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JBL MP255s subs

Discussion in 'Amps and Cabs [BG]' started by Phat Ham, Apr 16, 2003.


  1. Phat Ham

    Phat Ham

    Feb 13, 2000
    DC
    Anyone have any experience with these. My friend is thinking about getting a couple of them for his PA. The only thing that concerns me is the throw of the speakers. Would your standard vented box design be better suited for smaller rooms than a folded horn design? Are these even folded horns?

    http://www.jblpro.com/pages/mi/series_200_tbl.htm
     
  2. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    No they're not folded horns. They appear to be a band-pass design. that's about as much as I can tell you, sorry.
     
  3. Nope.

    It's just a vented box with non-parallel walls and a rounded baffle. It has an F3 of 64 Hz which is fine for a PA system not supporting bass.
     
  4. Why wouldn't it be ok to run bass through a PA using these cabs?:confused:
     
  5. Phat Ham

    Phat Ham

    Feb 13, 2000
    DC
    woops forgot to mention that the MP255s is the cab at the bottom of the page in the link I provided.

    [​IMG]

    The JBL site calls them "bandpass" as was stated before, but I have no idea what that is.
     
  6. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I did a quick net-search and a couple of different sites refered to them as bandpass - I just took their word for it given that I couldn't see the configuration inside the cab.
     
  7. Imff terrifmmfly sorffmmy

    < yank >

    that's better, had to remove foot from mouth...

    you are correct, they are a bandpass design. And he's a big boy, too.
     
  8. I played an outdoor gig last year where a couple of those subs along with dual 15 cabs were used in the pa gear. It was the loudest gig I ever played. Everytime a hit a string everybody on the stage and in front of us just shook. Couldn't really make out notes because there was way too much bass. Nevermind the insane fog the sound guy had going.

    Anyway, they should be great for pa use. JBL is a great company.
     
  9. geshel

    geshel

    Oct 2, 2001
    Seattle
    PH,

    Bandpass (in terms of speaker enclosures) means that the drivers don't fire directly into the listening space. Instead they driver fires into another chamber, which is ported like a ported speaker. The output of the port is the only output from the system. This acts as a low-pass filter, so in conjunction with the natural low-end roll off (high-pass behavior) of a speaker, the combined response is "band-pass".

    In the case of these speakers the rear chamber of the driver is sealed.

    Bandpass boxes can be made more efficient, in the range they respond, than a similar sealed or vented box. The compromise is transient response - they can also have worse transient response than either. These are probably "OK" on most accounts - they have a decent frequency range, and I don't think JBL makes anything terribly crappy :).

    These should work OK in smaller venues - as they're not horns, they don't have the same throw characteristics. Two of them could be pretty overpowering though!
     
  10. The tiny Bose stereo speakers are bandpass designs. They're a real bitch to engineer properly, as the 6th order type has dual chambers and both most be tuned correctly to interact with the driver. The stress on the driver cone from both chambers is enormous because the design damps the cone movement to about NIL.

    The group delay component is awful in BP types, which is why they tend to sound muddy. But... they do the job in a very narrow range.
     
  11. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Question - which would have a worse group delay, a bandbass sub or a folded horn sub?
     
  12. Phat Ham

    Phat Ham

    Feb 13, 2000
    DC
    Thanks for the explanation. I (or I guess I should say my friend) am not expecting the greatest sound out of these, but considering the relatively cheap price they seem like a good deal. Most of the gigs we do are in frat houses, so they aren't real big rooms, and the acoustics of those places are always terrible. I was mainly worried that if the throw of these things was really long then you would only hear them from outside of the frat.
     
  13. geshel

    geshel

    Oct 2, 2001
    Seattle
    Well it really depends - on the Q of the driver / the box alignment etc. You can have a folded horn where the rear chamber is sealed, and I don't think the horn loading makes the transient response worse (I could be wrong - but I thought the main downsides to horns were a little increased distortion at some frequencies, and the size).