All that Helmholtz business

[iolair]

Sorry for the misunderstanding.....the crap I was referring to is mine, not yours and in fact it is old news to me, since

it was done 20 to 25 years ago!

quote:

>>If you do not keep an open mind you will simply end up like the professor that confidently predicted the impossibility

of exceeding 150 mph in the quarter mile.....jeeze, how embarrassing!<<

Again, I was referring to the understanding/acceptance of my stuff, not yours!

I read your paper, and it's good stuff!



Outside in as opposed to inside out! If you bottom line it, induction science is

based on intelligent restrictions per rpm data points.....if not, a 55 gallon drum would be an appropriate port size for

all induction systems

>>BTW2...Nice car.<<

Thanks Sam, I appreaciate that! Here is a photo of the donor car!



John

[Nishant Jain]

I'm looking to implement an Acoustic Impedance Transform test into our intake design system, having read Sam's paper.

But I'm quite weak in my acoustics knowledge, and am confused about how to proceed with the testing.

Do I simply measure p/p ratio or voltage output against different frequencies to find resonance? I dont know how to go about calculating the effective acoustic impedance of the system, so I cant make the impedance vs rpm graphs that are shown in the paper?

can someone point me in the correct direction? i know it must sound pretty basic after the extensive conversations i've read up on the forum about this topic, but i think everyone happened to skip over this one bit!

[Jersey Tom]

Wow. Takin' it back to the old school with this one.

It has been a while since I looked over Sam's paper, and I don't have it in front of me, but I could have sworn it went through and showed how to calculate the impedance of the system vs RPM?

[Nishant Jain]

Yeah, it has equations for closed and open ended pipes. We're supposed to construct the full intake system from that.

The problem is, I do not know what kind of values to put in some of the variables. For example, length (L) would be in feet, inches, mm? Also, some of the constants I do not know the value to.

Again then, reading the posts here, nobody seems to ask about such things. So I can only presume that they know already! Or, as I was wondering, maybe it isn't needed at all. As I see it, measuring only for the resonant frequency is not a very accurate determination, as compared to having impedance values.

[Sam Zimmerman]

Originally posted by Nishant Jain:
I'm looking to implement an Acoustic Impedance Transform test into our intake design system, having read Sam's paper.

But I'm quite weak in my acoustics knowledge, and am confused about how to proceed with the testing.

Do I simply measure p/p ratio or voltage output against different frequencies to find resonance? I dont know how to go about calculating the effective acoustic impedance of the system, so I cant make the impedance vs rpm graphs that are shown in the paper?

can someone point me in the correct direction? i know it must sound pretty basic after the extensive conversations i've read up on the forum about this topic, but i think everyone happened to skip over this one bit!

In the paper I described the DVT method. I haven't worked in this field for about three years, but here it is from memory. You need a prototype intake, a large loudspeaker, and an acoustic microphone. You do the test twice, once with the microphone in front of the loudspeaker and once with the microphone in the same location but with an intake positioned so that the microphone will measure the intake resonate frequencies.

Record sound power vs. frequency for both cases. Plot the ratio of the two sound powers (with and without the intake) as a function of frequency and you will get your resonate frequencies.

If you design a plenum with plungers in the ends and runners that allow for their length to be changed easily you can work through several geometries rather quickly.

I hope this is vauge enough that you have to do your own planning and thinking but detailed enough for you to figure it out. If you are still struggling, take it to your acoustics professor and have him/her help you out. If that doesn't work, have a beer and work on something else for a while.

Good luck.

[Nishant Jain]

@Sam: Thanks a lot, Sam. I was thinking along similar lines, and it is a great help to know how to go about it. I'm figuring out the impedances now.

I'll buzz you again if there are hitches.

Thanks again.

Nishant Jain.

[Nishant Jain]

So I set up the test. I'm using a freeware off the internet to record sound-waves from my microphone. And it gives me the graphical amplitude for one frequency at a time, so I have to run it over and over for the different frequencies.

The problem: the amplitudes don't seem to vary at all! Over a large frequency stretch, they only get higher and higher to peak into a square shape and then don't change.

I cant locate any resonance OR anti-resonance!

Is this a microphone problem maybe? Or would it just be better to use a multimeter/CRO tapped on the microphone instead of a freeware? Or is it something else altogether?

[Drew Price]

It looks like the signal input to your computer is maxing out. Maybe try some kind of attenuator on the end of your microphone (foam, like a wind-shield for the mics, or some cloth or something) or try moving it farther away? Or turn the gain or input levels down, or try a different mic and/or soundcard.



Best,
Drew

[Jevon]

Drew's got it. It looks like you are saturating your input. You said the amplitude gets higher and higher and then peaks. Well, It's still going higher you just aren't measuring it.

You can easily adjust this in software. I've never used the program you are using but it looks like you will need to turn down the volume slider in your "Realtime Analyzer RAL" window. Also make sure you properly adjust your "Line-In" volume for your sound card in the control panel. Conversely, you could turn down your output levels.

Adjust the levels so that the maximum amplitude you intend to record does not get cut off.

Regards,

Jevon

[Mikey Antonakakis]

Man, this was a good thread, worth the three year bump!

To anyone else who might read this thread, I highly recommend Ricardo WAVE, as long as you give yourself a few months to learn the software. Once you get the hang of it, you can start from scratch with intake and exhaust models and have torque curves and just about any other data you'd ever want in a matter of hours. I have yet to prove the simulations for myself, but once we get our dyno running, I'll be sure to start a thread on here (although I'll really only have one set of intake and exhaust geometries to work with).