Advantages of duel or more subwoofers?

Discussion in 'Archived Threads 2001-2004' started by Vaughan, Nov 28, 2002.

  1. Vaughan

    Vaughan Agent

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    I currently have a paradigm servo 15, which in my opinion is one of best subwoofers that is available because not only is it capable of 115db of sound pressure at 20hz (although I reached 113db at this frequency from my couch)but also because it can reach 10hz.I am thinking of buying another servo 15, but am having doubts as to whether another R20000(I live in South Africa) would give me a sizable increase in maximum sound pressure. Can anyone give advice or share a thought reqarding this?
     
  2. Phil_DC

    Phil_DC Stunt Coordinator

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    I just installed a second M&K 350THX sub in my system,all I can say is WOW!
    Adding a second sub is supposed to give you up to an additional 6db output, but it sure seems like a lot more than that.
    I watched "We Were Soldiers DVD" and you would swear the war was in my living room.[​IMG]
    If I were you I would see about getting a floor demo loaner from your dealer and try it on your system and see for yourself.
     
  3. Dustin B

    Dustin B Producer

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    Coupled properly, like Phil said you can get roughly a 6dB increase across the sub's passband.

    I don't know what size your room is but I have no idea how you are getting 115dB at 20hz from a single Servo15. I wonder if you have a roommode around 20hz. Without some serious, and I mean serious room gain that ain't possible. I don't know what THD level the Servo15 limits itself to and I also don't know how heavily they will roll off down below 20hz, but be confident it is rolled off heavily below 20hz. Cone excursion sky rockets as you get down below 20hz in a sealed design. You have to move sooo much air to make serious bass at 10hz.

    The Servo15 is a great sub, but it can't do that cleanly. And the Servo circuit should prevent it from playing with ungodly THD levels.

    Tom Nousaine's average of max output with a 10% THD limit for the Servo15 over a 25-63hz range (1/3 octave spacing I think) was just over 107dB measured from 2m in a 7000ft^3 room.
     
  4. Vaughan

    Vaughan Agent

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    Dustin , my subwoofer is corner loaded and my rooms overall dimensions are very small about 6m by 6m.I will be moving soon as of 10 January.Now the servo 15 cannot and will not produce extremely high spl at say 10 HERZ.But in my room I could get 113db at 20hz(Keep in mind that spl meter is inaccurate at low bass frequencies)so my overall output will be 2 or 3 dbs short.
     
  5. Dustin B

    Dustin B Producer

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    A 6m by 6m room will have a nasty room mode around 30hz. Both the width and length of the room will be reinforcing this mode.

    What SPL meter are you using. The Radio Shack meter is down 7.5dB at 20hz. So whatever you read off of it will be 7.5dB lower than your actual level at 20hz. Are you sure you room isn't closer to 8.5m by 8.5m.
     
  6. Ted Ross

    Ted Ross Second Unit

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    I went dual VTF-2s & noticed a huge difference. I could now run them in max extension mode & get good output at 20hz. I liked it so much Im thinking of getting a third.

    Dustin, how do you calculate a "room mode". Id be curious to what my room would figure out to be.
     
  7. Dustin B

    Dustin B Producer

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    For a rough calculation divide 565 by whatever the room dimension is in feet.

    The speed of sound is ~1130 feet per second. So when you divide 565 by the room dimension in feet you will get the frequency at which a half wave length will form a standing wave.

    6m x 3.3ft/m = 19.8ft

    565ft/s / 19.8ft = 28.5hz

    When two of your room dimensions are the same, then you'll have a very large peak at that frequency as you'll have two dimensions forming the same standing wave.

    A cube shaped room is the worst shape possible for in room bass response. You'll have 3 dimensions forming the same standing wave. The peak could even be too much to EQ out.


    Vaughan, do you have an EQ for your sub? If not you should consider getting one. With a square room it could really benefit you.
     
  8. mark alan

    mark alan Supporting Actor

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    Completely off topic Vaughan, but where in SA do you live (if you don't mind me asking)?

    I have been to your country a lot on business, and I am completly in love with the place.
     
  9. Vaughan

    Vaughan Agent

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    Mark I live in Cape Town.
     
  10. steve nn

    steve nn Cinematographer

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    I have realized a +6db boost with two subs stacked in a corner. If I part them I get a +3db boost with one of them along a long wall. If I part them with both subs in two certain corners,"The end corners of a rectangular room"-- I get a +5db boost.
     
  11. Lewis Besze

    Lewis Besze Producer

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  12. mark rush

    mark rush Stunt Coordinator

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    Add the second sub, you will really be impressed,{about 6db gain with coupling} but you will not notice as much if you ever add a third sub{about 3db}
     
  13. Ted Ross

    Ted Ross Second Unit

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    I thought it was 6db for each identical sub added, not 6db for the second & 3db for the third-or am I wrong?
     
  14. Michael R Price

    Michael R Price Screenwriter

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    It's 6db per doubling of amplitude, so going from two to four subs would net a 6db increase. Either way, such gains might not be useful if you are not stressing the capabilities of one subwoofer.
     
  15. Ted Ross

    Ted Ross Second Unit

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    Ah, that makes sense. After messing around with my dual vtf-2s I discovered something. When I 1st set them up I calibrated the subs with VE about +4db hot(79db). After watching some movies I still didnt have the "shake the walls" bass. I then upped the sub level another 4db & now my "tower of power" literally shakes the house's foundation. Thats the bass Im looking for & now im happy, but Im surprised on how much I had to up my bass over the VE ref level.
     
  16. Vaughan

    Vaughan Agent

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    Mark, If this is correct then one additional subwoofer irrespective of being identicle will provide 3 db of maximum sound pressure if put in one corner and upto 6 db if put side by side or on top of the first subwoofer.A third subwoofer should give 3 db in the other corner and a fourth(Heaven forbid!)subwoofer will give either 3 db on top of the third sub or up to 6 db. If you have read my duel svs ultra review then you know that I also have a servo 15 which I have not utilised due to time contraints.However I will give my review of all three subwoofers working together(JJESSSIS CRRIPES),and maybe I could try to borrow another servo 15 just for kicks.I have never had THIS much fun, hahaha!!
     
  17. steve nn

    steve nn Cinematographer

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    Hay Ted have you tried calibrating each sub individually. This will put them at the same output. The top sub will need just a little more gain most likely. If you calibrate +2db each sub you should come out +8db when you fire both up and measure with meter. What do you think?
     
  18. Ted Ross

    Ted Ross Second Unit

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    Steve, what I did was turn off one sub-feed it a 30hz tone at a fixed volume level & took a spl reading a few inches from the sub. i then turned that sub off & turned the other one on -fed it the same tone at the same volume & calibrated the sub gain till it read roughly what the 1st sub put out. I then turned both on & calibrated with VE & the spl meter. however, as you can see in my above post, I wasnt happy with the VE calibrated output.
     
  19. mark rush

    mark rush Stunt Coordinator

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    Well Mike is right on the sub gain, you get your biggest gain when you add the second sub, with coupling, double the speaker and power, it add's up to 5.5 to almost 6 db of gain if they are side by side or stacked, when you add the third sub you are not doubling the power or speaker size, so you get almost 3 db, right now my 2 pw2200's stacked are doing the job, but we all want more!!![​IMG]
     
  20. steve nn

    steve nn Cinematographer

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    You know this is going to sound odd but I have been digressing back to small. I know I have 30 inches of woof in the corner and I really do like it but I have been playing with my little 100 watt-8" sub lately. In-fact I went ahead and ordered one of the 10" DLS subs from Parts Express a few days ago to give it a run. I have found placing a rookie sub under a corner table next to my seating and running it 10db hot at -18 to -30, works pretty good for HT.[​IMG] I have it firing right into the end of the couch so it gives the feeling of a bigger sub. No way to get more extension though. My thought is "How much can I get out of a little". Ted I never have been happy with sub calibration for HT. I know where calibration is for reference sake. Do you sit close to a wall Ted or more in the middle of the room? If I understand your previous post you are at +8db now. That was the mark for me to.
     

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