Please help me eq/place my sub - plots inside!

Discussion in 'Home Theater Projects' started by Kincade, Jun 11, 2004.

  1. Kincade

    Kincade Second Unit

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    So i've taken readings of the BP1503 based sub I built here:

    http://www.hometheaterforum.com/htfo...hreadid=200777

    Below I have the plots. I took readings at the 3 main listening positions (the middle however is the MAIN position) with the sub placed both at the right front and left front corners. All the measurements are corrected using the excel spreadsheet on the BFD guide (snapbug.ws).

    At Wayne F's suggestion in the other snapbug thread, I took measurements WITH my mains on, as I like to listen to music as well.

    These 3 graphs represent the sub placed at the right front corner, and illustrate listening from the couches and recliner, oriented exactly as I listed in the diagram below:

    [​IMG]

    These 3 graphs represent the sub placed at the left front corner, and illustrate listening from the couches and recliner, oriented exactly as I listed in the diagram below:

    [​IMG]

    This is the room orientation:

    [​IMG]

    So, which location is a better starting point for eq'ing? I haven't touched the BFD yet, because i'd like to get placement correct first.

    Thanks for any advice!
     
  2. Wayne A. Pflughaupt

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    I’m surprised to see such a difference between the right and left locations in that room – I guess that entryway makes more of an impact than you might think.

    The question (which is the best corner) is really academic, because the BFD can equalize any of these curves. However, from the standpoint of which would be easiest (i.e., require the fewest filters) the left corner looks better.

    On the other hand, since the left couch extends so far to the front of the room, keeping the sub on the right will keep it further away from viewers – might be less prone to overwhelm.

    One think to keep in mind, Kincade: It will be impossible to get perfect response for all seats in this room. This is common in rooms that are essentially rectangular. I’d EQ for the center sweet spot, since that’s where you’d be sitting for music. “Perfect” response is more important for music than movies.

    However, if this is primarily a movie room, you might want to consider an averaging curve that doesn’t give perfect response to any particular seat, but improves from what you would have with no equalization.

    Regards,
    Wayne A. Pflughaupt
     
  3. Kincade

    Kincade Second Unit

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    Wayne,

    I think that the little entryway is exactly what is changing it so much left to right. That's the primary reason I decided to try both corners...

    I'd like to eq for the center spot, as that's where I do my listening on multichannel music.

    So you think the left side looks easier to EQ? I was thinking the left side (bottom graph) looked much more peaky on the left and right positions, and only slightly flatter in the center position.

    FWIW, i'm taking reading with my mains on as well - per your suggestion in an earlier BFD thread.
     
  4. Kincade

    Kincade Second Unit

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    Well, I did another plot today, both from the main listening position; left and right. This time instead of using the autosound 2000 CD's, I downloaded the sine waves from snapbug.

    The result is much different, and how that's possible, I don't know.

    Blue is sub on left, pink is sub on right.

    [​IMG]

    So who knows... I think I'm just going to leave it on the right, and try to EQ that.

    Also, in the BFD guide it says this:

    "Something that you should remember to do when you are setting up your BFD is add a foot to the value you enter for sub distance in your pre/pro or receiver set up. The 1 msec DSP processing delay in the BFD would account for approximately a foot in distance. If you add a foot to the distance you tell your pre/pro or receiver that your sub is from your ears, then it will advance the sound the 1 msec required. This will compensate for the BFD's delay."

    However, I do not have a delay setting for my sub. Only the center, side, and rear surrounds. How do I compensate for the delay?

    If you have any insight as to what is going on here, please let me know! [​IMG]
     
  5. Wayne A. Pflughaupt

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    The right one certainly looks good. Amazingly good. The fact that the low spot between 63-71Hz is so wide, and the fact that it wasn’t there when the sub was on the left, should indicate that it’s not a null. You’ll probably be able to equalize it away.

    A continuously variable phase control would do the same thing. If you can’t do it electronically, the only alternative is physically moving it.

    However, in your case, since your sub is so close to the mains, it’s really nothing to worry about. I have no delay on mine and I’ve never noticed any ill effects.

    Regards,
    Wayne A. Pflughaupt
     
  6. Ethan Winer

    Ethan Winer Stunt Coordinator

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    Kincade,

    > I took readings at the 3 main listening positions <

    Those 1/6 octave measurements hide most of the detail. I guarantee that the peaks are higher, and the nulls are much deeper, than what's shown in your graphs. You need to measure to at least 1 Hz resolution to really see the true response. I do not say this to discourage you! But you risk making things much worse when you start fiddling with the EQ for two reasons:

    1) The exact center frequency of the peaks and nulls is surely different from what the graphs show. If you have a deviation that falls near, but not on, one of 1/6 octave frequencies, you'll be tweaking the wrong frequency. This can make the response worse, yet you'll never know it and the graph may even look perfectly flat.

    2) Since the magnitude of the peaks and nulls is not what you think either, the amount of EQ compensation will be incorrect.

    I regularly measure rooms (using the ETF program) where a peak and deep null both fall within the same 1/6 octave band. Tests that use 1/3 or 1/6 or even 1/12 octave bands average all the values within the band. So these tests can display a perfectly flat response even when there's a big peak and also a deep null.

    --Ethan
     
  7. Kincade

    Kincade Second Unit

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    Ethan,

    Thanks for the response. So is everyone that uses the BFD w/ the Snapbug worksheet acutally making things worse? It comes very highly recommended.

    What do you recommend to measure with? That's the only worksheet i've been able to find that has correction values built into it. I do have the autosound 2000 CD w/ 1 Hz intervals from 10-98 Hz, but no way to measure them...
     
  8. Wayne A. Pflughaupt

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    Kincade,

    I have some disagreements with Ethan’s recommendations that you might want to consider.

    Again, I won’t contest that you can have a peak and null within the same 1/6-octave band. But what Ethan fails to consider is that nulls and peaks that narrow and/or that close together are virtually inaudible in the bass frequencies. This is because ultra-narrow problems like that are easily masked by the program material and the adjacent frequencies.

    Just to give you an example of how difficult it is to hear narrow low frequency problems, I have a 1/6-octave peak in my response at 45Hz (i.e., it shows up there with sine-wave tones, but not at 40 or 50Hz) that I can’t address because I’m using 1/3-octave equalizers. I forget how bad it is – probably several dB. The test track I use to verify good bass response and proper house curve (after all the reading, charting and tweaking) has a bass line that runs up and down the neck of the instrument, from the lowest notes to high notes. All notes are at the same volume; all are heard equally well. Furthmore, I’ve never noticed a “hot spot” with any other musical recordings, either. In other words, while my response does not measure perfectly, it nevertheless sounds perfect. There is no audible evidence of that 1/6-octave peak.

    There are other, more practical reasons why to not be concerned with a hundred per-frequency readings.

    As Ethan alluded, you will surely find that the individual readings will be all over the map. It will be common to find deviations of several dB between each frequency, or deviations only a few frequencies wide. I haven’t dealt with per-frequency readings before, but people have sent me every-other-frequency readings to analyze (i.e., even-numbered readings), and this is what I’ve seen. You’ll drive yourself crazy trying to deal with all those tiny aberrations and in doing so the tendency will be to over-equalize. You’ll probably “burn” all 24 of the BFD’s available filters, most of them set to ridiculously narrow bandwidths like 1/20 or 1/40-octave trying to “fix” inaudible “problems.” This is not an efficient way to use an equalizer.

    Bottom line, Kincade, as countless dozens have done before you, you can successfully equalize your sub using only 1/6-octave readings, and you’ll be happy with the results. If you really want to go to the nth degree, you can use 1/12-octave spacing. But there is no need to be concerned with 1Hz, per-frequency readings.

    Regards,
    Wayne A. Pflughaupt
     
  9. Ethan Winer

    Ethan Winer Stunt Coordinator

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    Kincade,

    > So is everyone that uses the BFD w/ the Snapbug worksheet acutally making things worse? <

    I say may make things worse, not will. The real issue is there's no way to know what you've done - good or bad - when the best resolution you have is only 1/6 octave.

    > What do you recommend to measure with? <

    I use the ETF program from www.acoustisoft.com. It's only $150 yet does all the important measurements the very expensive systems do. And it can resolve low frequency response to better than 1 Hz.

    > That's the only worksheet i've been able to find <

    Those correction tables should be taken with a large grain of salt. None of these inexpensive microphones are calibrated, and I assure you every one is different from every other one. All those correction charts can give you is an average of the errors at best, or the response someone measured for their one unit at worst.

    The good news is most inexpensive omnidirectional microphones are reasonably accurate in the bass range, which is all you can hope to correct with EQ anyway.

    --Ethan
     
  10. Kincade

    Kincade Second Unit

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    Wayne,

    I guess that is what is confusing me - while Ethan is saying it's nowhere good enough, i've read over and over about people using the 1/6 octave sheet on Sonny's website, and being very happy with the results.

    Your reasoning about same samples per octave rings true as well, seems like it would keep it linear.

    If I do decide to do 1/12 octave readings, can I use the PEQ located here? I've dowloaded that, but can't seem to download the 1/12 octave tones. So i'm not sure it'll work anyway.

    Lastly - I think I can get this pretty flat using the spreadsheets out there. However, after all this reading, I know what a house curve IS; but i'm still not sure how to do it properly. A gentle slope from 30-100 hz of 5db, or a more radical slope of 15-20 db? How do I know which to use?
     
  11. Kincade

    Kincade Second Unit

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    Ethan,

    thanks for your assistance! It looks like there's a trial version of the ETF software. What Mic would I use with it? Might be kinda cool to mess around with, if nothing else.
     
  12. Ethan Winer

    Ethan Winer Stunt Coordinator

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    Wayne,

    You make some good points.

    > That doesn’t sound like they “made their response worse” because they didn’t nail the exact frequency <

    Agreed. Again I said may, not will.

    > Ethan fails to keep in mind the difference between musical octaves and individual frequencies. <

    Believe me, I'm fully aware of that. I suppose I could have said 1/48 or 1/96 octave, but at low frequencies 1 Hz makes sense and is easy. Even at 300 Hz, which is as high as I usually measure rooms, I always see significant changes at frequencies 1 Hz apart (near peak and null centers), so 1 Hz resolution even that high in frequency is reasonable to aim for.

    > what Ethan fails to consider is that nulls and peaks that narrow and/or that close together are virtually inaudible in the bass frequencies. <

    No, NO, NO! [​IMG]

    A deep null that's so narrow it affects a single note is still a huge problem when the bass player plays that note. Likewise for a big peak.

    > I have a 1/6-octave peak in my response at 45Hz ... The test track I use ... has a bass line that runs up and down the neck <

    This is more complex than you might think, and it depends on the tone the bass player is using. Even with a deep sounding tone with few audible harmonics, the primary component is the second harmonic. Indeed, the second harmonic is typically 10 or more dB louder than the fundamental. So the low A string on a bass at 55 Hz really has much more energy at 110 Hz. Other harmonics can seem to fill in these holes, so it's not like you notice a note changing in volume. Rather, what really changes is the timbre, and that's much more subtle.

    Another big factor is your ears are several inches apart. So one ear is often in a null zone while the other is not. Unless a deep null affects both ears equally, which is rare, you won't notice the null so much.

    > You’ll drive yourself crazy trying to deal with all those tiny aberrations and in doing so the tendency will be to over-equalize. <

    I agree with that completely. Even a great sounding room has a low frequency response that would be laughable on any electronic gear.

    > there is no need to be concerned with 1Hz, per-frequency readings. <

    If you need further convincing, have a look at some of the articles on my company's web site. In particular, see my recent article from Electronic Musician magazine that discusses these issues in detail. Also see the videos on our site which show the result of 1 Hz testing.

    --Ethan
     
  13. Ethan Winer

    Ethan Winer Stunt Coordinator

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    Kincade,

    > i've read over and over about people using the 1/6 octave sheet on Sonny's website, and being very happy with the results. <

    This is going to sound condescending, but that's not my intent. Every day at another site I won't mention I see people praising esoteric tweaks that cannot possibly have any audible effect. For example cable elevators. The placebo effect is so strong, especially with inexperienced listeners, that I'll give "user testimony" only 50% credibility. That said, you probably can make your system better with 1/6 octave tests and a BFD. My original point here was merely to show the inadequacy of such testing, and not be fooled into thinking what you measure is truly what you have.

    > What Mic would I use with it? <

    Many people use the $50 Radio Shack sound level meter. I have a very expensive calibrated mike and also the RS meter, and at low frequencies they both give the same results. In the presence of nulls that are 25-35 dB deep, a few dB here or there due to the mike is no big deal. But whatever mike you do use it must have an omnidirectional pickup pattern. If it's also a condenser type, that's even better still (for higher frequencies).

    --Ethan
     
  14. Wayne A. Pflughaupt

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    Kincade,

    Each room will require a different slope; the smaller the room, the steeper the slope will be. I like to use 100Hz and 32Hz as reference points. When the house curve is correct, they should both sound like they're at the same volume (although 32Hz will measure higher). Once you’ve established the measured differential between the two, the goal is to achieve as straight a line as possible between the two points.

    I’ve found that it sounds best to shelve the house curve at about 30-32Hz. Extending the curve upward below that point got me a lot of extraneous and unnatural sounding effects, like car doors that slam with the low-end “umph” of a distant explosion. Also made music unnaturally bottom-heavy, too. It never hurts to experiment, though – you might find you like it better with the slope continuing to rise, or shelving at a different point.

    Regards,
    Wayne A. Pflughaupt
     
  15. Kincade

    Kincade Second Unit

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    Thanks Wayne; I think i'll just experiment to see what sounds right. So there's no hard and fast rule on what 32 vs 100 should read on a db meter, relative to each other, if the house curve is set properly?

    The 1/12 octave tone worksheet is really a moot point, as I cant find anywhere to download the tones from. And I REALLY can't afford the ETF software and another Mic right now. I'll probably just EQ it w/ the 1/6 tones and see how it pans out.
     
  16. Kincade

    Kincade Second Unit

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    Thanks Wayne; I think i'll just experiment to see what sounds right. So there's no hard and fast rule on what 32 vs 100 should read on a db meter, relative to each other, if the house curve is set properly?

    The 1/12 octave tone worksheet is really a moot point, as I cant find anywhere to download the tones from. And I REALLY can't afford the ETF software and another Mic right now. I'll probably just EQ it w/ the 1/6 tones and see how it pans out.
     
  17. Kincade

    Kincade Second Unit

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    Ethan,

    Thanks for all the tips. I'm worried about overcomplicating this, and even if I bought the ETF software, i'd be worried that after all is said and done, I wouldn't have enough eq's on the BFD to straighten the curve.

    Thanks again!
     
  18. Kincade

    Kincade Second Unit

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    Ethan,

    Thanks for all the tips. I'm worried about overcomplicating this, and even if I bought the ETF software, i'd be worried that after all is said and done, I wouldn't have enough eq's on the BFD to straighten the curve.

    Thanks again!
     
  19. Kincade

    Kincade Second Unit

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    Just in interest, I emailed Doug ETF about the program, and asked him what I would need:



    So, for now, I think i'm going to stay w/ the 1/6 octave method. I can't afford a $300 program right now, that may or may not work for me...
     
  20. Kincade

    Kincade Second Unit

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    Just in interest, I emailed Doug ETF about the program, and asked him what I would need:



    So, for now, I think i'm going to stay w/ the 1/6 octave method. I can't afford a $300 program right now, that may or may not work for me...
     

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