Parametric EQ or a resonator for correcting room modes?

Discussion in 'Pro Audio' started by Tommi, Jan 15, 2004.

  1. Tommi

    Tommi Guest

    It is my understanding that today's parametric equalizers are linear enough
    so that they can be used in correcting the control room's room modes.

    In short: Is this true?

    I want to get rid of my 75 and 150 Hz modes finally, and I've never built a

    Which one would you prefer, a good parametric eq or a resonator, and why?

    I'm thinking that a parametric eq gives you total freedom over how you want
    to correct the room, but it adds phase delays and so on.

    If I wanted to correct my 75 Hz resonance, for example, with a very narrow Q
    from a parametric, would it really affect the phase that much?
    Tommi, Jan 15, 2004
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  2. Tommi

    Rick Powell Guest

    The purist in me would want to correct the room as much as possible.
    When you correct with EQ and don't at least minimize the room mode
    resonance, what you are doing in essence is establishing a very narrow
    "sweet spot". Also, there are a lot of funny things that can happen
    in a poorly-corrected room like comb filtering and wave cancellation,
    where what you think you hear isn't what you really hear, even though
    the "snapshot" reads OK on a RTA. It's not just about the frequency
    balance. Malcolm Chisholm had a good story on a studio he worked at
    once where all the bass was being sucked up into a wall, which
    unintentionally acted as a broadband membrane bass trap. I'm sure
    there a lot of folks a lot more well-versed than I who can explain why
    you'd want to solve the acoustics first.

    Although I know a guy who has RTA'd his control room and put a global
    EQ on his monitors to "correct" it, this is often thought of as a
    "'70's" approach to monitor correction...because it was a lot more
    common approach then.

    If you want a good source for Helmholtz resonator design, including
    calculating slot width, etc., for the specific frequency to be
    treated, go to John Sayers' site.

    Rick Powell, Jan 16, 2004
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  3. An EQ on your monitors is a rather messy band-aid to cover up, rather
    than fix, the problem of the room modes. But in my opinion, the
    resonator is kind of a band-aid too. Ideally you'd change the size and
    shape of the room to fix this problem for real rather than try and
    "tune it out." Obviously that's not practical, but it's the
    technically correct solution.

    Justin Ulysses Morse, Jan 16, 2004
  4. Tommi

    Per Karlsson Guest

    The EQ can't help you. Resonance isn't just a frequency thing but also
    - and more importantly - a time thing, and EQ can never correct that.
    Per Karlsson, Jan 16, 2004
  5. Tommi

    Tim Padrick Guest

    Tim Padrick, Jan 16, 2004
  6. Tommi

    Chris Whealy Guest

    Personally, I would try and solve the problem as close to its source as
    possible. In your case, the problem is the room geometry. If you have
    the space, and it is aesthetically suitable, try some Helmholtz
    resonators in the corners of the room tuned to 75Hz. My guess is that
    if you kill the 75Hz mode, then a large part of the 150Hz mode will go
    away as well, seeing as you've knock out the fundamental.

    Chris Whealy, Jan 16, 2004
  7. One thing I can say is either fix the room right or leave it alone. Believe
    it or not you can make it worse than all already is by doing the wrong thing
    (cheap foam corner traps, etc.).
    Ricky W. Hunt, Jan 16, 2004
  8. Tommi

    Jay Levitt Guest

    This is particularly interesting reading for me, since last night, after
    three years of on-again, off-again work, my money-pit 20x14 one-room
    studio was finally declared "completed" (as if such things ever are).

    Now, a great deal of effort went into room design, acoustic modelling,
    diffusers, materials, speaker selection, preamp mods, etc. However, at
    the end of that process, we were left not with an ideal, empty, ray-
    traced room, but with an actual space, with stuff on the counters and
    instruments that reflect and absorb sound, and even a few humans. So
    the designer used a stereo 5-band parametric (a custom-modified Klark-
    Teknic) to roll off two or three dB here and there to get the curve a
    little flatter - though he certainly used his ears as much as, if not
    more than, MLSSA.

    It sounds great to me; the difference is night and day, listening is
    more pleasurable than ever, and I'm able to hear deeper into a mix than
    I was before. But I'm new at all this. Thoughts? Do folks consider it
    better to have a little EQ to make things flatter, or absolutely no EQ
    and learn how your space translates?
    Jay Levitt, Jan 16, 2004
  9. Tommi

    Buster Mudd Guest

    Indeed...and half the time it won't even be able to cover up the
    problem, making it a very ineffective (& expensive) band-aid. An EQ
    can compensate for problems in the frequency domain. But a room mode
    is the result of problems in the time domain (time it takes for
    pressure wave to bounce off wall/ceiling & combine w/ itself in phase,
    reinforcing that frequency), not the frequency domain. It simply
    manifests itself as a frequency arifact.

    If you have a standing wave at 75Hz & you try to attenuate 75Hz via
    equalization in your monitors, you *still* have a standing wave at
    75Hz! Wrong tool for the job.

    Fix the room.
    Buster Mudd, Jan 16, 2004
  10. Tommi

    Roni Jules Guest

    The consensus seems pretty clear -don't do it and for very good
    reasons. Clearly, if this were 1973 the consensus might go the other

    I suggest that if its not too much of a bother try eq'ing the 'room'
    and A/B the result.

    The results I obtained did not bother me so much as far as bass
    response was concerned but more to do with spacial imaging and a clean
    open sound. When mixing, using pan-pot stereo this was not so
    bothersome since depth of stereo image is not so critical. However,
    when using stereo mic techniques the reults with an eq in the monitor
    chain were unacceptable.

    The cure, for me, was worse than the illness. This may be different in
    your case.
    Roni Jules, Jan 16, 2004
  11. Tommi

    Tommi Guest

    Hey, thanks for the answers everyone.

    Helped a lot.
    Tommi, Jan 17, 2004
  12. Tommi

    Ty Ford Guest

    Mr. Hunt speaks the unvarnished truth. The guy at the local music store will
    smile and sell you an equalizer. He's smiling because he's THAT much closer
    to his draw.


    Ty Ford

    **Until the worm goes away, I have put "not" in front of my email address.
    Please remove it if you want to email me directly.
    Ty Ford, Jan 17, 2004
  13. Seems very well covered already, but one thought: the sound directly
    from the speaker(s) and the sound from room reflections happen
    sequentially. We're superbly well made to know the difference and
    to be able to concentrate on the *first* one.

    Equalizers are limited to affecting both direct and reflecting sound.
    So they're wonderful for helping make a good direct speaker output,
    but much less suited to anything else. They're just too far upstream.

    Chris Hornbeck
    "We all agree that your theory is crazy. But what divides us is the
    question, is your theory crazy enough to be true?"
    -- Neils Bohr
    Chris Hornbeck, Jan 17, 2004
  14. Tommi

    Jay Levitt Guest

    Ah, interesting. Four of the five bands were in the mids and highs, but
    we did also flatten out a slight hump around 50-70Hz. These were all
    relatively smooth bumps and dips, not tight notches, and it sounds like
    room modes would be very clear peaks, so I guess I'd have to know more
    about what was causing the un-flatness of my room to know if we did the
    right thing. Time to take that advanced acoustics course.
    Jay Levitt, Jan 17, 2004
  15. Tommi

    Jay Levitt Guest

    This definitely wasn't localized; it was audible from all around the
    room, and from both left and right speakers. It could even have been
    the speakers themselves; I'm using SLS's wonderful S8Rs, and while
    they're spec'd flat +/- 2dB from 44-20KHz, that certainly leaves room
    for a gradual 2dB hump at the low end. There were other issues in the
    highs that were more present on one speaker or the other, which seems
    more likely to be the room.

    Thanks, Ethan. You've always been a great resource here, but I didn't
    realize there was a whole reading list to go with! I'll have to check
    that out after the morning coffee takes effect.
    Jay Levitt, Jan 18, 2004
  16. Tommi

    Bob Olhsson Guest

    "Flat" is great however introducing colorations into a speaker system in a
    misguided attempt to compensate for room colorations does not create a flat
    system. This is why "flat" systems suck, they often are farther from being
    REALLY flat than most unequalized rooms are.

    Bob Olhsson Audio Mastery, Nashville TN
    Mastering, Audio for Picture, Mix Evaluation and Quality Control
    Over 40 years making people sound better than they ever imagined!
    Bob Olhsson, Jan 21, 2004
  17. Tommi

    xy Guest

    thanks for the link. i've been wanting to get a better handle on
    helmholz resonators myself.
    xy, Jan 22, 2004
  18. Tommi

    xy Guest

    i think boss or roland has a "complete" studio for about $399. it's
    in one little box, and it has mic modelers and amp modelers. so all
    you need is an sm-58 and a squier strat and that's it.
    xy, Jan 22, 2004
  19. Tommi

    xy Guest

    i think the composite material of the walls themselves have something
    do to with it. because walls other than something like 100% thick
    granite are going to have an uneven reflection/absorption response.
    so even if a room had perfect dimensions, the materials and thickness
    of the walls/ceiling/floor must also be "perfect" to render it.
    that's my guess anyway.

    so i guess the idea is to get as statistically close to perfect as you
    can, but understand that 100% perfect is impossible. i'm guessing it
    costs exponentially more and more money to get infinitely closer to
    xy, Jan 22, 2004
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