Random thoughts thread

[babydriver]

Originally Posted by jawn

The problem with sound tests is that it requires exacting test setups. You'd have to use the same equipment in the same configuration for each exhaust. You can easily skew one way or the other just by not having your meters calibrated cleanly, if the distances are slightly off, or if the background noise is different. It's like when folks post up "decibel" ratings from phone apps - it's meaningless without a calibration and knowing the test distances and configuration.

The only way to do it would be all at once in a closed environment. Crowd-sourcing would be a good way of getting a lot of bad data.

The only way that a closed environment would be preferable would be if it were an anechoic chamber. You couldn't do this in a garage, even a large one like in a shop for example, because the room resonances of the garage will be excited by the exhaust sound and skew the dB level. There is a way around this: go to a place where there is very little background noise, in the middle of an open area with no walls nearby (a big empty Chick-Fil-A or Hobby Lobby parking lot on a Sunday, for example.) The idea is to get rid of any near boundary reflections, except the ground. This is almost as good as an anechoic chamber. Use a standard distance (whatever the CHP uses?) and the same type of microphone/db meter for each case. The best choice for a mike would be something like a PZM, which would lie on the ground, effectively eliminating any reflection from the pavement and also extending the response curve. That would be important in the case of a muffler, since so many of the sounds are low.

Even having accurate dB levels won't tell the whole story, though, because the frequency spectrum also determines at least some of the quality. That is why "fart cans" are so annoying; they emphasize one frequency at the expense of everything else.

The speaker industry does something very close to what you're describing, measuring dB's at a specific distance under a specific set of repeatable conditions (anechoic chamber, set power input level), etc. Frequency response is also taken. In the case of speakers, there is also the use of a Fast Fourier Transform to gain information in the time dimension, but it would not be necessary for this idea.

Ideally, you'd want a standard temp (27C) for the test, but it should have minimal impact on the dB rating of a muffler! Just not in the snow, as it will MUFFLE the sound to a certain degree. I'm talking to you now, Tcoat. If you are in a quiet area, outdoors, you can probably ignore any background noise as sound decreases in intensity at the square of the distance. The volume of the muffler simply will swamp any background noise.

The data could be presented as dB at a specified distance (1 meter is used a lot for loudspeakers but that won't work with a dual exhaust...) and an averaged frequency response curve. Two sets of measurements could be used; dB/freq spectrum at idle and peak dB in neutral. Several vrooms at idle could be collected and the peak volume found. You could also have an average volume at peak throttle or a set RMP (5000?).

Getting all the various exhaust combinations together for measurement is the big problem. Seriously, guys, if you want to do this sort of measurement, I pretty much know exactly how it can be done. I also know about several audio-related software tools that could help capture and make sense of the data. All you would need is a laptop, the appropriate software and a calibrated microphone (and these are getting cheaper all the time).

Is the goal to avoid getting pulled over by the CHiPs, or is it to have the loudest possible exhaust system?

[babydriver]

Originally Posted by Tectoniic

Well today officially blows, I had to go into a snow bank to avoid hitting the cars ahead of me after one spun out and the other slammed on the brakes. Luckily no one was hurt but I cracked the passenger side of my front bumper. I was less than 500 yards from work and was 15 minutes early but with how long it took the tow to get there I was an hour and 40 minutes late.

A new bumper is whatever and after having it paint matched I'm sure it will end up close to ~600 all said and done. I'm worried about a small chip in the paint on the body where the passenger side reflector was pushed up and broke through the paint to the metal. The spot is maybe an 1/8" long by 1/16" wide and would not be visible once a new reflector is in there but now I'm worried about rust....Happy Holidays everyone, i'm gonna be drinking tonight.

Primer it and cover it. As you said, the side mirror will cover it anyway. No rust!

[RichardsFRS]

Hmmm
My ass hurts from doing weighted lunges and duck walks

[Tcoat]

Originally Posted by babydriver

The only way that a closed environment would be preferable would be if it was in an anechoic chamber. You couldn't do this in a garage, even a large one like in a shop for example, because the room resonances of the garage will be excited by the exhaust sound and skew the dB level. There is a way around this: go to a place where there is very little background noise, in the middle of an open area with no walls nearby (a big parking lot.) The idea is to get rid of any near boundary reflections, except the ground. This is almost as good as an anechoic chamber. Use a standard distance (whatever the CHP uses?) and the same type of microphone/db meter for each case. The best choice for a mike would be something like a PZM, which would lie on the ground, effectively eliminating any reflection from the pavement and also extending the response curve. That would be important in the case of a muffler, since so many of the sounds are low.

Even having accurate dB levels won't tell the whole story, though, because the frequency spectrum also determines at least some of the quality. That is why "fart cans" are so annoying; they emphasize one frequency at the expense of everything else.

The speaker industry does something very close to what you're describing, measuring dB's at a specific distance under a specific set of repeatable conditions (anechoic chamber, set power input level), etc. Frequency response is also taken. In the case of speakers, there is also the use of a Fast Fourier Transform to gain information in the time dimension, but it would not be necessary for this idea.

Ideally, you'd want a standard temp (27C) for the test, but it should have minimal impact on the dB rating of a muffler! Just not in the snow, as it will MUFFLE the sound to a certain degree. I'm talking to you now, Tcoat. If you are in a quiet area, outdoors, you can probably ignore any background noise as sound decreases in intensity at the square of the distance. The volume of the muffler simply will swamp any background noise.

The data could be presented as dB at a specified distance (1 meter is used a lot for loudspeakers) and an averaged frequency response curve. How you get all the various exhaust combinations together for measurement is the big problem.

Seriously, guys, if you want to do this sort of measurement, I pretty much know exactly how it can be done. I also know about several audio-related software tools that could help make sense of the data.

Is the goal to avoid getting pulled over by the CHiPs, or is it to have the loudest possible exhaust system?

Annnnd like I said, half will say I did it wrong. I haven't even posted the method, data strips or my findings yet and there are "better" ways being thrown into the ring.


You guys are way over thinking this. We are not looking at fine tuning the placement of high fidelity speakers here just a close enough reading of an exhaust.


Although I can see that this project is doomed from the start I will do up MY findings and post them. I will not however, debate my methodology or results as they are what they are and I am satisfied they are as accurate as possible in a non controlled setting.

[babydriver]

Originally Posted by Tcoat

I will not however, debate my methodology or results as they are what they are and I am satisfied they are as accurate as possible in a non controlled setting.

That's fair, but I hope you'll state the methodology along with the results.

[Tcoat]

Originally Posted by babydriver

That's fair, but I hope you'll state the methodolody along with the results.

Will provide the complete methodology but like I said will not debate it's merit or short comings. I did a lot of prep to try and find a easy method that anybody could do (with the understanding it is not controlled) since I know that everybody else does not have access to the $10K worth of test equipment I do.

[Ultramaroon]

Originally Posted by Special_K

Found Jared... I'm ashamed to find out he drives an 86.

[Ultramaroon]

Originally Posted by jawn

The only way to do it would be all at once in a closed environment.

It'd be kinda hard to breathe, though.

[WhiteFRS69]

have a Store meeting in the next 45 minutes

finding out with we are closing down shop or if the company is being sold off

should be interesting

[jawn]

Originally Posted by Ultramaroon

It'd be kinda hard to breathe, though.

Well, there would need to be air, otherwise we wouldn't have *any* sound.

[MisterSheep]

Originally Posted by WhiteFRS69

have a Store meeting in the next 45 minutes

finding out with we are closing down shop or if the company is being sold off

should be interesting

Goodluck!

[MonoRaven]

Originally Posted by jawn

The problem with sound tests is that it requires exacting test setups. You'd have to use the same equipment in the same configuration for each exhaust. You can easily skew one way or the other just by not having your meters calibrated cleanly, if the distances are slightly off, or if the background noise is different. It's like when folks post up "decibel" ratings from phone apps - it's meaningless without a calibration and knowing the test distances and configuration.

The only way to do it would be all at once in a closed environment. Crowd-sourcing would be a good way of getting a lot of bad data.

And what kind of shitstorm do you think you will start doing it that way?

[jawn]

Originally Posted by MonoRaven

And what kind of shitstorm do you think you will start doing it that way?

As much as I'm on here, I have better things to do with my time.

[babydriver]

Originally Posted by jawn

Well, there would need to be air, otherwise we wouldn't have *any* sound.

In space, no one can hear your muffler scream.