. Exhaust is an acoustical system, not an electrical one, so we're talking about the amplitude ratio, which is what we measure with an spl meter. So 6db here is the standard for double.
It's frequently assumed that listeners perceive 6db as a doubling of the volume level because of the dual scales, but it's not actually true because the human ear doesn't perceive volume linearly. 6db is double the sound pressure, but not necessarily double the sound intensity. Most audio engineers consider 10db to be the rule of thumb for doubling the subjective volume. (but then it depends on the weighting you use)
We could theoretically do some rough math here and say 97db is just short of 50% louder than 93db to the listener, but that would require that we know the measurement methodology, since doubling the distance from an audio source inherently reduces the amplitude by 6db in an acoustically neutral environment. Double can come fast if you are close-micing the source.
It's frequently assumed that listeners perceive 6db as a doubling of the volume level because of the dual scales, but it's not actually true because the human ear doesn't perceive volume linearly. 6db is double the sound pressure, but not necessarily double the sound intensity. Most audio engineers consider 10db to be the rule of thumb for doubling the subjective volume. (but then it depends on the weighting you use)
We could theoretically do some rough math here and say 97db is just short of 50% louder than 93db to the listener, but that would require that we know the measurement methodology, since doubling the distance from an audio source inherently reduces the amplitude by 6db in an acoustically neutral environment. Double can come fast if you are close-micing the source.
So I posted earlier that I installed the TopSpeed axle back muffler delete. It was a huge jump up (in sound) from the Tanabes and I was thinking no way I keep this. I had only really heard it while being inside the car but after yesterday, having to valet and hear him backing it into a spot which also happened to be aimed right at the outside patio of the place, it was turning heads and sounded extremely nice.
Registered Member
Joined: Jul 2015
Posts: 1,397
Likes: 335
From: Maryland
So I posted earlier that I installed the TopSpeed axle back muffler delete. It was a huge jump up (in sound) from the Tanabes and I was thinking no way I keep this. I had only really heard it while being inside the car but after yesterday, having to valet and hear him backing it into a spot which also happened to be aimed right at the outside patio of the place, it was turning heads and sounded extremely nice.
Do you have a coupe or sedan? The Invidia Gemini for the coupe is WAY different than the Invidia Q300 for the sedan. That may be why opinions differ so dramatically. The q300 is a very quiet setup, just a bit deeper and more noticeable than stock, that is what I am running now, with stock cats.
Mine's a sedan. The main issue with the Invidia wasn't the volume level but the terrible highway drone. Around town it actually sounded pretty good, but everyone who road in the car at highway speeds (i.e. 70 - 75 mph) commented on how bad it was. I was using the car for business at the time and ended up having to pull off the exhaust off the car because the drone would give me headaches on longer trips. I ended up combining the Invidia crossover and mid-pipe with a Tanabe Axle back and that sounded MUCH better but still had a little too much drone for my tastes. Finally just went back to just the Tanabe axle back and combined it with the Tanabe y-pipe and have been happy with it since. My second exhaust was an FI system, but before they offered it with resonators. I actually really liked that exhaust but without the resonators it also had a little too much drone. I'm now talking with FI about doing a custom set-up for my sedan using the round coupe mufflers in carbon fiber along with 18" resonators.
Last edited by ZahyMatar; May 9, 2017 at 04:30 PM.
Registered User
Joined: Jan 2016
Posts: 27
Likes: 4
From: MN
I recently removed the resonators from my Top Speed Y back exhaust. They were rubbing/rattling against the rear sway bar. Here's a quick flyby.
It is a little bit louder inside but no drone. Definitely enhanced the tone of the exhaust. Next plan is to get the Top Speed Y pipe and HFC.
It is a little bit louder inside but no drone. Definitely enhanced the tone of the exhaust. Next plan is to get the Top Speed Y pipe and HFC.
Glad to hear that someone else already has this set-up, Zahy. Drone is my main concern as to why I haven't pulled the trigger on this set-up from FI yet. I'm currently running OEM cats to help keep drone to a minimum and I'll most likely keep the OEM cats with the new set-up too. Can you tell me at what RPM's you are experiencing the most drone?
