ampeg isovent (?)

Discussion in 'Amps and Cabs [BG]' started by I.'.I.'.Nakoa, May 15, 2001.

  1. I.'.I.'.Nakoa

    I.'.I.'.Nakoa Guest

    Aug 10, 2000
    Fort Worth.
    my friend has an ampeg 410 and 15 all in one cab. its older, and ive been told its called an isovent. can anyone tell me anything about these cabs?!? thanks
  2. Rickenbackerman


    Apr 17, 2001
    Laurel MD
    An isovent has two 15's in an isobaric configuration like this <> and two tens up top. They supposedly have huge bottom end.
  3. rickbass

    rickbass Supporting Member

    That's a cool amp, if you don't mind the weight. I saw one on eBay and would have bought it, if hadn't just bought an amp a couple of months earlier.

    The only reason it got pulled was low sales, not anything performance related. I guess people were scared away by the radical design departure from the norm.

    The 15's were wired out of phase to create kind of a "tugging" effect.
  4. The advantage to an isobaric configuration is the required cabinet volume for the 15" driver is cut in half without negative effect on the response. Most 15" drivers want 4.5 to 20 cubic feet for optimum response in a ported enclosure, so this is a substantial benefit.

    The disadvantages are the weight of two drivers vs a single driver, a -3dB loss in SPL, and the cost of the additional driver.
  5. I.'.I.'.Nakoa

    I.'.I.'.Nakoa Guest

    Aug 10, 2000
    Fort Worth.
    thank you all very much for the replies. well, maybe this isnt the isovent, but it is an older 410 and 15 configuration ampeg cab. i still want it. anyone have pics of an isovent?
  6. Bob Gollihur

    Bob Gollihur

    Mar 22, 2000
    New Joisey Shore
    Big Cheese Emeritus: Gollihur Music
  7. I.'.I.'.Nakoa

    I.'.I.'.Nakoa Guest

    Aug 10, 2000
    Fort Worth.
    thanks for the pic! no thats not the cab. grrr. idd still take one though mmmmhmmm.
  8. Ampeg still makes a cabinet in that configuration. It's called the SVT1540. Check it out at

    You may be thinking of the line that came out four years ago or so. I think Victor Wooten endorsed them. The cab had a 15" firing down at a 45 degree angle, two tens, and two eights, if memory serves. They're pretty good cabs, but heavy and rather wide.

    Ampeg also made a 2x12 isovent cabinet at one point. One speaker fired straight out, the other fired down. I think they were in a push-pull configuration.
  9. The thing you're talking about is actually called "compound". Two speakers coupled in counterphase on one air volume, most of the times ported. Usually used for stereo hifi subwoofers.

    Isobaric is just a closed cab.
    Isovent is an old system which incorporates a resistive port (called "variovent").

    Well, if memory serves me right, anyway.

  10. Sorry my friend, but you are incorrect on this one.

    An isobaric configuration is specifically where one side of cone A is acoustically coupled to one side of cone B. The most common is the clamshell (face to face) configuration. Less common is a subchamber with a small airspace between the drivers, where both face the same direction. This has disadvantages with the added compliance of the enclosed air space, and poses cooling problems for the driver(s) inside the chamber.

    The isobaric configuration reduces the required cabinet volume by 50%. The cost is a -3dB drop in SPL.
  11. I stand corrected, but we seem to be both right. Vance Dickason's "Loudspeaker Cookbook" states that "Compound" is the same thing as "Isobarik" (with a K).

    But where did the word isovent come from? That must be something else than isobarik, I guess.