In room measurements

Collapse
This topic is closed.
X
X
 
  • Time
  • Show
Clear All
new posts
  • sfdoddsy
    Senior Member
    • Sep 2000
    • 496

    In room measurements

    Just wondering how people recommend going about in room measurements, especially for big dipoles. What signals, mic distances and programs etc.

    I'm currently using TrueRTA with a Behringer ECM into the soundcard of my Toshiba 5005 laptop, with pink noise generated by TrueRTA and output from the soundcards SPDIF output.

    Alas, the line in and out aren't particularly working in my laptop so I may need to shell out for an external card.

    Also, for some reason the burst thing on True RTA is also not working.

    Thanks

    Steve




    Steve's DIY Dipoles
    Steve's OB Journey
  • JonMarsh
    Mad Max Moderator
    • Aug 2000
    • 15213

    #2
    This is not a simple topic... and if you take a look at some of the measurement efforts for dipoles like Magneplanars, such as at Stereophile magazine, you'll see that conventional methods will sometimes give you some strange looking results, particularly if you try to correlate the measurements with what you hear.

    You could go to a lot of effort to measure the dipoles in a way to ignore or minimize the affect of the room, and you could do this in a variety of ways... but, is that really the useful way to go? Because, you'll be listening to them in your room, not outdoors, not in a specialized measurement setup.

    Now, with monopole systems, it's not too hard to make some recommendations. Some of these will still hold pretty well for dipoles.

    First, you can do MLS measurements gated so that reflections from walls and ceiling are not in the picture, because the total travel time exceeds your measurement window. This is the only way to get quasi anechoic measurements in a home listening room. Becuse of the proximity to the floor for the typical woofer in typical placement, that bounce or interface will still be there. This is why Roy Allison did his work on driver positioning, and coming up with some ideas about how to position drivers so as to minimize the destructive effects of boundary reflections.

    Then, there's the affect which you always have in a real room of boundary reflections. For a monopole design, you can at least calculate this for various positions, taking into account the LF roll off of the system nearfield, and determine a positioning which, in combination with the boundary lift (or as it's often called, room gain), will produce a relatively flat in room response. Then, the other variable is listener position; or measurment position; this can be evaluated theoretically with tools like the room spreadsheet from Stereophile, or tools like RPG Room Optimizer. This process just tells you roughly where the speaker should be in the room, and where some good listener positions are.

    Then, at that point, you might evaluate either using long gated MLS sweeeps or a narrow band RTA. Expect that the high frequencies will be rolled off a bit, because this is measuring the direct and indirect response, or total power response, and highs will be absorbed more quickly than lows in most cases, unless you've got a concrete box for a listening room.

    For a dipole system, figuring out a good location is not so simple, and myself, I would use an iterative approach. But frankly, I'd use roughly the same starting position as the Cardas approach, particularly in the development phase. That means the panels are going to be well out from the walls, so there will be some opportunity to develope a good figure 8 or cardiod pattern. Of course, if you won't listen to them that way, then moving them closer to the wall and measuring and tuning there may be the only choice; but I expect you'll see more problematic results in getting smooth low to midbass response.

    In the 70's I used to sell and install Magneplanars, and the problems were exactly the same. Setup is very important, and to tune them for realistic response, without a "fat" upper midbass, and too much cancellation in the lower bass, they needed room away from the walls. I don't think our cone type dipoles can be optimized any differently; my testing and development work with the Arvo's is done at a minimum distance from the rear wall of 6-7 feet, about 2 meters. I think anything less may introduce problems. Just my opinion, but our experience playing with and setting up ThomasW's Whispers was exactly the same. Side wall is not very critical, though your still need some room. Three feet minimum seems OK.

    So, my point would be to measure and tune the region above 200 Hz using MLS in quasi anechoic mode, then tune the positioning and EQ, and measure at listening position with tools with either a long gate on MLS, or narrow band RTA. And dont' be afraid to experiment with listening and speaker position- get everything as good as you can through positioning before you tweak the EQ, IMO.

    -Jon




    Earth First!
    _______________________________
    We'll screw up the other planets later....
    the AudioWorx
    Natalie P
    M8ta
    Modula Neo DCC
    Modula MT XE
    Modula Xtreme
    Isiris
    Wavecor Ardent

    SMJ
    Minerva Monitor
    Calliope
    Ardent D

    In Development...
    Isiris Mk II updates- in final test stage!
    Obi-Wan
    Saint-Saëns Symphonique/AKA SMJ-40
    Modula PWB
    Calliope CC Supreme
    Natalie P Ultra
    Natalie P Supreme
    Janus BP1 Sub


    Resistance is not futile, it is Volts divided by Amperes...
    Just ask Mr. Ohm....

    Comment

    • Dennis H
      Ultra Senior Member
      • Aug 2002
      • 3791

      #3
      SL addresses positioning in one of his papers. As Jon says, side to side isn't as critical but you can still get big front to back modes with a dipole. SL's recommendation is to put the speakers the same distance from the wall in front of the listener as the chair is from the wall behind the listener. That way the reflections cancel. Say, for example, the room is 20 feet long and you put the speakers at 5 and the listener at 15. The plus wave comes from the front of the speaker and travels 15 to the back wall and another 5 to the listener for 20 total. The minus wave travels 5 to the front wall and then 15 to the listener for 20 total. Voila, the plus and minus reflections cancel and you're left with just the direct sound. In theory......

      Comment

      • sfdoddsy
        Senior Member
        • Sep 2000
        • 496

        #4
        I don't have listening position probelms as there is only one place my speakers can go in my current room, and fortunately that gives about 8 feet or more behind them.

        What I'd like to do is get the very best out of them, and that I guess knowing exactly what is going on in room now.

        They are flat when measured at the seetspot with TrueRTA now, but I'm going to start playing with the ETF demo and say what that says.


        Steve




        Steve's DIY Dipoles
        Steve's OB Journey

        Comment

        • JonMarsh
          Mad Max Moderator
          • Aug 2000
          • 15213

          #5
          Hey Steve,

          If they are "flat" with TrueRTA now, at the "sweet spot", they may be a skosh "hot" in the direct sound on the top end- ETF would be a good sanity check- look at the direct sound in MLS from 200Hz to 20 kHz. If that's OK, you should be done.

          Is there something you're hearing and not satisfied with that is driving you to do additional measurements?

          -Jon




          Earth First!
          _______________________________
          We'll screw up the other planets later....
          the AudioWorx
          Natalie P
          M8ta
          Modula Neo DCC
          Modula MT XE
          Modula Xtreme
          Isiris
          Wavecor Ardent

          SMJ
          Minerva Monitor
          Calliope
          Ardent D

          In Development...
          Isiris Mk II updates- in final test stage!
          Obi-Wan
          Saint-Saëns Symphonique/AKA SMJ-40
          Modula PWB
          Calliope CC Supreme
          Natalie P Ultra
          Natalie P Supreme
          Janus BP1 Sub


          Resistance is not futile, it is Volts divided by Amperes...
          Just ask Mr. Ohm....

          Comment

          • sfdoddsy
            Senior Member
            • Sep 2000
            • 496

            #6
            When I say flat, I mean flat at my desired curve, which is a downward slope like this:



            Apart from the anomaly in my 'critique' post they sound wonderful, and that appears to be a prepro problem. I just get a bit anal sometimes.






            Steve's DIY Dipoles
            Steve's OB Journey

            Comment

            • JonMarsh
              Mad Max Moderator
              • Aug 2000
              • 15213

              #7
              This is exactly the kind of curve you want to see on an RTA measurement; it should correlate well with fairly flat axial response. Though, there is a possiblity that the "ideal" RTA for a dipole will be flatter than for a sealed box, since there's less room contribution in the lower mid through midbass. Still, trust your ears.. this should be quite nice sounding.

              ~Jon




              Earth First!
              _______________________________
              We'll screw up the other planets later....
              the AudioWorx
              Natalie P
              M8ta
              Modula Neo DCC
              Modula MT XE
              Modula Xtreme
              Isiris
              Wavecor Ardent

              SMJ
              Minerva Monitor
              Calliope
              Ardent D

              In Development...
              Isiris Mk II updates- in final test stage!
              Obi-Wan
              Saint-Saëns Symphonique/AKA SMJ-40
              Modula PWB
              Calliope CC Supreme
              Natalie P Ultra
              Natalie P Supreme
              Janus BP1 Sub


              Resistance is not futile, it is Volts divided by Amperes...
              Just ask Mr. Ohm....

              Comment

              • sfdoddsy
                Senior Member
                • Sep 2000
                • 496

                #8
                Your nice comments are music to my ears.

                :LOL:

                I've posted more accurate 1/24 octave measurements at my site. including before and after room EQ for those interested.



                Cheers

                Steve




                Steve's DIY Dipoles
                Steve's OB Journey

                Comment

                • sfdoddsy
                  Senior Member
                  • Sep 2000
                  • 496

                  #9
                  Well, I've finally got myself an external soundcard (the new Soundblaster MP3+) so I can start playing seriously with ETF and MLS measurements.

                  When trying for quasi-anechoic measurements, what gating is it best to use, and where should I position the mic in relation to the speakers... 6 inches... 12 inches... 3 feet... next room?

                  And at what height... tweeter level... ear level?

                  And any tips for woofer measuring? Ground Plane... mouth of the frame?

                  Thanks to all.

                  Steve




                  Steve's DIY Dipoles
                  Steve's OB Journey

                  Comment

                  Working...
                  😀
                  😂
                  🥰
                  😘
                  🤢
                  😎
                  😞
                  😡
                  👍
                  👎
                  Searching...Please wait.
                  An unexpected error was returned: 'Your submission could not be processed because you have logged in since the previous page was loaded.

                  Please push the back button and reload the previous window.'
                  An unexpected error was returned: 'Your submission could not be processed because the token has expired.

                  Please push the back button and reload the previous window.'
                  An internal error has occurred and the module cannot be displayed.
                  There are no results that meet this criteria.
                  Search Result for "|||"