New Theater = poor bass

Discussion in 'Home Theater Projects' started by Ian_J, Mar 31, 2004.

  1. Ian_J

    Ian_J Stunt Coordinator

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    May I be so bold as to implore you gentlemen for some assistance?

    Ahhhhhhh, seriously, HELP!

    I’m getting muddy bass between 80 and 45hz (I think). I say this only because it is most apparent in music.

    Details:

    My theater is almost complete (everything but carpet & seating / I’m currently using a futon) but being an impatient American, I already installed my speakers. Unfortunately, the bass isn’t what I expected. I’ve begun to read up on room modes, peaks, nulls, frequency response and all the other things that influence the sound of a room. Prior to construction I did confirm that my room measurements would not create a HUGE problem. I was hoping that someone could point me in the right direction so that I can find a “quick fix” while I read up on room acoustics and find the “best fix”.

    So, here is my non-technical description of the problem.

    My room dimensions are 16’ 8” long x 11’ 8” wide x 7’ 6” tall (w/ a soffit - 6” deep by 13” wide). My fronts are full range speakers (Axiom M60s) and I have two 10” subs to compliment the fronts. Mids and Highs are very clear and accurate although I’m sure I need to address some reflection points. The bass however, is loud and muddy at certain frequencies. When the bass guitar dips down low, the bass increases in volume and becomes muddy. It is so prominent that it nearly cancels out the mids and highs. One thing I have noticed is that the corners of the room amplify the base. I knew this could happen but I never realized it could be so extreme (bass is nearly doubled in the corners). I should mention that my sub is in the corner and my mains are pushed to the sides of the room pretty far too (about 1.5’ from the wall). I should also note that the problem occurs with 2 channel and 2.1 channel music. LFE effects during movies sound good and are powerful enough to shake the couch. The problem seems to only occur when listening to music.

    So, any suggestions or links would be greatly appreciated.

    Quick edit: I should also add that my walls are staggered stud construction w/ 5/8" fireboard. They are extremely, extremely solid.
     
  2. Brian Corr

    Brian Corr Supporting Actor

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    Ian,

    First, I wouldn't worry just yet. Wait until the carpet and regular seating is installed.

    Then run out and get a radio shack spl meter and find a nice disc with some test tones that go down to at least 20hz. This way, you can take some measurements and get a better idea of where your problem areas are. Chart the measurements in Excel to see your curve.

    A cheap and popular fix for bass is the Behringer Feedback Destroyer DSP1124. It's a parametic EQ and can be found for about $120.

    After taking measurements with the RS SPL, you use the EQ to flatten out the dips and peaks. Do a search on this forum for Behringer, house curve, feedback destroyer, etc and you will find tons of info on improving bass response.

    But wait until you get carpet, as that will change the way things sound.

    You may also want to pull your speakers in from the walls a little bit and get the subs out of the corners. The corners will typically help boost output but will make room modes worse (the dips and peaks bigger). Just moving the subs away from the walls may help improve the sound enough for your liking.
     
  3. Neil Joseph

    Neil Joseph Lead Actor

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    The things Brian mentions is a good starting point to try to address the bass difficulties. When you perform the bass sweeps, pay particular attention to the interaction between those full range towers and the subwoofers. Since the main speakers can in fact handle much bass of their own, this only complicates the speaker issue. Toss in not one but two subwoofers and this becomes a challanging speaker placement and/or cutoff adjustment issue.
     
  4. Wayne A. Pflughaupt

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    Ian,

    Brian and Neil have pointed you in the right direction.

    That’s why it usually works best to have multiple subs in the same corner, but with your symmetrical room you can get results nearly as good in the front two corners. The main penalty will be a 1-2dB loss of maximum SPL. The BFD equalizer Brian mentioned is stereo, so you will be able to EQ the subs separately.

    Regards,
    Wayne A. Pflughaupt
     
  5. Ian_J

    Ian_J Stunt Coordinator

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    Thanks for the information.

    Last night I confirmed that my two towers are set to small and I eliminated one of the subs. I then moved the remaining subwoofer near the center of the front wall. This greatly reduced the overall impact or perceived volume of the bass but it did not tighten it up much. Even when listening in two-channel stereo the bass from the towers is loud and muddy. From what little I’ve learned about room modes, additional sound treatments will not eliminate the standing waves that are causing the problem. They will simply reduce the perceived volume of the bass. Is this correct?

    Ian
     
  6. Wayne A. Pflughaupt

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    Room treatments are for altering acoustics relating to the “liveness” or “deadness” of a room. Typically it’s accomplished with soft materials for absorption, and moderately hard surfaces of a specific design to aid in diffusion (i.e., breaking up and dispersing sound waves). The result is reduced reflections, reverberation, etc.

    This has little if anything to do with dealing with standing waves or nulls. Typically bass traps are used for the former, but they are not nearly as effective or economical as equalization.

    Ian, until you get to a point where you can take some meaningful measurements and find out exactly where (in the frequency spectrum) you’re having problems, you’re shooting in the dark – flying by the seat of your pants, as it were.

    Until that time just use your ear and whatever means you have available o make improvements. Moving the sub around is a good start.

    However, it sounds like your mains have prodigious bass response, despite being set to small. This would not be an unnatural side effect for large full-range speakers being used in a room as small as yours, because smaller rooms exaggerate bass response.

    Add to this the fact that Axiom characterizes your M60s as being capable of delivering “ultra-clean, high-volume levels in large rooms” (emphasis added) and it’s not hard to see why you’re having “bass overload.”

    So try moving them away from the wall, or using the receiver’s tone controls to reduce it for the time being. Or a combination of the two.

    But your best bet in the end may be to trade in the oversized M60s for smaller speakers that are more suitable for your room. The M60s are a waste of space, money and capability for your room, and will forever be severely under-utilized. Axiom recommends the M22 or M3 for “moderate to smaller sized rooms.”

    Regards,
    Wayne A. Pflughaupt
     
  7. Ian_J

    Ian_J Stunt Coordinator

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    Wayne,

    I’ve considered the Axioms as the culprit. I didn’t foresee a problem with the M60s. I planned on using them as small speakers for HT and running them 2 channel for music. Unfortunately, as you’ve pointed out, I may have been mistaken. My Axioms came from my family room upstairs (600 sq feet). My dedicated HT is about 200 sq feet.

    I’ve been researching the BFD and it seems to be a good solution to the problem. However, also as suggested, I’m going to complete the room and add some treatments before buying new equipment or trading out old.

    Regardless, thank you for you help. At least I know that the situation is not hopeless. I’ll update the thread when I apply a solution.

    Ian
     

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