Sub calibration question (VTF-3)

Discussion in 'Archived Threads 2001-2004' started by Mike Sloan, Oct 8, 2002.

  1. Mike Sloan

    Mike Sloan Second Unit

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    From reading numerous posts on the forum it appears that the general consensus is to max out the gain level on the sub itself and bring the sub into reference with the subwoofer output on the receiver.In most cases the volume or gain level at the sub is simply a filter which cuts input level flowing to the amp (especially true when using outboard pro amps, but often true with plate amps as well. I currently own the HSU VTF-3 and have found that I can't turn the sub's volume 1/2 way up without exceeding calibration levels even with the receiver's sub out set at (minus)12. I have heard that it has a huge amount of gain. Is this a characteristic of the VTF-3?
     
  2. jeff lam

    jeff lam Screenwriter

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    This just tells you that the input sensitivity of the plate amp is so low that you can't turn it up to max without exceeding callibration. This does not mean you will lose performance on the amp, the amp will still clip if given a high enough preamp signal.
    Take a look at This Thread
    pay attention especially to my posts and Vince's posts. This has lots of info on plate amp's and their different input sensitivities/impedances.
    In your case and in the case in the thread in the link you will find that maxing out the gain like how Vince suggests is not possible. Vince states that most plate amps work much like pro amps in the gain stage where you need to run them wide open. I have found in all plate amps I have worked with or heard about, this is not the case. My old Def tech sub, the Partsexpress amps, and now the VTF3 amp, and I'm sure the SVS amps as well(since I have not heard of anyone running a SVS plate amp wide open) are all impossible to run full open to achieve proper calibration levels unless your preamp is very very weak and does not provide a normal signal even at it's lowest setting. In most cases anyone who disagrees with Vince will regret doing so as Vince has vast knowledge of many concepts. However in this case I believe the method of running the sub output level on the receiver 1/4 way up and pushing the gain on the amp up until proper calibration is reached is the best method to calibrate the sub. You will not lose any performance from the amp by not running it full open.
     
  3. Mike Sloan

    Mike Sloan Second Unit

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    Jeff,
    That's basically what I did and I was able to get it close to reference. With the sub all the way up and the receiver all the way down the sub was at 96Db when the other speakers were at 75Db. Ended up with the sub at about 1/4 and the receiver at -5. I sent an E-mail to DR. HSU and he said the same thing you said regarding calibration. He further stated that running the gain all the way up will further amplify any undesirable signals that may have crept in. I am glad I didn't try and watch LOTR! EXPLOSION!
     
  4. Ned

    Ned Supporting Actor

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    Mike-

    maxing the gain is for those who have a passive sub with a separate power amplifier. On a plate amp you want the receiver LFE level around its midpoint and the plate gain at whatever is needed for that to output the right amount when calibrating - usually 1/4 to 1/2 gain.
     
  5. jeff lam

    jeff lam Screenwriter

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    I'm sure Vince is correct with some of the plate amps around. But from the ones I have seen/worked with and others I have heard about from others, most plate amps have too low an input sensitivity to run them wide open. Now with Pro amps such as what I am running (Crown CE1000) my tempest with, the input sensitivity is about 3-4x's higher than the PE plate amps, therefore it is almost required to run it wide open to get it to reference calibration.

    The plate amp doesn't boost the signal at all, it just takes much less signal at the input stage to drive it to full power.
     
  6. Bolivar G

    Bolivar G Second Unit

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    I been having trouble calibrating my VTF-3 also. Have to turn the volume lvl way down on the plate amp to get ref lvl of 75. But then I dont like how the bass sounds, very low and week. So I end up turning up the volume knob by ear to my pleasure of bass, screwing what ever the spl meter says [​IMG]
    It ends up just past the 1/2 mark. And my 4802 sub lvl is at -6 DB. I think my sub is way to much for my small room but I'll never send it back, gotta have my bass [​IMG]
     
  7. jeff lam

    jeff lam Screenwriter

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    Bolivar G,
    My guess is you watch movies at relatively low levels. Am I right? Usually this is the responce from people that watch movies at low levels because with the sub calibrated at the same level as the rest of the speakers, the sub/bass seems low and weak which is normal. The general rule is the lower the listening level, the hotter the sub needs to be to get that dynamic sound back due to our ears being less sensitive to bass. Just be carefull to pull the sub back down to equal level if you decide to play at full reference.
     
  8. Bolivar G

    Bolivar G Second Unit

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    I watch alot of my movies on the weekends Late at night.
    So yes I cant crank it up loud at night.
    But even during the day when I really crank it up, I still like that extra kick and 75db still seams weak. I must be a bass junkie [​IMG]
    The except to this was LOTR, I had to turn it down , to much bass [​IMG]
     

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