sealed or ported midbass drivers

Discussion in 'Archived Threads 2001-2004' started by Ron D Core, Apr 17, 2002.

  1. Ron D Core

    Ron D Core Stunt Coordinator

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    I've been in the process of designing a pair of 4 way loudspeakers. The plan is to go with two Focal 8V4411 8" mid-bass drivers in each speaker for (60-80)-1500 Hz. The high pass will depend on the sub, which will be one BPD 1201 for each tower. Should I put the 8's in a ported sealed or aperiodiclly vented enclosure? I want a flat response, with as much efficiency as possible. The crossovers will be 2nd order Linkwitz Rileys. I would like to keep the volume as low as possible while making no sacrifices with the sound. Any suggestions? Thanks.
     
  2. Marc Bodin

    Marc Bodin Extra

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    Ported does give you an increase in efficiency, but generally does not have a flat response.

    AP is the least efficient but have a flat resonse. It also allows you to use a small enclosure.

    Sealed provides a flat response and is the easiest to build. I would probably go sealed with your midbass.
     
  3. Greg Monfort

    Greg Monfort Supporting Actor

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    WRT vented, etc., it depends on the driver/required LF cutoff, though sealed or Aperiodic would in theory be preferred. Ideally you want the FR to be flat for at least two octaves on either side of a 2nd order XO, so for an 80Hz XO this means the 8"ers need to be flat to 20Hz and the sub out to 320Hz, but of course this isn't practical. Better I think to use 4th order so that it becomes 40-160Hz, which these don't do if the specs from the Focal site are close to yours.

    Going with a 10" (slightly more SD than two 8"), or two, with a lower Fs may be the better choice in this case. A baffle stepped Eminence Beta 10CX yields a bit more SPL with less power, will require ~ the same Vb, and may cost less than two of the Focals (I don't keep up with pricing). WRT off axis response, ~30deg off axis is acceptable for most applications, so the 10" just barely squeaks in at ~1618Hz, though ideally it would need to go to 3kHz for a 1.5kHz/4th XO. The 8" makes it to ~2158Hz, but the 10" reduces reflections, which I consider a plus.

    Personally, I use one or two 12" or 15" and limit the XO point to ~500-800Hz for this BW, then mate them to the appropriate wide BW horn to get around such issues (among other reasons), with the tradeoff of relatively large size.

    If you want to stick with dual 8"ers then I figure about the best you can do effciency wise is to tune it flat to the XO point with a Q = 0.7 (max flat) vented, and its rolloff combined with a 4th order XO gets the job done as best as can be expected. If you go with sealed, the XO will need to be higher.

    GM
     

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