Which corner for the sub?

Discussion in 'Archived Threads 2001-2004' started by Rick Radford, Jan 19, 2002.

  1. Rick Radford

    Rick Radford Supporting Actor

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    Guys, this is one of the first times I've tried this. So if the image doesn't load.. or is too big to d/l, etc. my apologies.
    I took a screen shot of an overlay from ETF of some low freq response tests I ran today. I pasted it in Paint and saved it so I could upload it to a web page for posting here.
    I'm sure there are easier ways to do this and make the file size smaller but that's beyond my knowledge at this point. I couldn't get an lf.etf file to upload to the page.
    Which corner would be best to put the sub in for eq purposes? I'm guessing the right front corner (blue). The red line is the left front corner.
    Interestingly enough, I first had the sub in the RF corner. But after running some spl/Avia/VE tests, thought the LF corner would be better. I dial down the sub input by ~5 dB to get the same spls if I have the sub in the LF corner vs the RF corner. This seems confusing when I read it. Hope it makes sense to you.
    [​IMG]
     
  2. Pete Mazz

    Pete Mazz Supporting Actor

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    Blue is definitely flatter. Did you adjust the SPL in the overlay? The red peak would probably move above its current position by about 4 dB to get some of the other areas of the curve to line up.

    In Paint, after you paste, save in JPG format. It'll be a smaller size file and will display on more systems.

    Pete
     
  3. Rick Radford

    Rick Radford Supporting Actor

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  4. Pete Mazz

    Pete Mazz Supporting Actor

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    It's pretty new to me too!

    If you use the third button on the left of the Overlay window, another window will pop up allowing you to select one of the measurements to adjust. Below that is a slider that you can set to the level of movement for each Update. It looks like if you select the red measurement and moved it up by about 4dB it will line up closer to the blue measurement. The relative levels don't really matter when you look at these, just the curve itself. Try it and you'll see what I mean as the graphs come closer together.

    Pete

    Edit: Wrong button....fixed.
     
  5. Rick Radford

    Rick Radford Supporting Actor

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    Pete,
    I still don't understand how or why you would think to make a spl adjustment. Ah, wait a minute. This bumps the curve up so that they start at the same spl. This shows the LF has about 5 dB more than the RF (actually, 4.4 dB at 20 Hz).
    I'm trying to understand what ETF does. I made all measurements with the same Master Volume (since the level checks stayed within the -10 to 0 dB range). Should I have altered the MV so that the level checks always produced the same readings?
    I opened up the overlay and adjusted the red line by 4.4 spl in the parameter adjust window. Here's the new graph.
    [​IMG]
     
  6. Rick Radford

    Rick Radford Supporting Actor

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    Here's another question about ETF.

    Would you expect to get more accurate results from the test by using a higher spl level and turning up the RS spl meter to a higher setting? Maybe this would reduce background noise influence?

    For the most recent tests, I used a spl meter setting of 70 and kept the spls down since the family was sleeping. I thought if the level checks were good, it would be ok.. but I was wondering about the PC cooling fan noise with the lowered spls. And another factor might be when the house air handler kicks in. I have a large cold air return in the HT room.

    BruceD? Wayne P? You have any thoughts on this?
     
  7. Pete Mazz

    Pete Mazz Supporting Actor

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    Since you're measuring the sub at different locations in the room, don't worry about SPLs. You're more concerned with the shape of the curve. The only reason to adjust the relation of the curves to one another is to get a better feel for how each measurement/movement changes the curve. If you want a SPL, just use the RS meter on its own, it's quicker.

    Regarding volume levels, IMO, you should try to take measurements using a level that you listen at, and adjusting the input of the mic lower.

    Pete
     
  8. Rick Radford

    Rick Radford Supporting Actor

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    thanks for your input, Pete.
    I guess my main concern is that I interpret the graphs correctly and make adjustments using generally accepted procedures.
    There are so many variables that can affect the sound, not to mention all the variables in the ETF software that can affect the graphs.
    The design engineer had definite goals in mind when designing the software. But someone inexperienced like me will have to guess what the program is supposed to do.. until operational experience overcomes that initial confusement. [​IMG]
    OTOH, is it possible that you might not like the sound of the system after eq'ing flat response curves? Nah! [​IMG]
     

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