Exhaust resonance ... How do YOU define it?
Before owning this Corvette, I owned a 1999 Camaro Z28 (automatic transmission) with a Borla exhaust. I loved the sound of the exhaust and figured that I could just get a Borla for the Corvette to get the same sound. But then I started reading about and listening to exhuasts on this and other Corvette bulletin boards. What I read, I did not like. When speaking of C4 exhaust systems, almost everyone speaks about RESONANCE. Some people don't like resonance, so they spend their money on a Corsa exhaust. Others still don't like resonance, but they like the sound of the exhaust even more. So, they buy one of the many exhuast systems for a C4 that all seem to create resonance to one degree or another.
My question is, How do YOU define resonance in your Corvette? The Borla on my Camaro was loud. After four hour trips to Blacksburg, I would get out of the car and my ears would ring as if the world had just gone dead silent. This didn't bother me. I loved listening to the exhaust. However, I get the distinct impression that when people refer to resonance with their Corvettes that they mean the exhaust is making things vibrate and rattle inside of their car. Nothing rattled or vibrated inside of my Camaro, and I could still have a conversation with my passenger if the windows were rolled up. Is there someting about the LT4 and LT1 engines that makes an exhaust sound different than an LS1 run through a similar exhaust system?
The bottom line is that these systems are expensive and I don't want to spend major dollars on a system that will either be too quiet with no resonance (basically stock) or sound great but rattle the inside of my car apart. I only want an exhaust system because the stupid stock setup makes no noise. I could put this thing on a Cadillac. Heck, my brother's 1988 V6 Camaro stock exhaust sounds better. What fun is going fast if the whole world doesn't hear you coming and going?
Anyway, if you read this far, please let me know what your definition of resonance is with regard to your aftermarket exhaust system. Thank you for any and all replies.
Originally Posted by Nick S
I can't help you with your question, but I definitely like your style!
First let me say that adding an aftermarket exhaust to our cars should be mandatory...at least I think so.
Resonance (to me) is the "hum" that you get (inside the car) from the exhaust at certain rpm's. It sounds to me like your Z28 had a good exhaust note & you can expect the same from an aftermarket system for your 'vette. If you could stand the sound of your "Z" then I don't see why a good system on the LT4 won't please you either. You can hear my Magnaflow sytem on my webpage. You can get this stainless steel system for less than $350 shipped from www.performancepeddler.com BUT you must call them and negotiate a price. The system made a big difference on my car and the "resonance" is almost non-existent. Now my 'vette sounds like a .....'vette should!
Btw...I could have spent more on a system but after hearing only good things about the Magnaflow (look & sound great) I decided to give them a go and I'm happy I did.
GM Hot Cam - EM Longtube Headers - BBK 52mm TB - PCMforless Tune
B&M Shifter - Meziere HD EWP - SLP CAI - Big Mouth Air Dam
Grand Sport Calipers - BP Drilled & Slotted Black Rotors
Magnaflow SS 3" Exhaust - RD EWP Camber Brace
Goodyear Eagle F1 GS-D3's in 285's & 315's
Goodridge SS Lines - Hawk HPS Pads
GM 30mm/26mm Solid Sway Bars
QA1 12way Adjustable Shocks
Lowered Front & Rear
~ 4.10 Gears ~
Yeah, the Camaro had a sort of humming sound when cruising. I didn't know that was resonance. I just thought it was normal. From what I have been reading, I was afraid that resonance meant that screws started falling out of your ceiling and things started vibrating around/apart in the cabin from the exhaust. From people's descriptions in various posts, that is what I thought was happening and why people avoided certain exhausts. If that hum that I experienced in the Camaro is resonance, then bring on the resonance. Heck, at NASCAR races, I like to keep the headsets off to listen to 43 unmuffled exhausts. Thank you for the reply. That helps me a lot.
Anyone else have any thoughts on resonance?
Some exhausts are just loud. They don't have resonance, they are just loud all the time. But to me, resonance is a noice only at certain rpms. And can be pretty loud at low throttle openings. For example, my car is quieter in 5th cruising at 65mph than it is in 6th at 65mph cruising. The fact that the engine gets louder from dropping rpms is indicitive of resonance to me. If it were just a loud exhaust, it would be louder in 5th and loud in 6th at the same road speed.
Aurora40,Thank you for the reply. It looks like you too are telling me that resonance isn't so much a vibrating of the interior of the car as it is a certain sound/noise. These replies are helping me to clarify what is meant by resonance. Apparently, resonance is a specific yet subtle sound made at a specific engine RPM rather than some kind of bone rattling, brain shaking noise made from interior vibration at a certain RPM.
Anyone else have any ideas? Maybe I'm too simple to intuitively understand what resonance is; however, creating a good definition of what resonance is through each person's experience is really helpful to me in making a decision about an exhaust system.
to me resonance is the drone pitch of the exhaust during every gear change and at cruising rpms. it has nothing to do with vibration of any kind. as you mentioned, you could run your camaro for a few hours, get out and be effectively deaf to the world. that is resonance in my opinion. to many, it is offensive and reduces the pleasure of their driving experience. to most others (myself included), i am from your school, bring on the rumble from the exhaust!! real or perceived, every "throaty" car exhaust exudes power to me!! i agree that the first change that one makes to a car should be to open up the exhaust and let the car breath (yeah, i know it's exhaust not breath, but to me it helps define the personality of my ride!!) BTW the 78 pace car i am putting back together has been modified to have true dual exhausts (no cat), no mufflers, just ansa resonators and dual tips!!
What an absolutely EXCELLENT question! Resonance is a term used quite frequently...but not very understood.
I am by no means a physics expert...(and I did NOT stay at a Holiday Inn Express last night ). My backgound is mostly electronics...but there are quite a few concepts that carry across different fields...resonance being one of them.
There will most likely be an "error" or two...but I will do my best. Here goes:
Physics. The increase in amplitude of oscillation of an electric or mechanical system exposed to a periodic force whose frequency is equal or very close to the natural undamped frequency of the system.
Acoustics. Intensification and prolongation of sound, especially of a musical tone, produced by sympathetic vibration.
These two definitions are actually pretty much saying the same thing...just different "applications" (if you will).
Basically...everything has a resonant frequency...that is a frequency at which it naturally vibrates if given an external stimulus. A guitar is a perfect example of mechanical resonance...when you "pluck" a guitar string it vibrates and produces a sound...the frequency at which it vibrates is it's resonant frequency. The level of sound that is produced is determined by the amplitude...or how far the guitar string travels back and forth after it is plucked. Of course the sound is loudest when the string is first plucked, and gets lower as the amplitude of vibration decreases, to the point where the string stops vibrating. Now imagine a shaft of some sort attached to the guitar string that's driven by a motor or something that mechanically can move the same guitar string back and forth. As the motor speed is increased the string is moved back and forth (or oscillating) faster. When the oscillation frequency becomes high enough, you start to hear sound coming from the guitar (not that this would really work...this is just an attempt to explain a concept as I understand it). As the oscillation frequency increases, so does the pitch of the sound coming from the guitar...BUT the important thing is that the sound level does not increase...ONLY the pitch. As you reach the resonant frequency of that guitar string things change...the sound DOES start becoming louder, because of the "Physics" definition above...because there is a periodic force being applied to the string AT it's resonant frequency...and the amplitude of the oscillation is greatly increased. Think of resonance as the ability of the string to actually generate it's own energy to oscillate and produce a sound...if it weren't able to do that then when you pluck it it would simply return immediately back to it's "rest" position and you would hear nothing. The string's own resonance energy is added to the external periodic force, amplifying the amplitude of oscillation...making the sound from the guitar louder. By the way...the term "natural frequency" mentioned in the first definition is the same thing as resonant frequency.
Another good mechanical example is a speaker. A speaker has a defined frequency response (within the range of human hearing of course )...subwoofers a low frequency response, tweeters a high frequency response...etc. Let's take a subwoofer that has a frequency response of 20Hz to 100Hz (just as an example). A speaker cone moves by applying electrical current through an electromagnet, moving the cone back and forth. If you were to apply a current oscillating at a rate of 200Hz our subwoofer with a response range of 20Hz to 100Hz...nothing would happen because the "periodic force" being applied is outside the range of the subwoofer. Now, this subwoofer also has a resonant frequency...if the resonant frequency were to fall within the response range of the subwoofer...well you can imagine what would happen...you'd get a very large increase in sound level from the subwoofer at it's resonant frequency...very likely enough to tear the cone. For this reason the resonant frequency must fall outside of the useable frequency range of the subwoofer.
Now, the cockpit of your car also has a resonant frequency...but in a little different way...more related to the second definition above and sound waves. If a pressure wave is generated inside the car, it will bounce back and forth at some frequency...resonant frequency. When you are driving the exhaust is producing sound waves at varying frequencies...well guess what happens when the "sympathetic vibration" (see definition above) of sound waves coming from your exhaust exactly matches the resonant frequency of your cockpit! That's when it starts to sound like there's an F-15 taking off next to you...and when you find out exactly what's still rattling inside the car!
Another concept mentioned in the above definitions is "damping". The best example I can come up with of damping is a suspension system. Say for example you have a car (with something a little softer than a Vette suspension ) sitting still...but it has no shock absorbers on it. The springs of the suspension have a resonant frequency. If you push down on a corner of the car as far down as it will go, then release it, it will come up above the "rest" position, then back down past "rest", then back above a little less, then back down a little less...until it stops bouncing. This action is the same thing that happens with the guitar string...it oscillates at resonant frequency, and the amplitude of oscillation gets smaller over time. If you were to plot the position of the guitar string, or the fender of the car, over time on an X/Y graph, you would get a sine wave that gets smaller and smaller over time. This is an underdamped sinusoidal response (also called "simple harmonic motion). Now, add a shock absorber and perform the same experiment. If the shock absorber is "damping" correctly then the fender will come back up and "overshoot" the "rest" position only once, and settle immediately after that first "overshoot" to the "rest" position. This is known as being "critically damped". If the shock absorber is over-damping the spring, then there will be no "overshoot" and the corner of the car will take a longer time to come back to rest position.
Oh also forgot to add...you would be AMAZED at how much difference simply extending the tailpipes a couple of inches will make in decreasing resonance in the cockpit from exhaust sound!
*sigh* ...a man after my own heart...
Originally Posted by Nick S
I was tickled PINK when I was able to buy a chambered exhaust system and have it installed on the 78 several years ago. It was installed in late fall and I picked it up at the end of the day and drove around with the windows down and my ears freezing but I had the BIGGEST grin on my face!
I LOVED the rumble and roar! Exactly what a muscle car should sound like.
For me, resonanace is defined as a certain sound that I get from my exhaust at certain rpms. I don't get it under hard acceleration, but at regular acceleration I have a "buzz" noise at about 2500 in town speeds, so I try to avoid that rpm.
ps... Great info, Bill!
Huh.....Yeah.....umm.... My thoughts exactly.
Originally Posted by geekinavette
Originally Posted by JEFNLSA
And I absolutely love the TV HooverChair 7000!!
Originally Posted by JEFNLSA
Common sense is like deodorant. The folks who need it most never seem to use it and there's no polite way to tell them.
I think that your essay on resonance was excellent. The scientific explanation of resonance complements everyone else's first hand descriptions of resonance from their vehicles' exhaust.
When referring to exhaust, resonance is a certain sound that is produced on the inside of the car from the pulses of the exhaust gas passing through the exhaust system. The presence of this sound does not mean that the inside of the car is vibrating or rattling uncontrollably (physically and visibly shaking). However, the sound is a result of the materials inside the cabin of the car resonating. The tone and loudness of the sound created varies based on the velocity of the exhaust being forced through the system (which is determined by engine speed, RPM).
Is that definition accurate? Does that seem to be what we have all been saying when we have described resonance?
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