resources for air impedance

[mlapalme]

Hey guys,

I am looking for a good beginner resource where i can learn about air impedance. I have been obsessed with ports for longer than I can remember and having been left a bit disappionted with the results of my recent foray into transmission lines....

I believe I need a better understanding of the fundamentals.


There's hope that a book off amazon could solve the cure but a good formula would be a guide as well.


Regards,

Marc

 

[GM]

Why? It's all on the net for the 'asking'..........

What was disappointing about TLs? Did you read through all that MJK has published? Quarter Wavelength Loudspeaker Design

How about here? Resonance Concepts

GM

 

[mlapalme]

Thanks GM,

Asking google is great but finding something specific in relation to a topic can be difficult to find... Just thought somebody here would have a good recommendation.


As for the transmission line, yes, I have read alot of material and have done several sims using different types of approaches and although the outcome works; It was underwhelming for the application that I chose.


There is room for improvement however, and that's where I'm hoping to deepen my understanding a bit and thought some direction would be advisable. I will probably just find a rabbit hole on the net somewhere and try to dig my way out as I usually do 😉


Regards

Ps: that site is a good resource. thanks for that.

 

[GM]

You're welcome!

Hmm, surprised my two links weren't of more help on both subjects, but I have pretty good luck w/Google, so hopefully these two slightly different searches will yield enough info for the acoustic impedance of air:

acoustic impedance of air - Google Search

acoustic impedance of air formula - Google Search

GM

 

[David McBean]

but a good formula would be a guide as well.

Not sure how much it helps, but the formula for "air impedance" at a given surface is defined as:

Za = p / U

Where:

Za = acoustic impedance (unit is newton-sec/m^5 or mks acoustic ohm)

p = sound pressure (unit is newton/m^2)

U = volume velocity (unit is m^3/sec)

Za, p and U are complex quantities, having real and imaginary components.

 

[mlapalme]

Not sure how much it helps, but the formula for "air impedance" at a given surface is defined as:

Za = p / U

Where:

Za = acoustic impedance (unit is newton-sec/m^5 or mks acoustic ohm)

p = sound pressure (unit is newton/m^2)

U = volume velocity (unit is m^3/sec)

Za, p and U are complex quantities, having real and imaginary components.

I have pulled this equation from gm's links and appreciate the clarification.


You said.

"Za, p and U are complex quantities, having real and imaginary components."

Your words have given me alot of intrigue.


Much appreciated.

 

[David McBean]

"Za, p and U are complex quantities, having real and imaginary components."

Just to clarify:

Za = Ra + j * Xa

Where:

Za = complex acoustic impedance
Ra = real acoustic resistance
Xa = real acoustic reactance
j = imaginary operator (-1) ^ 0.5

Za = p / U is the generalised complex acoustic equivalent to Ohm's Law equation V = I * R, rearranged as R = V / I.

Pressure p is the complex acoustic analog to electrical voltage V, volume velocity U is the complex acoustic analog to electrical current I, and impedance Za is the complex acoustic analog to electrical resistance R. Lumped-element simulation models use the acoustic equivalents to electrical circuit networks, when analysing loudspeaker systems.

 

[tschrama]

acoustic imepedance air = Speed of sound x density = 400

 

[David McBean]

acoustic imepedance air = Speed of sound x density = 400

Acoustic impedance = p / U, as previously stated.
The unit of acoustic impedance is newton-sec/m^5 or mks acoustic ohm.

Characteristic impedance = p0 * c where p0 = air density and c = sound velocity.
The unit of characteristic impedance is newton-sec/m^3 or mks rayl.

Two different things 🙂.