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REW for finding best Sub placement

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  • REW for finding best Sub placement

    Well it has been a crazy few weeks at my house. Specifically the last few days. Yesterday I was certain I was going to have to sell my whole system, then I got home, and had a very pleasant surprise waiting for me. So, for the time being, I get to keep my 18.2's.

    I started tinkering with REW software on my MacBook Pro a couple weeks ago. I know just enough about it to prove myself an idiot. Anyway, I had used the Subwoofer crawl method to determine where to put my 18.2's in the past. After running REW, I had massive peaks and troughs. So I decided to put the Mic in the Listening Position, and move the 18.2's all around the room, and take measurements to see which spots provided the flattest response on there own.

    This is what I had when I just did the Sub crawl method. This resulted in stacking both 18.2's in the back left corner.

    And then this is what I had using the REW method. This resulted in placing both 18.2's in the front center of the room.

    Both measurements were taken using the subwoofer signal generator directly from the REW program on my laptop into the Subs. The AVR was totally bypassed. I need to figure out how to run the signal through my AVR and include Audyssey in the mix. Any suggestions?

    I was amazed at what a difference placement alone had on the response in room.

  • #2
    That great news bukiwhitey! Hope things keep stable - these are tough times for sure.

    You can't really control what Audyssey does for the subs (speaking for the Onkyo), once it's run, it will usually improve and flatten everything. You can go back in and tweak the speakers after running it, but other than that, it's either on of off.

    Frankly, +/- 5 you found with moving things around is quite good. Is this with the mains on, too? To tweak it more, you may be able to either change the distance setting of the subs if you have a .2 sub outputs, or can play a bit with the phase on the Dayton, one at a time to accomplish a similar change. Otherwise, you will need to get an external EQ like the mini DSP, Behringer DCX or DSP, eD eQ.2, SMS-1 to name just a few. Some are automatic like Audyssey, some are more manual and need REW to manipulate the settings.

    So, your first step is run Audyssey, and see what that does with the FR. Afterwords, double check your crossover settings, make sure it didn't set you speakers to large setting (in most cases, a bad thing). If it sounds or looks worse, just turn Audyssey off.

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    • #3
      This is just with the Subs on. No other speakers were used.

      I have an Onkyo as well. I will run Audyssey tonight, and see how it sounds.

      What is the best way to connect my laptop to the Onkyo in order to run a FR with Audyssey in the mix?

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      • #4
        Originally posted by bukiwhitey
        This is just with the Subs on.
        Ok - then there is no crossover being used now? When you add the mains, without this intended drop-off up high (or low pass filter) for the subs, and down low (or high pass filter) for the speakers at the same crossover frequency, you are doubling your output where both speakers and subs operate which gives a large bump in that area.
        The picture below has a mid-range crossover of around 350 Hz. You are looking for the same curves crossing at about 80 Hz for the subwoofers.



        Audyssey automatically adds the correct attenuation to both ends at what it thinks the best crossover point should be. This is the integration or bass management that people speak of.

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        • #5
          I doubt I will ever run sweeps with REW again. The Real Time Analyzer (RTA) feature in REW is so much easier and allows for more accurate results quickly. This is the method I used at our GTG at HuskerOmaha's this past weekend. This method takes into account the actual signal chain and allows you to make changes on the fly and instantly see their affect (if your system lets you make changes on the fly during playback).

          The RTA measures with exactly the same accuracy as the sweeps. I tested it several times and the results were always identical. The downside is I don't think you can use the measurement captured by the RTA for the waterfall, impulse or other REW features. You are only using it for SPL across the frequency spectrum.

          Since you aren't using sweeps, you need to have a signal for REW to measure. Using the Generator module in REW you can save the Pink PN with a length of 131072. Click on "Save PN to WAV file..." and save it somewhere. If you have an HTPC connected to your receiver, just use that to play the file. Otherwise you need to burn the file to a CD for playback on a CD, DVD, or Blu-ray player.

          The file is a two channel file so you will need bass management on in your receiver for it to be sent to your sub. When first measuring I would recommend muting the mains and just using the sub for measuring. If you can't mute the mains you should still be okay since a crossover is being used.

          With the file playing through your signal chain, calibrate the SPL in REW by opening the SPL Meter module and clicking "Calibrate." In the signal source windows select "Use an external signal" and click "OK." Use an SPL meter at the mic location to measure the SPL. Increase your system volume to about 75-80 dB. Now enter the reading in the SPL Meter module to calibrate REW.

          With the Pink PN file still playing, now open the RTA module. Click the setting button in the top right of the module and set it to the following:

          Mode: RTA 1/48 Octave
          FFT Length: 131072
          Averages: None
          Window: Rectangular
          Max Overlap: 87.5%
          Update Interval: 1

          Click the settings button again to close the settings flyout. Now click the red start/stop button in the RTA. You should see a frequency readout appear. I like to window it from 10 Hz - 200 Hz. This is showing the frequency response at the mic position. To make the "crawl method" faster, you can put your sub in the listening position and then move the mic around the room to find the flattest frequency response. You can also change from "Averages: None" to something like "32." This will use the last 32 readings. You can move the mic around to different seats to get an average of a larger area.

          If you want to save the measurement just click the "Save" icon at the top of the screen. You can now use the measurement for generating filters or to compare to other measurements. If you are averaging an area, you need to click save as soon as you finish moving the mic around.

          After your sub is in the location with the best response, you can unmute one of the mains and look at the crossover region on the RTA. Adjust your distance setting until you get the smoothest response at the crossover region. At the GTG, sealed subs needed about 2 ft more than mains, ported subs (folded port) 5-7 ft, and horn subs 14-17 ft. You can also make changes to the crossover frequency and see which has the smoothest response and which sounds best to you.

          At the GTG it took about 4-6 minutes to measure the sub, set the distance setting, generate filters, enter the filters into the Parametric Equalizer in JRiver Media Center, and save the final measurement showing the flat frequency response.

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          • #6
            Awesome information!!!

            Thank you very much!

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            • #7
              Hi mojave, I have been wanting to study up on the RTA feature in REW software. Thank you so much for this information!:applause:

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              • #8
                Mojave,

                Just so I am clear. This method will allow me to see what impact Audyssey has in my room at the LP.

                Play the PN file through my Onkyo, disable main speakers, calibrate subs to 75-80 db, leave Audyssey on, run RTA, and save chart.

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                • #9
                  Originally posted by bukiwhitey
                  Mojave,

                  Just so I am clear. This method will allow me to see what impact Audyssey has in my room at the LP.

                  Play the PN file through my Onkyo, disable main speakers, calibrate subs to 75-80 db, leave Audyssey on, run RTA, and save chart.
                  Yes, that should work.

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