MAJOR bass cancellation probs.(bass traps?) HELP PLEASE

Discussion in 'Home Theater Projects' started by Mike<>P, May 10, 2004.

  1. Mike<>P

    Mike<>P Extra

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    Hey folks, I'm just about done with the construction my new theater/listening room and I think I've created a monster.

    Like a typical guy I set up the electronics first. What I have now is a large room with virtually zero bass at the listening position. Of course at the corners and along walls there is a decent quantity of bass but it is quite muddy. When I leave the room and go(through the door)into the kitchen there is the loudest bass I have ever heard, in a house at least.

    The bass at the listening position sounds so bad it almost messes with your equilibrium. Sort of an out of phase sound(yes all the drivers are in phase) The only bass to be heard there is sort of a resonant bass, in other words it has ZERO impact(though if it did it still would sound like crap)

    So, from what I have gathered over the phone with various people and also on the internet, I have reflection/cancellation issues. Bass traps seem to be the only solution to my problem.

    I guess my questions are;

    2) Has anyone heard the effectiveness of bass traps.
    3) If bass traps are the solution, is it a sure bet. In other words will the proper amount of traps TOTALLY cure the problem.

    If anyone has any questions please ask. I will be making posts, including pix, reguarding other specifics including components, speakers, general photos, etc..... Thanks
     
  2. Rutgar

    Rutgar Second Unit

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    In my opinion, you'll be wasting your money and time buying bass traps. You didn't say anything about your gear. Do you have a subwoofer? If so, there is a current thread in the "Speakers/Subwoofer" section of this forum that is very helpful in setting it up. If you don't have a Subwoofer, and money isn't a big problem, the new Velodyne "Digital Drive" subs will allow you to "tune" the low end of your system for a smooth Bass response. A cheap alternative to this particular Sub is the Behringer "BFD Feedback Destroyer". It is a Parametric equalizer that costs about $120.00 at most professional music gear stores (such as Guitar Center). To set it up, you need to also get a Radio Shack sound level meter. Here is a link that tells you how to set it up, step by step. Hope this info helps.

    http://www.snapbug.ws/bfd.htm

    - Rutgar
     
  3. Mike<>P

    Mike<>P Extra

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    I have 2 subs w/3 15" drivers total. One Klipsch KSW15 and a DIY dual 15" Titanic ported box.I am in the process of building a web page @yahoo so I'll be able to post pix of my rack and speakers. I figured I could just attach an image like an e-mail to post pix.....sorry. It'll be done in a little while.
     
  4. Rutgar

    Rutgar Second Unit

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    I also run two subs (two Velodyne ULD-15's). Right now, I have them in opposite corners of the room, and have almost perfect response (without the BFD). It took me a lot of experimenting to finally get them right. Also I corrected the link in my first post. It should work now.

    - Rutgar
     
  5. Mike<>P

    Mike<>P Extra

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    I have tried every position(except opposite corners)with the subs with the same outcome. Even w/o the subs on,my mains have very very little bass in the listening position. They are Klipsch Cornwall II's which are VERY good at producing bass. In my last room which was only 13x15 they,for the average joe,were more than adequate w/o using a sub. The room before that was 24x24 with a 25' cathedral ceiling and they also sounded excellent. Which leads me to believe it's my room acoustics.

    I even played one of those dedicated rap bass cd's(read MEGABASS)with and w/o the subs and still the room exibited the same response but I go out into the kitchen and there the bass is! In other words I'm standing outside the cancellation zone(or what is now appearing to be the twilight zone!)

    Anyway,I'm still working on getting some pix up( i guess I need to have 15 posts in order to do so) so please be patient. In the meantime I'll try the opposite corner placement. Thanks,Rutgar
     
  6. Wayne A. Pflughaupt

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    Hi Mike,


    This tells me that you probably have your seating position in the center of the room (i.e., away from any boundaries). The problem you’re having will be typical in a large room like yours. It’s very common for bass to be stronger along boundaries and weaker in the center. I don’t know what you can do about it, except get more potent subs, move the seating closer to a boundary, or reduce the size of the room.

    Regards,
    Wayne
     
  7. Ronald Epstein

    Ronald Epstein Founder
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    Folks,

    Mike (the author of this thread) sent me these
    pictures to upload for all of you to see....

    [​IMG]

    [​IMG]

    [​IMG]
     
  8. Mike<>P

    Mike<>P Extra

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    Gee,thanks Wayne![​IMG] thats real encouraging news! From what I understand the cancellation is caused by reflecting waves off the surfaces in the room interacting with each other thus destroying themselves. In other words the waves have nowhere to go. Bass traps, from what I understand, absorb low frequency energy and in turn give it a place to go. Therefore the bass would be louder and more defined due to the theoretical lack of bass energy bouncing back. Kind of like listening to a killer car stereo with the windows up. Roll the windows down and the bass gets much louder. The waves are allowed to escape thus minimal cancellation occurs.

    Indeed I do have a large room 21x31 but like I said earlier my now bass problematic mains sounded great in the 24x24 room. The major differences between the rooms are the old room had a smaller 20x10 room off of it(w/o dividing walls),two doorways(one to the kitchen,one to a bedroom)and a hallway. Also it is a log home with well...log walls-not particularly airtight and very good for diffusing sound waves.

    Yes the listening point is 2-3' beyond the center point of my current room not unlike the log cabin room.(maybe I should kick my parents out and move back home!)

    It would seem like I am really sold on the bass trap idea but I believe all signs point to this type of phenomenon, maybe I'm wrong but it sure makes sense.Any elaboration or other input is appreciated. Thanks again,Wayne
     
  9. Rutgar

    Rutgar Second Unit

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    Mike, before you spend lots of money on Bass Traps, I would click on the link that I supplied in my first post, go to the section that supplies the links for test tones and the Microsoft Excel spreadsheet, download the spreadsheet, and test tones, burn the test tones to an audio CD. Then buy the Radio Shack sound level meter, take measurements at your listening area, use the spread sheet to plot what you're listening to. That way, you'll have a clear idea of what you're dealing with in your room. I would suggest taking measurments with both subs, as well as each individually, and at different posistions. In other words experiment. Bass Traps are expensive if you buy them, and they're a pain build, if you make them. Plus, they're very hard to tune the room with. Moreover, as Wayne said, they really do nothing for "suckouts". The meter, spreadsheet, and test tones are cheap and easy way to get a really good look at what's going on your room. Trust me, I've gone through what you're going through. I have two very large Bass Traps now sitting in my garage, because they're useless. I put them in the same catagorie as "Bi-Wiring" and painting one side of your CD's green.

    Keep us informed on your progress.

    - Rutgar
     
  10. Ethan Winer

    Ethan Winer Stunt Coordinator

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    Mike,

    > Has anyone heard the effectiveness of bass traps ... will the proper amount of traps TOTALLY cure the problem. <

    I see a lot of misinformation here about bass traps, so let me clear things up for you.

    Yes, bass traps absolutely work. They flatten the low frequency response by reducing the reflections that cause both peaks and nulls. Just as important, they reduce the effects of modal ringing, which is not unlike reverb at low frequencies.

    However, it is impossible for any acoustic treatment to totally flatten the response. To do that you'd have to cover literally every surface on all the walls, floor, and ceiling with traps that absorb 100% at all low frequencies. But bass traps absolutely can make a huge improvement in the perceived fullness and clarity of bass instruments.

    All untreated rooms have many peaks and severe nulls throughout the entire low. Peaks are rarely more than a few dB, but nulls are typically 30 dB deep and often even more. This is the root cause of your lack of bass at the listening position. To give absolute numbers, good bass traps can reduce a null that's 35 dB deep and make it only 10-15 dB deep. While this may seem like the response is still terrible, in fact a 20 dB increase is a huge increase in level.

    I'll also mention that you cannot correct these acoustic problems with EQ.

    --Ethan
     
  11. Mike<>P

    Mike<>P Extra

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    Rutgar, I tried placing the subs in opposite corners but it sounded bad. There was a little more bass but it was very muddy and very directional.

    However, what I did was turn off BOTH subs and my 2nd set of mains and just played the Cornwalls. I figured I should start from a beginning point. I said earlier(I think) that the whole system sounded sort of out of phase, so I switched the phase on one of the Cornwalls and just like that the bass returned. This tells me one of two things. 1) the speakers just sound better out of phase in this room or....2) I had the speakers checked/cleaned by a Klipsch Pro dealer and possibly one of the bass drivers/crossovers was installed out of phase, and by switching the polarity at the back the phase was partially corrected. I'll take them apart and recheck the connections.

    Good news,kind of. When I turn the sub back on, indeed I can feel the bass in the music but the sub bass is still very lame . I have a Paradigm x-30 which has a variable 0-180' phase adjustment but I have yet to hear any significant difference in SQ when tweaking it.

    My tweaking efforts will continue.I will also try the 'several rolls of insulation stacked in the corners trick'. I have read here and on another acoustics web site that it is a quickie test as to the potential effectiveness of actual bass traps. If there is a difference, great, I will make some DIY traps using rigid fiberglass similar to RealTraps. If not the insulation can be returned and I will burn down my addition and start over. Just kidding....(maybe!)[​IMG]

    Thanks
     
  12. Mike<>P

    Mike<>P Extra

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    Thanks, Ethan. I have to apologise though. My intention wasn't to take any biz away from your company. I didn't even see your post till I was done with my last one. But, I did get the idea of using rigid fiberglass from your site(I think). There was something about not being able to supply DIY'ers with the fiberglass due to shipping.

    I absolutely agree with your post. In theory the traps should have a major impact on my acoustical issues. But, I will continue farting around with phase configurations before cotinuing on.

    Common sense tells me that if you EQ problematic frequencies way down you still wouldn't hear them. The acoustic properties of the room haven't changed and therefore cancellation, which seems to be my problem, would still occur.

    Any and all opinions are very much appreciated.
     
  13. Ethan Winer

    Ethan Winer Stunt Coordinator

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    Mike,

    > My intention wasn't to take any biz away from your company. <

    I didn't take it that way at all. I'm here to help people, not to sell stuff. The biggest problem I see is the huge amount of misunderstanding about acoustic treatment in general. As long as people continue to put $12,000 loudspeakers in a room with no bass traps, I'll continue my efforts to educate. I've been stressing the importance of acoustics and bass traps for 25 years. I've been in the treatment business for less than two years. And yes, you probably read the suggestion to use bales of raw fiberglass in my Acoustics FAQ!

    > In theory the traps should have a major impact on my acoustical issues <

    Not only theory, but in practice. All of the points I made are shown in the video on my company's web site, including the fact that bass traps reduce the effects of nulls as well as peaks.

    > I will continue farting around with phase configurations before continuing on. <

    Absolutely. You should always get things as good as possible using the means already available first.

    > Common sense tells me that if you EQ problematic frequencies way down you still wouldn't hear them. <

    Yes, and for a number of reasons, not just because 20 dB of gain in a null is still a null. [​IMG] The text below explains it in more depth.

    --Ethan

     
  14. Wayne A. Pflughaupt

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    Ethan,

    Just to be clear, you're saying that bass traps will help the problem Mike has - i.e., the bass is "hot" around all the boundaries of the room and dead in the middle of the room? In other words, they'll deal with the former problem and simultaneously not aggravate the latter?

    Regards,
    Wayne
     
  15. Rutgar

    Rutgar Second Unit

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    The guy is trying to sell him something Wayne. Many people here know that it's not a myth, that bass can be equalized using a product like the BFD. And it's waaaay cheaper than Bass Traps. Takes up a lot less space too.

    Don't get me wrong. I have some absorption panels as well. But, out of the fifteen or so, of commercial absorption panels that I have, only five of them are currently in my theater room. The rest are in the garage along with a bunch of large diffusion panels and Bass Traps.
    And, as I indicated before, none of that stuff, ever helped with my Bass problems.

    - Rutgar
     
  16. Ethan Winer

    Ethan Winer Stunt Coordinator

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    Wayne,

    > you're saying that bass traps will ... deal with the former problem and simultaneously not aggravate the latter? <

    Yes, that's exactly what I'm saying. Please stop by my company's web site and read some of the technical articles. If you have high-speed Internet, watch the videos too.

    I'll also address Rut's comments: I'm not here to sell anything. Rather, my goal is merely to explain acoustics because it is so poorly understood. However, I frequently find myself having to dispell misinformation like the myths that bass traps reduce only peaks, or that EQ can cure room acoustics problems.

    I've been a professional audio engineer for more than 30 years, and I'm well known in the business for the dozens of technical articles I've written for pro audio magazines. Lately I spend much of my day showing people how to avoid having to buy acoustic treatment products. In particular, my Acoustics FAQ at ethanwiner.com/acoustics.html and Bass Traps article at ethanwiner.com/basstrap.html explain these in great detail. I offer this as a public service to the pro audio community, and more recently to audiophiles and home theater enthusiasts as well. I also host an Acoustics forum at the MusicPlayer network (publisher of several audio magazines), where I answer questions about my acoustics articles and help people build their own acoustic treatment.

    Thanks.

    --Ethan
     
  17. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    Truisms:
    Bass traps "can" help.
    EQ is NOT the answer for room nulls (but CAN be used to lower peaks).

    You may have tried this, but I'll suggest just in case: try stacking your subs and listen to the effect. As was pointed out, using two subs in separate locations can actually cause cancellations, depending on room and speaker placement geometry. One way to place a sub is to put the sub in your listening position, then walk around the room and listen or measure and you'll discover spots that are nulls, spots that are peaks and spots that are in-between (have decent bass). The in-between spots are candidates for sub placement.
     
  18. Ethan Winer

    Ethan Winer Stunt Coordinator

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    Hank,

    > EQ is NOT the answer for room nulls (but CAN be used to lower peaks) <

    Good point, and I'll clarify by distinguishing between peaks that are caused by room modes versus peaks caused by the more general case of acoustic interference.

    Peaks in the response due to room modes / dimensions can be tamed somewhat with EQ because the frequency of the peaks stays the same in different places around the room. But there are other peaks whose frequencies change depending on how far away you are from the various room boundaries. Trying to reduce those with EQ is futile.

    --Ethan
     
  19. Rutgar

    Rutgar Second Unit

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    Hmm, I guess according to you, Velodyne's new "Flagship" Digital Drive Subwoofers are useless since low frequencies can't be smoothed out by EQ. NOT!

    - Rutgar
     
  20. Wayne A. Pflughaupt

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    No need to start a debate. It’s a well-established fact that equalizers don’t eliminate low frequency room problems, they just compensate for them. Some people can live with that, some can't.

    True, but you have to keep in mind that not all under-represented points are nulls. The ones that are not can usually be addressed quite nicely with equalization.

    Regards,
    Wayne A. Pflughaupt
     

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