AFMG Network Forum
AFMG Network Forum Index -> AFMG EASERA -> Compare Two Channels for Transmission Loss Evaluation
Post new topic  Reply to topic View previous topic :: View next topic 
Compare Two Channels for Transmission Loss Evaluation
PostPosted: Tue Nov 27, 2007 5:00 pm Reply with quote
Gerry Pehl
Member
 
Joined: 26 Nov 2007
Posts: 1
Location: Twin Cities, Minnesota, USA




Hello EASERA Users,

As I was looking at the manual I came across the the measurement set up for comparing two channels for transmission loss evaluation on page 36.

I thought that was ridiculously cool, I've looking for that feature for years!

The icon even depicts a wall between the mics- awesome!

So can anyone offer any thoughts or point me to some resources on the proper way to do it in the field? A discussion on the SAC list brought up the point that no matter where the in room reference mic is it's in the pressure zones of some frequencies, and varying based on how proximity to which boundaries. And the distance required to be in the far field, outside of a building, for example would often be prohibitively far.

Practically speaking I thought I'd set up an experiment and just see what happens at various mic locations, but I wonder if there's an accepted way of doing this- can the magnitude and phase of the frequencies of the pressure zones be calculated or measured and reference out, for example?


Thanks for any thoughts on the matter!


Take Care,

Gerry
View user's profile Send private message Send e-mail
PostPosted: Wed Dec 19, 2007 3:49 pm Reply with quote
Stefan
Member
 
Joined: 19 Apr 2005
Posts: 167
Location: Berlin, Germany




Hello Gerry,

we have experimented with this measurement setup a bit. But our practical experience is limited to roughly measuring transmission through samples of some acoustic materials. Because the sample was fairly small-sized (like 0.1-0.2 sqm.) and rather thin, the microphones were placed quite close to the sample (less than 0.3 m).

Similar to the in-situ absorption measurements, you will have to make sure that you capture mainly the direct / transmitted sound, not reflections or diffracted energy. Windowing will help with that but limit you in the lower frequencies, of course. You will also have to make sure that you properly compensate for the propagation loss due to the distance between the microphones.

I cannot comment very much on the measurement of transmission through whole walls, but I know some EASERA owners have done that already. We will try to get some more information for you.

Stefan
View user's profile Send private message Send e-mail Visit poster's website
PostPosted: Thu Nov 13, 2008 9:36 pm Reply with quote
ameachin
Member
 
Joined: 04 Nov 2008
Posts: 3
Location: UK




Hi Gerry

I don't know if you are still interested in this, but...
You might find some useful guidance in ISO 140-4, the standard for sound insulation measurement between rooms. This says: "Obtain the average sound pressure level by using a single microphone moved from position to position, or by an array of fixed microphones, or by a continuously moving or oscillating microphone. Thesound pressure levels at the different microphone positions shall be averaged on an energy basis". It also states that all measurement positions should be at least 0.5m from a room boundary.

Hope that's useful,
Alistair
View user's profile Send private message Visit poster's website
AFMG Network Forum Index -> AFMG EASERA
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
All times are GMT  
Page 1 of 1  

  
  
 Post new topic  Reply to topic  


Powered by phpBB © 2001-2003 phpBB Group
Theme created by Vjacheslav Trushkin
Variation by CodeWeavers and AFMG