Question on measurement setup

Discussion in 'Room Set Up, Audio Theory, and Measurements' started by JoshK, Oct 20, 2014.

  1. So I was going to start on measuring my horns this weekend, but Murphy reared his ugly head and my laptop with all my software is dead, as in won't finish loading Windows.


    However, as I have actually never ran measurement before, I was hoping to clarify the setup. I was planning to use ARTA, but I have other software too.


    I am not really certain about the loopback part. I get the laptop to soundcard to amp to DUT and mic plugged into soundcard, but what exactly is the loopback for? Is it necessary? My amp doesn't have preouts, so this is a concern.


    Also, in regards to gain while measuring. Should the gain on the mic input be turned all the way up? How about the amp? That is probably going to be deafeningly loud.
     
  2. Here is where I am at.
     

    Attached Files:

  3. [​IMG]


    This makes sense to me. I guess I just saw some guides that mention loopback and was confused. I my case the mic preamp is also my soundcard, so the setup looks slightly different.


    http://www.mh-audio.nl/Measuring_LoudspeakersComp.asp


    This link shows other setups but no explanation of what they are doing.
     
  4. The mic doesn't require phantom power?

    For the loop back, I ignore the amp, even though an amp can have roll of up high it's usually so high I'm not concerned. And if its now low, I want to include it because that's what I get. So I just loop the sound card output into its own input. Then if the sound card has any roll offs it is compensated for when you do the loop back measurement.

    Did you buy Arta? I emailed the address on the website about buying it and never got a reply. How much is it? I'm really close to buying sound easy but checking out my options first.
     
  5. The Focusrite powers the mic.


    Ah, so that is what the loopback is about. OK, I get it now. Had a suspicion, but wasn't sure.


    I bought ARTA a little while back, maybe 6 months ago. I can't remember the exact process. I have Soundeasy too, but so many more people who I follow use ARTA, I thought it would be easier to converse easily. I have holmimpulse as well.
     
  6. Anyone have any good suggestions for how to measure my big horns with intended bandwidth of 200hz up to 2khz? Its pretty much a no go to take them outside (they weigh 150lbs each and they are very awkwardly shaped). I have a relatively small room (14x24x11) with high ceilings. Its quite cluttered.


    My thinking was this:
    First measure the impedance of the driver free air. Then measure its impedance mounted to the horn. This tells me something about the horn loading effect.
    Next measure the combo with the mic at the mouth of the horn so that I can see what the low end is like. Next measure at 1m to see what the top end is like and examine the impulse response for where my first reflection limit the data.


    Does that sound about right?
     
  7. Seems like a plan to me. With 11ft ceilings you're very lucky. IME, clutter isn't really that much of a problem. But what ever you can do to get rid of it would help. Just get the center of the waveguide up at 5'6" and let 'er rip. That should give you a gate frequency down around 200hz. Sure, not ideal for your intended bandwidth, but will give you lots of information. That bandwidth is the hardest IMO. 200 to 400hz is very tricky. Maybe a ground plane measurement in your room if you cleaned up some of the clutter?
     
  8. The thing I've found with a 200-300hz gate is that the resolution is quite low. Yeah, you get data but it has a way of masking what's really going on below 1khz. My current speaker measures quite well under 1khz with an in-room gated measurement. I took everything outside, got it up in the air, and I was able to get about 8ms of clean data. It showed several significant peaks and dips from 500-900hz due to cabinet diffraction and my waveguide shadowing the top of the woofer. These were hidden completely by the shorter gate.
     
  9. Nate makes a good point. Basically an octave or more above the gate is useless. I thought you could combine a GP to fill that in, but didn't make much sense in my post :eek: Nate, what software are you using? I find Holm does a better job in this regard than REW. But I know REW has different windowing options that I haven't played with, so who knows. I think you use Arta though??

    Josh, if you decide to stick with Arta and don't want your SoundEasy anymore, let me know I'd happily buy it from you.
     
  10. I use a bit of everything :eek:


    The in-room data I referred to was done in REW and ARTA showed a similar result. The outdoor was done in Holm so Geddes could add it to his Polar Map database. I'll have to compare Holm with ARTA when I'm setup to do some indoor stuff. Interestingly, the diffraction issues showed up in the in-room measurements from the lp, but at the time I thought it was room effects.


    Just for kicks, here's a comparison of the data I'm talking about. This was taken in Holm with the mic about 9' from the speaker, and the speaker about 9' off the ground. The gray trace is 8ms, the yellow is 3ms. The frequency resolution for 3ms is about 250hz, and 125hz for the 8ms gate. I eq'd the diffraction in this measurement but you can see the ripple around 700hz.


    I agree with tux, the combo gp and 1m gated is probably the best you can do. You're still limited on the gp though due to your room dimensions.
     

    Attached Files:

  11. #11 RickyTerzis, Oct 3, 2017
    Last edited: Nov 17, 2017
    Hi..i am a new user here. In my case my current speaker measures quite well under 1khz with an in-room gated measurement. I took everything outside, got it up in the air, and I was able to get about 8ms of clean data. It showed several significant peaks and dips from 500-900hz due to cabinet diffraction and my waveguide shadowing the top of the woofer.

    smt prototype assembly
     

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