1. Join Now

    AVForums.com uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Question to Eric concerning servo in subs - am i having it or not?

Discussion in 'Subwoofers' started by Nazgul9, Mar 17, 2003.

  1. Nazgul9

    Nazgul9
    Guest

    Products Owned:
    0
    Products Wanted:
    0
    Ratings:
    +0
    Just a question to Eric or whoever is able to tell me. I own a Jamo D7Sub subwoofer and in the manual it says the sub has a "motional feed back servo control" which is for reducing the excessive wobbling of the driver, therefore improving timing, reducing distortion and indirectly reaching lower frequencies (to put it in simple and few words, the manual for the whole D7 system can be downloaded here: http://www.jamospeakers.com/consumer/products/products_add.php3?id=D 7ATX&tab=3). So is this technology mentioned the same servo technology that is used in Velodyne and Paradigm products or is it something completely different? Has someone else on this forum this Jamo sub or am i the only one?
     
  2. uncle eric

    uncle eric
    Guest

    Products Owned:
    0
    Products Wanted:
    0
    Ratings:
    +0
    Hi Nazgul,
    Welcome to the forums.

    The 400 watt 15inch Jamo is indeed an active servo subwoofer using an accelerometer in much the same way as the Velodyne HGS series.

    However, like the majority of subwoofers that have passed THX Ultra 2 certification thus far, (and there are still only a few), you will actually need X 2 Pieces of Jamo D7's to hit the required spec of 20Hz at 106db's at no more than 4% distortion.

    The 1250 watt (3000 watts peak) Velodyne HGS-15 or HGS-18 will do it on its own and pass the spec as a single subwoofer.
     
  3. Nazgul9

    Nazgul9
    Guest

    Products Owned:
    0
    Products Wanted:
    0
    Ratings:
    +0
    Thanks for the reply and for the welcome! :)

    Wow, i have a servo sub! Cool! It makes me feel better now. :D I'm a bit exaggarating of course, after all servo isn't everything in a sub and the implementation of it may be different, but nevertheless - since the Velodynes are so well regarded - somehow it gives me a certain confidence of having quite a good sub. Yes, i know that two of my subs are required to fully pass the THX Ultra 2 specifications, it's written in the manual, but since my room is small (about 18 square meters) i don't have a problem with that. Sure, a HGS-18 would be like a dream come true, but unfortunately as a poor student the means are limited. :(

    But there are things about my sub which give me a headache. Maybe you can give me some advice what to do. The first thing is clicking noise (i don't know how to describe it otherwise since my english isn't the best) which is coming out of my sub when playing very low frequencies, below 30Hz. In movies there is rarely a situation where the problem occurs, probably because such low frequencies aren't common in movies but i have a test tone generator (the receiver is connected to a computer) and playing with it i was able to reproduce the phenomenon. I was playing a 25Hz sinus and the clicking was constantly there. And i don't mean playing it loud, i had it at a rather low volume i would say. When playing lower frequencies the clicking was even worse in a manner that i feared of damaging the sub. How can that be considering that two of the units are fully THX Ultra 2 capable and i don't even hit the 20Hz mark but was at 25Hz and at quite low volumes? Could the sub be faulty? The weird thing is that the same test tone generator has a sweeping (is it the right word?) test tone which goes from 200Hz down to 15Hz or something and when playing that sound the clicking was absent(!?). The second disturbing fact is the lack of punchy bass for my taste. Although i'm really not sure if it's the fault of the sub or the other equipment (which is consisting of an Onkyo 595 with fixed crossover at 80Hz and a set of B&W 300's driving them as small). The sub is placed in a corner, could that be the problem? Maybe i should position it further away from the walls, because i read something from you on this forum regarding sub placement in which corner placement is stated as inferior. Or should i try the boundary gain compensation input on the sub, but since my listening position is almost in the center of the room i doubt that would do something as i recall reading that this special method of affecting the signal is only vital in case the listening position is close to a wall, not the sub?

    Any help would be appreciated.
     
  4. Paul Smith

    Paul Smith
    Active Member

    Joined:
    Apr 15, 2002
    Messages:
    2,033
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    66
    Location:
    Berkshire
    Ratings:
    +142
    Hi,
    I have a Jamo 3015THX subwoofer in my setup (a similar but older Jamo 15" 400watt Servo sub).

    It just so happens that over the weekend I was playing about with Test Tones and alternative positions for my sub(s), because of this I can tell you that mine definately doesn't make any clicking noises at all.

    As for "the lack of punchy bass" this is not a problem I have encountered, I must confess I have not heard the Onkyo 595 but Perhaps the HCC review of it gives the answer to this problem:

    "Less impressive is the bass. Bass lines and sound effects reach down as low as any other in this test, but there is a distinct lack of power, leaving explosions and crescendos sounding rather underwhelming."

    Perhaps this is the lack of punch that you are hearing in your system.

    Paul. :)
     
  5. Nazgul9

    Nazgul9
    Guest

    Products Owned:
    0
    Products Wanted:
    0
    Ratings:
    +0
    Well i for sure have the intention to go to my dealer and show it (the clicking noise) to them and hopefully they will fix it or give me another unit. I can't believe that this behavior is normal for a THX Ultra 2 capable woofer, no way. I haven't done it yet because, to be honest, the sub is rather big and heavy and it's quite a difficult operation, but i'll do it, before the warranty will expire and i'll have to pay.

    I'm also suspecting the receiver to be the cause for this certain lack of punchy bass. I've read several articles about the lower priced Onkyo products and their lack of amplification power when driving all five channels simultaneously. For this reason (and others) i've already determined to buy the NAD T752 (any comments about this unit?) for it's excellent powerful amps and it's bass delivering. When obtaining the new receiver (in a month or so) i'll also purchase a new TV and a DVD player and will rearrange my room a bit, so it'll be a good opportunity to play with the sub placement to see if that way as well the bass can be improved in some areas.
     
  6. Paul Smith

    Paul Smith
    Active Member

    Joined:
    Apr 15, 2002
    Messages:
    2,033
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    66
    Location:
    Berkshire
    Ratings:
    +142
    It all seems like a sensible course of action to take,
    As for the NAD T752 (I haven't heard that amp either) but if you do a search on the forum though you'll see plenty of people have tried it and given thier own views on it.
    Cheers,

    Paul.
     

Share This Page

Loading...