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Room correction, how do they measure the bass?

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  • Room correction, how do they measure the bass?

    I know some home theatre receivers include measurement microphones that are used by the receivers for some degree of room correction/setup.

    My question is, how well does this typically work at the lowest frequencies?

    I had thought bass was a challenge to measure in-room, and I was under the impression that standing waves can be a challenge to EQ-out anyhow.

    Has anyone used this feature on a receiver and how did it work for you?

  • #2
    Room modes in the bass region will be difficult to "fix" with EQ. They move in frequency based on where you are in the room, and the magnitude is generally higher than you'd want to apply EQ to. If you want to fix bass modes, use multiple subwoofers and experiment with locations until you're satisfied.

    I've not liked the result of any "automatic room correction" feature yet, however I haven't used very advanced receivers. I have tried EMO-Q and the results were inconsistent and dissapointing. I was left with what I found to be muffled and bass heavy. I got similar results from another receiver with basic Audessey.

    When I've set up room EQ manually, I take an average of the multiple listening locations and EQ from there. It does not make much sense to me to EQ a room to a single point, unless your room only has single seat. For DIY builders I don't know why anyone would put all the work into fine tuning a crossover for their speaker, and then leave the room EQ to some automatic algorithm. Get a receiver that allows manual adjustment like Emotiva or Yamaha Aventage.
    Don't waste your money on a new set of speakers, you get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

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    • #3
      Contrary to what you believe, "fixing" the bass is what most room correction software do best.

      Think about what correcting bass involves. For the lowest frequencies, the frequency response is exactly the same as the power response. This make things a whole lot easier since all you have to do to correct is the frequency response of the bass.

      Bass is problematic in room because of room modes. This causes dips and peaks of the frequency response. The software can easily be programmed to ignore the dips and correctly fix the peak to get a smoother response at one location. The fix is valid only for one location, which is just the limits of physics since the room modes act differently depending on where you listen, so of course any fix only work for one location. Manual correction cannot achieve anything fundamentally better.

      One thing to note is that most room corrections simply correct on the frequency domain, but not the time domain. A peak in the response caused by a room mode will ring a lot longer. Therefore, while the frequency response could look flat, the listener can still hear the decay from the ringing. This is why flat bass can sound different in different rooms. More advanced room correction based on FIR filtering can alleviate this to a degree.

      I find that Audyssey generally does a very good job fixing the frequency response of the bass frequencies. However even XT32 does not do much to correct things in the time domain. Dirac does an excellent job fixing the response both in the frequency and time domain. It is however significantly more expensive.

      Now going back to the first sentence in my response, most room correction software is quite bad at fixing the response above 300Hz or so (or more accurately, above the Schroeder frequency). Reasons are because most are measuring and trying to correct a speaker's power response, which will generally make the direct sound have random peaks and dips that will sound bad to us as we are very sensitive to the direct sound of the speaker (and hence the obsession with the frequency response graphs). Most room correction cannot tell between the direct vs reflected sound. This is especially problematic since we are much more sensitive of ringing and time domain errors at higher frequencies than bass.

      I've never heard of a room correction software that does a good job above the Schroeder frequency. Dirac does the best, and it is the only one to actually make an improvement. But, the default setting tends to sound too bright as they try to flatten the measured response of the speaker, which is the power response. All speakers have a decreasing power response since the tweeter beams at higher frequencies. If you have a flat power response, the on axis response must be very treble heavy, which is why it sounds bright. Audyssey XT sounds kinda bad. The XT32 is a lot better, but still not really an improvement. Anthem ARC doesn't even try because they are aware of the problems mentioned here and realized they'd just make things worse. MCACC is just downright bad.

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      • #4
        I've never been satisfied with on board room correction. I agree with bcodemz, they tend to end up sounding overly bright and often harsh. Where I disagree, kinda, is their ability to get the bass somewhat right, as that hasn't been my experience. I also find them inconsistent, I can run the calibration several times, using the exact same mic placement, and end up hearing different results as well as seeing different level and delay settings. I'm using an Onkyo preamp/processor with Audyssey MultEQ XT32, don't like it. It's bypassed and external DSPs are doing all EQ and delays.

        As to the OP, I don't know. I find it hard to believe those cheap little mics do a great job at measuring anything, even though there is likely a generic calibration file embedded into the software.

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        • #5
          What brought this up for me is reading a post by Sean Olive (of Harman/JBL). He said their target (anechoic) speaker curve is about a 1db/octave drop (10db over 20-20k) because a typical ("good") listening room adds about 1db/octave back.

          That, all that is typically necessary is some bass correction.

          That got me to thinking about the integration of my "sub" via EQ and I realized that getting the bass right has been the most difficult part of any of my recent setups.

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          • #6
            Hi Phil,

            Bcodemz makes very good points.

            Some more reading you may be interested in.

            http://www.bodziosoftware.com.au/Ult...r_Manual_5.pdf Page 69-83

            http://www.bodziosoftware.com.au/UE6_Manual.pdf Page 2-5

            Best Regards,
            Bohdan

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            • #7
              I was actually pleasantly surprised at how well the Yamaha YPAO did. Granted, I never expected it to address the low end nodes in the room, as previously mentioned that is beyond EQ correction. It did however to a good frequency balance of levels across all channels, verified by a REW sweep after. The only changes I made after setup were to add 4dB to the sub and re-balance the L/R levels to even (it had altered them about 2dB one way or the other). My room is for movies and TV 95% of the time, and very casual music listening the other 5%.
              Electronics engineer, woofer enthusiast, and musician.
              Wogg Music

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              • #8
                Originally posted by philthien View Post
                I know some home theatre receivers include measurement microphones that are used by the receivers for some degree of room correction/setup.My question is, how well does this typically work at the lowest frequencies?...Has anyone used this feature on a receiver and how did it work for you?
                Not myself,,,but such a receiver on a friend's system: To my ears, overall it was uneven, and lost detail, bass was "woolly". Part of it being related to "issues" mentioned ( in the link bohdan just posted. )
                "Not a Speaker Designer - Not even on the Internet"
                "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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                • #9
                  Originally posted by Sydney View Post

                  Not myself,,,but such a receiver on a friend's system: To my ears, overall it was uneven, and lost detail, bass was "woolly". Part of it being related to "issues" mentioned ( in the link bohdan just posted. )
                  It is interesting that we have a couple of posters saying bass correction should be the easiest aspect, as then some people with practical experience indicating it hasn't worked great.

                  OTOH, I once had a Yamaha cassette deck with the worst implementation of Dolby noise reduction you've ever heard. I think it actually added hiss to my recordings. I was disappointed with it and thought it was funny when a trusted salesman at a shop I frequented, that didn't know I had the top of the line Yamaha deck, mentioned out of the blue that he felt Yamaha had the absolute worst implementation of Dolby around.

                  My point being maybe it is easy but the designers still biff it.

                  Comment


                  • #10
                    Originally posted by philthien View Post
                    ...It is interesting that we have a couple of posters saying bass correction should be the easiest aspect, as then some people with practical experience indicating it hasn't worked great....
                    I'm willing to look at this in a case by case basis. I probably would have been more thorough in experimenting with it then my friend was. He is of the type that tends to put more faith in the technology, without knowing the principles involved and aspects that would skew the outcomes. Not knowing how to run the feature right was part of it as well as interpreting the outcome .
                    "Not a Speaker Designer - Not even on the Internet"
                    "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                    Comment

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