Posted by joamonte (A) on July 05, 2009 at 02:32:52

In Reply to: RE: Hmmmmmm... posted by KlausR. on July 03, 2009 at 23:19:52

Can share with us your ETC of the front 50ms of your room?

I am curious about the ETC of a room without early reflection control will look like, but I agree with you if the room is big enough and the speaker is small enough, early reflection control is not a must.....

Above picture is mine ETC graph in my very small 4.5 meter L X 2.9 meter W X 2.6 meter H listening room....

I am using broadband diffuser at side and front wall , and custom make BAD panel at ceiling and back wall ,no absorption is used at early reflection point, given the small size of the room and the big floor stander speaker I used (Marten Coltrane) , without all the diffuser at early reflection point, the ETC look really bad, as all the wall is pretty close to the speaker.

• ETC - KlausR. 13:32:06 07/05/09 (2)
  In Reply to: RE: Hmmmmmm... posted by joamonte on July 05, 2009 at 02:32:52

  I don't have any measurements of my room, and I don't think that measurements that are not correlated to human perception are of much use. In his paper
  
  "The detection of reflections in typical rooms", JAES 1989, p.539
  
  the authors (Olive & Toole) present ETC of the IEC room some of the threshold experiments were conducted in, in both treated and untreated conditions. The difference is clear, but since early reflections are merged with the direct sound within a time window, the size of which depends on the signal type (50 ms for speech, 80 ms for slow music) they do not represent any danger, if you will.
  
  Lipshitz and Vanderkooy have written a paper about ETC
  
  http://www.aes.org/e-lib/browse.cfm?elib=5837
  
  which is maybe interesting reading (haven't yet read it myself).
  
  It appears that when Dick Heyser introduced his TDS technique in the late 60's, for the first time it was possible to "see" early reflections, which initiated the different concepts of a reflection free zone in studio control rooms. No psychoacoustic research, no listening tests were made to connect the measurement to human perception:
  
  Voetmann, "50 years of control room design", AES paper 7140.
  
  So personally, I do not read too much into a measurement, ETC or other, when human perception is not taken into account.
  
  My room is 4.9 x 8.6 x 2.5 m, speakers are 75 x 40 x 45 cm (h x w x d).
  
  Klaus
  
  
  
  

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  • RE: ETC - joamonte 14:32:37 07/08/09 (1)
    In Reply to: RE: ETC posted by KlausR. on July 05, 2009 at 13:32:06

    Well....I am disagree with you on the part you mention room measurement is not important ,to me used only "human perception" to judge a room most of the time could be too subjective; I mean ,how do you know what is ACTUALLY happen in the first 6 ms or 30ms of early reflection, by using ear only if you hear something is affecting the sound quality ? human brain are too slow to response to what the ear have received...
    
    But I sure for those believe absorption on early reflection point is best solution in any room acoustic treatment should read below pdf....."Broadband reflection"~~ hmmmm...It do make a lot of sense to me...LOL.;-D

    • http://www.linkwitzlab.com/AES'07/AES123-final2.pdf   (Open in New Window)

    
    

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    • RE: ETC - KlausR. 01:40:57 07/09/09 (0)
      In Reply to: RE: ETC posted by joamonte on July 08, 2009 at 14:32:37

      To give you one example: some people say that comb filters are a problem and the proof is that they appear in measurements (e.g. Fig.1 on
      http://www.realtraps.com/rfz.htm)

      BUT

      How do you know that what you measure is indeed audible?

      You don't unless you go to the lab and run psychoacoustic experiments with comb filters. This has been done and subsequently thresholds of audibility do exist but simple measurements not taking such thresholds into acount are preety much meaningless:

      Salomons (1995), “Coloration and binaural decoloration of sound due to reflections”, Thesis, Delft University

      http://www.darenet.nl/en/page/repository.item/show?saharaIdentifier=tuddare:oai:tudelft.nl:200755

      The same goes for "what happens in the first 6 or 30 ms of early reflections". The precedence effect has been studied very extensively so perceptional scientists have a good idea of what is going on:

      Litovsky et al. (1999), “The precedence effect”, J. of Acoust. Soc. of America, vol. 106, p.1633

      I'm not saying "do not measure but listen instead", I'm saying" measure but correlate what you've been measuring to how humans hear.

      Klaus

      
      
      

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      Edits: 07/09/09

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