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how to get FLAT freq response???

Discussion in 'Archived Threads 2001-2004' started by rodneyH, Oct 24, 2001.

  1. rodneyH

    rodneyH Supporting Actor

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    I have a room that is 12X13X10. I get a huge bass peak at about 45-50 Hz and 75-90 Hz, my dad has a bigger room and gets the peaks at other Hz. I tried to place my speakers in different locations, but hardly got ANY change. Is there an answer outside of filling my walls with lead (seriously, have an uncle who did this), or tearing down the room and starting from scratch. It seems that all walls will increase the frequency at some point, so I guess everyone has this problem and just lives with it, or is there an answer???
     
  2. Guy Kuo

    Guy Kuo Supporting Actor

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    Look at the ongoing threads about parametric equalizers and subwoofers. There is your solution.
    ------------------
    Guy Kuo
    www.ovationsw.com
    Ovation Software, the Home of AVIA DVD
     
  3. Howard Halligan

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    I think you need acoustical treatment ...specifically bass traps to break up the standing waves ... an inexpensive source is www.partsexpress.com or you could go the DIY route.
     
  4. rodneyH

    rodneyH Supporting Actor

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    Guy, that might work for my sub, but what about my mains?? Perhaps I should set them to "small" mode (even though they are full range), and get the equilizer for the sub. The only problem is that my preamp X's over at 80Hz when set to SMALL, so I will still get the peak around 80-90 Hz (but maybe it will be much less. ANY MORE ADVICE??
    My other issue is that I have both SACD and DVD-a, so I need the mains to be full range, but perhaps If I get the outlaw ICBM, this could solve that problem as well??
    I am not sure about the bass traps (very very ugly) perhaps I can think of a more cosmetic way to accomplish the same thing.
     
  5. Kevin C Brown

    Kevin C Brown Producer

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    Rodney- I agree, acoustical treatment should be tried 1st, because this can eliminate problems, rather than equilization approaches, which typically only move the problem frequencies around the room (or just creates problems at other frequencies).
    You don't necessarily need Bass Traps, which are quite expensive in my opinion for what they do.
    1st off, the room should be carpeted, if possible.
    2nd, you should, if possible, have "diffuse" material behind your speakers. Anything to cut down relfections; drapes, black light velvet posters, whatever! [​IMG]
    Now, place a mirror on the side walls such looking at the mirror from your chosen spot of listening, you can see your main speakers. You should have "diffuse" material here too. Same thing: reduces reflections.
    (I can't do anything about my front wall, but I have a sliding glass door on one side covered with drapes, and the other wall opens up to the kitchen, which also removes those reflections.)
    Bass Traps usually go in the rear corners.
    And, your speakers should be at least 3 ft away from any wall, if possible.
    Someone mentioned the Russel Herchesman (sp?) dude from SGHT on another thread. I don't like everything he says, but he does talk alot about the room's effect on speaker performance. A lot of other info sources out there as well that hopefully people will post about.
    Me? You know those cardboard things that fabric stores use to wrap the fabric around? Maybe 1 ft by 3 ft by 3/4"? I just a use couple of these wrapped with 1/4" foam, then asthetically pleasing fabric, and use them in my back corners. Total cost? About $10 each. Cheapest and best "tweak" I ever did.
    One last suggestion is to glue, nail, somehow attach those cardboard egg containers over all your walls. Poor man's anechoic chamber! But the spousal-acceptance-factor for that is really poor.
    ------------------
     
  6. rodneyH

    rodneyH Supporting Actor

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    Kevin, thanx for your help. I actually have on one side wall (left) a double door (glass doors) that opens up to the other room (but they aren't covered). on the other side wall (right) I have a fairly large window with wood blinds (I would think that this would break up the reflections), also behind and to the side of me, I have 2 other fairly large windows with the same blinds). Behind and in the corner my front Right speaker (Right main is about 1.5-2 feet away from corner/wall) I have the SVS sub which is corner loaded, on the Left I have nothing (perhaps that is a big problem), and it is only about 1-1.5 feet away from the corner/wall (not good), while my. In the middle I have my TV, Center and my entertainment center (perhaps I need to move my speakers closer, and put the entertainent center in the corner (this sounds (logically) like it would be the best case, do you agree???)
    I guess I need to move the speakers around and closer together to see (hear) if it gets better before I try and move the center.
    any other ideas??
     
  7. rodneyH

    rodneyH Supporting Actor

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    btw, the room is carpeted with a very plush carpet, concrete floor.
    also, Why would a mirror on a side wall be benificial??
     
  8. Brian Corr

    Brian Corr Supporting Actor

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    Rodney,
    You simply use the mirror temporarily on the side wall to determine where you need to put acoustical treatment.
     
  9. Guy Kuo

    Guy Kuo Supporting Actor

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    His complaints are primarily with bass frequencies. The usual thin wall treatments aren't going to touch those much at all as the absorbance at
     
  10. BruceD

    BruceD Screenwriter

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    You will be surprised at what a parametric EQ on the bass only can do to reduce "peak" boominess at all bass frequencies, including the 90Hz frequency even though the crossover is at 80Hz.
    Here's why;
    1) The peaks at 45Hz produce resonances at 90Hz, so reducing the 45 will also tend to reduce the 90.
    2) Also, by 90Hz, an 80Hz low-pass crossover has not reduced the 90Hz output by much i.e. the crossover reduces output gradually over the next octave (from 80Hz up to 160Hz). This is called the slope of the crossover, like 18dB/octave.
    So, using a parametric EQ like the Behringerr BFD 1100P on the low-pass bass signal path just before the bass-amp input allows for multiple low frequency peak attenuation and much cleaner bass output.
    Hope this helps.
    BruceD
     
  11. Kevin C Brown

    Kevin C Brown Producer

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    Actually, I just read 2 subwoofer reviews in the latest SGHT where they talk about equalization to fix low freq peaks (or valleys).
    I wouldn't have thought that it would work as well as it did. The trick is to be able to find the problem frequency, *and* the spread around that frequency. (Most parametric equalizers don't give you control over the width of the peak you're trying to tame.)
    Infinity (cheaper) was one, and I think Revel (more expensive) was the other.
    Learn somethin' new every day!
    ------------------
     
  12. Guy Kuo

    Guy Kuo Supporting Actor

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    Ehh? I thought the width control for the filtering was a pretty standard feature of parametric EQ's. On 1/3 octave EQ's I'd expect the width of effect to be non-adjustable, but with a parametric I expect to have that degree of control.
     
  13. rodneyH

    rodneyH Supporting Actor

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    so would I just run my mains is "small" mode and use the ICBM with SACD and DVD-a??
     
  14. Wayne A. Pflughaupt

    Moderator

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    Rodney,
    For optimal sub response, you need to put your sub in a corner. This will give the maximum gain and extension. You can expect at least one or two humps in response, due to room modes, but a parametric EQ can and will eliminate these. Equalizers don’t “move problem frequencies around the room,” and a parametric EQ has bandwidth adjustment from 3 octaves wide to a super-narrow 1/20 octave (depending on the particular model), so they can be set with surgical precision so as to not bother any other frequencies.
    Forget all those stories you’ve heard about moving a sub around to get the best response. That’s for people who don’t have a dedicated parametric EQ. Ultimately they end up sacrificing extension and maximum output for response characteristics they can live with. The equalizers will take care of that, and then you will have it all: The highest SPL, the lowest extension and the smoothest response.
    Best of all, they’re cheap. You can get a used single-channel parametric EQ for under $150 on e-bay.
    Regards,
    Wayne A. Pflughaupt
    ------------------
    My Equipment List
     
  15. Gary Thomas

    Gary Thomas Second Unit

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    Wayne..can you list two or three eq's you'd recommend. I saw a Rane-15 on ebay for $200. Is that a good deal?
    ------------------
    DVD's
    HT Pic's
     
  16. Gregg Loewen

    Gregg Loewen Video Standards Instructor, THX Ltd.
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  17. BruceD

    BruceD Screenwriter

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    Yes the BFD typically goes for $160 on the web.
    The BFD 1100P allows fine tuning the bandwidth of the parametric EQ to 1/60th of an octave.
    This should allow everyone to eliminate any peak or multiple peaks in their listerning rooms for the low frequency (bass) signal path.
    BruceD
     
  18. Kevin C Brown

    Kevin C Brown Producer

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    Do any of these EQ units give you the method of finding the problem freqs and the width of the peaks (or valleys)?
    (I.e., somehow a test tone generator with a microphone.)
    ------------------
     
  19. Kevin C Brown

    Kevin C Brown Producer

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    Never mind. Just found the other thread!
    "Which equalizer to tame my SVS induced room peaks?"
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  20. BruceD

    BruceD Screenwriter

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    For a complete tuning system, I would go with ETF5 software on a PC (I use a notebook).
    Includes:
    - sound generation (MLS signals fed to amplifier inputs) no demo disk needed
    - can use RS SPL meter's RCA mic output as line input to PC
    - generates frequency graphs on PC screen (FFT analysis)
    Very sophisticated tool for inexpensive price $150.
    ETF website
    Bruce
    [Edited last by BruceD on October 27, 2001 at 08:46 PM]
     

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