Comb Filtering : Please engineer / smarty-pants ... learn me sumtin

Discussion in 'General Audio Discussion' started by biscuithead, Nov 10, 2017.

  1. biscuithead

    biscuithead Me likes the eargasm retroplasm... Subscriber

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    I've stacked New large advents and they sounded really good-

    I've had 12 different pair of speakers screaming from 2000WPC and it sounded loud-

    Yesterday I stacked some B&W Matrix 1s on top of some Matrix 3s and it didn't sound "Right" . I wired them in series, and had the 3s first in line... then switched the wiring... same/same...

    I've read the Wikipedia definition and I understand the lead/lag principal of comb filtering...

    But-

    Is it just sometimes LUCK that determines whether two speakers are going to compliment or comb?

    Or am I not respecting the science enough to know how to "amend" the scene to allow them to time correctly...?
     
  2. whoaru99

    whoaru99 Epic Member

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    I'd say that series wiring of speakers, especially dissimilar ones, can introduce its own set of issues completely independent of combing.

    I presume series was chosen for concerns of amplifier safety. But, I propose that you parallel wire them and see what happens. Keeping the volume moderate should pose little risk to the amp for a short test.
     
  3. biscuithead

    biscuithead Me likes the eargasm retroplasm... Subscriber

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    I have them hooked to MC-60s right now... but I do have a B&K amp that is 2ohm stable... I'll try that! Why didn't I think of that? Thanks!
     
  4. Lapslah

    Lapslah Active Member

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    As you probably know, the main concept behind the B&W Matrix series was to tighten up performance by use of extremely inert cabinets. I find that the most sonically noticeable way my Matrix 1, Series 2s differ from other speakers I've owned is in the tightness of their sound (no ringing of the cabinets), resulting in outstanding imaging. I suspect that the comb filtering you're experiencing is the result of this precise imaging which would emphasize null points, and would be less noticeable using speakers with more "smear". I'm not sure why you're stacking, but I'd experiment with minute variations in front-to-back placement between the upper and lower speakers to see if there's any change. At least this would help you pinpoint the source of the problem to acoustical or electrical.
     
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  5. Todd Dodds

    Todd Dodds AK Subscriber Subscriber

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    I got stacks aplenty. But I have no idea what comb filtering is. Guess I'm going a Googlin'...
     
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  6. biscuithead

    biscuithead Me likes the eargasm retroplasm... Subscriber

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    Again, I never thought about physically moving the 1s neared or further... genius!

    * I also do not know why I am stacking these... I was so impressed with the Matrix 1s, that it led me to hunt down some Matrix 3s. When I had the Matrix 3s dialed in... I thought, ok, now I'll add the 1s into the mix... Ultimately, I suspect I'll abandon this exercise. I thought I'd try and learn something though.
     
  7. Todd Dodds

    Todd Dodds AK Subscriber Subscriber

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    So far as the dissimilar issue Whoareu99 notes, I've got Bozak Symphony's on top of Altec 19's, which I usually run separately, but occasionally run together successfully using separeate amps and split signal. The fore/aft placement makes a big difference.

    Do MC-60's have gain controls like the MC-30's?
     
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  8. biscuithead

    biscuithead Me likes the eargasm retroplasm... Subscriber

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    Yeah I do this with my Klipsch heritage collection... but I use different amps and such like you. I rarely use two pair at once, unless I'm mad at my wife and I want to escalate it to another level. I have stacked many different speakers though. I really liked my two pair of Heresy with that B&K , but imaging always suffers when using two different pair.

    Do your Bozaks and Altecs image well together? If so, this is rare...
     
  9. Todd Dodds

    Todd Dodds AK Subscriber Subscriber

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    Acceptable imaging, but not GOOD imaging. I've got stacked DQ-10's that are much better, though still won't knock your socks off, especially compared to something like your B&W.
     
  10. whoaru99

    whoaru99 Epic Member

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    You don't have the speakers wired in series, so that's a bit non-congruent to my point about series-wired speakers being a potential factor aside from anything else.
     
  11. whoaru99

    whoaru99 Epic Member

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    Simply put, it is a finger-like (or comb-like) pattern of constructive and destructive interference. In effect, when you walk around the room or side to side/up or down in front of the speakers and hear variance in the levels as the sound waves combine constructively and seem louder or destructively where there is cancellation and reduced level.
     
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  12. 604man

    604man Active Member

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    Comb filtering....

     
  13. tonyk

    tonyk AK Subscriber Subscriber

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    I almost spit my coffee out.:rflmao:

    I went down that road once.

    You'd be surprised how loud a big pair of Maggies will play when you're pissed.
     
  14. E-Stat

    E-Stat Super Member

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    I've done that before but now use a single pair in the garage. It all depends upon your choice of tradeoffs. Double Advents can sound more impressive, but lose imaging specificity and focus to these ears. But then, I found that I was especially sensitive to coherency issues since I was a teenager - which I why I prefer full range stats today.

    Spacing multiple drivers wider than the wavelengths they reproduce will create multiple, overlapping waves of the signal and blur resolution. Which is usually only a challenge with tweeters. In the case of double New Advents, the distance between the tweeter centers is about 10" - which translates to a frequency of about 1350 hz.

    There's no *fixing* that unless you physically move the drivers closer together. With multi-driver line arrays like Scaena, Pipedreams, IDS, etc., you'll note the drivers are located very close together to minimize or eliminate that factor.
     
    Last edited: Nov 10, 2017
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  15. Todd Dodds

    Todd Dodds AK Subscriber Subscriber

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    I should've been more clear. I have run them in parallel and series in the past, and finally decided to quit fighting and run them on seperate amps with volume controls.
     
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  16. toddalin

    toddalin Super Member

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    I don't think that is "comb filtering" so much as "reflective destruction/cancellation" which I guess could be construed as a form of comb filtering, but not what most people think of in this context.

    When most people think of comb filtering, they are thinking of two separate speakers located in proximity producing the same/similar spectra where their waves can add or subtract from each other depending on the placement of the listener relative to the two sources.

    The more disimilar the two waves, the less likelihood of comb filtering.
     
    Last edited: Nov 10, 2017
  17. 432HzBob

    432HzBob AK Subscriber Subscriber

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    I don't know why it is but I learned about comb filtering here on AK and seems to be true.
    I stacked some Dynaco A-25's on top of the JBL L-101's.
    Thought It would give something like a stage setup at a 70's Who concert.
    Nope.
    Sounds worse with all 4 going (seperate amps) than just the 2 JBL's or 2 Dynaco's themselves.
    I don;t understand why. I always thought it would give a Phil Spector wall of sound effect.
    Nope. Maybe at low volumes it's ok, but not over 20 watts or so starts to sound ill defined and sloppy.
     
  18. mfrench

    mfrench AK Subscriber Subscriber

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    Get ready to have your mind blown!
    Alvin Lucier: Homage to James Tenney, for Double Contrabass, and Pure Sine Wave Oscillators

    this is a wonderful compositional study of phase cancellations and comb filtering.
    It gets really good around 9m45s, if you don't want the whole 16minute of this.
    I got to record a performance of this one once.

    Hint: Listen for how drastically the bass notes change the unwavering oscillating tones (or vice versa).

    edit, to add (it is a reverse redundant post of one on page two of this thread):
    This is my recording of the same, ^, from around that same 9m45s mark.
    sample of mine: https://soundcloud.com/user-271082364/live-phase-cancellation-comb-filtering
    Lots of peripheral crap in this one - sorry.
    Scene: Art Museum, abstract art exhibit, and this performance. The audience was quiet and respectful; but the kids in the day care next door, and the street noise,.... [rolls eyes smilie here][slaps forehead smilie here]
    Hey,.. At least it gets you an idea of what went down.
     
    Last edited: Nov 10, 2017
  19. Todd Dodds

    Todd Dodds AK Subscriber Subscriber

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    Really good around 9m45s? Dude, it was ROCKING!
    Gosh, this morning I didn't even know what comb filtering was, and now I'm all ready to follow the, er, band.
     
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  20. 604man

    604man Active Member

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    What Is Comb Filtering & How Does It Relate To Room Acoustics?

     
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