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Reaching reference level with a sub?

Discussion in 'Archived Threads 2001-2004' started by Greg Br, Jan 30, 2002.

  1. Greg Br

    Greg Br Second Unit

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    I am reading more and more about this and am a bit confused, as usual when it comes to this stuff. I have calibrated my HT and I know what reference level is for me after calibrations. Obviously the reference level for a sub is somewhat different as I have read many posts saying that it would take two SVS 16-46 subs to reach reference levels of bass, based on room size, power, etc. What exactly does this "reference level" mean in this terminology.

    Also in terms of using a amplifier or any power source what is the difference between 4ohm and 8ohm, I have an idea but would like a better understanding. If my receiver is 100w x 2 channels is that 4ohm or 8ohm?

    Thanks

    Greg
     
  2. Bhagi Katbamna

    Bhagi Katbamna Supporting Actor

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    Reference level is 105dB at the listening position with the 5 man channels and 115dB with the dedicated low frequency effects channel. The LFE channel is usually used from 20Hz to 200Hz. It is very difficult for any sub(or 2) to produce 115dB at 20 Hz at the listening position.
     
  3. Greg_R

    Greg_R Screenwriter

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    It also depends on the room dimensions & if the room has any openings (to other rooms, etc.). It's easier to reproduce high SPL in a smaller, sealed room (less air to move). Setting the rest of the speakers to small will add an additional demand on the subwoofer/s. As Bhagi mentioned, reproducing low frequencies at these levels with minimal distorion requires serious effort.

    In HT, specs are assumed to be 8ohm unless otherwise stated. However, since a speaker's impedance (ohm) ratings change (based on frequency & other issues) it's good to have an amp that is capable of driving these lower impedances.
     
  4. Greg Br

    Greg Br Second Unit

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    Wow, 115dB is some serious heat, most subs I have read are lucky to hit [email protected] . I serously doubt my wife could take anything close to that!!!
     
  5. Scott Page

    Scott Page Stunt Coordinator

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    Also, if your sub is reproducing bass from the other channels, then it needs to produce MORE than 115 dBs for reference. the 115 figure is LFE only. If I recall correctly what SVS Tom said, the sub has to put out about 125 dBs at the listening position when producing bass from other channels too.

    That is why multiple SVS subs are so popular.
     
  6. Greg Br

    Greg Br Second Unit

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    So I am upgrading to the 16-46+ here in the next few weeks, I have a JBL PB-12 and I have to say for the middle HZ its not all that bad, should I hook it up to handle the rear surround bass and set those speakers to large. I also have decent front towers that can produce some good bass, would it be better to set those to large so it would be easier to reach reference levels with the SVS, although most articles are a proponet of setting everything to small and the LFE to subwoofer and not both.

    Also if my towers are halfway decent would it make better sense to set the crossover at around 50hz to take more of the load of off the svs or the pb12.
     
  7. Scott Page

    Scott Page Stunt Coordinator

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    I recommend selling the JBL, and putting the money into a Baringer Feedback Destroyer (around $120) so you can EQ the SVS sub. By doing so you will avoid the big problems associated with having two different types of subs, and will get the most performance out of your SVS. By EQ'ing it, you will smoothout peaks which will give you more output where it is intended. It might even be able to play louder than it would have with the SVS and the JBL combined. Sound better too.

    Set everything to small. I have very nice high quality full-size fronts (Vandersteen 3A's), that extend low, but small is always recommended (by no less than Mr. Vandersteen himself). Setting all speakers to small will often result in improved sound all the way around as it takes the stress off of the reciever and the speakers thereby improving the midrange.

    Don't listen to the resident powered-tower freak around here who recommends no sub and settings fronts as large. That is simply bad advise by someone trying to jusify their poor purchase decision.
     
  8. Bob_A

    Bob_A Supporting Actor

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  9. Scott Page

    Scott Page Stunt Coordinator

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    Oops,

    I think I meant those recommending powered fronts as large with a sub, effectively having 3 subs in 3 different locations. Whatever. Set all speakers small and have all sub/subs in the same corner and of the same model if more than one.
     
  10. gene avallon

    gene avallon Stunt Coordinator

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    just got new 2 46 plus up and running.star wars 110 db in the sweet spot,just coasting

    gene
     
  11. Steve Stogel

    Steve Stogel Supporting Actor

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    I think that Tom says you should get 121dB at 20Hz at your seat with bass management. So your sub, unless you're right on top of it, probably has to produce in the range of 125dB+ at 20Hz (yikes).
    As far as which subs to get, talk to Ron or Tom at SVS, but I'd be willing to bet that they'd recommend the 20-39+ unless you listen to a whole lot of pipe organ stuff. It will also come with a port blocker (or two?) so that you can change the tuning to something closer to the 16+. BUT the 16, even the plus series I would imagine (?), are a lot more likely to bottom out than the 20s. Having the tuning point that low really stresses out the driver in the 25-35Hz range (pretty common on DVDs). Check out this chart Tom posted. http://www.hometheaterforum.com/htfo...ottom+and+out. Now, the 16+ may be harder to bottom out, but to me it looks like the 20 is the perfect combination of punch and extension, IMO.
    Steve
     
  12. gene avallon

    gene avallon Stunt Coordinator

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    I got about 110 to 115 siting in the sweet spot holding the meter in my hands.set on fast reading.

    gene
     
  13. MarcVH

    MarcVH Second Unit

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    What was the limiting factor at 110-115 db? Did it start distorting too much, or bottom out, or did the amp start clipping, or... ?
     
  14. Jason Wolters

    Jason Wolters Stunt Coordinator

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  15. gene avallon

    gene avallon Stunt Coordinator

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    marc
    me I couldnt take much more the amp was no where near clipping,did not clip once, it hit highs of 120 I was holding the shack meter in my hand it wasnt like one steady tone. BOOOOM,BOOM. CRASH. YOU WANT ME TO TEST IT HIGHER?YOU PAY THE DOCTOR BILLS.
    GENE [​IMG] [​IMG] [​IMG] [​IMG]
     
  16. Bhagi Katbamna

    Bhagi Katbamna Supporting Actor

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    Setting your mains to large, results in (with most processors/receivers) no signal to subwoofer with PCM.
     
  17. MarcVH

    MarcVH Second Unit

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    Fair enough. I was curious because the reviews I've seen of the CS-Ultra say that their SPL limiting factor was when the amp started clipping, but wasn't sure if the CS+ driver might give out sooner.

    I suspect I'm not alone in pondering whether a single 16-46CS+ would suffice for a typically-sized room, or it should be upgraded to either a 20-39 or dual 16-46s to get sufficient volume. Fortunately I'm not in a position to purchase quite yet, so I can wait for some graphs and such.
     
  18. Rick Radford

    Rick Radford Supporting Actor

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    Jason,

    Do a search here and on the DIY Advanced area for Behringer or BFD. I've recently jumped into this arena and am pleased with the results.

    The BFD 1124p is the current model and goes for ~$129 US via etailer.

    You can do it the hard way (RS meter, test tone CD and pencil and paper, Excel graph) or the easy way (ETF5 or Spectraplus RTA software). Once you get through the learning curve of the software, taking measurements is a breeze.

    There are a couple of sites that offer help with the BFD setup too. Let me know if you don't come across them. They're just a couple of weeks old.
     
  19. Tom Vodhanel

    Tom Vodhanel Cinematographer

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    quick hits,
    1) the 121dB requirement assumes all 5 full range channels will have high amptitude bass on them...and be folded into the LFE channel and sent to the sub(s). If you have all speakers set to small...then the subs will need 115dB of headroom.
    I'm not sure how many DVDs have all 5 channels filled with deep bass at high amptitudes simultanesouly....probably about 3 out of 30,000. I would say 99.9% of the time...you may need 118-120dBs of headroom down to the 30-25hz range,116-118dBs down to the 20-24hz range,and 115dB
     
  20. Jason Wolters

    Jason Wolters Stunt Coordinator

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