3 replies to this topic

[aether]

Hello, I'm a student looking to build an impedance tube setup and need some expert knowledge on the microphones. For those unfamiliar with impedance tube they basically setup a standing wave along the length of the tube and the pressure is measured at various locations which in turn allows you to calculate the acoustic impedance at the sample end. Here is a pic:



I am currently using very cheap microphones (<$10) as a quick mock up and they are proving quite unreliable. My budget would preferably be in the few hundred dollar range, the less the better

For this application:
-the smaller the width the better (ie 1/2" or 1/4")
-unidirectional, the only pressure I'm interested in is from the plane waves at the surface of the tube.
-I am using measurement equipment that has a maximum input voltage of +-7 V @ 50 ohms, so I'm not sure which power system to use. Currently with the cheap electret mics, I am just using a simple op amp pre-amplifier. Can I get away with not having a high voltage phantom power setup?
-Flat frequency response is not so important as I will be measuring relative changes at specific frequencies. My biggest need is for them to be highly repeatable so to have very small changes with temperature and a linear response with amplitude.

Could you suggest any microphones that you have used or know of that could perform this task well? Thanks for your time!

[rhythmboy]

Hi aether, welcome to SP!

In that price range, I suggest:

- Behringer C-2 condenser, the cheapest at $90-100 for a pair: http://www.behringer...oducts/C-2.aspx



- Earthworks SR25, more expensive at around $600-800US each: http://www.earthwork...-series-2/sr25/



- Rode NT-5, in the middle at about $500 for a matched pair: http://www.rodemic.com/mics/nt5-s


It sounds like for what you are after, the C-2's may well do the job. Hope this helps

[Spectrum]

aether, on 26 January 2012 - 03:16 AM, said:

Hello, I'm a student looking to build an impedance tube setup and need some expert knowledge on the microphones. For those unfamiliar with impedance tube they basically setup a standing wave along the length of the tube and the pressure is measured at various locations which in turn allows you to calculate the acoustic impedance at the sample end. Here is a pic:

You have me intrigued! I get the idea of standing waves from the frequencies that align themselves with the length / tuning of the tube, and you're taking measurements and analysing them at various points along the tube (that's kinda right, yeah?), but curious how is it used in practice? And what is it typically used for? Even Google's left me stumped.

[Jon S]

As i understand it you use an impedance tube to measure the absorption coeffecient of different materials, for use in soundproofing/roomtreatment. Done by measuring pressure on one side of the material with a sound source vs sound pressure on the otherside via transmission through the material. I think...